Tcl_OpenTcpClient(3) Tcl Library Procedures Tcl_OpenTcpClient(3)______________________________________________________________________________NAME
Tcl_OpenTcpClient, Tcl_MakeTcpClientChannel, Tcl_OpenTcpServer - proce‐
dures 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 connec‐
tion.
int myport (in) A port number for the
client's end of the socket.
If 0, a port number is allo‐
cated 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 asyn‐
chronously 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 con‐
nection 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 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 inter‐
face 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 con‐
nected 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 inter‐
preter's result.
The newly created channel is not registered in the supplied inter‐
preter; to register it, use Tcl_RegisterChannel. If one of the stan‐
dard 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 inter‐
preter; to register it, use Tcl_RegisterChannel. If one of the stan‐
dard 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 con‐
nects 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 mak‐
ing 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 dis‐
patch 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 inter‐
preter; to register it, use Tcl_RegisterChannel. If one of the stan‐
dard 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 ALSOTcl_OpenFileChannel(3), Tcl_RegisterChannel(3), vwait(n)KEYWORDS
channel, client, server, socket, TCP
Tcl 8.0 Tcl_OpenTcpClient(3)
