socket

require "builtins.scripts.socket"

The function returns a list with the sockets ready for reading, a list with the sockets ready for writing and an error message. The error message is "timeout" if a timeout condition was met and nil otherwise. The returned tables are doubly keyed both by integers and also by the sockets themselves, to simplify the test if a specific socket has changed status. Recvt and sendt parameters can be empty tables or nil. Non-socket values (or values with non-numeric indices) in these arrays will be silently ignored. The returned tables are doubly keyed both by integers and also by the sockets themselves, to simplify the test if a specific socket has changed status. This function can monitor a limited number of sockets, as defined by the constant socket._SETSIZE. This number may be as high as 1024 or as low as 64 by default, depending on the system. It is usually possible to change this at compile time. Invoking select with a larger number of sockets will raise an error. A known bug in WinSock causes select to fail on non-blocking TCP sockets. The function may return a socket as writable even though the socket is not ready for sending. Calling select with a server socket in the receive parameter before a call to accept does not guarantee accept will return immediately. Use the settimeout method or accept might block forever. If you close a socket and pass it to select, it will be ignored. (Using select with non-socket objects: Any object that implements getfd and dirty can be used with select, allowing objects from other libraries to be used within a socket.select driven loop.)

Parameters

• recvt: Record<string | number, unknown> — array with the sockets to test for characters available for reading.
• sendt: Record<string | number, unknown> — array with sockets that are watched to see if it is OK to immediately write on them.
• timeout?: number — the maximum amount of time (in seconds) to wait for a change in status. Nil, negative or omitted timeout value allows the function to block indefinitely.

Returns

• sockets_r: Record<string | number, unknown> — a list with the sockets ready for reading.
• sockets_w: Record<string | number, unknown> — a list with the sockets ready for writing.
• error: string | nil — an error message. "timeout" if a timeout condition was met, otherwise nil.

Creates and returns an IPv6 TCP master object. A master object can be transformed into a server object with the method listen (after a call to bind) or into a client object with the method connect. The only other method supported by a master object is the close method. Note: The TCP object returned will have the option "ipv6-v6only" set to true.

Returns

• tcp_master: master | nil — a new IPv6 TCP master object, or nil in case of error.
• error: string | nil — the error message, or nil if no error occurred.

Creates and returns an unconnected IPv6 UDP object. Unconnected objects support the sendto, receive, receivefrom, getoption, getsockname, setoption, settimeout, setpeername, setsockname, and close methods. The setpeername method is used to connect the object. Note: The UDP object returned will have the option "ipv6-v6only" set to true.

Returns

• udp_unconnected: unconnected | nil — a new unconnected IPv6 UDP object, or nil in case of error.
• error: string | nil — the error message, or nil if no error occurred.

This function converts from an IPv4 address to host name. The address can be an IPv4 address or a host name.

Parameters

• address: string — an IPv4 address or host name.

Returns

• hostname: string | nil — the canonic host name of the given address, or nil in case of an error.
• resolved: Record<string | number, unknown> | string — a table with all information returned by the resolver, or if an error occurs, the error message string.

This function converts a host name to IPv4 address. The address can be an IP address or a host name.

Parameters

• address: string — a hostname or an IP address.

Returns

• ip_address: string | nil — the first IP address found for the hostname, or nil in case of an error.
• resolved: Record<string | number, unknown> | string — a table with all information returned by the resolver, or if an error occurs, the error message string.

Returns the standard host name for the machine as a string.

Returns

• hostname: string — the host name for the machine.

This function converts a host name to IPv4 or IPv6 address. The supplied address can be an IPv4 or IPv6 address or host name. The function returns a table with all information returned by the resolver:

{ [1] = { family = family-name-1, addr = address-1 }, ... [n] = { family = family-name-n, addr = address-n } }

Here, family contains the string "inet" for IPv4 addresses, and "inet6" for IPv6 addresses. In case of error, the function returns nil followed by an error message.

Parameters

• address: string — a hostname or an IPv4 or IPv6 address.

Returns

• resolved: Record<string | number, unknown> | nil — a table with all information returned by the resolver, or if an error occurs, nil.
• error: string | nil — the error message, or nil if no error occurred.

This function converts an address to host name. The supplied address can be an IPv4 or IPv6 address or host name. The function returns a table with all information returned by the resolver:

{ [1] = host-name-1, ... [n] = host-name-n, }

Parameters

• address: string — a hostname or an IPv4 or IPv6 address.

