void AsyncServerSocket::bind()

in folly/io/async/AsyncServerSocket.cpp [440:569]

• 97 lines of code
• 24 McCabe index (conditional complexity)

void AsyncServerSocket::bind(uint16_t port) {
  struct addrinfo hints, *res0;
  char sport[sizeof("65536")];

  memset(&hints, 0, sizeof(hints));
  hints.ai_family = AF_UNSPEC;
  hints.ai_socktype = SOCK_STREAM;
  hints.ai_flags = AI_PASSIVE | AI_NUMERICSERV;
  snprintf(sport, sizeof(sport), "%u", port);

  // On Windows the value we need to pass to bind to all available
  // addresses is an empty string. Everywhere else, it's nullptr.
  constexpr const char* kWildcardNode = kIsWindows ? "" : nullptr;
  if (getaddrinfo(kWildcardNode, sport, &hints, &res0)) {
    throw std::invalid_argument(
        "Attempted to bind address to socket with "
        "bad getaddrinfo");
  }

  SCOPE_EXIT { freeaddrinfo(res0); };

  auto setupAddress = [&](struct addrinfo* res) {
    auto s = netops::socket(res->ai_family, res->ai_socktype, res->ai_protocol);
    // IPv6/IPv4 may not be supported by the kernel
    if (s == NetworkSocket() && errno == EAFNOSUPPORT) {
      return;
    }
    CHECK_NE(s, NetworkSocket());

    try {
      setupSocket(s, res->ai_family);
    } catch (...) {
      closeNoInt(s);
      throw;
    }

    if (res->ai_family == AF_INET6) {
      int v6only = 1;
      CHECK(
          0 ==
          netops::setsockopt(
              s, IPPROTO_IPV6, IPV6_V6ONLY, &v6only, sizeof(v6only)));
    }

    // Bind to the socket
    if (netops::bind(s, res->ai_addr, socklen_t(res->ai_addrlen)) != 0) {
      folly::throwSystemError(
          errno,
          "failed to bind to async server socket for port ",
          SocketAddress::getPortFrom(res->ai_addr),
          " family ",
          SocketAddress::getFamilyNameFrom(res->ai_addr, "<unknown>"));
    }

#if defined(__linux__)
    if (noTransparentTls_) {
      // Ignore return value, errors are ok
      netops::setsockopt(s, SOL_SOCKET, SO_NO_TRANSPARENT_TLS, nullptr, 0);
    }
#endif

    SocketAddress address;
    address.setFromLocalAddress(s);

    sockets_.emplace_back(eventBase_, s, this, address.getFamily());
  };

  const int kNumTries = 25;
  for (int tries = 1; true; tries++) {
    // Prefer AF_INET6 addresses. RFC 3484 mandates that getaddrinfo
    // should return IPv6 first and then IPv4 addresses, but glibc's
    // getaddrinfo(nullptr) with AI_PASSIVE returns:
    // - 0.0.0.0 (IPv4-only)
    // - :: (IPv6+IPv4) in this order
    // See: https://sourceware.org/bugzilla/show_bug.cgi?id=9981
    for (struct addrinfo* res = res0; res; res = res->ai_next) {
      if (res->ai_family == AF_INET6) {
        setupAddress(res);
      }
    }

    // If port == 0, then we should try to bind to the same port on ipv4 and
    // ipv6.  So if we did bind to ipv6, figure out that port and use it.
    if (sockets_.size() == 1 && port == 0) {
      SocketAddress address;
      address.setFromLocalAddress(sockets_.back().socket_);
      snprintf(sport, sizeof(sport), "%u", address.getPort());
      freeaddrinfo(res0);
      CHECK_EQ(0, getaddrinfo(nullptr, sport, &hints, &res0));
    }

    try {
      for (struct addrinfo* res = res0; res; res = res->ai_next) {
        if (res->ai_family != AF_INET6) {
          setupAddress(res);
        }
      }
    } catch (const std::system_error&) {
      // If we can't bind to the same port on ipv4 as ipv6 when using
      // port=0 then we will retry again before giving up after
      // kNumTries attempts.  We do this by closing the sockets that
      // were opened, then restarting from scratch.
      if (port == 0 && !sockets_.empty() && tries != kNumTries) {
        for (const auto& socket : sockets_) {
          if (socket.socket_ == NetworkSocket()) {
            continue;
          } else if (
              const auto shutdownSocketSet = wShutdownSocketSet_.lock()) {
            shutdownSocketSet->close(socket.socket_);
          } else {
            closeNoInt(socket.socket_);
          }
        }
        sockets_.clear();
        snprintf(sport, sizeof(sport), "%u", port);
        freeaddrinfo(res0);
        CHECK_EQ(0, getaddrinfo(nullptr, sport, &hints, &res0));
        continue;
      }

      throw;
    }

    break;
  }

  if (sockets_.empty()) {
    throw std::runtime_error("did not bind any async server socket for port");
  }
}