OpenMCL Sockets


Table of Contents

Overview
Functional Reference
make-socket [Function]
accept-connection [Function]
dotted-to-ipaddr [Function]
ipaddr-to-dotted [Function]
ipaddr-to-hostname [Function]
lookup-hostname [Function]
lookup-port [Function]
receive-from [Function]
send-to [Function]
shutdown [Function]
socket-os-fd [Function]
remote-port [Function]
local-host [Function]
local-port [Function]
socket-connect [Function]
socket-format [Function]
socket-type [Function]
socket-error [Class]
socket-error-code [Function]
socket-error-identifier [Function]
socket-error-situation [Function]
close [method]

Overview

OpenMCL supports the socket abstraction for interprocess communication. A socket represents a connection to another process, typically (but not necessarily) a TCP/IP network connection to a client or server running on some other machine on the network.

All symbols mentioned in this documentation are exported from the CCL package. As of version 0.13, these symbols are additionally exported from the OPENMCL-SOCKET package.

A socket is created by make-socket. The type of socket created depends on the arguments to make-socket. These types are currently supported:

tcp-stream

A buffered bi-directional stream over a TCP/IP connection. tcp-stream is a subclass of stream, and you can read and write to it using all the usual stream functions. Created by (make-socket :addess-family :internet :type :stream :connect :active ...) or by (accept-connection ...).

file-socket-stream

A buffered bi-directional stream over a "UNIX domain" connection. file-socket-stream is a subclass of stream, and you can read and write to it using all the usual stream functions. Created by (make-socket :address-family :file :type :stream :connect :active ...) or by (accept-connection ...),

listener-socket

A passive socket used to listen for incoming TCP/IP connections on a particular port. A listener-socket is not a stream. It doesn't support I/O. It can only be used to create new tcp-streams by accept-connection. Created by (make-socket :type :stream :connect :passive ...)

file-listener-socket

A passive socket used to listen for incoming UNIX domain connections named by a file in the local filesystem. A listener-socket is not a stream. It doesn't support I/O. It can only be used to create new file-socket-streams by accept-connection. Created by (make-socket :address-family :file :type :stream :connect :passive ...)

udp-socket

A socket representing a packet-based UDP/IP connection. A udp-socket supports I/O but it is not a stream. Instead, you must use the special functions send-to and receive-from to read and write to it. Created by (make-socket :type :datagram ...)

Functional Reference

make-socket [Function]

Syntax

make-socket &key address-family type connect eol format remote-host remote-port local-host local-port local-filename remote-filename keepalive reuse-address nodelay broadcast linger backlog

Description

Creates and returns a new socket

Arguments

 

address-family

The address/protocol family of this socket. Currently only :internet (the default), meaning IP, and :file, referring to UNIX domain addresses, are supported.

type

One of :stream (the default) to request a connection-oriented socket, or :datagram to request a connectionless socket. The default is :stream.

connect

This argument is only relevant to sockets of type :stream. One of :active (the default) to request a :passive to request a file or TCP listener socket.

eol

This argument is currently ignored (it is accepted for compatibility with Franz Allegro).

format

One of :text (the default), :binary, or :bivalent. This argument is ignored for :stream sockets for now, as :stream sockets are currently always bivalent (i.e. they support both character and byte I/O). For :datagram sockets, the format determines the type of buffer created by receive-from.

remote-host

Required for TCP streams, it specifies the host to connect to (in any format acceptable to lookup-hostname). Ignored for listener sockets. For UDP sockets, it can be used to specify a default host for subsequent calls to send-to or receive-from.

remote-port

Required for TCP streams, it specifies the port to connect to (in any format acceptable to lookup-port). Ignored for listener sockets. For UDP sockets, it can be used to specify a default port for subsequent calls to for subsequent calls to send-to or receive-from.

remote-filename

Required for file-socket streams, it specifies the name of a file in the local filesystem (e.g., NOT mounted via NFS, AFP, SMB, ...) which names and controls access to a UNIX-domain socket.

local-host

Allows you to specify a local host address for a listener or UDP socket, for the rare case where you want to restrict connections to those coming to a specific local address for security reasons.

local-port

Specify a local port for a socket. Most useful for listener sockets, where it is the port on which the socket will listen for connections.

