nghttp2/lib/nghttp2_stream.c

/*
 * nghttp2 - HTTP/2 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_stream.h"

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

#include "nghttp2_session.h"
#include "nghttp2_helper.h"

/* Maximum distance between any two stream's cycle in the same
   prirority queue.  Imagine stream A's cycle is A, and stream B's
   cycle is B, and A < B.  The cycle is unsigned 32 bit integer, it
   may get overflow.  Because of how we calculate the next cycle
   value, if B - A is less than or equals to
   NGHTTP2_MAX_CYCLE_DISTANCE, A and B are in the same scale, in other
   words, B is really greater than or equal to A.  Otherwise, A is a
   result of overflow, and it is actually A > B if we consider that
   fact. */
#define NGHTTP2_MAX_CYCLE_DISTANCE (16384 * 256 + 255)

static int stream_less(const void *lhsx, const void *rhsx) {
  const nghttp2_stream *lhs, *rhs;

  lhs = nghttp2_struct_of(lhsx, nghttp2_stream, pq_entry);
  rhs = nghttp2_struct_of(rhsx, nghttp2_stream, pq_entry);

  if (lhs->cycle == rhs->cycle) {
    return lhs->seq < rhs->seq;
  }

  if (lhs->cycle < rhs->cycle) {
    return rhs->cycle - lhs->cycle <= NGHTTP2_MAX_CYCLE_DISTANCE;
  }

  return lhs->cycle - rhs->cycle > NGHTTP2_MAX_CYCLE_DISTANCE;
}

void nghttp2_stream_init(nghttp2_stream *stream, int32_t stream_id,
                         uint8_t flags, nghttp2_stream_state initial_state,
                         int32_t weight, int32_t remote_initial_window_size,
                         int32_t local_initial_window_size,
                         void *stream_user_data, nghttp2_mem *mem) {
  nghttp2_map_entry_init(&stream->map_entry, (key_type)stream_id);
  nghttp2_pq_init(&stream->obq, stream_less, mem);

  stream->stream_id = stream_id;
  stream->flags = flags;
  stream->state = initial_state;
  stream->shut_flags = NGHTTP2_SHUT_NONE;
  stream->stream_user_data = stream_user_data;
  stream->item = NULL;
  stream->remote_window_size = remote_initial_window_size;
  stream->local_window_size = local_initial_window_size;
  stream->recv_window_size = 0;
  stream->consumed_size = 0;
  stream->recv_reduction = 0;
  stream->window_update_queued = 0;

  stream->dep_prev = NULL;
  stream->dep_next = NULL;
  stream->sib_prev = NULL;
  stream->sib_next = NULL;

  stream->closed_prev = NULL;
  stream->closed_next = NULL;

  stream->weight = weight;
  stream->sum_dep_weight = 0;

  stream->http_flags = NGHTTP2_HTTP_FLAG_NONE;
  stream->content_length = -1;
  stream->recv_content_length = 0;
  stream->status_code = -1;

  stream->queued = 0;
  stream->descendant_last_cycle = 0;
  stream->cycle = 0;
  stream->pending_penalty = 0;
  stream->descendant_next_seq = 0;
  stream->seq = 0;
  stream->last_writelen = 0;
}

void nghttp2_stream_free(nghttp2_stream *stream) {
  nghttp2_pq_free(&stream->obq);
  /* We don't free stream->item.  If it is assigned to aob, then
     active_outbound_item_reset() will delete it.  Otherwise,
     nghttp2_stream_close() or session_del() will delete it. */
}

void nghttp2_stream_shutdown(nghttp2_stream *stream, nghttp2_shut_flag flag) {
  stream->shut_flags = (uint8_t)(stream->shut_flags | flag);
}

/*
 * Returns nonzero if |stream| is active.  This function does not take
 * into account its descendants.
 */
static int stream_active(nghttp2_stream *stream) {
  return stream->item &&
         (stream->flags & NGHTTP2_STREAM_FLAG_DEFERRED_ALL) == 0;
}