Returns

• resolved: Record<string | number, unknown> | nil — a table with all information returned by the resolver, or if an error occurs, nil.
• error: string | nil — the error message, or nil if no error occurred.

This function is a shortcut that creates and returns a TCP client object connected to a remote address at a given port. Optionally, the user can also specify the local address and port to bind (locaddr and locport), or restrict the socket family to "inet" or "inet6". Without specifying family to connect, whether a tcp or tcp6 connection is created depends on your system configuration.

Parameters

• address: string — the address to connect to.
• port: number — the port to connect to.
• locaddr?: string — optional local address to bind to.
• locport?: number — optional local port to bind to.
• family?: string — optional socket family to use, "inet" or "inet6".

Returns

• tcp_client: client | nil — a new IPv6 TCP client object, or nil in case of error.
• error: string | nil — the error message, or nil if no error occurred.

Creates and returns an unconnected IPv4 UDP object. Unconnected objects support the sendto, receive, receivefrom, getoption, getsockname, setoption, settimeout, setpeername, setsockname, and close methods. The setpeername method is used to connect the object.

Returns

• udp_unconnected: unconnected | nil — a new unconnected IPv4 UDP object, or nil in case of error.
• error: string | nil — the error message, or nil if no error occurred.

This function drops a number of arguments and returns the remaining. It is useful to avoid creation of dummy variables: D is the number of arguments to drop. Ret1 to retN are the arguments. The function returns retD+1 to retN.

// Instead of doing the following with dummy variables:
// get the status code and separator from SMTP server reply
const [dummy1, dummy2, code, sep] = string.find(line, "^(%d%d%d)(.?)");

// You can skip a number of variables:
// get the status code and separator from SMTP server reply
const [code, sep] = socket.skip(2, string.find(line, "^(%d%d%d)(.?)"));

Parameters

• d: number — the number of arguments to drop.
• ret1?: unknown — argument 1.
• ret2?: unknown — argument 2.
• retN?: unknown — argument N.

Returns

• retD+1: unknown | nil — argument D+1.
• retD+2: unknown | nil — argument D+2.
• retN: unknown | nil — argument N.

Creates and returns an IPv4 TCP master object. A master object can be transformed into a server object with the method listen (after a call to bind) or into a client object with the method connect. The only other method supported by a master object is the close method.

Returns

• tcp_master: master | nil — a new IPv4 TCP master object, or nil in case of error.
• error: string | nil — the error message, or nil if no error occurred.

This function creates and returns a clean try function that allows for cleanup before the exception is raised. The finalizer function will be called in protected mode (see protect).

// Perform operations on an open socket c:
// create a try function that closes 'c' on error
const try_ = socket.newtry(() => c.close());
// do everything reassured c will be closed
try_(c.send("hello there?\r\n"));
const answer = try_(c.receive());
// ...
try_(c.send("good bye\r\n"));
c.close();

Parameters

• finalizer: function() — a function that will be called before the try throws the exception.

Returns

• try: (...args: unknown[]) => unknown — the customized try function.

Converts a function that throws exceptions into a safe function. This function only catches exceptions thrown by try functions. It does not catch normal Lua errors. Beware that if your function performs some illegal operation that raises an error, the protected function will catch the error and return it as a string. This is because try functions uses errors as the mechanism to throw exceptions.

const dostuff = socket.protect(() => {
  let try_ = socket.newtry();
  const c = try_(socket.connect("myserver.com", 80));
  try_ = socket.newtry(() => c.close());
  try_(c.send("hello?\r\n"));
  const answer = try_(c.receive());
  c.close();
});

const [n, error] = dostuff();

Parameters

• func: (...args: unknown[]) => unknown — a function that calls a try function (or assert, or error) to throw exceptions.

Returns

• safe_func: function(function()) — an equivalent function that instead of throwing exceptions, returns nil followed by an error message.

Returns the time in seconds, relative to the system epoch (Unix epoch time since January 1, 1970 (UTC) or Windows file time since January 1, 1601 (UTC)). You should use the values returned by this function for relative measurements only.

// How to use the gettime() function to measure running time:
const t = socket.gettime();
// do stuff
print(`${socket.gettime() - t} seconds elapsed`);

Returns

• seconds: number — the number of seconds elapsed.

Freezes the program execution during a given amount of time.

Parameters

• time: number — the number of seconds to sleep for.

