/*
 * 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 "shrpx_http2_upstream.h"

#include <netinet/tcp.h>
#include <assert.h>
#include <cerrno>
#include <sstream>

#include "shrpx_client_handler.h"
#include "shrpx_https_upstream.h"
#include "shrpx_downstream.h"
#include "shrpx_downstream_connection.h"
#include "shrpx_config.h"
#include "shrpx_http.h"
#include "shrpx_worker.h"
#include "http2.h"
#include "util.h"
#include "base64.h"
#include "app_helper.h"
#include "template.h"

using namespace nghttp2;

namespace shrpx {

namespace {
int on_stream_close_callback(nghttp2_session *session, int32_t stream_id,
                             uint32_t error_code, void *user_data) {
  auto upstream = static_cast<Http2Upstream *>(user_data);
  if (LOG_ENABLED(INFO)) {
    ULOG(INFO, upstream) << "Stream stream_id=" << stream_id
                         << " is being closed";
  }

  auto downstream = static_cast<Downstream *>(
      nghttp2_session_get_stream_user_data(session, stream_id));

  if (!downstream) {
    return 0;
  }

  upstream->consume(stream_id, downstream->get_request_datalen());

  downstream->reset_request_datalen();

  if (downstream->get_request_state() == Downstream::CONNECT_FAIL) {
    upstream->remove_downstream(downstream);
    // downstream was deleted

    return 0;
  }

  downstream->set_request_state(Downstream::STREAM_CLOSED);

  if (downstream->get_response_state() == Downstream::MSG_COMPLETE) {
    // At this point, downstream response was read
    if (!downstream->get_upgraded() &&
        !downstream->get_response_connection_close()) {
      // Keep-alive
      downstream->detach_downstream_connection();
    }

    upstream->remove_downstream(downstream);
    // downstream was deleted

    return 0;
  }

  // At this point, downstream read may be paused.

  // If shrpx_downstream::push_request_headers() failed, the
  // error is handled here.
  upstream->remove_downstream(downstream);
  // downstream was deleted

  // How to test this case? Request sufficient large download
  // and make client send RST_STREAM after it gets first DATA
  // frame chunk.

  return 0;
}
} // namespace

int Http2Upstream::upgrade_upstream(HttpsUpstream *http) {
  int rv;

  // to deduce :scheme and :authority, first we have to parse request
  // URI.
  http_parser_url u = {};
  auto &url = http->get_downstream()->get_request_path();

  std::string scheme, authority;
  rv = http_parser_parse_url(url.c_str(), url.size(), 0, &u);
  if (rv == 0) {
    http2::copy_url_component(scheme, &u, UF_SCHEMA, url.c_str());
    http2::copy_url_component(authority, &u, UF_HOST, url.c_str());
  }
  if (scheme.empty()) {
    if (handler_->get_ssl()) {
      scheme = "https";
    } else {
      scheme = "http";
    }
  }
  if (!authority.empty()) {
    if (authority.find(":") != std::string::npos) {
      authority = "[" + authority;
      authority += "]";
    }
    if (u.field_set & (1 << UF_PORT)) {
      authority += ":";
      authority += util::utos(u.port);
    }
  }

  auto http2_settings = http->get_downstream()->get_http2_settings();
  util::to_base64(http2_settings);

  auto settings_payload =
      base64::decode(std::begin(http2_settings), std::end(http2_settings));

  rv = nghttp2_session_upgrade(
      session_, reinterpret_cast<const uint8_t *>(settings_payload.c_str()),
      settings_payload.size(), nullptr);
  if (rv != 0) {
    if (LOG_ENABLED(INFO)) {
      ULOG(INFO, this) << "nghttp2_session_upgrade() returned error: "
                       << nghttp2_strerror(rv);
    }
    return -1;
  }
  pre_upstream_.reset(http);
  auto downstream = http->pop_downstream();
  downstream->reset_upstream(this);
  downstream->set_stream_id(1);
  downstream->reset_upstream_rtimer();
  downstream->set_stream_id(1);
  downstream->set_priority(0);
  downstream->set_request_http2_authority(authority);
  downstream->set_request_http2_scheme(scheme);

  auto ptr = downstream.get();

  nghttp2_session_set_stream_user_data(session_, 1, ptr);
  downstream_queue_.add_pending(std::move(downstream));
  downstream_queue_.mark_active(ptr);

  if (LOG_ENABLED(INFO)) {
    ULOG(INFO, this) << "Connection upgraded to HTTP/2";
  }

  return 0;
}

void Http2Upstream::start_settings_timer() {
  ev_timer_start(handler_->get_loop(), &settings_timer_);
}

void Http2Upstream::stop_settings_timer() {
  ev_timer_stop(handler_->get_loop(), &settings_timer_);
}

namespace {
int on_header_callback(nghttp2_session *session, const nghttp2_frame *frame,
                       const uint8_t *name, size_t namelen,
                       const uint8_t *value, size_t valuelen, uint8_t flags,
                       void *user_data) {
  if (get_config()->upstream_frame_debug) {
    verbose_on_header_callback(session, frame, name, namelen, value, valuelen,
                               flags, user_data);
  }
  if (frame->hd.type != NGHTTP2_HEADERS) {
    return 0;
  }
  auto upstream = static_cast<Http2Upstream *>(user_data);
  auto downstream = static_cast<Downstream *>(
      nghttp2_session_get_stream_user_data(session, frame->hd.stream_id));
  if (!downstream) {
    return 0;
  }

  if (downstream->get_request_headers_sum() > Downstream::MAX_HEADERS_SUM) {
    if (downstream->get_response_state() == Downstream::MSG_COMPLETE) {
      return 0;
    }

    if (LOG_ENABLED(INFO)) {
      ULOG(INFO, upstream) << "Too large header block size="
                           << downstream->get_request_headers_sum();
    }

    // just ignore header fields if this is trailer part.
    if (frame->headers.cat == NGHTTP2_HCAT_HEADERS) {
      return 0;
    }

    if (upstream->error_reply(downstream, 431) != 0) {
      return NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE;
    }

    return 0;
  }

  if (frame->headers.cat == NGHTTP2_HCAT_HEADERS) {
    // just store header fields for trailer part
    downstream->add_request_trailer(name, namelen, value, valuelen,
                                    flags & NGHTTP2_NV_FLAG_NO_INDEX, -1);
    return 0;
  }

  auto token = http2::lookup_token(name, namelen);

  downstream->add_request_header(name, namelen, value, valuelen,
                                 flags & NGHTTP2_NV_FLAG_NO_INDEX, token);
  return 0;
}
} // namespace

namespace {
int on_begin_headers_callback(nghttp2_session *session,
                              const nghttp2_frame *frame, void *user_data) {
  auto upstream = static_cast<Http2Upstream *>(user_data);

  if (frame->headers.cat != NGHTTP2_HCAT_REQUEST) {
    return 0;
  }
  if (LOG_ENABLED(INFO)) {
    ULOG(INFO, upstream) << "Received upstream request HEADERS stream_id="
                         << frame->hd.stream_id;
  }

  auto handler = upstream->get_client_handler();