/*
 * Returns nonzero if |stream| or one of its descendants is active
 */
static int stream_subtree_active(nghttp2_stream *stream) {
  return stream_active(stream) || !nghttp2_pq_empty(&stream->obq);
}

/*
 * Returns next cycle for |stream|.
 */
static void stream_next_cycle(nghttp2_stream *stream, uint32_t last_cycle) {
  uint32_t penalty;

  penalty = (uint32_t)stream->last_writelen * NGHTTP2_MAX_WEIGHT +
            stream->pending_penalty;

  stream->cycle = last_cycle + penalty / (uint32_t)stream->weight;
  stream->pending_penalty = penalty % (uint32_t)stream->weight;
}

static int stream_obq_push(nghttp2_stream *dep_stream, nghttp2_stream *stream) {
  int rv;

  for (; dep_stream && !stream->queued;
       stream = dep_stream, dep_stream = dep_stream->dep_prev) {
    stream_next_cycle(stream, dep_stream->descendant_last_cycle);
    stream->seq = dep_stream->descendant_next_seq++;

    DEBUGF(fprintf(stderr, "stream: stream=%d obq push cycle=%d\n",
                   stream->stream_id, stream->cycle));

    DEBUGF(fprintf(stderr, "stream: push stream %d to stream %d\n",
                   stream->stream_id, dep_stream->stream_id));

    rv = nghttp2_pq_push(&dep_stream->obq, &stream->pq_entry);
    if (rv != 0) {
      return rv;
    }
    stream->queued = 1;
  }

  return 0;
}

/*
 * Removes |stream| from parent's obq.  If removal of |stream| makes
 * parent's obq empty, and parent is not active, then parent is also
 * removed.  This process is repeated recursively.
 */
static void stream_obq_remove(nghttp2_stream *stream) {
  nghttp2_stream *dep_stream;

  dep_stream = stream->dep_prev;

  if (!stream->queued) {
    return;
  }

  for (; dep_stream; stream = dep_stream, dep_stream = dep_stream->dep_prev) {
    DEBUGF(fprintf(stderr, "stream: remove stream %d from stream %d\n",
                   stream->stream_id, dep_stream->stream_id));

    nghttp2_pq_remove(&dep_stream->obq, &stream->pq_entry);

    assert(stream->queued);

    stream->queued = 0;
    stream->cycle = 0;
    stream->pending_penalty = 0;
    stream->descendant_last_cycle = 0;
    stream->last_writelen = 0;

    if (stream_subtree_active(dep_stream)) {
      return;
    }
  }
}

/*
 * Moves |stream| from |src|'s obq to |dest|'s obq.  Removal from
 * |src|'s obq is just done calling nghttp2_pq_remove(), so it does
 * not recursively remove |src| and ancestors, like
 * stream_obq_remove().
 */
static int stream_obq_move(nghttp2_stream *dest, nghttp2_stream *src,
                           nghttp2_stream *stream) {
  if (!stream->queued) {
    return 0;
  }

  DEBUGF(fprintf(stderr, "stream: remove stream %d from stream %d (move)\n",
                 stream->stream_id, src->stream_id));

  nghttp2_pq_remove(&src->obq, &stream->pq_entry);
  stream->queued = 0;

  return stream_obq_push(dest, stream);
}

void nghttp2_stream_reschedule(nghttp2_stream *stream) {
  nghttp2_stream *dep_stream;

  assert(stream->queued);

  dep_stream = stream->dep_prev;

  for (; dep_stream; stream = dep_stream, dep_stream = dep_stream->dep_prev) {
    nghttp2_pq_remove(&dep_stream->obq, &stream->pq_entry);

    stream_next_cycle(stream, dep_stream->descendant_last_cycle);
    stream->seq = dep_stream->descendant_next_seq++;

    nghttp2_pq_push(&dep_stream->obq, &stream->pq_entry);

