text: /*
   *
   * 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.
   *
   */
  
  /* FIXME: "posix" files shouldn't be depending on _GNU_SOURCE */
  #ifndef _GNU_SOURCE
  #define _GNU_SOURCE
  #endif
  
  #include <grpc/support/port_platform.h>
  
  #include "src/core/lib/iomgr/port.h"
  
  #ifdef GRPC_POSIX_SOCKET_TCP_SERVER
  
  #include <errno.h>
  #include <fcntl.h>
  #include <netinet/in.h>
  #include <netinet/tcp.h>
  #include <string.h>
  #include <sys/socket.h>
  #include <sys/stat.h>
  #include <sys/types.h>
  #include <unistd.h>
  
  #include <string>
  
  #include "absl/strings/str_cat.h"
  #include "absl/strings/str_format.h"
  
  #include <grpc/support/alloc.h>
  #include <grpc/support/log.h>
  #include <grpc/support/sync.h>
  #include <grpc/support/time.h>
  
  #include "src/core/lib/channel/channel_args.h"
  #include "src/core/lib/gpr/strerror.h"
  #include "src/core/lib/gpr/string.h"
  #include "src/core/lib/gprpp/memory.h"
  #include "src/core/lib/iomgr/exec_ctx.h"
  #include "src/core/lib/iomgr/resolve_address.h"
  #include "src/core/lib/iomgr/sockaddr.h"
  #include "src/core/lib/iomgr/sockaddr_utils.h"
  #include "src/core/lib/iomgr/socket_utils_posix.h"
  #include "src/core/lib/iomgr/tcp_posix.h"
  #include "src/core/lib/iomgr/tcp_server.h"
  #include "src/core/lib/iomgr/tcp_server_utils_posix.h"
  #include "src/core/lib/iomgr/unix_sockets_posix.h"
  
  static grpc_error* tcp_server_create(grpc_closure* shutdown_complete,
                                       const grpc_channel_args* args,
                                       grpc_tcp_server** server) {
    grpc_tcp_server* s =
        static_cast<grpc_tcp_server*>(gpr_zalloc(sizeof(grpc_tcp_server)));
    s->so_reuseport = grpc_is_socket_reuse_port_supported();
    s->expand_wildcard_addrs = false;
    for (size_t i = 0; i < (args == nullptr ? 0 : args->num_args); i++) {
      if (0 == strcmp(GRPC_ARG_ALLOW_REUSEPORT, args->args[i].key)) {
        if (args->args[i].type == GRPC_ARG_INTEGER) {
          s->so_reuseport = grpc_is_socket_reuse_port_supported() &&
                            (args->args[i].value.integer != 0);
        } else {
          gpr_free(s);
          return GRPC_ERROR_CREATE_FROM_STATIC_STRING(GRPC_ARG_ALLOW_REUSEPORT
                                                      " must be an integer");
        }
      } else if (0 == strcmp(GRPC_ARG_EXPAND_WILDCARD_ADDRS, args->args[i].key)) {
        if (args->args[i].type == GRPC_ARG_INTEGER) {
          s->expand_wildcard_addrs = (args->args[i].value.integer != 0);
        } else {
          gpr_free(s);
          return GRPC_ERROR_CREATE_FROM_STATIC_STRING(
              GRPC_ARG_EXPAND_WILDCARD_ADDRS " must be an integer");
        }
      }
    }
    gpr_ref_init(&s->refs, 1);
    gpr_mu_init(&s->mu);
    s->active_ports = 0;
    s->destroyed_ports = 0;
    s->shutdown = false;
    s->shutdown_starting.head = nullptr;
    s->shutdown_starting.tail = nullptr;
    s->shutdown_complete = shutdown_complete;
    s->on_accept_cb = nullptr;
    s->on_accept_cb_arg = nullptr;
    s->head = nullptr;
    s->tail = nullptr;
    s->nports = 0;
    s->channel_args = grpc_channel_args_copy(args);
    s->fd_handler = nullptr;
    gpr_atm_no_barrier_store(&s->next_pollset_to_assign, 0);
    *server = s;
    return GRPC_ERROR_NONE;
  }
  
