Provided by: tcl8.6-doc_8.6.13+dfsg-2_all 
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.
_________________________________________________________________________________________________
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
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
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 successfully 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 standard 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 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
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 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(3tcl), Tcl_RegisterChannel(3tcl), vwait(3tcl)
KEYWORDS
channel, client, server, socket, TCP