    DEBUGF(fprintf(stderr, "stream: stream=%d obq resched cycle=%d\n",
                   stream->stream_id, stream->cycle));

    dep_stream->last_writelen = stream->last_writelen;
  }
}

void nghttp2_stream_change_weight(nghttp2_stream *stream, int32_t weight) {
  nghttp2_stream *dep_stream;
  uint32_t last_cycle;
  int32_t old_weight;
  uint32_t wlen_penalty;

  if (stream->weight == weight) {
    return;
  }

  old_weight = stream->weight;
  stream->weight = weight;

  dep_stream = stream->dep_prev;

  if (!dep_stream) {
    return;
  }

  dep_stream->sum_dep_weight += weight - old_weight;

  if (!stream->queued) {
    return;
  }

  nghttp2_pq_remove(&dep_stream->obq, &stream->pq_entry);

  wlen_penalty = (uint32_t)stream->last_writelen * NGHTTP2_MAX_WEIGHT;

  /* Compute old stream->pending_penalty we used to calculate
     stream->cycle */
  stream->pending_penalty =
      (uint32_t)((stream->pending_penalty + (uint32_t)old_weight -
                  (wlen_penalty % (uint32_t)old_weight)) %
                 (uint32_t)old_weight);

  last_cycle = stream->cycle -
               (wlen_penalty + stream->pending_penalty) / (uint32_t)old_weight;

  /* Now we have old stream->pending_penalty and new stream->weight in
     place */
  stream_next_cycle(stream, last_cycle);

  if (stream->cycle < dep_stream->descendant_last_cycle &&
      (dep_stream->descendant_last_cycle - stream->cycle) <=
          NGHTTP2_MAX_CYCLE_DISTANCE) {
    stream->cycle = dep_stream->descendant_last_cycle;
  }

  /* Continue to use same stream->seq */

  nghttp2_pq_push(&dep_stream->obq, &stream->pq_entry);

  DEBUGF(fprintf(stderr, "stream: stream=%d obq resched cycle=%d\n",
                 stream->stream_id, stream->cycle));
}

static nghttp2_stream *stream_last_sib(nghttp2_stream *stream) {
  for (; stream->sib_next; stream = stream->sib_next)
    ;

  return stream;
}

int32_t nghttp2_stream_dep_distributed_weight(nghttp2_stream *stream,
                                              int32_t weight) {
  weight = stream->weight * weight / stream->sum_dep_weight;

  return nghttp2_max(1, weight);
}

#ifdef STREAM_DEP_DEBUG

static void ensure_inactive(nghttp2_stream *stream) {
  nghttp2_stream *si;

  if (stream->queued) {
    fprintf(stderr, "stream(%p)=%d, stream->queued = 1; want 0\n", stream,
            stream->stream_id);
    assert(0);
  }

  if (stream_active(stream)) {
    fprintf(stderr, "stream(%p)=%d, stream_active(stream) = 1; want 0\n",
            stream, stream->stream_id);
    assert(0);
  }

  if (!nghttp2_pq_empty(&stream->obq)) {
    fprintf(stderr, "stream(%p)=%d, nghttp2_pq_size() = %zu; want 0\n", stream,
            stream->stream_id, nghttp2_pq_size(&stream->obq));
    assert(0);
  }

  for (si = stream->dep_next; si; si = si->sib_next) {
    ensure_inactive(si);
  }
}

static void check_queued(nghttp2_stream *stream) {
  nghttp2_stream *si;
  int queued;