  // TODO Use priority 0 for now
  auto downstream = make_unique<Downstream>(upstream, handler->get_mcpool(),
                                            frame->hd.stream_id, 0);
  nghttp2_session_set_stream_user_data(session, frame->hd.stream_id,
                                       downstream.get());

  downstream->reset_upstream_rtimer();

  // Although, we deprecated minor version from HTTP/2, we supply
  // minor version 0 to use via header field in a conventional way.
  downstream->set_request_major(2);
  downstream->set_request_minor(0);

  upstream->add_pending_downstream(std::move(downstream));

  return 0;
}
} // namespace

int Http2Upstream::on_request_headers(Downstream *downstream,
                                      const nghttp2_frame *frame) {
  if (downstream->get_response_state() == Downstream::MSG_COMPLETE) {
    return 0;
  }

  auto &nva = downstream->get_request_headers();

  if (LOG_ENABLED(INFO)) {
    std::stringstream ss;
    for (auto &nv : nva) {
      ss << TTY_HTTP_HD << nv.name << TTY_RST << ": " << nv.value << "\n";
    }
    ULOG(INFO, this) << "HTTP request headers. stream_id="
                     << downstream->get_stream_id() << "\n" << ss.str();
  }

  if (get_config()->http2_upstream_dump_request_header) {
    http2::dump_nv(get_config()->http2_upstream_dump_request_header, nva);
  }

  auto content_length =
      downstream->get_request_header(http2::HD_CONTENT_LENGTH);
  if (content_length) {
    // libnghttp2 guarantees this can be parsed
    auto len = util::parse_uint(content_length->value);
    downstream->set_request_content_length(len);
  }

  auto authority = downstream->get_request_header(http2::HD__AUTHORITY);
  auto path = downstream->get_request_header(http2::HD__PATH);
  auto method = downstream->get_request_header(http2::HD__METHOD);
  auto scheme = downstream->get_request_header(http2::HD__SCHEME);

  // presence of mandatory header fields are guaranteed by libnghttp2.

  // For HTTP/2 proxy, we request :authority.
  if (method->value != "CONNECT" && get_config()->http2_proxy && !authority) {
    rst_stream(downstream, NGHTTP2_PROTOCOL_ERROR);
    return 0;
  }

  downstream->set_request_method(http2::value_to_str(method));
  downstream->set_request_http2_scheme(http2::value_to_str(scheme));
  downstream->set_request_http2_authority(http2::value_to_str(authority));
  downstream->set_request_path(http2::value_to_str(path));

  if (!(frame->hd.flags & NGHTTP2_FLAG_END_STREAM)) {
    downstream->set_request_http2_expect_body(true);
  }

  downstream->inspect_http2_request();

  downstream->set_request_state(Downstream::HEADER_COMPLETE);
  if (frame->hd.flags & NGHTTP2_FLAG_END_STREAM) {
    downstream->disable_upstream_rtimer();

    downstream->set_request_state(Downstream::MSG_COMPLETE);
  }

  start_downstream(downstream);

  return 0;
}

void Http2Upstream::start_downstream(Downstream *downstream) {
  if (downstream_queue_.can_activate(
          downstream->get_request_http2_authority())) {
    initiate_downstream(downstream);
    return;
  }

  downstream_queue_.mark_blocked(downstream);
}

void Http2Upstream::initiate_downstream(Downstream *downstream) {
  int rv;

  rv = downstream->attach_downstream_connection(
      handler_->get_downstream_connection());
  if (rv != 0) {
    // downstream connection fails, send error page
    if (error_reply(downstream, 503) != 0) {
      rst_stream(downstream, NGHTTP2_INTERNAL_ERROR);
    }

    downstream->set_request_state(Downstream::CONNECT_FAIL);

    downstream_queue_.mark_failure(downstream);

    return;
  }
  rv = downstream->push_request_headers();
  if (rv != 0) {

    if (error_reply(downstream, 503) != 0) {
      rst_stream(downstream, NGHTTP2_INTERNAL_ERROR);
    }

    downstream_queue_.mark_failure(downstream);

    return;
  }

  downstream_queue_.mark_active(downstream);

  return;
}

namespace {
int on_frame_recv_callback(nghttp2_session *session, const nghttp2_frame *frame,
                           void *user_data) {
  if (get_config()->upstream_frame_debug) {
    verbose_on_frame_recv_callback(session, frame, user_data);
  }
  auto upstream = static_cast<Http2Upstream *>(user_data);

  switch (frame->hd.type) {
  case NGHTTP2_DATA: {
    auto downstream = static_cast<Downstream *>(
        nghttp2_session_get_stream_user_data(session, frame->hd.stream_id));
    if (!downstream) {
      return 0;
    }

    if (frame->hd.flags & NGHTTP2_FLAG_END_STREAM) {
      downstream->disable_upstream_rtimer();

      downstream->end_upload_data();
      downstream->set_request_state(Downstream::MSG_COMPLETE);
    }

    return 0;
  }
  case NGHTTP2_HEADERS: {
    auto downstream = static_cast<Downstream *>(
        nghttp2_session_get_stream_user_data(session, frame->hd.stream_id));
    if (!downstream) {
      return 0;
    }

    if (frame->headers.cat == NGHTTP2_HCAT_REQUEST) {
      downstream->reset_upstream_rtimer();

      return upstream->on_request_headers(downstream, frame);
    }

    if (frame->hd.flags & NGHTTP2_FLAG_END_STREAM) {
      downstream->disable_upstream_rtimer();

      downstream->end_upload_data();
      downstream->set_request_state(Downstream::MSG_COMPLETE);
    }

    return 0;
  }
  case NGHTTP2_SETTINGS:
    if ((frame->hd.flags & NGHTTP2_FLAG_ACK) == 0) {
      return 0;
    }
    upstream->stop_settings_timer();
    return 0;
  case NGHTTP2_GOAWAY:
    if (LOG_ENABLED(INFO)) {
      auto debug_data = util::ascii_dump(frame->goaway.opaque_data,
                                         frame->goaway.opaque_data_len);

