Tcl_OpenTcpClient(3) Tcl (8.0) Tcl_OpenTcpClient(3)
_________________________________________________________________
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
interp-
>result.
int port (in) A port number
to connect to
as a client
or to listen
on as a
server.
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
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Tcl_OpenTcpClient(3) Tcl (8.0) Tcl_OpenTcpClient(3)
of the
socket. If
0, a port
number is
allocated at
random.
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
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Tcl_OpenTcpClient(3) Tcl (8.0) Tcl_OpenTcpClient(3)
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 interp->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.
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Tcl_OpenTcpClient(3) Tcl (8.0) Tcl_OpenTcpClient(3)
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 interp->result is non-NULL, an error message is left in
interp->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
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Tcl_OpenTcpClient(3) Tcl (8.0) Tcl_OpenTcpClient(3)
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. On the Macintosh platform, the socket |
handle is a StreamPtr.
SEE ALSO
Tcl_OpenFileChannel(3), Tcl_RegisterChannel(3), vwait(n)
KEYWORDS
client, server, TCP
Page 5 (printed 2/19/99)
