docs » hs.socket.udp

Talk to custom protocols using asynchronous UDP sockets.

For TCP sockets see hs.socket.

You can do a lot of neat trivial and non-trivial things with these. A simple ping ponger:

function ping(data, addr)
  print(data)
  addr = hs.socket.parseAddress(addr)
  hs.timer.doAfter(1, function()
    client:send("ping", addr.host, addr.port)
  end)
end

function pong(data, addr)
  print(data)
  addr = hs.socket.parseAddress(addr)
  hs.timer.doAfter(1, function()
    server:send("pong", addr.host, addr.port)
  end)
end

server = hs.socket.udp.server(9001, pong):receive()
client = hs.socket.udp.new(ping):send("ping", "localhost", 9001):receive()

Resulting in the following endless exchange:

20:26:56    LuaSkin: (secondary thread): Data written to UDP socket
            LuaSkin: (secondary thread): Data read from UDP socket
ping
20:26:57    LuaSkin: (secondary thread): Data written to UDP socket
            LuaSkin: (secondary thread): Data read from UDP socket
pong
20:26:58    LuaSkin: (secondary thread): Data written to UDP socket
            LuaSkin: (secondary thread): Data read from UDP socket
ping
20:26:59    LuaSkin: (secondary thread): Data written to UDP socket
            LuaSkin: (secondary thread): Data read from UDP socket
pong
...

You can do some silly things with a callback factory and enabling broadcasting:

local function callbackMaker(name)
  local fun = function(data, addr)
    addr = hs.socket.parseAddress(addr)
    print(name.." received data:\n"..data.."\nfrom host: "..addr.host.." port: "..addr.port)
  end
  return fun
end

local listeners = {}
local port = 9001

for i=1,3 do
  table.insert(listeners, hs.socket.udp.new(callbackMaker("listener "..i)):reusePort():listen(port):receive())
end

broadcaster = hs.socket.udp.new():broadcast()
broadcaster:send("hello!", "255.255.255.255", port)

Since neither IPv4 nor IPv6 have been disabled, the broadcast is received on both protocols ('dual-stack' IPv6 addresses shown):

listener 2 received data:
hello!
from host: ::ffff:192.168.0.3 port: 53057
listener 1 received data:
hello!
from host: ::ffff:192.168.0.3 port: 53057
listener 3 received data:
hello!
from host: ::ffff:192.168.0.3 port: 53057
listener 1 received data:
hello!
from host: 192.168.0.3 port: 53057
listener 3 received data:
hello!
from host: 192.168.0.3 port: 53057
listener 2 received data:
hello!
from host: 192.168.0.3 port: 53057

API Overview

Variables - Configurable values

timeout

Functions - API calls offered directly by the extension

parseAddress

Constructors - API calls which return an object, typically one that offers API methods

new
server

Methods - API calls which can only be made on an object returned by a constructor

broadcast
close
closed
connect
connected
enableIPv
info
listen
pause
preferIPv
read
readOne
receive
receiveOne
reusePort
send
setBufferSize
setCallback
setTimeout
write

API Documentation

Variables

timeout

Signature	`hs.socket.udp.timeout`
Type	Variable
Description	Timeout for the socket operations, in seconds.
Notes	New `hs.socket.udp` objects will be created with this timeout value, but can individually change it with the `hs.socket.udp:setTimeout` method. If the timeout value is negative, the operations will not use a timeout. The default value is `-1`.
Source	extensions/socket/socket.lua line 173

Functions

parseAddress

Signature	`hs.socket.udp.parseAddress(sockaddr) -> table or nil`
Type	Function
Description	Alias for `hs.socket.parseAddress`
Parameters
Returns
Source	extensions/socket/socket.lua line 184

Constructors

new

Signature	`hs.socket.udp.new([fn]) -> hs.socket.udp object`
Type	Constructor
Description	Creates an unconnected asynchronous UDP socket object.
Parameters	`fn` - An optional callback function for reading data from the socket, settable here for convenience.
Returns	An `hs.socket.udp` object.
Source	extensions/socket/libsocket_udp.m line 111

server

Signature	`hs.socket.udp.server(port[, fn]) -> hs.socket.udp object`
Type	Constructor
Description	Creates a UDP socket, and binds it to a port for listening.
Parameters	`port` - A port number [0-65535]. Ports [1-1023] are privileged. Port 0 allows the OS to select any available port. `fn` - An optional callback function for reading data from the socket, settable here for convenience.
Returns	An `hs.socket.udp` object.
Source	extensions/socket/socket.lua line 208