      ULOG(INFO, upstream) << "GOAWAY received: last-stream-id="
                           << frame->goaway.last_stream_id
                           << ", error_code=" << frame->goaway.error_code
                           << ", debug_data=" << debug_data;
    }
    return 0;
  default:
    return 0;
  }
}
} // namespace

namespace {
int on_data_chunk_recv_callback(nghttp2_session *session, uint8_t flags,
                                int32_t stream_id, const uint8_t *data,
                                size_t len, void *user_data) {
  auto upstream = static_cast<Http2Upstream *>(user_data);
  auto downstream = static_cast<Downstream *>(
      nghttp2_session_get_stream_user_data(session, stream_id));

  if (!downstream || !downstream->get_downstream_connection()) {
    if (upstream->consume(stream_id, len) != 0) {
      return NGHTTP2_ERR_CALLBACK_FAILURE;
    }

    return 0;
  }

  downstream->reset_upstream_rtimer();

  if (downstream->push_upload_data_chunk(data, len) != 0) {
    upstream->rst_stream(downstream, NGHTTP2_INTERNAL_ERROR);

    if (upstream->consume(stream_id, len) != 0) {
      return NGHTTP2_ERR_CALLBACK_FAILURE;
    }

    return 0;
  }

  return 0;
}
} // namespace

namespace {
int on_frame_send_callback(nghttp2_session *session, const nghttp2_frame *frame,
                           void *user_data) {
  if (get_config()->upstream_frame_debug) {
    verbose_on_frame_send_callback(session, frame, user_data);
  }
  auto upstream = static_cast<Http2Upstream *>(user_data);
  auto handler = upstream->get_client_handler();

  switch (frame->hd.type) {
  case NGHTTP2_DATA:
  case NGHTTP2_HEADERS: {
    if ((frame->hd.flags & NGHTTP2_FLAG_END_STREAM) == 0) {
      return 0;
    }
    // RST_STREAM if request is still incomplete.
    auto stream_id = frame->hd.stream_id;
    auto downstream = static_cast<Downstream *>(
        nghttp2_session_get_stream_user_data(session, stream_id));

    if (!downstream) {
      return 0;
    }

    // For tunneling, issue RST_STREAM to finish the stream.
    if (downstream->get_upgraded() ||
        nghttp2_session_get_stream_remote_close(session, stream_id) == 0) {
      if (LOG_ENABLED(INFO)) {
        ULOG(INFO, upstream)
            << "Send RST_STREAM to "
            << (downstream->get_upgraded() ? "tunneled " : "")
            << "stream stream_id=" << downstream->get_stream_id()
            << " to finish off incomplete request";
      }

      upstream->rst_stream(downstream, NGHTTP2_NO_ERROR);
    }

    return 0;
  }
  case NGHTTP2_SETTINGS:
    if ((frame->hd.flags & NGHTTP2_FLAG_ACK) == 0) {
      upstream->start_settings_timer();
    }
    return 0;
  case NGHTTP2_PUSH_PROMISE: {
    auto promised_stream_id = frame->push_promise.promised_stream_id;
    auto downstream = make_unique<Downstream>(upstream, handler->get_mcpool(),
                                              promised_stream_id, 0);

    nghttp2_session_set_stream_user_data(session, promised_stream_id,
                                         downstream.get());

    downstream->disable_upstream_rtimer();

    downstream->set_request_major(2);
    downstream->set_request_minor(0);

    for (size_t i = 0; i < frame->push_promise.nvlen; ++i) {
      auto &nv = frame->push_promise.nva[i];
      auto token = http2::lookup_token(nv.name, nv.namelen);
      switch (token) {
      case http2::HD__METHOD:
        downstream->set_request_method({nv.value, nv.value + nv.valuelen});
        break;
      case http2::HD__SCHEME:
        downstream->set_request_http2_scheme(
            {nv.value, nv.value + nv.valuelen});
        break;
      case http2::HD__AUTHORITY:
        downstream->set_request_http2_authority(
            {nv.value, nv.value + nv.valuelen});
        break;
      case http2::HD__PATH:
        downstream->set_request_path({nv.value, nv.value + nv.valuelen});
        break;
      }
      downstream->add_request_header(nv.name, nv.namelen, nv.value, nv.valuelen,
                                     nv.flags & NGHTTP2_NV_FLAG_NO_INDEX,
                                     token);
    }

    downstream->inspect_http2_request();

    downstream->set_request_state(Downstream::MSG_COMPLETE);

    // a bit weird but start_downstream() expects that given
    // downstream is in pending queue.
    auto ptr = downstream.get();
    upstream->add_pending_downstream(std::move(downstream));
    upstream->start_downstream(ptr);

    return 0;
  }
  case NGHTTP2_GOAWAY:
    if (LOG_ENABLED(INFO)) {
      auto debug_data = util::ascii_dump(frame->goaway.opaque_data,
                                         frame->goaway.opaque_data_len);

      ULOG(INFO, upstream) << "Sending GOAWAY: last-stream-id="
                           << frame->goaway.last_stream_id
                           << ", error_code=" << frame->goaway.error_code
                           << ", debug_data=" << debug_data;
    }
    return 0;
  default:
    return 0;
  }
}
} // namespace

namespace {
int on_frame_not_send_callback(nghttp2_session *session,
                               const nghttp2_frame *frame, int lib_error_code,
                               void *user_data) {
  auto upstream = static_cast<Http2Upstream *>(user_data);
  if (LOG_ENABLED(INFO)) {
    ULOG(INFO, upstream) << "Failed to send control frame type="
                         << static_cast<uint32_t>(frame->hd.type)
                         << ", lib_error_code=" << lib_error_code << ":"
                         << nghttp2_strerror(lib_error_code);
  }
  if (frame->hd.type == NGHTTP2_HEADERS &&
      lib_error_code != NGHTTP2_ERR_STREAM_CLOSED &&
      lib_error_code != NGHTTP2_ERR_STREAM_CLOSING) {
    // To avoid stream hanging around, issue RST_STREAM.
    auto downstream = static_cast<Downstream *>(
        nghttp2_session_get_stream_user_data(session, frame->hd.stream_id));
    if (downstream) {
      upstream->rst_stream(downstream, NGHTTP2_INTERNAL_ERROR);
    }
  }
  return 0;
}
} // namespace

namespace {
uint32_t infer_upstream_rst_stream_error_code(uint32_t downstream_error_code) {
  // NGHTTP2_REFUSED_STREAM is important because it tells upstream
  // client to retry.
  switch (downstream_error_code) {
  case NGHTTP2_NO_ERROR:
  case NGHTTP2_REFUSED_STREAM:
    return downstream_error_code;
  default:
    return NGHTTP2_INTERNAL_ERROR;
  }
}
} // namespace

namespace {
void settings_timeout_cb(struct ev_loop *loop, ev_timer *w, int revents) {
  auto upstream = static_cast<Http2Upstream *>(w->data);
  auto handler = upstream->get_client_handler();
  ULOG(INFO, upstream) << "SETTINGS timeout";
  if (upstream->terminate_session(NGHTTP2_SETTINGS_TIMEOUT) != 0) {
    delete handler;
    return;
  }
  handler->signal_write();
}
} // namespace