  static void finish_shutdown(grpc_tcp_server* s) {
    gpr_mu_lock(&s->mu);
    GPR_ASSERT(s->shutdown);
    gpr_mu_unlock(&s->mu);
    if (s->shutdown_complete != nullptr) {
      grpc_core::ExecCtx::Run(DEBUG_LOCATION, s->shutdown_complete,
                              GRPC_ERROR_NONE);
    }
  
    gpr_mu_destroy(&s->mu);
  
    while (s->head) {
      grpc_tcp_listener* sp = s->head;
      s->head = sp->next;
      gpr_free(sp);
    }
    grpc_channel_args_destroy(s->channel_args);
    delete s->fd_handler;
  
    gpr_free(s);
  }
  
  static void destroyed_port(void* server, grpc_error* /*error*/) {
    grpc_tcp_server* s = static_cast<grpc_tcp_server*>(server);
    gpr_mu_lock(&s->mu);
    s->destroyed_ports++;
    if (s->destroyed_ports == s->nports) {
      gpr_mu_unlock(&s->mu);
      finish_shutdown(s);
    } else {
      GPR_ASSERT(s->destroyed_ports < s->nports);
      gpr_mu_unlock(&s->mu);
    }
  }
  
  /* called when all listening endpoints have been shutdown, so no further
     events will be received on them - at this point it's safe to destroy
     things */
  static void deactivated_all_ports(grpc_tcp_server* s) {
    /* delete ALL the things */
    gpr_mu_lock(&s->mu);
  
    GPR_ASSERT(s->shutdown);
  
    if (s->head) {
      grpc_tcp_listener* sp;
      for (sp = s->head; sp; sp = sp->next) {
        grpc_unlink_if_unix_domain_socket(&sp->addr);
        GRPC_CLOSURE_INIT(&sp->destroyed_closure, destroyed_port, s,
                          grpc_schedule_on_exec_ctx);
        grpc_fd_orphan(sp->emfd, &sp->destroyed_closure, nullptr,
                       "tcp_listener_shutdown");
      }
      gpr_mu_unlock(&s->mu);
    } else {
      gpr_mu_unlock(&s->mu);
      finish_shutdown(s);
    }
  }
  
  static void tcp_server_destroy(grpc_tcp_server* s) {
    gpr_mu_lock(&s->mu);
  
    GPR_ASSERT(!s->shutdown);
    s->shutdown = true;
  
    /* shutdown all fd's */
    if (s->active_ports) {
      grpc_tcp_listener* sp;
      for (sp = s->head; sp; sp = sp->next) {
        grpc_fd_shutdown(
            sp->emfd, GRPC_ERROR_CREATE_FROM_STATIC_STRING("Server destroyed"));
      }
      gpr_mu_unlock(&s->mu);
    } else {
      gpr_mu_unlock(&s->mu);
      deactivated_all_ports(s);
    }
  }
  
  /* event manager callback when reads are ready */
  static void on_read(void* arg, grpc_error* err) {
    grpc_tcp_listener* sp = static_cast<grpc_tcp_listener*>(arg);
    grpc_pollset* read_notifier_pollset;
    if (err != GRPC_ERROR_NONE) {
      goto error;
    }
  
    /* loop until accept4 returns EAGAIN, and then re-arm notification */
    for (;;) {
      grpc_resolved_address addr;
      memset(&addr, 0, sizeof(addr));
      addr.len = static_cast<socklen_t>(sizeof(struct sockaddr_storage));
      /* Note: If we ever decide to return this address to the user, remember to
         strip off the ::ffff:0.0.0.0/96 prefix first. */
      int fd = grpc_accept4(sp->fd, &addr, 1, 1);
      if (fd < 0) {
        switch (errno) {
          case EINTR:
            continue;
          case EAGAIN:
            grpc_fd_notify_on_read(sp->emfd, &sp->read_closure);
            return;
          default:
            gpr_mu_lock(&sp->server->mu);
            if (!sp->server->shutdown_listeners) {
              gpr_log(GPR_ERROR, "Failed accept4: %s",
                      grpc_core::StrError(errno).c_str());
            } else {
              /* if we have shutdown listeners, accept4 could fail, and we
                 needn't notify users */
            }
            gpr_mu_unlock(&sp->server->mu);
            goto error;
        }
      }
  
