Module socket

Overview

The socket module allows exchanging data via BSD sockets with a local or remote host in connection-oriented (TCP) or datagram-oriented (UDP) mode. Semantics of the calls in the socket API closely follow semantics of the corresponding POSIX calls.

The functions for setting up and connecting are socket, sysconnect, tcp_connect. The functions for sending data are send, sendto, write, syswrite. The functions for receiving data are recv, recvfrom, read. The functions for waiting before sending/receiving data are wait, readable, writable. The functions for setting flags are nonblock, setsockopt. The functions for stopping and disconnecting are shutdown, close. The functions for error checking are errno, error.

Index

Below is a list of all socket functions.

Typically a socket session will begin with the setup functions, will set one or more flags, will have a loop with sending and receiving functions, will end with the teardown functions – as an example at the end of this section will show. Throughout, there may be error-checking and waiting functions for synchronization. To prevent a fiber containing socket functions from “blocking” other fibers, the implicit yield rules will cause a yield so that other processes may take over, as is the norm for cooperative multitasking.

For all examples in this section the socket name will be sock and the function invocations will look like sock:function_name(...).

socket.__call(domain, type, protocol)¶

Create a new TCP or UDP socket. The argument values are the same as in the Linux socket(2) man page.

Return:	an unconnected socket, or nil.
Rtype:	userdata

Example:

socket('AF_INET', 'SOCK_STREAM', 'tcp')

socket.tcp_connect(host[, port[, timeout]])¶

Connect a socket to a remote host.

Parameters:	host (string) – URL or IP address port (number) – port number timeout (number) – number of seconds to wait
Return:	(if error) {nil, error-message-string}. (if no error) a new socket object.
Rtype:	socket object, which may be viewed as a table

Example:

sock, e = socket.tcp_connect('127.0.0.1', 3301)
if sock == nil then print(e) end

socket.getaddrinfo(host, port[, timeout[, {option-list}]])¶

socket.getaddrinfo(host, port[, {option-list}])

The socket.getaddrinfo() function is useful for finding information about a remote site so that the correct arguments for sock:sysconnect() can be passed. This function may use the worker_pool_threads configuration parameter.

Parameters:	host (string) – URL or IP address port (number/string) – port number as a numeric or string timeout (number) – maximum number of seconds to wait options (table) – type – preferred socket type family – desired address family for the returned addresses protocol flags – additional options (see details here)
Return:	(if error) {nil, error-message-string}. (if no error) A table containing these fields: “host”, “family”, “type”, “protocol”, “port”.
Rtype:	table

Example:

tarantool> socket.getaddrinfo('tarantool.org', 'http')
---
- - host: 188.93.56.70
    family: AF_INET
    type: SOCK_STREAM
    protocol: tcp
    port: 80
  - host: 188.93.56.70
    family: AF_INET
    type: SOCK_DGRAM
    protocol: udp
    port: 80
...
-- To find the available values for the options use the following:
tarantool> socket.internal.AI_FLAGS -- or SO_TYPE, or DOMAIN
---
- AI_ALL: 256
  AI_PASSIVE: 1
  AI_NUMERICSERV: 4096
  AI_NUMERICHOST: 4
  AI_V4MAPPED: 2048
  AI_ADDRCONFIG: 1024
  AI_CANONNAME: 2
...

socket.tcp_server(host, port, handler-function-or-table[, timeout])¶

The socket.tcp_server() function makes Tarantool act as a server that can accept connections. Usually the same objective is accomplished with box.cfg{listen=…}.

Parameters:	host (string) – host name or IP port (number) – host port, may be 0 handler-function-or-table (function/table) – what to execute when a connection occurs timeout (number) – host resolving timeout in seconds
Return:	(if error) {nil, error-message-string}. (if no error) a new socket object.
Rtype:	socket object, which may be viewed as a table

The handler-function-or-table parameter may be simply a function name / function declaration: handler_function. Or it may be a table: {handler = handler_function [, prepare = prepare_function] [, name = name] }. handler_function is mandatory; it may have a parameter = the socket; it is executed once after accept() happens (once per connection); it is for continuous operation after the connection is made. prepare_function is optional; it may have parameters = the socket object and a table with client information; it should return either a backlog value or nothing; it is executed only once before bind() on the listening socket (not once per connection). Examples:

socket.tcp_server('localhost', 3302, function (s) loop_loop() end)
socket.tcp_server('localhost', 3302, {handler=hfunc, name='name'})
socket.tcp_server('localhost', 3302, {handler=hfunc, prepare=pfunc})

For fuller examples see Use tcp_server to accept file contents sent with socat and Use tcp_server with handler and prepare.

socket.bind(host, port)¶

Bind a socket to the given host/port. This is equivalent to socket_object:bind(), but is done on the result of require('socket'), rather than on the socket object.

