class SF::UdpSocket

• SF::UdpSocket
• SF::Socket
• Reference
• Object

Overview

Specialized socket using the UDP protocol

A UDP socket is a connectionless socket. Instead of connecting once to a remote host, like TCP sockets, it can send to and receive from any host at any time.

It is a datagram protocol: bounded blocks of data (datagrams) are transfered over the network rather than a continuous stream of data (TCP). Therefore, one call to send will always match one call to receive (if the datagram is not lost), with the same data that was sent.

The UDP protocol is lightweight but unreliable. Unreliable means that datagrams may be duplicated, be lost or arrive reordered. However, if a datagram arrives, its data is guaranteed to be valid.

UDP is generally used for real-time communication (audio or video streaming, real-time games, etc.) where speed is crucial and lost data doesn't matter much.

Sending and receiving data can use either the low-level or the high-level functions. The low-level functions process a raw sequence of bytes, whereas the high-level interface uses packets (see SF::Packet), which are easier to use and provide more safety regarding the data that is exchanged. You can look at the SF::Packet class to get more details about how they work.

It is important to note that UdpSocket is unable to send datagrams bigger than MaxDatagramSize. In this case, it returns an error and doesn't send anything. This applies to both raw data and packets. Indeed, even packets are unable to split and recompose data, due to the unreliability of the protocol (dropped, mixed or duplicated datagrams may lead to a big mess when trying to recompose a packet).

If the socket is bound to a port, it is automatically unbound from it when the socket is destroyed. However, you can unbind the socket explicitly with the Unbind function if necessary, to stop receiving messages or make the port available for other sockets.

Usage example:

# ----- The client -----

# Create a socket and bind it to the port 55001
socket = SF::UdpSocket.new
socket.bind(55001)

# Send a message to 192.168.1.50 on port 55002
message = "Hi, I am #{SF::IpAddress.local_address}"
socket.send(message.to_slice, "192.168.1.50", 55002)

# Receive an answer (most likely from 192.168.1.50, but could be anyone else)
buffer = Slice(UInt8).new(1024)
status, received, sender, port = socket.receive(buffer)
puts "#{sender} said: #{buffer}"

# ----- The server -----

# Create a socket and bind it to the port 55002
socket = SF::UdpSocket.new
socket.bind(55002)

# Receive a message from anyone
buffer = Slice(UInt8).new(1024)
status, received, sender, port = socket.receive(buffer)
puts "#{sender} said: #{buffer}"

# Send an answer
message = "Welcome #{sender}"
socket.send(message.to_slice, sender, port)

See also: SF::Socket, SF::TcpSocket, SF::Packet

Defined in:

network/obj.cr

Constant Summary

MaxDatagramSize = 65507

The maximum number of bytes that can be sent in a single UDP datagram

Constructors

• .new

  Default constructor

Instance Method Summary

• #bind(port : Int, address : IpAddress = IpAddress::Any) : Socket::Status

  Bind the socket to a specific port

• #finalize

  Destructor

• #local_port : UInt16

  Get the port to which the socket is bound locally

• #receive(data : Slice) : Tuple(Socket::Status, Int32, IpAddress, UInt16)

  Receive raw data from a remote peer

• #receive(packet : Packet) : Tuple(Socket::Status, IpAddress, UInt16)

  Receive a formatted packet of data from a remote peer

• #send(data : Slice, remote_address : IpAddress, remote_port : Int) : Socket::Status

  Send raw data to a remote peer

• #send(packet : Packet, remote_address : IpAddress, remote_port : Int) : Socket::Status

  Send a formatted packet of data to a remote peer

• #unbind

  Unbind the socket from the local port to which it is bound

Constructor Detail

Instance Method Detail