nghttp2/lib/nghttp2_session.c

/*
 * nghttp2 - HTTP/2.0 C Library
 *
 * Copyright (c) 2012 Tatsuhiro Tsujikawa
 *
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
 * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
 * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */
#include "nghttp2_session.h"

#include <string.h>
#include <stddef.h>
#include <stdio.h>
#include <assert.h>

#include "nghttp2_helper.h"
#include "nghttp2_net.h"

/*
 * Returns non-zero if the number of outgoing opened streams is larger
 * than or equal to
 * remote_settings[NGHTTP2_SETTINGS_MAX_CONCURRENT_STREAMS].
 */
static int nghttp2_session_is_outgoing_concurrent_streams_max
(nghttp2_session *session)
{
  return session->remote_settings[NGHTTP2_SETTINGS_MAX_CONCURRENT_STREAMS]
    <= session->num_outgoing_streams;
}

/*
 * Returns non-zero if the number of incoming opened streams is larger
 * than or equal to
 * local_settings[NGHTTP2_SETTINGS_MAX_CONCURRENT_STREAMS].
 */
static int nghttp2_session_is_incoming_concurrent_streams_max
(nghttp2_session *session)
{
  return session->local_settings[NGHTTP2_SETTINGS_MAX_CONCURRENT_STREAMS]
    <= session->num_incoming_streams;
}

/*
 * Returns non-zero if |lib_error| is non-fatal error.
 */
static int nghttp2_is_non_fatal(int lib_error)
{
  return lib_error < 0 && lib_error > NGHTTP2_ERR_FATAL;
}

int nghttp2_is_fatal(int lib_error)
{
  return lib_error < NGHTTP2_ERR_FATAL;
}

/* Returns the pushed stream's priority based on the associated stream
   |stream|. */
static int32_t nghttp2_pushed_stream_pri(nghttp2_stream *stream)
{
  return stream->pri == NGHTTP2_PRI_LOWEST ?
    (int32_t)NGHTTP2_PRI_LOWEST : stream->pri + 1;
}

/* Returns nonzero if the |stream| is in reserved(remote) state */
static int state_reserved_remote(nghttp2_session *session,
                                 nghttp2_stream *stream)
{
  return stream->state == NGHTTP2_STREAM_RESERVED &&
    !nghttp2_session_is_my_stream_id(session, stream->stream_id);
}

/* Returns nonzero if the |stream| is in reserved(local) state */
static int state_reserved_local(nghttp2_session *session,
                                nghttp2_stream *stream)
{
  return stream->state == NGHTTP2_STREAM_RESERVED &&
    nghttp2_session_is_my_stream_id(session, stream->stream_id);
}

int nghttp2_session_terminate_session(nghttp2_session *session,
                                      nghttp2_error_code error_code)
{
  if(session->goaway_flags & NGHTTP2_GOAWAY_FAIL_ON_SEND) {
    return 0;
  }
  session->goaway_flags |= NGHTTP2_GOAWAY_FAIL_ON_SEND;
  if(session->goaway_flags & NGHTTP2_GOAWAY_SEND) {
    return 0;
  }
  return nghttp2_submit_goaway(session, NGHTTP2_FLAG_NONE, error_code,
                               NULL, 0);
}

int nghttp2_session_is_my_stream_id(nghttp2_session *session,
                                    int32_t stream_id)
{
  int r;
  if(stream_id == 0) {
    return 0;
  }
  r = stream_id % 2;
  return (session->server && r == 0) || (!session->server && r == 1);
}

nghttp2_stream* nghttp2_session_get_stream(nghttp2_session *session,
                                           int32_t stream_id)
{
  return (nghttp2_stream*)nghttp2_map_find(&session->streams, stream_id);
}

static int nghttp2_outbound_item_compar(const void *lhsx, const void *rhsx)
{
  const nghttp2_outbound_item *lhs, *rhs;
  lhs = (const nghttp2_outbound_item*)lhsx;
  rhs = (const nghttp2_outbound_item*)rhsx;
  if(lhs->pri == rhs->pri) {
    return (lhs->seq < rhs->seq) ? -1 : ((lhs->seq > rhs->seq) ? 1 : 0);
  } else {
    return lhs->pri - rhs->pri;
  }
}

static void nghttp2_inbound_frame_reset(nghttp2_session *session)
{
  nghttp2_inbound_frame *iframe = &session->iframe;
  /* A bit risky code, since if this function is called from
     nghttp2_session_new(), we rely on the fact that
     iframe->frame.hd.type is 0, so that no free is performed. */
  switch(iframe->frame.hd.type) {
  case NGHTTP2_HEADERS:
    nghttp2_frame_headers_free(&iframe->frame.headers);
    break;
  case NGHTTP2_PRIORITY:
    nghttp2_frame_priority_free(&iframe->frame.priority);
    break;
  case NGHTTP2_RST_STREAM:
    nghttp2_frame_rst_stream_free(&iframe->frame.rst_stream);
    break;
  case NGHTTP2_SETTINGS:
    nghttp2_frame_settings_free(&iframe->frame.settings);
    break;
  case NGHTTP2_PUSH_PROMISE:
    nghttp2_frame_push_promise_free(&iframe->frame.push_promise);
    break;
  case NGHTTP2_PING:
    nghttp2_frame_ping_free(&iframe->frame.ping);
    break;
  case NGHTTP2_GOAWAY:
    nghttp2_frame_goaway_free(&iframe->frame.goaway);
    break;
  case NGHTTP2_WINDOW_UPDATE:
    nghttp2_frame_window_update_free(&iframe->frame.window_update);
    break;
  }
  memset(&iframe->frame, 0, sizeof(nghttp2_frame));
  iframe->state = NGHTTP2_IB_READ_HEAD;
  iframe->left = NGHTTP2_FRAME_HEAD_LENGTH;
  iframe->niv = 0;
  iframe->payloadleft = 0;
  iframe->padlen = 0;
  iframe->error_code = 0;
  iframe->buflen = 0;
}

static void init_settings(uint32_t *settings)
{
  settings[NGHTTP2_SETTINGS_HEADER_TABLE_SIZE] =
    NGHTTP2_HD_DEFAULT_MAX_BUFFER_SIZE;
  settings[NGHTTP2_SETTINGS_ENABLE_PUSH] = 1;
  settings[NGHTTP2_SETTINGS_MAX_CONCURRENT_STREAMS] =
    NGHTTP2_INITIAL_MAX_CONCURRENT_STREAMS;
  settings[NGHTTP2_SETTINGS_INITIAL_WINDOW_SIZE] =
    NGHTTP2_INITIAL_WINDOW_SIZE;
}

typedef struct {
  nghttp2_session *session;
  int rv;
} header_cb_arg;

static int nghttp2_session_new(nghttp2_session **session_ptr,
                               const nghttp2_session_callbacks *callbacks,
                               void *user_data,
                               int server,
                               uint32_t opt_set_mask,
                               const nghttp2_opt_set *opt_set)
{
  int r;
  nghttp2_hd_side side_deflate, side_inflate;
  *session_ptr = malloc(sizeof(nghttp2_session));
  if(*session_ptr == NULL) {
    r = NGHTTP2_ERR_NOMEM;
    goto fail_session;
  }
  memset(*session_ptr, 0, sizeof(nghttp2_session));

  /* next_stream_id is initialized in either
     nghttp2_session_client_new2 or nghttp2_session_server_new2 */

  (*session_ptr)->next_seq = 0;

  if((opt_set_mask & NGHTTP2_OPT_NO_AUTO_STREAM_WINDOW_UPDATE) &&
     opt_set->no_auto_stream_window_update) {
    (*session_ptr)->opt_flags |= NGHTTP2_OPTMASK_NO_AUTO_STREAM_WINDOW_UPDATE;
  }
  if((opt_set_mask & NGHTTP2_OPT_NO_AUTO_CONNECTION_WINDOW_UPDATE) &&
     opt_set->no_auto_connection_window_update) {
    (*session_ptr)->opt_flags |=
      NGHTTP2_OPTMASK_NO_AUTO_CONNECTION_WINDOW_UPDATE;
  }
  if((opt_set_mask & NGHTTP2_OPT_PAD_ALIGNMENT) &&
     opt_set->pad_alignment >= 8) {
    (*session_ptr)->pad_alignment = opt_set->pad_alignment;
  } else {
    (*session_ptr)->pad_alignment = NGHTTP2_PAD_ALIGNMENT;
  }

  (*session_ptr)->remote_window_size = NGHTTP2_INITIAL_CONNECTION_WINDOW_SIZE;
  (*session_ptr)->recv_window_size = 0;
  (*session_ptr)->recv_reduction = 0;
  (*session_ptr)->local_window_size = NGHTTP2_INITIAL_CONNECTION_WINDOW_SIZE;

  (*session_ptr)->goaway_flags = NGHTTP2_GOAWAY_NONE;
  (*session_ptr)->last_stream_id = 0;

  (*session_ptr)->inflight_niv = -1;

  if(server) {
    (*session_ptr)->server = 1;
    side_deflate = NGHTTP2_HD_SIDE_RESPONSE;
    side_inflate = NGHTTP2_HD_SIDE_REQUEST;
  } else {
    side_deflate = NGHTTP2_HD_SIDE_REQUEST;
    side_inflate = NGHTTP2_HD_SIDE_RESPONSE;
  }
  r = nghttp2_hd_deflate_init(&(*session_ptr)->hd_deflater, side_deflate);
  if(r != 0) {
    goto fail_hd_deflater;
  }
  r = nghttp2_hd_inflate_init(&(*session_ptr)->hd_inflater, side_inflate);
  if(r != 0) {
    goto fail_hd_inflater;
  }
  r = nghttp2_map_init(&(*session_ptr)->streams);
  if(r != 0) {
    goto fail_map;
  }
  r = nghttp2_pq_init(&(*session_ptr)->ob_pq, nghttp2_outbound_item_compar);
  if(r != 0) {
    goto fail_ob_pq;
  }
  r = nghttp2_pq_init(&(*session_ptr)->ob_ss_pq, nghttp2_outbound_item_compar);
  if(r != 0) {
    goto fail_ob_ss_pq;
  }

  (*session_ptr)->aob.framebuf = malloc
    (NGHTTP2_INITIAL_OUTBOUND_FRAMEBUF_LENGTH);
  if((*session_ptr)->aob.framebuf == NULL) {
    r = NGHTTP2_ERR_NOMEM;
    goto fail_aob_framebuf;
  }
  (*session_ptr)->aob.framebufmax = NGHTTP2_INITIAL_OUTBOUND_FRAMEBUF_LENGTH;

  memset((*session_ptr)->remote_settings, 0,
         sizeof((*session_ptr)->remote_settings));
  memset((*session_ptr)->local_settings, 0,
         sizeof((*session_ptr)->local_settings));

  init_settings((*session_ptr)->remote_settings);
  init_settings((*session_ptr)->local_settings);

  if(opt_set_mask & NGHTTP2_OPT_PEER_MAX_CONCURRENT_STREAMS) {
    (*session_ptr)->remote_settings[NGHTTP2_SETTINGS_MAX_CONCURRENT_STREAMS] =
      opt_set->peer_max_concurrent_streams;
  }

  (*session_ptr)->callbacks = *callbacks;
  (*session_ptr)->user_data = user_data;

  nghttp2_inbound_frame_reset(*session_ptr);

  return 0;

 fail_aob_framebuf:
  nghttp2_pq_free(&(*session_ptr)->ob_ss_pq);
 fail_ob_ss_pq:
  nghttp2_pq_free(&(*session_ptr)->ob_pq);
 fail_ob_pq:
  nghttp2_map_free(&(*session_ptr)->streams);
 fail_map:
  nghttp2_hd_inflate_free(&(*session_ptr)->hd_inflater);
 fail_hd_inflater:
  nghttp2_hd_deflate_free(&(*session_ptr)->hd_deflater);
 fail_hd_deflater:
  free(*session_ptr);
 fail_session:
  return r;
}

int nghttp2_session_client_new(nghttp2_session **session_ptr,
                               const nghttp2_session_callbacks *callbacks,
                               void *user_data)
{
  return nghttp2_session_client_new2(session_ptr, callbacks, user_data,
                                     0, NULL);
}

int nghttp2_session_client_new2(nghttp2_session **session_ptr,
                                const nghttp2_session_callbacks *callbacks,
                                void *user_data,
                                uint32_t opt_set_mask,
                                const nghttp2_opt_set *opt_set)
{
  int r;
  /* For client side session, header compression is disabled. */
  r = nghttp2_session_new(session_ptr, callbacks, user_data, 0,
                          opt_set_mask, opt_set);
  if(r == 0) {
    /* IDs for use in client */
    (*session_ptr)->next_stream_id = 1;
  }
  return r;
}

int nghttp2_session_server_new(nghttp2_session **session_ptr,
                               const nghttp2_session_callbacks *callbacks,
                               void *user_data)
{
  return nghttp2_session_server_new2(session_ptr, callbacks, user_data,
                                     0, NULL);
}

int nghttp2_session_server_new2(nghttp2_session **session_ptr,
                                const nghttp2_session_callbacks *callbacks,
                                void *user_data,
                                uint32_t opt_set_mask,
                                const nghttp2_opt_set *opt_set)
{
  int r;
  /* Enable header compression on server side. */
  r = nghttp2_session_new(session_ptr, callbacks, user_data, 1,
                          opt_set_mask, opt_set);
  if(r == 0) {
    /* IDs for use in client */
    (*session_ptr)->next_stream_id = 2;
  }
  return r;
}

static int nghttp2_free_streams(nghttp2_map_entry *entry, void *ptr)
{
  nghttp2_stream_free((nghttp2_stream*)entry);
  free(entry);
  return 0;
}

static void nghttp2_session_ob_pq_free(nghttp2_pq *pq)
{
  while(!nghttp2_pq_empty(pq)) {
    nghttp2_outbound_item *item = (nghttp2_outbound_item*)nghttp2_pq_top(pq);
    nghttp2_outbound_item_free(item);
    free(item);
    nghttp2_pq_pop(pq);
  }
  nghttp2_pq_free(pq);
}

static void nghttp2_active_outbound_item_reset
(nghttp2_active_outbound_item *aob)
{
  nghttp2_outbound_item_free(aob->item);
  free(aob->item);
  aob->item = NULL;
  aob->framebuflen = aob->framebufoff = aob->framebufmark = 0;
}

void nghttp2_session_del(nghttp2_session *session)
{
  if(session == NULL) {
    return;
  }
  free(session->inflight_iv);
  nghttp2_inbound_frame_reset(session);
  nghttp2_map_each_free(&session->streams, nghttp2_free_streams, NULL);
  nghttp2_map_free(&session->streams);
  nghttp2_session_ob_pq_free(&session->ob_pq);
  nghttp2_session_ob_pq_free(&session->ob_ss_pq);
  nghttp2_hd_deflate_free(&session->hd_deflater);
  nghttp2_hd_inflate_free(&session->hd_inflater);
  nghttp2_active_outbound_item_reset(&session->aob);
  free(session->aob.framebuf);
  free(session);
}

static int outbound_item_update_pri
(nghttp2_outbound_item *item, nghttp2_stream *stream)
{
  if(item->frame_cat == NGHTTP2_CAT_CTRL) {
    if(((nghttp2_frame*)item->frame)->hd.stream_id != stream->stream_id) {
      return 0;
    }
    switch(((nghttp2_frame*)item->frame)->hd.type) {
    case NGHTTP2_HEADERS:
    case NGHTTP2_PUSH_PROMISE:
      break;
    default:
      return 0;
    }
  } else {
    if(((nghttp2_private_data*)item->frame)->hd.stream_id != stream->stream_id) {
      return 0;
    }
  }
  item->pri = stream->pri;
  return 1;
}

static int update_stream_pri(void *ptr, void *arg)
{
  nghttp2_outbound_item *item = (nghttp2_outbound_item*)ptr;
  nghttp2_stream *stream = (nghttp2_stream*)arg;
  return outbound_item_update_pri(item, stream);
}

void nghttp2_session_reprioritize_stream
(nghttp2_session *session, nghttp2_stream *stream, int32_t pri)
{
  if(stream->pri == pri) {
    return;
  }
  stream->pri = pri;
  /* For submitted frames, we only update initial priority, so the
     structure of the queue will remain unchanged. */
  nghttp2_pq_update(&session->ob_pq, update_stream_pri, stream);
  nghttp2_pq_update(&session->ob_ss_pq, update_stream_pri, stream);
  if(stream->deferred_data) {
    stream->deferred_data->pri = pri;
  }
  if(session->aob.item) {
    outbound_item_update_pri(session->aob.item, stream);
  }
}

int nghttp2_session_add_frame(nghttp2_session *session,
                              nghttp2_frame_category frame_cat,
                              void *abs_frame,
                              void *aux_data)
{
  /* TODO Return error if stream is not found for the frame requiring
     stream presence. */
  int r = 0;
  nghttp2_outbound_item *item;
  item = malloc(sizeof(nghttp2_outbound_item));
  if(item == NULL) {
    return NGHTTP2_ERR_NOMEM;
  }
  item->frame_cat = frame_cat;
  item->frame = abs_frame;
  item->aux_data = aux_data;
  item->seq = session->next_seq++;
  /* Set priority to the default value at the moment. */
  item->pri = NGHTTP2_PRI_DEFAULT;
  if(frame_cat == NGHTTP2_CAT_CTRL) {
    nghttp2_frame *frame = (nghttp2_frame*)abs_frame;
    nghttp2_stream *stream = NULL;
    switch(frame->hd.type) {
    case NGHTTP2_HEADERS:
      if(frame->hd.stream_id == -1) {
        /* Initial HEADERS, which will open stream */
        item->pri = frame->headers.pri;
      } else {
        /* Otherwise, the frame must have stream ID. We use its
           priority value. */
        stream = nghttp2_session_get_stream(session, frame->hd.stream_id);
        if(stream) {
          item->pri = stream->pri;
        }
      }
      break;
    case NGHTTP2_PRIORITY:
      item->pri = -1;
      break;
    case NGHTTP2_RST_STREAM:
      stream = nghttp2_session_get_stream(session, frame->hd.stream_id);
      if(stream) {
        stream->state = NGHTTP2_STREAM_CLOSING;
      }
      item->pri = -1;
      break;
    case NGHTTP2_SETTINGS:
      item->pri = NGHTTP2_OB_PRI_SETTINGS;
      break;
    case NGHTTP2_PUSH_PROMISE:
      /* Use priority of associated stream */
      stream = nghttp2_session_get_stream(session, frame->hd.stream_id);
      if(stream) {
        item->pri = stream->pri;
      }
      break;
    case NGHTTP2_PING:
      /* Ping has highest priority. */
      item->pri = NGHTTP2_OB_PRI_PING;
      break;
    case NGHTTP2_GOAWAY:
      /* Should GOAWAY have higher priority? */
      break;
    case NGHTTP2_WINDOW_UPDATE:
      item->pri = -1;
      break;
    }
    if(frame->hd.type == NGHTTP2_HEADERS &&
       (frame->hd.stream_id == -1 ||
        (stream && stream->state == NGHTTP2_STREAM_RESERVED))) {
      /* We push request HEADERS and push response HEADERS to
         dedicated queue because their transmission is affected by
         SETTINGS_MAX_CONCURRENT_STREAMS */
      /* TODO If 2 HEADERS are submitted for reserved stream, then
         both of them are queued into ob_ss_pq, which is not
         desirable. */
      r = nghttp2_pq_push(&session->ob_ss_pq, item);
    } else {
      r = nghttp2_pq_push(&session->ob_pq, item);
    }
  } else if(frame_cat == NGHTTP2_CAT_DATA) {
    nghttp2_private_data *data_frame = (nghttp2_private_data*)abs_frame;
    nghttp2_stream *stream;
    stream = nghttp2_session_get_stream(session, data_frame->hd.stream_id);
    if(stream) {
      item->pri = stream->pri;
    }
    r = nghttp2_pq_push(&session->ob_pq, item);
  } else {
    /* Unreachable */
    assert(0);
  }
  if(r != 0) {
    free(item);
    return r;
  }
  return 0;
}

int nghttp2_session_add_rst_stream(nghttp2_session *session,
                                   int32_t stream_id,
                                   nghttp2_error_code error_code)
{
  int r;
  nghttp2_frame *frame;
  frame = malloc(sizeof(nghttp2_frame));
  if(frame == NULL) {
    return NGHTTP2_ERR_NOMEM;
  }
  nghttp2_frame_rst_stream_init(&frame->rst_stream, stream_id, error_code);
  r = nghttp2_session_add_frame(session, NGHTTP2_CAT_CTRL, frame, NULL);
  if(r != 0) {
    nghttp2_frame_rst_stream_free(&frame->rst_stream);
    free(frame);
    return r;
  }
  return 0;
}

nghttp2_stream* nghttp2_session_open_stream(nghttp2_session *session,
                                            int32_t stream_id,
                                            uint8_t flags, int32_t pri,
                                            nghttp2_stream_state initial_state,
                                            void *stream_user_data)
{
  int r;
  nghttp2_stream *stream = malloc(sizeof(nghttp2_stream));
  if(stream == NULL) {
    return NULL;
  }
  nghttp2_stream_init(stream, stream_id, flags, pri, initial_state,
                      session->remote_settings
                      [NGHTTP2_SETTINGS_INITIAL_WINDOW_SIZE],
                      session->local_settings
                      [NGHTTP2_SETTINGS_INITIAL_WINDOW_SIZE],
                      stream_user_data);
  r = nghttp2_map_insert(&session->streams, &stream->map_entry);
  if(r != 0) {
    free(stream);
    return NULL;
  }
  if(initial_state == NGHTTP2_STREAM_RESERVED) {
    if(nghttp2_session_is_my_stream_id(session, stream_id)) {
      /* half closed (remote) */
      nghttp2_stream_shutdown(stream, NGHTTP2_SHUT_RD);
    } else {
      /* half closed (local) */
      nghttp2_stream_shutdown(stream, NGHTTP2_SHUT_WR);
    }
    /* Reserved stream does not count in the concurrent streams
       limit. That is one of the DOS vector. */
  } else {
    if(nghttp2_session_is_my_stream_id(session, stream_id)) {
      ++session->num_outgoing_streams;
    } else {
      ++session->num_incoming_streams;
    }
  }
  return stream;
}