Methods

broadcast

Signature	`hs.socket.udp:broadcast([flag]) -> self or nil`
Type	Method
Description	Enables broadcasting on the underlying socket.
Parameters	`flag` - An optional boolean: `true` to enable broadcasting, `false` to disable it. Defaults to `true`.
Returns	The `hs.socket.udp` object, or `nil` if an error occurred.
Notes	By default, the underlying socket in the OS will not allow you to send broadcast messages. In order to send broadcast messages, you need to enable this functionality in the socket. A broadcast is a UDP message to addresses like "192.168.255.255" or "255.255.255.255" that is delivered to every host on the network. The reason this is generally disabled by default (by the OS) is to prevent accidental broadcast messages from flooding the network.
Source	extensions/socket/libsocket_udp.m line 418

close

Signature	`hs.socket.udp:close() -> self`
Type	Method
Description	Immediately closes the socket, freeing it for reuse. Any pending send operations are discarded.
Parameters	None
Returns	The `hs.socket.udp` object.
Source	extensions/socket/libsocket_udp.m line 222

closed

Signature	`hs.socket.udp:closed() -> bool`
Type	Method
Description	Returns the closed status of the socket.
Parameters	None
Returns	`true` if the socket is closed, otherwise `false`.
Notes	UDP sockets are typically meant to be connectionless. Sending a packet anywhere, regardless of whether or not the destination receives it, opens the socket until it is explicitly closed. An active listening socket will not be closed, but will not be 'connected' unless the `hs.socket.udp:connect` method has been called.
Source	extensions/socket/libsocket_udp.m line 675

connect

Signature	`hs.socket.udp:connect(host, port[, fn]) -> self or nil`
Type	Method
Description	Connects an unconnected socket.
Parameters	`host` - A string containing the hostname or IP address. `port` - A port number [1-65535]. `fn` - An optional single-use callback function to execute after establishing the connection. The callback receives no parameters.
Returns	The `hs.socket.udp` object, or `nil` if an error occurred.
Notes	By design, UDP is a connectionless protocol, and connecting is not needed. Choosing to connect to a specific host/port has the following effect: You will only be able to send data to the connected host/port; You will only be able to receive data from the connected host/port; You will receive ICMP messages that come from the connected host/port, such as "connection refused". The actual process of connecting a UDP socket does not result in any communication on the socket, it simply changes the internal state of the socket. You cannot bind a socket for listening after it has been connected. You can only connect a socket once.
Source	extensions/socket/libsocket_udp.m line 145

connected

Signature	`hs.socket.udp:connected() -> bool`
Type	Method
Description	Returns the connection status of the socket.
Parameters	None
Returns	`true` if connected, otherwise `false`.
Notes	UDP sockets are typically meant to be connectionless. This method will only return `true` if the `hs.socket.udp:connect` method has been explicitly called.
Source	extensions/socket/libsocket_udp.m line 652

enableIPv

Signature	`hs.socket.udp:enableIPv(version[, flag]) -> self or nil`
Type	Method
Description	Enables or disables IPv4 or IPv6 on the underlying socket. By default, both are enabled.
Parameters	`version` - A number containing the IP version (4 or 6) to enable or disable. `flag` - A boolean: `true` to enable the chosen IP version, `false` to disable it. Defaults to `true`.
Returns	The `hs.socket.udp` object, or `nil` if an error occurred.
Notes	Must be called before binding the socket. If you want to create an IPv6-only server, do something like: `hs.socket.udp.new(callback):enableIPv(4, false):listen(port):receive()` The convenience constructor `hs.socket.server` will automatically bind the socket and requires closing and relistening to use this method.
Source	extensions/socket/libsocket_udp.m line 486

