# class TCPServer

`TCPServer` represents a TCP/IP server socket.

A simple TCP server may look like:

    require 'socket'

    server = TCPServer.new 2000 # Server bind to port 2000
    loop do
      client = server.accept    # Wait for a client to connect
      client.puts "Hello !"
      client.puts "Time is #{Time.now}"
      client.close
    end

A more usable server (serving multiple clients):

    require 'socket'

    server = TCPServer.new 2000
    loop do
      Thread.start(server.accept) do |client|
        client.puts "Hello !"
        client.puts "Time is #{Time.now}"
        client.close
      end
    end

### Public Class Methods

new([hostname,] port) → tcpserver click to toggle source

Creates a new server socket bound to port.

If hostname is given, the socket is bound to it.

    serv = TCPServer.new("127.0.0.1", 28561)
    s = serv.accept
    s.puts Time.now
    s.close

Internally, `TCPServer.new` calls getaddrinfo() function to obtain addresses. If getaddrinfo() returns multiple addresses, `TCPServer.new` tries to create a server socket for each address and returns first one that is successful.

    static VALUE
    tcp_svr_init(int argc, VALUE *argv, VALUE sock)
    {
        VALUE hostname, port;

        rb_scan_args(argc, argv, "011", &hostname, &port);
        return rsock_init_inetsock(sock, hostname, port, Qnil, Qnil, INET_SERVER, Qnil, Qnil);
    }

### Public Instance Methods

accept → tcpsocket click to toggle source

Accepts an incoming connection. It returns a new `TCPSocket` object.

    TCPServer.open("127.0.0.1", 14641) {|serv|
      s = serv.accept
      s.puts Time.now
      s.close
    }

    static VALUE
    tcp_accept(VALUE sock)
    {
        rb_io_t *fptr;
        union_sockaddr from;
        socklen_t fromlen;

        GetOpenFile(sock, fptr);
        fromlen = (socklen_t)sizeof(from);
        return rsock_s_accept(rb_cTCPSocket, fptr->fd, &from.addr, &fromlen);
    }

accept_nonblock([options]) → tcpsocket click to toggle source

Accepts an incoming connection using accept(2) after O_NONBLOCK is set for the underlying file descriptor. It returns an accepted `TCPSocket` for the incoming connection.

### Example¶ ↑

    require 'socket'
    serv = TCPServer.new(2202)
    begin # emulate blocking accept
      sock = serv.accept_nonblock
    rescue IO::WaitReadable, Errno::EINTR
      IO.select([serv])
      retry
    end
    # sock is an accepted socket.

Refer to `Socket#accept` for the exceptions that may be thrown if the call to `TCPServer#accept_nonblock` fails.

`TCPServer#accept_nonblock` may raise any error corresponding to accept(2) failure, including Errno::EWOULDBLOCK.

If the exception is Errno::EWOULDBLOCK, Errno::EAGAIN, Errno::ECONNABORTED, Errno::EPROTO, it is extended by `IO::WaitReadable`. So `IO::WaitReadable` can be used to rescue the exceptions for retrying accept_nonblock.

By specifying a keyword argument exception to `false`, you can indicate that `accept_nonblock` should not raise an `IO::WaitReadable` exception, but return the symbol `:wait_readable` instead.

### See¶ ↑

- `TCPServer#accept`

- `Socket#accept`

    # File ext/socket/lib/socket.rb, line 1313
    def accept_nonblock(exception: true)
      __accept_nonblock(exception)
    end

listen( int ) → 0 click to toggle source

Listens for connections, using the specified `int` as the backlog. A call to listen only applies if the `socket` is of type SOCK_STREAM or SOCK_SEQPACKET.

### Parameter¶ ↑

- `backlog` - the maximum length of the queue for pending connections.

### Example 1¶ ↑

    require 'socket'
    include Socket::Constants
    socket = Socket.new( AF_INET, SOCK_STREAM, 0 )
    sockaddr = Socket.pack_sockaddr_in( 2200, 'localhost' )
    socket.bind( sockaddr )
    socket.listen( 5 )

### Example 2 (listening on an arbitrary port, unix-based systems only):¶ ↑

    require 'socket'
    include Socket::Constants
    socket = Socket.new( AF_INET, SOCK_STREAM, 0 )
    socket.listen( 1 )

### Unix-based Exceptions¶ ↑

On unix based systems the above will work because a new `sockaddr` struct is created on the address ADDR_ANY, for an arbitrary port number as handed off by the kernel. It will not work on Windows, because Windows requires that the `socket` is bound by calling bind before it can listen.

If the backlog amount exceeds the implementation-dependent maximum queue length, the implementation's maximum queue length will be used.

On unix-based based systems the following system exceptions may be raised if the call to listen fails:

- Errno::EBADF - the socket argument is not a valid file descriptor

- Errno::EDESTADDRREQ - the socket is not bound to a local address, and the protocol does not support listening on an unbound socket

- Errno::EINVAL - the socket is already connected

- Errno::ENOTSOCK - the socket argument does not refer to a socket

- Errno::EOPNOTSUPP - the socket protocol does not support listen

- Errno::EACCES - the calling process does not have appropriate privileges

- Errno::EINVAL - the socket has been shut down

- Errno::ENOBUFS - insufficient resources are available in the system to complete the call

### Windows Exceptions¶ ↑

On Windows systems the following system exceptions may be raised if the call to listen fails:

- Errno::ENETDOWN - the network is down

- Errno::EADDRINUSE - the socket's local address is already in use. This usually occurs during the execution of bind but could be delayed if the call to bind was to a partially wildcard address (involving ADDR_ANY) and if a specific address needs to be committed at the time of the call to listen

- Errno::EINPROGRESS - a Windows Sockets 1.1 call is in progress or the service provider is still processing a callback function

- Errno::EINVAL - the `socket` has not been bound with a call to bind.

- Errno::EISCONN - the `socket` is already connected

- Errno::EMFILE - no more socket descriptors are available

- Errno::ENOBUFS - no buffer space is available

- Errno::ENOTSOC - `socket` is not a socket

- Errno::EOPNOTSUPP - the referenced `socket` is not a type that supports the listen method

### See¶ ↑

- listen manual pages on unix-based systems

- listen function in Microsoft's Winsock functions reference

    VALUE
    rsock_sock_listen(VALUE sock, VALUE log)
    {
        rb_io_t *fptr;
        int backlog;

        backlog = NUM2INT(log);
        GetOpenFile(sock, fptr);
        if (listen(fptr->fd, backlog) < 0)
    	rb_sys_fail("listen(2)");

        return INT2FIX(0);
    }

sysaccept → file_descriptor click to toggle source

Returns a file descriptor of a accepted connection.

    TCPServer.open("127.0.0.1", 28561) {|serv|
      fd = serv.sysaccept
      s = IO.for_fd(fd)
      s.puts Time.now
      s.close
    }

    static VALUE
    tcp_sysaccept(VALUE sock)
    {
        rb_io_t *fptr;
        union_sockaddr from;
        socklen_t fromlen;

        GetOpenFile(sock, fptr);
        fromlen = (socklen_t)sizeof(from);
        return rsock_s_accept(0, fptr->fd, &from.addr, &fromlen);
    }