# class UDPSocket

- UDPSocket
- IPSocket
- Socket
- IO
- Reference
- Object

##
Overview

A User Datagram Protocol (UDP) socket.

UDP runs on top of the Internet Protocol (IP) and was developed for applications that do not require reliability, acknowledgement, or flow control features at the transport layer. This simple protocol provides transport layer addressing in the form of UDP ports and an optional checksum capability.

UDP is a very simple protocol. Messages, so called datagrams, are sent to other hosts on an IP network without the need to set up special transmission channels or data paths beforehand. The UDP socket only needs to be opened for communication. It listens for incoming messages and sends outgoing messages on request.

This implementation supports both IPv4 and IPv6 addresses. For IPv4 addresses you must use `Socket::Family::INET` family (default) or `Socket::Family::INET6` for IPv6 # addresses.

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

Usage example:

    require "socket"

    # Create server
    server = UDPSocket.new
    server.bind "localhost", 1234

    # Create client and connect to server
    client = UDPSocket.new
    client.connect "localhost", 1234

    # Send a text message to server
    client.send "message"

    # Receive text message from client
    message, client_addr = server.receive

    # Close client and server
    client.close
    server.close

The `send` methods may sporadically fail with `Socket::ConnectError` when sending datagrams to a non-listening server. Wrap with an exception handler to prevent raising. Example:

    begin
      client.send(message, @destination)
    rescue ex : Socket::ConnectError
      p ex.inspect
    end

##
Defined in:

socket/udp_socket.cr

##
Constructors

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

##
Instance Method Summary

- #join_group(address : IPAddress)

  A host must become a member of a multicast group before it can receive datagrams sent to the group.

- #leave_group(address : IPAddress)

  Drops membership to the specified group.

- #multicast_hops : Int32

  Returns the current value of the `hoplimit` field on uni-cast packets.

- #multicast_hops=(val : Int)

  The multicast hops option controls the `hoplimit` field on uni-cast packets.

- #multicast_interface(address : IPAddress)

  For hosts with multiple interfaces, each multicast transmission is sent from the primary network interface.

- #multicast_interface(index : UInt32)

  For hosts with multiple interfaces, each multicast transmission is sent from the primary network interface.

- #multicast_loopback=(val : Bool)

  Sets whether transmitted multicast packets should be copied and sent back to the originator, if the host has joined the multicast group.

- #multicast_loopback? : Bool

  Reports whether transmitted multicast packets should be copied and sent back to the originator.

- #receive(message : Bytes) : Tuple(Int32, IPAddress)

  Receives a binary message from the previously bound address.

- #receive(max_message_size = 512) : Tuple(String, IPAddress)

  Receives a text message from the previously bound address.

### Instance methods inherited from class `IPSocket`

bind(addr) bind, close close, connect(addr, timeout = nil, &) connect, 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, 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

### Constructor methods inherited from class `Socket`

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

### Class methods inherited from class `Socket`

fcntl(fd, cmd, arg = 0) fcntl, ip?(string : String) ip?, udp(family : Family, blocking = false) udp

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

fcntl(fd, cmd, arg = 0) fcntl

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

evented_close : Nil evented_close, evented_read(slice : Bytes, errno_msg : String, &) : Int32 evented_read, evented_reopen : Nil evented_reopen, evented_send(slice : Bytes, errno_msg : String, &) : Int32 evented_send, evented_write(slice : Bytes, errno_msg : String, &) : Nil evented_write, read_timeout : Time::Span | Nil read_timeout, read_timeout=(read_timeout : Number) : Number
read_timeout=(timeout : Time::Span | Nil) : Time::Span | Nil read_timeout=, write_timeout : Time::Span | Nil write_timeout, write_timeout=(write_timeout : Number) : Number
write_timeout=(timeout : Time::Span | Nil) : Time::Span | Nil write_timeout=

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

buffer_size : Int32 buffer_size, buffer_size=(value) buffer_size=, close : Nil close, flush flush, flush_on_newline=(flush_on_newline) 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) read_buffering=, read_buffering? : Bool read_buffering?, rewind rewind, sync=(sync) 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(limit : Int, chomp = false) : String | Nil
gets(delimiter : Char, limit : Int, chomp = false) : String | Nil
gets(delimiter : Char, chomp = false) : String | Nil
gets(delimiter : String, chomp = false) : String | Nil
gets(chomp = true) : 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, args : Array | Tuple) : Nil
printf(format_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) 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, dst, limit : Int) : Int64
copy(src, dst) : Int64 copy, pipe(read_blocking = false, write_blocking = false) : Tuple(IO::FileDescriptor, IO::FileDescriptor)
pipe(read_blocking = false, write_blocking = false, &) 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, root : String)
from_json(string_or_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(family : Family = Family::INET) #

##
Instance Method Detail

def join_group(address : IPAddress) #

A host must become a member of a multicast group before it can receive datagrams sent to the group. Raises `Socket::Error` if an incompatible address is provided.

def leave_group(address : IPAddress) #

Drops membership to the specified group. Memberships are automatically dropped when the socket is closed or the process exits. Raises `Socket::Error` if an incompatible address is provided.

def multicast_hops : Int32 #

Returns the current value of the `hoplimit` field on uni-cast packets. Datagrams with a `hoplimit` of `1` are not forwarded beyond the local network. Multicast datagrams with a `hoplimit` of `0` will not be transmitted on any network, but may be delivered locally if the sending host belongs to the destination group and multicast loopback is enabled.

def multicast_hops=(val : Int) #

The multicast hops option controls the `hoplimit` field on uni-cast packets. If `-1` is specified, the kernel will use a default value. If a value of `0` to `255` is specified, the packet will have the specified value as `hoplimit`. Other values are considered invalid and `Socket::Error` will be raised. Datagrams with a `hoplimit` of `1` are not forwarded beyond the local network. Multicast datagrams with a `hoplimit` of `0` will not be transmitted on any network, but may be delivered locally if the sending host belongs to the destination group and multicast loopback is enabled.

def multicast_interface(address : IPAddress) #

For hosts with multiple interfaces, each multicast transmission is sent from the primary network interface. This function overrides the default IPv4 interface address for subsequent transmissions. Setting the interface to `0.0.0.0` will select the default interface. Raises `Socket::Error` unless the socket is IPv4 and an IPv4 address is provided.

def multicast_interface(index : UInt32) #

For hosts with multiple interfaces, each multicast transmission is sent from the primary network interface. This function overrides the default IPv6 interface for subsequent transmissions. Setting the interface to index `0` will select the default interface.

def multicast_loopback=(val : Bool) #

Sets whether transmitted multicast packets should be copied and sent back to the originator, if the host has joined the multicast group.

def multicast_loopback? : Bool #

Reports whether transmitted multicast packets should be copied and sent back to the originator.

def receive(message : Bytes) : Tuple(Int32, IPAddress) #

Receives a binary message from the previously bound address.

    require "socket"

    server = UDPSocket.new
    server.bind "localhost", 1234

    message = Bytes.new(32)
    bytes_read, client_addr = server.receive(message)

def receive(max_message_size = 512) : Tuple(String, IPAddress) #

Receives a text message from the previously bound address.

    require "socket"

    server = UDPSocket.new
    server.bind("localhost", 1234)

    message, client_addr = server.receive