  if (stream->queued) {
    if (!stream_subtree_active(stream)) {
      fprintf(stderr,
              "stream(%p)=%d, stream->queued == 1, but "
              "stream_active() == %d and nghttp2_pq_size(&stream->obq) = %zu\n",
              stream, stream->stream_id, stream_active(stream),
              nghttp2_pq_size(&stream->obq));
      assert(0);
    }
    if (!stream_active(stream)) {
      queued = 0;
      for (si = stream->dep_next; si; si = si->sib_next) {
        if (si->queued) {
          ++queued;
        }
      }
      if (queued == 0) {
        fprintf(stderr, "stream(%p)=%d, stream->queued == 1, and "
                        "!stream_active(), but no descendants is queued\n",
                stream, stream->stream_id);
        assert(0);
      }
    }

    for (si = stream->dep_next; si; si = si->sib_next) {
      check_queued(si);
    }
  } else {
    if (stream_active(stream) || !nghttp2_pq_empty(&stream->obq)) {
      fprintf(stderr, "stream(%p) = %d, stream->queued == 0, but "
                      "stream_active(stream) == %d and "
                      "nghttp2_pq_size(&stream->obq) = %zu\n",
              stream, stream->stream_id, stream_active(stream),
              nghttp2_pq_size(&stream->obq));
      assert(0);
    }
    for (si = stream->dep_next; si; si = si->sib_next) {
      ensure_inactive(si);
    }
  }
}

static void check_sum_dep(nghttp2_stream *stream) {
  nghttp2_stream *si;
  int32_t n = 0;
  for (si = stream->dep_next; si; si = si->sib_next) {
    n += si->weight;
  }
  if (n != stream->sum_dep_weight) {
    fprintf(stderr, "stream(%p)=%d, sum_dep_weight = %d; want %d\n", stream,
            stream->stream_id, n, stream->sum_dep_weight);
    assert(0);
  }
  for (si = stream->dep_next; si; si = si->sib_next) {
    check_sum_dep(si);
  }
}

static void check_dep_prev(nghttp2_stream *stream) {
  nghttp2_stream *si;
  for (si = stream->dep_next; si; si = si->sib_next) {
    if (si->dep_prev != stream) {
      fprintf(stderr, "si->dep_prev = %p; want %p\n", si->dep_prev, stream);
      assert(0);
    }
    check_dep_prev(si);
  }
}

#endif /* STREAM_DEP_DEBUG */

#ifdef STREAM_DEP_DEBUG
static void validate_tree(nghttp2_stream *stream) {
  nghttp2_stream *si;

  if (!stream) {
    return;
  }

  for (; stream->dep_prev; stream = stream->dep_prev)
    ;

  assert(stream->stream_id == 0);
  assert(!stream->queued);

  fprintf(stderr, "checking...\n");
  if (nghttp2_pq_empty(&stream->obq)) {
    fprintf(stderr, "root obq empty\n");
    for (si = stream->dep_next; si; si = si->sib_next) {
      ensure_inactive(si);
    }
  } else {
    for (si = stream->dep_next; si; si = si->sib_next) {
      check_queued(si);
    }
  }

  check_sum_dep(stream);
  check_dep_prev(stream);
}
#else /* !STREAM_DEP_DEBUG */
static void validate_tree(nghttp2_stream *stream _U_) {}
#endif /* !STREAM_DEP_DEBUG*/

static int stream_update_dep_on_attach_item(nghttp2_stream *stream) {
  int rv;

  rv = stream_obq_push(stream->dep_prev, stream);
  if (rv != 0) {
    return rv;
  }

  validate_tree(stream);
  return 0;
}

static int stream_update_dep_on_detach_item(nghttp2_stream *stream) {
  if (nghttp2_pq_empty(&stream->obq)) {
    stream_obq_remove(stream);
  }

  validate_tree(stream);

  return 0;
}

int nghttp2_stream_attach_item(nghttp2_stream *stream,
                               nghttp2_outbound_item *item) {
  int rv;

  assert((stream->flags & NGHTTP2_STREAM_FLAG_DEFERRED_ALL) == 0);
  assert(stream->item == NULL);