Parameters:	host (string) – URL or IP address port (number) – port number
Return:	(if error) {nil, error-message-string}. (if no error) A table which may have information about the bind result.
Rtype:	table

object socket_object¶

socket_object:sysconnect(host, port)¶

Connect an existing socket to a remote host. The argument values are the same as in tcp_connect(). The host must be an IP address.

Parameters:

• Either:

  • host - a string representation of an IPv4 address or an IPv6 address;
  • port - a number.

• Or:

  • host - a string containing “unix/”;
  • port - a string containing a path to a unix socket.

• Or:

  • host - a number, 0 (zero), meaning “all local interfaces”;
  • port - a number. If a port number is 0 (zero), the socket will be bound to a random local port.

Return:	the socket object value may change if sysconnect() succeeds.
Rtype:	boolean

Example:

socket = require('socket')
sock = socket('AF_INET', 'SOCK_STREAM', 'tcp')
sock:sysconnect(0, 3301)

socket_object:send(data)¶

socket_object:write(data)¶

Send data over a connected socket.

Parameters:	data (string) – what is to be sent
Return:	the number of bytes sent.
Rtype:	number

Possible errors: nil on error.

socket_object:syswrite(size)¶

Write as much data as possible to the socket buffer if non-blocking. Rarely used. For details see this description.

socket_object:recv(size)¶

Read size bytes from a connected socket. An internal read-ahead buffer is used to reduce the cost of this call.

Parameters:	size (integer) – maximum number of bytes to receive. See Recommended size.
Return:	a string of the requested length on success.
Rtype:	string

Possible errors: On error, returns an empty string, followed by status, errno, errstr. In case the writing side has closed its end, returns the remainder read from the socket (possibly an empty string), followed by “eof” status.

socket_object:read(limit[, timeout])¶

socket_object:read(delimiter[, timeout])

socket_object:read({options}[, timeout])

Read from a connected socket until some condition is true, and return the bytes that were read. Reading goes on until limit bytes have been read, or a delimiter has been read, or a timeout has expired. Unlike socket_object:recv (which uses an internal read-ahead buffer), socket_object:read depends on the socket’s buffer.

Parameters:	limit (integer) – maximum number of bytes to read, for example 50 means “stop after 50 bytes” delimiter (string) – separator for example ? means “stop after a question mark”; this parameter can accept a table of separators, for example, delimiter = {"\n", "\r"} timeout (number) – maximum number of seconds to wait, for example 50 means “stop after 50 seconds”. options (table) – chunk=limit and/or delimiter=delimiter, for example {chunk=5,delimiter='x'}.
Return:	an empty string if there is nothing more to read, or a nil value if error, or a string up to limit bytes long, which may include the bytes that matched the delimiter expression.
Rtype:	string

socket_object:sysread(size)¶

Return data from the socket buffer if non-blocking. In case the socket is blocking, sysread() can block the calling process. Rarely used. For details, see also this description.

Parameters:	size (integer) – maximum number of bytes to read, for example 50 means “stop after 50 bytes”
Return:	an empty string if there is nothing more to read, or a nil value if error, or a string up to size bytes long.
Rtype:	string

socket_object:bind(host[, port])¶

Bind a socket to the given host/port. A UDP socket after binding can be used to receive data (see socket_object.recvfrom). A TCP socket can be used to accept new connections, after it has been put in listen mode.

Parameters:	host (string) – URL or IP address port (number) – port number
Return:	true for success, false for error. If return is false, use socket_object:errno() or socket_object:error() to see details.
Rtype:	boolean

socket_object:listen(backlog)¶

Start listening for incoming connections.

Parameters:	backlog – on Linux the listen backlog backlog may be from /proc/sys/net/core/somaxconn, on BSD the backlog may be SOMAXCONN.
Return:	true for success, false for error.
Rtype:	boolean.

socket_object:accept()¶

Accept a new client connection and create a new connected socket. It is good practice to set the socket’s blocking mode explicitly after accepting.

Return:	new socket if success.
Rtype:	userdata

Possible errors: nil.

socket_object:sendto(host, port, data)¶

Send a message on a UDP socket to a specified host.

