text: /*
   *
   * Copyright 2017 gRPC authors.
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   *
   */
  
  #include "src/core/ext/transport/chttp2/transport/internal.h"
  
  #include <limits.h>
  #include <math.h>
  #include <string.h>
  
  #include <grpc/support/alloc.h>
  #include <grpc/support/log.h>
  #include <grpc/support/string_util.h>
  #include <grpc/support/useful.h>
  
  #include "src/core/lib/support/string.h"
  
  static uint32_t grpc_chttp2_target_announced_window(
      const grpc_chttp2_transport_flowctl* tfc);
  
  #ifndef NDEBUG
  
  typedef struct {
    int64_t remote_window;
    int64_t target_window;
    int64_t announced_window;
    int64_t remote_window_delta;
    int64_t local_window_delta;
    int64_t announced_window_delta;
    uint32_t local_init_window;
    uint32_t local_max_frame;
  } shadow_flow_control;
  
  static void pretrace(shadow_flow_control* shadow_fc,
                       grpc_chttp2_transport_flowctl* tfc,
                       grpc_chttp2_stream_flowctl* sfc) {
    shadow_fc->remote_window = tfc->remote_window;
    shadow_fc->target_window = grpc_chttp2_target_announced_window(tfc);
    shadow_fc->announced_window = tfc->announced_window;
    if (sfc != NULL) {
      shadow_fc->remote_window_delta = sfc->remote_window_delta;
      shadow_fc->local_window_delta = sfc->local_window_delta;
      shadow_fc->announced_window_delta = sfc->announced_window_delta;
    }
  }
  
  #define TRACE_PADDING 30
  
  static char* fmt_int64_diff_str(int64_t old, int64_t new) {
    char* str;
    if (old != new) {
      gpr_asprintf(&str, "%" PRId64 " -> %" PRId64 "", old, new);
    } else {
      gpr_asprintf(&str, "%" PRId64 "", old);
    }
    char* str_lp = gpr_leftpad(str, ' ', TRACE_PADDING);
    gpr_free(str);
    return str_lp;
  }
  
  static char* fmt_uint32_diff_str(uint32_t old, uint32_t new) {
    char* str;
    if (new > 0 && old != new) {
      gpr_asprintf(&str, "%" PRIu32 " -> %" PRIu32 "", old, new);
    } else {
      gpr_asprintf(&str, "%" PRIu32 "", old);
    }
    char* str_lp = gpr_leftpad(str, ' ', TRACE_PADDING);
    gpr_free(str);
    return str_lp;
  }
  
  static void posttrace(shadow_flow_control* shadow_fc,
                        grpc_chttp2_transport_flowctl* tfc,
                        grpc_chttp2_stream_flowctl* sfc, char* reason) {
    uint32_t acked_local_window =
        tfc->t->settings[GRPC_SENT_SETTINGS]
                        [GRPC_CHTTP2_SETTINGS_INITIAL_WINDOW_SIZE];
    uint32_t remote_window =
        tfc->t->settings[GRPC_PEER_SETTINGS]
                        [GRPC_CHTTP2_SETTINGS_INITIAL_WINDOW_SIZE];
    char* trw_str =
        fmt_int64_diff_str(shadow_fc->remote_window, tfc->remote_window);
    char* tlw_str = fmt_int64_diff_str(shadow_fc->target_window,
                                       grpc_chttp2_target_announced_window(tfc));
    char* taw_str =
        fmt_int64_diff_str(shadow_fc->announced_window, tfc->announced_window);
    char* srw_str;
    char* slw_str;
    char* saw_str;
    if (sfc != NULL) {
      srw_str = fmt_int64_diff_str(shadow_fc->remote_window_delta + remote_window,
                                   sfc->remote_window_delta + remote_window);
      slw_str =
          fmt_int64_diff_str(shadow_fc->local_window_delta + acked_local_window,
                             sfc->local_window_delta + acked_local_window);
      saw_str = fmt_int64_diff_str(
          shadow_fc->announced_window_delta + acked_local_window,
          sfc->announced_window_delta + acked_local_window);
    } else {
      srw_str = gpr_leftpad("", ' ', TRACE_PADDING);
      slw_str = gpr_leftpad("", ' ', TRACE_PADDING);
      saw_str = gpr_leftpad("", ' ', TRACE_PADDING);
    }
    gpr_log(GPR_DEBUG,
            "%p[%u][%s] | %s | trw:%s, ttw:%s, taw:%s, srw:%s, slw:%s, saw:%s",
            tfc, sfc != NULL ? sfc->s->id : 0, tfc->t->is_client ? "cli" : "svr",
            reason, trw_str, tlw_str, taw_str, srw_str, slw_str, saw_str);
    gpr_free(trw_str);
    gpr_free(tlw_str);
    gpr_free(taw_str);
    gpr_free(srw_str);
    gpr_free(slw_str);
    gpr_free(saw_str);
  }
  
