Tcl_OpenTcpClient(3)					      Tcl Library Procedures					      Tcl_OpenTcpClient(3)

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NAME

       Tcl_OpenTcpClient, Tcl_MakeTcpClientChannel, Tcl_OpenTcpServer - procedures to open channels 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 interface 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.
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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_OpenFileChannel.

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 contain-
       ing 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 operating 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 success-
       fully or fails. If the channel is in nonblocking mode, the input or output 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 stan-
       dard channel.

TCL_MAKETCPCLIENTCHANNEL
       Tcl_MakeTcpClientChannel creates a Tcl_Channel around an existing, platform specific, handle 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 stan-
       dard 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 information 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 stan-
       dard 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)