/*
 * Closes stream with stream ID |stream_id|. The |error_code|
 * indicates the reason of the closure.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * NGHTTP2_ERR_INVALID_ARGUMENT
 *   The stream is not found.
 * NGHTTP2_ERR_CALLBACK_FAILURE
 *   The callback function failed.
 */
int nghttp2_session_close_stream(nghttp2_session *session, int32_t stream_id,
                                 nghttp2_error_code error_code)
{
  nghttp2_stream *stream = nghttp2_session_get_stream(session, stream_id);
  if(!stream) {
    return NGHTTP2_ERR_INVALID_ARGUMENT;
  }
  /* We call on_stream_close_callback even if stream->state is
     NGHTTP2_STREAM_INITIAL. This will happen while sending request
     HEADERS, a local endpoint receives RST_STREAM for that stream. It
     may be PROTOCOL_ERROR, but without notifying stream closure will
     hang the stream in a local endpoint.
  */
  /* TODO Should on_stream_close_callback be called against
     NGHTTP2_STREAM_RESERVED? It is actually not opened yet. */
  if(stream->state != NGHTTP2_STREAM_RESERVED) {
    if(session->callbacks.on_stream_close_callback) {
      if(session->callbacks.on_stream_close_callback
         (session, stream_id,
          error_code,
          session->user_data) != 0) {
        return NGHTTP2_ERR_CALLBACK_FAILURE;
      }
    }
    if(nghttp2_session_is_my_stream_id(session, stream_id)) {
      --session->num_outgoing_streams;
    } else {
      --session->num_incoming_streams;
    }
  }
  nghttp2_map_remove(&session->streams, stream_id);
  nghttp2_stream_free(stream);
  free(stream);
  return 0;
}

/*
 * Closes stream with stream ID |stream_id| if both transmission and
 * reception of the stream were disallowed. The |error_code| indicates
 * the reason of the closure.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * NGHTTP2_ERR_INVALID_ARGUMENT
 *   The stream is not found.
 * NGHTTP2_ERR_CALLBACK_FAILURE
 *   The callback function failed.
 */
int nghttp2_session_close_stream_if_shut_rdwr(nghttp2_session *session,
                                              nghttp2_stream *stream)
{
  if((stream->shut_flags & NGHTTP2_SHUT_RDWR) == NGHTTP2_SHUT_RDWR) {
    return nghttp2_session_close_stream(session, stream->stream_id,
                                        NGHTTP2_NO_ERROR);
  }
  return 0;
}

/*
 * Check that we can send a frame to the |stream|. This function
 * returns 0 if we can send a frame to the |frame|, or one of the
 * following negative error codes:
 *
 * NGHTTP2_ERR_STREAM_CLOSED
 *   The stream is already closed.
 * NGHTTP2_ERR_STREAM_SHUT_WR
 *   The stream is half-closed for transmission.
 */
static int nghttp2_predicate_stream_for_send(nghttp2_stream *stream)
{
  if(stream == NULL) {
    return NGHTTP2_ERR_STREAM_CLOSED;
  }
  if(stream->shut_flags & NGHTTP2_SHUT_WR) {
    return NGHTTP2_ERR_STREAM_SHUT_WR;
  }
  return 0;
}

/*
 * This function checks HEADERS frame |frame|, which opens stream, can
 * be sent at this time.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * NGHTTP2_ERR_START_STREAM_NOT_ALLOWED
 *     New stream cannot be created because GOAWAY is already sent or
 *     received.
 * NGHTTP2_ERR_STREAM_ID_NOT_AVAILABLE
 *     Stream ID has reached the maximum value. Therefore no stream ID
 *     is available.
 */
static int nghttp2_session_predicate_request_headers_send
(nghttp2_session *session, nghttp2_headers *frame)
{
  if(session->goaway_flags) {
    /* When GOAWAY is sent or received, peer must not send new request
       HEADERS. */
    return NGHTTP2_ERR_START_STREAM_NOT_ALLOWED;
  }
  /* All 32bit signed stream IDs are spent. */
  if(session->next_stream_id > INT32_MAX) {
    return NGHTTP2_ERR_STREAM_ID_NOT_AVAILABLE;
  }
  return 0;
}

/*
 * This function checks HEADERS, which is the first frame from the
 * server, with the stream ID |stream_id| can be sent at this time.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * NGHTTP2_ERR_STREAM_CLOSED
 *     The stream is already closed or does not exist.
 * NGHTTP2_ERR_STREAM_SHUT_WR
 *     The transmission is not allowed for this stream (e.g., a frame
 *     with END_STREAM flag set has already sent)
 * NGHTTP2_ERR_INVALID_STREAM_ID
 *     The stream ID is invalid.
 * NGHTTP2_ERR_STREAM_CLOSING
 *     RST_STREAM was queued for this stream.
 * NGHTTP2_ERR_INVALID_STREAM_STATE
 *     The state of the stream is not valid.
 */
static int nghttp2_session_predicate_response_headers_send
(nghttp2_session *session, int32_t stream_id)
{
  nghttp2_stream *stream = nghttp2_session_get_stream(session, stream_id);
  int r;
  r = nghttp2_predicate_stream_for_send(stream);
  if(r != 0) {
    return r;
  }
  if(nghttp2_session_is_my_stream_id(session, stream_id)) {
    return NGHTTP2_ERR_INVALID_STREAM_ID;
  }
  if(stream->state == NGHTTP2_STREAM_OPENING) {
    return 0;
  }
  if(stream->state == NGHTTP2_STREAM_CLOSING) {
    return NGHTTP2_ERR_STREAM_CLOSING;
  }
  return NGHTTP2_ERR_INVALID_STREAM_STATE;
}

/*
 * This function checks HEADERS for reserved stream can be sent. The
 * stream |stream_id| must be reserved state and the |session| is
 * server side.
 *
 * This function returns 0 if it succeeds, or one of the following
 * error codes:
 *
 * NGHTTP2_ERR_STREAM_CLOSED
 *   The stream is already closed.
 * NGHTTP2_ERR_STREAM_SHUT_WR
 *   The stream is half-closed for transmission.
 * NGHTTP2_ERR_PROTO
 *   The stream is not reserved state
 * NGHTTP2_ERR_STREAM_CLOSED
 *   RST_STREAM was queued for this stream.
 */
static int nghttp2_session_predicate_push_response_headers_send
(nghttp2_session *session, int32_t stream_id)
{
  nghttp2_stream *stream = nghttp2_session_get_stream(session, stream_id);
  int r;
  /* TODO Should disallow HEADERS if GOAWAY has already been issued? */
  r = nghttp2_predicate_stream_for_send(stream);
  if(r != 0) {
    return r;
  }
  if(stream->state != NGHTTP2_STREAM_RESERVED) {
    return NGHTTP2_ERR_PROTO;
  }
  if(stream->state == NGHTTP2_STREAM_CLOSING) {
    return NGHTTP2_ERR_STREAM_CLOSING;
  }
  return 0;
}

/*
 * This function checks frames belongs to the stream |stream_id| can
 * be sent.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * NGHTTP2_ERR_STREAM_CLOSED
 *     The stream is already closed or does not exist.
 * NGHTTP2_ERR_STREAM_SHUT_WR
 *     The transmission is not allowed for this stream (e.g., a frame
 *     with END_STREAM flag set has already sent)
 * NGHTTP2_ERR_STREAM_CLOSING
 *     RST_STREAM was queued for this stream.
 * NGHTTP2_ERR_INVALID_STREAM_STATE
 *     The state of the stream is not valid.
 */
static int nghttp2_session_predicate_stream_frame_send
(nghttp2_session* session, int32_t stream_id)
{
  nghttp2_stream *stream = nghttp2_session_get_stream(session, stream_id);
  int r;
  r = nghttp2_predicate_stream_for_send(stream);
  if(r != 0) {
    return r;
  }
  if(nghttp2_session_is_my_stream_id(session, stream_id)) {
    if(stream->state == NGHTTP2_STREAM_CLOSING) {
      return NGHTTP2_ERR_STREAM_CLOSING;
    }
    return 0;
  }
  if(stream->state == NGHTTP2_STREAM_OPENED) {
    return 0;
  }
  if(stream->state == NGHTTP2_STREAM_CLOSING) {
    return NGHTTP2_ERR_STREAM_CLOSING;
  }
  return NGHTTP2_ERR_INVALID_STREAM_STATE;
}

/*
 * This function checks HEADERS, which is neither stream-opening nor
 * first response header, with the stream ID |stream_id| can be sent
 * at this time.
 */
static int nghttp2_session_predicate_headers_send(nghttp2_session *session,
                                                  int32_t stream_id)
{
  return nghttp2_session_predicate_stream_frame_send(session, stream_id);
}

/*
 * This function checks PRIORITY frame with stream ID |stream_id| can
 * be sent at this time.
 */
static int nghttp2_session_predicate_priority_send
(nghttp2_session *session, int32_t stream_id)
{
  nghttp2_stream *stream;
  stream = nghttp2_session_get_stream(session, stream_id);
  if(stream == NULL) {
    return NGHTTP2_ERR_STREAM_CLOSED;
  }
  if(stream->state == NGHTTP2_STREAM_CLOSING) {
    return NGHTTP2_ERR_STREAM_CLOSING;
  }
  /* PRIORITY must not be sent in reserved(local) */
  if(state_reserved_local(session, stream)) {
    return NGHTTP2_ERR_INVALID_STREAM_STATE;
  }
  /* Sending PRIORITY in reserved(remote) state is OK */
  return 0;
}

/*
 * This function checks PUSH_PROMISE frame |frame| with stream ID
 * |stream_id| can be sent at this time.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * NGHTTP2_ERR_START_STREAM_NOT_ALLOWED
 *     New stream cannot be created because GOAWAY is already sent or
 *     received.
 * NGHTTP2_ERR_STREAM_ID_NOT_AVAILABLE
 *     Stream ID has reached the maximum value. Therefore no stream ID
 *     is available.
 * NGHTTP2_ERR_PROTO
 *     The client side attempts to send PUSH_PROMISE, or the server
 *     sends PUSH_PROMISE for the stream not initiated by the client.
 * NGHTTP2_ERR_STREAM_CLOSED
 *     The stream is already closed or does not exist.
 * NGHTTP2_ERR_STREAM_CLOSING
 *     RST_STREAM was queued for this stream.
 * NGHTTP2_ERR_STREAM_SHUT_WR
 *     The transmission is not allowed for this stream (e.g., a frame
 *     with END_STREAM flag set has already sent)
 * NGHTTP2_ERR_PUSH_DISABLED
 *     The remote peer disabled reception of PUSH_PROMISE.
 */
static int nghttp2_session_predicate_push_promise_send
(nghttp2_session *session, int32_t stream_id)
{
  int rv;
  nghttp2_stream *stream;
  if(nghttp2_session_is_my_stream_id(session, stream_id)) {
    /* The associated stream must be initiated by the remote peer */
    return NGHTTP2_ERR_PROTO;
  }
  stream = nghttp2_session_get_stream(session, stream_id);
  rv = nghttp2_predicate_stream_for_send(stream);
  if(rv != 0) {
    return rv;
  }
  if(session->remote_settings[NGHTTP2_SETTINGS_ENABLE_PUSH] == 0) {
    return NGHTTP2_ERR_PUSH_DISABLED;
  }
  if(stream->state == NGHTTP2_STREAM_CLOSING) {
    return NGHTTP2_ERR_STREAM_CLOSING;
  }
  if(session->goaway_flags) {
    /* When GOAWAY is sent or received, peer must not promise new
       stream ID */
    return NGHTTP2_ERR_START_STREAM_NOT_ALLOWED;
  }
  /* All 32bit signed stream IDs are spent. */
  if(session->next_stream_id > INT32_MAX) {
    return NGHTTP2_ERR_STREAM_ID_NOT_AVAILABLE;
  }
  return 0;
}

/*
 * This function checks WINDOW_UPDATE with the stream ID |stream_id|
 * can be sent at this time. Note that END_STREAM flag of the previous
 * frame does not affect the transmission of the WINDOW_UPDATE frame.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * NGHTTP2_ERR_STREAM_CLOSED
 *     The stream is already closed or does not exist.
 * NGHTTP2_ERR_STREAM_CLOSING
 *     RST_STREAM was queued for this stream.
 * NGHTTP2_ERR_INVALID_STREAM_STATE
 *     The state of the stream is not valid.
 */
static int nghttp2_session_predicate_window_update_send
(nghttp2_session *session, int32_t stream_id)
{
  nghttp2_stream *stream;
  if(stream_id == 0) {
    /* Connection-level window update */
    return 0;
  }
  stream = nghttp2_session_get_stream(session, stream_id);
  if(stream == NULL) {
    return NGHTTP2_ERR_STREAM_CLOSED;
  }
  if(stream->state == NGHTTP2_STREAM_CLOSING) {
    return NGHTTP2_ERR_STREAM_CLOSING;
  }
  if(stream->state == NGHTTP2_STREAM_RESERVED) {
    return NGHTTP2_ERR_INVALID_STREAM_STATE;
  }
  return 0;
}

/*
 * This function checks SETTINGS can be sent at this time.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * NGHTTP2_ERR_TOO_MANY_INFLIGHT_SETTINGS
 *     There is already another in-flight SETTINGS.  Note that the
 *     current implementation only allows 1 in-flight SETTINGS frame
 *     without ACK flag set.
 */
static int nghttp2_session_predicate_settings_send(nghttp2_session *session,
                                                   nghttp2_frame *frame)
{
  if((frame->hd.flags & NGHTTP2_FLAG_ACK) == 0 &&
     session->inflight_niv != -1) {
    return NGHTTP2_ERR_TOO_MANY_INFLIGHT_SETTINGS;
  }
  return 0;
}

/*
 * Returns the maximum length of next data read. If the
 * connection-level and/or stream-wise flow control are enabled, the
 * return value takes into account those current window sizes.
 */
static size_t nghttp2_session_next_data_read(nghttp2_session *session,
                                             nghttp2_stream *stream)
{
  int32_t window_size = NGHTTP2_DATA_PAYLOAD_LENGTH;
  /* Take into account both connection-level flow control here */
  window_size = nghttp2_min(window_size, session->remote_window_size);
  window_size = nghttp2_min(window_size, stream->remote_window_size);
  if(window_size > 0) {
    return window_size;
  }
  return 0;
}

/*
 * This function checks DATA with the stream ID |stream_id| can be
 * sent at this time.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * NGHTTP2_ERR_STREAM_CLOSED
 *     The stream is already closed or does not exist.
 * NGHTTP2_ERR_STREAM_SHUT_WR
 *     The transmission is not allowed for this stream (e.g., a frame
 *     with END_STREAM flag set has already sent)
 * NGHTTP2_ERR_DEFERRED_DATA_EXIST
 *     Another DATA frame has already been deferred.
 * NGHTTP2_ERR_STREAM_CLOSING
 *     RST_STREAM was queued for this stream.
 * NGHTTP2_ERR_INVALID_STREAM_STATE
 *     The state of the stream is not valid.
 */
static int nghttp2_session_predicate_data_send(nghttp2_session *session,
                                               int32_t stream_id)
{
  nghttp2_stream *stream = nghttp2_session_get_stream(session, stream_id);
  int r;
  r = nghttp2_predicate_stream_for_send(stream);
  if(r != 0) {
    return r;
  }
  if(stream->deferred_data != NULL) {
    /* stream->deferred_data != NULL means previously queued DATA
       frame has not been sent. We don't allow new DATA frame is sent
       in this case. */
    return NGHTTP2_ERR_DEFERRED_DATA_EXIST;
  }
  if(nghttp2_session_is_my_stream_id(session, stream_id)) {
    /* Request body data */
    /* If stream->state is NGHTTP2_STREAM_CLOSING, RST_STREAM was
       queued but not yet sent. In this case, we won't send DATA
       frames. */
    if(stream->state == NGHTTP2_STREAM_CLOSING) {
      return NGHTTP2_ERR_STREAM_CLOSING;
    }
    if(stream->state == NGHTTP2_STREAM_RESERVED) {
      return NGHTTP2_ERR_INVALID_STREAM_STATE;
    }
    return 0;
  }
  /* Response body data */
  if(stream->state == NGHTTP2_STREAM_OPENED) {
    return 0;
  }
  if(stream->state == NGHTTP2_STREAM_CLOSING) {
    return NGHTTP2_ERR_STREAM_CLOSING;
  }
  return NGHTTP2_ERR_INVALID_STREAM_STATE;
}