  static char* urgency_to_string(grpc_chttp2_flowctl_urgency urgency) {
    switch (urgency) {
      case GRPC_CHTTP2_FLOWCTL_NO_ACTION_NEEDED:
        return "no action";
      case GRPC_CHTTP2_FLOWCTL_UPDATE_IMMEDIATELY:
        return "update immediately";
      case GRPC_CHTTP2_FLOWCTL_QUEUE_UPDATE:
        return "queue update";
      default:
        GPR_UNREACHABLE_CODE(return "unknown");
    }
    GPR_UNREACHABLE_CODE(return "unknown");
  }
  
  static void trace_action(grpc_chttp2_transport_flowctl* tfc,
                           grpc_chttp2_flowctl_action action) {
    char* iw_str = fmt_uint32_diff_str(
        tfc->t->settings[GRPC_SENT_SETTINGS]
                        [GRPC_CHTTP2_SETTINGS_INITIAL_WINDOW_SIZE],
        action.initial_window_size);
    char* mf_str = fmt_uint32_diff_str(
        tfc->t->settings[GRPC_SENT_SETTINGS][GRPC_CHTTP2_SETTINGS_MAX_FRAME_SIZE],
        action.max_frame_size);
    gpr_log(GPR_DEBUG, "t[%s],  s[%s], settings[%s] iw:%s mf:%s",
            urgency_to_string(action.send_transport_update),
            urgency_to_string(action.send_stream_update),
            urgency_to_string(action.send_setting_update), iw_str, mf_str);
    gpr_free(iw_str);
    gpr_free(mf_str);
  }
  
  #define PRETRACE(tfc, sfc)       \
    shadow_flow_control shadow_fc; \
    GRPC_FLOW_CONTROL_IF_TRACING(pretrace(&shadow_fc, tfc, sfc))
  #define POSTTRACE(tfc, sfc, reason) \
    GRPC_FLOW_CONTROL_IF_TRACING(posttrace(&shadow_fc, tfc, sfc, reason))
  #define TRACEACTION(tfc, action) \
    GRPC_FLOW_CONTROL_IF_TRACING(trace_action(tfc, action))
  #else
  #define PRETRACE(tfc, sfc)
  #define POSTTRACE(tfc, sfc, reason)
  #define TRACEACTION(tfc, action)
  #endif
  
  /* How many bytes of incoming flow control would we like to advertise */
  static uint32_t grpc_chttp2_target_announced_window(
      const grpc_chttp2_transport_flowctl* tfc) {
    return (uint32_t)GPR_MIN(
        (int64_t)((1u << 31) - 1),
        tfc->announced_stream_total_over_incoming_window +
            tfc->t->settings[GRPC_SENT_SETTINGS]
                            [GRPC_CHTTP2_SETTINGS_INITIAL_WINDOW_SIZE]);
  }
  
  // we have sent data on the wire, we must track this in our bookkeeping for the
  // remote peer's flow control.
  void grpc_chttp2_flowctl_sent_data(grpc_chttp2_transport_flowctl* tfc,
                                     grpc_chttp2_stream_flowctl* sfc,
                                     int64_t size) {
    PRETRACE(tfc, sfc);
    tfc->remote_window -= size;
    sfc->remote_window_delta -= size;
    POSTTRACE(tfc, sfc, "  data sent");
  }
  
  static void announced_window_delta_preupdate(grpc_chttp2_transport_flowctl* tfc,
                                               grpc_chttp2_stream_flowctl* sfc) {
    if (sfc->announced_window_delta > 0) {
      tfc->announced_stream_total_over_incoming_window -=
          sfc->announced_window_delta;
    } else {
      tfc->announced_stream_total_under_incoming_window +=
          -sfc->announced_window_delta;
    }
  }
  
  static void announced_window_delta_postupdate(
      grpc_chttp2_transport_flowctl* tfc, grpc_chttp2_stream_flowctl* sfc) {
    if (sfc->announced_window_delta > 0) {
      tfc->announced_stream_total_over_incoming_window +=
          sfc->announced_window_delta;
    } else {
      tfc->announced_stream_total_under_incoming_window -=
          -sfc->announced_window_delta;
    }
  }
  
