path: root/src/core/lib/iomgr/tcp_posix.cc

/*
 *
 * Copyright 2015 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/lib/iomgr/port.h"

#ifdef GRPC_POSIX_SOCKET

#include "src/core/lib/iomgr/network_status_tracker.h"
#include "src/core/lib/iomgr/tcp_posix.h"

#include <errno.h>
#include <stdbool.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <unistd.h>

#include <grpc/slice.h>
#include <grpc/support/alloc.h>
#include <grpc/support/log.h>
#include <grpc/support/string_util.h>
#include <grpc/support/sync.h>
#include <grpc/support/time.h>
#include <grpc/support/useful.h>

#include "src/core/lib/channel/channel_args.h"
#include "src/core/lib/debug/stats.h"
#include "src/core/lib/debug/trace.h"
#include "src/core/lib/iomgr/ev_posix.h"
#include "src/core/lib/iomgr/executor.h"
#include "src/core/lib/profiling/timers.h"
#include "src/core/lib/slice/slice_internal.h"
#include "src/core/lib/slice/slice_string_helpers.h"
#include "src/core/lib/support/string.h"

#ifdef GRPC_HAVE_MSG_NOSIGNAL
#define SENDMSG_FLAGS MSG_NOSIGNAL
#else
#define SENDMSG_FLAGS 0
#endif

#ifdef GRPC_MSG_IOVLEN_TYPE
typedef GRPC_MSG_IOVLEN_TYPE msg_iovlen_type;
#else
typedef size_t msg_iovlen_type;
#endif

grpc_tracer_flag grpc_tcp_trace = GRPC_TRACER_INITIALIZER(false, "tcp");

typedef struct {
  grpc_endpoint base;
  grpc_fd *em_fd;
  int fd;
  bool finished_edge;
  double target_length;
  double bytes_read_this_round;
  gpr_refcount refcount;
  gpr_atm shutdown_count;

  int min_read_chunk_size;
  int max_read_chunk_size;

  /* garbage after the last read */
  grpc_slice_buffer last_read_buffer;

  grpc_slice_buffer *incoming_buffer;
  grpc_slice_buffer *outgoing_buffer;
  /** slice within outgoing_buffer to write next */
  size_t outgoing_slice_idx;
  /** byte within outgoing_buffer->slices[outgoing_slice_idx] to write next */
  size_t outgoing_byte_idx;

  grpc_closure *read_cb;
  grpc_closure *write_cb;
  grpc_closure *release_fd_cb;
  int *release_fd;

  grpc_closure read_done_closure;
  grpc_closure write_done_closure;

  char *peer_string;

  grpc_resource_user *resource_user;
  grpc_resource_user_slice_allocator slice_allocator;
} grpc_tcp;

typedef struct backup_poller {
  gpr_mu *pollset_mu;
  grpc_closure run_poller;
} backup_poller;

#define BACKUP_POLLER_POLLSET(b) ((grpc_pollset *)((b) + 1))

static gpr_atm g_uncovered_notifications_pending;
static gpr_atm g_backup_poller; /* backup_poller* */

static void tcp_handle_read(grpc_exec_ctx *exec_ctx, void *arg /* grpc_tcp */,
                            grpc_error *error);
static void tcp_handle_write(grpc_exec_ctx *exec_ctx, void *arg /* grpc_tcp */,
                             grpc_error *error);
static void tcp_drop_uncovered_then_handle_write(grpc_exec_ctx *exec_ctx,
                                                 void *arg /* grpc_tcp */,
                                                 grpc_error *error);

static void done_poller(grpc_exec_ctx *exec_ctx, void *bp,
                        grpc_error *error_ignored) {
  backup_poller *p = (backup_poller *)bp;
  if (GRPC_TRACER_ON(grpc_tcp_trace)) {
    gpr_log(GPR_DEBUG, "BACKUP_POLLER:%p destroy", p);
  }
  grpc_pollset_destroy(exec_ctx, BACKUP_POLLER_POLLSET(p));
  gpr_free(p);
}