static ssize_t nghttp2_session_prep_frame(nghttp2_session *session,
                                          nghttp2_outbound_item *item)
{
  ssize_t framebuflen = 0;
  if(item->frame_cat == NGHTTP2_CAT_CTRL) {
    nghttp2_frame *frame;
    frame = nghttp2_outbound_item_get_ctrl_frame(item);
    switch(frame->hd.type) {
    case NGHTTP2_HEADERS: {
      nghttp2_headers_aux_data *aux_data;
      aux_data = (nghttp2_headers_aux_data*)item->aux_data;
      if(frame->hd.stream_id == -1) {
        /* initial HEADERS, which opens stream */
        int r;
        frame->headers.cat = NGHTTP2_HCAT_REQUEST;
        r = nghttp2_session_predicate_request_headers_send(session,
                                                           &frame->headers);
        if(r != 0) {
          return r;
        }
        frame->hd.stream_id = session->next_stream_id;
        session->next_stream_id += 2;
      } else if(nghttp2_session_predicate_push_response_headers_send
                (session, frame->hd.stream_id) == 0) {
        frame->headers.cat = NGHTTP2_HCAT_PUSH_RESPONSE;
      } else if(nghttp2_session_predicate_response_headers_send
                (session, frame->hd.stream_id) == 0) {
        frame->headers.cat = NGHTTP2_HCAT_RESPONSE;
      } else {
        int r;
        frame->headers.cat = NGHTTP2_HCAT_HEADERS;
        r = nghttp2_session_predicate_headers_send(session,
                                                   frame->hd.stream_id);
        if(r != 0) {
          return r;
        }
      }
      framebuflen = nghttp2_frame_pack_headers(&session->aob.framebuf,
                                               &session->aob.framebufmax,
                                               &session->aob.framebufoff,
                                               &frame->headers,
                                               &session->hd_deflater,
                                               session->pad_alignment);
      if(framebuflen < 0) {
        return framebuflen;
      }
      switch(frame->headers.cat) {
      case NGHTTP2_HCAT_REQUEST: {
        if(nghttp2_session_open_stream
           (session, frame->hd.stream_id,
            NGHTTP2_STREAM_FLAG_NONE,
            frame->headers.pri,
            NGHTTP2_STREAM_INITIAL,
            aux_data ? aux_data->stream_user_data : NULL) == NULL) {
          return NGHTTP2_ERR_NOMEM;
        }
        break;
      }
      case NGHTTP2_HCAT_PUSH_RESPONSE: {
        if(aux_data && aux_data->stream_user_data) {
          nghttp2_stream *stream;
          stream = nghttp2_session_get_stream(session, frame->hd.stream_id);
          stream->stream_user_data = aux_data->stream_user_data;
        }
        break;
      }
      default:
        break;
      }
      break;
    }
    case NGHTTP2_PRIORITY: {
      int r;
      r = nghttp2_session_predicate_priority_send
        (session, frame->hd.stream_id);
      if(r != 0) {
        return r;
      }
      framebuflen = nghttp2_frame_pack_priority(&session->aob.framebuf,
                                                &session->aob.framebufmax,
                                                &frame->priority);
      if(framebuflen < 0) {
        return framebuflen;
      }
      break;
    }
    case NGHTTP2_RST_STREAM:
      framebuflen = nghttp2_frame_pack_rst_stream(&session->aob.framebuf,
                                                  &session->aob.framebufmax,
                                                  &frame->rst_stream);
      if(framebuflen < 0) {
        return framebuflen;
      }
      break;
    case NGHTTP2_SETTINGS: {
      int r;
      r = nghttp2_session_predicate_settings_send(session, frame);
      if(r != 0) {
        return r;
      }
      framebuflen = nghttp2_frame_pack_settings(&session->aob.framebuf,
                                                &session->aob.framebufmax,
                                                &frame->settings);
      if(framebuflen < 0) {
        return framebuflen;
      }
      break;
    }
    case NGHTTP2_PUSH_PROMISE: {
      int r;
      nghttp2_stream *stream;
      r = nghttp2_session_predicate_push_promise_send(session,
                                                      frame->hd.stream_id);
      if(r != 0) {
        return r;
      }
      frame->push_promise.promised_stream_id = session->next_stream_id;
      session->next_stream_id += 2;
      framebuflen = nghttp2_frame_pack_push_promise(&session->aob.framebuf,
                                                    &session->aob.framebufmax,
                                                    &frame->push_promise,
                                                    &session->hd_deflater);
      if(framebuflen < 0) {
        return framebuflen;
      }
      stream = nghttp2_session_get_stream(session, frame->hd.stream_id);
      assert(stream);
      if(nghttp2_session_open_stream
         (session, frame->push_promise.promised_stream_id,
          NGHTTP2_STREAM_FLAG_PUSH,
          nghttp2_pushed_stream_pri(stream),
          NGHTTP2_STREAM_RESERVED,
          NULL) == NULL) {
        return NGHTTP2_ERR_NOMEM;
      }
      break;
    }
    case NGHTTP2_PING:
      framebuflen = nghttp2_frame_pack_ping(&session->aob.framebuf,
                                            &session->aob.framebufmax,
                                            &frame->ping);
      if(framebuflen < 0) {
        return framebuflen;
      }
      break;
    case NGHTTP2_WINDOW_UPDATE: {
      int r;
      r = nghttp2_session_predicate_window_update_send
        (session, frame->hd.stream_id);
      if(r != 0) {
        return r;
      }
      framebuflen = nghttp2_frame_pack_window_update(&session->aob.framebuf,
                                                     &session->aob.framebufmax,
                                                     &frame->window_update);
      if(framebuflen < 0) {
        return framebuflen;
      }
      break;
    }
    case NGHTTP2_GOAWAY:
      if(session->goaway_flags & NGHTTP2_GOAWAY_SEND) {
        /* TODO The spec does not mandate that both endpoints have to
           exchange GOAWAY. This implementation allows receiver of
           first GOAWAY can sent its own GOAWAY to tell the remote
           peer that last-stream-id. */
        return NGHTTP2_ERR_GOAWAY_ALREADY_SENT;
      }
      framebuflen = nghttp2_frame_pack_goaway(&session->aob.framebuf,
                                              &session->aob.framebufmax,
                                              &frame->goaway);
      if(framebuflen < 0) {
        return framebuflen;
      }
      break;
    default:
      framebuflen = NGHTTP2_ERR_INVALID_ARGUMENT;
    }
  } else if(item->frame_cat == NGHTTP2_CAT_DATA) {
    size_t next_readmax;
    nghttp2_stream *stream;
    nghttp2_private_data *data_frame;
    int r;
    data_frame = nghttp2_outbound_item_get_data_frame(item);
    r = nghttp2_session_predicate_data_send(session, data_frame->hd.stream_id);
    if(r != 0) {
      return r;
    }
    stream = nghttp2_session_get_stream(session, data_frame->hd.stream_id);
    /* Assuming stream is not NULL */
    assert(stream);
    next_readmax = nghttp2_session_next_data_read(session, stream);
    if(next_readmax == 0) {
      nghttp2_stream_defer_data(stream, item, NGHTTP2_DEFERRED_FLOW_CONTROL);
      return NGHTTP2_ERR_DEFERRED;
    }
    framebuflen = nghttp2_session_pack_data(session,
                                            &session->aob.framebuf,
                                            &session->aob.framebufmax,
                                            &session->aob.framebufoff,
                                            next_readmax,
                                            data_frame);
    if(framebuflen == NGHTTP2_ERR_DEFERRED) {
      nghttp2_stream_defer_data(stream, item, NGHTTP2_DEFERRED_NONE);
      return NGHTTP2_ERR_DEFERRED;
    } else if(framebuflen == NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE) {
      r = nghttp2_session_add_rst_stream(session, data_frame->hd.stream_id,
                                         NGHTTP2_INTERNAL_ERROR);
      if(r == 0) {
        return framebuflen;
      } else {
        return r;
      }
    } else if(framebuflen < 0) {
      return framebuflen;
    }
  } else {
    /* Unreachable */
    assert(0);
  }
  return framebuflen;
}

nghttp2_outbound_item* nghttp2_session_get_ob_pq_top
(nghttp2_session *session)
{
  return (nghttp2_outbound_item*)nghttp2_pq_top(&session->ob_pq);
}

nghttp2_outbound_item* nghttp2_session_get_next_ob_item
(nghttp2_session *session)
{
  if(nghttp2_pq_empty(&session->ob_pq)) {
    if(nghttp2_pq_empty(&session->ob_ss_pq)) {
      return NULL;
    } else {
      /* Return item only when concurrent connection limit is not
         reached */
      if(nghttp2_session_is_outgoing_concurrent_streams_max(session)) {
        return NULL;
      } else {
        return nghttp2_pq_top(&session->ob_ss_pq);
      }
    }
  } else {
    if(nghttp2_pq_empty(&session->ob_ss_pq)) {
      return nghttp2_pq_top(&session->ob_pq);
    } else {
      nghttp2_outbound_item *item, *headers_item;
      item = nghttp2_pq_top(&session->ob_pq);
      headers_item = nghttp2_pq_top(&session->ob_ss_pq);
      if(nghttp2_session_is_outgoing_concurrent_streams_max(session) ||
         item->pri < headers_item->pri ||
         (item->pri == headers_item->pri &&
          item->seq < headers_item->seq)) {
        return item;
      } else {
        return headers_item;
      }
    }
  }
}

nghttp2_outbound_item* nghttp2_session_pop_next_ob_item
(nghttp2_session *session)
{
  if(nghttp2_pq_empty(&session->ob_pq)) {
    if(nghttp2_pq_empty(&session->ob_ss_pq)) {
      return NULL;
    } else {
      /* Pop item only when concurrent connection limit is not
         reached */
      if(nghttp2_session_is_outgoing_concurrent_streams_max(session)) {
        return NULL;
      } else {
        nghttp2_outbound_item *item;
        item = nghttp2_pq_top(&session->ob_ss_pq);
        nghttp2_pq_pop(&session->ob_ss_pq);
        return item;
      }
    }
  } else {
    if(nghttp2_pq_empty(&session->ob_ss_pq)) {
      nghttp2_outbound_item *item;
      item = nghttp2_pq_top(&session->ob_pq);
      nghttp2_pq_pop(&session->ob_pq);
      return item;
    } else {
      nghttp2_outbound_item *item, *headers_item;
      item = nghttp2_pq_top(&session->ob_pq);
      headers_item = nghttp2_pq_top(&session->ob_ss_pq);
      if(nghttp2_session_is_outgoing_concurrent_streams_max(session) ||
         item->pri < headers_item->pri ||
         (item->pri == headers_item->pri &&
          item->seq < headers_item->seq)) {
        nghttp2_pq_pop(&session->ob_pq);
        return item;
      } else {
        nghttp2_pq_pop(&session->ob_ss_pq);
        return headers_item;
      }
    }
  }
}

static int session_call_before_frame_send(nghttp2_session *session,
                                          nghttp2_frame *frame)
{
  int rv;
  if(session->callbacks.before_frame_send_callback) {
    /* Adjust frame length to deal with CONTINUATION frame */
    size_t origlen = frame->hd.length;
    frame->hd.length =
      session->aob.framebuflen - NGHTTP2_FRAME_HEAD_LENGTH;
    rv = session->callbacks.before_frame_send_callback(session, frame,
                                                       session->user_data);
    frame->hd.length = origlen;
    if(rv != 0) {
      return NGHTTP2_ERR_CALLBACK_FAILURE;
    }
  }
  return 0;
}

static int session_call_on_frame_send(nghttp2_session *session,
                                      nghttp2_frame *frame)
{
  int rv;
  if(session->callbacks.on_frame_send_callback) {
    rv = session->callbacks.on_frame_send_callback(session, frame,
                                                   session->user_data);
    if(rv != 0) {
      return NGHTTP2_ERR_CALLBACK_FAILURE;
    }
  }
  return 0;
}

/*
 * Called after a frame is sent.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * NGHTTP2_ERR_NOMEM
 *     Out of memory.
 * NGHTTP2_ERR_CALLBACK_FAILURE
 *     The callback function failed.
 */
static int nghttp2_session_after_frame_sent(nghttp2_session *session)
{
  int rv;
  nghttp2_outbound_item *item = session->aob.item;
  if(item->frame_cat == NGHTTP2_CAT_CTRL) {
    nghttp2_frame *frame;
    frame = nghttp2_outbound_item_get_ctrl_frame(session->aob.item);
    if(frame->hd.type == NGHTTP2_HEADERS ||
       frame->hd.type == NGHTTP2_PUSH_PROMISE) {
      if(session->aob.framebufmark < session->aob.framebuflen) {
        nghttp2_frame_hd cont_hd;
        cont_hd.length = nghttp2_min(session->aob.framebuflen -
                                     session->aob.framebufmark,
                                     NGHTTP2_MAX_FRAME_LENGTH);
        cont_hd.type = NGHTTP2_CONTINUATION;
        if(cont_hd.length + session->aob.framebufmark ==
           session->aob.framebuflen) {
          cont_hd.flags = NGHTTP2_FLAG_END_HEADERS;
          cont_hd.flags |=
            (NGHTTP2_FLAG_PAD_HIGH | NGHTTP2_FLAG_PAD_LOW) & frame->hd.flags;
        } else {
          cont_hd.flags = NGHTTP2_FLAG_NONE;
        }
        cont_hd.stream_id = frame->hd.stream_id;
        nghttp2_frame_pack_frame_hd(session->aob.framebuf +
                                    session->aob.framebufmark -
                                    NGHTTP2_FRAME_HEAD_LENGTH,
                                    &cont_hd);
        session->aob.framebufmark += cont_hd.length;
        session->aob.framebufoff -= NGHTTP2_FRAME_HEAD_LENGTH;
        return 0;
      }
    }
    rv = session_call_on_frame_send(session, frame);
    if(nghttp2_is_fatal(rv)) {
      return rv;
    }
    switch(frame->hd.type) {
    case NGHTTP2_HEADERS: {
      nghttp2_headers_aux_data *aux_data;
      nghttp2_stream *stream =
        nghttp2_session_get_stream(session, frame->hd.stream_id);
      if(!stream) {
        break;
      }
      switch(frame->headers.cat) {
      case NGHTTP2_HCAT_REQUEST: {
        stream->state = NGHTTP2_STREAM_OPENING;
        if(frame->hd.flags & NGHTTP2_FLAG_END_STREAM) {
          nghttp2_stream_shutdown(stream, NGHTTP2_SHUT_WR);
        }
        rv = nghttp2_session_close_stream_if_shut_rdwr(session, stream);
        if(nghttp2_is_fatal(rv)) {
          return rv;
        }
        /* We assume aux_data is a pointer to nghttp2_headers_aux_data */
        aux_data = (nghttp2_headers_aux_data*)item->aux_data;
        if(aux_data && aux_data->data_prd) {
          /* nghttp2_submit_data() makes a copy of aux_data->data_prd */
          rv = nghttp2_submit_data(session, NGHTTP2_FLAG_END_STREAM,
                                   frame->hd.stream_id, aux_data->data_prd);
          if(nghttp2_is_fatal(rv)) {
            return rv;
          }
          /* If r is not fatal, the only possible error is closed
             stream, so we have nothing to do here. */
        }
        break;
      }
      case NGHTTP2_HCAT_RESPONSE:
      case NGHTTP2_HCAT_PUSH_RESPONSE:
        stream->state = NGHTTP2_STREAM_OPENED;
        if(frame->hd.flags & NGHTTP2_FLAG_END_STREAM) {
          nghttp2_stream_shutdown(stream, NGHTTP2_SHUT_WR);
        }
        rv = nghttp2_session_close_stream_if_shut_rdwr(session, stream);
        if(nghttp2_is_fatal(rv)) {
          return rv;
        }
        /* We assume aux_data is a pointer to nghttp2_headers_aux_data */
        aux_data = (nghttp2_headers_aux_data*)item->aux_data;
        if(aux_data && aux_data->data_prd) {
          rv = nghttp2_submit_data(session, NGHTTP2_FLAG_END_STREAM,
                                   frame->hd.stream_id, aux_data->data_prd);
          if(nghttp2_is_fatal(rv)) {
            return rv;
          }
          /* If r is not fatal, the only possible error is closed
             stream, so we have nothing to do here. */
        }
        break;
      case NGHTTP2_HCAT_HEADERS:
        if(frame->hd.flags & NGHTTP2_FLAG_END_STREAM) {
          nghttp2_stream_shutdown(stream, NGHTTP2_SHUT_WR);
        }
        rv = nghttp2_session_close_stream_if_shut_rdwr(session, stream);
        if(nghttp2_is_fatal(rv)) {
          return rv;
        }
        break;
      }
      break;
    }
    case NGHTTP2_PRIORITY: {
      nghttp2_stream *stream;
      stream = nghttp2_session_get_stream(session, frame->hd.stream_id);
      if(!stream) {
        break;
      }
      /* Only update priority of the stream, only if it is not pushed
         stream and is initiated by local peer, or it is pushed stream
         and is initiated by remote peer */
      if(((stream->flags & NGHTTP2_STREAM_FLAG_PUSH) == 0 &&
          nghttp2_session_is_my_stream_id(session, frame->hd.stream_id)) ||
         ((stream->flags & NGHTTP2_STREAM_FLAG_PUSH) &&
          !nghttp2_session_is_my_stream_id(session, frame->hd.stream_id))) {
        nghttp2_session_reprioritize_stream(session, stream,
                                            frame->priority.pri);
      }
      break;
    }
    case NGHTTP2_RST_STREAM:
      rv = nghttp2_session_close_stream(session, frame->hd.stream_id,
                                       frame->rst_stream.error_code);
      if(nghttp2_is_fatal(rv)) {
        return rv;
      }
      break;
    case NGHTTP2_SETTINGS: {
      size_t i;
      if(frame->hd.flags & NGHTTP2_FLAG_ACK) {
        break;
      }
      /* Only update max concurrent stream here. Applying it without
         ACK is safe because we can respond to the exceeding streams
         with REFUSED_STREAM and client will retry later. */
      for(i = frame->settings.niv; i > 0; --i) {
        if(frame->settings.iv[i - 1].settings_id ==
           NGHTTP2_SETTINGS_MAX_CONCURRENT_STREAMS) {
          session->local_settings[NGHTTP2_SETTINGS_MAX_CONCURRENT_STREAMS] =
            frame->settings.iv[i - 1].value;
          break;
        }
      }
      assert(session->inflight_niv == -1);
      session->inflight_iv = frame->settings.iv;
      session->inflight_niv = frame->settings.niv;
      frame->settings.iv = NULL;
      frame->settings.niv = 0;
      break;
    }
    case NGHTTP2_PUSH_PROMISE:
      /* nothing to do */
      break;
    case NGHTTP2_PING:
      /* nothing to do */
      break;
    case NGHTTP2_GOAWAY:
      session->goaway_flags |= NGHTTP2_GOAWAY_SEND;
      break;
    case NGHTTP2_WINDOW_UPDATE:
      /* nothing to do */
      break;
    }
    nghttp2_active_outbound_item_reset(&session->aob);
    return 0;
  } else if(item->frame_cat == NGHTTP2_CAT_DATA) {
    nghttp2_private_data *data_frame;
    nghttp2_outbound_item* next_item;
    nghttp2_stream *stream;

    data_frame = nghttp2_outbound_item_get_data_frame(session->aob.item);
    stream = nghttp2_session_get_stream(session, data_frame->hd.stream_id);
    /* We update flow control window after a frame was completely
       sent. This is possible because we choose payload length not to
       exceed the window */
    session->remote_window_size -= data_frame->hd.length;
    if(stream) {
      stream->remote_window_size -= data_frame->hd.length;
    }

    if(session->callbacks.on_frame_send_callback) {
      nghttp2_frame public_data_frame;
      nghttp2_frame_data_init(&public_data_frame.data, data_frame);
      rv = session_call_on_frame_send(session, &public_data_frame);
      if(nghttp2_is_fatal(rv)) {
        return rv;
      }
    }