info

Signature	`hs.socket.udp:info() -> table`
Type	Method
Description	Returns information about the socket.
Parameters	None
Returns	A table containing the following keys: connectedAddress - `string` (`sockaddr` struct) connectedHost - `string` connectedPort - `number` isClosed - `boolean` isConnected - `boolean` isIPv4 - `boolean` isIPv4Enabled - `boolean` isIPv4Preferred - `boolean` isIPv6 - `boolean` isIPv6Enabled - `boolean` isIPv6Preferred - `boolean` isIPVersionNeutral - `boolean` localAddress - `string` (`sockaddr` struct) localAddress_IPv4 - `string` (`sockaddr` struct) localAddress_IPv6 - `string` (`sockaddr` struct) localHost - `string` localHost_IPv4 - `string` localHost_IPv6 - `string` localPort - `number` localPort_IPv4 - `number` localPort_IPv6 - `number` maxReceiveIPv4BufferSize - `number` maxReceiveIPv6BufferSize - `number` timeout - `number` userData - `string`
Source	extensions/socket/libsocket_udp.m line 699

listen

Signature	`hs.socket.udp:listen(port) -> self or nil`
Type	Method
Description	Binds an unconnected socket to a port for listening.
Parameters	`port` - A port number [0-65535]. Ports [1-1023] are privileged. Port 0 allows the OS to select any available port.
Returns	The `hs.socket.udp` object, or `nil` if an error occurred.
Source	extensions/socket/libsocket_udp.m line 192

pause

Signature	`hs.socket.udp:pause() -> self`
Type	Method
Description	Suspends reading of packets from the socket.
Parameters	None
Returns	The `hs.socket.udp` object
Notes	Call one of the receive methods to resume.
Source	extensions/socket/libsocket_udp.m line 243

preferIPv

Signature	`hs.socket.udp:preferIPv([version]) -> self`
Type	Method
Description	Sets the preferred IP version: IPv4, IPv6, or neutral (first to resolve).
Parameters	`version` - An optional number containing the IP version to prefer. Anything but 4 or 6 else sets the default neutral behavior.
Returns	The `hs.socket.udp` object.
Notes	If a DNS lookup returns only IPv4 results, the socket will automatically use IPv4. If a DNS lookup returns only IPv6 results, the socket will automatically use IPv6. If a DNS lookup returns both IPv4 and IPv6 results, then the protocol used depends on the configured preference.
Source	extensions/socket/libsocket_udp.m line 523

read

Signature	`hs.socket.udp:read(delimiter[, tag]) -> self`
Type	Method
Description	Alias for `hs.socket.udp:receive`
Parameters
Returns
Source	extensions/socket/socket.lua line 237

readOne

Signature	`hs.socket.udp:readOne(delimiter[, tag]) -> self`
Type	Method
Description	Alias for `hs.socket.udp:receiveOne`
Parameters
Returns
Source	extensions/socket/socket.lua line 243

receive

Signature	`hs.socket.udp:receive([fn]) -> self or nil`
Type	Method
Description	Reads packets from the socket as they arrive.
Parameters	`fn` - Optionally supply the read callback here.
Returns	The `hs.socket.udp` object, or `nil` if an error occurred.
Notes	Results are passed to the callback function, which must be set to use this method. There are two modes of operation for receiving packets: one-at-a-time & continuous. In one-at-a-time mode, you call receiveOne every time you are ready process an incoming UDP packet. Receiving packets one-at-a-time may be better suited for implementing certain state machine code where your state machine may not always be ready to process incoming packets. In continuous mode, the callback is invoked immediately every time incoming udp packets are received. Receiving packets continuously is better suited to real-time streaming applications. You may switch back and forth between one-at-a-time mode and continuous mode. If the socket is currently in one-at-a-time mode, calling this method will switch it to continuous mode.
Source	extensions/socket/libsocket_udp.m line 295