static void run_poller(grpc_exec_ctx *exec_ctx, void *bp,
                       grpc_error *error_ignored) {
  backup_poller *p = (backup_poller *)bp;
  if (GRPC_TRACER_ON(grpc_tcp_trace)) {
    gpr_log(GPR_DEBUG, "BACKUP_POLLER:%p run", p);
  }
  gpr_mu_lock(p->pollset_mu);
  grpc_millis deadline = grpc_exec_ctx_now(exec_ctx) + 13 * GPR_MS_PER_SEC;
  GRPC_STATS_INC_TCP_BACKUP_POLLER_POLLS(exec_ctx);
  GRPC_LOG_IF_ERROR(
      "backup_poller:pollset_work",
      grpc_pollset_work(exec_ctx, BACKUP_POLLER_POLLSET(p), NULL, deadline));
  gpr_mu_unlock(p->pollset_mu);
  /* last "uncovered" notification is the ref that keeps us polling, if we get
   * there try a cas to release it */
  if (gpr_atm_no_barrier_load(&g_uncovered_notifications_pending) == 1 &&
      gpr_atm_full_cas(&g_uncovered_notifications_pending, 1, 0)) {
    gpr_mu_lock(p->pollset_mu);
    bool cas_ok = gpr_atm_full_cas(&g_backup_poller, (gpr_atm)p, 0);
    if (GRPC_TRACER_ON(grpc_tcp_trace)) {
      gpr_log(GPR_DEBUG, "BACKUP_POLLER:%p done cas_ok=%d", p, cas_ok);
    }
    gpr_mu_unlock(p->pollset_mu);
    if (GRPC_TRACER_ON(grpc_tcp_trace)) {
      gpr_log(GPR_DEBUG, "BACKUP_POLLER:%p shutdown", p);
    }
    grpc_pollset_shutdown(exec_ctx, BACKUP_POLLER_POLLSET(p),
                          GRPC_CLOSURE_INIT(&p->run_poller, done_poller, p,
                                            grpc_schedule_on_exec_ctx));
  } else {
    if (GRPC_TRACER_ON(grpc_tcp_trace)) {
      gpr_log(GPR_DEBUG, "BACKUP_POLLER:%p reschedule", p);
    }
    GRPC_CLOSURE_SCHED(exec_ctx, &p->run_poller, GRPC_ERROR_NONE);
  }
}

static void drop_uncovered(grpc_exec_ctx *exec_ctx, grpc_tcp *tcp) {
  backup_poller *p = (backup_poller *)gpr_atm_acq_load(&g_backup_poller);
  gpr_atm old_count =
      gpr_atm_no_barrier_fetch_add(&g_uncovered_notifications_pending, -1);
  if (GRPC_TRACER_ON(grpc_tcp_trace)) {
    gpr_log(GPR_DEBUG, "BACKUP_POLLER:%p uncover cnt %d->%d", p, (int)old_count,
            (int)old_count - 1);
  }
  GPR_ASSERT(old_count != 1);
}

static void cover_self(grpc_exec_ctx *exec_ctx, grpc_tcp *tcp) {
  backup_poller *p;
  gpr_atm old_count =
      gpr_atm_no_barrier_fetch_add(&g_uncovered_notifications_pending, 2);
  if (GRPC_TRACER_ON(grpc_tcp_trace)) {
    gpr_log(GPR_DEBUG, "BACKUP_POLLER: cover cnt %d->%d", (int)old_count,
            2 + (int)old_count);
  }
  if (old_count == 0) {
    GRPC_STATS_INC_TCP_BACKUP_POLLERS_CREATED(exec_ctx);
    p = (backup_poller *)gpr_zalloc(sizeof(*p) + grpc_pollset_size());
    if (GRPC_TRACER_ON(grpc_tcp_trace)) {
      gpr_log(GPR_DEBUG, "BACKUP_POLLER:%p create", p);
    }
    grpc_pollset_init(BACKUP_POLLER_POLLSET(p), &p->pollset_mu);
    gpr_atm_rel_store(&g_backup_poller, (gpr_atm)p);
    GRPC_CLOSURE_SCHED(
        exec_ctx,
        GRPC_CLOSURE_INIT(&p->run_poller, run_poller, p,
                          grpc_executor_scheduler(GRPC_EXECUTOR_LONG)),
        GRPC_ERROR_NONE);
  } else {
    while ((p = (backup_poller *)gpr_atm_acq_load(&g_backup_poller)) == NULL) {
      // spin waiting for backup poller
    }
  }
  if (GRPC_TRACER_ON(grpc_tcp_trace)) {
    gpr_log(GPR_DEBUG, "BACKUP_POLLER:%p add %p", p, tcp);
  }
  grpc_pollset_add_fd(exec_ctx, BACKUP_POLLER_POLLSET(p), tcp->em_fd);
  if (old_count != 0) {
    drop_uncovered(exec_ctx, tcp);
  }
}

static void notify_on_read(grpc_exec_ctx *exec_ctx, grpc_tcp *tcp) {
  if (GRPC_TRACER_ON(grpc_tcp_trace)) {
    gpr_log(GPR_DEBUG, "TCP:%p notify_on_read", tcp);
  }
  GRPC_CLOSURE_INIT(&tcp->read_done_closure, tcp_handle_read, tcp,
                    grpc_schedule_on_exec_ctx);
  grpc_fd_notify_on_read(exec_ctx, tcp->em_fd, &tcp->read_done_closure);
}