    if(stream && data_frame->eof &&
       (data_frame->hd.flags & NGHTTP2_FLAG_END_STREAM)) {
      nghttp2_stream_shutdown(stream, NGHTTP2_SHUT_WR);
      rv = nghttp2_session_close_stream_if_shut_rdwr(session, stream);
      if(nghttp2_is_fatal(rv)) {
        return rv;
      }
    }
    /* If session is closed or RST_STREAM was queued, we won't send
       further data. */
    if(data_frame->eof ||
       nghttp2_session_predicate_data_send(session,
                                           data_frame->hd.stream_id) != 0) {
      nghttp2_active_outbound_item_reset(&session->aob);
      return 0;
    }
    /* Assuming stream is not NULL */
    assert(stream);
    next_item = nghttp2_session_get_next_ob_item(session);
    /* If priority of this stream is higher or equal to other stream
       waiting at the top of the queue, we continue to send this
       data. */
    if(next_item == NULL || session->aob.item->pri < next_item->pri) {
      size_t next_readmax;
      next_readmax = nghttp2_session_next_data_read(session, stream);
      if(next_readmax == 0) {
        nghttp2_stream_defer_data(stream, session->aob.item,
                                  NGHTTP2_DEFERRED_FLOW_CONTROL);
        session->aob.item = NULL;
        nghttp2_active_outbound_item_reset(&session->aob);
        return 0;
      }
      rv = nghttp2_session_pack_data(session,
                                     &session->aob.framebuf,
                                     &session->aob.framebufmax,
                                     &session->aob.framebufoff,
                                     next_readmax,
                                     data_frame);
      if(nghttp2_is_fatal(rv)) {
        return rv;
      }
      if(rv == NGHTTP2_ERR_DEFERRED) {
        nghttp2_stream_defer_data(stream, session->aob.item,
                                  NGHTTP2_DEFERRED_NONE);
        session->aob.item = NULL;
        nghttp2_active_outbound_item_reset(&session->aob);
        return 0;
      }
      if(rv == NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE) {
        /* Stop DATA frame chain and issue RST_STREAM to close the
           stream.  We don't return
           NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE intentionally. */
        rv = nghttp2_session_add_rst_stream(session,
                                            data_frame->hd.stream_id,
                                            NGHTTP2_INTERNAL_ERROR);
        nghttp2_active_outbound_item_reset(&session->aob);
        if(nghttp2_is_fatal(rv)) {
          return rv;
        }
        return 0;
      }
      assert(rv >= 0);
      session->aob.framebuflen = session->aob.framebufmark = rv;
      return 0;
    }
    /* Update seq to interleave other streams with the same
       priority. */
    session->aob.item->seq = session->next_seq++;
    rv = nghttp2_pq_push(&session->ob_pq, session->aob.item);
    if(nghttp2_is_fatal(rv)) {
      return rv;
    }
    session->aob.item = NULL;
    nghttp2_active_outbound_item_reset(&session->aob);
    return 0;
  }
  /* Unreachable */
  assert(0);
}

int nghttp2_session_send(nghttp2_session *session)
{
  int r;
  while(1) {
    const uint8_t *data;
    size_t datalen;
    ssize_t sentlen;
    if(session->aob.item == NULL) {
      nghttp2_outbound_item *item;
      ssize_t framebuflen;
      item = nghttp2_session_pop_next_ob_item(session);
      if(item == NULL) {
        break;
      }
      framebuflen = nghttp2_session_prep_frame(session, item);
      if(framebuflen == NGHTTP2_ERR_DEFERRED) {
        continue;
      }
      if(framebuflen < 0) {
        /* TODO If the error comes from compressor, the connection
           must be closed. */
        if(item->frame_cat == NGHTTP2_CAT_CTRL &&
           session->callbacks.on_frame_not_send_callback &&
           nghttp2_is_non_fatal(framebuflen)) {
          /* The library is responsible for the transmission of
             WINDOW_UPDATE frame, so we don't call error callback for
             it. */
          nghttp2_frame *frame = nghttp2_outbound_item_get_ctrl_frame(item);
          if(frame->hd.type != NGHTTP2_WINDOW_UPDATE) {
            if(session->callbacks.on_frame_not_send_callback
               (session, frame, framebuflen, session->user_data) != 0) {
              return NGHTTP2_ERR_CALLBACK_FAILURE;
            }
          }
        }
        nghttp2_outbound_item_free(item);
        free(item);

        if(framebuflen == NGHTTP2_ERR_HEADER_COMP) {
          /* If header compression error occurred, should terminiate
             connection. */
          framebuflen = nghttp2_session_terminate_session
            (session, NGHTTP2_INTERNAL_ERROR);
        }
        if(nghttp2_is_fatal(framebuflen)) {
          return framebuflen;
        } else {
          continue;
        }
      }
      session->aob.item = item;
      session->aob.framebuflen = framebuflen;

      if(item->frame_cat == NGHTTP2_CAT_CTRL) {
        nghttp2_frame *frame = nghttp2_outbound_item_get_ctrl_frame(item);
        session->aob.framebufmark =
          session->aob.framebufoff +
          frame->hd.length + NGHTTP2_FRAME_HEAD_LENGTH;
        r = session_call_before_frame_send(session, frame);
        if(nghttp2_is_fatal(r)) {
          return r;
        }
      } else {
        nghttp2_private_data *frame;
        frame = nghttp2_outbound_item_get_data_frame(session->aob.item);
        /* session->aob.framebufmark = session->aob.framebuflen; */
        session->aob.framebufmark =
          session->aob.framebufoff +
          frame->hd.length + NGHTTP2_FRAME_HEAD_LENGTH;
      }
    }

    data = session->aob.framebuf + session->aob.framebufoff;
    datalen = session->aob.framebufmark - session->aob.framebufoff;
    sentlen = session->callbacks.send_callback(session, data, datalen, 0,
                                               session->user_data);
    if(sentlen < 0) {
      if(sentlen == NGHTTP2_ERR_WOULDBLOCK) {
        return 0;
      } else {
        return NGHTTP2_ERR_CALLBACK_FAILURE;
      }
    } else {
      session->aob.framebufoff += sentlen;
      if(session->aob.framebufoff == session->aob.framebufmark) {
        /* Frame has completely sent */
        r = nghttp2_session_after_frame_sent(session);
        if(r < 0) {
          /* FATAL */
          assert(r < NGHTTP2_ERR_FATAL);
          return r;
        }
      }
    }
  }
  return 0;
}

static ssize_t nghttp2_recv(nghttp2_session *session, uint8_t *buf, size_t len)
{
  ssize_t r;
  r = session->callbacks.recv_callback
    (session, buf, len, 0, session->user_data);
  if(r > 0) {
    if((size_t)r > len) {
      return NGHTTP2_ERR_CALLBACK_FAILURE;
    }
  } else if(r < 0) {
    if(r != NGHTTP2_ERR_WOULDBLOCK && r != NGHTTP2_ERR_EOF) {
      r = NGHTTP2_ERR_CALLBACK_FAILURE;
    }
  }
  return r;
}

static int nghttp2_session_call_on_frame_received
(nghttp2_session *session, nghttp2_frame *frame)
{
  int rv;
  if(session->callbacks.on_frame_recv_callback) {
    rv = session->callbacks.on_frame_recv_callback(session, frame,
                                                   session->user_data);
    if(rv != 0) {
      return NGHTTP2_ERR_CALLBACK_FAILURE;
    }
  }
  return 0;
}

static int session_call_on_begin_headers(nghttp2_session *session,
                                         nghttp2_frame *frame)
{
  int rv;
  DEBUGF(fprintf(stderr, "Call on_begin_headers callback stream_id=%d\n",
                 frame->hd.stream_id));
  if(session->callbacks.on_begin_headers_callback) {
    rv = session->callbacks.on_begin_headers_callback(session, frame,
                                                      session->user_data);
    if(rv != 0) {
      return NGHTTP2_ERR_CALLBACK_FAILURE;
    }
  }
  return 0;
}

static int session_call_on_header(nghttp2_session *session,
                                  const nghttp2_frame *frame,
                                  const nghttp2_nv *nv)
{
  int rv;
  if(session->callbacks.on_header_callback) {
    rv = session->callbacks.on_header_callback(session, frame,
                                               nv->name, nv->namelen,
                                               nv->value, nv->valuelen,
                                               session->user_data);
    if(rv == NGHTTP2_ERR_PAUSE ||
       rv == NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE) {
      return rv;
    }
    if(rv != 0) {
      return NGHTTP2_ERR_CALLBACK_FAILURE;
    }
  }
  return 0;
}

/*
 * Checks whether received stream_id is valid.
 * This function returns 1 if it succeeds, or 0.
 */
static int nghttp2_session_is_new_peer_stream_id(nghttp2_session *session,
                                                 int32_t stream_id)
{
  if(stream_id == 0 || session->last_recv_stream_id >= stream_id) {
    return 0;
  }
  if(session->server) {
    return stream_id % 2 == 1;
  } else {
    return stream_id % 2 == 0;
  }
}

static int session_detect_idle_stream(nghttp2_session *session,
                                      int32_t stream_id)
{
  /* Assume that stream object with stream_id does not exist */
  if(nghttp2_session_is_my_stream_id(session, stream_id)) {
    if(session->next_stream_id >= (uint32_t)stream_id) {
      return 1;
    }
    return 0;
  }
  if(nghttp2_session_is_new_peer_stream_id(session, stream_id)) {
    return 1;
  }
  return 0;
}

/*
 * Validates received HEADERS frame |frame| with NGHTTP2_HCAT_REQUEST
 * or NGHTTP2_HCAT_PUSH_RESPONSE category, which both opens new
 * stream.
 *
 * This function returns 0 if it succeeds, or non-zero
 * nghttp2_error_code.
 */
static int nghttp2_session_validate_request_headers(nghttp2_session *session,
                                                    nghttp2_headers *frame)
{
  if(nghttp2_session_is_incoming_concurrent_streams_max(session)) {
    /* The spec does not clearly say what to do when max concurrent
       streams number is reached. The mod_spdy sends
       NGHTTP2_REFUSED_STREAM and we think it is reasonable. So we
       follow it. */
    return NGHTTP2_REFUSED_STREAM;
  }
  return 0;
}

/*
 * Inflates header block in the memory pointed by |in| with |inlen|
 * bytes. If this function returns NGHTTP2_ERR_PAUSE, the caller must
 * call this function again, until it returns 0 or one of negative
 * error code.  If |call_header_cb| is zero, the on_header_callback
 * are not invoked and the function never return NGHTTP2_ERR_PAUSE. If
 * the given |in| is the last chunk of header block, the |final| must
 * be nonzero. If header block is successfully processed (which is
 * indicated by the return value 0, NGHTTP2_ERR_PAUSE or
 * NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE), the number of processed
 * input bytes is assigned to the |*readlen_ptr|.
 *
 * This function return 0 if it succeeds, or one of the negative error
 * codes:
 *
 * NGHTTP2_ERR_CALLBACK_FAILURE
 *     The callback function failed.
 * NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE
 *     The callback returns this error code, indicating that this
 *     stream should be RST_STREAMed.
 * NGHTTP2_ERR_NOMEM
 *     Out of memory.
 * NGHTTP2_ERR_PAUSE
 *     The callback function returned NGHTTP2_ERR_PAUSE
 * NGHTTP2_ERR_HEADER_COMP
 *     Header decompression failed
 */
static ssize_t inflate_header_block(nghttp2_session *session,
                                    nghttp2_frame *frame,
                                    size_t *readlen_ptr,
                                    uint8_t *in, size_t inlen,
                                    int final, int call_header_cb)
{
  ssize_t rv;
  int inflate_flags;
  nghttp2_nv nv;
  *readlen_ptr = 0;

  DEBUGF(fprintf(stderr, "processing header block %zu bytes\n", inlen));
  for(;;) {
    inflate_flags = 0;
    rv = nghttp2_hd_inflate_hd(&session->hd_inflater, &nv, &inflate_flags,
                               in, inlen, final);
    if(nghttp2_is_fatal(rv)) {
      return rv;
    }
    if(rv < 0) {
      rv = nghttp2_session_terminate_session(session,
                                             NGHTTP2_COMPRESSION_ERROR);
      if(rv != 0) {
        return rv;
      }
      return NGHTTP2_ERR_HEADER_COMP;
    }
    in += rv;
    inlen -= rv;
    *readlen_ptr += rv;
    if(call_header_cb && (inflate_flags & NGHTTP2_HD_INFLATE_EMIT)) {
      rv = session_call_on_header(session, frame, &nv);
      /* This handles NGHTTP2_ERR_PAUSE and
         NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE as well */
      if(rv != 0) {
        return rv;
      }
    }
    if(inflate_flags & NGHTTP2_HD_INFLATE_FINAL) {
      nghttp2_hd_inflate_end_headers(&session->hd_inflater);
      break;
    }
    if((inflate_flags & NGHTTP2_HD_INFLATE_EMIT) == 0 && inlen == 0) {
      break;
    }
  }
  return 0;
}

/*
 * Handles frame size error.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * NGHTTP2_ERR_NOMEM
 *   Out of memory.
 */
static int session_handle_frame_size_error(nghttp2_session *session,
                                           nghttp2_frame *frame)
{
  /* TODO Currently no callback is called for this error, because we
     call this callback before reading any payload */
  return nghttp2_session_terminate_session(session, NGHTTP2_FRAME_SIZE_ERROR);
}

static int nghttp2_session_handle_invalid_stream
(nghttp2_session *session,
 nghttp2_frame *frame,
 nghttp2_error_code error_code)
{
  int r;
  r = nghttp2_session_add_rst_stream(session, frame->hd.stream_id, error_code);
  if(r != 0) {
    return r;
  }
  if(session->callbacks.on_invalid_frame_recv_callback) {
    if(session->callbacks.on_invalid_frame_recv_callback
       (session, frame, error_code, session->user_data) != 0) {
      return NGHTTP2_ERR_CALLBACK_FAILURE;
    }
  }
  return 0;
}

static int nghttp2_session_inflate_handle_invalid_stream
(nghttp2_session *session,
 nghttp2_frame *frame,
 nghttp2_error_code error_code)
{
  int rv;
  rv = nghttp2_session_handle_invalid_stream(session, frame, error_code);
  if(nghttp2_is_fatal(rv)) {
    return rv;
  }
  return NGHTTP2_ERR_IGN_HEADER_BLOCK;
}

/*
 * Handles invalid frame which causes connection error.
 */
static int nghttp2_session_handle_invalid_connection
(nghttp2_session *session,
 nghttp2_frame *frame,
 nghttp2_error_code error_code)
{
  if(session->callbacks.on_invalid_frame_recv_callback) {
    if(session->callbacks.on_invalid_frame_recv_callback
       (session, frame, error_code, session->user_data) != 0) {
      return NGHTTP2_ERR_CALLBACK_FAILURE;
    }
  }
  return nghttp2_session_terminate_session(session, error_code);
}

static int nghttp2_session_inflate_handle_invalid_connection
(nghttp2_session *session,
 nghttp2_frame *frame,
 nghttp2_error_code error_code)
{
  int rv;
  rv = nghttp2_session_handle_invalid_connection(session, frame, error_code);
  if(nghttp2_is_fatal(rv)) {
    return rv;
  }
  return NGHTTP2_ERR_IGN_HEADER_BLOCK;
}

/*
 * Decompress header blocks of incoming request HEADERS and also call
 * additional callbacks. This function can be called again if this
 * function returns NGHTTP2_ERR_PAUSE.
 *
 * This function returns 0 if it succeeds, or one of negative error
 * codes:
 *
 * NGHTTP2_ERR_CALLBACK_FAILURE
 *     The callback function failed.
 * NGHTTP2_ERR_NOMEM
 *     Out of memory.
 */
int nghttp2_session_end_request_headers_received(nghttp2_session *session,
                                                 nghttp2_frame *frame,
                                                 nghttp2_stream *stream)
{
  if(frame->hd.flags & NGHTTP2_FLAG_END_STREAM) {
    nghttp2_stream_shutdown(stream, NGHTTP2_SHUT_RD);
  }
  /* Here we assume that stream is not shutdown in NGHTTP2_SHUT_WR */
  return 0;
}

/*
 * Decompress header blocks of incoming (push-)response HEADERS and
 * also call additional callbacks. This function can be called again
 * if this function returns NGHTTP2_ERR_PAUSE.
 *
 * This function returns 0 if it succeeds, or one of negative error
 * codes:
 *
 * NGHTTP2_ERR_CALLBACK_FAILURE
 *     The callback function failed.
 * NGHTTP2_ERR_NOMEM
 *     Out of memory.
 */
int nghttp2_session_end_response_headers_received(nghttp2_session *session,
                                                  nghttp2_frame *frame,
                                                  nghttp2_stream *stream)
{
  int rv;
  if(frame->hd.flags & NGHTTP2_FLAG_END_STREAM) {
    /* This is the last frame of this stream, so disallow
       further receptions. */
    nghttp2_stream_shutdown(stream, NGHTTP2_SHUT_RD);
    rv = nghttp2_session_close_stream_if_shut_rdwr(session, stream);
    if(nghttp2_is_fatal(rv)) {
      return rv;
    }
  }
  return 0;
}

/*
 * Decompress header blocks of incoming HEADERS and also call
 * additional callbacks. This function can be called again if this
 * function returns NGHTTP2_ERR_PAUSE.
 *
 * This function returns 0 if it succeeds, or one of negative error
 * codes:
 *
 * NGHTTP2_ERR_CALLBACK_FAILURE
 *     The callback function failed.
 * NGHTTP2_ERR_NOMEM
 *     Out of memory.
 */
int nghttp2_session_end_headers_received(nghttp2_session *session,
                                         nghttp2_frame *frame,
                                         nghttp2_stream *stream)
{
  int rv;
  if(frame->hd.flags & NGHTTP2_FLAG_END_STREAM) {
    if(!nghttp2_session_is_my_stream_id(session, frame->hd.stream_id)) {
    }
    nghttp2_stream_shutdown(stream, NGHTTP2_SHUT_RD);
    rv = nghttp2_session_close_stream_if_shut_rdwr(session, stream);
    if(nghttp2_is_fatal(rv)) {
      return rv;
    }
  }
  return 0;
}

static int session_after_header_block_received(nghttp2_session *session)
{
  int rv;
  nghttp2_frame *frame = &session->iframe.frame;
  nghttp2_stream *stream;

  /* We call on_frame_recv_callback regardless of the existence of
     stream */
  rv = nghttp2_session_call_on_frame_received(session, frame);
  if(nghttp2_is_fatal(rv)) {
    return rv;
  }
  if(frame->hd.type !=  NGHTTP2_HEADERS) {
    return 0;
  }
  stream = nghttp2_session_get_stream(session, frame->hd.stream_id);
  if(!stream) {
    return 0;
  }
  switch(frame->headers.cat) {
  case NGHTTP2_HCAT_REQUEST:
    return nghttp2_session_end_request_headers_received
      (session, frame, stream);
  case NGHTTP2_HCAT_RESPONSE:
  case NGHTTP2_HCAT_PUSH_RESPONSE:
    return nghttp2_session_end_response_headers_received
      (session, frame, stream);
  case NGHTTP2_HCAT_HEADERS:
    return nghttp2_session_end_headers_received(session, frame, stream);
  default:
    assert(0);
  }
  return 0;
}

int nghttp2_session_on_request_headers_received(nghttp2_session *session,
                                                nghttp2_frame *frame)
{
  int rv = 0;
  nghttp2_error_code error_code;
  nghttp2_stream *stream;
  if(frame->hd.stream_id == 0) {
    return nghttp2_session_inflate_handle_invalid_connection
      (session, frame, NGHTTP2_PROTOCOL_ERROR);
  }
  if(session->goaway_flags) {
    /* We don't accept new stream after GOAWAY is sent or received. */
    return NGHTTP2_ERR_IGN_HEADER_BLOCK;
  }
  if(!nghttp2_session_is_new_peer_stream_id(session, frame->hd.stream_id)) {
    /* The spec says if an endpoint receives a HEADERS with invalid
       stream ID, it MUST issue connection error with error code
       PROTOCOL_ERROR */
    return nghttp2_session_inflate_handle_invalid_connection
      (session, frame, NGHTTP2_PROTOCOL_ERROR);
  }
  session->last_recv_stream_id = frame->hd.stream_id;

  error_code = nghttp2_session_validate_request_headers(session,
                                                        &frame->headers);
  if(error_code != NGHTTP2_NO_ERROR) {
    return nghttp2_session_inflate_handle_invalid_stream
      (session, frame, error_code);
  }

  stream = nghttp2_session_open_stream(session,
                                       frame->hd.stream_id,
                                       NGHTTP2_STREAM_FLAG_NONE,
                                       frame->headers.pri,
                                       NGHTTP2_STREAM_OPENING,
                                       NULL);
  if(!stream) {
    return NGHTTP2_ERR_NOMEM;
  }
  session->last_proc_stream_id = session->last_recv_stream_id;
  rv = session_call_on_begin_headers(session, frame);
  if(rv != 0) {
    return rv;
  }
  return 0;
}

int nghttp2_session_on_response_headers_received(nghttp2_session *session,
                                                 nghttp2_frame *frame,
                                                 nghttp2_stream *stream)
{
  int rv;
  /* This function is only called if stream->state ==
     NGHTTP2_STREAM_OPENING and stream_id is local side initiated. */
  assert(stream->state == NGHTTP2_STREAM_OPENING &&
         nghttp2_session_is_my_stream_id(session, frame->hd.stream_id));
  if(frame->hd.stream_id == 0) {
    return nghttp2_session_inflate_handle_invalid_connection
      (session, frame, NGHTTP2_PROTOCOL_ERROR);
  }
  if(stream->shut_flags & NGHTTP2_SHUT_RD) {
    /* half closed (remote): from the spec:

