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

[Gustaf N. <ne...@wu...>]

Dear Mathew,

The answer for your this problem is probably in the call of 
blink1_openById(devid);

Without looking into this call, I would suspect first from my experience 
with NaviServer IoT projects a permission problem when accessing the 
hardware interface.
For security reasons, NaviServer switches to a nonprivileged user ...

all the best -g

On 25.06.24 16:18, Matthew Burke wrote:
> 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
>
>
>
>
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