  // We have received data from the wire. We must track this in our own flow
  // control bookkeeping.
  // Returns an error if the incoming frame violates our flow control.
  grpc_error* grpc_chttp2_flowctl_recv_data(grpc_chttp2_transport_flowctl* tfc,
                                            grpc_chttp2_stream_flowctl* sfc,
                                            int64_t incoming_frame_size) {
    uint32_t sent_init_window =
        tfc->t->settings[GRPC_SENT_SETTINGS]
                        [GRPC_CHTTP2_SETTINGS_INITIAL_WINDOW_SIZE];
    uint32_t acked_init_window =
        tfc->t->settings[GRPC_ACKED_SETTINGS]
                        [GRPC_CHTTP2_SETTINGS_INITIAL_WINDOW_SIZE];
    PRETRACE(tfc, sfc);
    if (incoming_frame_size > tfc->announced_window) {
      char* msg;
      gpr_asprintf(&msg,
                   "frame of size %" PRId64 " overflows local window of %" PRId64,
                   incoming_frame_size, tfc->announced_window);
      grpc_error* err = GRPC_ERROR_CREATE_FROM_COPIED_STRING(msg);
      gpr_free(msg);
      return err;
    }
  
    if (sfc != NULL) {
      int64_t acked_stream_window =
          sfc->announced_window_delta + acked_init_window;
      int64_t sent_stream_window = sfc->announced_window_delta + sent_init_window;
      if (incoming_frame_size > acked_stream_window) {
        if (incoming_frame_size <= sent_stream_window) {
          gpr_log(
              GPR_ERROR,
              "Incoming frame of size %" PRId64
              " exceeds local window size of %" PRId64
              ".\n"
              "The (un-acked, future) window size would be %" PRId64
              " which is not exceeded.\n"
              "This would usually cause a disconnection, but allowing it due to"
              "broken HTTP2 implementations in the wild.\n"
              "See (for example) https://github.com/netty/netty/issues/6520.",
              incoming_frame_size, acked_stream_window, sent_stream_window);
        } else {
          char* msg;
          gpr_asprintf(&msg, "frame of size %" PRId64
                             " overflows local window of %" PRId64,
                       incoming_frame_size, acked_stream_window);
          grpc_error* err = GRPC_ERROR_CREATE_FROM_COPIED_STRING(msg);
          gpr_free(msg);
          return err;
        }
      }
  
      announced_window_delta_preupdate(tfc, sfc);
      sfc->announced_window_delta -= incoming_frame_size;
      announced_window_delta_postupdate(tfc, sfc);
      sfc->local_window_delta -= incoming_frame_size;
    }
  
    tfc->announced_window -= incoming_frame_size;
  
    POSTTRACE(tfc, sfc, "  data recv");
    return GRPC_ERROR_NONE;
  }
  
  // Returns a non zero announce integer if we should send a transport window
  // update
  uint32_t grpc_chttp2_flowctl_maybe_send_transport_update(
      grpc_chttp2_transport_flowctl* tfc) {
    PRETRACE(tfc, NULL);
    uint32_t target_announced_window = grpc_chttp2_target_announced_window(tfc);
    uint32_t threshold_to_send_transport_window_update =
        tfc->t->outbuf.count > 0 ? 3 * target_announced_window / 4
                                 : target_announced_window / 2;
    if (tfc->announced_window <= threshold_to_send_transport_window_update &&
        tfc->announced_window != target_announced_window) {
      uint32_t announce = (uint32_t)GPR_CLAMP(
          target_announced_window - tfc->announced_window, 0, UINT32_MAX);
      tfc->announced_window += announce;
      POSTTRACE(tfc, NULL, "t updt sent");
      return announce;
    }
    GRPC_FLOW_CONTROL_IF_TRACING(
        gpr_log(GPR_DEBUG, "%p[0][%s] will not send transport update", tfc,
                tfc->t->is_client ? "cli" : "svr"));
    return 0;
  }
  
  // Returns a non zero announce integer if we should send a stream window update
  uint32_t grpc_chttp2_flowctl_maybe_send_stream_update(
      grpc_chttp2_transport_flowctl* tfc, grpc_chttp2_stream_flowctl* sfc) {
    PRETRACE(tfc, sfc);
    if (sfc->local_window_delta > sfc->announced_window_delta) {
      uint32_t announce = (uint32_t)GPR_CLAMP(
          sfc->local_window_delta - sfc->announced_window_delta, 0, UINT32_MAX);
      announced_window_delta_preupdate(tfc, sfc);
      sfc->announced_window_delta += announce;
      announced_window_delta_postupdate(tfc, sfc);
      POSTTRACE(tfc, sfc, "s updt sent");
      return announce;
    }
    GRPC_FLOW_CONTROL_IF_TRACING(
        gpr_log(GPR_DEBUG, "%p[%u][%s] will not send stream update", tfc,
                sfc->s->id, tfc->t->is_client ? "cli" : "svr"));
    return 0;
  }
  
