"lpadmin ... -o printer-is-shared=true" does not work for ipp queues without visible reason

[michaelrsweet]

Version: 2.1.0
CUPS.org User: jsmeix.suse

I have a remote CUPS server with a queue "foo".

On the local system I create a raw queue that only forwards

to the queue "foo" on the remote CUPS server:

lpadmin -p foofwd -v ipp://server.domain/printers/foo -E

echo $?

0

I can print from the local system via the local foofwd queue.

Now I like to share that foofwd queue on my local system:

lpadmin -p foofwd -o printer-is-shared=true

echo $?

0

In /var/log/cups/error_log (with LogLevel debug) there is:

D ... CUPS-Add-Modify-Printer ipp://localhost:631/printers/foofwd
D ... cupsdIsAuthorized: username="root"
I ... Setting foofwd printer-is-shared to 1 (was 0.)
...

I Saving printers.conf...

But in /etc/cups/printers.conf the foofwd queue is still "Shared No"

In contrast "printer-is-shared=true" works for a "raw" queue

where the DeviceUri is not "ipp://...":

lpadmin -p bar -v socket://dummy.example.org -E

---

it has by default "Shared Yes" in /etc/cups/printers.conf

and I can toggle it as I like with

lpadmin -p bar -o printer-is-shared=false

---

versus

lpadmin -p bar -o printer-is-shared=true

---

I found that this behaviour was already reported in
https://www.cups.org/pipermail/cups/2014-June/026272.html
but without an aswer that explains why CUPS
does not share an ipp print queue.

Therefore I report it now as a bug because
ther are thre issues with that behaviour:

When "lpadmin ... -o printer-is-shared=..." does not work,
it should at least report an error or warning.

"man lpadmin" does not tell anything that
sharing an ipp print queue does not work.

https://www.cups.org/documentation.php/doc-2.1/sharing.html
does not tell anything that sharing an ipp print queue does not work.

There is no debug message in /var/log/cups/error_log
that could help to dind out what the reason is
why sharing an ipp print queue does not work.
Actually the messages in /var/log/cups/error_log
seem to show that it has worked:
"Setting foofwd printer-is-shared to 1 (was 0.)"

I assume there is a good reason why sharing an ipp print queue
does not work but then this reason should be at least documented.

Additionally it is perhaps a minor bug that lpadmin does
neither show an error message nor return an error exit code
in this case.

[michaelrsweet]

CUPS.org User: mike

Johannes,

You cannot re-share a remote printer - this change was made several years ago because it causes a lot of problems when the final server requires authentication.

That said, you should probably be getting an error from lpadmin when you try to set the printer-is-shared attribute to 1... Will use this bug to track that change.

[michaelrsweet]

CUPS.org User: jsmeix.suse

I think the basic question is what "remote printer" means.

I know that the local cupsd cannot re-share a queue that it got
via annoucement from a remote cupsd (e.g. one cannot re-share
a traditional CUPS Browsing reference to a remote queue).

But in my case here my foofwd queue is a local queue
(locally created with lpadmin for the local cupsd)
which has an entry in /etc/cups/printers.conf.

I do not want to re-share it.
I like to share it.

I thought that all queues that exist in /etc/cups/printers.conf
are local queues and that all local queues can be shared.

In my case it seems one cannot share a local queue depending
in an obscure way on its specific DeviceURI.

Initially I detected this behaviour with CUPS 1.3.9 on SLES11
and then I verified that it still exists with CUPS 2.1.0.

In CHANGES-1.3.txt I detected now this entry

• The scheduler did not prevent remote queues from being
  shared/published.

  which seems to match this issue here but there is no information
  that describes what exactly is meant with "remote queues" here.

For example if local queues with any ipp//... DeviceURI
could not be shared, it would be impossible to share
a local queue for a network printer that is accessed
via an ipp//... DeviceURI.