local-filename

Required for file-listener-sockets. Specifies the name of a file in the local filesystem which is used to name a UNIX-domain socket. The actual filesystem file should not previously exist when the file-listener-socket is created; its parent directory should exist and be writable by the caller. The file used to name the socket will be deleted when the file-listener-socket is closed.

keepalive

If true, enables the periodic transmission of "keepalive" messages.

reuse-address

If true, allows the reuse of local ports in listener sockets, overriding some TCP/IP protocol specifications. You will need this if you are debugging a server..

nodelay

If true, disables Nagle's algorithm, which tries to minimize TCP packet fragmentation by introducing transmission delays in the absence of replies. Try setting this if you are using a protocol which involves sending a steady stream of data with no replies and are seeing significant degradations in throughput.

broadcast

If true, requests permission to broadcast datagrams on a UDP socket.

linger

If specified and non-nil, should be the number of seconds the OS is allowed to wait for data to be pushed through when a close is done. Only relevant for TCP sockets.

backlog

For a listener socket, specifies the number of connections which can be pending but not accepted. The default is 5, which is also the maximum on some operating systems.

accept-connection [Function]

Syntax

accept-connection (socket listener-socket) &key wait

Description

Extracts the first connection on the queue of pending connections, accepts it (i.e. completes the connection startup protocol) and returns a new tcp-stream or file-socket-stream representing the newly established connection. The tcp stream inherits any properties of the listener socket that are relevant (e.g. :keepalive, :nodelay, etc.) The original listener socket continues to be open listening for more connections, so you can call accept-connection on it again.

Arguments

 

socket

The listener-socket to listen on.

wait

If true (the default), and there are no connections waiting to be accepted, waits until one arrives. If false, returns NIL immediately.

dotted-to-ipaddr [Function]

Syntax

dotted-to-ipaddr dotted &key errorp

Description

Converts a dotted-string representation of a host address to a 32-bit unsigned IP address.

Arguments

 

dotted

A string representing an IP address in the "nn.nn.nn.nn" format

errorp

If true (the default) an error is signaled if dotted is invalid. If false, NIL is returned.

ipaddr-to-dotted [Function]

Syntax

ipaddr-to-dotted ipaddr &key values

Description

Converts a 32-bit unsigned IP address into octets.

Arguments

 

ipaddr

A 32-bit integer representing an internet host address

values

If false (the default), returns a string in the form "nn.nn.nn.nn". If true, returns four values representing the four octets of the address as unsigned 8-bit integers.

ipaddr-to-hostname [Function]

Syntax

ipaddr-to-hostname ipaddr &key ignore-cache

Description

Converts a 32-bit unsigned IP address into a host name string

Arguments

 

ipaddr

a 32-bit integer representing an internet host address

ignore-cache

This argument is ignored (it is accepted for compatibility with Franz Allegro)

lookup-hostname [Function]

Syntax

lookup-hostname host

Description

Converts a host spec in any of the acceptable formats into a 32-bit unsigned IP address

Arguments

 

host

Specifies the host. It can be either a host name string such as "clozure.com", or a dotted address string such as "192.168.0.1", or a 32-bit unsigned IP address such as 3232235521.

lookup-port [Function]

Syntax

lookup-port port protocol

Description

Finds the port number for the specified port and protocol

Arguments

 

port

Specifies the port. It can be either a string, such as "http" or a symbol, such as :http, or an unsigned port number. Note that a string is case-sensitive. A symbol is lowercased before lookup.

protocol

Must be one of "tcp" or "udp".

receive-from [Function]

Syntax

receive-from (socket udp-socket) size &key buffer extract offset

Description

Reads a UDP packet from a socket. If no packets are available, waits for a packet to arrive. Returns four values:

  1. The buffer with the data

  2. The number of bytes read

  3. The 32-bit unsigned IP address of the sender of the data

  4. The port number of the sender of the data

Arguments

 

socket

The socket to read from

size

Maximum number of bytes to read. If the packet is larger than this, any extra bytes are discarded.

buffer

If specified, must be either a string or a byte vector which will be used to read in the data. If not specified, a new buffer will be created (of type determined by socket-format).

extract

If true, the subsequence of the buffer corresponding only to the data read in is extracted and returned as the first value. If false (the default) the original buffer is returned even if it is only partially filled.

offset

Specifies the start offset into the buffer at which data is to be stored. The default is 0.

send-to [Function]

Syntax

send-to (socket udp-socket) buffer size &key remote-host remote-port offset

Description

Send a UDP packet over a socket.