receiveOne

Signature	`hs.socket.udp:receiveOne([fn]) -> self or nil`
Type	Method
Description	Reads a single packet from the socket.
Parameters	`fn` - Optionally supply the read callback here.
Returns	The `hs.socket.udp` object, or `nil` if an error occurred.
Notes	Results are passed to the callback function, which must be set to use this method. There are two modes of operation for receiving packets: one-at-a-time & continuous. In one-at-a-time mode, you call receiveOne every time you are ready process an incoming UDP packet. Receiving packets one-at-a-time may be better suited for implementing certain state machine code where your state machine may not always be ready to process incoming packets. In continuous mode, the callback is invoked immediately every time incoming udp packets are received. Receiving packets continuously is better suited to real-time streaming applications. You may switch back and forth between one-at-a-time mode and continuous mode. If the socket is currently in continuous mode, calling this method will switch it to one-at-a-time mode
Source	extensions/socket/libsocket_udp.m line 321

reusePort

Signature	`hs.socket.udp:reusePort([flag]) -> self or nil`
Type	Method
Description	Enables port reuse on the socket.
Parameters	`flag` - An optional boolean: `true` to enable port reuse, `false` to disable it. Defaults to `true`.
Returns	The `hs.socket.udp` object, or `nil` if an error occurred.
Notes	By default, only one socket can be bound to a given IP address & port at a time. To enable multiple processes to simultaneously bind to the same address & port, you need to enable this functionality in the socket. All processes that wish to use the address & port simultaneously must all enable reuse port on the socket bound to that port. Must be called before binding the socket.
Source	extensions/socket/libsocket_udp.m line 452

send

Signature	`hs.socket.udp:send(message[, host, port][, tag, fn]) -> self`
Type	Method
Description	Sends a packet to the destination address.
Parameters	`message` - A string containing data to be sent on the socket. `host` - A string containing the hostname or IP address. `port` - A port number [1-65535]. `tag` - An optional integer to assist with labeling writes. `fn` - An optional single-use callback function to execute after sending the packet. The callback receives the tag parameter provided here.
Returns	The `hs.socket.udp` object.
Notes	For non-connected sockets, the remote destination is specified for each packet. If the socket has been explicitly connected with `connect`, only the message parameter and an optional tag and/or write callback can be supplied. Recall that connecting is optional for a UDP socket. For connected sockets, data can only be sent to the connected address.
Source	extensions/socket/libsocket_udp.m line 347

setBufferSize

Signature	`hs.socket.udp:setBufferSize(size[, version]) -> self`
Type	Method
Description	Sets the maximum size of the buffer that will be allocated for receive operations.
Parameters	`size` - An number containing the receive buffer size in bytes. `version` - An optional number containing the IP version for which to set the buffer size. Anything but 4 or 6 else sets the same size for both.
Returns	The `hs.socket.udp` object.
Notes	The default maximum size is 9216 bytes. The theoretical maximum size of any IPv4 UDP packet is `UINT16_MAX = 65535`. The theoretical maximum size of any IPv6 UDP packet is `UINT32_MAX = 4294967295`. Since the OS notifies us of the size of each received UDP packet, the actual allocated buffer size for each packet is exact. In practice the size of UDP packets is generally much smaller than the max. Most protocols will send and receive packets of only a few bytes, or will set a limit on the size of packets to prevent fragmentation in the IP layer. If you set the buffer size too small, the sockets API in the OS will silently discard any extra data.
Source	extensions/socket/libsocket_udp.m line 555

setCallback

Signature	`hs.socket.udp:setCallback([fn]) -> self`
Type	Method
Description	Sets the read callback for the socket.
Parameters	`fn` - An optional callback function to process data read from the socket. `nil` or no argument clears the callback. The callback receives 2 parameters: `data` - The data read from the socket as a string. `sockaddr` - The sending address as a binary socket address structure. See `parseAddress`.
Returns	The `hs.socket.udp` object.
Notes	A callback must be set in order to read data from the socket.
Source	extensions/socket/libsocket_udp.m line 597

setTimeout

Signature	`hs.socket.udp:setTimeout(timeout) -> self`
Type	Method
Description	Sets the timeout for the socket operations.
Parameters	`timeout` - A number containing the timeout duration, in seconds.
Returns	The `hs.socket.udp` object.
Notes	If the timeout value is negative, the operations will not use a timeout, which is the default.
Source	extensions/socket/libsocket_udp.m line 628

write

Signature	`hs.socket.udp:write(message[, tag]) -> self`
Type	Method
Description	Alias for `hs.socket.udp:send`
Parameters
Returns
Source	extensions/socket/socket.lua line 249