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OpenDarwin 7.2.1 - man page for socket (opendarwin section n)

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socket(n)			      Tcl Built-In Commands				socket(n)

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NAME
       socket - Open a TCP network connection

SYNOPSIS
       socket ?options? host port

       socket -server command ?options? port
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DESCRIPTION
       This  command  opens a network socket and returns a channel identifier that may be used in
       future invocations of commands like read, puts and flush.  At present only the TCP network
       protocol is supported;  future releases may include support for additional protocols.  The
       socket command may be used to open either the client  or  server  side  of  a  connection,
       depending on whether the -server switch is specified.

       Note  that  the	default  encoding  for all sockets is the system encoding, as returned by
       encoding system.  Most of the time, you will need to use fconfigure to alter this to some-
       thing  else, such as utf-8 (ideal for communicating with other Tcl processes) or iso8859-1
       (useful for many network protocols, especially the older ones).

CLIENT SOCKETS
       If the -server 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.
       Port and host specify a port to connect to;  there must be a server accepting  connections
       on this port.  Port is an integer port number (or service name, where supported and under-
       stood by the host operating system) and	host  is  either  a  domain-style  name  such  as
       www.sunlabs.com	or  a  numerical IP address such as 127.0.0.1.	Use localhost to refer to
       the host on which the command is invoked.

       The following options may also be present before host to  specify  additional  information
       about the connection:

       -myaddr addr
	      Addr 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.

       -myport port
	      Port specifies an integer port number (or service name, where supported and  under-
	      stood 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.

       -async The -async 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 socket returns. When a gets or flush is done on the
	      socket before the connection attempt succeeds or fails, if the socket is in  block-
	      ing  mode,  the  operation will wait until the connection is completed or fails. If
	      the socket is in nonblocking mode and a gets or flush is done on the socket  before
	      the  connection  attempt	succeeds  or fails, the operation returns immediately and
	      fblocked on the socket returns 1.

SERVER SOCKETS
       If the -server option is specified then the new socket will be a server for the port given
       by  port  (either an integer or a service name, where supported and understood by the host
       operating system).  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 command 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.

       The following additional option may also be specified before host:

       -myaddr addr
	      Addr 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.

       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.

       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
       vwait command or calling the C procedure  Tcl_DoOneEvent,  then	no  connections  will  be
       accepted.

       If port is specified as zero, the operating system will allocate an unused port for use as
       a server socket.  The port number actually allocated my	be  retrieved  from  the  created
       server  socket  using the fconfigure command to retrieve the -sockname option as described
       below.

CONFIGURATION OPTIONS
       The fconfigure command can be used to query several  readonly  configuration  options  for
       socket channels:

       -error 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.

       -sockname
	      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.

       -peername
	      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  can-
	      not  be  computed,  the second element of the list is identical to the address, its
	      first element.

SEE ALSO
       fconfigure(n), flush(n), open(n), read(n)

KEYWORDS
       bind, channel, connection, domain name, host, network address, socket, tcp

Tcl					       8.0					socket(n)
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