'\" '\" Copyright (c) 1996 Sun Microsystems, Inc. '\" Copyright (c) 1998-1999 by Scriptics Corporation. '\" '\" See the file "license.terms" for information on usage and redistribution '\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. '\" '\" RCS: @(#) $Id: socket.n,v 1.1.1.1 2007/07/10 15:04:23 duncan Exp $ '\" The definitions below are for supplemental macros used in Tcl/Tk '\" manual entries. '\" '\" .AP type name in/out ?indent? '\" Start paragraph describing an argument to a library procedure. '\" type is type of argument (int, etc.), in/out is either "in", "out", '\" or "in/out" to describe whether procedure reads or modifies arg, '\" and indent is equivalent to second arg of .IP (shouldn't ever be '\" needed; use .AS below instead) '\" '\" .AS ?type? ?name? '\" Give maximum sizes of arguments for setting tab stops. Type and '\" name are examples of largest possible arguments that will be passed '\" to .AP later. If args are omitted, default tab stops are used. '\" '\" .BS '\" Start box enclosure. From here until next .BE, everything will be '\" enclosed in one large box. '\" '\" .BE '\" End of box enclosure. '\" '\" .CS '\" Begin code excerpt. '\" '\" .CE '\" End code excerpt. '\" '\" .VS ?version? ?br? '\" Begin vertical sidebar, for use in marking newly-changed parts '\" of man pages. The first argument is ignored and used for recording '\" the version when the .VS was added, so that the sidebars can be '\" found and removed when they reach a certain age. If another argument '\" is present, then a line break is forced before starting the sidebar. '\" '\" .VE '\" End of vertical sidebar. '\" '\" .DS '\" Begin an indented unfilled display. '\" '\" .DE '\" End of indented unfilled display. '\" '\" .SO '\" Start of list of standard options for a Tk widget. The '\" options follow on successive lines, in four columns separated '\" by tabs. '\" '\" .SE '\" End of list of standard options for a Tk widget. '\" '\" .OP cmdName dbName dbClass '\" Start of description of a specific option. cmdName gives the '\" option's name as specified in the class command, dbName gives '\" the option's name in the option database, and dbClass gives '\" the option's class in the option database. '\" '\" .UL arg1 arg2 '\" Print arg1 underlined, then print arg2 normally. '\" '\" RCS: @(#) $Id: man.macros,v 1.1.1.1 2007/07/10 15:04:23 duncan Exp $ '\" '\" # Set up traps and other miscellaneous stuff for Tcl/Tk man pages. .if t .wh -1.3i ^B .nr ^l \n(.l .ad b '\" # Start an argument description .de AP .ie !"\\$4"" .TP \\$4 .el \{\ . ie !"\\$2"" .TP \\n()Cu . el .TP 15 .\} .ta \\n()Au \\n()Bu .ie !"\\$3"" \{\ \&\\$1 \\fI\\$2\\fP (\\$3) .\".b .\} .el \{\ .br .ie !"\\$2"" \{\ \&\\$1 \\fI\\$2\\fP .\} .el \{\ \&\\fI\\$1\\fP .\} .\} .. '\" # define tabbing values for .AP .de AS .nr )A 10n .if !"\\$1"" .nr )A \\w'\\$1'u+3n .nr )B \\n()Au+15n .\" .if !"\\$2"" .nr )B \\w'\\$2'u+\\n()Au+3n .nr )C \\n()Bu+\\w'(in/out)'u+2n .. .AS Tcl_Interp Tcl_CreateInterp in/out '\" # BS - start boxed text '\" # ^y = starting y location '\" # ^b = 1 .de BS .br .mk ^y .nr ^b 1u .if n .nf .if n .ti 0 .if n \l'\\n(.lu\(ul' .if n .fi .. '\" # BE - end boxed text (draw box now) .de BE .nf .ti 0 .mk ^t .ie n \l'\\n(^lu\(ul' .el \{\ .\" Draw four-sided box normally, but don't draw top of .\" box if the box started on an earlier page. .ie !\\n(^b-1 \{\ \h'-1.5n'\L'|\\n(^yu-1v'\l'\\n(^lu+3n\(ul'\L'\\n(^tu+1v-\\n(^yu'\l'|0u-1.5n\(ul' .\} .el \}\ \h'-1.5n'\L'|\\n(^yu-1v'\h'\\n(^lu+3n'\L'\\n(^tu+1v-\\n(^yu'\l'|0u-1.5n\(ul' .\} .\} .fi .br .nr ^b 0 .. '\" # VS - start vertical sidebar '\" # ^Y = starting y location '\" # ^v = 1 (for troff; for nroff this doesn't matter) .de VS .if !"\\$2"" .br .mk ^Y .ie n 'mc \s12\(br\s0 .el .nr ^v 1u .. '\" # VE - end of vertical sidebar .de VE .ie n 'mc .el \{\ .ev 2 .nf .ti 0 .mk ^t \h'|\\n(^lu+3n'\L'|\\n(^Yu-1v\(bv'\v'\\n(^tu+1v-\\n(^Yu'\h'-|\\n(^lu+3n' .sp -1 .fi .ev .\} .nr ^v 0 .. '\" # Special macro to handle page bottom: finish off current '\" # box/sidebar if in box/sidebar mode, then invoked standard '\" # page bottom macro. .de ^B .ev 2 'ti 0 'nf .mk ^t .if \\n(^b \{\ .