iccery-v2-mac/docs/13-print-linux.md

13 — Linux CUPS printing

Line numbers refer to ICCery v0.8.5 (/tmp/ICCery at analysis time) and the Gronod ArgyllCMS 3.5.0 fork.

Linux (src-tauri/src/print/unix.rs)

No libcups FFI. Shell out to CUPS CLI: lpstat, lpoptions, lp. lpr is never used.

Enumeration

Command	Parser	Result
lpstat -e	parse_lpstat_e	destination names, one per non-empty trimmed line
lpstat -p	parse_lpstat_p	(name, status) from lines printer <name> …. Status: idle → Idle; printing/now printing → Printing; disabled/stopped → Stopped; else Unknown
lpstat -d	parse_lpstat_d	system default destination: <name>
lpoptions -p <name>	extract_printer_display_name	printer-info= value, quotes stripped

merge_printer_info: destinations first (status from -p or "Idle"), then any -p names not already seen. Each entry calls lpoptions for display_name (N printers = N extra processes).

If both -e fails and -p cannot even be spawned, error "Failed to execute 'lpstat': …". Otherwise partial data is OK.

Capabilities / PPD

lpoptions -p <printer> -l parsed by parse_lpoptions_l (unix.rs:181-229):

PPD key (before /)	Destination
InputSlot, MediaSource	trays (1-based index id, * stripped)
PageSize, MediaSize	paper_sizes
CNIJMediaType, MediaType, StpMediaType, EPIJ_Medi	media_types (id = name = token)

Then, if /etc/cups/ppd/<printer>.ppd is readable, parse_ppd_media_types replaces media_types with id/name pairs from *CNIJMediaType , *MediaType , *StpMediaType , *EPIJ_Medi lines (id/Human Name:).

macOS typically has PPDs under ~/Library/Printers or a CUPS temp copy, not /etc/cups/ppd/, so the PPD-file enrichment is Linux-centric. macOS still gets media types from lpoptions -l.

Driver color bypass detection (detect_driver_color_bypass, unix.rs:251-272)

First-match order:

Probe substring	Key	Value	Meaning
CNIJIntent2	CNIJIntent2	4	Canon "Off (No Color Adjustment)"
CNIJIntent	CNIJIntent	4	older Canon
EPIJ_CCor	EPIJ_CCor	0	Epson Color Settings — 0 disables correction (preferred over CMat if both exist)
EPIJ_CMat	EPIJ_CMat	3	Epson "Off (No Color Adjustment)"
StpColorCorrection	StpColorCorrection	Uncorrected	Gutenprint
ColorCorrection	ColorCorrection	Uncorrected	generic
EpsonColorMode	EpsonColorMode	Off	Epson

EPIJ_OSColMat is not auto-detected (but is forwarded if captured on macOS). ColorModel is forwarded if captured, not auto-set on Linux except the Gray fallback below.

Media type key (detect_media_type_key, unix.rs:274-284)

CNIJMediaType > EPIJ_Medi > StpMediaType > MediaType.

Linux build_lp_args / print_target (unix.rs:362-457)

lp -d <printer> -t "ICCery Target - <filename>"
   [-o raw]                            # default
   OR [-o ColorModel=Gray -o cm-calibration]   # ppd_uncorrected_passthrough == true
   [-o orientation-requested=3|4]
   [-o PageSize=<paper_size>]
   [-o MediaType=<media_type>]         # generic key only — does not call detect_media_type_key
   <tiff_path>

• raw queue: CUPS skips filters (no cgpdftoraster, no PPD color). The TIFF is sent as the job payload. Printers that cannot consume raw TIFF need the checkbox fallback.
• Fallback ColorModel=Gray + cm-calibration: documented as "uncorrected CUPS passthrough" for devices that reject raw TIFF. Gray is a surprising choice for color targets — it is the historical CUPS "don't color-manage" trick, not a conversion of the image to grayscale at the app layer. Still a rewrite risk: a color TIFF with ColorModel=Gray may be wrong on some drivers.
• No ColorSync flags (those are macOS-only).
• No auto driver-bypass injection on Linux (Canon/Epson PPD keys are not added unless the user typed them — and there is no Linux Preferences dialog to capture them).
• paper_source / cups_options ignored.
• lp failure: stderr, else stdout, else exit code, wrapped as "CUPS print job failed: …".
• Missing file: "Target TIFF file not found: …".

Linux Preferences

commands.rs:1364-1368 — show_printer_properties is a no-op Ok(None). There is no CUPS web-UI (http://localhost:631) launcher, no system-config-printer, no gtk-print-unix-dialog. The #btnPrinterProperties click therefore always looks like a cancel on Linux.

lp vs lpr

Always lp (Command::new("lp")). lpr is never invoked. lp is the CUPS System V client and is what -o name=value and -d dest are specified against. lpr BSD syntax (-P, -o still works on CUPS) was not used.

CUPS options string parser (parse_cups_options_string, unix.rs:286-332)

Shared with macOS. Whitespace-separated name=value; double quotes toggle; quotes stripped from both sides; tokens without = skipped; AP_D_InputSlot= yields ("",) empty value.

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