static void notify_on_write(grpc_exec_ctx *exec_ctx, grpc_tcp *tcp) {
  if (GRPC_TRACER_ON(grpc_tcp_trace)) {
    gpr_log(GPR_DEBUG, "TCP:%p notify_on_write", tcp);
  }
  cover_self(exec_ctx, tcp);
  GRPC_CLOSURE_INIT(&tcp->write_done_closure,
                    tcp_drop_uncovered_then_handle_write, tcp,
                    grpc_schedule_on_exec_ctx);
  grpc_fd_notify_on_write(exec_ctx, tcp->em_fd, &tcp->write_done_closure);
}

static void tcp_drop_uncovered_then_handle_write(grpc_exec_ctx *exec_ctx,
                                                 void *arg, grpc_error *error) {
  if (GRPC_TRACER_ON(grpc_tcp_trace)) {
    gpr_log(GPR_DEBUG, "TCP:%p got_write: %s", arg, grpc_error_string(error));
  }
  drop_uncovered(exec_ctx, (grpc_tcp *)arg);
  tcp_handle_write(exec_ctx, arg, error);
}

static void add_to_estimate(grpc_tcp *tcp, size_t bytes) {
  tcp->bytes_read_this_round += (double)bytes;
}

static void finish_estimate(grpc_tcp *tcp) {
  /* If we read >80% of the target buffer in one read loop, increase the size
     of the target buffer to either the amount read, or twice its previous
     value */
  if (tcp->bytes_read_this_round > tcp->target_length * 0.8) {
    tcp->target_length =
        GPR_MAX(2 * tcp->target_length, tcp->bytes_read_this_round);
  } else {
    tcp->target_length =
        0.99 * tcp->target_length + 0.01 * tcp->bytes_read_this_round;
  }
  tcp->bytes_read_this_round = 0;
}

static size_t get_target_read_size(grpc_tcp *tcp) {
  grpc_resource_quota *rq = grpc_resource_user_quota(tcp->resource_user);
  double pressure = grpc_resource_quota_get_memory_pressure(rq);
  double target =
      tcp->target_length * (pressure > 0.8 ? (1.0 - pressure) / 0.2 : 1.0);
  size_t sz = (((size_t)GPR_CLAMP(target, tcp->min_read_chunk_size,
                                  tcp->max_read_chunk_size)) +
               255) &
              ~(size_t)255;
  /* don't use more than 1/16th of the overall resource quota for a single read
   * alloc */
  size_t rqmax = grpc_resource_quota_peek_size(rq);
  if (sz > rqmax / 16 && rqmax > 1024) {
    sz = rqmax / 16;
  }
  return sz;
}

static grpc_error *tcp_annotate_error(grpc_error *src_error, grpc_tcp *tcp) {
  return grpc_error_set_str(
      grpc_error_set_int(src_error, GRPC_ERROR_INT_FD, tcp->fd),
      GRPC_ERROR_STR_TARGET_ADDRESS,
      grpc_slice_from_copied_string(tcp->peer_string));
}

static void tcp_handle_read(grpc_exec_ctx *exec_ctx, void *arg /* grpc_tcp */,
                            grpc_error *error);
static void tcp_handle_write(grpc_exec_ctx *exec_ctx, void *arg /* grpc_tcp */,
                             grpc_error *error);

static void tcp_shutdown(grpc_exec_ctx *exec_ctx, grpc_endpoint *ep,
                         grpc_error *why) {
  grpc_tcp *tcp = (grpc_tcp *)ep;
  grpc_fd_shutdown(exec_ctx, tcp->em_fd, why);
  grpc_resource_user_shutdown(exec_ctx, tcp->resource_user);
}

static void tcp_free(grpc_exec_ctx *exec_ctx, grpc_tcp *tcp) {
  grpc_fd_orphan(exec_ctx, tcp->em_fd, tcp->release_fd_cb, tcp->release_fd,
                 false /* already_closed */, "tcp_unref_orphan");
  grpc_slice_buffer_destroy_internal(exec_ctx, &tcp->last_read_buffer);
  grpc_resource_user_unref(exec_ctx, tcp->resource_user);
  gpr_free(tcp->peer_string);
  gpr_free(tcp);
}

