# class TCPSocket

`TCPSocket` represents a TCP/IP client socket.

A simple client may look like:

    require 'socket'

    s = TCPSocket.new 'localhost', 2000

    while line = s.gets # Read lines from socket
      puts line         # and print them
    end

    s.close             # close socket when done

### Public Class Methods

gethostbyname(hostname) → [official_hostname, alias_hostnames, address_family, *address_list]
Source

    static VALUE
    tcp_s_gethostbyname(VALUE obj, VALUE host)
    {
        rb_warn("TCPSocket.gethostbyname is deprecated; use Addrinfo.getaddrinfo instead.");
        struct rb_addrinfo *res =
            rsock_addrinfo(host, Qnil, AF_UNSPEC, SOCK_STREAM, AI_CANONNAME);
        return rsock_make_hostent(host, res, tcp_sockaddr);
    }

Use `Addrinfo.getaddrinfo` instead. This method is deprecated for the following reasons:

- The 3rd element of the result is the address family of the first address. The address families of the rest of the addresses are not returned.

- gethostbyname() may take a long time and it may block other threads. (GVL cannot be released since gethostbyname() is not thread safe.)

- This method uses gethostbyname() function already removed from POSIX.

This method lookups host information by hostname.

    TCPSocket.gethostbyname("localhost")
    #=> ["localhost", ["hal"], 2, "127.0.0.1"]

new(remote_host, remote_port, local_host=nil, local_port=nil, resolv_timeout: nil, connect_timeout: nil, fast_fallback: true)
Source

    static VALUE
    tcp_init(int argc, VALUE *argv, VALUE sock)
    {
        VALUE remote_host, remote_serv;
        VALUE local_host, local_serv;
        VALUE opt;
        static ID keyword_ids[4];
        VALUE kwargs[4];
        VALUE resolv_timeout = Qnil;
        VALUE connect_timeout = Qnil;
        VALUE fast_fallback = Qnil;
        VALUE test_mode_settings = Qnil;

        if (!keyword_ids[0]) {
            CONST_ID(keyword_ids[0], "resolv_timeout");
            CONST_ID(keyword_ids[1], "connect_timeout");
            CONST_ID(keyword_ids[2], "fast_fallback");
            CONST_ID(keyword_ids[3], "test_mode_settings");
        }

        rb_scan_args(argc, argv, "22:", &remote_host, &remote_serv,
                            &local_host, &local_serv, &opt);

        if (!NIL_P(opt)) {
            rb_get_kwargs(opt, keyword_ids, 0, 4, kwargs);
            if (kwargs[0] != Qundef) { resolv_timeout = kwargs[0]; }
            if (kwargs[1] != Qundef) { connect_timeout = kwargs[1]; }
            if (kwargs[2] != Qundef) { fast_fallback = kwargs[2]; }
            if (kwargs[3] != Qundef) { test_mode_settings = kwargs[3]; }
        }

        if (fast_fallback == Qnil) {
            fast_fallback = rb_ivar_get(rb_cSocket, tcp_fast_fallback);
            if (fast_fallback == Qnil) fast_fallback = Qtrue;
        }

        return rsock_init_inetsock(sock, remote_host, remote_serv,
                                   local_host, local_serv, INET_CLIENT,
                                   resolv_timeout, connect_timeout, fast_fallback,
                                   test_mode_settings);
    }

Opens a TCP connection to `remote_host` on `remote_port`. If `local_host` and `local_port` are specified, then those parameters are used on the local end to establish the connection.

Starting from Ruby 3.4, this method operates according to the Happy Eyeballs Version 2 (RFC 8305) algorithm by default, except on Windows.

For details on Happy Eyeballs Version 2, see `Socket.tcp_fast_fallback=`.

To make it behave the same as in Ruby 3.3 and earlier, explicitly specify the option fast_fallback:false. Or, setting `Socket.tcp_fast_fallback=`false will disable Happy Eyeballs Version 2 not only for this method but for all `Socket` globally.

When using `TCPSocket.new` on Windows, Happy Eyeballs Version 2 is not provided, and it behaves the same as in Ruby 3.3 and earlier.

:resolv_timeout

  Specifies the timeout in seconds from when the hostname resolution starts.

:connect_timeout

  This method sequentially attempts connecting to all candidate destination addresses.
  The `connect_timeout` specifies the timeout in seconds from the start of the connection attempt to the last candidate.
  By default, all connection attempts continue until the timeout occurs.
  When `fast_fallback:false` is explicitly specified,
  a timeout is set for each connection attempt and any connection attempt that exceeds its timeout will be canceled.

:fast_fallback

  Enables the Happy Eyeballs Version 2 algorithm (enabled by default).