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Модуль socket

Замечание

Документация находится в процессе перевода и может отставать от английской версии.

Модуль socket

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. Function names and signatures are mostly compatible with luasocket.

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.

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.

Параметры:
  • host (string) – URL or IP address
  • port (number) – port number
  • timeout (number) – timeout
Return:

a connected socket, if no error.

Rtype:

userdata

Example:

socket.tcp_connect('127.0.0.1', 3301)
socket.getaddrinfo(host, type[, {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.

Return:A table containing these fields: «host», «family», «type», «protocol», «port».
Rtype:table

Example:

socket.getaddrinfo('tarantool.org', 'http') will return variable information such as

---
- - 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
...
socket.tcp_server(host, port, handler-function[, 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=…}.

Параметры:
  • host (string) – host name or IP
  • port (number) – host port, may be 0
  • handler (function/table) – what to execute when a connection occurs
  • timeout (number) – number of seconds to wait before timing out

The handler-function parameter may be a function name (for example function_55), a function declaration (for example function () print('!') end), or a table including handler = function (for example {handler=function_55, name='A'}).

Example:

socket.tcp_server('localhost', 3302, function () end)

объект socket.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.

Параметры:
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.

Параметры:
  • size (integer) –
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({limit=limit}[, timeout])
socket_object:read({delimiter=delimiter}[, timeout])
socket_object:read({limit=limit, delimiter=delimiter}[, 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.

Параметры:
  • 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»
  • timeout (number) – maximum number of seconds to wait for example 50 means «stop after 50 seconds».
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.

Параметры:
  • 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.

Параметры:
  • host
  • port
Return:

a socket object on success

Rtype:

userdata

Possible errors: Returns nil, status, errno, errstr on error.

socket_object:listen(backlog)

Start listening for incoming connections.

Параметры:
  • 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.

Параметры:
Return:

the number of bytes sent.

Rtype:

number

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

socket_object:recvfrom(limit)

Receive a message on a UDP socket.

Параметры:
  • limit (integer) –
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.

Параметры:
  • 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 its userdata is garbage collected by Lua.

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.

Параметры:
  • 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.

Параметры:
  • 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)

Примеры

Use of a TCP socket over the Internet

In this example a connection is made over the internet between a Tarantool instance and tarantool.org, then an HTTP «head» message is sent, and a response is received: «HTTP/1.1 200 OK» or something else if the site has moved. This is not a useful way to communicate with this particular site, but shows that the system works.

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
...

Use of a UDP socket on localhost

Here is an example with datagrams. Set up two connections on 127.0.0.1 (localhost): sock_1 and sock_2. Using sock_2, send a message to sock_1. Using sock_1, receive a message. Display the received message. Close both connections.
This is not a useful way for a computer to communicate with itself, but shows that the system works.

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')
---
- true
...
tarantool> message = sock_1:recvfrom()
---
...
tarantool> message
---
- X
...
tarantool> sock_1:close()
---
- true
...
tarantool> sock_2:close()
---
- true
...

Use tcp_server to accept file contents sent with socat

Here is an example of the tcp_server function, reading strings from the client and printing them. On the client side, the Linux socat utility will be used to ship a whole file for the tcp_server function to read.

Start two shells. The first shell will be a server instance. The second shell will be the client.

On the first shell, start Tarantool and say:

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

The above code means: use tcp_server() to wait for a connection from any host on port 3302. When it happens, enter a loop that reads on the socket and prints what it reads. The «delimiter» for the read function is «\n» so each read() will read a string as far as the next line feed, including the line feed.

On the second shell, create a file that contains a few lines. The contents don’t matter. Suppose the first line contains A, the second line contains B, the third line contains C. Call this file «tmp.txt».

On the second shell, use the socat utility to ship the tmp.txt file to the server instance’s host and port:

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

Now watch what happens on the first shell. The strings «A», «B», «C» are printed.