#ifndef NDEBUG
#define TCP_UNREF(cl, tcp, reason) \
  tcp_unref((cl), (tcp), (reason), __FILE__, __LINE__)
#define TCP_REF(tcp, reason) tcp_ref((tcp), (reason), __FILE__, __LINE__)
static void tcp_unref(grpc_exec_ctx *exec_ctx, grpc_tcp *tcp,
                      const char *reason, const char *file, int line) {
  if (GRPC_TRACER_ON(grpc_tcp_trace)) {
    gpr_atm val = gpr_atm_no_barrier_load(&tcp->refcount.count);
    gpr_log(file, line, GPR_LOG_SEVERITY_DEBUG,
            "TCP unref %p : %s %" PRIdPTR " -> %" PRIdPTR, tcp, reason, val,
            val - 1);
  }
  if (gpr_unref(&tcp->refcount)) {
    tcp_free(exec_ctx, tcp);
  }
}

static void tcp_ref(grpc_tcp *tcp, const char *reason, const char *file,
                    int line) {
  if (GRPC_TRACER_ON(grpc_tcp_trace)) {
    gpr_atm val = gpr_atm_no_barrier_load(&tcp->refcount.count);
    gpr_log(file, line, GPR_LOG_SEVERITY_DEBUG,
            "TCP   ref %p : %s %" PRIdPTR " -> %" PRIdPTR, tcp, reason, val,
            val + 1);
  }
  gpr_ref(&tcp->refcount);
}
#else
#define TCP_UNREF(cl, tcp, reason) tcp_unref((cl), (tcp))
#define TCP_REF(tcp, reason) tcp_ref((tcp))
static void tcp_unref(grpc_exec_ctx *exec_ctx, grpc_tcp *tcp) {
  if (gpr_unref(&tcp->refcount)) {
    tcp_free(exec_ctx, tcp);
  }
}

static void tcp_ref(grpc_tcp *tcp) { gpr_ref(&tcp->refcount); }
#endif

static void tcp_destroy(grpc_exec_ctx *exec_ctx, grpc_endpoint *ep) {
  grpc_network_status_unregister_endpoint(ep);
  grpc_tcp *tcp = (grpc_tcp *)ep;
  grpc_slice_buffer_reset_and_unref_internal(exec_ctx, &tcp->last_read_buffer);
  TCP_UNREF(exec_ctx, tcp, "destroy");
}

static void call_read_cb(grpc_exec_ctx *exec_ctx, grpc_tcp *tcp,
                         grpc_error *error) {
  grpc_closure *cb = tcp->read_cb;

  if (GRPC_TRACER_ON(grpc_tcp_trace)) {
    gpr_log(GPR_DEBUG, "TCP:%p call_cb %p %p:%p", tcp, cb, cb->cb, cb->cb_arg);
    size_t i;
    const char *str = grpc_error_string(error);
    gpr_log(GPR_DEBUG, "read: error=%s", str);

    for (i = 0; i < tcp->incoming_buffer->count; i++) {
      char *dump = grpc_dump_slice(tcp->incoming_buffer->slices[i],
                                   GPR_DUMP_HEX | GPR_DUMP_ASCII);
      gpr_log(GPR_DEBUG, "READ %p (peer=%s): %s", tcp, tcp->peer_string, dump);
      gpr_free(dump);
    }
  }

  tcp->read_cb = NULL;
  tcp->incoming_buffer = NULL;
  GRPC_CLOSURE_RUN(exec_ctx, cb, error);
}

#define MAX_READ_IOVEC 4
static void tcp_do_read(grpc_exec_ctx *exec_ctx, grpc_tcp *tcp) {
  struct msghdr msg;
  struct iovec iov[MAX_READ_IOVEC];
  ssize_t read_bytes;
  size_t i;

  GPR_ASSERT(!tcp->finished_edge);
  GPR_ASSERT(tcp->incoming_buffer->count <= MAX_READ_IOVEC);
  GPR_TIMER_BEGIN("tcp_continue_read", 0);

  for (i = 0; i < tcp->incoming_buffer->count; i++) {
    iov[i].iov_base = GRPC_SLICE_START_PTR(tcp->incoming_buffer->slices[i]);
    iov[i].iov_len = GRPC_SLICE_LENGTH(tcp->incoming_buffer->slices[i]);
  }

  msg.msg_name = NULL;
  msg.msg_namelen = 0;
  msg.msg_iov = iov;
  msg.msg_iovlen = (msg_iovlen_type)tcp->incoming_buffer->count;
  msg.msg_control = NULL;
  msg.msg_controllen = 0;
  msg.msg_flags = 0;

  GRPC_STATS_INC_TCP_READ_OFFER(exec_ctx, tcp->incoming_buffer->length);
  GRPC_STATS_INC_TCP_READ_OFFER_IOV_SIZE(exec_ctx, tcp->incoming_buffer->count);