Waits for a remote connection on the server object and returns a client object representing that connection. Calling socket.select with a server object in the recvt parameter before a call to accept does not guarantee accept will return immediately. Use the settimeout method or accept might block until another client shows up.

Returns

• tcp_client: client | nil — if a connection is successfully initiated, a client object is returned, or nil in case of error.
• error: string | nil — the error message, or nil if no error occurred. The error is "timeout" if a timeout condition is met.

Closes the TCP object. The internal socket used by the object is closed and the local address to which the object was bound is made available to other applications. No further operations (except for further calls to the close method) are allowed on a closed socket. It is important to close all used sockets once they are not needed, since, in many systems, each socket uses a file descriptor, which are limited system resources. Garbage-collected objects are automatically closed before destruction, though.

Returns the local address information associated to the object.

Returns

• info: string — a string with local IP address, the local port number, and the family ("inet" or "inet6"). In case of error, the method returns nil.

Returns accounting information on the socket, useful for throttling of bandwidth.

Returns

• stats: string — a string with the number of bytes received, the number of bytes sent, and the age of the socket object in seconds.

Sets options for the TCP object. Options are only needed by low-level or time-critical applications. You should only modify an option if you are sure you need it.

Parameters

• option: string — the name of the option to set. The value is provided in the value parameter:

"keepalive" Setting this option to true enables the periodic transmission of messages on a connected socket. Should the connected party fail to respond to these messages, the connection is considered broken and processes using the socket are notified; "linger" Controls the action taken when unsent data are queued on a socket and a close is performed. The value is a table with the following keys:

• boolean on

• number timeout (seconds)

If the 'on' field is set to true, the system will block the process on the close attempt until it is able to transmit the data or until timeout has passed. If 'on' is false and a close is issued, the system will process the close in a manner that allows the process to continue as quickly as possible. It is not advised to set this to anything other than zero;

"reuseaddr" Setting this option indicates that the rules used in validating addresses supplied in a call to bind should allow reuse of local addresses; "tcp-nodelay" Setting this option to true disables the Nagle's algorithm for the connection; "ipv6-v6only" Setting this option to true restricts an inet6 socket to sending and receiving only IPv6 packets.

• value?: unknown — the value to set for the specified option.

Returns

• status: number | nil — the value 1, or nil in case of error.
• error: string | nil — the error message, or nil if no error occurred.

Gets options for the TCP object. See server:setoption for description of the option names and values.

Parameters

• option: string — the name of the option to get:

• "keepalive"

• "linger"

• "reuseaddr"

• "tcp-nodelay"

Returns

• value: unknown | nil — the option value, or nil in case of error.
• error: string | nil — the error message, or nil if no error occurred.

Resets accounting information on the socket, useful for throttling of bandwidth.

Parameters

• received: number — the new number of bytes received.
• sent: number — the new number of bytes sent.
• age: number — the new age in seconds.

Returns

• success: number | nil — the value 1 in case of success, or nil in case of error.

Changes the timeout values for the object. By default, all I/O operations are blocking. That is, any call to the methods send, receive, and accept will block indefinitely, until the operation completes. The settimeout method defines a limit on the amount of time the I/O methods can block. When a timeout is set and the specified amount of time has elapsed, the affected methods give up and fail with an error code. There are two timeout modes and both can be used together for fine tuning. Although timeout values have millisecond precision in LuaSocket, large blocks can cause I/O functions not to respect timeout values due to the time the library takes to transfer blocks to and from the OS and to and from the Lua interpreter. Also, function that accept host names and perform automatic name resolution might be blocked by the resolver for longer than the specified timeout value.

Parameters

• value: number — the amount of time to wait, in seconds. The nil timeout value allows operations to block indefinitely. Negative timeout values have the same effect.
• mode?: string — optional timeout mode to set:

"b" block timeout. Specifies the upper limit on the amount of time LuaSocket can be blocked by the operating system while waiting for completion of any single I/O operation. This is the default mode; "t" total timeout. Specifies the upper limit on the amount of time LuaSocket can block a Lua script before returning from a call.

Check the read buffer status. This is an internal method, any use is unlikely to be portable.

Returns

• status: boolean — true if there is any data in the read buffer, false otherwise.

Returns the underlying socket descriptor or handle associated to the object. This is an internal method, any use is unlikely to be portable.

Returns

• handle: number — the descriptor or handle. In case the object has been closed, the return will be -1.

Sets the underling socket descriptor or handle associated to the object. The current one is simply replaced, not closed, and no other change to the object state is made

Parameters

• handle: number — the descriptor or handle to set.

