[cups.bugs] [LOW] STR #3755: Autodetected LPD printers cannot detect or change print queue name via web interface

[Michael Tin]

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[STR New]

There is a bug with the way the CUPS web administration portal(the
interface on http://localhost:631) handles autodetected CUPS printers, if
that printer only allows LPD printing. 

Normally, LPD printers have a URI of lpd://<printer IP>:<port>/queuename.
/usr/lib/cups/backend/lpd more specifically will NOT allow you to print
without a queuename attached.

The problem is that OpenSolaris CUPS (or maybe CUPS in general) has when
it autodetects network printers is that it is impossible to edit the
printer URI once it has been "detected" by the CUPS web interface. When
you use the autodetect my printer feature, it fill outs the URI as
lpd://<printer ip>:port, but it misses detecting the LPD queue name. It is
also impossible to modify it from the web interface from the printer
administration page. At no point does it even bother to ask you what the
queue names are after it autodetects the printer as an LPD printer, nor
does it warn you that you need to fill in a queue name. Instead, it
silently happily accepts the auto-detected configuration and tries to
print, at which point it bombs out. 

It fails with some obscure message of:
D [01/Oct/2010:15:21:43 +0800] [Job 3] lpd_command returning -1
D [01/Oct/2010:15:21:43 +0800] [Job 3] Backend returned status 1 (failed)
D [01/Oct/2010:15:21:43 +0800] [Job 3] Printer stopped due to backend
errors; please consult the error_log file for details.
D [01/Oct/2010:15:21:43 +0800] [Job 3] End of messages
D [01/Oct/2010:15:21:43 +0800] [Job 3] printer-state=5(stopped)
D [01/Oct/2010:15:21:43 +0800] [Job 3]
printer-state-message="/usr/lib/cups/backend/lpd failed"


The solution I have found is to add the printer manually as an LPD/LPR
printer, at which case you can fill in the LPD URI.

The only reason I solved this problem is that at this point, the CUPS
interface shows you an example of an LPD URI which looks like:

lpd://hostname/queue

At that point, I could print quite happily and all was fine. CUPS should
warn you at even after it autodetects the LPD IP address, it still
requires a queue name to complete the add process. I kind of assumed that
CUPS had some sort of default queue name or something, but clearly this is
not the case. And on a second note, the CUPS printer URI should be editable
in the modify printer administration option.

Link: http://www.cups.org/str.php?L3755
Version: 1.4.2