  GPR_TIMER_BEGIN("recvmsg", 0);
  do {
    GRPC_STATS_INC_SYSCALL_READ(exec_ctx);
    read_bytes = recvmsg(tcp->fd, &msg, 0);
  } while (read_bytes < 0 && errno == EINTR);
  GPR_TIMER_END("recvmsg", read_bytes >= 0);

  if (read_bytes < 0) {
    /* NB: After calling call_read_cb a parallel call of the read handler may
     * be running. */
    if (errno == EAGAIN) {
      finish_estimate(tcp);
      /* We've consumed the edge, request a new one */
      notify_on_read(exec_ctx, tcp);
    } else {
      grpc_slice_buffer_reset_and_unref_internal(exec_ctx,
                                                 tcp->incoming_buffer);
      call_read_cb(exec_ctx, tcp,
                   tcp_annotate_error(GRPC_OS_ERROR(errno, "recvmsg"), tcp));
      TCP_UNREF(exec_ctx, tcp, "read");
    }
  } else if (read_bytes == 0) {
    /* 0 read size ==> end of stream */
    grpc_slice_buffer_reset_and_unref_internal(exec_ctx, tcp->incoming_buffer);
    call_read_cb(
        exec_ctx, tcp,
        tcp_annotate_error(
            GRPC_ERROR_CREATE_FROM_STATIC_STRING("Socket closed"), tcp));
    TCP_UNREF(exec_ctx, tcp, "read");
  } else {
    GRPC_STATS_INC_TCP_READ_SIZE(exec_ctx, read_bytes);
    add_to_estimate(tcp, (size_t)read_bytes);
    GPR_ASSERT((size_t)read_bytes <= tcp->incoming_buffer->length);
    if ((size_t)read_bytes < tcp->incoming_buffer->length) {
      grpc_slice_buffer_trim_end(
          tcp->incoming_buffer,
          tcp->incoming_buffer->length - (size_t)read_bytes,
          &tcp->last_read_buffer);
    }
    GPR_ASSERT((size_t)read_bytes == tcp->incoming_buffer->length);
    call_read_cb(exec_ctx, tcp, GRPC_ERROR_NONE);
    TCP_UNREF(exec_ctx, tcp, "read");
  }

  GPR_TIMER_END("tcp_continue_read", 0);
}

static void tcp_read_allocation_done(grpc_exec_ctx *exec_ctx, void *tcpp,
                                     grpc_error *error) {
  grpc_tcp *tcp = (grpc_tcp *)tcpp;
  if (GRPC_TRACER_ON(grpc_tcp_trace)) {
    gpr_log(GPR_DEBUG, "TCP:%p read_allocation_done: %s", tcp,
            grpc_error_string(error));
  }
  if (error != GRPC_ERROR_NONE) {
    grpc_slice_buffer_reset_and_unref_internal(exec_ctx, tcp->incoming_buffer);
    grpc_slice_buffer_reset_and_unref_internal(exec_ctx,
                                               &tcp->last_read_buffer);
    call_read_cb(exec_ctx, tcp, GRPC_ERROR_REF(error));
    TCP_UNREF(exec_ctx, tcp, "read");
  } else {
    tcp_do_read(exec_ctx, tcp);
  }
}

static void tcp_continue_read(grpc_exec_ctx *exec_ctx, grpc_tcp *tcp) {
  size_t target_read_size = get_target_read_size(tcp);
  if (tcp->incoming_buffer->length < target_read_size &&
      tcp->incoming_buffer->count < MAX_READ_IOVEC) {
    if (GRPC_TRACER_ON(grpc_tcp_trace)) {
      gpr_log(GPR_DEBUG, "TCP:%p alloc_slices", tcp);
    }
    grpc_resource_user_alloc_slices(exec_ctx, &tcp->slice_allocator,
                                    target_read_size, 1, tcp->incoming_buffer);
  } else {
    if (GRPC_TRACER_ON(grpc_tcp_trace)) {
      gpr_log(GPR_DEBUG, "TCP:%p do_read", tcp);
    }
    tcp_do_read(exec_ctx, tcp);
  }
}

static void tcp_handle_read(grpc_exec_ctx *exec_ctx, void *arg /* grpc_tcp */,
                            grpc_error *error) {
  grpc_tcp *tcp = (grpc_tcp *)arg;
  GPR_ASSERT(!tcp->finished_edge);
  if (GRPC_TRACER_ON(grpc_tcp_trace)) {
    gpr_log(GPR_DEBUG, "TCP:%p got_read: %s", tcp, grpc_error_string(error));
  }

  if (error != GRPC_ERROR_NONE) {
    grpc_slice_buffer_reset_and_unref_internal(exec_ctx, tcp->incoming_buffer);
    grpc_slice_buffer_reset_and_unref_internal(exec_ctx,
                                               &tcp->last_read_buffer);
    call_read_cb(exec_ctx, tcp, GRPC_ERROR_REF(error));
    TCP_UNREF(exec_ctx, tcp, "read");
  } else {
    tcp_continue_read(exec_ctx, tcp);
  }
}

static void tcp_read(grpc_exec_ctx *exec_ctx, grpc_endpoint *ep,
                     grpc_slice_buffer *incoming_buffer, grpc_closure *cb) {
  grpc_tcp *tcp = (grpc_tcp *)ep;
  GPR_ASSERT(tcp->read_cb == NULL);
  tcp->read_cb = cb;
  tcp->incoming_buffer = incoming_buffer;
  grpc_slice_buffer_reset_and_unref_internal(exec_ctx, incoming_buffer);
  grpc_slice_buffer_swap(incoming_buffer, &tcp->last_read_buffer);
  TCP_REF(tcp, "read");
  if (tcp->finished_edge) {
    tcp->finished_edge = false;
    notify_on_read(exec_ctx, tcp);
  } else {
    GRPC_CLOSURE_SCHED(exec_ctx, &tcp->read_done_closure, GRPC_ERROR_NONE);
  }
}