Parameters:	host (string) – URL or IP address port (number) – port number data (string) – what is to be sent
Return:	the number of bytes sent.
Rtype:	number

Possible errors: on error, returns nil and may return status, errno, errstr.

socket_object:recvfrom(size)¶

Receive a message on a UDP socket.

Parameters:	size (integer) – maximum number of bytes to receive. See Recommended size.
Return:	message, a table containing “host”, “family” and “port” fields.
Rtype:	string, table

Possible errors: on error, returns status, errno, errstr.

Example:

After message_content, message_sender = recvfrom(1) the value of message_content might be a string containing ‘X’ and the value of message_sender might be a table containing

message_sender.host = '18.44.0.1'
message_sender.family = 'AF_INET'
message_sender.port = 43065

socket_object:shutdown(how)¶

Shutdown a reading end, a writing end, or both ends of a socket.

Parameters:	how – socket.SHUT_RD, socket.SHUT_WR, or socket.SHUT_RDWR.
Return:	true or false.
Rtype:	boolean

socket_object:close()¶

Close (destroy) a socket. A closed socket should not be used any more. A socket is closed automatically when the Lua garbage collector removes its user data.

Return:	true on success, false on error. For example, if sock is already closed, sock:close() returns false.
Rtype:	boolean

socket_object:error()¶

socket_object:errno()¶

Retrieve information about the last error that occurred on a socket, if any. Errors do not cause throwing of exceptions so these functions are usually necessary.

Return:	result for sock:errno(), result for sock:error(). If there is no error, then sock:errno() will return 0 and sock:error().
Rtype:	number, string

socket_object:setsockopt(level, name, value)¶

Set socket flags. The argument values are the same as in the Linux getsockopt(2) man page. The ones that Tarantool accepts are:

• SO_ACCEPTCONN
• SO_BINDTODEVICE
• SO_BROADCAST
• SO_DEBUG
• SO_DOMAIN
• SO_ERROR
• SO_DONTROUTE
• SO_KEEPALIVE
• SO_MARK
• SO_OOBINLINE
• SO_PASSCRED
• SO_PEERCRED
• SO_PRIORITY
• SO_PROTOCOL
• SO_RCVBUF
• SO_RCVBUFFORCE
• SO_RCVLOWAT
• SO_SNDLOWAT
• SO_RCVTIMEO
• SO_SNDTIMEO
• SO_REUSEADDR
• SO_SNDBUF
• SO_SNDBUFFORCE
• SO_TIMESTAMP
• SO_TYPE

Setting SO_LINGER is done with sock:linger(active).

socket_object:getsockopt(level, name)¶

Get socket flags. For a list of possible flags see sock:setsockopt().

socket_object:linger([active])¶

Set or clear the SO_LINGER flag. For a description of the flag, see the Linux man page.

Parameters:	active (boolean) –
Return:	new active and timeout values.

socket_object:nonblock([flag])¶

• sock:nonblock() returns the current flag value.
• sock:nonblock(false) sets the flag to false and returns false.
• sock:nonblock(true) sets the flag to true and returns true.

This function may be useful before invoking a function which might otherwise block indefinitely.

socket_object:readable([timeout])¶

Wait until something is readable, or until a timeout value expires.

Return:	true if the socket is now readable, false if timeout expired;

socket_object:writable([timeout])¶

Wait until something is writable, or until a timeout value expires.

Return:	true if the socket is now writable, false if timeout expired;

socket_object:wait([timeout])¶

Wait until something is either readable or writable, or until a timeout value expires.

Return:	‘R’ if the socket is now readable, ‘W’ if the socket is now writable, ‘RW’ if the socket is now both readable and writable, ‘’ (empty string) if timeout expired;

socket_object:name()¶

The sock:name() function is used to get information about the near side of the connection. If a socket was bound to xyz.com:45, then sock:name will return information about [host:xyz.com, port:45]. The equivalent POSIX function is getsockname().

Return:	A table containing these fields: “host”, “family”, “type”, “protocol”, “port”.
Rtype:	table

socket_object:peer()¶

The sock:peer() function is used to get information about the far side of a connection. If a TCP connection has been made to a distant host tarantool.org:80, sock:peer() will return information about [host:tarantool.org, port:80]. The equivalent POSIX function is getpeername().