  // we have received a WINDOW_UPDATE frame for a transport
  void grpc_chttp2_flowctl_recv_transport_update(
      grpc_chttp2_transport_flowctl* tfc, uint32_t size) {
    PRETRACE(tfc, NULL);
    tfc->remote_window += size;
    POSTTRACE(tfc, NULL, "t updt recv");
  }
  
  // we have received a WINDOW_UPDATE frame for a stream
  void grpc_chttp2_flowctl_recv_stream_update(grpc_chttp2_transport_flowctl* tfc,
                                              grpc_chttp2_stream_flowctl* sfc,
                                              uint32_t size) {
    PRETRACE(tfc, sfc);
    sfc->remote_window_delta += size;
    POSTTRACE(tfc, sfc, "s updt recv");
  }
  
  void grpc_chttp2_flowctl_incoming_bs_update(grpc_chttp2_transport_flowctl* tfc,
                                              grpc_chttp2_stream_flowctl* sfc,
                                              size_t max_size_hint,
                                              size_t have_already) {
    PRETRACE(tfc, sfc);
    uint32_t max_recv_bytes;
    uint32_t sent_init_window =
        tfc->t->settings[GRPC_SENT_SETTINGS]
                        [GRPC_CHTTP2_SETTINGS_INITIAL_WINDOW_SIZE];
  
    /* clamp max recv hint to an allowable size */
    if (max_size_hint >= UINT32_MAX - sent_init_window) {
      max_recv_bytes = UINT32_MAX - sent_init_window;
    } else {
      max_recv_bytes = (uint32_t)max_size_hint;
    }
  
    /* account for bytes already received but unknown to higher layers */
    if (max_recv_bytes >= have_already) {
      max_recv_bytes -= (uint32_t)have_already;
    } else {
      max_recv_bytes = 0;
    }
  
    /* add some small lookahead to keep pipelines flowing */
    GPR_ASSERT(max_recv_bytes <= UINT32_MAX - sent_init_window);
    if (sfc->local_window_delta < max_recv_bytes) {
      uint32_t add_max_recv_bytes =
          (uint32_t)(max_recv_bytes - sfc->local_window_delta);
      sfc->local_window_delta += add_max_recv_bytes;
    }
    POSTTRACE(tfc, sfc, "app st recv");
  }
  
  void grpc_chttp2_flowctl_destroy_stream(grpc_chttp2_transport_flowctl* tfc,
                                          grpc_chttp2_stream_flowctl* sfc) {
    announced_window_delta_preupdate(tfc, sfc);
  }
  
  // Returns an urgency with which to make an update
  static grpc_chttp2_flowctl_urgency delta_is_significant(
      const grpc_chttp2_transport_flowctl* tfc, int32_t value,
      grpc_chttp2_setting_id setting_id) {
    int64_t delta = (int64_t)value -
                    (int64_t)tfc->t->settings[GRPC_LOCAL_SETTINGS][setting_id];
    // TODO(ncteisen): tune this
    if (delta != 0 && (delta <= -value / 5 || delta >= value / 5)) {
      return GRPC_CHTTP2_FLOWCTL_QUEUE_UPDATE;
    } else {
      return GRPC_CHTTP2_FLOWCTL_NO_ACTION_NEEDED;
    }
  }
  
  // Takes in a target and uses the pid controller to return a stabilized
  // guess at the new bdp.
  static double get_pid_controller_guess(grpc_chttp2_transport_flowctl* tfc,
                                         double target) {
    double bdp_error = target - grpc_pid_controller_last(&tfc->pid_controller);
    gpr_timespec now = gpr_now(GPR_CLOCK_MONOTONIC);
    gpr_timespec dt_timespec = gpr_time_sub(now, tfc->last_pid_update);
    double dt = (double)dt_timespec.tv_sec + dt_timespec.tv_nsec * 1e-9;
    if (dt > 0.1) {
      dt = 0.1;
    }
    double log2_bdp_guess =
        grpc_pid_controller_update(&tfc->pid_controller, bdp_error, dt);
    tfc->last_pid_update = now;
    return pow(2, log2_bdp_guess);
  }
  