But somehow this seems to work:

lpadmin -p baz -v ipp://dummy.example.org/something -E

less /etc/cups/printers.conf

...

...
DeviceURI ipp://dummy.example.org/something
...
Shared Yes
...

lpadmin -p baz -o printer-is-shared=false

less /etc/cups/printers.conf

...

...
Shared No
...

lpadmin -p baz -o printer-is-shared=true

less /etc/cups/printers.conf

...

Shared Yes

Therefore I think the real issue is to describe precisely
what "remote queue" actually means in CUPS.

Perhaps for queues that exist in /etc/cups/printers.conf

a new explicit entry

Remote [Yes/No]

could be provided to make it clear
which queue is a "remote queue" and which one is not.

Or alternatively and perhaps even more to the point

Shareable [Yes/No]

to make it clear which queue can be shared and which cannot.

In general regarding my current understanding of the terms
"local/remote queue" and "local/remote printer" see
https://en.opensuse.org/YaST_Printer

(excerpt):

There is a difference between "local/remote queue"
and "local/remote printer":

• "Local queue" means a print queue which is configured
  on the local computer...

• "Remote queue" means a print queue which exists on whatever
  computer in the network or on whatever network printer.

• "Local printer" means a printer device which is directly
  connected to the local computer (usually a USB printer).

• "Remote printer" means a printer device which is not directly
  connected to the local computer (usually a printer with

  a built-in network interface).

Now I am confused regarding a network printer that is accessed
via an ipp//... DeviceURI versus a queue on a remote CUPS server.

According to my current understanding in both cases
the recipient is a "remote IPP queue" that exists
in the network printer or on the remote CUPS server
so that both cases should behave the same.

In particular I am confused about a (hypothetical?)
big-and-fat network printer that has CUPS built in
and is accessed only via IPP.

Could one share queues in /etc/cups/printers.conf
for network printers with built-in CUPS?

[michaelrsweet]

CUPS.org User: jsmeix.suse

I guess I found the hardcoded DeviceURI magic that distinguishes
between what is a "Remote Printer" and a "Local Raw Printer"
in scheduler/printers.c

(excerpt):

load_ppd(cupsd_printer_t *p) ...

...

else if (((!strncmp(p->device_uri, "ipp://", 6) ||
           !strncmp(p->device_uri, "ipps://", 7)) &&
          (strstr(p->device_uri, "/printers/") != NULL ||
           strstr(p->device_uri, "/classes/") != NULL)) ||
         ((strstr(p->device_uri, "._ipp.") != NULL ||
           strstr(p->device_uri, "._ipps.") != NULL) &&
          !strcmp(p->device_uri + strlen(p->device_uri) - 5, "/cups")))
{
 /*
  * Tell the client this is really a hard-wired remote printer.
  */

  p->type |= CUPS_PRINTER_REMOTE;

...

 /*
  * Then set the make-and-model accordingly...
  */

  ippAddString(p->ppd_attrs, IPP_TAG_PRINTER, IPP_TAG_TEXT,
               "printer-make-and-model", NULL, "Remote Printer");

 /*
  * Print all files directly...
  */

  p->raw    = 1;
  p->remote = 1;
}
else
{
 /*
  * Otherwise we have neither - treat this as a "dumb" printer
  * with no PPD file...
  */

  ippAddString(p->ppd_attrs, IPP_TAG_PRINTER, IPP_TAG_TEXT,
               "printer-make-and-model", NULL, "Local Raw Printer");

  p->raw = 1;
}

---

and its hardcoded consequence also in scheduler/printers.c

(excerpt)

cupsdSetPrinterAttrs(cupsd_printer_t *p) ...

...

/*

• Force sharing off for remote queues...
  */

  if (p->type & CUPS_PRINTER_REMOTE)

  p->shared = 0;

[michaelrsweet]

CUPS.org User: jsmeix.suse

Furthermore there is in scheduler/printers.c

load_ppd(cupsd_printer_t *p) ...