  DEBUGF(fprintf(stderr, "stream: stream=%d attach item=%p\n",
                 stream->stream_id, item));

  stream->item = item;

  rv = stream_update_dep_on_attach_item(stream);
  if (rv != 0) {
    /* This may relave stream->queued == 1, but stream->item == NULL.
       But only consequence of this error is fatal one, and session
       destruction.  In that execution path, these inconsistency does
       not matter. */
    stream->item = NULL;
    return rv;
  }

  return 0;
}

int nghttp2_stream_detach_item(nghttp2_stream *stream) {
  DEBUGF(fprintf(stderr, "stream: stream=%d detach item=%p\n",
                 stream->stream_id, stream->item));

  stream->item = NULL;
  stream->flags = (uint8_t)(stream->flags & ~NGHTTP2_STREAM_FLAG_DEFERRED_ALL);

  return stream_update_dep_on_detach_item(stream);
}

int nghttp2_stream_defer_item(nghttp2_stream *stream, uint8_t flags) {
  assert(stream->item);

  DEBUGF(fprintf(stderr, "stream: stream=%d defer item=%p cause=%02x\n",
                 stream->stream_id, stream->item, flags));

  stream->flags |= flags;

  return stream_update_dep_on_detach_item(stream);
}

int nghttp2_stream_resume_deferred_item(nghttp2_stream *stream, uint8_t flags) {
  assert(stream->item);

  DEBUGF(fprintf(stderr, "stream: stream=%d resume item=%p flags=%02x\n",
                 stream->stream_id, stream->item, flags));

  stream->flags = (uint8_t)(stream->flags & ~flags);

  if (stream->flags & NGHTTP2_STREAM_FLAG_DEFERRED_ALL) {
    return 0;
  }

  return stream_update_dep_on_attach_item(stream);
}

int nghttp2_stream_check_deferred_item(nghttp2_stream *stream) {
  return stream->item && (stream->flags & NGHTTP2_STREAM_FLAG_DEFERRED_ALL);
}

int nghttp2_stream_check_deferred_by_flow_control(nghttp2_stream *stream) {
  return stream->item &&
         (stream->flags & NGHTTP2_STREAM_FLAG_DEFERRED_FLOW_CONTROL);
}

static int update_initial_window_size(int32_t *window_size_ptr,
                                      int32_t new_initial_window_size,
                                      int32_t old_initial_window_size) {
  int64_t new_window_size = (int64_t)(*window_size_ptr) +
                            new_initial_window_size - old_initial_window_size;
  if (INT32_MIN > new_window_size ||
      new_window_size > NGHTTP2_MAX_WINDOW_SIZE) {
    return -1;
  }
  *window_size_ptr = (int32_t)new_window_size;
  return 0;
}

int nghttp2_stream_update_remote_initial_window_size(
    nghttp2_stream *stream, int32_t new_initial_window_size,
    int32_t old_initial_window_size) {
  return update_initial_window_size(&stream->remote_window_size,
                                    new_initial_window_size,
                                    old_initial_window_size);
}

int nghttp2_stream_update_local_initial_window_size(
    nghttp2_stream *stream, int32_t new_initial_window_size,
    int32_t old_initial_window_size) {
  return update_initial_window_size(&stream->local_window_size,
                                    new_initial_window_size,
                                    old_initial_window_size);
}

void nghttp2_stream_promise_fulfilled(nghttp2_stream *stream) {
  stream->state = NGHTTP2_STREAM_OPENED;
  stream->flags = (uint8_t)(stream->flags & ~NGHTTP2_STREAM_FLAG_PUSH);
}

int nghttp2_stream_dep_find_ancestor(nghttp2_stream *stream,
                                     nghttp2_stream *target) {
  for (; stream; stream = stream->dep_prev) {
    if (stream == target) {
      return 1;
    }
  }
  return 0;
}

int nghttp2_stream_dep_insert(nghttp2_stream *dep_stream,
                              nghttp2_stream *stream) {
  nghttp2_stream *si;
  int rv;

