Provided by: tcl-xpa_2.1.17-1_amd64 
NAME
XPATcl - the XPA Interface to the Tcl/Tk Environment
SYNOPSIS
Tcl/Tk programs can act as XPA clients and/or servers using the Tcl interface to XPA that
is contained in the libtclxpa.so shared object.
Server Routines
set xpa [xpanew class name help sproc sdata smode rproc rdata rmode]
xpafree xpa
set xpa [xpanew class name help iproc idata imode]
set xpa [xpacmdnew class name]
xpacmdadd xpa name help sproc sdata smode rproc rdata rmode
xpacmddel xpa cmd
set val [xparec xpa option]
options: name, class, method, cmdfd, datafd, cmdchan, datachan
xpasetbuf xpa buf len
xpaerror xpa message
xpamessage xpa message
Client Routines
set xpa [xpaopen mode]
xpaclose xpa
set got [xpaget xpa template paramlist mode bufs lens names errs n]
set got [xpaget xpa template paramlist mode chans names errs n]
set got [xpaset xpa template paramlist mode buf len names errs n]
set got [xpasetfd xpa template paramlist mode chan names errs n]
set got [xpainfo xpa template paramlist mode names errs n]
# NB: 2.1 calling sequence change
# set got [xpaaccess template type] (2.0.5)
set got [xpaaccess xpa template paramlist mode names errs n]
set got [xpanslookup template type classes names methods]
DESCRIPTION
You can call XPANew(), XPACmdNew(), or XPAInfoNew() within a C routine to add C\-based XPA
server callbacks to a TCL/Tk program that uses a Tcl/Tk event loop (either vwait() or the
Tk event loop); Such a program does not need or want to use the XPA event loop.
Therefore, in order to add XPA access points to the Tcl/Tk loop, the following routine
should be called beforehand:
int XPATclAddInput(XPA xpa);
Normally, the xpa argument is NULL, meaning that all current XPA access points are
registered with the event loop. However, if a single XPA access point is to be added
(i.e., after the event loop is started) then the handle of that XPA access point can be
passed to this routine.
The significance of the XPA/TCL interface goes beyond the support for using XPA inside C
code. The interface allows you to write XPA servers and to make calls to the XPA client
interface within the Tcl environment using the Tcl language directly. The XPA/Tcl
interface can be loaded using the following package command:
package require tclxpa 2.0
Alternatively, you can load the shared object (called libtclxpa.so ) directly:
load .../libtclxpa.so tclxpa
Once the tclxpa package is loaded, you can use Tcl versions of XPA routines to define XPA
servers or make client XPA calls. The interface for these routines is designed to match
the Unix XPA interface as nearly as possible. Please refer to XPA Servers and XPA Clients
for general information about these routines.
The file test.tcl in the XPA source directory gives examples for using the XPA/Tcl
interface.
The following notes describe the minor differences between the interfaces.
XPANew
set xpa [xpanew class name help sproc sdata smode rproc rdata rmode]
rproc and sproc routines are routines. The calling sequence of the rproc routine is
identical to its C counterpart:
proc rec_cb { xpa client_data paramlist buf len } { ... }
The sproc routine, however is slightly different from its C counterpart because of the
difficulty of passing data back from the callback to C:
proc sendcb { xpa client_data paramlist } { ... }
Note that the C\-based server's char **buf and int *len arguments are missing from the Tcl
callback. This is because we did not know how to fill buf with data and pass it back to
the C routines for communication with the client. Instead, the Tcl server callback uses
the following routine to set buf and len:
xpasetbuf xpa buf len
where:
arg explanation
------ -----------
xpa the first argument of the server callback
buf the data to be returned to the client
len data length in bytes, (if absent, use length of the buf object)
When this routine is called, a copy of buf is saved for transmission to the client.
The fact that buf is duplicated means that TCL server writers might wish to perform the
I/O directly within the callback, rather than have XPA do it automatically at the end of
the routine. To do this, set:
fillbuf=false
in the xpanew smode and then perform I/O through the Tcl channel obtained from:
set dchan [xparec $xpa datachan]
where:
arg explanation
------ -----------
xpa the first argument of the server callback
datachan literal string "datachan" that returns the data channel
len data length in bytes, (if absent, use length of the buf object)
NB: datachan and cmdchan are not available under Windows. It is necessary to use the "raw"
equivalents: datafd and cmdfd.
The same considerations apply to the rproc for receive servers: a copy of the incoming
data is generated to pass to the receive callback. This copy again can be avoided by using
"fillbuf=false" in the rmode and then reading the incoming data from datachan.
The send and receive callback routines can use the xpaerror and xpamessage routines to
send errors and messages back to the client. If you also want tcl itself to field an
error condition, use the standard return call:
return ?\-code c? ?\-errorinfo i? ?\-errorcode ec? string
See the Tcl man page for more info.
XPARec
The Tcl xparec procedure supplies server routines with access to information that is
available via macros in the C interface:
set val [xparec xpa <option>]
where option is: name, class, method, cmdfd, datafd, cmdchan, datachan. Note that two
additional identifiers, cmdchan and datachan, have been added to to provide Tcl channels
corresponding to datafd and cmdfd. (These latter might still be retrieved in Tcl and
passed back to a C routines.) An additional option called "version" can be used to
determine the XPA version used to build the Tcl interface. Note that the standard options
require a valid XPA handle, but "version" does not (since it simply reports the value of
the XPA_VERSION definition in the XPA source include file).
NB: datachan and cmdchan are not available under Windows. It is necessary to use the "raw"
equivalents: datafd and cmdfd.
macro explanation
------ -----------
class class of this xpa
name name of this xpa
method method string (inet or local connect info)
cmdchan Tcl channel of command socket
datachan Tcl channel of data socket
cmdfd fd of command socket
datafd fd of data socket
sendian endian\-ness of server ("little" or "big")
cendian endian\-ness of client ("little" or "big"
version XPA version used to build this code
Under Windows, the Tcl event handler cannot automatically sense when an XPA socket is
ready for IO (i.e. Tcl_CreateFileHandler() is not available under Windows). The Windows
Tcl event handler therefore must be awakened occasionally for check for XPA events. This
is done using the standard Tcl_SetMaxBlockTime() call. The time parameter is defined in
tclloop.c and is currently set to 1000 microseconds (1/1000 of a second).
The version option can be used to differentiate between source code versions. It was
created to support legacy Tcl code that needs to maintain the 2.0.5 calling sequence for
xpaaccess. You can use a version test such as:
if [catch { xparec "" version } version] {
puts "pre\-2.1.0e"
} else {
puts [split $version .]
}
SEE ALSO
See xpa(7) for a list of XPA help pages