/* returns true if done, false if pending; if returning true, *error is set */
#define MAX_WRITE_IOVEC 1000
static bool tcp_flush(grpc_exec_ctx *exec_ctx, grpc_tcp *tcp,
                      grpc_error **error) {
  struct msghdr msg;
  struct iovec iov[MAX_WRITE_IOVEC];
  msg_iovlen_type iov_size;
  ssize_t sent_length;
  size_t sending_length;
  size_t trailing;
  size_t unwind_slice_idx;
  size_t unwind_byte_idx;

  for (;;) {
    sending_length = 0;
    unwind_slice_idx = tcp->outgoing_slice_idx;
    unwind_byte_idx = tcp->outgoing_byte_idx;
    for (iov_size = 0; tcp->outgoing_slice_idx != tcp->outgoing_buffer->count &&
                       iov_size != MAX_WRITE_IOVEC;
         iov_size++) {
      iov[iov_size].iov_base =
          GRPC_SLICE_START_PTR(
              tcp->outgoing_buffer->slices[tcp->outgoing_slice_idx]) +
          tcp->outgoing_byte_idx;
      iov[iov_size].iov_len =
          GRPC_SLICE_LENGTH(
              tcp->outgoing_buffer->slices[tcp->outgoing_slice_idx]) -
          tcp->outgoing_byte_idx;
      sending_length += iov[iov_size].iov_len;
      tcp->outgoing_slice_idx++;
      tcp->outgoing_byte_idx = 0;
    }
    GPR_ASSERT(iov_size > 0);

    msg.msg_name = NULL;
    msg.msg_namelen = 0;
    msg.msg_iov = iov;
    msg.msg_iovlen = iov_size;
    msg.msg_control = NULL;
    msg.msg_controllen = 0;
    msg.msg_flags = 0;

    GRPC_STATS_INC_TCP_WRITE_SIZE(exec_ctx, sending_length);
    GRPC_STATS_INC_TCP_WRITE_IOV_SIZE(exec_ctx, iov_size);

    GPR_TIMER_BEGIN("sendmsg", 1);
    do {
      /* TODO(klempner): Cork if this is a partial write */
      GRPC_STATS_INC_SYSCALL_WRITE(exec_ctx);
      sent_length = sendmsg(tcp->fd, &msg, SENDMSG_FLAGS);
    } while (sent_length < 0 && errno == EINTR);
    GPR_TIMER_END("sendmsg", 0);

    if (sent_length < 0) {
      if (errno == EAGAIN) {
        tcp->outgoing_slice_idx = unwind_slice_idx;
        tcp->outgoing_byte_idx = unwind_byte_idx;
        return false;
      } else if (errno == EPIPE) {
        *error = grpc_error_set_int(GRPC_OS_ERROR(errno, "sendmsg"),
                                    GRPC_ERROR_INT_GRPC_STATUS,
                                    GRPC_STATUS_UNAVAILABLE);
        return true;
      } else {
        *error = tcp_annotate_error(GRPC_OS_ERROR(errno, "sendmsg"), tcp);
        return true;
      }
    }

    GPR_ASSERT(tcp->outgoing_byte_idx == 0);
    trailing = sending_length - (size_t)sent_length;
    while (trailing > 0) {
      size_t slice_length;

      tcp->outgoing_slice_idx--;
      slice_length = GRPC_SLICE_LENGTH(
          tcp->outgoing_buffer->slices[tcp->outgoing_slice_idx]);
      if (slice_length > trailing) {
        tcp->outgoing_byte_idx = slice_length - trailing;
        break;
      } else {
        trailing -= slice_length;
      }
    }

    if (tcp->outgoing_slice_idx == tcp->outgoing_buffer->count) {
      *error = GRPC_ERROR_NONE;
      return true;
    }
  };
}

static void tcp_handle_write(grpc_exec_ctx *exec_ctx, void *arg /* grpc_tcp */,
                             grpc_error *error) {
  grpc_tcp *tcp = (grpc_tcp *)arg;
  grpc_closure *cb;