Return:	A table containing these fields: “host”, “family”, “type”, “protocol”, “port”.
Rtype:	table

socket.iowait(fd, read-or-write-flags[, timeout])¶

The socket.iowait() function is used to wait until read-or-write activity occurs for a file descriptor.

Parameters:	fd – file descriptor read-or-write-flags – ‘R’ or 1 = read, ‘W’ or 2 = write, ‘RW’ or 3 = read|write. timeout – number of seconds to wait

If the fd parameter is nil, then there will be a sleep until the timeout. If the timeout parameter is nil or unspecified, then timeout is infinite.

Ordinarily the return value is the activity that occurred (‘R’ or ‘W’ or ‘RW’ or 1 or 2 or 3). If the timeout period goes by without any reading or writing, the return is an error = ETIMEDOUT.

Example: socket.iowait(sock:fd(), 'r', 1.11)

LuaSocket wrapper functions

The LuaSocket API has functions that are equivalent to the ones described above, with different names and parameters, for example connect() rather than tcp_connect(). Tarantool supports these functions so that third-party packages which depend on them will work.

The LuaSocket project is on github. The API description is in the LuaSocket manual (click the “introduction” and “reference” links at the bottom of the manual’s main page).

A Tarantool example is Use of a socket with LuaSocket wrapper functions.

Recommended size

For recv and recvfrom: use the optional size parameter to limit the number of bytes to receive. A fixed size such as 512 is often reasonable; a pre-calculated size that depends on context – such as the message format or the state of the network – is often better. For recvfrom, be aware that a size greater than the Maximum Transmission Unit can cause inefficient transport. For Mac OS X, be aware that the size can be tuned by changing sysctl net.inet.udp.maxdgram.

If size is not stated: Tarantool will make an extra call to calculate how many bytes are necessary. This extra call takes time, therefore not stating size may be inefficient.

If size is stated: on a UDP socket, excess bytes are discarded. On a TCP socket, excess bytes are not discarded and can be received by the next call.

Examples

tarantool> socket = require('socket')
---
...
tarantool> sock = socket.tcp_connect('tarantool.org', 80)
---
...
tarantool> type(sock)
---
- table
...
tarantool> sock:error()
---
- null
...
tarantool> sock:send("HEAD / HTTP/1.0\r\nHost: tarantool.org\r\n\r\n")
---
- 40
...
tarantool> sock:read(17)
---
- HTTP/1.1 302 Move
...
tarantool> sock:close()
---
- true
...

tarantool> socket = require('socket')
---
...
tarantool> sock = socket.connect('tarantool.org', 80)
---
...
tarantool> sock:settimeout(0.001)
---
- 1
...
tarantool> sock:send("HEAD / HTTP/1.0\r\nHost: tarantool.org\r\n\r\n")
---
- 40
...
tarantool> sock:receive(17)
---
- null
- Connection timed out
...
tarantool> sock:close()
---
- 1
...

tarantool> socket = require('socket')
---
...
tarantool> sock_1 = socket('AF_INET', 'SOCK_DGRAM', 'udp')
---
...
tarantool> sock_1:bind('127.0.0.1')
---
- true
...
tarantool> sock_2 = socket('AF_INET', 'SOCK_DGRAM', 'udp')
---
...
tarantool> sock_2:sendto('127.0.0.1', sock_1:name().port,'X')
---
- 1
...
tarantool> message = sock_1:recvfrom(512)
---
...
tarantool> message
---
- X
...
tarantool> sock_1:close()
---
- true
...
tarantool> sock_2:close()
---
- true
...

box.cfg{}
socket = require('socket')
socket.tcp_server('0.0.0.0', 3302,
{
  handler = function(s)
    while true do
      local request
      request = s:read("\n");
      if request == "" or request == nil then
        break
      end
      print(request)
    end
  end,
  prepare = function()
    print('Initialized')
  end
}
)

$ socat TCP:localhost:3302 ./tmp.txt

box.cfg{}
socket = require('socket')
sock = socket.tcp_server(
  '0.0.0.0',
  3302,
  {prepare =
     function(sock)
       print('listening on socket ' .. sock:fd())
       sock:setsockopt('SOL_SOCKET','SO_REUSEADDR',true)
       return 5
     end,
   handler =
    function(sock, from)
      print('accepted connection from: ')
      print('  host: ' .. from.host)
      print('  family: ' .. from.family)
      print('  port: ' .. from.port)
    end
  }
)

box.cfg{}
require('socket').tcp_connect('127.0.0.1', 3302)