[naviserver-devel] Problem with a Tcl extension and NaviServer

[Matthew B. <mm...@gm...>]

Hello!

I am writing a Tcl extension in C to wrap a driver for a USB LED status
light. The extension runs fine from tclsh but there are issues running it
from a Tcl  page under NaviServer.

The extension implements one command via Tcl_CreateObjCommand. The command
proc implements a number of sub-commands broken into two categories:
device-independent functionality, e.g. count the number of status lights
that are plugged in, and device-dependent functionality, e.g. attach to a
status light, display a particular color, etc

The device-independent sub-commands work when run in a Tcl page. For
example, this page runs fine when served from NaviServer:


package require blink

set n [blink enumerate]

ns_return 200 text/html "
There are <strong>$n</strong> devices plugged in.
"


In order to have a device display a color, etc., you first have to run the
"open" command. And that's not working. So here's an example Tcl page:


package require blink

set d [blink open 0]
set q [ns_conn query]
set s [ns_parsequery $q]

set red [ns_set get $s red 255]
set green [ns_set get $s green 0]
set blue [ns_set get $s blue 0]

blink set $d $red $green $blue

ns_return 200 text/html "
    <p>Query: [ns_conn query]</p>

    <ul>
    <li>Red: $red</li>
    <li>Green: $green</li>
    <li>Blue: $blue</li>
    </ul>
"


When this page is served, I get an error in the line: set d [blink open 0].

There is a C struct, Blinker,  that contains data about the attached
device. My C code first allocates
memory for the struct


blinkPtr = (Blinker *)Tcl_Alloc(sizeof(Blinker));


and this seems to work -- blinkPtr is non-NULL after the assignment. Then
there is a function from the driver library that actually attaches to the
device:

blinkPtr->device = blink1_openById(devid);

It should return the memory address of an allocated structure that's part
of the USB library. But the function returns NULL. (Just to reiterate, this
works fine when run from tclsh and returns a non-NULL value.)

I'm assuming there is some sort of memory protection or similar that I need
to take into account. Any suggestions on what to look at would be greatly
appreciated.

Thanks,

Matt

P.S. This is on macOS 14.3. I'm compiling the extension as follows:

clang -dynamiclib -DUSE_TCL_STUBS -I/usr/local/ns/include
-L/usr/local/ns/lib -ltclstub8.6 -o blink.dylib blink.c -L/usr/local/lib
-lBlink1