# class TCPServer

- TCPServer
- TCPSocket
- IPSocket
- Socket
- IO
- Reference
- Object

##
Overview

A Transmission Control Protocol (TCP/IP) server.

NOTE To use `TCPServer`, you must explicitly import it with `require "socket"`

Usage example:

    require "socket"

    def handle_client(client)
      message = client.gets
      client.puts message
    end

    server = TCPServer.new("localhost", 1234)
    while client = server.accept?
      spawn handle_client(client)
    end

Options:

- host local interface to bind on, or `::` to bind on all local interfaces.
- port specific port to bind on, or `0` to receive an "ephemeral" (free, assigned by kernel) port.
- backlog to specify how many pending connections are allowed.
- reuse_port to enable multiple processes to bind to the same port (`SO_REUSEPORT`).

##
Included Modules

- Socket::Server

##
Defined in:

socket/tcp_server.cr

##
Constructors

- .new(host : String, port : Int, backlog : Int = SOMAXCONN, dns_timeout = nil, reuse_port : Bool = false)

  Binds a socket to the host and port combination.

- .new(family : Family = Family::INET)

  Creates a new `TCPServer`, waiting to be bound.

- .new(port : Int, backlog = SOMAXCONN, reuse_port = false)

  Creates a new TCP server, listening on all local interfaces (`::`).

- .new(*, fd : Handle, family : Family = Family::INET)

  Creates a TCPServer from an existing system file descriptor or socket handle.

##
Class Method Summary

- .open(port : Int, backlog = SOMAXCONN, reuse_port = false, &)

  Creates a new TCP server, listening on all interfaces, and yields it to the block.

- .open(host, port, backlog = SOMAXCONN, reuse_port = false, &)

  Creates a new TCP server and yields it to the block.

##
Instance Method Summary

- #accept? : TCPSocket | Nil

  Accepts an incoming connection.

### Instance methods inherited from module `Socket::Server`

accept : IO
accept(&) accept, accept? : IO | Nil
accept?(&) accept?

### Instance methods inherited from class `TCPSocket`

tcp_keepalive_count tcp_keepalive_count, tcp_keepalive_count=(val : Int) tcp_keepalive_count=, tcp_keepalive_idle tcp_keepalive_idle, tcp_keepalive_idle=(val : Int) tcp_keepalive_idle=, tcp_keepalive_interval tcp_keepalive_interval, tcp_keepalive_interval=(val : Int) tcp_keepalive_interval=, tcp_nodelay=(val : Bool) tcp_nodelay=, tcp_nodelay? : Bool tcp_nodelay?

### Constructor methods inherited from class `TCPSocket`

new(family : Family = Family::INET, blocking = nil)
new(host : String, port, dns_timeout = nil, connect_timeout = nil, blocking = nil)
new(*, fd : Handle, family : Family = Family::INET, blocking = nil) new

### Class methods inherited from class `TCPSocket`

open(host : String, port, &) open

### Instance methods inherited from class `IPSocket`

bind(addr) bind, close close, connect(addr, timeout = nil, &) connect, ipv6_only=(val : Bool) : Bool ipv6_only=, ipv6_only? : Bool ipv6_only?, local_address : Socket::IPAddress local_address, remote_address : Socket::IPAddress remote_address

### Instance methods inherited from class `Socket`

accept : Socket accept, accept? : Socket | Nil accept?, bind(host : String, port : Int) : Nil
bind(port : Int)
bind(addr : Socket::Address) : Nil bind, blocking blocking, blocking=(value) blocking=, broadcast=(val : Bool) broadcast=, broadcast? : Bool broadcast?, close_on_exec=(arg : Bool) close_on_exec=, close_on_exec? close_on_exec?, close_read close_read, close_write close_write, closed? : Bool closed?, connect(host : String, port : Int, connect_timeout = nil) : Nil
connect(addr, timeout = nil) : Nil
connect(addr, timeout = nil, &) connect, family : Family family, fcntl(cmd, arg = 0) fcntl, fd fd, finalize finalize, inspect(io : IO) : Nil inspect, keepalive=(val : Bool) keepalive=, keepalive? keepalive?, linger linger, linger=(val : Int | Nil) linger=, listen(backlog : Int = SOMAXCONN) : Nil
listen(backlog : Int = SOMAXCONN, &) listen, protocol : Protocol protocol, read_timeout : Time::Span | Nil read_timeout, read_timeout=(read_timeout : Time::Span | Nil)
read_timeout=(read_timeout : Number) : Number read_timeout=, receive(message : Bytes) : Tuple(Int32, Address)
receive(max_message_size = 512) : Tuple(String, Address) receive, recv_buffer_size : Int32 recv_buffer_size, recv_buffer_size=(val : Int32) recv_buffer_size=, reuse_address=(val : Bool) reuse_address=, reuse_address? : Bool reuse_address?, reuse_port=(val : Bool) reuse_port=, reuse_port? : Bool reuse_port?, send(message, to addr : Address) : Int32
send(message) : Int32 send, send_buffer_size : Int32 send_buffer_size, send_buffer_size=(val : Int32) send_buffer_size=, tty? tty?, type : Type type, write_timeout : Time::Span | Nil write_timeout, write_timeout=(write_timeout : Time::Span | Nil)
write_timeout=(write_timeout : Number) : Number write_timeout=