Binds a master object to address and port on the local host.

Parameters

• address: string — an IP address or a host name. If address is "*", the system binds to all local interfaces using the INADDR_ANY constant.
• port: number — the port to commect to, in the range [0..64K). If port is 0, the system automatically chooses an ephemeral port.

Returns

• status: number | nil — the value 1, or nil in case of error.
• error: string | nil — the error message, or nil if no error occurred.

Closes the TCP object. The internal socket used by the object is closed and the local address to which the object was bound is made available to other applications. No further operations (except for further calls to the close method) are allowed on a closed socket. It is important to close all used sockets once they are not needed, since, in many systems, each socket uses a file descriptor, which are limited system resources. Garbage-collected objects are automatically closed before destruction, though.

Attempts to connect a master object to a remote host, transforming it into a client object. Client objects support methods send, receive, getsockname, getpeername, settimeout, and close. Note that the function socket.connect is available and is a shortcut for the creation of client sockets.

Parameters

• address: string — an IP address or a host name. If address is "*", the system binds to all local interfaces using the INADDR_ANY constant.
• port: number — the port to commect to, in the range [0..64K). If port is 0, the system automatically chooses an ephemeral port.

Returns

• status: number | nil — the value 1, or nil in case of error.
• error: string | nil — the error message, or nil if no error occurred.

Returns the local address information associated to the object.

Returns

• info: string — a string with local IP address, the local port number, and the family ("inet" or "inet6"). In case of error, the method returns nil.

Returns accounting information on the socket, useful for throttling of bandwidth.

Returns

• stats: string — a string with the number of bytes received, the number of bytes sent, and the age of the socket object in seconds.

Specifies the socket is willing to receive connections, transforming the object into a server object. Server objects support the accept, getsockname, setoption, settimeout, and close methods.

Parameters

• backlog: number — the number of client connections that can be queued waiting for service. If the queue is full and another client attempts connection, the connection is refused.

Returns

• status: number | nil — the value 1, or nil in case of error.
• error: string | nil — the error message, or nil if no error occurred.

Resets accounting information on the socket, useful for throttling of bandwidth.

Parameters

• received: number — the new number of bytes received.
• sent: number — the new number of bytes sent.
• age: number — the new age in seconds.

Returns

• success: number | nil — the value 1 in case of success, or nil in case of error.

Changes the timeout values for the object. By default, all I/O operations are blocking. That is, any call to the methods send, receive, and accept will block indefinitely, until the operation completes. The settimeout method defines a limit on the amount of time the I/O methods can block. When a timeout is set and the specified amount of time has elapsed, the affected methods give up and fail with an error code. There are two timeout modes and both can be used together for fine tuning. Although timeout values have millisecond precision in LuaSocket, large blocks can cause I/O functions not to respect timeout values due to the time the library takes to transfer blocks to and from the OS and to and from the Lua interpreter. Also, function that accept host names and perform automatic name resolution might be blocked by the resolver for longer than the specified timeout value.

Parameters

• value: number — the amount of time to wait, in seconds. The nil timeout value allows operations to block indefinitely. Negative timeout values have the same effect.
• mode?: string — optional timeout mode to set:

"b" block timeout. Specifies the upper limit on the amount of time LuaSocket can be blocked by the operating system while waiting for completion of any single I/O operation. This is the default mode; "t" total timeout. Specifies the upper limit on the amount of time LuaSocket can block a Lua script before returning from a call.

Check the read buffer status. This is an internal method, any use is unlikely to be portable.

Returns

• status: boolean — true if there is any data in the read buffer, false otherwise.

Returns the underlying socket descriptor or handle associated to the object. This is an internal method, any use is unlikely to be portable.

Returns

• handle: number — the descriptor or handle. In case the object has been closed, the return will be -1.

Sets the underling socket descriptor or handle associated to the object. The current one is simply replaced, not closed, and no other change to the object state is made

Parameters

• handle: number — the descriptor or handle to set.

Closes the TCP object. The internal socket used by the object is closed and the local address to which the object was bound is made available to other applications. No further operations (except for further calls to the close method) are allowed on a closed socket. It is important to close all used sockets once they are not needed, since, in many systems, each socket uses a file descriptor, which are limited system resources. Garbage-collected objects are automatically closed before destruction, though.

Returns information about the remote side of a connected client object. It makes no sense to call this method on server objects.

