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Tcl_OpenTcpClient(3)		      Tcl Library Procedures		     Tcl_OpenTcpClient(3)

_________________________________________________________________________________________________

NAME
       Tcl_OpenTcpClient,  Tcl_MakeTcpClientChannel, Tcl_OpenTcpServer - procedures to open chan-
       nels using TCP sockets

SYNOPSIS
       #include <tcl.h>

       Tcl_Channel
       Tcl_OpenTcpClient(interp, port, host, myaddr, myport, async)

       Tcl_Channel
       Tcl_MakeTcpClientChannel(sock)

       Tcl_Channel
       Tcl_OpenTcpServer(interp, port, myaddr, proc, clientData)

ARGUMENTS
       Tcl_Interp *interp (in)			  Tcl interpreter to use for error reporting.  If
						  non-NULL  and an error occurs, an error message
						  is left in the interpreter's result.

       int port (in)				  A port number to connect to as a client  or  to
						  listen on as a server.

       const char *host (in)			  A  string specifying a host name or address for
						  the remote end of the connection.

       int myport (in)				  A port number  for  the  client's  end  of  the
						  socket.   If	0,  a port number is allocated at
						  random.

       const char *myaddr (in)			  A string specifying the host	name  or  address
						  for  network interface to use for the local end
						  of the connection.  If NULL, a  default  inter-
						  face is chosen.

       int async (in)				  If  nonzero,	the  client  socket  is connected
						  asynchronously to the server.

       ClientData sock (in)			  Platform-specific handle for client TCP socket.

       Tcl_TcpAcceptProc *proc (in)		  Pointer to a procedure to invoke  each  time	a
						  new connection is accepted via the socket.

       ClientData clientData (in)		  Arbitrary one-word value to pass to proc.
_________________________________________________________________

DESCRIPTION
       These functions are convenience procedures for creating channels that communicate over TCP
       sockets.  The operations on a channel are described in  the  manual  entry  for	Tcl_Open-
       FileChannel.

TCL_OPENTCPCLIENT
       Tcl_OpenTcpClient  opens  a  client TCP socket connected to a port on a specific host, and
       returns a channel that can be used to communicate with the server. The host to connect  to
       can be specified either as a domain name style name (e.g. www.sunlabs.com), or as a string
       containing the alphanumeric representation of its four-byte address (e.g.  127.0.0.1). Use
       the  string  localhost  to  connect  to	a TCP socket on the host on which the function is
       invoked.

       The myaddr and myport arguments allow a client to specify an address for the local end  of
       the connection.	If myaddr is NULL, then an interface is chosen automatically by the oper-
       ating system.  If myport is 0, then a port number is chosen at  random  by  the	operating
       system.

       If  async  is zero, the call to Tcl_OpenTcpClient returns only after the client socket has
       either successfully connected to the server, or the attempted connection has  failed.   If
       async  is  nonzero the socket is connected asynchronously and the returned channel may not
       yet be connected to the server when the call to Tcl_OpenTcpClient returns. If the  channel
       is  in  blocking  mode  and an input or output operation is done on the channel before the
       connection is completed or fails, that operation will wait  until  the  connection  either
       completes  successfully or fails. If the channel is in nonblocking mode, the input or out-
       put operation will return immediately and a subsequent call  to	Tcl_InputBlocked  on  the
       channel will return nonzero.

       The returned channel is opened for reading and writing.	If an error occurs in opening the
       socket, Tcl_OpenTcpClient returns NULL  and  records  a	POSIX  error  code  that  can  be
       retrieved with Tcl_GetErrno.  In addition, if interp is non-NULL, an error message is left
       in the interpreter's result.

       The newly created channel is not registered in the supplied interpreter; to  register  it,
       use  Tcl_RegisterChannel.   If  one  of the standard channels, stdin, stdout or stderr was
       previously closed, the act of creating the new channel also assigns it  as  a  replacement
       for the standard channel.

TCL_MAKETCPCLIENTCHANNEL
       Tcl_MakeTcpClientChannel creates a Tcl_Channel around an existing, platform specific, han-
       dle for a client TCP socket.

       The newly created channel is not registered in the supplied interpreter; to  register  it,
       use  Tcl_RegisterChannel.   If  one  of the standard channels, stdin, stdout or stderr was
       previously closed, the act of creating the new channel also assigns it  as  a  replacement
       for the standard channel.

TCL_OPENTCPSERVER
       Tcl_OpenTcpServer  opens  a  TCP socket on the local host on a specified port and uses the
       Tcl event mechanism to accept requests from clients to connect to it. The myaddr  argument
       specifies  the network interface.  If myaddr is NULL the special address INADDR_ANY should
       be used to allow connections from any network interface.  Each time a client  connects  to
       this  socket,  Tcl creates a channel for the new connection and invokes proc with informa-
       tion about the channel. Proc must match the following prototype:
	      typedef void Tcl_TcpAcceptProc(
		      ClientData clientData,
		      Tcl_Channel channel,
		      char *hostName,
		      int port);

       The clientData argument will be the same as the clientData argument to  Tcl_OpenTcpServer,
       channel will be the handle for the new channel, hostName points to a string containing the
       name of the client host making the connection, and port will  contain  the  client's  port
       number.	 The  new  channel is opened for both input and output.  If proc raises an error,
       the connection is closed automatically.	Proc has no return value, but  if  it  wishes  to
       reject the connection it can close channel.

       Tcl_OpenTcpServer  normally returns a pointer to a channel representing the server socket.
       If an error occurs, Tcl_OpenTcpServer returns NULL and records a POSIX error code that can
       be  retrieved  with  Tcl_GetErrno.   In addition, if the interpreter is non-NULL, an error
       message is left in the interpreter's result.

       The channel returned by Tcl_OpenTcpServer cannot be used for either input or  output.   It
       is  simply  a  handle for the socket used to accept connections.  The caller can close the
       channel to shut down the server and disallow further connections from new clients.

       TCP server channels operate correctly only in applications that	dispatch  events  through
       Tcl_DoOneEvent or through Tcl commands such as vwait; otherwise Tcl will never notice that
       a connection request from a remote client is pending.

       The newly created channel is not registered in the supplied interpreter; to  register  it,
       use  Tcl_RegisterChannel.   If  one  of the standard channels, stdin, stdout or stderr was
       previously closed, the act of creating the new channel also assigns it  as  a  replacement
       for the standard channel.

PLATFORM ISSUES
       On  Unix  platforms, the socket handle is a Unix file descriptor as returned by the socket
       system call.  On the Windows platform, the socket handle is a SOCKET  as  defined  in  the
       WinSock API.

SEE ALSO
       Tcl_OpenFileChannel(3), Tcl_RegisterChannel(3), vwait(n)

KEYWORDS
       client, server, TCP

Tcl					       8.0			     Tcl_OpenTcpClient(3)
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