### Constructor methods inherited from class `Socket`

new(family : Family, type : Type, protocol : Protocol = Protocol::IP, blocking = nil)
new(fd, family : Family, type : Type, protocol : Protocol = Protocol::IP, blocking = nil) new, tcp(family : Family, blocking = nil) : self tcp, udp(family : Family, blocking = nil) : self udp, unix(type : Type = Type::STREAM, blocking = nil) : self unix

### Class methods inherited from class `Socket`

fcntl(fd, cmd, arg = 0) fcntl, get_blocking(fd : Handle) : Bool get_blocking, ip?(string : String) ip?, set_blocking(fd : Handle, value : Bool) set_blocking

### Instance methods inherited from module `Crystal::System::Socket`

__evloop_data : EventLoop::Polling::Arena::Index __evloop_data, __evloop_data=(__evloop_data : EventLoop::Polling::Arena::Index) __evloop_data=, close_volatile_fd? : Int32 | Nil close_volatile_fd?, socket_close(&)
socket_close socket_close

### Class methods inherited from module `Crystal::System::Socket`

fcntl(fd, cmd, arg = 0) fcntl, get_blocking(fd : Handle) get_blocking, set_blocking(fd : Handle, value : Bool) set_blocking, socket(family, type, protocol, blocking) : Handle socket, socketpair(type : ::Socket::Type, protocol : ::Socket::Protocol, blocking : Bool) : Tuple(Handle, Handle) socketpair

### Instance methods inherited from module `IO::Buffered`

buffer_size : Int32 buffer_size, buffer_size=(value) buffer_size=, close : Nil close, flush : self flush, flush_on_newline=(flush_on_newline : Bool) : Bool flush_on_newline=, flush_on_newline? : Bool flush_on_newline?, peek : Bytes peek, pos : Int64 pos, read(slice : Bytes) : Int32 read, read_buffering=(read_buffering : Bool) : Bool read_buffering=, read_buffering? : Bool read_buffering?, rewind : self rewind, sync=(sync : Bool) : Bool sync=, sync? : Bool sync?, unbuffered_close unbuffered_close, unbuffered_flush unbuffered_flush, unbuffered_read(slice : Bytes) unbuffered_read, unbuffered_rewind unbuffered_rewind, unbuffered_write(slice : Bytes) unbuffered_write, write(slice : Bytes) : Nil write

### Instance methods inherited from class `IO`

<<(obj : _) : self <<, close close, closed? : Bool closed?, each_byte(&) : Nil
each_byte each_byte, each_char(&) : Nil
each_char each_char, each_line(*args, **options, &block : String -> ) : Nil
each_line(*args, **options) each_line, encoding : String encoding, flush flush, getb_to_end : Bytes getb_to_end, gets(delimiter : Char, limit : Int, chomp = false) : String | Nil
gets(chomp : Bool = true) : String | Nil
gets(limit : Int, chomp : Bool = false) : String | Nil
gets(delimiter : Char, chomp : Bool = false) : String | Nil
gets(delimiter : String, chomp = false) : String | Nil gets, gets_to_end : String gets_to_end, peek : Bytes | Nil peek, pos pos, pos=(value) pos=, print(obj : _) : Nil
print(*objects : _) : Nil print, printf(format_string : String, args : Array | Tuple) : Nil
printf(format_string : String, *args) : Nil printf, puts(string : String) : Nil
puts(obj : _) : Nil
puts : Nil
puts(*objects : _) : Nil puts, read(slice : Bytes) read, read_at(offset, bytesize, & : IO -> ) read_at, read_byte : UInt8 | Nil read_byte, read_bytes(type, format : IO::ByteFormat = IO::ByteFormat::SystemEndian) read_bytes, read_char : Char | Nil read_char, read_fully(slice : Bytes) : Int32 read_fully, read_fully?(slice : Bytes) : Int32 | Nil read_fully?, read_line(*args, **options) : String read_line, read_string(bytesize : Int) : String read_string, read_utf8(slice : Bytes) : Int32 read_utf8, read_utf8_byte : UInt8 | Nil read_utf8_byte, rewind rewind, seek(offset, whence : Seek = Seek::Set) seek, set_encoding(encoding : String, invalid : Symbol | Nil = nil) : Nil set_encoding, skip(bytes_count : Int) : Nil skip, skip_to_end : Nil skip_to_end, tell tell, tty? : Bool tty?, write(slice : Bytes) : Nil write, write_byte(byte : UInt8) : Nil write_byte, write_bytes(object : _, format : IO::ByteFormat = IO::ByteFormat::SystemEndian) : Nil write_bytes, write_string(slice : Bytes) : Nil write_string, write_utf8(slice : Bytes) : Nil write_utf8

### Class methods inherited from class `IO`

copy(src : IO, dst : IO, limit : Int) : Int64
copy(src : IO, dst : IO) : Int64 copy, pipe(read_blocking : Bool | Nil = nil, write_blocking : Bool | Nil = nil) : Tuple(IO::FileDescriptor, IO::FileDescriptor)
pipe(read_blocking = nil, write_blocking = nil, &) pipe, same_content?(stream1 : IO, stream2 : IO) : Bool same_content?

