I managed to upgrade the printer firmware using its embedded webserver UI (from SAYAWLPP1N001.2137A.00 created 2021-09-06, to SAYAWLPP1N002.2423A.00 to 2024-06-03). Unfortunately this did not help.
However, I got my hands on the ipptool utility, and this is where it really gets interesting. I have now made the printer available via two channels: - directly over WiFi - via USB and Debian cups (host A), as before When I invoke the get-printer attributes on the printer directly like this: ipptool -j http://192.168.2.102:631/ipp/print get-printer-attributes.test > direct.json then the "media-supported" key in the output is correct - no empty values. However when I do it through the cups server on host A like this: ipptool -j http://192.168.192.1:631/printers/kotlownia2 get-printer-attributes.test > via-cups.json I get output with empty values, and an error just like the one found earlier in host B's error_log: "media-supported": Bad keyword value "" - invalid character (RFC 8011 section 5.1.4). So it looks like it's cups itself that injects the invalid empty values! The printer's response is (and probably was) correct! The exact difference of the critical part is as follows: --- direct_.json 2024-10-04 16:39:26.402511781 +0200 +++ via-cups_.json 2024-10-04 16:40:06.891135645 +0200 @@ -1,29 +1,36 @@ "media-supported": [ - "na_executive_7.25x10.5in", - "na_letter_8.5x11in", - "na_legal_8.5x14in", + "na_5x7_5x7in", + "oe_photo-l_3.5x5in", + "na_index-4x6_4x6in", + "na_foolscap_8.5x13in", "na_govt-letter_8x10in", - "na_invoice_5.5x8.5in", - "iso_a5_148x210mm", "iso_a4_210x297mm", + "iso_a5_148x210mm", + "iso_a6_105x148mm", "iso_b5_176x250mm", "jis_b5_182x257mm", - "jpn_oufuku_148x200mm", - "jpn_hagaki_100x148mm", - "iso_a6_105x148mm", - "na_index-4x6_4x6in", - "om_small-photo_100x150mm", - "na_5x7_5x7in", - "na_index-5x8_5x8in", + "na_legal_8.5x14in", "na_number-10_4.125x9.5in", - "iso_dl_110x220mm", "iso_c6_114x162mm", + "iso_dl_110x220mm", + "na_executive_7.25x10.5in", + "na_index-5x8_5x8in", + "na_letter_8.5x11in", "jpn_chou3_120x235mm", "jpn_chou4_90x205mm", - "oe_photo-l_3.5x5in", - "jpn_photo-2l_127x177.8mm", - "na_foolscap_8.5x13in", + "jpn_hagaki_100x148mm", + "custom_199.9x151.05mm_199.9x151.05mm", + "na_invoice_5.5x8.5in", + "oe_executive-fb_7.25x10.5in", + "oe_legal-fb_8.5x14in", + "oe_statement-fb_5.5x8.5in", + "om_b-5-fb_175.94x249.94mm", + "", + "om_envelope-dl-fb_109.98x219.96mm", + "om_envelope-c-6-fb_113.96x161.97mm", + "", + "oe_8-5x-13-fb_8.5x13in", "custom_min_3.5x5in", - "custom_max_8.5x14in" + "custom_max_5x14in" ], - "media-default": "iso_a4_210x297mm", + "media-default": "unknown",