namespace {
void shutdown_timeout_cb(struct ev_loop *loop, ev_timer *w, int revents) {
  auto upstream = static_cast<Http2Upstream *>(w->data);
  auto handler = upstream->get_client_handler();
  upstream->submit_goaway();
  handler->signal_write();
}
} // namespace

namespace {
void prepare_cb(struct ev_loop *loop, ev_prepare *w, int revents) {
  auto upstream = static_cast<Http2Upstream *>(w->data);
  upstream->check_shutdown();
}
} // namespace

void Http2Upstream::submit_goaway() {
  auto last_stream_id = nghttp2_session_get_last_proc_stream_id(session_);
  nghttp2_submit_goaway(session_, NGHTTP2_FLAG_NONE, last_stream_id,
                        NGHTTP2_NO_ERROR, nullptr, 0);
}

void Http2Upstream::check_shutdown() {
  int rv;
  if (shutdown_handled_) {
    return;
  }

  auto worker = handler_->get_worker();

  if (worker->get_graceful_shutdown()) {
    shutdown_handled_ = true;
    rv = nghttp2_submit_shutdown_notice(session_);
    if (rv != 0) {
      ULOG(FATAL, this) << "nghttp2_submit_shutdown_notice() failed: "
                        << nghttp2_strerror(rv);
      return;
    }
    handler_->signal_write();
    ev_timer_start(handler_->get_loop(), &shutdown_timer_);
  }
}

nghttp2_session_callbacks *create_http2_upstream_callbacks() {
  int rv;
  nghttp2_session_callbacks *callbacks;

  rv = nghttp2_session_callbacks_new(&callbacks);

  if (rv != 0) {
    return nullptr;
  }

  nghttp2_session_callbacks_set_on_stream_close_callback(
      callbacks, on_stream_close_callback);

  nghttp2_session_callbacks_set_on_frame_recv_callback(callbacks,
                                                       on_frame_recv_callback);

  nghttp2_session_callbacks_set_on_data_chunk_recv_callback(
      callbacks, on_data_chunk_recv_callback);

  nghttp2_session_callbacks_set_on_frame_send_callback(callbacks,
                                                       on_frame_send_callback);

  nghttp2_session_callbacks_set_on_frame_not_send_callback(
      callbacks, on_frame_not_send_callback);

  nghttp2_session_callbacks_set_on_header_callback(callbacks,
                                                   on_header_callback);

  nghttp2_session_callbacks_set_on_begin_headers_callback(
      callbacks, on_begin_headers_callback);

  if (get_config()->padding) {
    nghttp2_session_callbacks_set_select_padding_callback(
        callbacks, http::select_padding_callback);
  }

  return callbacks;
}

Http2Upstream::Http2Upstream(ClientHandler *handler)
    : downstream_queue_(
          get_config()->http2_proxy
              ? get_config()->downstream_connections_per_host
              : get_config()->downstream_proto == PROTO_HTTP
                    ? get_config()->downstream_connections_per_frontend
                    : 0,
          !get_config()->http2_proxy),
      handler_(handler), session_(nullptr), data_pending_(nullptr),
      data_pendinglen_(0), shutdown_handled_(false) {

  int rv;

  rv = nghttp2_session_server_new2(&session_,
                                   get_config()->http2_upstream_callbacks, this,
                                   get_config()->http2_option);

  assert(rv == 0);

  flow_control_ = true;

  // TODO Maybe call from outside?
  std::array<nghttp2_settings_entry, 2> entry;
  entry[0].settings_id = NGHTTP2_SETTINGS_MAX_CONCURRENT_STREAMS;
  entry[0].value = get_config()->http2_max_concurrent_streams;

  entry[1].settings_id = NGHTTP2_SETTINGS_INITIAL_WINDOW_SIZE;
  entry[1].value = (1 << get_config()->http2_upstream_window_bits) - 1;

  rv = nghttp2_submit_settings(session_, NGHTTP2_FLAG_NONE, entry.data(),
                               entry.size());
  if (rv != 0) {
    ULOG(ERROR, this) << "nghttp2_submit_settings() returned error: "
                      << nghttp2_strerror(rv);
  }

  if (get_config()->http2_upstream_connection_window_bits > 16) {
    int32_t delta = (1 << get_config()->http2_upstream_connection_window_bits) -
                    1 - NGHTTP2_INITIAL_CONNECTION_WINDOW_SIZE;
    rv = nghttp2_submit_window_update(session_, NGHTTP2_FLAG_NONE, 0, delta);

    if (rv != 0) {
      ULOG(ERROR, this) << "nghttp2_submit_window_update() returned error: "
                        << nghttp2_strerror(rv);
    }
  }

  if (!get_config()->altsvcs.empty()) {
    // Set max_age to 24hrs, which is default for alt-svc header
    // field.
    for (auto &altsvc : get_config()->altsvcs) {
      rv = nghttp2_submit_altsvc(
          session_, NGHTTP2_FLAG_NONE, 0, 86400, altsvc.port,
          reinterpret_cast<const uint8_t *>(altsvc.protocol_id),
          altsvc.protocol_id_len,
          reinterpret_cast<const uint8_t *>(altsvc.host), altsvc.host_len,
          reinterpret_cast<const uint8_t *>(altsvc.origin), altsvc.origin_len);

      if (rv != 0) {
        ULOG(ERROR, this) << "nghttp2_submit_altsvc() returned error: "
                          << nghttp2_strerror(rv);
      }
    }
  }

  // We wait for SETTINGS ACK at least 10 seconds.
  ev_timer_init(&settings_timer_, settings_timeout_cb, 10., 0.);

  settings_timer_.data = this;

  // timer for 2nd GOAWAY.  HTTP/2 spec recommend 1 RTT.  We wait for
  // 2 seconds.
  ev_timer_init(&shutdown_timer_, shutdown_timeout_cb, 2., 0);
  shutdown_timer_.data = this;

  ev_prepare_init(&prep_, prepare_cb);
  prep_.data = this;
  ev_prepare_start(handler_->get_loop(), &prep_);

  handler_->reset_upstream_read_timeout(
      get_config()->http2_upstream_read_timeout);

  handler_->signal_write();
}

Http2Upstream::~Http2Upstream() {
  nghttp2_session_del(session_);
  ev_prepare_stop(handler_->get_loop(), &prep_);
  ev_timer_stop(handler_->get_loop(), &shutdown_timer_);
  ev_timer_stop(handler_->get_loop(), &settings_timer_);
}

int Http2Upstream::on_read() {
  ssize_t rv = 0;
  auto rb = handler_->get_rb();
  auto rlimit = handler_->get_rlimit();

  if (rb->rleft()) {
    rv = nghttp2_session_mem_recv(session_, rb->pos, rb->rleft());
    if (rv < 0) {
      if (rv != NGHTTP2_ERR_BAD_PREFACE) {
        ULOG(ERROR, this) << "nghttp2_session_recv() returned error: "
                          << nghttp2_strerror(rv);
      }
      return -1;
    }