      /* For UNIX sockets, the accept call might not fill up the member sun_path
       * of sockaddr_un, so explicitly call getsockname to get it. */
      if (grpc_is_unix_socket(&addr)) {
        memset(&addr, 0, sizeof(addr));
        addr.len = static_cast<socklen_t>(sizeof(struct sockaddr_storage));
        if (getsockname(fd, reinterpret_cast<struct sockaddr*>(addr.addr),
                        &(addr.len)) < 0) {
          gpr_log(GPR_ERROR, "Failed getsockname: %s",
                  grpc_core::StrError(errno).c_str());
          close(fd);
          goto error;
        }
      }
  
      grpc_set_socket_no_sigpipe_if_possible(fd);
  
      std::string addr_str = grpc_sockaddr_to_uri(&addr);
      if (GRPC_TRACE_FLAG_ENABLED(grpc_tcp_trace)) {
        gpr_log(GPR_INFO, "SERVER_CONNECT: incoming connection: %s",
                addr_str.c_str());
      }
  
      std::string name = absl::StrCat("tcp-server-connection:", addr_str);
      grpc_fd* fdobj = grpc_fd_create(fd, name.c_str(), true);
  
      read_notifier_pollset = (*(sp->server->pollsets))
          [static_cast<size_t>(gpr_atm_no_barrier_fetch_add(
               &sp->server->next_pollset_to_assign, 1)) %
           sp->server->pollsets->size()];
  
      grpc_pollset_add_fd(read_notifier_pollset, fdobj);
  
      // Create acceptor.
      grpc_tcp_server_acceptor* acceptor =
          static_cast<grpc_tcp_server_acceptor*>(gpr_malloc(sizeof(*acceptor)));
      acceptor->from_server = sp->server;
      acceptor->port_index = sp->port_index;
      acceptor->fd_index = sp->fd_index;
      acceptor->external_connection = false;
  
      sp->server->on_accept_cb(
          sp->server->on_accept_cb_arg,
          grpc_tcp_create(fdobj, sp->server->channel_args, addr_str.c_str()),
          read_notifier_pollset, acceptor);
    }
  
    GPR_UNREACHABLE_CODE(return );
  
  error:
    gpr_mu_lock(&sp->server->mu);
    if (0 == --sp->server->active_ports && sp->server->shutdown) {
      gpr_mu_unlock(&sp->server->mu);
      deactivated_all_ports(sp->server);
    } else {
      gpr_mu_unlock(&sp->server->mu);
    }
  }
  
  /* Treat :: or 0.0.0.0 as a family-agnostic wildcard. */
  static grpc_error* add_wildcard_addrs_to_server(grpc_tcp_server* s,
                                                  unsigned port_index,
                                                  int requested_port,
                                                  int* out_port) {
    grpc_resolved_address wild4;
    grpc_resolved_address wild6;
    unsigned fd_index = 0;
    grpc_dualstack_mode dsmode;
    grpc_tcp_listener* sp = nullptr;
    grpc_tcp_listener* sp2 = nullptr;
    grpc_error* v6_err = GRPC_ERROR_NONE;
    grpc_error* v4_err = GRPC_ERROR_NONE;
    *out_port = -1;
  
    if (grpc_tcp_server_have_ifaddrs() && s->expand_wildcard_addrs) {
      return grpc_tcp_server_add_all_local_addrs(s, port_index, requested_port,
                                                 out_port);
    }
  
    grpc_sockaddr_make_wildcards(requested_port, &wild4, &wild6);
    /* Try listening on IPv6 first. */
    if ((v6_err = grpc_tcp_server_add_addr(s, &wild6, port_index, fd_index,
                                           &dsmode, &sp)) == GRPC_ERROR_NONE) {
      ++fd_index;
      requested_port = *out_port = sp->port;
      if (dsmode == GRPC_DSMODE_DUALSTACK || dsmode == GRPC_DSMODE_IPV4) {
        return GRPC_ERROR_NONE;
      }
    }
    /* If we got a v6-only socket or nothing, try adding 0.0.0.0. */
    grpc_sockaddr_set_port(&wild4, requested_port);
    if ((v4_err = grpc_tcp_server_add_addr(s, &wild4, port_index, fd_index,
                                           &dsmode, &sp2)) == GRPC_ERROR_NONE) {
      *out_port = sp2->port;
      if (sp != nullptr) {
        sp2->is_sibling = 1;
        sp->sibling = sp2;
      }
    }
    if (*out_port > 0) {
      if (v6_err != GRPC_ERROR_NONE) {
        gpr_log(GPR_INFO,
                "Failed to add :: listener, "
                "the environment may not support IPv6: %s",
                grpc_error_string(v6_err));
        GRPC_ERROR_UNREF(v6_err);
      }
      if (v4_err != GRPC_ERROR_NONE) {
        gpr_log(GPR_INFO,
                "Failed to add 0.0.0.0 listener, "
                "the environment may not support IPv4: %s",
                grpc_error_string(v4_err));
        GRPC_ERROR_UNREF(v4_err);
      }
      return GRPC_ERROR_NONE;
    } else {
      grpc_error* root_err = GRPC_ERROR_CREATE_FROM_STATIC_STRING(
          "Failed to add any wildcard listeners");
      GPR_ASSERT(v6_err != GRPC_ERROR_NONE && v4_err != GRPC_ERROR_NONE);
      root_err = grpc_error_add_child(root_err, v6_err);
      root_err = grpc_error_add_child(root_err, v4_err);
      return root_err;
    }
  }
  