       If an endpoint receives additional frames for a stream that is
       in this state it MUST respond with a stream error (Section
       5.4.2) of type STREAM_CLOSED.
    */
    return nghttp2_session_inflate_handle_invalid_stream
      (session, frame, NGHTTP2_STREAM_CLOSED);
  }
  stream->state = NGHTTP2_STREAM_OPENED;
  rv = session_call_on_begin_headers(session, frame);
  if(rv != 0) {
    return rv;
  }
  return 0;
}

int nghttp2_session_on_push_response_headers_received(nghttp2_session *session,
                                                      nghttp2_frame *frame,
                                                      nghttp2_stream *stream)
{
  int rv = 0;
  assert(stream->state == NGHTTP2_STREAM_RESERVED);
  if(frame->hd.stream_id == 0) {
    return nghttp2_session_inflate_handle_invalid_connection
      (session, frame, NGHTTP2_PROTOCOL_ERROR);
  }
  if(session->goaway_flags) {
    /* We don't accept new stream after GOAWAY is sent or received. */
    return NGHTTP2_ERR_IGN_HEADER_BLOCK;
  }
  rv = nghttp2_session_validate_request_headers(session, &frame->headers);
  if(rv != 0) {
    return nghttp2_session_inflate_handle_invalid_stream(session, frame, rv);
  }
  nghttp2_stream_promise_fulfilled(stream);
  ++session->num_incoming_streams;
  rv = session_call_on_begin_headers(session, frame);
  if(rv != 0) {
    return rv;
  }
  return 0;
}

int nghttp2_session_on_headers_received(nghttp2_session *session,
                                        nghttp2_frame *frame,
                                        nghttp2_stream *stream)
{
  int r = 0;
  if(frame->hd.stream_id == 0) {
    return nghttp2_session_inflate_handle_invalid_connection
      (session, frame, NGHTTP2_PROTOCOL_ERROR);
  }
  if(stream->state == NGHTTP2_STREAM_RESERVED) {
    /* reserved. The valid push response HEADERS is processed by
       nghttp2_session_on_push_response_headers_received(). This
       generic HEADERS is called invalid cases for HEADERS against
       reserved state. */
    return nghttp2_session_inflate_handle_invalid_connection
      (session, frame, NGHTTP2_PROTOCOL_ERROR);
  }
  if((stream->shut_flags & NGHTTP2_SHUT_RD)) {
    /* half closed (remote): from the spec:

       If an endpoint receives additional frames for a stream that is
       in this state it MUST respond with a stream error (Section
       5.4.2) of type STREAM_CLOSED.
    */
    return nghttp2_session_inflate_handle_invalid_stream
      (session, frame, NGHTTP2_STREAM_CLOSED);
  }
  if(nghttp2_session_is_my_stream_id(session, frame->hd.stream_id)) {
    if(stream->state == NGHTTP2_STREAM_OPENED) {
      r = session_call_on_begin_headers(session, frame);
      if(r != 0) {
        return r;
      }
      return 0;
    } else if(stream->state == NGHTTP2_STREAM_CLOSING) {
      /* This is race condition. NGHTTP2_STREAM_CLOSING indicates
         that we queued RST_STREAM but it has not been sent. It will
         eventually sent, so we just ignore this frame. */
      return NGHTTP2_ERR_IGN_HEADER_BLOCK;
    } else {
      return nghttp2_session_inflate_handle_invalid_stream
        (session, frame, NGHTTP2_PROTOCOL_ERROR);
    }
  }
  /* If this is remote peer initiated stream, it is OK unless it
     has sent END_STREAM frame already. But if stream is in
     NGHTTP2_STREAM_CLOSING, we discard the frame. This is a race
     condition. */
  if(stream->state != NGHTTP2_STREAM_CLOSING) {
    r = session_call_on_begin_headers(session, frame);
    if(r != 0) {
      return r;
    }
    return 0;
  }
  return NGHTTP2_ERR_IGN_HEADER_BLOCK;
}

static int session_process_headers_frame(nghttp2_session *session)
{
  int rv;
  nghttp2_inbound_frame *iframe = &session->iframe;
  nghttp2_frame *frame = &iframe->frame;
  nghttp2_stream *stream;

  rv = nghttp2_frame_unpack_headers_payload(&frame->headers,
                                            iframe->buf, iframe->buflen);
  if(rv != 0) {
    return nghttp2_session_terminate_session(session, NGHTTP2_PROTOCOL_ERROR);
  }
  stream = nghttp2_session_get_stream(session, frame->hd.stream_id);
  if(!stream) {
    frame->headers.cat = NGHTTP2_HCAT_REQUEST;
    return nghttp2_session_on_request_headers_received(session, frame);
  }

  if(nghttp2_session_is_my_stream_id(session, frame->hd.stream_id)) {
    if(stream->state == NGHTTP2_STREAM_OPENING) {
      frame->headers.cat = NGHTTP2_HCAT_RESPONSE;
      return nghttp2_session_on_response_headers_received(session, frame,
                                                          stream);
    }
    frame->headers.cat = NGHTTP2_HCAT_HEADERS;
    return nghttp2_session_on_headers_received(session, frame, stream);
  }
  if(stream->state == NGHTTP2_STREAM_RESERVED) {
    frame->headers.cat = NGHTTP2_HCAT_PUSH_RESPONSE;
    return nghttp2_session_on_push_response_headers_received(session, frame,
                                                             stream);
  }
  frame->headers.cat = NGHTTP2_HCAT_HEADERS;
  return nghttp2_session_on_headers_received(session, frame, stream);
}

int nghttp2_session_on_priority_received(nghttp2_session *session,
                                         nghttp2_frame *frame)
{
  nghttp2_stream *stream;
  if(frame->hd.stream_id == 0) {
    return nghttp2_session_handle_invalid_connection(session, frame,
                                                     NGHTTP2_PROTOCOL_ERROR);
  }
  stream = nghttp2_session_get_stream(session, frame->hd.stream_id);
  if(!stream) {
    if(session_detect_idle_stream(session, frame->hd.stream_id)) {
      return nghttp2_session_handle_invalid_connection(session, frame,
                                                       NGHTTP2_PROTOCOL_ERROR);
    }
    return 0;
  }
  if(state_reserved_remote(session, stream)) {
    return nghttp2_session_handle_invalid_connection(session, frame,
                                                     NGHTTP2_PROTOCOL_ERROR);
  }
  /* Only update priority of the stream, only if it is not pushed
     stream and is initiated by remote peer, or it is pushed stream
     and is initiated by local peer */
  if(((stream->flags & NGHTTP2_STREAM_FLAG_PUSH) == 0 &&
      !nghttp2_session_is_my_stream_id(session, frame->hd.stream_id)) ||
     ((stream->flags & NGHTTP2_STREAM_FLAG_PUSH) &&
      nghttp2_session_is_my_stream_id(session, frame->hd.stream_id))) {
    nghttp2_session_reprioritize_stream(session, stream,
                                        frame->priority.pri);
  }
  return nghttp2_session_call_on_frame_received(session, frame);
}

static int session_process_priority_frame(nghttp2_session *session)
{
  nghttp2_inbound_frame *iframe = &session->iframe;
  nghttp2_frame *frame = &iframe->frame;

  nghttp2_frame_unpack_priority_payload(&frame->priority,
                                        iframe->buf, iframe->buflen);
  return nghttp2_session_on_priority_received(session, frame);
}

int nghttp2_session_on_rst_stream_received(nghttp2_session *session,
                                           nghttp2_frame *frame)
{
  int rv;
  nghttp2_stream *stream;
  if(frame->hd.stream_id == 0) {
    return nghttp2_session_handle_invalid_connection(session, frame,
                                                     NGHTTP2_PROTOCOL_ERROR);
  }
  stream = nghttp2_session_get_stream(session, frame->hd.stream_id);
  if(!stream) {
    if(session_detect_idle_stream(session, frame->hd.stream_id)) {
      return nghttp2_session_handle_invalid_connection(session, frame,
                                                       NGHTTP2_PROTOCOL_ERROR);
    }
  }

  rv = nghttp2_session_call_on_frame_received(session, frame);
  if(rv != 0) {
    return rv;
  }
  rv = nghttp2_session_close_stream(session, frame->hd.stream_id,
                                    frame->rst_stream.error_code);
  if(rv != 0 && nghttp2_is_fatal(rv)) {
    return rv;
  }
  return 0;
}

static int session_process_rst_stream_frame(nghttp2_session *session)
{
  nghttp2_inbound_frame *iframe = &session->iframe;
  nghttp2_frame *frame = &iframe->frame;

  nghttp2_frame_unpack_rst_stream_payload(&frame->rst_stream,
                                          iframe->buf, iframe->buflen);
  return nghttp2_session_on_rst_stream_received(session, frame);
}

static int nghttp2_update_remote_initial_window_size_func
(nghttp2_map_entry *entry,
 void *ptr)
{
  int rv;
  nghttp2_update_window_size_arg *arg;
  nghttp2_stream *stream;
  arg = (nghttp2_update_window_size_arg*)ptr;
  stream = (nghttp2_stream*)entry;
  rv = nghttp2_stream_update_remote_initial_window_size(stream,
                                                        arg->new_window_size,
                                                        arg->old_window_size);
  if(rv != 0) {
    return nghttp2_session_add_rst_stream(arg->session, stream->stream_id,
                                          NGHTTP2_FLOW_CONTROL_ERROR);
  }
  /* If window size gets positive, push deferred DATA frame to
     outbound queue. */
  if(stream->deferred_data &&
     (stream->deferred_flags & NGHTTP2_DEFERRED_FLOW_CONTROL) &&
     stream->remote_window_size > 0 &&
     arg->session->remote_window_size > 0) {
    rv = nghttp2_pq_push(&arg->session->ob_pq, stream->deferred_data);
    if(rv != 0) {
      /* FATAL */
      assert(rv < NGHTTP2_ERR_FATAL);
      return rv;
    }
    nghttp2_stream_detach_deferred_data(stream);
  }
  return 0;
}

/*
 * Updates the remote initial window size of all active streams.  If
 * error occurs, all streams may not be updated.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * NGHTTP2_ERR_NOMEM
 *     Out of memory.
 */
static int nghttp2_session_update_remote_initial_window_size
(nghttp2_session *session,
 int32_t new_initial_window_size)
{
  nghttp2_update_window_size_arg arg;
  arg.session = session;
  arg.new_window_size = new_initial_window_size;
  arg.old_window_size =
    session->remote_settings[NGHTTP2_SETTINGS_INITIAL_WINDOW_SIZE];
  return nghttp2_map_each(&session->streams,
                          nghttp2_update_remote_initial_window_size_func,
                          &arg);
}

static int nghttp2_update_local_initial_window_size_func
(nghttp2_map_entry *entry,
 void *ptr)
{
  int rv;
  nghttp2_update_window_size_arg *arg;
  nghttp2_stream *stream;
  arg = (nghttp2_update_window_size_arg*)ptr;
  stream = (nghttp2_stream*)entry;
  rv = nghttp2_stream_update_local_initial_window_size(stream,
                                                       arg->new_window_size,
                                                       arg->old_window_size);
  if(rv != 0) {
    return nghttp2_session_add_rst_stream(arg->session, stream->stream_id,
                                          NGHTTP2_FLOW_CONTROL_ERROR);
  }
  if(!(arg->session->opt_flags &
       NGHTTP2_OPTMASK_NO_AUTO_STREAM_WINDOW_UPDATE)) {
    if(nghttp2_should_send_window_update(stream->local_window_size,
                                         stream->recv_window_size)) {
      rv = nghttp2_session_add_window_update(arg->session,
                                             NGHTTP2_FLAG_NONE,
                                             stream->stream_id,
                                             stream->recv_window_size);
      if(rv != 0) {
        return rv;
      }
      stream->recv_window_size = 0;
    }
  }
  return 0;
}

/*
 * Updates the local initial window size of all active streams.  If
 * error occurs, all streams may not be updated.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * NGHTTP2_ERR_NOMEM
 *     Out of memory.
 */
static int nghttp2_session_update_local_initial_window_size
(nghttp2_session *session,
 int32_t new_initial_window_size,
 int32_t old_initial_window_size)
{
  nghttp2_update_window_size_arg arg;
  arg.session = session;
  arg.new_window_size = new_initial_window_size;
  arg.old_window_size = old_initial_window_size;
  return nghttp2_map_each(&session->streams,
                          nghttp2_update_local_initial_window_size_func,
                          &arg);
}

/*
 * Apply SETTINGS values |iv| having |niv| elements to the local
 * settings. SETTINGS_MAX_CONCURRENT_STREAMS is not applied here
 * because it has been already applied on transmission of SETTINGS
 * frame.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * NGHTTP2_ERR_HEADER_COMP
 *     The header table size is out of range
 * NGHTTP2_ERR_NOMEM
 *     Out of memory
 */
int nghttp2_session_update_local_settings(nghttp2_session *session,
                                          nghttp2_settings_entry *iv,
                                          size_t niv)
{
  int rv;
  size_t i;
  int32_t new_initial_window_size = -1;
  int32_t header_table_size = -1;
  uint8_t header_table_size_seen = 0;
  /* Use the value last seen. */
  for(i = 0; i < niv; ++i) {
    switch(iv[i].settings_id) {
    case NGHTTP2_SETTINGS_HEADER_TABLE_SIZE:
      header_table_size_seen = 1;
      header_table_size = iv[i].value;
      break;
    case NGHTTP2_SETTINGS_INITIAL_WINDOW_SIZE:
      new_initial_window_size = iv[i].value;
      break;
    }
  }
  if(header_table_size_seen) {
    if(header_table_size < 0 ||
       header_table_size > NGHTTP2_MAX_HEADER_TABLE_SIZE) {
      return NGHTTP2_ERR_HEADER_COMP;
    }
    rv = nghttp2_hd_change_table_size(&session->hd_inflater.ctx,
                                      header_table_size);
    if(rv != 0) {
      return rv;
    }
  }
  if(new_initial_window_size != -1) {
    rv = nghttp2_session_update_local_initial_window_size
      (session,
       new_initial_window_size,
       session->local_settings[NGHTTP2_SETTINGS_INITIAL_WINDOW_SIZE]);
    if(rv != 0) {
      return rv;
    }
  }
  for(i = 0; i < niv; ++i) {
    /* SETTINGS_MAX_CONCURRENT_STREAMS has already been applied on
       transmission of the SETTINGS frame. */
    if(iv[i].settings_id > 0 && iv[i].settings_id <= NGHTTP2_SETTINGS_MAX &&
       iv[i].settings_id != NGHTTP2_SETTINGS_MAX_CONCURRENT_STREAMS) {
      session->local_settings[iv[i].settings_id] = iv[i].value;
    }
  }
  return 0;
}

int nghttp2_session_on_settings_received(nghttp2_session *session,
                                         nghttp2_frame *frame,
                                         int noack)
{
  int rv;
  int i;
  int check[NGHTTP2_SETTINGS_MAX+1];
  if(frame->hd.stream_id != 0) {
    return nghttp2_session_handle_invalid_connection(session, frame,
                                                     NGHTTP2_PROTOCOL_ERROR);
  }
  if(frame->hd.flags & NGHTTP2_FLAG_ACK) {
    if(frame->settings.niv != 0) {
      return nghttp2_session_handle_invalid_connection
        (session, frame, NGHTTP2_FRAME_SIZE_ERROR);
    }
    if(session->inflight_niv == -1) {
      return nghttp2_session_handle_invalid_connection(session, frame,
                                                       NGHTTP2_PROTOCOL_ERROR);
    }
    rv = nghttp2_session_update_local_settings(session, session->inflight_iv,
                                               session->inflight_niv);
    free(session->inflight_iv);
    session->inflight_iv = NULL;
    session->inflight_niv = -1;
    if(rv != 0) {
      nghttp2_error_code error_code = NGHTTP2_INTERNAL_ERROR;
      if(nghttp2_is_fatal(rv)) {
        return rv;
      }
      if(rv == NGHTTP2_ERR_HEADER_COMP) {
        error_code = NGHTTP2_COMPRESSION_ERROR;
      }
      return nghttp2_session_handle_invalid_connection(session, frame,
                                                       error_code);
    }
    return nghttp2_session_call_on_frame_received(session, frame);
  }
  /* Check ID/value pairs and persist them if necessary. */
  memset(check, 0, sizeof(check));
  for(i = (int)frame->settings.niv - 1; i >= 0; --i) {
    nghttp2_settings_entry *entry = &frame->settings.iv[i];
    /* The spec says the settings values are processed in the order
       they appear in the payload. In other words, if the multiple
       values for the same ID were found, use the last one and ignore
       the rest. */
    if(entry->settings_id > NGHTTP2_SETTINGS_MAX || entry->settings_id <= 0 ||
       check[entry->settings_id] == 1) {
      continue;
    }
    check[entry->settings_id] = 1;
    switch(entry->settings_id) {
    case NGHTTP2_SETTINGS_HEADER_TABLE_SIZE:
      if(entry->value > NGHTTP2_MAX_HEADER_TABLE_SIZE) {
        return nghttp2_session_handle_invalid_connection
          (session, frame, NGHTTP2_COMPRESSION_ERROR);
      }
      rv = nghttp2_hd_change_table_size(&session->hd_deflater.ctx,
                                        entry->value);
      if(rv != 0) {
        if(nghttp2_is_fatal(rv)) {
          return rv;
        } else {
          return nghttp2_session_handle_invalid_connection
            (session, frame, NGHTTP2_COMPRESSION_ERROR);
        }
      }
      break;
    case NGHTTP2_SETTINGS_ENABLE_PUSH:
      if(entry->value != 0 && entry->value != 1) {
        return nghttp2_session_handle_invalid_connection
          (session, frame, NGHTTP2_PROTOCOL_ERROR);
      }
      break;
    case NGHTTP2_SETTINGS_INITIAL_WINDOW_SIZE:
      /* Update the initial window size of the all active streams */
      /* Check that initial_window_size < (1u << 31) */
      if(entry->value > NGHTTP2_MAX_WINDOW_SIZE) {
        return nghttp2_session_handle_invalid_connection
          (session, frame, NGHTTP2_FLOW_CONTROL_ERROR);
      }
      rv = nghttp2_session_update_remote_initial_window_size
        (session, entry->value);
      if(nghttp2_is_fatal(rv)) {
        return rv;
      }
      if(rv != 0) {
        return nghttp2_session_handle_invalid_connection
          (session, frame, NGHTTP2_FLOW_CONTROL_ERROR);
      }
      break;
    }
    session->remote_settings[entry->settings_id] = entry->value;
  }
  if(!noack) {
    rv = nghttp2_session_add_settings(session, NGHTTP2_FLAG_ACK, NULL, 0);
    if(rv != 0) {
      if(nghttp2_is_fatal(rv)) {
        return rv;
      }
      return nghttp2_session_handle_invalid_connection
        (session, frame, NGHTTP2_INTERNAL_ERROR);
    }
  }
  return nghttp2_session_call_on_frame_received(session, frame);
}

static int session_process_settings_frame(nghttp2_session *session)
{
  int rv;
  nghttp2_inbound_frame *iframe = &session->iframe;
  nghttp2_frame *frame = &iframe->frame;

  rv = nghttp2_frame_unpack_settings_payload(&frame->settings,
                                             iframe->iv, iframe->niv);
  if(rv != 0) {
    assert(nghttp2_is_fatal(rv));
    return rv;
  }
  return nghttp2_session_on_settings_received(session, frame, 0 /* ACK */);
}