    // nghttp2_session_mem_recv should consume all input bytes on
    // success.
    assert(static_cast<size_t>(rv) == rb->rleft());
    rb->reset();
    rlimit->startw();
  }

  auto wb = handler_->get_wb();
  if (nghttp2_session_want_read(session_) == 0 &&
      nghttp2_session_want_write(session_) == 0 && wb->rleft() == 0) {
    if (LOG_ENABLED(INFO)) {
      ULOG(INFO, this) << "No more read/write for this HTTP2 session";
    }
    return -1;
  }

  handler_->signal_write();
  return 0;
}

// After this function call, downstream may be deleted.
int Http2Upstream::on_write() {
  auto wb = handler_->get_wb();

  if (data_pending_) {
    auto n = std::min(wb->wleft(), data_pendinglen_);
    wb->write(data_pending_, n);
    if (n < data_pendinglen_) {
      data_pending_ += n;
      data_pendinglen_ -= n;
      return 0;
    }

    data_pending_ = nullptr;
    data_pendinglen_ = 0;
  }

  for (;;) {
    const uint8_t *data;
    auto datalen = nghttp2_session_mem_send(session_, &data);

    if (datalen < 0) {
      ULOG(ERROR, this) << "nghttp2_session_mem_send() returned error: "
                        << nghttp2_strerror(datalen);
      return -1;
    }
    if (datalen == 0) {
      break;
    }
    auto n = wb->write(data, datalen);
    if (n < static_cast<decltype(n)>(datalen)) {
      data_pending_ = data + n;
      data_pendinglen_ = datalen - n;
      return 0;
    }
  }

  if (nghttp2_session_want_read(session_) == 0 &&
      nghttp2_session_want_write(session_) == 0 && wb->rleft() == 0) {
    if (LOG_ENABLED(INFO)) {
      ULOG(INFO, this) << "No more read/write for this HTTP2 session";
    }
    return -1;
  }

  return 0;
}

ClientHandler *Http2Upstream::get_client_handler() const { return handler_; }

int Http2Upstream::downstream_read(DownstreamConnection *dconn) {
  auto downstream = dconn->get_downstream();

  if (downstream->get_request_state() == Downstream::STREAM_CLOSED) {
    // If upstream HTTP2 stream was closed, we just close downstream,
    // because there is no consumer now. Downstream connection is also
    // closed in this case.
    remove_downstream(downstream);
    // downstream was deleted

    return 0;
  }

  if (downstream->get_response_state() == Downstream::MSG_RESET) {
    // The downstream stream was reset (canceled). In this case,
    // RST_STREAM to the upstream and delete downstream connection
    // here. Deleting downstream will be taken place at
    // on_stream_close_callback.
    rst_stream(downstream,
               infer_upstream_rst_stream_error_code(
                   downstream->get_response_rst_stream_error_code()));
    downstream->pop_downstream_connection();
    // dconn was deleted
    dconn = nullptr;
  } else if (downstream->get_response_state() == Downstream::MSG_BAD_HEADER) {
    if (error_reply(downstream, 502) != 0) {
      return -1;
    }
    downstream->pop_downstream_connection();
    // dconn was deleted
    dconn = nullptr;
  } else {
    auto rv = downstream->on_read();
    if (rv == SHRPX_ERR_EOF) {
      return downstream_eof(dconn);
    }
    if (rv != 0) {
      if (rv != SHRPX_ERR_NETWORK) {
        if (LOG_ENABLED(INFO)) {
          DCLOG(INFO, dconn) << "HTTP parser failure";
        }
      }
      return downstream_error(dconn, Downstream::EVENT_ERROR);
    }
    // Detach downstream connection early so that it could be reused
    // without hitting server's request timeout.
    if (downstream->get_response_state() == Downstream::MSG_COMPLETE &&
        !downstream->get_response_connection_close()) {
      // Keep-alive
      downstream->detach_downstream_connection();
    }
  }

  handler_->signal_write();

  // At this point, downstream may be deleted.

  return 0;
}

int Http2Upstream::downstream_write(DownstreamConnection *dconn) {
  int rv;
  rv = dconn->on_write();
  if (rv == SHRPX_ERR_NETWORK) {
    return downstream_error(dconn, Downstream::EVENT_ERROR);
  }
  if (rv != 0) {
    return -1;
  }
  return 0;
}

int Http2Upstream::downstream_eof(DownstreamConnection *dconn) {
  auto downstream = dconn->get_downstream();

  if (LOG_ENABLED(INFO)) {
    DCLOG(INFO, dconn) << "EOF. stream_id=" << downstream->get_stream_id();
  }
  if (downstream->get_request_state() == Downstream::STREAM_CLOSED) {
    // If stream was closed already, we don't need to send reply at
    // the first place. We can delete downstream.
    remove_downstream(downstream);
    // downstream was deleted

    return 0;
  }

  // Delete downstream connection. If we don't delete it here, it will
  // be pooled in on_stream_close_callback.
  downstream->pop_downstream_connection();
  // dconn was deleted
  dconn = nullptr;
  // downstream wil be deleted in on_stream_close_callback.
  if (downstream->get_response_state() == Downstream::HEADER_COMPLETE) {
    // Server may indicate the end of the request by EOF
    if (LOG_ENABLED(INFO)) {
      ULOG(INFO, this) << "Downstream body was ended by EOF";
    }
    downstream->set_response_state(Downstream::MSG_COMPLETE);