  static grpc_error* clone_port(grpc_tcp_listener* listener, unsigned count) {
    grpc_tcp_listener* sp = nullptr;
    std::string addr_str;
    grpc_error* err;
  
    for (grpc_tcp_listener* l = listener->next; l && l->is_sibling; l = l->next) {
      l->fd_index += count;
    }
  
    for (unsigned i = 0; i < count; i++) {
      int fd = -1;
      int port = -1;
      grpc_dualstack_mode dsmode;
      err = grpc_create_dualstack_socket(&listener->addr, SOCK_STREAM, 0, &dsmode,
                                         &fd);
      if (err != GRPC_ERROR_NONE) return err;
      err = grpc_tcp_server_prepare_socket(listener->server, fd, &listener->addr,
                                           true, &port);
      if (err != GRPC_ERROR_NONE) return err;
      listener->server->nports++;
      addr_str = grpc_sockaddr_to_string(&listener->addr, true);
      sp = static_cast<grpc_tcp_listener*>(gpr_malloc(sizeof(grpc_tcp_listener)));
      sp->next = listener->next;
      listener->next = sp;
      /* sp (the new listener) is a sibling of 'listener' (the original
         listener). */
      sp->is_sibling = 1;
      sp->sibling = listener->sibling;
      listener->sibling = sp;
      sp->server = listener->server;
      sp->fd = fd;
      sp->emfd = grpc_fd_create(
          fd,
          absl::StrFormat("tcp-server-listener:%s/clone-%d", addr_str.c_str(), i)
              .c_str(),
          true);
      memcpy(&sp->addr, &listener->addr, sizeof(grpc_resolved_address));
      sp->port = port;
      sp->port_index = listener->port_index;
      sp->fd_index = listener->fd_index + count - i;
      GPR_ASSERT(sp->emfd);
      while (listener->server->tail->next != nullptr) {
        listener->server->tail = listener->server->tail->next;
      }
    }
  
    return GRPC_ERROR_NONE;
  }
  
  static grpc_error* tcp_server_add_port(grpc_tcp_server* s,
                                         const grpc_resolved_address* addr,
                                         int* out_port) {
    grpc_tcp_listener* sp;
    grpc_resolved_address sockname_temp;
    grpc_resolved_address addr6_v4mapped;
    int requested_port = grpc_sockaddr_get_port(addr);
    unsigned port_index = 0;
    grpc_dualstack_mode dsmode;
    grpc_error* err;
    *out_port = -1;
    if (s->tail != nullptr) {
      port_index = s->tail->port_index + 1;
    }
    grpc_unlink_if_unix_domain_socket(addr);
  