int nghttp2_session_on_push_promise_received(nghttp2_session *session,
                                             nghttp2_frame *frame)
{
  int rv;
  nghttp2_stream *stream;
  nghttp2_stream *promised_stream;
  if(frame->hd.stream_id == 0) {
    return nghttp2_session_inflate_handle_invalid_connection
      (session, frame, NGHTTP2_PROTOCOL_ERROR);
  }
  if(session->local_settings[NGHTTP2_SETTINGS_ENABLE_PUSH] == 0) {
    return nghttp2_session_inflate_handle_invalid_connection
      (session, frame, NGHTTP2_PROTOCOL_ERROR);
  }
  if(session->goaway_flags) {
    /* We just dicard PUSH_PROMISE after GOAWAY is sent or
       received. */
    return NGHTTP2_ERR_IGN_HEADER_BLOCK;
  }
  if(!nghttp2_session_is_new_peer_stream_id
     (session, frame->push_promise.promised_stream_id)) {
    /* The spec says if an endpoint receives a PUSH_PROMISE with
       illegal stream ID is subject to a connection error of type
       PROTOCOL_ERROR. */
    return nghttp2_session_inflate_handle_invalid_connection
      (session, frame, NGHTTP2_PROTOCOL_ERROR);
  }
  session->last_recv_stream_id = frame->push_promise.promised_stream_id;
  if(!nghttp2_session_is_my_stream_id(session, frame->hd.stream_id)) {
    return nghttp2_session_inflate_handle_invalid_connection
      (session, frame, NGHTTP2_PROTOCOL_ERROR);
  }
  stream = nghttp2_session_get_stream(session, frame->hd.stream_id);
  if(!stream || stream->state == NGHTTP2_STREAM_CLOSING) {
    if(!stream) {
      if(session_detect_idle_stream(session, frame->hd.stream_id)) {
        return nghttp2_session_handle_invalid_connection
          (session, frame, NGHTTP2_PROTOCOL_ERROR);
      }
    }
    rv = nghttp2_session_add_rst_stream
      (session, frame->push_promise.promised_stream_id,
       NGHTTP2_REFUSED_STREAM);
    if(rv != 0) {
      return rv;
    }
    return NGHTTP2_ERR_IGN_HEADER_BLOCK;
  }
  if(stream->shut_flags & NGHTTP2_SHUT_RD) {
    if(session->callbacks.on_invalid_frame_recv_callback) {
      if(session->callbacks.on_invalid_frame_recv_callback
         (session, frame, NGHTTP2_PROTOCOL_ERROR, session->user_data) != 0) {
        return NGHTTP2_ERR_CALLBACK_FAILURE;
      }
    }
    rv = nghttp2_session_add_rst_stream
      (session, frame->push_promise.promised_stream_id,
       NGHTTP2_PROTOCOL_ERROR);
    if(rv != 0) {
      return rv;
    }
    return NGHTTP2_ERR_IGN_HEADER_BLOCK;
  }
  promised_stream = nghttp2_session_open_stream
    (session,
     frame->push_promise.promised_stream_id,
     NGHTTP2_STREAM_FLAG_PUSH,
     nghttp2_pushed_stream_pri(stream),
     NGHTTP2_STREAM_RESERVED,
     NULL);
  if(!promised_stream) {
    return NGHTTP2_ERR_NOMEM;
  }
  session->last_proc_stream_id = session->last_recv_stream_id;
  rv = session_call_on_begin_headers(session, frame);
  if(rv != 0) {
    return rv;
  }
  return 0;
}

static int session_process_push_promise_frame(nghttp2_session *session)
{
  int rv;
  nghttp2_inbound_frame *iframe = &session->iframe;
  nghttp2_frame *frame = &iframe->frame;

  rv = nghttp2_frame_unpack_push_promise_payload(&frame->push_promise,
                                                 iframe->buf, iframe->buflen);
  if(rv != 0) {
    return nghttp2_session_terminate_session(session, NGHTTP2_PROTOCOL_ERROR);
  }
  return nghttp2_session_on_push_promise_received(session, frame);
}

int nghttp2_session_on_ping_received(nghttp2_session *session,
                                     nghttp2_frame *frame)
{
  int r = 0;
  if(frame->hd.stream_id != 0) {
    return nghttp2_session_handle_invalid_connection(session, frame,
                                                     NGHTTP2_PROTOCOL_ERROR);
  }
  if((frame->hd.flags & NGHTTP2_FLAG_ACK) == 0) {
    /* Peer sent ping, so ping it back */
    r = nghttp2_session_add_ping(session, NGHTTP2_FLAG_ACK,
                                 frame->ping.opaque_data);
    if(r != 0) {
      return r;
    }
  }
  return nghttp2_session_call_on_frame_received(session, frame);
}

static int session_process_ping_frame(nghttp2_session *session)
{
  nghttp2_inbound_frame *iframe = &session->iframe;
  nghttp2_frame *frame = &iframe->frame;

  nghttp2_frame_unpack_ping_payload(&frame->ping,
                                    iframe->buf, iframe->buflen);
  return nghttp2_session_on_ping_received(session, frame);
}

int nghttp2_session_on_goaway_received(nghttp2_session *session,
                                       nghttp2_frame *frame)
{
  if(frame->hd.stream_id != 0) {
    return nghttp2_session_handle_invalid_connection(session, frame,
                                                     NGHTTP2_PROTOCOL_ERROR);
  }
  session->last_stream_id = frame->goaway.last_stream_id;
  session->goaway_flags |= NGHTTP2_GOAWAY_RECV;
  return nghttp2_session_call_on_frame_received(session, frame);
}

static int session_process_goaway_frame(nghttp2_session *session)
{
  nghttp2_inbound_frame *iframe = &session->iframe;
  nghttp2_frame *frame = &iframe->frame;

  nghttp2_frame_unpack_goaway_payload(&frame->goaway,
                                      iframe->buf, iframe->buflen);
  return nghttp2_session_on_goaway_received(session, frame);
}

static int nghttp2_push_back_deferred_data_func(nghttp2_map_entry *entry,
                                                void *ptr)
{
  nghttp2_session *session;
  nghttp2_stream *stream;
  session = (nghttp2_session*)ptr;
  stream = (nghttp2_stream*)entry;
  /* If DATA frame is deferred due to flow control, push it back to
     outbound queue. */
  if(stream->deferred_data &&
     (stream->deferred_flags & NGHTTP2_DEFERRED_FLOW_CONTROL) &&
     stream->remote_window_size > 0) {
    int rv;
    rv = nghttp2_pq_push(&session->ob_pq, stream->deferred_data);
    if(rv == 0) {
      nghttp2_stream_detach_deferred_data(stream);
    } else {
      /* FATAL */
      assert(rv < NGHTTP2_ERR_FATAL);
      return rv;
    }
  }
  return 0;
}

/*
 * Push back deferred DATA frames to queue if they are deferred due to
 * connection-level flow control.
 */
static int nghttp2_session_push_back_deferred_data(nghttp2_session *session)
{
  return nghttp2_map_each(&session->streams,
                          nghttp2_push_back_deferred_data_func, session);
}

static int session_on_connection_window_update_received
(nghttp2_session *session, nghttp2_frame *frame)
{
  int rv;
  /* Handle connection-level flow control */
  if(NGHTTP2_MAX_WINDOW_SIZE - frame->window_update.window_size_increment <
     session->remote_window_size) {
    return nghttp2_session_handle_invalid_connection
      (session, frame, NGHTTP2_FLOW_CONTROL_ERROR);
  }
  session->remote_window_size += frame->window_update.window_size_increment;
  /* To queue the DATA deferred by connection-level flow-control, we
     have to check all streams. Bad. */
  if(session->remote_window_size > 0) {
    rv = nghttp2_session_push_back_deferred_data(session);
    if(rv != 0) {
      /* FATAL */
      assert(rv < NGHTTP2_ERR_FATAL);
      return rv;
    }
  }
  return nghttp2_session_call_on_frame_received(session, frame);
}

static int session_on_stream_window_update_received
(nghttp2_session *session, nghttp2_frame *frame)
{
  int rv;
  nghttp2_stream *stream;
  stream = nghttp2_session_get_stream(session, frame->hd.stream_id);
  if(!stream) {
    if(session_detect_idle_stream(session, frame->hd.stream_id)) {
      return nghttp2_session_handle_invalid_connection(session, frame,
                                                       NGHTTP2_PROTOCOL_ERROR);
    }
    return 0;
  }
  if(stream->state == NGHTTP2_STREAM_RESERVED) {
    return nghttp2_session_handle_invalid_connection
      (session, frame, NGHTTP2_PROTOCOL_ERROR);
  }
  if(NGHTTP2_MAX_WINDOW_SIZE - frame->window_update.window_size_increment <
     stream->remote_window_size) {
    return nghttp2_session_handle_invalid_stream(session, frame,
                                                 NGHTTP2_FLOW_CONTROL_ERROR);
  }
  stream->remote_window_size += frame->window_update.window_size_increment;
  if(stream->remote_window_size > 0 &&
     session->remote_window_size > 0 &&
     stream->deferred_data != NULL &&
     (stream->deferred_flags & NGHTTP2_DEFERRED_FLOW_CONTROL)) {
    rv = nghttp2_pq_push(&session->ob_pq, stream->deferred_data);
    if(rv != 0) {
      /* FATAL */
      assert(rv < NGHTTP2_ERR_FATAL);
      return rv;
    }
    nghttp2_stream_detach_deferred_data(stream);
  }
  return nghttp2_session_call_on_frame_received(session, frame);
}

int nghttp2_session_on_window_update_received(nghttp2_session *session,
                                              nghttp2_frame *frame)
{
  if(frame->hd.stream_id == 0) {
    return session_on_connection_window_update_received(session, frame);
  } else {
    return session_on_stream_window_update_received(session, frame);
  }
}

static int session_process_window_update_frame(nghttp2_session *session)
{
  nghttp2_inbound_frame *iframe = &session->iframe;
  nghttp2_frame *frame = &iframe->frame;

  nghttp2_frame_unpack_window_update_payload(&frame->window_update,
                                             iframe->buf, iframe->buflen);
  return nghttp2_session_on_window_update_received(session, frame);
}

/* static int get_error_code_from_lib_error_code(int lib_error_code) */
/* { */
/*   switch(lib_error_code) { */
/*   case NGHTTP2_ERR_HEADER_COMP: */
/*     return NGHTTP2_COMPRESSION_ERROR; */
/*   case NGHTTP2_ERR_FRAME_SIZE_ERROR: */
/*     return NGHTTP2_FRAME_SIZE_ERROR; */
/*   default: */
/*     return NGHTTP2_PROTOCOL_ERROR; */
/*   } */
/* } */

int nghttp2_session_on_data_received(nghttp2_session *session,
                                     nghttp2_frame *frame)
{
  int rv = 0;
  nghttp2_stream *stream;

  /* We call on_frame_recv_callback even if stream has been closed
     already */
  rv = nghttp2_session_call_on_frame_received(session, frame);
  if(nghttp2_is_fatal(rv)) {
    return rv;
  }

  stream = nghttp2_session_get_stream(session, frame->hd.stream_id);
  if(!stream) {
    /* This should be treated as stream error, but it results in lots
       of RST_STREAM. So just ignore frame against nonexistent stream
       for now. */
    return 0;
  }
  if(frame->hd.flags & NGHTTP2_FLAG_END_STREAM) {
    nghttp2_stream_shutdown(stream, NGHTTP2_SHUT_RD);
    rv = nghttp2_session_close_stream_if_shut_rdwr(session, stream);
    if(nghttp2_is_fatal(rv)) {
      return rv;
    }
  }
  return 0;
}

/* For errors, this function only returns FATAL error. */
static int nghttp2_session_process_data_frame(nghttp2_session *session)
{
  int r;
  nghttp2_frame *public_data_frame = &session->iframe.frame;
  r = nghttp2_session_on_data_received(session, public_data_frame);
  if(nghttp2_is_fatal(r)) {
    return r;
  } else {
    return 0;
  }
}

/*
 * Now we have SETTINGS synchronization, flow control error can be
 * detected strictly. If DATA frame is received with length > 0 and
 * current received window size + delta length is strictly larger than
 * local window size, it is subject to FLOW_CONTROL_ERROR, so return
 * -1. Note that local_window_size is calculated after SETTINGS ACK is
 * received from peer, so peer must honor this limit. If the resulting
 * recv_window_size is strictly larger than NGHTTP2_MAX_WINDOW_SIZE,
 * return -1 too.
 */
static int adjust_recv_window_size(int32_t *recv_window_size_ptr,
                                   int32_t delta,
                                   int32_t local_window_size)
{
  if(*recv_window_size_ptr > local_window_size - delta ||
     *recv_window_size_ptr > NGHTTP2_MAX_WINDOW_SIZE - delta) {
    return -1;
  }
  *recv_window_size_ptr += delta;
  return 0;
}

/*
 * Accumulates received bytes |delta_size| for stream-level flow
 * control and decides whether to send WINDOW_UPDATE to that
 * stream. If NGHTTP2_OPT_NO_AUTO_STREAM_WINDOW_UPDATE is set,
 * WINDOW_UPDATE will not be sent.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * NGHTTP2_ERR_NOMEM
 *     Out of memory.
 */
static int nghttp2_session_update_recv_stream_window_size
(nghttp2_session *session,
 nghttp2_stream *stream,
 int32_t delta_size)
{
  int rv;
  rv = adjust_recv_window_size(&stream->recv_window_size, delta_size,
                               stream->local_window_size);
  if(rv != 0) {
    return nghttp2_session_add_rst_stream(session, stream->stream_id,
                                          NGHTTP2_FLOW_CONTROL_ERROR);
  }
  if(!(session->opt_flags & NGHTTP2_OPTMASK_NO_AUTO_STREAM_WINDOW_UPDATE)) {
    /* We have to use local_settings here because it is the constraint
       the remote endpoint should honor. */
    if(nghttp2_should_send_window_update(stream->local_window_size,
                                         stream->recv_window_size)) {
      rv = nghttp2_session_add_window_update(session,
                                            NGHTTP2_FLAG_NONE,
                                            stream->stream_id,
                                            stream->recv_window_size);
      if(rv == 0) {
        stream->recv_window_size = 0;
      } else {
        return rv;
      }
    }
  }
  return 0;
}

/*
 * Accumulates received bytes |delta_size| for connection-level flow
 * control and decides whether to send WINDOW_UPDATE to the
 * connection.  If NGHTTP2_OPT_NO_AUTO_CONNECTION_WINDOW_UPDATE is
 * set, WINDOW_UPDATE will not be sent.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * NGHTTP2_ERR_NOMEM
 *     Out of memory.
 */
static int nghttp2_session_update_recv_connection_window_size
(nghttp2_session *session,
 int32_t delta_size)
{
  int rv;
  rv = adjust_recv_window_size(&session->recv_window_size, delta_size,
                               session->local_window_size);
  if(rv != 0) {
    return nghttp2_session_terminate_session(session,
                                             NGHTTP2_FLOW_CONTROL_ERROR);
  }
  if(!(session->opt_flags &
       NGHTTP2_OPTMASK_NO_AUTO_CONNECTION_WINDOW_UPDATE)) {
    if(nghttp2_should_send_window_update(session->local_window_size,
                                         session->recv_window_size)) {
      /* Use stream ID 0 to update connection-level flow control
         window */
      rv = nghttp2_session_add_window_update(session,
                                            NGHTTP2_FLAG_NONE,
                                            0,
                                            session->recv_window_size);
      if(rv == 0) {
        session->recv_window_size = 0;
      } else {
        return rv;
      }
    }
  }
  return 0;
}

/*
 * Checks that we can receive the DATA frame for stream, which is
 * indicated by |session->iframe.frame.hd.stream_id|. If it is a
 * connection error situation, GOAWAY frame will be issued by this
 * function.
 *
 * If the DATA frame is allowed, returns 0.
 *
 * This function returns 0 if it succeeds, or one of the following
 * negative error codes:
 *
 * NGHTTP2_ERR_IGN_PAYLOAD
 *   The reception of DATA frame is connection error; or should be
 *   ignored.
 * NGHTTP2_ERR_NOMEM
 *   Out of memory.
 */
static int nghttp2_session_on_data_received_fail_fast(nghttp2_session *session)
{
  int rv;
  nghttp2_stream *stream;
  int32_t stream_id = session->iframe.frame.hd.stream_id;
  if(stream_id == 0) {
    /* The spec says that if a DATA frame is received whose stream ID
       is 0, the recipient MUST respond with a connection error of
       type PROTOCOL_ERROR. */
    goto fail;
  }
  stream = nghttp2_session_get_stream(session, stream_id);
  if(!stream) {
    if(session_detect_idle_stream(session, stream_id)) {
      goto fail;
    }
    return NGHTTP2_ERR_IGN_PAYLOAD;
  }
  if(stream->shut_flags & NGHTTP2_SHUT_RD) {
    goto fail;
  }
  if(nghttp2_session_is_my_stream_id(session, stream_id)) {
    if(stream->state == NGHTTP2_STREAM_CLOSING) {
      return NGHTTP2_ERR_IGN_PAYLOAD;
    }
    if(stream->state != NGHTTP2_STREAM_OPENED) {
      goto fail;
    }
    return 0;
  }
  if(stream->state == NGHTTP2_STREAM_RESERVED) {
    goto fail;
  }
  if(stream->state == NGHTTP2_STREAM_CLOSING) {
    return NGHTTP2_ERR_IGN_PAYLOAD;
  }
  return 0;
 fail:
  rv = nghttp2_session_terminate_session(session, NGHTTP2_PROTOCOL_ERROR);
  if(nghttp2_is_fatal(rv)) {
    return rv;
  }
  return NGHTTP2_ERR_IGN_PAYLOAD;
}

static size_t inbound_frame_payload_readlen(nghttp2_inbound_frame *iframe,
                                         const uint8_t *in,
                                         const uint8_t *last)
{
  return nghttp2_min((size_t)(last - in), iframe->payloadleft);
}

static size_t inbound_frame_buf_read(nghttp2_inbound_frame *iframe,
                                     const uint8_t *in, const uint8_t *last)
{
  size_t readlen = nghttp2_min((size_t)(last - in), iframe->left);
  memcpy(iframe->buf + iframe->buflen, in, readlen);
  iframe->buflen += readlen;
  iframe->left -= readlen;
  return readlen;
}

/*
 * Unpacks SETTINGS entry in |iframe->buf|.
 *
 * This function returns 0 if it succeeds, or -1.
 */
static int inbound_frame_set_settings_entry(nghttp2_inbound_frame *iframe)
{
  nghttp2_settings_entry iv;
  size_t i;

  nghttp2_frame_unpack_settings_entry(&iv, iframe->buf);
  switch(iv.settings_id) {
  case NGHTTP2_SETTINGS_HEADER_TABLE_SIZE:
  case NGHTTP2_SETTINGS_ENABLE_PUSH:
  case NGHTTP2_SETTINGS_MAX_CONCURRENT_STREAMS:
  case NGHTTP2_SETTINGS_INITIAL_WINDOW_SIZE:
    break;
  default:
    return -1;
  }
  for(i = 0; i < iframe->niv; ++i) {
    if(iframe->iv[i].settings_id == iv.settings_id) {
      iframe->iv[i] = iv;
      break;
    }
  }
  if(i == iframe->niv) {
    iframe->iv[iframe->niv++] = iv;
  }
  return 0;
}

/*
 * Checks PAD_HIGH and PAD_LOW flags and set next state
 * accordingly. If padding is set, this function returns 1. If no
 * padding is set, this function returns 0. On error, returns -1.
 */
static int inbound_frame_handle_pad(nghttp2_inbound_frame *iframe,
                                    nghttp2_frame_hd *hd)
{
  if(hd->flags & NGHTTP2_FLAG_PAD_HIGH) {
    if((hd->flags & NGHTTP2_FLAG_PAD_LOW) == 0) {
      return -1;
    }
    iframe->state = NGHTTP2_IB_READ_NBYTE;
    iframe->left = 2;
    return 1;
  }
  if(hd->flags & NGHTTP2_FLAG_PAD_LOW) {
    iframe->state = NGHTTP2_IB_READ_NBYTE;
    iframe->left = 1;
    return 1;
  }
  DEBUGF(fprintf(stderr, "no padding\n"));
  return 0;
}