    // For tunneled connection, MSG_COMPLETE signals
    // downstream_data_read_callback to send RST_STREAM after pending
    // response body is sent. This is needed to ensure that RST_STREAM
    // is sent after all pending data are sent.
    on_downstream_body_complete(downstream);
  } else if (downstream->get_response_state() != Downstream::MSG_COMPLETE) {
    // If stream was not closed, then we set MSG_COMPLETE and let
    // on_stream_close_callback delete downstream.
    if (error_reply(downstream, 502) != 0) {
      return -1;
    }
  }
  handler_->signal_write();
  // At this point, downstream may be deleted.
  return 0;
}

int Http2Upstream::downstream_error(DownstreamConnection *dconn, int events) {
  auto downstream = dconn->get_downstream();

  if (LOG_ENABLED(INFO)) {
    if (events & Downstream::EVENT_ERROR) {
      DCLOG(INFO, dconn) << "Downstream network/general error";
    } else {
      DCLOG(INFO, dconn) << "Timeout";
    }
    if (downstream->get_upgraded()) {
      DCLOG(INFO, dconn) << "Note: this is tunnel connection";
    }
  }

  if (downstream->get_request_state() == Downstream::STREAM_CLOSED) {
    remove_downstream(downstream);
    // downstream was deleted

    return 0;
  }

  // Delete downstream connection. If we don't delete it here, it will
  // be pooled in on_stream_close_callback.
  downstream->pop_downstream_connection();
  // dconn was deleted
  dconn = nullptr;

  if (downstream->get_response_state() == Downstream::MSG_COMPLETE) {
    // For SSL tunneling, we issue RST_STREAM. For other types of
    // stream, we don't have to do anything since response was
    // complete.
    if (downstream->get_upgraded()) {
      rst_stream(downstream, NGHTTP2_NO_ERROR);
    }
  } else {
    if (downstream->get_response_state() == Downstream::HEADER_COMPLETE) {
      if (downstream->get_upgraded()) {
        on_downstream_body_complete(downstream);
      } else {
        rst_stream(downstream, NGHTTP2_INTERNAL_ERROR);
      }
    } else {
      unsigned int status;
      if (events & Downstream::EVENT_TIMEOUT) {
        status = 504;
      } else {
        status = 502;
      }
      if (error_reply(downstream, status) != 0) {
        return -1;
      }
    }
    downstream->set_response_state(Downstream::MSG_COMPLETE);
  }
  handler_->signal_write();
  // At this point, downstream may be deleted.
  return 0;
}

int Http2Upstream::rst_stream(Downstream *downstream, uint32_t error_code) {
  if (LOG_ENABLED(INFO)) {
    ULOG(INFO, this) << "RST_STREAM stream_id=" << downstream->get_stream_id()
                     << " with error_code=" << error_code;
  }
  int rv;
  rv = nghttp2_submit_rst_stream(session_, NGHTTP2_FLAG_NONE,
                                 downstream->get_stream_id(), error_code);
  if (rv < NGHTTP2_ERR_FATAL) {
    ULOG(FATAL, this) << "nghttp2_submit_rst_stream() failed: "
                      << nghttp2_strerror(rv);
    DIE();
  }
  return 0;
}

int Http2Upstream::terminate_session(uint32_t error_code) {
  int rv;
  rv = nghttp2_session_terminate_session(session_, error_code);
  if (rv != 0) {
    return -1;
  }
  return 0;
}

namespace {
ssize_t downstream_data_read_callback(nghttp2_session *session,
                                      int32_t stream_id, uint8_t *buf,
                                      size_t length, uint32_t *data_flags,
                                      nghttp2_data_source *source,
                                      void *user_data) {
  int rv;
  auto downstream = static_cast<Downstream *>(source->ptr);
  auto upstream = static_cast<Http2Upstream *>(downstream->get_upstream());
  auto body = downstream->get_response_buf();
  assert(body);

  auto dconn = downstream->get_downstream_connection();

  if (body->rleft() == 0 && dconn &&
      downstream->get_response_state() != Downstream::MSG_COMPLETE) {
    // Try to read more if buffer is empty.  This will help small
    // buffer and make priority handling a bit better.
    if (upstream->downstream_read(dconn) != 0) {
      return NGHTTP2_ERR_CALLBACK_FAILURE;
    }
  }

  auto nread = body->remove(buf, length);
  auto body_empty = body->rleft() == 0;

  if (body_empty &&
      downstream->get_response_state() == Downstream::MSG_COMPLETE) {

    *data_flags |= NGHTTP2_DATA_FLAG_EOF;

    if (!downstream->get_upgraded()) {
      auto &trailers = downstream->get_response_trailers();
      if (!trailers.empty()) {
        std::vector<nghttp2_nv> nva;
        nva.reserve(trailers.size());
        http2::copy_headers_to_nva(nva, trailers);
        if (!nva.empty()) {
          rv = nghttp2_submit_trailer(session, stream_id, nva.data(),
                                      nva.size());
          if (rv != 0) {
            if (nghttp2_is_fatal(rv)) {
              return NGHTTP2_ERR_CALLBACK_FAILURE;
            }
          } else {
            *data_flags |= NGHTTP2_DATA_FLAG_NO_END_STREAM;
          }
        }
      }
    }
  }

  if (body_empty) {
    downstream->disable_upstream_wtimer();
  } else {
    downstream->reset_upstream_wtimer();
  }

  if (nread > 0 && downstream->resume_read(SHRPX_NO_BUFFER, nread) != 0) {
    return NGHTTP2_ERR_CALLBACK_FAILURE;
  }

  if (nread == 0 && ((*data_flags) & NGHTTP2_DATA_FLAG_EOF) == 0) {
    return NGHTTP2_ERR_DEFERRED;
  }

  if (nread > 0) {
    downstream->add_response_sent_bodylen(nread);
  }

  return nread;
}
} // namespace

int Http2Upstream::error_reply(Downstream *downstream,
                               unsigned int status_code) {
  int rv;
  auto html = http::create_error_html(status_code);
  downstream->set_response_http_status(status_code);
  auto body = downstream->get_response_buf();
  body->append(html.c_str(), html.size());
  downstream->set_response_state(Downstream::MSG_COMPLETE);

  nghttp2_data_provider data_prd;
  data_prd.source.ptr = downstream;
  data_prd.read_callback = downstream_data_read_callback;

  auto content_length = util::utos(html.size());
  auto status_code_str = util::utos(status_code);
  auto nva =
      make_array(http2::make_nv_ls(":status", status_code_str),
                 http2::make_nv_ll("content-type", "text/html; charset=UTF-8"),
                 http2::make_nv_lc("server", get_config()->server_name),
                 http2::make_nv_ls("content-length", content_length));

  rv = nghttp2_submit_response(session_, downstream->get_stream_id(),
                               nva.data(), nva.size(), &data_prd);
  if (rv < NGHTTP2_ERR_FATAL) {
    ULOG(FATAL, this) << "nghttp2_submit_response() failed: "
                      << nghttp2_strerror(rv);
    return -1;
  }

  return 0;
}

void
Http2Upstream::add_pending_downstream(std::unique_ptr<Downstream> downstream) {
  downstream_queue_.add_pending(std::move(downstream));
}

void Http2Upstream::remove_downstream(Downstream *downstream) {
  if (downstream->accesslog_ready()) {
    handler_->write_accesslog(downstream);
  }

  nghttp2_session_set_stream_user_data(session_, downstream->get_stream_id(),
                                       nullptr);

  auto next_downstream = downstream_queue_.remove_and_get_blocked(downstream);