    /* Check if this is a wildcard port, and if so, try to keep the port the same
       as some previously created listener. */
    if (requested_port == 0) {
      for (sp = s->head; sp; sp = sp->next) {
        sockname_temp.len =
            static_cast<socklen_t>(sizeof(struct sockaddr_storage));
        if (0 ==
            getsockname(sp->fd,
                        reinterpret_cast<grpc_sockaddr*>(&sockname_temp.addr),
                        &sockname_temp.len)) {
          int used_port = grpc_sockaddr_get_port(&sockname_temp);
          if (used_port > 0) {
            memcpy(&sockname_temp, addr, sizeof(grpc_resolved_address));
            grpc_sockaddr_set_port(&sockname_temp, used_port);
            requested_port = used_port;
            addr = &sockname_temp;
            break;
          }
        }
      }
    }
    if (grpc_sockaddr_is_wildcard(addr, &requested_port)) {
      return add_wildcard_addrs_to_server(s, port_index, requested_port,
                                          out_port);
    }
    if (grpc_sockaddr_to_v4mapped(addr, &addr6_v4mapped)) {
      addr = &addr6_v4mapped;
    }
    if ((err = grpc_tcp_server_add_addr(s, addr, port_index, 0, &dsmode, &sp)) ==
        GRPC_ERROR_NONE) {
      *out_port = sp->port;
    }
    return err;
  }
  
  /* Return listener at port_index or NULL. Should only be called with s->mu
     locked. */
  static grpc_tcp_listener* get_port_index(grpc_tcp_server* s,
                                           unsigned port_index) {
    unsigned num_ports = 0;
    grpc_tcp_listener* sp;
    for (sp = s->head; sp; sp = sp->next) {
      if (!sp->is_sibling) {
        if (++num_ports > port_index) {
          return sp;
        }
      }
    }
    return nullptr;
  }
  
  unsigned tcp_server_port_fd_count(grpc_tcp_server* s, unsigned port_index) {
    unsigned num_fds = 0;
    gpr_mu_lock(&s->mu);
    grpc_tcp_listener* sp = get_port_index(s, port_index);
    for (; sp; sp = sp->sibling) {
      ++num_fds;
    }
    gpr_mu_unlock(&s->mu);
    return num_fds;
  }
  
  static int tcp_server_port_fd(grpc_tcp_server* s, unsigned port_index,
                                unsigned fd_index) {
    gpr_mu_lock(&s->mu);
    grpc_tcp_listener* sp = get_port_index(s, port_index);
    for (; sp; sp = sp->sibling, --fd_index) {
      if (fd_index == 0) {
        gpr_mu_unlock(&s->mu);
        return sp->fd;
      }
    }
    gpr_mu_unlock(&s->mu);
    return -1;
  }
  
  static void tcp_server_start(grpc_tcp_server* s,
                               const std::vector<grpc_pollset*>* pollsets,
                               grpc_tcp_server_cb on_accept_cb,
                               void* on_accept_cb_arg) {
    size_t i;
    grpc_tcp_listener* sp;
    GPR_ASSERT(on_accept_cb);
    gpr_mu_lock(&s->mu);
    GPR_ASSERT(!s->on_accept_cb);
    GPR_ASSERT(s->active_ports == 0);
    s->on_accept_cb = on_accept_cb;
    s->on_accept_cb_arg = on_accept_cb_arg;
    s->pollsets = pollsets;
    sp = s->head;
    while (sp != nullptr) {
      if (s->so_reuseport && !grpc_is_unix_socket(&sp->addr) &&
          pollsets->size() > 1) {
        GPR_ASSERT(GRPC_LOG_IF_ERROR(
            "clone_port", clone_port(sp, (unsigned)(pollsets->size() - 1))));
        for (i = 0; i < pollsets->size(); i++) {
          grpc_pollset_add_fd((*pollsets)[i], sp->emfd);
          GRPC_CLOSURE_INIT(&sp->read_closure, on_read, sp,
                            grpc_schedule_on_exec_ctx);
          grpc_fd_notify_on_read(sp->emfd, &sp->read_closure);
          s->active_ports++;
          sp = sp->next;
        }
      } else {
        for (i = 0; i < pollsets->size(); i++) {
          grpc_pollset_add_fd((*pollsets)[i], sp->emfd);
        }
        GRPC_CLOSURE_INIT(&sp->read_closure, on_read, sp,
                          grpc_schedule_on_exec_ctx);
        grpc_fd_notify_on_read(sp->emfd, &sp->read_closure);
        s->active_ports++;
        sp = sp->next;
      }
    }
    gpr_mu_unlock(&s->mu);
  }
  
  grpc_tcp_server* tcp_server_ref(grpc_tcp_server* s) {
    gpr_ref_non_zero(&s->refs);
    return s;
  }
  