\" Draw three-sided box if this is the box's first page, .\" draw two sides but no top otherwise. .ie !\\n(^b-1 \h'-1.5n'\L'|\\n(^yu-1v'\l'\\n(^lu+3n\(ul'\L'\\n(^tu+1v-\\n(^yu'\h'|0u'\c .el \h'-1.5n'\L'|\\n(^yu-1v'\h'\\n(^lu+3n'\L'\\n(^tu+1v-\\n(^yu'\h'|0u'\c .\} .if \\n(^v \{\ .nr ^x \\n(^tu+1v-\\n(^Yu \kx\h'-\\nxu'\h'|\\n(^lu+3n'\ky\L'-\\n(^xu'\v'\\n(^xu'\h'|0u'\c .\} .bp 'fi .ev .if \\n(^b \{\ .mk ^y .nr ^b 2 .\} .if \\n(^v \{\ .mk ^Y .\} .. '\" # DS - begin display .de DS .RS .nf .sp .. '\" # DE - end display .de DE .fi .RE .sp .. '\" # SO - start of list of standard options .de SO .SH "STANDARD OPTIONS" .LP .nf .ta 5.5c 11c .ft B .. '\" # SE - end of list of standard options .de SE .fi .ft R .LP See the \\fBoptions\\fR manual entry for details on the standard options. .. '\" # OP - start of full description for a single option .de OP .LP .nf .ta 4c Command-Line Name: \\fB\\$1\\fR Database Name: \\fB\\$2\\fR Database Class: \\fB\\$3\\fR .fi .IP .. '\" # CS - begin code excerpt .de CS .RS .nf .ta .25i .5i .75i 1i .. '\" # CE - end code excerpt .de CE .fi .RE .. .de UL \\$1\l'|0\(ul'\\$2 .. .TH socket n 8.0 Tcl "Tcl Built-In Commands" .BS '\" Note: do not modify the .SH NAME line immediately below! .SH NAME socket \- Open a TCP network connection .SH SYNOPSIS .sp \fBsocket \fR?\fIoptions\fR? \fIhost port\fR .sp \fBsocket\fR \fB\-server \fIcommand\fR ?\fIoptions\fR? \fIport\fR .BE .SH DESCRIPTION .PP This command opens a network socket and returns a channel identifier that may be used in future invocations of commands like \fBread\fR, \fBputs\fR and \fBflush\fR. At present only the TCP network protocol is supported; future releases may include support for additional protocols. The \fBsocket\fR command may be used to open either the client or server side of a connection, depending on whether the \fB\-server\fR switch is specified. .PP Note that the default encoding for \fIall\fR sockets is the system encoding, as returned by \fBencoding system\fR. Most of the time, you will need to use \fBfconfigure\fR to alter this to something else, such as \fIutf\-8\fR (ideal for communicating with other Tcl processes) or \fIiso8859\-1\fR (useful for many network protocols, especially the older ones). .SH "CLIENT SOCKETS" .PP If the \fB\-server\fR option is not specified, then the client side of a connection is opened and the command returns a channel identifier that can be used for both reading and writing. \fIPort\fR and \fIhost\fR specify a port to connect to; there must be a server accepting connections on this port. \fIPort\fR is an integer port number (or service name, where supported and understood by the host operating system) and \fIhost\fR is either a domain-style name such as \fBwww.tcl.tk\fR or a numerical IP address such as \fB127.0.0.1\fR. Use \fIlocalhost\fR to refer to the host on which the command is invoked. .PP The following options may also be present before \fIhost\fR to specify additional information about the connection: .TP \fB\-myaddr\fI addr\fR \fIAddr\fR gives the domain-style name or numerical IP address of the client-side network interface to use for the connection. This option may be useful if the client machine has multiple network interfaces. If the option is omitted then the client-side interface will be chosen by the system software. .TP \fB\-myport\fI port\fR \fIPort\fR specifies an integer port number (or service name, where supported and understood by the host operating system) to use for the client's side of the connection. If this option is omitted, the client's port number will be chosen at random by the system software. .TP \fB\-async\fR The \fB\-async\fR option will cause the client socket to be connected asynchronously. This means that the socket will be created immediately but may not yet be connected to the server, when the call to \fBsocket\fR returns. When a \fBgets\fR or \fBflush\fR is done on the socket before the connection attempt succeeds or fails, if the socket is in blocking