...

if (ppdFindAttr(ppd, "APRemoteQueueID", NULL))
  p->type |= CUPS_PRINTER_REMOTE;

---

but that is the only place in the CUPS 2.1.0 sources
where I can find "APRemoteQueueID".

Now I wonder what "APRemoteQueueID" is?

[michaelrsweet]

CUPS.org User: jsmeix.suse

This is only a guess but perhaps I am on the right track:

When there is a queue in /etc/cups/printers.conf
with a DeviceURI that points to a remote CUPS queue
(e.g. when the DeviceURI has the form "ipp://.../printers/...")
then the local cupsd does not treat such a queue as
a "dumb" queue with no PPD file (i.e. as a local raw queue)
instead
it seems the local cupsd treats such a queue like the
traditional CUPS Browsing reference to a remote CUPS queue.

In particular for such a queue one gets printer specific PPD options
from the remote CUPS queue when one asks the local cupsd

via "lpoptions -l":

lpoptions -h localhost -p foofwd -l

Resolution/Resolution : *600 ...
MediaType/Media Type : *Auto PlainPaperL PlainPaper ...
InputSlot/Paper Source: *Auto Manual Cas1 Cas2 Cas3 ...
OutputBin/Paper Destination: *Auto TrayA TrayB TrayC
Duplex/Duplex: *None DuplexNoTumble DuplexTumble
BindEdge/BindingEdge: *Left Top
Booklet/Booklet Printing: *None Left
Collate/Collate: False *True Group StapleCollate ...
StapleLocation/Staple Location: None *TopLeft Top ...

PageSize/Page Size: Letter Legal A5 *A4 ...

This is unexpected because my "foofwd" queue has no PPD file.

If my above assumption is right the problem is that
the cupsd makes a hardcoded decision that a local queue
without PPD file and DeviceURI that points to a remote CUPS queue
behaves in a special way.

According to my current understanding the solution should be
to make it explicit in /etc/cups/printers.conf
how such a queue should behave:
Either as local raw queue
or as some kind of reference or proxy for a remote CUPS queue.

When setting up such a queue the cupsd can of course set
a default for its behaviour but I think it must still
be possible that the admin enforces his desired behaviour.

In short:
I think it must be possible to set up a "dumb" local raw queue
with a DeviceURI that points to a remote CUPS queue.

[michaelrsweet]

CUPS.org User: mike

Raw queues are the only ones to be flagged as remote queues, and then only IPP queues that point to a CUPS server (/cups on the end for Bonjour URIs, /classes and /printers for ipp/ipps URIs).

Source changes (to produce an error) are below.

[michaelrsweet]

"str4738.patch":

Index: scheduler/ipp.c

--- scheduler/ipp.c (revision 12973)
+++ scheduler/ipp.c (working copy)
@@ -978,6 +978,16 @@
if ((attr = ippFindAttribute(con->request, "printer-is-shared",
IPP_TAG_BOOLEAN)) != NULL)
{

• if (pclass->type & CUPS_PRINTER_REMOTE)
• {

• /*
  

•  \* Cannot re-share remote printers.
  

•  */
  

•  send_ipp_status(con, IPP_BAD_REQUEST, _("Cannot change printer-is-shared for remote queues."));
  

•  return;
  

• }

if (pclass->shared && !attr->values[0].boolean)
cupsdDeregisterPrinter(pclass, 1);

@@ -2471,6 +2481,16 @@
return;
}

• if (printer->type & CUPS_PRINTER_REMOTE)
• {

• /*
  

•  \* Cannot re-share remote printers.
  

•  */
  

•  send_ipp_status(con, IPP_BAD_REQUEST, _("Cannot change printer-is-shared for remote queues."));
  

•  return;
  

• }

if (printer->shared && !attr->values[0].boolean)
cupsdDeregisterPrinter(printer, 1);