  static void tcp_server_shutdown_starting_add(grpc_tcp_server* s,
                                               grpc_closure* shutdown_starting) {
    gpr_mu_lock(&s->mu);
    grpc_closure_list_append(&s->shutdown_starting, shutdown_starting,
                             GRPC_ERROR_NONE);
    gpr_mu_unlock(&s->mu);
  }
  
  static void tcp_server_unref(grpc_tcp_server* s) {
    if (gpr_unref(&s->refs)) {
      grpc_tcp_server_shutdown_listeners(s);
      gpr_mu_lock(&s->mu);
      grpc_core::ExecCtx::RunList(DEBUG_LOCATION, &s->shutdown_starting);
      gpr_mu_unlock(&s->mu);
      tcp_server_destroy(s);
    }
  }
  
  static void tcp_server_shutdown_listeners(grpc_tcp_server* s) {
    gpr_mu_lock(&s->mu);
    s->shutdown_listeners = true;
    /* shutdown all fd's */
    if (s->active_ports) {
      grpc_tcp_listener* sp;
      for (sp = s->head; sp; sp = sp->next) {
        grpc_fd_shutdown(sp->emfd,
                         GRPC_ERROR_CREATE_FROM_STATIC_STRING("Server shutdown"));
      }
    }
    gpr_mu_unlock(&s->mu);
  }
  
  namespace {
  class ExternalConnectionHandler : public grpc_core::TcpServerFdHandler {
   public:
    explicit ExternalConnectionHandler(grpc_tcp_server* s) : s_(s) {}
  
    // TODO(yangg) resolve duplicate code with on_read
    void Handle(int listener_fd, int fd, grpc_byte_buffer* buf) override {
      grpc_pollset* read_notifier_pollset;
      grpc_resolved_address addr;
      memset(&addr, 0, sizeof(addr));
      addr.len = static_cast<socklen_t>(sizeof(struct sockaddr_storage));
      grpc_core::ExecCtx exec_ctx;
  
      if (getpeername(fd, reinterpret_cast<struct sockaddr*>(addr.addr),
                      &(addr.len)) < 0) {
        gpr_log(GPR_ERROR, "Failed getpeername: %s",
                grpc_core::StrError(errno).c_str());
        close(fd);
        return;
      }
      grpc_set_socket_no_sigpipe_if_possible(fd);
      std::string addr_str = grpc_sockaddr_to_uri(&addr);
      if (grpc_tcp_trace.enabled()) {
        gpr_log(GPR_INFO, "SERVER_CONNECT: incoming external connection: %s",
                addr_str.c_str());
      }
      std::string name = absl::StrCat("tcp-server-connection:", addr_str);
      grpc_fd* fdobj = grpc_fd_create(fd, name.c_str(), true);
      read_notifier_pollset =
          (*(s_->pollsets))[static_cast<size_t>(gpr_atm_no_barrier_fetch_add(
                                &s_->next_pollset_to_assign, 1)) %
                            s_->pollsets->size()];
      grpc_pollset_add_fd(read_notifier_pollset, fdobj);
      grpc_tcp_server_acceptor* acceptor =
          static_cast<grpc_tcp_server_acceptor*>(gpr_malloc(sizeof(*acceptor)));
      acceptor->from_server = s_;
      acceptor->port_index = -1;
      acceptor->fd_index = -1;
      acceptor->external_connection = true;
      acceptor->listener_fd = listener_fd;
      acceptor->pending_data = buf;
      s_->on_accept_cb(s_->on_accept_cb_arg,
                       grpc_tcp_create(fdobj, s_->channel_args, addr_str.c_str()),
                       read_notifier_pollset, acceptor);
    }
  
   private:
    grpc_tcp_server* s_;
  };
  }  // namespace
  
  static grpc_core::TcpServerFdHandler* tcp_server_create_fd_handler(
      grpc_tcp_server* s) {
    s->fd_handler = new ExternalConnectionHandler(s);
    return s->fd_handler;
  }
  
  grpc_tcp_server_vtable grpc_posix_tcp_server_vtable = {
      tcp_server_create,        tcp_server_start,
      tcp_server_add_port,      tcp_server_create_fd_handler,
      tcp_server_port_fd_count, tcp_server_port_fd,
      tcp_server_ref,           tcp_server_shutdown_starting_add,
      tcp_server_unref,         tcp_server_shutdown_listeners};
  
  #endif /* GRPC_POSIX_SOCKET_TCP_SERVER */
  