  if (error != GRPC_ERROR_NONE) {
    cb = tcp->write_cb;
    tcp->write_cb = NULL;
    cb->cb(exec_ctx, cb->cb_arg, error);
    TCP_UNREF(exec_ctx, tcp, "write");
    return;
  }

  if (!tcp_flush(exec_ctx, tcp, &error)) {
    if (GRPC_TRACER_ON(grpc_tcp_trace)) {
      gpr_log(GPR_DEBUG, "write: delayed");
    }
    notify_on_write(exec_ctx, tcp);
  } else {
    cb = tcp->write_cb;
    tcp->write_cb = NULL;
    if (GRPC_TRACER_ON(grpc_tcp_trace)) {
      const char *str = grpc_error_string(error);
      gpr_log(GPR_DEBUG, "write: %s", str);
    }

    GRPC_CLOSURE_RUN(exec_ctx, cb, error);
    TCP_UNREF(exec_ctx, tcp, "write");
  }
}

static void tcp_write(grpc_exec_ctx *exec_ctx, grpc_endpoint *ep,
                      grpc_slice_buffer *buf, grpc_closure *cb) {
  grpc_tcp *tcp = (grpc_tcp *)ep;
  grpc_error *error = GRPC_ERROR_NONE;

  if (GRPC_TRACER_ON(grpc_tcp_trace)) {
    size_t i;

    for (i = 0; i < buf->count; i++) {
      char *data =
          grpc_dump_slice(buf->slices[i], GPR_DUMP_HEX | GPR_DUMP_ASCII);
      gpr_log(GPR_DEBUG, "WRITE %p (peer=%s): %s", tcp, tcp->peer_string, data);
      gpr_free(data);
    }
  }

  GPR_TIMER_BEGIN("tcp_write", 0);
  GPR_ASSERT(tcp->write_cb == NULL);

  if (buf->length == 0) {
    GPR_TIMER_END("tcp_write", 0);
    GRPC_CLOSURE_SCHED(
        exec_ctx, cb,
        grpc_fd_is_shutdown(tcp->em_fd)
            ? tcp_annotate_error(GRPC_ERROR_CREATE_FROM_STATIC_STRING("EOF"),
                                 tcp)
            : GRPC_ERROR_NONE);
    return;
  }
  tcp->outgoing_buffer = buf;
  tcp->outgoing_slice_idx = 0;
  tcp->outgoing_byte_idx = 0;

  if (!tcp_flush(exec_ctx, tcp, &error)) {
    TCP_REF(tcp, "write");
    tcp->write_cb = cb;
    if (GRPC_TRACER_ON(grpc_tcp_trace)) {
      gpr_log(GPR_DEBUG, "write: delayed");
    }
    notify_on_write(exec_ctx, tcp);
  } else {
    if (GRPC_TRACER_ON(grpc_tcp_trace)) {
      const char *str = grpc_error_string(error);
      gpr_log(GPR_DEBUG, "write: %s", str);
    }
    GRPC_CLOSURE_SCHED(exec_ctx, cb, error);
  }

  GPR_TIMER_END("tcp_write", 0);
}

static void tcp_add_to_pollset(grpc_exec_ctx *exec_ctx, grpc_endpoint *ep,
                               grpc_pollset *pollset) {
  grpc_tcp *tcp = (grpc_tcp *)ep;
  grpc_pollset_add_fd(exec_ctx, pollset, tcp->em_fd);
}

static void tcp_add_to_pollset_set(grpc_exec_ctx *exec_ctx, grpc_endpoint *ep,
                                   grpc_pollset_set *pollset_set) {
  grpc_tcp *tcp = (grpc_tcp *)ep;
  grpc_pollset_set_add_fd(exec_ctx, pollset_set, tcp->em_fd);
}

static char *tcp_get_peer(grpc_endpoint *ep) {
  grpc_tcp *tcp = (grpc_tcp *)ep;
  return gpr_strdup(tcp->peer_string);
}

static int tcp_get_fd(grpc_endpoint *ep) {
  grpc_tcp *tcp = (grpc_tcp *)ep;
  return tcp->fd;
}

static grpc_resource_user *tcp_get_resource_user(grpc_endpoint *ep) {
  grpc_tcp *tcp = (grpc_tcp *)ep;
  return tcp->resource_user;
}

static const grpc_endpoint_vtable vtable = {
    tcp_read,     tcp_write,   tcp_add_to_pollset,    tcp_add_to_pollset_set,
    tcp_shutdown, tcp_destroy, tcp_get_resource_user, tcp_get_peer,
    tcp_get_fd};