Returns

• info: string — a string with the IP address of the peer, the port number that peer is using for the connection, and the family ("inet" or "inet6"). In case of error, the method returns nil.

Returns the local address information associated to the object.

Returns

• info: string — a string with local IP address, the local port number, and the family ("inet" or "inet6"). In case of error, the method returns nil.

Returns accounting information on the socket, useful for throttling of bandwidth.

Returns

• stats: string — a string with the number of bytes received, the number of bytes sent, and the age of the socket object in seconds.

Reads data from a client object, according to the specified read pattern. Patterns follow the Lua file I/O format, and the difference in performance between patterns is negligible.

Parameters

• pattern?: string | number — the read pattern that can be any of the following:

"*a" reads from the socket until the connection is closed. No end-of-line translation is performed; "*l" reads a line of text from the socket. The line is terminated by a LF character (ASCII 10), optionally preceded by a CR character (ASCII 13). The CR and LF characters are not included in the returned line. In fact, all CR characters are ignored by the pattern. This is the default pattern; number causes the method to read a specified number of bytes from the socket.

• prefix?: string — an optional string to be concatenated to the beginning of any received data before return.

Returns

• data: string | nil — the received pattern, or nil in case of error.
• error: string | nil — the error message, or nil if no error occurred. The error message can be the string "closed" in case the connection was closed before the transmission was completed or the string "timeout" in case there was a timeout during the operation.
• partial: string | nil — a (possibly empty) string containing the partial that was received, or nil if no error occurred.

Sends data through client object. The optional arguments i and j work exactly like the standard string.sub Lua function to allow the selection of a substring to be sent. Output is not buffered. For small strings, it is always better to concatenate them in Lua (with the .. operator) and send the result in one call instead of calling the method several times.

Parameters

• data: string — the string to be sent.
• i?: number — optional starting index of the string.
• j?: number — optional end index of string.

Returns

• index: number | nil — the index of the last byte within [i, j] that has been sent, or nil in case of error. Notice that, if i is 1 or absent, this is effectively the total number of bytes sent.
• error: string | nil — the error message, or nil if no error occurred. The error message can be "closed" in case the connection was closed before the transmission was completed or the string "timeout" in case there was a timeout during the operation.
• lastindex: number | nil — in case of error, the index of the last byte within [i, j] that has been sent. You might want to try again from the byte following that. nil if no error occurred.

Sets options for the TCP object. Options are only needed by low-level or time-critical applications. You should only modify an option if you are sure you need it.

Parameters

• option: string — the name of the option to set. The value is provided in the value parameter:

"keepalive" Setting this option to true enables the periodic transmission of messages on a connected socket. Should the connected party fail to respond to these messages, the connection is considered broken and processes using the socket are notified; "linger" Controls the action taken when unsent data are queued on a socket and a close is performed. The value is a table with the following keys:

• boolean on

• number timeout (seconds)

If the 'on' field is set to true, the system will block the process on the close attempt until it is able to transmit the data or until timeout has passed. If 'on' is false and a close is issued, the system will process the close in a manner that allows the process to continue as quickly as possible. It is not advised to set this to anything other than zero;

"reuseaddr" Setting this option indicates that the rules used in validating addresses supplied in a call to bind should allow reuse of local addresses; "tcp-nodelay" Setting this option to true disables the Nagle's algorithm for the connection; "ipv6-v6only" Setting this option to true restricts an inet6 socket to sending and receiving only IPv6 packets.

• value?: unknown — the value to set for the specified option.

Returns

• status: number | nil — the value 1, or nil in case of error.
• error: string | nil — the error message, or nil if no error occurred.

Gets options for the TCP object. See client:setoption for description of the option names and values.

Parameters

• option: string — the name of the option to get:

• "keepalive"

• "linger"

• "reuseaddr"

• "tcp-nodelay"

Returns

• value: unknown | nil — the option value, or nil in case of error.
• error: string | nil — the error message, or nil if no error occurred.

Resets accounting information on the socket, useful for throttling of bandwidth.

Parameters

• received: number — the new number of bytes received.
• sent: number — the new number of bytes sent.
• age: number — the new age in seconds.

Returns

• success: number | nil — the value 1 in case of success, or nil in case of error.