  DEBUGF(fprintf(stderr,
                 "stream: dep_insert dep_stream(%p)=%d, stream(%p)=%d\n",
                 dep_stream, dep_stream->stream_id, stream, stream->stream_id));

  stream->sum_dep_weight = dep_stream->sum_dep_weight;
  dep_stream->sum_dep_weight = stream->weight;

  if (dep_stream->dep_next) {
    for (si = dep_stream->dep_next; si; si = si->sib_next) {
      si->dep_prev = stream;
      if (si->queued) {
        rv = stream_obq_move(stream, dep_stream, si);
        if (rv != 0) {
          return rv;
        }
      }
    }

    if (stream_subtree_active(stream)) {
      rv = stream_obq_push(dep_stream, stream);
      if (rv != 0) {
        return rv;
      }
    }

    stream->dep_next = dep_stream->dep_next;
  }

  dep_stream->dep_next = stream;
  stream->dep_prev = dep_stream;

  validate_tree(stream);

  return 0;
}

static void set_dep_prev(nghttp2_stream *stream, nghttp2_stream *dep) {
  for (; stream; stream = stream->sib_next) {
    stream->dep_prev = dep;
  }
}

static void link_dep(nghttp2_stream *dep_stream, nghttp2_stream *stream) {
  dep_stream->dep_next = stream;
  if (stream) {
    stream->dep_prev = dep_stream;
  }
}

static void link_sib(nghttp2_stream *a, nghttp2_stream *b) {
  a->sib_next = b;
  if (b) {
    b->sib_prev = a;
  }
}

static void insert_link_dep(nghttp2_stream *dep_stream,
                            nghttp2_stream *stream) {
  nghttp2_stream *sib_next;

  assert(stream->sib_prev == NULL);

  sib_next = dep_stream->dep_next;

  link_sib(stream, sib_next);

  link_dep(dep_stream, stream);
}

static void unlink_sib(nghttp2_stream *stream) {
  nghttp2_stream *prev, *next, *dep_next;

  prev = stream->sib_prev;
  dep_next = stream->dep_next;

  assert(prev);

  if (dep_next) {
    /*
     *  prev--stream(--sib_next--...)
     *         |
     *        dep_next
     */

    link_sib(prev, dep_next);

    set_dep_prev(dep_next, stream->dep_prev);

    if (stream->sib_next) {
      link_sib(stream_last_sib(dep_next), stream->sib_next);
    }
  } else {
    /*
     *  prev--stream(--sib_next--...)
     */
    next = stream->sib_next;

    prev->sib_next = next;

    if (next) {
      next->sib_prev = prev;
    }
  }
}

static void unlink_dep(nghttp2_stream *stream) {
  nghttp2_stream *prev, *next, *dep_next;

  prev = stream->dep_prev;
  dep_next = stream->dep_next;

  assert(prev);

  if (dep_next) {
    /*
     * prev
     *   |
     * stream(--sib_next--...)
     *   |
     * dep_next
     */
    link_dep(prev, dep_next);

    set_dep_prev(dep_next, stream->dep_prev);

    if (stream->sib_next) {
      link_sib(stream_last_sib(dep_next), stream->sib_next);
    }

  } else if (stream->sib_next) {
    /*
     * prev
     *   |
     * stream--sib_next
     */
    next = stream->sib_next;

    next->sib_prev = NULL;

    link_dep(prev, next);
  } else {
    prev->dep_next = NULL;
  }
}

void nghttp2_stream_dep_add(nghttp2_stream *dep_stream,
                            nghttp2_stream *stream) {
  DEBUGF(fprintf(stderr, "stream: dep_add dep_stream(%p)=%d, stream(%p)=%d\n",
                 dep_stream, dep_stream->stream_id, stream, stream->stream_id));

  dep_stream->sum_dep_weight += stream->weight;

  if (dep_stream->dep_next == NULL) {
    link_dep(dep_stream, stream);
  } else {
    insert_link_dep(dep_stream, stream);
  }

  validate_tree(stream);
}

int nghttp2_stream_dep_remove(nghttp2_stream *stream) {
  nghttp2_stream *dep_prev, *si;
  int32_t sum_dep_weight_delta;
  int rv;