/*
 * Computes number of padding based on flags. This function returns
 * the calculated length if it succeeds, or -1.
 */
static ssize_t inbound_frame_compute_pad(nghttp2_inbound_frame *iframe)
{
  size_t padlen;
  padlen = iframe->buf[0];
  if(iframe->frame.hd.flags & NGHTTP2_FLAG_PAD_HIGH) {
    padlen <<= 8;
    padlen |= iframe->buf[1];
    ++padlen;
  }
  ++padlen;
  DEBUGF(fprintf(stderr, "padlen=%zu\n", padlen));
  if(padlen > iframe->frame.hd.length) {
    return -1;
  }
  iframe->padlen = padlen;
  return padlen;
}

/*
 * This function returns the effective payload length in the data of
 * length |readlen| when the remaning payload is |payloadleft|. The
 * |payloadleft| does not include |readlen|. If padding was started
 * strictly before this data chunk, this function returns -1.
 */
static ssize_t inbound_frame_effective_readlen(nghttp2_inbound_frame *iframe,
                                               size_t payloadleft,
                                               size_t readlen)
{
  size_t trail_padlen = nghttp2_frame_trail_padlen(&iframe->frame,
                                                   iframe->padlen);

  if(trail_padlen > payloadleft) {
    size_t padlen;
    padlen = trail_padlen - payloadleft;
    if(readlen < padlen) {
      return -1;
    } else {
      return readlen - padlen;
    }
  }
  return readlen;
}

ssize_t nghttp2_session_mem_recv(nghttp2_session *session,
                                 const uint8_t *in, size_t inlen)
{
  const uint8_t *first = in, *last = in + inlen;
  nghttp2_inbound_frame *iframe = &session->iframe;
  size_t readlen;
  int rv;
  int busy = 0;
  nghttp2_frame_hd cont_hd;

  for(;;) {
    switch(iframe->state) {
    case NGHTTP2_IB_READ_HEAD:
      DEBUGF(fprintf(stderr, "[IB_READ_HEAD]\n"));
      readlen = inbound_frame_buf_read(iframe, in, last);
      in += readlen;
      if(iframe->left) {
        return in - first;
      }

      nghttp2_frame_unpack_frame_hd(&iframe->frame.hd, iframe->buf);
      iframe->payloadleft = iframe->frame.hd.length;
      iframe->buflen = 0;

      switch(iframe->frame.hd.type) {
      case NGHTTP2_DATA: {
        DEBUGF(fprintf(stderr, "DATA\n"));
        /* Check stream is open. If it is not open or closing,
           ignore payload. */
        busy = 1;
        rv = nghttp2_session_on_data_received_fail_fast(session);
        if(rv == NGHTTP2_ERR_IGN_PAYLOAD) {
          DEBUGF(fprintf(stderr, "DATA not allowed stream_id=%d\n",
                         iframe->frame.hd.stream_id));
          iframe->state = NGHTTP2_IB_IGN_DATA;
          break;
        }
        if(nghttp2_is_fatal(rv)) {
          return rv;
        }
        rv = inbound_frame_handle_pad(iframe, &iframe->frame.hd);
        if(rv < 0) {
          iframe->state = NGHTTP2_IB_IGN_DATA;
          rv = nghttp2_session_terminate_session(session,
                                                 NGHTTP2_PROTOCOL_ERROR);
          if(nghttp2_is_fatal(rv)) {
            return rv;
          }
          break;
        }
        if(rv == 0) {
          iframe->state = NGHTTP2_IB_READ_DATA;
          break;
        }
        break;
      }
      case NGHTTP2_HEADERS:
        DEBUGF(fprintf(stderr, "HEADERS\n"));
        rv = inbound_frame_handle_pad(iframe, &iframe->frame.hd);
        if(rv < 0) {
          busy = 1;
          iframe->state = NGHTTP2_IB_IGN_PAYLOAD;
          rv = nghttp2_session_terminate_session(session,
                                                 NGHTTP2_PROTOCOL_ERROR);
          if(nghttp2_is_fatal(rv)) {
            return rv;
          }
          break;
        }
        if(rv == 1) {
          break;
        }
        if(iframe->frame.hd.flags & NGHTTP2_FLAG_PRIORITY) {
          if(iframe->payloadleft < 4) {
            busy = 1;
            iframe->state = NGHTTP2_IB_FRAME_SIZE_ERROR;
            break;
          }
          iframe->state = NGHTTP2_IB_READ_NBYTE;
          iframe->left = 4;
          break;
        }
        rv = session_process_headers_frame(session);
        if(nghttp2_is_fatal(rv)) {
          return rv;
        }
        busy = 1;
        if(rv == NGHTTP2_ERR_IGN_HEADER_BLOCK) {
          iframe->state = NGHTTP2_IB_IGN_HEADER_BLOCK;
          break;
        }
        iframe->state = NGHTTP2_IB_READ_HEADER_BLOCK;
        break;
      case NGHTTP2_PRIORITY:
      case NGHTTP2_RST_STREAM:
      case NGHTTP2_WINDOW_UPDATE:
        if(iframe->payloadleft != 4) {
          busy = 1;
          iframe->state = NGHTTP2_IB_FRAME_SIZE_ERROR;
          break;
        }
        iframe->state = NGHTTP2_IB_READ_NBYTE;
        iframe->left = 4;
        break;
      case NGHTTP2_SETTINGS:
        DEBUGF(fprintf(stderr, "SETTINGS\n"));
        if((iframe->frame.hd.length % NGHTTP2_FRAME_SETTINGS_ENTRY_LENGTH) ||
           ((iframe->frame.hd.flags & NGHTTP2_FLAG_ACK) &&
            iframe->payloadleft > 0)) {
          busy = 1;
          iframe->state = NGHTTP2_IB_FRAME_SIZE_ERROR;
          break;
        }
        iframe->state = NGHTTP2_IB_READ_SETTINGS;
        if(iframe->payloadleft) {
          iframe->left = NGHTTP2_FRAME_SETTINGS_ENTRY_LENGTH;
          break;
        }
        busy = 1;
        iframe->left = 0;
        break;
      case NGHTTP2_PUSH_PROMISE:
        if(iframe->payloadleft < 4) {
          busy = 1;
          iframe->state = NGHTTP2_IB_FRAME_SIZE_ERROR;
          break;
        }
        iframe->state = NGHTTP2_IB_READ_NBYTE;
        iframe->left = 4;
        break;
      case NGHTTP2_PING:
        if(iframe->payloadleft != 8) {
          busy = 1;
          iframe->state = NGHTTP2_IB_FRAME_SIZE_ERROR;
          break;
        }
        iframe->state = NGHTTP2_IB_READ_NBYTE;
        iframe->left = 8;
        break;
      case NGHTTP2_GOAWAY:
        if(iframe->payloadleft < 8) {
          busy = 1;
          iframe->state = NGHTTP2_IB_FRAME_SIZE_ERROR;
          break;
        }
        iframe->state = NGHTTP2_IB_READ_NBYTE;
        iframe->left = 8;
        break;
      default:
        /* Receiving unknown frame type and CONTINUATION in this state
           are subject to connection error of type PROTOCOL_ERROR */
        rv = nghttp2_session_terminate_session(session,
                                               NGHTTP2_PROTOCOL_ERROR);
        if(nghttp2_is_fatal(rv)) {
          return rv;
        }
        busy = 1;
        iframe->state = NGHTTP2_IB_IGN_PAYLOAD;
        break;
      }
      break;
    case NGHTTP2_IB_READ_NBYTE:
      DEBUGF(fprintf(stderr, "[IB_READ_NBYTE]\n"));
      readlen = inbound_frame_buf_read(iframe, in, last);
      in += readlen;
      iframe->payloadleft -= readlen;
      DEBUGF(fprintf(stderr, "readlen=%zu, payloadleft=%zu, left=%zu\n",
                     readlen, iframe->payloadleft, iframe->left));
      if(iframe->left) {
        return in - first;
      }
      switch(iframe->frame.hd.type) {
      case NGHTTP2_DATA:
        busy = 1;
        rv = inbound_frame_compute_pad(iframe);
        if(rv < 0) {
          rv = nghttp2_session_terminate_session(session,
                                                 NGHTTP2_PROTOCOL_ERROR);
          if(nghttp2_is_fatal(rv)) {
            return rv;
          }
          iframe->state = NGHTTP2_IB_IGN_DATA;
          break;
        }
        iframe->frame.data.padlen = rv;
        iframe->state = NGHTTP2_IB_READ_DATA;
        break;
      case NGHTTP2_HEADERS:
        if(iframe->padlen == 0 &&
           iframe->frame.hd.flags & NGHTTP2_FLAG_PAD_LOW) {
          rv = inbound_frame_compute_pad(iframe);
          if(rv < 0) {
            busy = 1;
            rv = nghttp2_session_terminate_session(session,
                                                   NGHTTP2_PROTOCOL_ERROR);
            if(nghttp2_is_fatal(rv)) {
              return rv;
            }
            iframe->state = NGHTTP2_IB_IGN_PAYLOAD;
            break;
          }
          iframe->frame.headers.padlen = rv;
          if(iframe->frame.hd.flags & NGHTTP2_FLAG_PRIORITY) {
            if(iframe->payloadleft < 4) {
              busy = 1;
              iframe->state = NGHTTP2_IB_FRAME_SIZE_ERROR;
              break;
            }
            iframe->state = NGHTTP2_IB_READ_NBYTE;
            iframe->left = 4;
            iframe->buflen = 0;
            break;
          }
        }
        rv = session_process_headers_frame(session);
        if(nghttp2_is_fatal(rv)) {
          return rv;
        }
        busy = 1;
        if(rv == NGHTTP2_ERR_IGN_HEADER_BLOCK) {
          iframe->state = NGHTTP2_IB_IGN_HEADER_BLOCK;
          break;
        }
        iframe->state = NGHTTP2_IB_READ_HEADER_BLOCK;
        break;
      case NGHTTP2_PRIORITY:
        rv = session_process_priority_frame(session);
        if(nghttp2_is_fatal(rv)) {
          return rv;
        }
        nghttp2_inbound_frame_reset(session);
        break;
      case NGHTTP2_RST_STREAM:
        rv = session_process_rst_stream_frame(session);
        if(nghttp2_is_fatal(rv)) {
          return rv;
        }
        nghttp2_inbound_frame_reset(session);
        break;
      case NGHTTP2_PUSH_PROMISE:
        rv = session_process_push_promise_frame(session);
        if(nghttp2_is_fatal(rv)) {
          return rv;
        }
        busy = 1;
        if(rv == NGHTTP2_ERR_IGN_HEADER_BLOCK) {
          iframe->state = NGHTTP2_IB_IGN_HEADER_BLOCK;
          break;
        }
        iframe->state = NGHTTP2_IB_READ_HEADER_BLOCK;
        break;
      case NGHTTP2_PING:
        rv = session_process_ping_frame(session);
        if(nghttp2_is_fatal(rv)) {
          return rv;
        }
        nghttp2_inbound_frame_reset(session);
        break;
      case NGHTTP2_GOAWAY:
        busy = 1;
        iframe->state = NGHTTP2_IB_READ_GOAWAY_DEBUG;
        break;
      case NGHTTP2_WINDOW_UPDATE:
        rv = session_process_window_update_frame(session);
        if(nghttp2_is_fatal(rv)) {
          return rv;
        }
        nghttp2_inbound_frame_reset(session);
        break;
      default:
        /* This is unknown frame */
        nghttp2_inbound_frame_reset(session);
        break;
      }
      break;
    case NGHTTP2_IB_READ_HEADER_BLOCK:
    case NGHTTP2_IB_IGN_HEADER_BLOCK: {
      ssize_t data_readlen;
#ifdef DEBUGBUILD
      if(iframe->state == NGHTTP2_IB_READ_HEADER_BLOCK) {
        fprintf(stderr, "[IB_READ_HEADER_BLOCK]\n");
      } else {
        fprintf(stderr, "[IB_IGN_HEADER_BLOCK]\n");
      }
#endif /* DEBUGBUILD */
      readlen = inbound_frame_payload_readlen(iframe, in, last);
      DEBUGF(fprintf(stderr, "readlen=%zu, payloadleft=%zu\n",
                     readlen, iframe->payloadleft - readlen));

      data_readlen = inbound_frame_effective_readlen
        (iframe, iframe->payloadleft - readlen, readlen);
      if(data_readlen >= 0) {
        size_t trail_padlen;
        size_t hd_proclen = 0;
        trail_padlen = nghttp2_frame_trail_padlen(&iframe->frame,
                                                  iframe->padlen);
        DEBUGF(fprintf(stderr, "block final=%d\n",
                       (iframe->frame.hd.flags &
                        NGHTTP2_FLAG_END_HEADERS) &&
                       iframe->payloadleft - data_readlen == trail_padlen));

        rv = inflate_header_block
          (session, &iframe->frame, &hd_proclen,
           (uint8_t*)in, data_readlen,
           (iframe->frame.hd.flags &
            NGHTTP2_FLAG_END_HEADERS) &&
           iframe->payloadleft - data_readlen == trail_padlen,
           iframe->state == NGHTTP2_IB_READ_HEADER_BLOCK);

        if(nghttp2_is_fatal(rv)) {
          return rv;
        }

        if(rv == NGHTTP2_ERR_PAUSE) {
          in += hd_proclen;
          iframe->payloadleft -= hd_proclen;

          return in - first;
        }

        in += readlen;
        iframe->payloadleft -= readlen;

        if(rv == NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE) {
          /* The application says no more headers. We decompress the
             rest of the header block but not invoke on_header_callback
             and on_frame_recv_callback. */
          rv = nghttp2_session_add_rst_stream(session,
                                              iframe->frame.hd.stream_id,
                                              NGHTTP2_INTERNAL_ERROR);
          if(nghttp2_is_fatal(rv)) {
            return rv;
          }
          busy = 1;
          iframe->state = NGHTTP2_IB_IGN_HEADER_BLOCK;
          break;
        }
        if(rv == NGHTTP2_ERR_HEADER_COMP) {
          /* GOAWAY is already issued */
          if(iframe->payloadleft == 0) {
            nghttp2_inbound_frame_reset(session);
          } else {
            busy = 1;
            iframe->state = NGHTTP2_IB_IGN_PAYLOAD;
          }
          break;
        }
      } else {
        in += readlen;
        iframe->payloadleft -= readlen;
      }

      if(iframe->payloadleft) {
        break;
      }
      if((iframe->frame.hd.flags & NGHTTP2_FLAG_END_HEADERS) == 0) {
        iframe->left = NGHTTP2_FRAME_HEAD_LENGTH;
        iframe->error_code = 0;
        iframe->buflen = 0;
        iframe->padlen = 0;
        if(iframe->state == NGHTTP2_IB_READ_HEADER_BLOCK) {
          iframe->state = NGHTTP2_IB_EXPECT_CONTINUATION;
        } else {
          iframe->state = NGHTTP2_IB_IGN_CONTINUATION;
        }
      } else {
        if(iframe->state == NGHTTP2_IB_READ_HEADER_BLOCK) {
          rv = session_after_header_block_received(session);
          if(nghttp2_is_fatal(rv)) {
            return rv;
          }
        }
        nghttp2_inbound_frame_reset(session);
      }
      break;
    }
    case NGHTTP2_IB_IGN_PAYLOAD:
      DEBUGF(fprintf(stderr, "[IB_IGN_PAYLOAD]\n"));
      readlen = inbound_frame_payload_readlen(iframe, in, last);
      iframe->payloadleft -= readlen;
      in += readlen;
      DEBUGF(fprintf(stderr, "readlen=%zu, payloadleft=%zu\n",
                     readlen, iframe->payloadleft));
      if(iframe->payloadleft) {
        break;
      }
      nghttp2_inbound_frame_reset(session);
      break;
    case NGHTTP2_IB_FRAME_SIZE_ERROR:
      DEBUGF(fprintf(stderr, "[IB_FRAME_SIZE_ERROR]\n"));
      rv = session_handle_frame_size_error(session, &iframe->frame);
      if(nghttp2_is_fatal(rv)) {
        return rv;
      }
      busy = 1;
      iframe->state = NGHTTP2_IB_IGN_PAYLOAD;
      break;
    case NGHTTP2_IB_READ_SETTINGS:
      DEBUGF(fprintf(stderr, "[IB_READ_SETTINGS]\n"));
      readlen = inbound_frame_buf_read(iframe, in, last);
      iframe->payloadleft -= readlen;
      in += readlen;
      DEBUGF(fprintf(stderr, "readlen=%zu, payloadleft=%zu\n",
                     readlen, iframe->payloadleft));
      if(iframe->left) {
        break;
      }
      if(readlen > 0) {
        rv = inbound_frame_set_settings_entry(iframe);
        if(rv != 0) {
          DEBUGF(fprintf(stderr, "bad settings\n"));
          rv = nghttp2_session_terminate_session(session,
                                                 NGHTTP2_PROTOCOL_ERROR);
          if(nghttp2_is_fatal(rv)) {
            return rv;
          }
          if(iframe->payloadleft == 0) {
            nghttp2_inbound_frame_reset(session);
            break;
          }
          iframe->state = NGHTTP2_IB_IGN_PAYLOAD;
          break;
        }
      }
      if(iframe->payloadleft) {
        iframe->left = NGHTTP2_FRAME_SETTINGS_ENTRY_LENGTH;
        iframe->buflen = 0;
        break;
      }
      rv = session_process_settings_frame(session);
      if(nghttp2_is_fatal(rv)) {
        return rv;
      }
      nghttp2_inbound_frame_reset(session);
      break;
    case NGHTTP2_IB_READ_GOAWAY_DEBUG:
      DEBUGF(fprintf(stderr, "[IB_READ_GOAWAY_DEBUG]\n"));
      readlen = inbound_frame_payload_readlen(iframe, in, last);
      iframe->payloadleft -= readlen;
      in += readlen;
      DEBUGF(fprintf(stderr, "readlen=%zu, payloadleft=%zu\n",
                     readlen, iframe->payloadleft));
      if(iframe->payloadleft) {
        break;
      }
      rv = session_process_goaway_frame(session);
      if(nghttp2_is_fatal(rv)) {
        return rv;
      }
      nghttp2_inbound_frame_reset(session);
      break;
    case NGHTTP2_IB_EXPECT_CONTINUATION:
    case NGHTTP2_IB_IGN_CONTINUATION:
#ifdef DEBUGBUILD
      if(iframe->state == NGHTTP2_IB_EXPECT_CONTINUATION) {
        fprintf(stderr, "[IB_EXPECT_CONTINUATION]\n");
      } else {
        fprintf(stderr, "[IB_IGN_CONTINUATION]\n");
      }
#endif /* DEBUGBUILD */
      readlen = inbound_frame_buf_read(iframe, in, last);
      in += readlen;
      if(iframe->left) {
        return in - first;
      }
      nghttp2_frame_unpack_frame_hd(&cont_hd, iframe->buf);
      iframe->payloadleft = cont_hd.length;
      if(cont_hd.type != NGHTTP2_CONTINUATION ||
         cont_hd.stream_id != iframe->frame.hd.stream_id) {
        DEBUGF(fprintf(stderr, "expected stream_id=%d, type=%d, but "
                       "got stream_id=%d, type=%d\n",
                       iframe->frame.hd.stream_id, NGHTTP2_CONTINUATION,
                       cont_hd.stream_id, cont_hd.type));
        rv = nghttp2_session_terminate_session(session,
                                               NGHTTP2_PROTOCOL_ERROR);
        if(nghttp2_is_fatal(rv)) {
          return rv;
        }
        /* Mark inflater bad so that we won't perform further decoding */
        session->hd_inflater.ctx.bad = 1;
        busy = 1;
        iframe->state = NGHTTP2_IB_IGN_PAYLOAD;
        break;
      }
      iframe->frame.hd.flags |= cont_hd.flags &
        (NGHTTP2_FLAG_END_HEADERS |
         NGHTTP2_FLAG_PAD_HIGH | NGHTTP2_FLAG_PAD_LOW);