Arguments

 

socket

The socket to write to

buffer

A vector containing the data to send. It must be either a string or a byte vector (either one is acceptable regardless of the stream format).

size

Number of bytes to send

remote-host

The host to send the packet to, in any format acceptable to lookup-hostname. The default is the remote host specified in the call to make-socket.

remote-port

The port to send the packet to, in any format acceptable to lookup-port. The default is the remote port specified in the call to make-socket.

offset

The offset in the buffer where the packet data starts

shutdown [Function]

Syntax

shutdown socket &key direction

Description

Shuts down part of a bidirectional connection. This is useful if e.g. you need to read responses after sending an end-of-file signal.

Arguments

 

socket

The socket to shut down (typically a tcp-stream)

direction

One of :input to disallow further input, or :output to disallow further output.

socket-os-fd [Function]

Syntax

ocket-os-fd socket

Description

Returns the native OS's representation of the socket, or NIL if the socket is closed. On Unix, this is the Unix 'file descriptor', a small non-negative integer. Note that it is rather dangerous to mess around with tcp-stream fd's, as there is all sorts of buffering and asynchronous I/O going on above the OS level. listener-socket and udp-socket fd's are safer to mess with directly as there is less magic going on.

Arguments

 

socket

The socket

remote-host

[Function]

Syntax

remote-host socket

Description

Returns the 32-bit unsigned IP address of the remote host, or NIL if the socket is not connected.

Arguments

 

socket

The socket

remote-port [Function]

Syntax

remote-port socket

Description

Returns the remote port number, or NIL if the socket is not connected.

Arguments

 

socket

The socket

local-host [Function]

Syntax

ocal-host socket

Description

Returns 32-bit unsigned IP address of the local host.

Arguments

 

socket

The socket

local-port [Function]

Syntax

local-port socket

Description

Returns the local port number

Arguments

 

socket

The socket

socket-address-family [Function]

Syntax

socket-address-family socket

Description

Returns :internet or :file, as appropriate.

Arguments

 

socket

The socket

socket-connect [Function]

Syntax

socket-connect socket

Description

Returns :active for tcp-stream, :passive for listener-socket, and NIL for udp-socket

Arguments

 

socket

The socket

socket-format [Function]

Syntax

socket-format socket

Description

Returns the socket format as specified by the :format argument to make-socket.

Arguments

 

socket

The socket

socket-type [Function]

Syntax

socket-type socket

Description

returns :stream for tcp-stream and listener-socket, and :datagram for udp-socket.

Arguments

 

socket

The socket

socket-error [Class]

Description

The class of OS errors signaled by socket functions

Superclasses

simple-error

socket-error-code [Function]

Syntax

socket-error-code socket-error

Description

The OS error code of the error

Arguments

socket-error

the condition

socket-error-identifier [Function]

Syntax

socket-error-identifier socket-error

Description

A symbol representing the error code in a more OS-independent way.

One of: :address-in-use :connection-aborted :no-buffer-space :connection-timed-out :connection-refused :host-unreachable :host-down :network-down :address-not-available :network-reset :connection-reset :shutdown :access-denied or :unknown.

Arguments

 

socket-error

the condition

socket-error-situation [Function]

Syntax

socket-error-situation socket-error

Description

A string describing the context where the error happened. On Linux, this is the name of the system call which returned the error.

Arguments

 

socket-error

the condition

close [method]

Syntax

close (socket socket) &key abort

Description

The close generic function can be applied to sockets. It releases the operating system resources associated with the socket.

Arguments

 

socket

The socket to close

abort

If false (the default), closes the socket in an orderly fashion, finishing up any buffered pending I/O, before closing the connection. If true, aborts/ignores pending I/O. (For listener and udp sockets, this argument is effectively ignored since there is never any buffered I/O to clean up).

with-open-socket

[Macro]

Syntax

with-open-socket (var . make-socket-args) &body body

Description

executes body with var bound to the result of applying make-socket to make-socket-args. The socket gets closed on exit.

Arguments

 

var

variable to bind

make-socket-args

arguments suitable for passing to make-socket

body

body to execute