  DEBUGF(fprintf(stderr, "stream: dep_remove stream(%p)=%d\n", stream,
                 stream->stream_id));

  /* Distribute weight of |stream| to direct descendants */
  sum_dep_weight_delta = -stream->weight;

  for (si = stream->dep_next; si; si = si->sib_next) {
    si->weight = nghttp2_stream_dep_distributed_weight(stream, si->weight);

    sum_dep_weight_delta += si->weight;

    if (si->queued) {
      rv = stream_obq_move(stream->dep_prev, stream, si);
      if (rv != 0) {
        return rv;
      }
    }
  }

  assert(stream->dep_prev);

  dep_prev = stream->dep_prev;

  dep_prev->sum_dep_weight += sum_dep_weight_delta;

  if (stream->queued) {
    stream_obq_remove(stream);
  }

  if (stream->sib_prev) {
    unlink_sib(stream);
  } else {
    unlink_dep(stream);
  }

  stream->sum_dep_weight = 0;

  stream->dep_prev = NULL;
  stream->dep_next = NULL;
  stream->sib_prev = NULL;
  stream->sib_next = NULL;

  validate_tree(dep_prev);

  return 0;
}

int nghttp2_stream_dep_insert_subtree(nghttp2_stream *dep_stream,
                                      nghttp2_stream *stream) {
  nghttp2_stream *last_sib;
  nghttp2_stream *dep_next;
  nghttp2_stream *si;
  int rv;

  DEBUGF(fprintf(stderr, "stream: dep_insert_subtree dep_stream(%p)=%d "
                         "stream(%p)=%d\n",
                 dep_stream, dep_stream->stream_id, stream, stream->stream_id));

  stream->sum_dep_weight += dep_stream->sum_dep_weight;
  dep_stream->sum_dep_weight = stream->weight;

  if (dep_stream->dep_next) {
    dep_next = dep_stream->dep_next;

    link_dep(dep_stream, stream);

    if (stream->dep_next) {
      last_sib = stream_last_sib(stream->dep_next);

      link_sib(last_sib, dep_next);
    } else {
      link_dep(stream, dep_next);
    }

    for (si = dep_next; si; si = si->sib_next) {
      si->dep_prev = stream;
      if (si->queued) {
        rv = stream_obq_move(stream, dep_stream, si);
        if (rv != 0) {
          return rv;
        }
      }
    }
  } else {
    link_dep(dep_stream, stream);
  }

  if (stream_subtree_active(stream)) {
    rv = stream_obq_push(dep_stream, stream);
    if (rv != 0) {
      return rv;
    }
  }

  validate_tree(dep_stream);

  return 0;
}

int nghttp2_stream_dep_add_subtree(nghttp2_stream *dep_stream,
                                   nghttp2_stream *stream) {
  int rv;

  DEBUGF(fprintf(stderr, "stream: dep_add_subtree dep_stream(%p)=%d "
                         "stream(%p)=%d\n",
                 dep_stream, dep_stream->stream_id, stream, stream->stream_id));

  dep_stream->sum_dep_weight += stream->weight;

  if (dep_stream->dep_next) {
    insert_link_dep(dep_stream, stream);
  } else {
    link_dep(dep_stream, stream);
  }

  if (stream_subtree_active(stream)) {
    rv = stream_obq_push(dep_stream, stream);
    if (rv != 0) {
      return rv;
    }
  }

  validate_tree(dep_stream);

  return 0;
}

void nghttp2_stream_dep_remove_subtree(nghttp2_stream *stream) {
  nghttp2_stream *next, *dep_prev;