Changes the timeout values for the object. By default, all I/O operations are blocking. That is, any call to the methods send, receive, and accept will block indefinitely, until the operation completes. The settimeout method defines a limit on the amount of time the I/O methods can block. When a timeout is set and the specified amount of time has elapsed, the affected methods give up and fail with an error code. There are two timeout modes and both can be used together for fine tuning. Although timeout values have millisecond precision in LuaSocket, large blocks can cause I/O functions not to respect timeout values due to the time the library takes to transfer blocks to and from the OS and to and from the Lua interpreter. Also, function that accept host names and perform automatic name resolution might be blocked by the resolver for longer than the specified timeout value.

Parameters

• value: number — the amount of time to wait, in seconds. The nil timeout value allows operations to block indefinitely. Negative timeout values have the same effect.
• mode?: string — optional timeout mode to set:

"b" block timeout. Specifies the upper limit on the amount of time LuaSocket can be blocked by the operating system while waiting for completion of any single I/O operation. This is the default mode; "t" total timeout. Specifies the upper limit on the amount of time LuaSocket can block a Lua script before returning from a call.

Shuts down part of a full-duplex connection.

Parameters

• mode: string — which way of the connection should be shut down:

"both" disallow further sends and receives on the object. This is the default mode; "send" disallow further sends on the object; "receive" disallow further receives on the object.

Returns

• status: number — the value 1.

Check the read buffer status. This is an internal method, any use is unlikely to be portable.

Returns

• status: boolean — true if there is any data in the read buffer, false otherwise.

Returns the underlying socket descriptor or handle associated to the object. This is an internal method, any use is unlikely to be portable.

Returns

• handle: number — the descriptor or handle. In case the object has been closed, the return will be -1.

Sets the underling socket descriptor or handle associated to the object. The current one is simply replaced, not closed, and no other change to the object state is made

Parameters

• handle: number — the descriptor or handle to set.

Closes a UDP object. The internal socket used by the object is closed and the local address to which the object was bound is made available to other applications. No further operations (except for further calls to the close method) are allowed on a closed socket. It is important to close all used sockets once they are not needed, since, in many systems, each socket uses a file descriptor, which are limited system resources. Garbage-collected objects are automatically closed before destruction, though.

Retrieves information about the peer associated with a connected UDP object. It makes no sense to call this method on unconnected objects.

Returns

• info: string — a string with the IP address of the peer, the port number that peer is using for the connection, and the family ("inet" or "inet6"). In case of error, the method returns nil.

Returns the local address information associated to the object. UDP sockets are not bound to any address until the setsockname or the sendto method is called for the first time (in which case it is bound to an ephemeral port and the wild-card address).

Returns

• info: string — a string with local IP address, a number with the local port, and the family ("inet" or "inet6"). In case of error, the method returns nil.

Receives a datagram from the UDP object. If the UDP object is connected, only datagrams coming from the peer are accepted. Otherwise, the returned datagram can come from any host.

Parameters

• size?: number — optional maximum size of the datagram to be retrieved. If there are more than size bytes available in the datagram, the excess bytes are discarded. If there are less then size bytes available in the current datagram, the available bytes are returned. If size is omitted, the maximum datagram size is used (which is currently limited by the implementation to 8192 bytes).

Returns

• datagram: string | nil — the received datagram, or nil in case of error.
• error: string | nil — the error message, or nil if no error occurred.

Gets an option value from the UDP object. See connected:setoption for description of the option names and values.

Parameters

• option: string — the name of the option to get:

• "dontroute"

• "broadcast"

• "reuseaddr"

• "reuseport"

• "ip-multicast-loop"

• "ipv6-v6only"

• "ip-multicast-if"

• "ip-multicast-ttl"

• "ip-add-membership"

• "ip-drop-membership"

Returns

• value: unknown | nil — the option value, or nil in case of error.
• error: string | nil — the error message, or nil if no error occurred.

Sends a datagram to the UDP peer of a connected object. In UDP, the send method never blocks and the only way it can fail is if the underlying transport layer refuses to send a message to the specified address (i.e. no interface accepts the address).

Parameters

• datagram: string — a string with the datagram contents. The maximum datagram size for UDP is 64K minus IP layer overhead. However datagrams larger than the link layer packet size will be fragmented, which may deteriorate performance and/or reliability.

Returns

• success: number | nil — the value 1 on success, or nil in case of error.
• error: string | nil — the error message, or nil if no error occurred.

Changes the peer of a UDP object. This method turns an unconnected UDP object into a connected UDP object or vice versa. For connected objects, outgoing datagrams will be sent to the specified peer, and datagrams received from other peers will be discarded by the OS. Connected UDP objects must use the send and receive methods instead of sendto and receivefrom. Since the address of the peer does not have to be passed to and from the OS, the use of connected UDP objects is recommended when the same peer is used for several transmissions and can result in up to 30% performance gains.