mode, the operation will wait until the connection is completed or fails. If the socket is in nonblocking mode and a \fBgets\fR or \fBflush\fR is done on the socket before the connection attempt succeeds or fails, the operation returns immediately and \fBfblocked\fR on the socket returns 1. .SH "SERVER SOCKETS" .PP If the \fB\-server\fR option is specified then the new socket will be a server for the port given by \fIport\fR (either an integer or a service name, where supported and understood by the host operating system; if \fIport\fR is zero, the operating system will allocate a free port to the server socket which may be discovered by using \fBfconfigure\fR to read the \fB\-sockname\fR option). Tcl will automatically accept connections to the given port. For each connection Tcl will create a new channel that may be used to communicate with the client. Tcl then invokes \fIcommand\fR with three additional arguments: the name of the new channel, the address, in network address notation, of the client's host, and the client's port number. .PP The following additional option may also be specified before \fIhost\fR: .TP \fB\-myaddr\fI addr\fR \fIAddr\fR gives the domain-style name or numerical IP address of the server-side network interface to use for the connection. This option may be useful if the server machine has multiple network interfaces. If the option is omitted then the server socket is bound to the special address INADDR_ANY so that it can accept connections from any interface. .PP Server channels cannot be used for input or output; their sole use is to accept new client connections. The channels created for each incoming client connection are opened for input and output. Closing the server channel shuts down the server so that no new connections will be accepted; however, existing connections will be unaffected. .PP Server sockets depend on the Tcl event mechanism to find out when new connections are opened. If the application doesn't enter the event loop, for example by invoking the \fBvwait\fR command or calling the C procedure \fBTcl_DoOneEvent\fR, then no connections will be accepted. .PP If \fIport\fR is specified as zero, the operating system will allocate an unused port for use as a server socket. The port number actually allocated may be retrieved from the created server socket using the \fBfconfigure\fR command to retrieve the \fB\-sockname\fR option as described below. .SH "CONFIGURATION OPTIONS" The \fBfconfigure\fR command can be used to query several readonly configuration options for socket channels: .TP \fB\-error\fR This option gets the current error status of the given socket. This is useful when you need to determine if an asynchronous connect operation succeeded. If there was an error, the error message is returned. If there was no error, an empty string is returned. .TP \fB\-sockname\fR This option returns a list of three elements, the address, the host name and the port number for the socket. If the host name cannot be computed, the second element is identical to the address, the first element of the list. .TP \fB\-peername\fR This option is not supported by server sockets. For client and accepted sockets, this option returns a list of three elements; these are the address, the host name and the port to which the peer socket is connected or bound. If the host name cannot be computed, the second element of the list is identical to the address, its first element. .PP .SH "EXAMPLES" Here is a very simple time server: .CS proc Server {channel clientaddr clientport} { puts "Connection from $clientaddr registered" puts $channel [clock format [clock seconds]] close $channel } \fBsocket\fR -server Server 9900 vwait forever .CE .PP And here is the corresponding client to talk to the server: .CS set server localhost set sockChan [\fBsocket\fR $server 9900] gets $sockChan line close $sockChan puts "The time on $server is $line" .CE .SH "SEE ALSO" fconfigure(n), flush(n), open(n), read(n) .SH KEYWORDS bind, channel, connection, domain name, host, network address, socket, tcp