  DEBUGF(fprintf(stderr, "stream: dep_remove_subtree stream(%p)=%d\n", stream,
                 stream->stream_id));

  assert(stream->dep_prev);

  dep_prev = stream->dep_prev;

  if (stream->sib_prev) {
    link_sib(stream->sib_prev, stream->sib_next);
  } else {
    next = stream->sib_next;

    link_dep(dep_prev, next);

    if (next) {
      next->sib_prev = NULL;
    }
  }

  dep_prev->sum_dep_weight -= stream->weight;

  if (stream->queued) {
    stream_obq_remove(stream);
  }

  validate_tree(dep_prev);

  stream->sib_prev = NULL;
  stream->sib_next = NULL;
  stream->dep_prev = NULL;
}

int nghttp2_stream_in_dep_tree(nghttp2_stream *stream) {
  return stream->dep_prev || stream->dep_next || stream->sib_prev ||
         stream->sib_next;
}

nghttp2_outbound_item *
nghttp2_stream_next_outbound_item(nghttp2_stream *stream) {
  nghttp2_pq_entry *ent;
  nghttp2_stream *si;

  for (;;) {
    if (stream_active(stream)) {
      /* Update ascendant's descendant_last_cycle here, so that we can
         assure that new stream is scheduled based on it. */
      for (si = stream; si->dep_prev; si = si->dep_prev) {
        si->dep_prev->descendant_last_cycle = si->cycle;
      }
      return stream->item;
    }
    ent = nghttp2_pq_top(&stream->obq);
    if (!ent) {
      return NULL;
    }
    stream = nghttp2_struct_of(ent, nghttp2_stream, pq_entry);
  }
}

nghttp2_stream_proto_state nghttp2_stream_get_state(nghttp2_stream *stream) {
  if (stream->flags & NGHTTP2_STREAM_FLAG_CLOSED) {
    return NGHTTP2_STREAM_STATE_CLOSED;
  }

  if (stream->flags & NGHTTP2_STREAM_FLAG_PUSH) {
    if (stream->shut_flags & NGHTTP2_SHUT_RD) {
      return NGHTTP2_STREAM_STATE_RESERVED_LOCAL;
    }

    if (stream->shut_flags & NGHTTP2_SHUT_WR) {
      return NGHTTP2_STREAM_STATE_RESERVED_REMOTE;
    }
  }

  if (stream->shut_flags & NGHTTP2_SHUT_RD) {
    return NGHTTP2_STREAM_STATE_HALF_CLOSED_REMOTE;
  }

  if (stream->shut_flags & NGHTTP2_SHUT_WR) {
    return NGHTTP2_STREAM_STATE_HALF_CLOSED_LOCAL;
  }

  if (stream->state == NGHTTP2_STREAM_IDLE) {
    return NGHTTP2_STREAM_STATE_IDLE;
  }

  return NGHTTP2_STREAM_STATE_OPEN;
}

nghttp2_stream *nghttp2_stream_get_parent(nghttp2_stream *stream) {
  return stream->dep_prev;
}

nghttp2_stream *nghttp2_stream_get_next_sibling(nghttp2_stream *stream) {
  return stream->sib_next;
}

nghttp2_stream *nghttp2_stream_get_previous_sibling(nghttp2_stream *stream) {
  return stream->sib_prev;
}

nghttp2_stream *nghttp2_stream_get_first_child(nghttp2_stream *stream) {
  return stream->dep_next;
}

int32_t nghttp2_stream_get_weight(nghttp2_stream *stream) {
  return stream->weight;
}

int32_t nghttp2_stream_get_sum_dependency_weight(nghttp2_stream *stream) {
  return stream->sum_dep_weight;
}

int32_t nghttp2_stream_get_stream_id(nghttp2_stream *stream) {
  return stream->stream_id;
}