Parameters

• "*": string — if address is "*" and the object is connected, the peer association is removed and the object becomes an unconnected object again.

Returns

• success: number | nil — the value 1 on success, or nil in case of error.
• error: string | nil — the error message, or nil if no error occurred.

Sets options for the UDP object. Options are only needed by low-level or time-critical applications. You should only modify an option if you are sure you need it.

Parameters

• option: string — the name of the option to set. The value is provided in the value parameter:

"dontroute" Indicates that outgoing messages should bypass the standard routing facilities. Receives a boolean value; "broadcast" Requests permission to send broadcast datagrams on the socket. Receives a boolean value; "reuseaddr" Indicates that the rules used in validating addresses supplied in a bind call should allow reuse of local addresses. Receives a boolean value; "reuseport" Allows completely duplicate bindings by multiple processes if they all set "reuseport" before binding the port. Receives a boolean value; "ip-multicast-loop" Specifies whether or not a copy of an outgoing multicast datagram is delivered to the sending host as long as it is a member of the multicast group. Receives a boolean value; "ipv6-v6only" Specifies whether to restrict inet6 sockets to sending and receiving only IPv6 packets. Receive a boolean value; "ip-multicast-if" Sets the interface over which outgoing multicast datagrams are sent. Receives an IP address; "ip-multicast-ttl" Sets the Time To Live in the IP header for outgoing multicast datagrams. Receives a number;

"ip-add-membership": Joins the multicast group specified. Receives a table with fields:

• string multiaddr (IP address)

• string interface (IP address)

"'ip-drop-membership"` Leaves the multicast group specified. Receives a table with fields:

• string multiaddr (IP address)

• string interface (IP address)

• value?: unknown — the value to set for the specified option.

Returns

• status: number | nil — the value 1, or nil in case of error.
• error: string | nil — the error message, or nil if no error occurred.

Changes the timeout values for the object. By default, the receive and receivefrom operations are blocking. That is, any call to the methods will block indefinitely, until data arrives. The settimeout function defines a limit on the amount of time the functions can block. When a timeout is set and the specified amount of time has elapsed, the affected methods give up and fail with an error code. In UDP, the send and sendto methods never block (the datagram is just passed to the OS and the call returns immediately). Therefore, the settimeout method has no effect on them.

Parameters

• value: number — the amount of time to wait, in seconds. The nil timeout value allows operations to block indefinitely. Negative timeout values have the same effect.

Closes a UDP object. The internal socket used by the object is closed and the local address to which the object was bound is made available to other applications. No further operations (except for further calls to the close method) are allowed on a closed socket. It is important to close all used sockets once they are not needed, since, in many systems, each socket uses a file descriptor, which are limited system resources. Garbage-collected objects are automatically closed before destruction, though.

Returns the local address information associated to the object. UDP sockets are not bound to any address until the setsockname or the sendto method is called for the first time (in which case it is bound to an ephemeral port and the wild-card address).

Returns

• info: string — a string with local IP address, a number with the local port, and the family ("inet" or "inet6"). In case of error, the method returns nil.

Receives a datagram from the UDP object. If the UDP object is connected, only datagrams coming from the peer are accepted. Otherwise, the returned datagram can come from any host.

Parameters

• size?: number — optional maximum size of the datagram to be retrieved. If there are more than size bytes available in the datagram, the excess bytes are discarded. If there are less then size bytes available in the current datagram, the available bytes are returned. If size is omitted, the maximum datagram size is used (which is currently limited by the implementation to 8192 bytes).

Returns

• datagram: string | nil — the received datagram, or nil in case of error.
• error: string | nil — the error message, or nil if no error occurred.

Works exactly as the receive method, except it returns the IP address and port as extra return values (and is therefore slightly less efficient).

Parameters

• size?: number — optional maximum size of the datagram to be retrieved.

Returns

• datagram: string | nil — the received datagram, or nil in case of error.
• ip_or_error: string — the IP address, or the error message in case of error.
• port: number | nil — the port number, or nil in case of error.

Gets an option value from the UDP object. See unconnected:setoption for description of the option names and values.