### Instance methods inherited from class `Reference`

==(other : self)
==(other : JSON::Any)
==(other : YAML::Any)
==(other) ==, dup dup, hash(hasher) hash, initialize initialize, inspect(io : IO) : Nil inspect, object_id : UInt64 object_id, pretty_print(pp) : Nil pretty_print, same?(other : Reference) : Bool
same?(other : Nil) same?, to_s(io : IO) : Nil to_s

### Constructor methods inherited from class `Reference`

new new, unsafe_construct(address : Pointer, *args, **opts) : self unsafe_construct

### Class methods inherited from class `Reference`

pre_initialize(address : Pointer) pre_initialize

### Instance methods inherited from class `Object`

! : Bool !, !=(other) !=, !~(other) !~, ==(other) ==, ===(other : JSON::Any)
===(other : YAML::Any)
===(other) ===, =~(other) =~, as(type : Class) as, as?(type : Class) as?, class class, dup dup, hash(hasher)
hash hash, in?(collection : Object) : Bool
in?(*values : Object) : Bool in?, inspect(io : IO) : Nil
inspect : String inspect, is_a?(type : Class) : Bool is_a?, itself itself, nil? : Bool nil?, not_nil!(message)
not_nil! not_nil!, pretty_inspect(width = 79, newline = "\n", indent = 0) : String pretty_inspect, pretty_print(pp : PrettyPrint) : Nil pretty_print, responds_to?(name : Symbol) : Bool responds_to?, tap(&) tap, to_json(io : IO) : Nil
to_json : String to_json, to_pretty_json(indent : String = " ") : String
to_pretty_json(io : IO, indent : String = " ") : Nil to_pretty_json, to_s(io : IO) : Nil
to_s : String to_s, to_yaml(io : IO) : Nil
to_yaml : String to_yaml, try(&) try, unsafe_as(type : T.class) forall T unsafe_as

### Class methods inherited from class `Object`

from_json(string_or_io : String | IO, root : String)
from_json(string_or_io : String | IO) from_json, from_yaml(string_or_io : String | IO) from_yaml

### Macros inherited from class `Object`

class_getter(*names, &block) class_getter, class_getter!(*names) class_getter!, class_getter?(*names, &block) class_getter?, class_property(*names, &block) class_property, class_property!(*names) class_property!, class_property?(*names, &block) class_property?, class_setter(*names) class_setter, def_clone def_clone, def_equals(*fields) def_equals, def_equals_and_hash(*fields) def_equals_and_hash, def_hash(*fields) def_hash, delegate(*methods, to object) delegate, forward_missing_to(delegate) forward_missing_to, getter(*names, &block) getter, getter!(*names) getter!, getter?(*names, &block) getter?, property(*names, &block) property, property!(*names) property!, property?(*names, &block) property?, setter(*names) setter

##
Constructor Detail

def self.new(host : String, port : Int, backlog : Int = SOMAXCONN, dns_timeout = nil, reuse_port : Bool = false) #

Binds a socket to the host and port combination.

def self.new(family : Family = Family::INET) #

Creates a new `TCPServer`, waiting to be bound.

def self.new(port : Int, backlog = SOMAXCONN, reuse_port = false) #

Creates a new TCP server, listening on all local interfaces (`::`).

def self.new(*, fd : Handle, family : Family = Family::INET) #

Creates a TCPServer from an existing system file descriptor or socket handle.

This adopts fd into the IO system that will reconfigure it as per the event loop runtime requirements.

NOTE On Windows, the handle must have been created with `WSA_FLAG_OVERLAPPED`.

##
Class Method Detail

def self.open(port : Int, backlog = SOMAXCONN, reuse_port = false, &) #

Creates a new TCP server, listening on all interfaces, and yields it to the block. Eventually closes the server socket when the block returns.

Returns the value of the block.

def self.open(host, port, backlog = SOMAXCONN, reuse_port = false, &) #

Creates a new TCP server and yields it to the block. Eventually closes the server socket when the block returns.

Returns the value of the block.

##
Instance Method Detail

def accept? : TCPSocket | Nil #

Accepts an incoming connection.

Returns the client `TCPSocket` or `nil` if the server is closed after invoking this method.

    require "socket"

    server = TCPServer.new(2022)
    loop do
      if socket = server.accept?
        # handle the client in a fiber
        spawn handle_connection(socket)
      else
        # another fiber closed the server
        break
      end
    end