#define MAX_CHUNK_SIZE 32 * 1024 * 1024

grpc_endpoint *grpc_tcp_create(grpc_exec_ctx *exec_ctx, grpc_fd *em_fd,
                               const grpc_channel_args *channel_args,
                               const char *peer_string) {
  int tcp_read_chunk_size = GRPC_TCP_DEFAULT_READ_SLICE_SIZE;
  int tcp_max_read_chunk_size = 4 * 1024 * 1024;
  int tcp_min_read_chunk_size = 256;
  grpc_resource_quota *resource_quota = grpc_resource_quota_create(NULL);
  if (channel_args != NULL) {
    for (size_t i = 0; i < channel_args->num_args; i++) {
      if (0 ==
          strcmp(channel_args->args[i].key, GRPC_ARG_TCP_READ_CHUNK_SIZE)) {
        grpc_integer_options options = {(int)tcp_read_chunk_size, 1,
                                        MAX_CHUNK_SIZE};
        tcp_read_chunk_size =
            grpc_channel_arg_get_integer(&channel_args->args[i], options);
      } else if (0 == strcmp(channel_args->args[i].key,
                             GRPC_ARG_TCP_MIN_READ_CHUNK_SIZE)) {
        grpc_integer_options options = {(int)tcp_read_chunk_size, 1,
                                        MAX_CHUNK_SIZE};
        tcp_min_read_chunk_size =
            grpc_channel_arg_get_integer(&channel_args->args[i], options);
      } else if (0 == strcmp(channel_args->args[i].key,
                             GRPC_ARG_TCP_MAX_READ_CHUNK_SIZE)) {
        grpc_integer_options options = {(int)tcp_read_chunk_size, 1,
                                        MAX_CHUNK_SIZE};
        tcp_max_read_chunk_size =
            grpc_channel_arg_get_integer(&channel_args->args[i], options);
      } else if (0 ==
                 strcmp(channel_args->args[i].key, GRPC_ARG_RESOURCE_QUOTA)) {
        grpc_resource_quota_unref_internal(exec_ctx, resource_quota);
        resource_quota = grpc_resource_quota_ref_internal(
            (grpc_resource_quota *)channel_args->args[i].value.pointer.p);
      }
    }
  }

  if (tcp_min_read_chunk_size > tcp_max_read_chunk_size) {
    tcp_min_read_chunk_size = tcp_max_read_chunk_size;
  }
  tcp_read_chunk_size = GPR_CLAMP(tcp_read_chunk_size, tcp_min_read_chunk_size,
                                  tcp_max_read_chunk_size);

  grpc_tcp *tcp = (grpc_tcp *)gpr_malloc(sizeof(grpc_tcp));
  tcp->base.vtable = &vtable;
  tcp->peer_string = gpr_strdup(peer_string);
  tcp->fd = grpc_fd_wrapped_fd(em_fd);
  tcp->read_cb = NULL;
  tcp->write_cb = NULL;
  tcp->release_fd_cb = NULL;
  tcp->release_fd = NULL;
  tcp->incoming_buffer = NULL;
  tcp->target_length = (double)tcp_read_chunk_size;
  tcp->min_read_chunk_size = tcp_min_read_chunk_size;
  tcp->max_read_chunk_size = tcp_max_read_chunk_size;
  tcp->bytes_read_this_round = 0;
  tcp->finished_edge = true;
  /* paired with unref in grpc_tcp_destroy */
  gpr_ref_init(&tcp->refcount, 1);
  gpr_atm_no_barrier_store(&tcp->shutdown_count, 0);
  tcp->em_fd = em_fd;
  grpc_slice_buffer_init(&tcp->last_read_buffer);
  tcp->resource_user = grpc_resource_user_create(resource_quota, peer_string);
  grpc_resource_user_slice_allocator_init(
      &tcp->slice_allocator, tcp->resource_user, tcp_read_allocation_done, tcp);
  /* Tell network status tracker about new endpoint */
  grpc_network_status_register_endpoint(&tcp->base);
  grpc_resource_quota_unref_internal(exec_ctx, resource_quota);

  return &tcp->base;
}

int grpc_tcp_fd(grpc_endpoint *ep) {
  grpc_tcp *tcp = (grpc_tcp *)ep;
  GPR_ASSERT(ep->vtable == &vtable);
  return grpc_fd_wrapped_fd(tcp->em_fd);
}

void grpc_tcp_destroy_and_release_fd(grpc_exec_ctx *exec_ctx, grpc_endpoint *ep,
                                     int *fd, grpc_closure *done) {
  grpc_network_status_unregister_endpoint(ep);
  grpc_tcp *tcp = (grpc_tcp *)ep;
  GPR_ASSERT(ep->vtable == &vtable);
  tcp->release_fd = fd;
  tcp->release_fd_cb = done;
  grpc_slice_buffer_reset_and_unref_internal(exec_ctx, &tcp->last_read_buffer);
  TCP_UNREF(exec_ctx, tcp, "destroy");
}

#endif