  if (next_downstream) {
    initiate_downstream(next_downstream);
  }
}

// WARNING: Never call directly or indirectly nghttp2_session_send or
// nghttp2_session_recv. These calls may delete downstream.
int Http2Upstream::on_downstream_header_complete(Downstream *downstream) {
  int rv;

  if (LOG_ENABLED(INFO)) {
    if (downstream->get_non_final_response()) {
      DLOG(INFO, downstream) << "HTTP non-final response header";
    } else {
      DLOG(INFO, downstream) << "HTTP response header completed";
    }
  }

  if (!get_config()->http2_proxy && !get_config()->client_proxy &&
      !get_config()->no_location_rewrite) {
    downstream->rewrite_location_response_header(
        downstream->get_request_http2_scheme());
  }

  size_t nheader = downstream->get_response_headers().size();
  auto nva = std::vector<nghttp2_nv>();
  // 3 means :status and possible server and via header field.
  nva.reserve(nheader + 3 + get_config()->add_response_headers.size());
  std::string via_value;
  auto response_status = util::utos(downstream->get_response_http_status());
  nva.push_back(http2::make_nv_ls(":status", response_status));

  http2::copy_headers_to_nva(nva, downstream->get_response_headers());

  if (downstream->get_non_final_response()) {
    if (LOG_ENABLED(INFO)) {
      log_response_headers(downstream, nva);
    }

    rv = nghttp2_submit_headers(session_, NGHTTP2_FLAG_NONE,
                                downstream->get_stream_id(), nullptr,
                                nva.data(), nva.size(), nullptr);

    downstream->clear_response_headers();

    if (rv != 0) {
      ULOG(FATAL, this) << "nghttp2_submit_headers() failed";
      return -1;
    }

    return 0;
  }

  if (!get_config()->http2_proxy && !get_config()->client_proxy) {
    nva.push_back(http2::make_nv_lc("server", get_config()->server_name));
  } else {
    auto server = downstream->get_response_header(http2::HD_SERVER);
    if (server) {
      nva.push_back(http2::make_nv_ls("server", (*server).value));
    }
  }

  auto via = downstream->get_response_header(http2::HD_VIA);
  if (get_config()->no_via) {
    if (via) {
      nva.push_back(http2::make_nv_ls("via", (*via).value));
    }
  } else {
    if (via) {
      via_value = (*via).value;
      via_value += ", ";
    }
    via_value += http::create_via_header_value(
        downstream->get_response_major(), downstream->get_response_minor());
    nva.push_back(http2::make_nv_ls("via", via_value));
  }

  for (auto &p : get_config()->add_response_headers) {
    nva.push_back(http2::make_nv(p.first, p.second));
  }

  if (LOG_ENABLED(INFO)) {
    log_response_headers(downstream, nva);
  }

  if (get_config()->http2_upstream_dump_response_header) {
    http2::dump_nv(get_config()->http2_upstream_dump_response_header,
                   nva.data(), nva.size());
  }

  nghttp2_data_provider data_prd;
  data_prd.source.ptr = downstream;
  data_prd.read_callback = downstream_data_read_callback;

  nghttp2_data_provider *data_prdptr;

  if (downstream->expect_response_body()) {
    data_prdptr = &data_prd;
  } else {
    data_prdptr = nullptr;
  }

  rv = nghttp2_submit_response(session_, downstream->get_stream_id(),
                               nva.data(), nva.size(), data_prdptr);
  if (rv != 0) {
    ULOG(FATAL, this) << "nghttp2_submit_response() failed";
    return -1;
  }

  // We need some conditions that must be fulfilled to initiate server
  // push.
  //
  // * Server push is disabled for http2 proxy, since incoming headers
  //   are mixed origins.  We don't know how to reliably determine the
  //   authority yet.
  //
  // * If downstream is http/2, it is likely that PUSH_PROMISE is
  //   coming from there, so we don't initiate PUSH_RPOMISE here.
  //
  // * We need 200 response code for associated resource.  This is too
  //   restrictive, we will review this later.
  //
  // * We requires GET or POST for associated resource.  Probably we
  //   don't want to push for HEAD request.  Not sure other methods
  //   are also eligible for push.
  if (!get_config()->no_server_push &&
      get_config()->downstream_proto == PROTO_HTTP &&
      !get_config()->http2_proxy && (downstream->get_stream_id() % 2) &&
      downstream->get_response_header(http2::HD_LINK) &&
      downstream->get_response_http_status() == 200 &&
      (downstream->get_request_method() == "GET" ||
       downstream->get_request_method() == "POST")) {

    if (prepare_push_promise(downstream) != 0) {
      return -1;
    }
  }

  return 0;
}

// WARNING: Never call directly or indirectly nghttp2_session_send or
// nghttp2_session_recv. These calls may delete downstream.
int Http2Upstream::on_downstream_body(Downstream *downstream,
                                      const uint8_t *data, size_t len,
                                      bool flush) {
  auto body = downstream->get_response_buf();
  body->append(data, len);

  if (flush) {
    nghttp2_session_resume_data(session_, downstream->get_stream_id());

    downstream->ensure_upstream_wtimer();
  }

  return 0;
}

// WARNING: Never call directly or indirectly nghttp2_session_send or
// nghttp2_session_recv. These calls may delete downstream.
int Http2Upstream::on_downstream_body_complete(Downstream *downstream) {
  if (LOG_ENABLED(INFO)) {
    DLOG(INFO, downstream) << "HTTP response completed";
  }

  if (!downstream->validate_response_bodylen()) {
    rst_stream(downstream, NGHTTP2_PROTOCOL_ERROR);
    downstream->set_response_connection_close(true);
    return 0;
  }

  nghttp2_session_resume_data(session_, downstream->get_stream_id());
  downstream->ensure_upstream_wtimer();

  return 0;
}

bool Http2Upstream::get_flow_control() const { return flow_control_; }

void Http2Upstream::pause_read(IOCtrlReason reason) {}

int Http2Upstream::resume_read(IOCtrlReason reason, Downstream *downstream,
                               size_t consumed) {
  if (get_flow_control()) {
    assert(downstream->get_request_datalen() >= consumed);

    if (consume(downstream->get_stream_id(), consumed) != 0) {
      return -1;
    }

    downstream->dec_request_datalen(consumed);
  }

  handler_->signal_write();
  return 0;
}

int Http2Upstream::on_downstream_abort_request(Downstream *downstream,
                                               unsigned int status_code) {
  int rv;

  rv = error_reply(downstream, status_code);

  if (rv != 0) {
    return -1;
  }

  handler_->signal_write();
  return 0;
}

int Http2Upstream::consume(int32_t stream_id, size_t len) {
  int rv;

  rv = nghttp2_session_consume(session_, stream_id, len);

  if (rv != 0) {
    ULOG(WARN, this) << "nghttp2_session_consume() returned error: "
                     << nghttp2_strerror(rv);
    return -1;
  }

