Trying to get status via cupsBackChannelRead does not work with this code.

[Johan Henselmans]

I am having problems trying to get the status from the printer I am writing a filter for.

The code I am using is:

				
	status = cupsSideChannelDoRequest(CUPS_SC_CMD_GET_BIDI, &data, &datalen, 5.0);

	// Read the response if the output was sent
	if (status == CUPS_SC_STATUS_OK & datalen==1){
	  bidi=(cups_sc_bidi_t)data;
	  // drain the pending output
	  status = cupsSideChannelDoRequest(CUPS_SC_CMD_DRAIN_OUTPUT, &data, &datalen, 5.0);

	  fprintf(stdout, "   <S2>"); //send status request, returns seven digit ticket count and prom version
	  fflush(stdout);
	  count = cupsBackChannelRead(backbuffer, sizeof(backbuffer), 0.0);
	  fprintf(stderr, "DEBUG: ***** backbuf  Read %i backchannel bytes in Setup*****\n", count);
	  if (count > 0){
	    fprintf(stderr, "DEBUG: ***** backbuffer: [");
            int i = 0;
            while (i < count){
	      fprintf(stderr, "%c", backbuffer[i]);
	      i++;
	    }
	    fprintf(stderr, "] *****\n");
	  }
	fflush(stderr);
	}
		

This should return 23 bytes of data. The result is that I do not get 23 bytes of data, but -1, and after that I get a
bunch of messages that some data is received. It seems that the cupsBackChannelRead is not waiting long enough for the
answer. I varied with different settings for the time-out, from 20.0 to 0.0 to -1.0 as per

http://www.cups.org/documentation.php/api-filter.html#cupsBackChannelRead

But the results are not what I would expect, sometimes I get 1 bytes, sometimes -1 bytes, sometime I get the full 23
bytes. Is there something that I am missing here?


D [06/Feb/2012:20:59:09 +0100] [Job 1786] ***** backbuf  Read -1 backchannel bytes in Setup*****
D [06/Feb/2012:20:59:09 +0100] [Job 1786] Read 1 bytes of back-channel data...
D [06/Feb/2012:20:59:09 +0100] [Job 1786] Read 1 bytes of back-channel data...
D [06/Feb/2012:20:59:09 +0100] [Job 1786] Read 1 bytes of back-channel data...
D [06/Feb/2012:20:59:09 +0100] [Job 1786] Read 1 bytes of back-channel data...
D [06/Feb/2012:20:59:09 +0100] [Job 1786] Read 1 bytes of back-channel data...
D [06/Feb/2012:20:59:09 +0100] [Job 1786] Read 2 bytes of back-channel data...
D [06/Feb/2012:20:59:09 +0100] [Job 1786] Read 1 bytes of back-channel data...
D [06/Feb/2012:20:59:09 +0100] [Job 1786] Read 1 bytes of back-channel data...
D [06/Feb/2012:20:59:09 +0100] [Job 1786] Read 1 bytes of back-channel data...
D [06/Feb/2012:20:59:09 +0100] [Job 1786] Read 1 bytes of back-channel data...
D [06/Feb/2012:20:59:09 +0100] [Job 1786] Read 1 bytes of back-channel data...
D [06/Feb/2012:20:59:09 +0100] [Job 1786] Read 1 bytes of back-channel data...
D [06/Feb/2012:20:59:09 +0100] [Job 1786] Read 1 bytes of back-channel data...
D [06/Feb/2012:20:59:09 +0100] [Job 1786] Read 1 bytes of back-channel data...
D [06/Feb/2012:20:59:09 +0100] [Job 1786] Read 1 bytes of back-channel data...
D [06/Feb/2012:20:59:09 +0100] [Job 1786] Read 1 bytes of back-channel data...
D [06/Feb/2012:20:59:09 +0100] [Job 1786] Read 1 bytes of back-channel data...
D [06/Feb/2012:20:59:09 +0100] [Job 1786] Read 1 bytes of back-channel data...
D [06/Feb/2012:20:59:09 +0100] [Job 1786] Read 1 bytes of back-channel data...
D [06/Feb/2012:20:59:09 +0100] [Job 1786] Read 1 bytes of back-channel data...
D [06/Feb/2012:20:59:09 +0100] [Job 1786] Read 1 bytes of back-channel data...
D [06/Feb/2012:20:59:09 +0100] [Job 1786] Read 1 bytes of back-channel data...

-- 
Kind Regards,

Johan Henselmans