Parameters

• option: string — the name of the option to get:

• "dontroute"

• "broadcast"

• "reuseaddr"

• "reuseport"

• "ip-multicast-loop"

• "ipv6-v6only"

• "ip-multicast-if"

• "ip-multicast-ttl"

• "ip-add-membership"

• "ip-drop-membership"

Returns

• value: unknown | nil — the option value, or nil in case of error.
• error: string | nil — the error message, or nil if no error occurred.

Sends a datagram to the specified IP address and port number. In UDP, the send method never blocks and the only way it can fail is if the underlying transport layer refuses to send a message to the specified address (i.e. no interface accepts the address).

Parameters

• datagram: string — a string with the datagram contents. The maximum datagram size for UDP is 64K minus IP layer overhead. However datagrams larger than the link layer packet size will be fragmented, which may deteriorate performance and/or reliability.
• ip: string — the IP address of the recipient. Host names are not allowed for performance reasons.
• port: number — the port number at the recipient.

Returns

• success: number | nil — the value 1 on success, or nil in case of error.
• error: string | nil — the error message, or nil if no error occurred.

Changes the peer of a UDP object. This method turns an unconnected UDP object into a connected UDP object or vice versa. For connected objects, outgoing datagrams will be sent to the specified peer, and datagrams received from other peers will be discarded by the OS. Connected UDP objects must use the send and receive methods instead of sendto and receivefrom. Since the address of the peer does not have to be passed to and from the OS, the use of connected UDP objects is recommended when the same peer is used for several transmissions and can result in up to 30% performance gains.

Parameters

• address: string — an IP address or a host name.
• port: number — the port number.

Returns

• success: number | nil — the value 1 on success, or nil in case of error.
• error: string | nil — the error message, or nil if no error occurred.

Binds the UDP object to a local address. This method can only be called before any datagram is sent through the UDP object, and only once. Otherwise, the system automatically binds the object to all local interfaces and chooses an ephemeral port as soon as the first datagram is sent. After the local address is set, either automatically by the system or explicitly by setsockname, it cannot be changed.

Parameters

• address: string — an IP address or a host name. If address is "*" the system binds to all local interfaces using the constant INADDR_ANY.
• port: number — the port number. If port is 0, the system chooses an ephemeral port.

Returns

• success: number | nil — the value 1 on success, or nil in case of error.
• error: string | nil — the error message, or nil if no error occurred.

Sets options for the UDP object. Options are only needed by low-level or time-critical applications. You should only modify an option if you are sure you need it.

Parameters

• option: string — the name of the option to set. The value is provided in the value parameter:

"dontroute" Indicates that outgoing messages should bypass the standard routing facilities. Receives a boolean value; "broadcast" Requests permission to send broadcast datagrams on the socket. Receives a boolean value; "reuseaddr" Indicates that the rules used in validating addresses supplied in a bind call should allow reuse of local addresses. Receives a boolean value; "reuseport" Allows completely duplicate bindings by multiple processes if they all set "reuseport" before binding the port. Receives a boolean value; "ip-multicast-loop" Specifies whether or not a copy of an outgoing multicast datagram is delivered to the sending host as long as it is a member of the multicast group. Receives a boolean value; "ipv6-v6only" Specifies whether to restrict inet6 sockets to sending and receiving only IPv6 packets. Receive a boolean value; "ip-multicast-if" Sets the interface over which outgoing multicast datagrams are sent. Receives an IP address; "ip-multicast-ttl" Sets the Time To Live in the IP header for outgoing multicast datagrams. Receives a number;

"ip-add-membership": Joins the multicast group specified. Receives a table with fields:

• string multiaddr (IP address)

• string interface (IP address)

"'ip-drop-membership"` Leaves the multicast group specified. Receives a table with fields:

• string multiaddr (IP address)

• string interface (IP address)

• value?: unknown — the value to set for the specified option.

Returns

• status: number | nil — the value 1, or nil in case of error.
• error: string | nil — the error message, or nil if no error occurred.

Changes the timeout values for the object. By default, the receive and receivefrom operations are blocking. That is, any call to the methods will block indefinitely, until data arrives. The settimeout function defines a limit on the amount of time the functions can block. When a timeout is set and the specified amount of time has elapsed, the affected methods give up and fail with an error code. In UDP, the send and sendto methods never block (the datagram is just passed to the OS and the call returns immediately). Therefore, the settimeout method has no effect on them.

Parameters

• value: number — the amount of time to wait, in seconds. The nil timeout value allows operations to block indefinitely. Negative timeout values have the same effect.

This constant has a string describing the current LuaSocket version.

This constant contains the maximum number of sockets that the select function can handle.