  return 0;
}

void
Http2Upstream::log_response_headers(Downstream *downstream,
                                    const std::vector<nghttp2_nv> &nva) const {
  std::stringstream ss;
  for (auto &nv : nva) {
    ss << TTY_HTTP_HD << nv.name << TTY_RST << ": " << nv.value << "\n";
  }
  ULOG(INFO, this) << "HTTP response headers. stream_id="
                   << downstream->get_stream_id() << "\n" << ss.str();
}

int Http2Upstream::on_timeout(Downstream *downstream) {
  if (LOG_ENABLED(INFO)) {
    ULOG(INFO, this) << "Stream timeout stream_id="
                     << downstream->get_stream_id();
  }

  rst_stream(downstream, NGHTTP2_NO_ERROR);

  return 0;
}

void Http2Upstream::on_handler_delete() {
  for (auto d = downstream_queue_.get_downstreams(); d; d = d->dlnext) {
    if (d->get_dispatch_state() == Downstream::DISPATCH_ACTIVE &&
        d->accesslog_ready()) {
      handler_->write_accesslog(d);
    }
  }
}

int Http2Upstream::on_downstream_reset(bool no_retry) {
  int rv;

  for (auto downstream = downstream_queue_.get_downstreams(); downstream;
       downstream = downstream->dlnext) {
    if (downstream->get_dispatch_state() != Downstream::DISPATCH_ACTIVE) {
      continue;
    }

    if (!downstream->request_submission_ready()) {
      rst_stream(downstream, NGHTTP2_INTERNAL_ERROR);
      downstream->pop_downstream_connection();
      continue;
    }

    downstream->pop_downstream_connection();

    downstream->add_retry();

    if (no_retry || downstream->no_more_retry()) {
      goto fail;
    }

    // downstream connection is clean; we can retry with new
    // downstream connection.

    rv = downstream->attach_downstream_connection(
        handler_->get_downstream_connection());
    if (rv != 0) {
      goto fail;
    }

    continue;

  fail:
    if (on_downstream_abort_request(downstream, 503) != 0) {
      return -1;
    }
    downstream->pop_downstream_connection();
  }

  handler_->signal_write();

  return 0;
}

int Http2Upstream::prepare_push_promise(Downstream *downstream) {
  int rv;
  http_parser_url u;
  memset(&u, 0, sizeof(u));
  rv = http_parser_parse_url(downstream->get_request_path().c_str(),
                             downstream->get_request_path().size(), 0, &u);
  if (rv != 0) {
    return 0;
  }
  const char *base;
  size_t baselen;
  if (u.field_set & (1 << UF_PATH)) {
    auto &f = u.field_data[UF_PATH];
    base = downstream->get_request_path().c_str() + f.off;
    baselen = f.len;
  } else {
    base = "/";
    baselen = 1;
  }
  for (auto &kv : downstream->get_response_headers()) {
    if (kv.token != http2::HD_LINK) {
      continue;
    }
    for (auto &link :
         http2::parse_link_header(kv.value.c_str(), kv.value.size())) {
      auto link_url = link.uri.first;
      auto link_urllen = link.uri.second - link.uri.first;

      const char *rel;
      size_t rellen;
      const char *relq = nullptr;
      size_t relqlen = 0;

      http_parser_url v;
      memset(&v, 0, sizeof(v));
      rv = http_parser_parse_url(link_url, link_urllen, 0, &v);
      if (rv != 0) {
        assert(link_urllen);
        if (link_url[0] == '/') {
          continue;
        }
        // treat link_url as relative URI.
        auto end = std::find(link_url, link_url + link_urllen, '#');
        auto q = std::find(link_url, end, '?');
        rel = link_url;
        rellen = q - link_url;
        if (q != end) {
          relq = q + 1;
          relqlen = end - relq;
        }
      } else {
        if (v.field_set & (1 << UF_HOST)) {
          continue;
        }
        if (v.field_set & (1 << UF_PATH)) {
          auto &f = v.field_data[UF_PATH];
          rel = link_url + f.off;
          rellen = f.len;
        } else {
          rel = "/";
          rellen = 1;
        }

        if (v.field_set & (1 << UF_QUERY)) {
          auto &f = v.field_data[UF_QUERY];
          relq = link_url + f.off;
          relqlen = f.len;
        }
      }
      auto path = http2::path_join(base, baselen, nullptr, 0, rel, rellen, relq,
                                   relqlen);
      rv = submit_push_promise(path, downstream);
      if (rv != 0) {
        return -1;
      }
    }
  }
  return 0;
}

int Http2Upstream::submit_push_promise(const std::string &path,
                                       Downstream *downstream) {
  int rv;
  std::vector<nghttp2_nv> nva;
  nva.reserve(downstream->get_request_headers().size());

  // juse use "GET" for now
  nva.push_back(http2::make_nv_ll(":method", "GET"));
  nva.push_back(
      http2::make_nv_ls(":scheme", downstream->get_request_http2_scheme()));
  nva.push_back(http2::make_nv_ls(":path", path));
  auto &authority = downstream->get_request_http2_authority();
  if (!authority.empty()) {
    nva.push_back(http2::make_nv_ls(":authority", authority));
  }

  for (auto &kv : downstream->get_request_headers()) {
    switch (kv.token) {
    // TODO generate referer
    case http2::HD__AUTHORITY:
    case http2::HD__SCHEME:
    case http2::HD__METHOD:
    case http2::HD__PATH:
      continue;
    case http2::HD_ACCEPT_ENCODING:
    case http2::HD_ACCEPT_LANGUAGE:
    case http2::HD_CACHE_CONTROL:
    case http2::HD_HOST:
    case http2::HD_USER_AGENT:
      nva.push_back(http2::make_nv(kv.name, kv.value, kv.no_index));
      break;
    }
  }

  rv = nghttp2_submit_push_promise(session_, NGHTTP2_FLAG_NONE,
                                   downstream->get_stream_id(), nva.data(),
                                   nva.size(), nullptr);

  if (rv < 0) {
    if (LOG_ENABLED(INFO)) {
      ULOG(INFO, this) << "nghttp2_submit_push_promise() failed: "
                       << nghttp2_strerror(rv);
    }
    if (nghttp2_is_fatal(rv)) {
      return -1;
    }
    return 0;
  }

  if (LOG_ENABLED(INFO)) {
    std::stringstream ss;
    for (auto &nv : nva) {
      ss << TTY_HTTP_HD << nv.name << TTY_RST << ": " << nv.value << "\n";
    }
    ULOG(INFO, this) << "HTTP push request headers. promised_stream_id=" << rv
                     << "\n" << ss.str();
  }

  return 0;
}

} // namespace shrpx