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Bad device URI "://" on network printers. Printing stopped working between 2.4.19 and 2.4.20

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
82/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
c
Domain
backend

Research direction

The bug is in create_local_printer in scheduler/ipp.c, where the device URI was split out of ptr into device_uri_ptr. Check the two places the report names (the httpSeparateURI call and the cupsdSetDeviceURI call) and see which still read ptr instead of device_uri_ptr. Done means a network printer's device URI parses without the :// error and a job can be queued, which you can confirm by reproducing the printer-creation path or running the scheduler's printer tests.

Written by the indexing model from the issue text.

Description

Describe the bug
Printing on a discovered network printer does not spawn jobs anymore and only throws errors in logs, no feedback in any UI (on my system).
This bug was probably introduced in 2.4.20, because a downgrade to 2.4.19 seems to fix my issue.

To Reproduce

  • Print a page using firefox, select "print with system dialog".
  • Observe that the network printer is listed, but "fetching information..." does not stop.
  • Printing does not spawn a job, the web UI of cups does not show any queued, failed or completed jobs.

Some logs:

# lpoptions -p <printername> -l
lpoptions: Unable to get PPD file for <printername>: No such file or directory

# tail /var/log/cups/error_log
E [24/Sep/2026:16:38:46 +0200] [Job 23] Files have gone away.
  W [08/Oct/2026:13:26:10 +0200] No limit for Set-Printer-Attributes defined in policy default - using CUPS-Add-Modify-Printers's policy.
  W [08/Oct/2026:13:26:10 +0200] No limit for Set-Printer-Attributes defined in policy authenticated - using CUPS-Add-Modify-Printers's policy.
  E [08/Oct/2026:13:26:10 +0200] [Job 24] Unable to queue job for destination "<printername>".
  E [08/Oct/2026:13:26:10 +0200] [Job 25] Unable to queue job for destination "<printername>".
  E [08/Oct/2026:13:26:10 +0200] [Job 26] Unable to queue job for destination "<printername>".
  E [09/Oct/2026:15:37:20 +0200] <printername>: Bad device URI "://".
  E [09/Oct/2026:15:37:20 +0200] [Client 1125] Returning IPP server-error-device-error for CUPS-Create-Local-Printer (ipps://localhost/printers/<printername>) from localhost.

System Information:

  • Arch Linux x86_64 7.2.9-arch1-1
  • Firefox
  • CUPS version 2.4.20

Guessed Cause:
https://github.com/OpenPrinting/cups/commit/3c86e2f5fc797030aea65f3d6104b1a3d84f4f88

-  const char	*ptr;			/* Pointer into attribute value */
+  const char	*ptr,			/* Pointer into attribute value */
+		*device_uri_ptr;	/* Pointer into device URI value */

In this commit, the variable ptr in function create_local_printer was split into two: ptr and device_uri_ptr.
But two references were forgotten to be updated to device_uri_ptr, such referencing the wrong string:

-    httpSeparateURI(HTTP_URI_CODING_ALL, ptr,
+    httpSeparateURI(HTTP_URI_CODING_ALL, device_uri_ptr,
                  scheme, sizeof(scheme), userpass, sizeof(userpass), host,
                  sizeof(host), &port, resource, sizeof(resource));

https://github.com/OpenPrinting/cups/blob/ef80eeaea51430a055948240eea3f28ef5354edf/scheduler/ipp.c#L5802-L5806

   else
-    cupsdSetDeviceURI(printer, ptr);
+    cupsdSetDeviceURI(printer, device_uri_ptr);

https://github.com/OpenPrinting/cups/blob/ef80eeaea51430a055948240eea3f28ef5354edf/scheduler/ipp.c#L5832-L5837

Dominant language
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