  // Take in a target and modifies it based on the memory pressure of the system
  static double get_target_under_memory_pressure(
      grpc_chttp2_transport_flowctl* tfc, double target) {
    // do not increase window under heavy memory pressure.
    double memory_pressure = grpc_resource_quota_get_memory_pressure(
        grpc_resource_user_quota(grpc_endpoint_get_resource_user(tfc->t->ep)));
    if (memory_pressure > 0.8) {
      target *= 1 - GPR_MIN(1, (memory_pressure - 0.8) / 0.1);
    }
    return target;
  }
  
  grpc_chttp2_flowctl_action grpc_chttp2_flowctl_get_action(
      grpc_chttp2_transport_flowctl* tfc, grpc_chttp2_stream_flowctl* sfc) {
    grpc_chttp2_flowctl_action action;
    memset(&action, 0, sizeof(action));
    uint32_t target_announced_window = grpc_chttp2_target_announced_window(tfc);
    if (tfc->announced_window < target_announced_window / 2) {
      action.send_transport_update = GRPC_CHTTP2_FLOWCTL_UPDATE_IMMEDIATELY;
    }
    // TODO(ncteisen): tune this
    if (sfc != NULL && !sfc->s->read_closed) {
      uint32_t sent_init_window =
          tfc->t->settings[GRPC_SENT_SETTINGS]
                          [GRPC_CHTTP2_SETTINGS_INITIAL_WINDOW_SIZE];
      if ((int64_t)sfc->local_window_delta >
              (int64_t)sfc->announced_window_delta &&
          (int64_t)sfc->announced_window_delta + sent_init_window <=
              sent_init_window / 2) {
        action.send_stream_update = GRPC_CHTTP2_FLOWCTL_UPDATE_IMMEDIATELY;
      } else if (sfc->local_window_delta > sfc->announced_window_delta) {
        action.send_stream_update = GRPC_CHTTP2_FLOWCTL_QUEUE_UPDATE;
      }
    }
    TRACEACTION(tfc, action);
    return action;
  }
  
  grpc_chttp2_flowctl_action grpc_chttp2_flowctl_get_bdp_action(
      grpc_chttp2_transport_flowctl* tfc) {
    grpc_chttp2_flowctl_action action;
    memset(&action, 0, sizeof(action));
    if (tfc->enable_bdp_probe) {
      action.need_ping = grpc_bdp_estimator_need_ping(&tfc->bdp_estimator);
  
      // get bdp estimate and update initial_window accordingly.
      int64_t estimate = -1;
      int32_t bdp = -1;
      if (grpc_bdp_estimator_get_estimate(&tfc->bdp_estimator, &estimate)) {
        double target = 1 + log2((double)estimate);
  
        // target might change based on how much memory pressure we are under
        // TODO(ncteisen): experiment with setting target to be huge under low
        // memory pressure.
        target = get_target_under_memory_pressure(tfc, target);
  
        // run our target through the pid controller to stabilize change.
        // TODO(ncteisen): experiment with other controllers here.
        double bdp_guess = get_pid_controller_guess(tfc, target);
  
        // Though initial window 'could' drop to 0, we keep the floor at 128
        bdp = GPR_MAX((int32_t)bdp_guess, 128);
  
        grpc_chttp2_flowctl_urgency init_window_update_urgency =
            delta_is_significant(tfc, bdp,
                                 GRPC_CHTTP2_SETTINGS_INITIAL_WINDOW_SIZE);
        if (init_window_update_urgency != GRPC_CHTTP2_FLOWCTL_NO_ACTION_NEEDED) {
          action.send_setting_update = init_window_update_urgency;
          action.initial_window_size = (uint32_t)bdp;
        }
      }
  
      // get bandwidth estimate and update max_frame accordingly.
      double bw_dbl = -1;
      if (grpc_bdp_estimator_get_bw(&tfc->bdp_estimator, &bw_dbl)) {
        // we target the max of BDP or bandwidth in microseconds.
        int32_t frame_size = (int32_t)GPR_CLAMP(
            GPR_MAX((int32_t)GPR_CLAMP(bw_dbl, 0, INT_MAX) / 1000, bdp), 16384,
            16777215);
        grpc_chttp2_flowctl_urgency frame_size_urgency = delta_is_significant(
            tfc, frame_size, GRPC_CHTTP2_SETTINGS_MAX_FRAME_SIZE);
        if (frame_size_urgency != GRPC_CHTTP2_FLOWCTL_NO_ACTION_NEEDED) {
          if (frame_size_urgency > action.send_setting_update) {
            action.send_setting_update = frame_size_urgency;
          }
          action.max_frame_size = (uint32_t)frame_size;
        }
      }
    }
  
    TRACEACTION(tfc, action);
    return action;
  }
  