      rv = inbound_frame_handle_pad(iframe, &cont_hd);
      if(rv < 0) {
        busy = 1;
        iframe->state = NGHTTP2_IB_IGN_PAYLOAD;
        rv = nghttp2_session_terminate_session(session,
                                               NGHTTP2_PROTOCOL_ERROR);
        if(nghttp2_is_fatal(rv)) {
          return rv;
        }
        break;
      }
      if(rv == 1) {
        if(iframe->state == NGHTTP2_IB_EXPECT_CONTINUATION) {
          iframe->state = NGHTTP2_IB_READ_PAD_CONTINUATION;
        } else {
          iframe->state = NGHTTP2_IB_IGN_PAD_CONTINUATION;
        }
        break;
      }

      busy = 1;
      if(iframe->state == NGHTTP2_IB_EXPECT_CONTINUATION) {
        iframe->state = NGHTTP2_IB_READ_HEADER_BLOCK;
      } else {
        iframe->state = NGHTTP2_IB_IGN_HEADER_BLOCK;
      }
      break;
    case NGHTTP2_IB_READ_PAD_CONTINUATION:
    case NGHTTP2_IB_IGN_PAD_CONTINUATION:
#ifdef DEBUGBUILD
      if(iframe->state == NGHTTP2_IB_READ_PAD_CONTINUATION) {
        fprintf(stderr, "[IB_READ_PAD_CONTINUATION]\n");
      } else {
        fprintf(stderr, "[IB_IGN_PAD_CONTINUATION]\n");
      }
#endif /* DEBUGBUILD */
      readlen = inbound_frame_buf_read(iframe, in, last);
      in += readlen;
      iframe->payloadleft -= readlen;
      DEBUGF(fprintf(stderr, "readlen=%zu, payloadleft=%zu, left=%zu\n",
                     readlen, iframe->payloadleft, iframe->left));
      if(iframe->left) {
        return in - first;
      }
      busy = 1;
      rv = inbound_frame_compute_pad(iframe);
      if(rv < 0) {
        rv = nghttp2_session_terminate_session(session,
                                               NGHTTP2_PROTOCOL_ERROR);
        if(nghttp2_is_fatal(rv)) {
          return rv;
        }
        iframe->state = NGHTTP2_IB_IGN_PAYLOAD;
        break;
      }
      iframe->padlen = rv;
      if(iframe->frame.hd.type == NGHTTP2_HEADERS) {
        iframe->frame.headers.padlen += rv;
      } else {
        iframe->frame.push_promise.padlen += rv;
      }
      if(iframe->state == NGHTTP2_IB_READ_PAD_CONTINUATION) {
        iframe->state = NGHTTP2_IB_READ_HEADER_BLOCK;
      } else {
        iframe->state = NGHTTP2_IB_IGN_HEADER_BLOCK;
      }
      break;
    case NGHTTP2_IB_READ_DATA:
      DEBUGF(fprintf(stderr, "[IB_READ_DATA]\n"));
      readlen = inbound_frame_payload_readlen(iframe, in, last);
      iframe->payloadleft -= readlen;
      in += readlen;
      DEBUGF(fprintf(stderr, "readlen=%zu, payloadleft=%zu\n",
                     readlen, iframe->payloadleft));
      if(readlen > 0) {
        ssize_t data_readlen;
        rv = nghttp2_session_update_recv_connection_window_size
          (session, readlen);
        if(nghttp2_is_fatal(rv)) {
          return rv;
        }
        if(iframe->payloadleft ||
           (iframe->frame.hd.flags & NGHTTP2_FLAG_END_STREAM) == 0) {
          nghttp2_stream *stream;
          stream = nghttp2_session_get_stream(session,
                                              iframe->frame.hd.stream_id);
          if(stream) {
            rv = nghttp2_session_update_recv_stream_window_size
              (session, stream, readlen);
            if(nghttp2_is_fatal(rv)) {
              return rv;
            }
          }
        }
        data_readlen = inbound_frame_effective_readlen
          (iframe, iframe->payloadleft, readlen);
        DEBUGF(fprintf(stderr, "data_readlen=%zu\n", data_readlen));
        if(data_readlen > 0 && session->callbacks.on_data_chunk_recv_callback) {
          rv = session->callbacks.on_data_chunk_recv_callback
            (session,
             iframe->frame.hd.flags,
             iframe->frame.hd.stream_id,
             in - readlen,
             data_readlen,
             session->user_data);
          if(rv == NGHTTP2_ERR_PAUSE) {
            /* Set type to NGHTTP2_DATA, so that we can see what was
               paused in nghttp2_session_continue() */
            session->iframe.error_code = NGHTTP2_ERR_PAUSE;
            return in - first;
          }
          if(nghttp2_is_fatal(rv)) {
            return NGHTTP2_ERR_CALLBACK_FAILURE;
          }
        }
      }
      if(iframe->payloadleft) {
        break;
      }
      rv = nghttp2_session_process_data_frame(session);
      if(nghttp2_is_fatal(rv)) {
        return rv;
      }
      nghttp2_inbound_frame_reset(session);
      break;
    case NGHTTP2_IB_IGN_DATA:
      DEBUGF(fprintf(stderr, "[IB_IGN_DATA]\n"));
      readlen = inbound_frame_payload_readlen(iframe, in, last);
      iframe->payloadleft -= readlen;
      in += readlen;
      DEBUGF(fprintf(stderr, "readlen=%zu, payloadleft=%zu\n",
                     readlen, iframe->payloadleft));
      if(readlen > 0) {
        /* Update connection-level flow control window for ignored
           DATA frame too */
        rv = nghttp2_session_update_recv_connection_window_size
          (session, readlen);
        if(nghttp2_is_fatal(rv)) {
          return rv;
        }
      }
      if(iframe->payloadleft) {
        break;
      }
      nghttp2_inbound_frame_reset(session);
      break;
    }
    if(!busy && in == last) {
      break;
    }
    busy = 0;
  }
  assert(in == last);
  return in - first;
}

int nghttp2_session_recv(nghttp2_session *session)
{
  uint8_t buf[NGHTTP2_INBOUND_BUFFER_LENGTH];
  while(1) {
    ssize_t readlen;
    readlen = nghttp2_recv(session, buf, sizeof(buf));
    if(readlen > 0) {
      ssize_t proclen = nghttp2_session_mem_recv(session, buf, readlen);
      if(proclen < 0) {
        return proclen;
      }
      assert(proclen == readlen);
    } else if(readlen == 0 || readlen == NGHTTP2_ERR_WOULDBLOCK) {
      return 0;
    } else if(readlen == NGHTTP2_ERR_EOF) {
      return readlen;
    } else if(readlen < 0) {
      return NGHTTP2_ERR_CALLBACK_FAILURE;
    }
  }
}

int nghttp2_session_want_read(nghttp2_session *session)
{
  /* If these flags are set, we don't want to read. The application
     should drop the connection. */
  if((session->goaway_flags & NGHTTP2_GOAWAY_FAIL_ON_SEND) &&
     (session->goaway_flags & NGHTTP2_GOAWAY_SEND)) {
    return 0;
  }
  /* Unless GOAWAY is sent or received, we always want to read
     incoming frames. After GOAWAY is sent or received, we are only
     interested in active streams. */
  return !session->goaway_flags || nghttp2_map_size(&session->streams) > 0;
}

int nghttp2_session_want_write(nghttp2_session *session)
{
  /* If these flags are set, we don't want to write any data. The
     application should drop the connection. */
  if((session->goaway_flags & NGHTTP2_GOAWAY_FAIL_ON_SEND) &&
     (session->goaway_flags & NGHTTP2_GOAWAY_SEND)) {
    return 0;
  }
  /*
   * Unless GOAWAY is sent or received, we want to write frames if
   * there is pending ones. If pending frame is request/push response
   * HEADERS and concurrent stream limit is reached, we don't want to
   * write them.  After GOAWAY is sent or received, we want to write
   * frames if there is pending ones AND there are active frames.
   */
  return (session->aob.item != NULL || !nghttp2_pq_empty(&session->ob_pq) ||
          (!nghttp2_pq_empty(&session->ob_ss_pq) &&
           !nghttp2_session_is_outgoing_concurrent_streams_max(session))) &&
    (!session->goaway_flags || nghttp2_map_size(&session->streams) > 0);
}

int nghttp2_session_add_ping(nghttp2_session *session, uint8_t flags,
                             uint8_t *opaque_data)
{
  int r;
  nghttp2_frame *frame;
  frame = malloc(sizeof(nghttp2_frame));
  if(frame == NULL) {
    return NGHTTP2_ERR_NOMEM;
  }
  nghttp2_frame_ping_init(&frame->ping, flags, opaque_data);
  r = nghttp2_session_add_frame(session, NGHTTP2_CAT_CTRL, frame, NULL);
  if(r != 0) {
    nghttp2_frame_ping_free(&frame->ping);
    free(frame);
  }
  return r;
}

int nghttp2_session_add_goaway(nghttp2_session *session,
                               int32_t last_stream_id,
                               nghttp2_error_code error_code,
                               uint8_t *opaque_data, size_t opaque_data_len)
{
  int r;
  nghttp2_frame *frame;
  uint8_t *opaque_data_copy = NULL;
  if(opaque_data_len) {
    if(opaque_data_len > UINT16_MAX - 8) {
      return NGHTTP2_ERR_INVALID_ARGUMENT;
    }
    opaque_data_copy = malloc(opaque_data_len);
    if(opaque_data_copy == NULL) {
      return NGHTTP2_ERR_NOMEM;
    }
    memcpy(opaque_data_copy, opaque_data, opaque_data_len);
  }
  frame = malloc(sizeof(nghttp2_frame));
  if(frame == NULL) {
    free(opaque_data_copy);
    return NGHTTP2_ERR_NOMEM;
  }
  nghttp2_frame_goaway_init(&frame->goaway, last_stream_id, error_code,
                            opaque_data_copy, opaque_data_len);
  r = nghttp2_session_add_frame(session, NGHTTP2_CAT_CTRL, frame, NULL);
  if(r != 0) {
    nghttp2_frame_goaway_free(&frame->goaway);
    free(frame);
  }
  return r;
}

int nghttp2_session_add_window_update(nghttp2_session *session, uint8_t flags,
                                      int32_t stream_id,
                                      int32_t window_size_increment)
{
  int r;
  nghttp2_frame *frame;
  frame = malloc(sizeof(nghttp2_frame));
  if(frame == NULL) {
    return NGHTTP2_ERR_NOMEM;
  }
  nghttp2_frame_window_update_init(&frame->window_update, flags,
                                   stream_id, window_size_increment);
  r = nghttp2_session_add_frame(session, NGHTTP2_CAT_CTRL, frame, NULL);
  if(r != 0) {
    nghttp2_frame_window_update_free(&frame->window_update);
    free(frame);
  }
  return r;
}

int nghttp2_session_add_settings(nghttp2_session *session, uint8_t flags,
                                 const nghttp2_settings_entry *iv, size_t niv)
{
  nghttp2_frame *frame;
  nghttp2_settings_entry *iv_copy;
  int r;
  if(!nghttp2_iv_check(iv, niv)) {
    return NGHTTP2_ERR_INVALID_ARGUMENT;
  }
  frame = malloc(sizeof(nghttp2_frame));
  if(frame == NULL) {
    return NGHTTP2_ERR_NOMEM;
  }
  iv_copy = nghttp2_frame_iv_copy(iv, niv);
  if(iv_copy == NULL) {
    free(frame);
    return NGHTTP2_ERR_NOMEM;
  }
  nghttp2_frame_settings_init(&frame->settings, flags, iv_copy, niv);
  r = nghttp2_session_add_frame(session, NGHTTP2_CAT_CTRL, frame, NULL);
  if(r != 0) {
    /* The only expected error is fatal one */
    assert(r < NGHTTP2_ERR_FATAL);
    nghttp2_frame_settings_free(&frame->settings);
    free(frame);
  }
  return r;
}

ssize_t nghttp2_session_pack_data(nghttp2_session *session,
                                  uint8_t **buf_ptr, size_t *buflen_ptr,
                                  size_t *bufoff_ptr,
                                  size_t datamax,
                                  nghttp2_private_data *frame)
{
  /* extra 2 bytes for PAD_HIGH and PAD_LOW. We allocate extra 2 bytes
     for padding. Based on the padding length, we adjust the starting
     offset of frame data. The starting offset is assigned into
     |*bufoff_ptr|. */
  size_t payloadoff = NGHTTP2_FRAME_HEAD_LENGTH + 2;
  ssize_t framelen = payloadoff + datamax;
  ssize_t rv;
  int eof_flags;
  uint8_t flags;
  ssize_t payloadlen;

  rv = nghttp2_reserve_buffer(buf_ptr, buflen_ptr, framelen);
  if(rv != 0) {
    return rv;
  }
  eof_flags = 0;
  payloadlen = frame->data_prd.read_callback
    (session, frame->hd.stream_id, (*buf_ptr) + payloadoff, datamax,
     &eof_flags, &frame->data_prd.source, session->user_data);

  if(payloadlen == NGHTTP2_ERR_DEFERRED ||
     payloadlen == NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE) {
    return payloadlen;
  }
  if(payloadlen < 0 || datamax < (size_t)payloadlen) {
    /* This is the error code when callback is failed. */
    return NGHTTP2_ERR_CALLBACK_FAILURE;
  }

  /* Clear flags, because this may contain previous flags of previous
     DATA */
  frame->hd.flags &= ~(NGHTTP2_FLAG_PAD_HIGH | NGHTTP2_FLAG_PAD_LOW);
  flags = 0;

  if(session->pad_alignment &&
     payloadlen > 0 && (size_t)payloadlen < datamax) {
    rv = nghttp2_frame_add_pad(buf_ptr, buflen_ptr, bufoff_ptr,
                               &flags, payloadlen, datamax,
                               session->pad_alignment);
    if(rv < 0) {
      return rv;
    }
    frame->padlen = rv;
    frame->hd.length = payloadlen + rv;
  } else {
    *bufoff_ptr = 2;
    frame->padlen = 0;
    frame->hd.length = payloadlen;
  }

  /* Set PAD flags so that we can supply frame to the callback with
     the correct flags */
  frame->hd.flags |= flags;

  memset(*buf_ptr + *bufoff_ptr, 0, NGHTTP2_FRAME_HEAD_LENGTH);
  nghttp2_put_uint16be(&(*buf_ptr)[*bufoff_ptr], frame->hd.length);

  if(eof_flags) {
    frame->eof = 1;
    if(frame->hd.flags & NGHTTP2_FLAG_END_STREAM) {
      flags |= NGHTTP2_FLAG_END_STREAM;
    }
  }
  (*buf_ptr)[*bufoff_ptr + 3] = flags;
  nghttp2_put_uint32be(&(*buf_ptr)[*bufoff_ptr + 4], frame->hd.stream_id);

  return frame->hd.length + NGHTTP2_FRAME_HEAD_LENGTH + *bufoff_ptr;
}

void* nghttp2_session_get_stream_user_data(nghttp2_session *session,
                                           int32_t stream_id)
{
  nghttp2_stream *stream;
  stream = nghttp2_session_get_stream(session, stream_id);
  if(stream) {
    return stream->stream_user_data;
  } else {
    return NULL;
  }
}

int nghttp2_session_set_stream_user_data(nghttp2_session *session,
                                         int32_t stream_id,
                                         void *stream_user_data)
{
  nghttp2_stream *stream;
  stream = nghttp2_session_get_stream(session, stream_id);
  if(!stream) {
    return NGHTTP2_ERR_INVALID_ARGUMENT;
  }
  stream->stream_user_data = stream_user_data;
  return 0;
}

int nghttp2_session_resume_data(nghttp2_session *session, int32_t stream_id)
{
  int r;
  nghttp2_stream *stream;
  stream = nghttp2_session_get_stream(session, stream_id);
  if(stream == NULL || stream->deferred_data == NULL ||
     (stream->deferred_flags & NGHTTP2_DEFERRED_FLOW_CONTROL)) {
    return NGHTTP2_ERR_INVALID_ARGUMENT;
  }
  r = nghttp2_pq_push(&session->ob_pq, stream->deferred_data);
  if(r == 0) {
    nghttp2_stream_detach_deferred_data(stream);
  }
  return r;
}

size_t nghttp2_session_get_outbound_queue_size(nghttp2_session *session)
{
  return nghttp2_pq_size(&session->ob_pq)+nghttp2_pq_size(&session->ob_ss_pq);
}

int32_t nghttp2_session_get_stream_effective_recv_data_length
(nghttp2_session *session, int32_t stream_id)
{
  nghttp2_stream *stream;
  stream = nghttp2_session_get_stream(session, stream_id);
  if(stream == NULL) {
    return -1;
  }
  return stream->recv_window_size < 0 ? 0 : stream->recv_window_size;
}

int32_t nghttp2_session_get_stream_effective_local_window_size
(nghttp2_session *session, int32_t stream_id)
{
  nghttp2_stream *stream;
  stream = nghttp2_session_get_stream(session, stream_id);
  if(stream == NULL) {
    return -1;
  }
  return stream->local_window_size;
}

int32_t nghttp2_session_get_effective_recv_data_length
(nghttp2_session *session)
{
  return session->recv_window_size < 0 ? 0 : session->recv_window_size;
}

int32_t nghttp2_session_get_effective_local_window_size
(nghttp2_session *session)
{
  return session->local_window_size;
}

int nghttp2_session_upgrade(nghttp2_session *session,
                            const uint8_t *settings_payload,
                            size_t settings_payloadlen,
                            void *stream_user_data)
{
  nghttp2_stream *stream;
  nghttp2_frame frame;
  nghttp2_settings_entry *iv;
  size_t niv;
  int rv;
  int max_conn_val_seen = 0;
  int ini_win_size_seen = 0;
  size_t i;

  if((!session->server && session->next_stream_id != 1) ||
     (session->server && session->last_recv_stream_id >= 1)) {
    return NGHTTP2_ERR_PROTO;
  }
  if(settings_payloadlen % NGHTTP2_FRAME_SETTINGS_ENTRY_LENGTH) {
    return NGHTTP2_ERR_INVALID_ARGUMENT;
  }
  rv = nghttp2_frame_unpack_settings_payload2(&iv, &niv, settings_payload,
                                              settings_payloadlen);
  if(rv != 0) {
    return rv;
  }
  for(i = 0; i < niv; ++i) {
    if(iv[i].settings_id == NGHTTP2_SETTINGS_MAX_CONCURRENT_STREAMS) {
      max_conn_val_seen = 1;
    } else if(iv[i].settings_id == NGHTTP2_SETTINGS_INITIAL_WINDOW_SIZE) {
      ini_win_size_seen = 1;
    }
  }
  if(!max_conn_val_seen || !ini_win_size_seen) {
    free(iv);
    return NGHTTP2_ERR_PROTO;
  }
  if(session->server) {
    memset(&frame.hd, 0, sizeof(frame.hd));
    frame.settings.iv = iv;
    frame.settings.niv = niv;
    rv = nghttp2_session_on_settings_received(session, &frame, 1 /* No ACK */);
  } else {
    rv = nghttp2_submit_settings(session, NGHTTP2_FLAG_NONE, iv, niv);
  }
  free(iv);
  if(rv != 0) {
    return rv;
  }
  stream = nghttp2_session_open_stream(session, 1, NGHTTP2_STREAM_FLAG_NONE,
                                       0, NGHTTP2_STREAM_OPENING,
                                       session->server ?
                                       NULL : stream_user_data);
  if(stream == NULL) {
    return NGHTTP2_ERR_NOMEM;
  }
  if(session->server) {
    nghttp2_stream_shutdown(stream, NGHTTP2_SHUT_RD);
    session->last_recv_stream_id = 1;
    session->last_proc_stream_id = 1;
  } else {
    nghttp2_stream_shutdown(stream, NGHTTP2_SHUT_WR);
    session->next_stream_id += 2;
  }
  return 0;
}