CUPS emitting duplicate operation attributes?

[sde1000]

I'm implementing an IPP printer that supports image/pwg-raster. I'm trying to test it by setting it up in CUPS, but I'm seeing the following invalid Print-Job request from CUPS (version 2.4.1):

00000000  01 01 00 02 00 00 00 05  01 47 00 12 61 74 74 72  |.........G..attr|
00000010  69 62 75 74 65 73 2d 63  68 61 72 73 65 74 00 05  |ibutes-charset..|
00000020  75 74 66 2d 38 48 00 1b  61 74 74 72 69 62 75 74  |utf-8H..attribut|
00000030  65 73 2d 6e 61 74 75 72  61 6c 2d 6c 61 6e 67 75  |es-natural-langu|
00000040  61 67 65 00 05 65 6e 2d  67 62 45 00 0b 70 72 69  |age..en-gbE..pri|
00000050  6e 74 65 72 2d 75 72 69  00 1e 69 70 70 3a 2f 2f  |nter-uri..ipp://|
00000060  6c 6f 63 61 6c 68 6f 73  74 3a 32 34 36 38 2f 69  |localhost:2468/i|
00000070  70 70 2f 70 72 69 6e 74  42 00 14 72 65 71 75 65  |pp/printB..reque|
00000080  73 74 69 6e 67 2d 75 73  65 72 2d 6e 61 6d 65 00  |sting-user-name.|
00000090  04 72 6f 6f 74 42 00 08  6a 6f 62 2d 6e 61 6d 65  |.rootB..job-name|
000000a0  00 0e 32 35 20 2d 20 54  65 73 74 20 50 61 67 65  |..25 - Test Page|
000000b0  49 00 0f 64 6f 63 75 6d  65 6e 74 2d 66 6f 72 6d  |I..document-form|
000000c0  61 74 00 10 69 6d 61 67  65 2f 70 77 67 2d 72 61  |at..image/pwg-ra|
000000d0  73 74 65 72 49 00 0f 64  6f 63 75 6d 65 6e 74 2d  |sterI..document-|
000000e0  66 6f 72 6d 61 74 00 18  61 70 70 6c 69 63 61 74  |format..applicat|
000000f0  69 6f 6e 2f 6f 63 74 65  74 2d 73 74 72 65 61 6d  |ion/octet-stream|
00000100  02 42 00 19 6a 6f 62 2d  6f 72 69 67 69 6e 61 74  |.B..job-originat|
00000110  69 6e 67 2d 68 6f 73 74  2d 6e 61 6d 65 00 09 6c  |ing-host-name..l|
00000120  6f 63 61 6c 68 6f 73 74  45 00 08 6a 6f 62 2d 75  |ocalhostE..job-u|
00000130  75 69 64 00 2d 75 72 6e  3a 75 75 69 64 3a 39 62  |uid.-urn:uuid:9b|
00000140  34 38 62 62 34 34 2d 30  39 36 33 2d 33 64 30 64  |48bb44-0963-3d0d|
00000150  2d 35 64 39 36 2d 63 61  38 39 31 64 64 32 64 62  |-5d96-ca891dd2db|
00000160  31 34 03 52 61 53 32 50  77 67 52 61 73 74 65 72  |14.RaS2PwgRaster|
00000170  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
*
00000270  00 00 00 00 00 00 00 00  00 00 00 00 00 02 58 00  |..............X.|
00000280  00 02 58 00 00 00 00 00  00 00 00 00 00 00 00 00  |..X.............|
00000290  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
(the rest of the pwg-raster data omitted)

Notice the duplicate document-format attribute.

Am I doing something wrong to make CUPS do this?

I notice that CUPS doesn't request the pwg-raster-document-resolution-supported and pwg-raster-document-type-supported attributes, it only requests these:

Keyword(compression-supported),
Keyword(copies-supported),
Keyword(cups-version),
Keyword(document-format-supported),
Keyword(job-password-encryption-supported),
Keyword(marker-colors),
Keyword(marker-high-levels),
Keyword(marker-levels),
Keyword(marker-low-levels),
Keyword(marker-message),
Keyword(marker-names),
Keyword(marker-types),
Keyword(media-col-supported),
Keyword(multiple-document-handling-supported),
Keyword(operations-supported),
Keyword(print-color-mode-supported),
Keyword(printer-alert),
Keyword(printer-alert-description),
Keyword(printer-is-accepting-jobs),
Keyword(printer-mandatory-job-attributes),
Keyword(printer-state),
Keyword(printer-state-message),
Keyword(printer-state-reasons)

[sde1000]

Hmm. If I fake up a value for media-col-supported then I get a valid Print-Job request from CUPS, and 24bpp 600×600dpi A4 PWG raster data (which isn't quite what I wanted, but is definitely progress!)

CUPS doesn't appear to do anything with media-col-supported (it doesn't request media-col-database or media-col-ready) but leaving it unsupported does seem to make it misbehave. It's still not requesting pwg-raster-document-resolution-supported and pwg-raster-document-type-supported.

[michaelrsweet]

Not sure why you are getting two document-format attributes - sounds like a potential bug although you aren't using the most recent version of CUPS... That said, when sending a print job CUPS only queries status and a few capability attributes - the others are only needed when setting up the print queue.

Anyways, the "media-col-supported" attribute is REQUIRED for AirPrint, IPP Everywhere, and Mopria, so you definitely want to report it with whichever "media-col" member attributes that you support.