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printserver/openspec/changes/add-cups-printserver-container/proposal.md
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juergen 30c685e085 Print via Brother BR-Script3 PostScript instead of the vendor driver
The HL-4150CDN emulates PostScript 3, so CUPS converts client documents to PostScript and forwards them to socket://<ip>:9100. The official BR-Script3 PPD turns device options (tray, duplex, colour, media type, toner save, ...) into setpagedevice instructions. This drops the i386 multiarch runtime and the broken Brother vendor filter chain, and removes the unused Brother Linux packages from the repo.
2026-10-18 16:54:33 +02:00

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# Proposal
## Why
Run a Podman container that shares the Brother HL-4150CDN network printer over
IPP/AirPrint, so clients on macOS, iOS/iPadOS, Linux and Windows can print.
The HL-4150CDN already emulates BR-Script3 (PostScript 3) and accepts PostScript
on its AppSocket/LPD ports, so the container can forward PostScript directly to
the printer instead of shipping Brother's 32-bit Linux CUPS wrapper plus
Ghostscript rasterisation. This removes the i386 dependency, the multiarch
runtime and the fragile vendor filter chain.
The previous approach (Brother Linux `.deb` packages) turned out not to work in
`debian:bookworm-slim`: the vendor filter `filterhl4150cdn` needs `file` (with
`a2ps` as a fallback), which are not installed, so it exits with an error and
produces no output. The official BR-Script3 PPD avoids that entire code path.
## What Changes
- Create a Containerfile for Podman based on Debian stable running CUPS, Avahi
and D-Bus (no i386 multiarch).
- Install Brother's official **BR-Script3 PPD** (committed under
`assets/Brother HL-4150CDN/ppd/`) so CUPS emits device options — paper source
(tray), duplex and colour/mono, plus media type, print quality, toner save and
secure print — as PostScript `setpagedevice`.
- Point the queue at the printer with a raw AppSocket URI (`socket://<ip>:9100`)
by default.
- Convert incoming client formats (URF/Apple Raster, PWG Raster, PDF, PostScript)
to PostScript inside CUPS and pass them through to the printer's PostScript
interpreter.
- Share the queue over IPP and advertise it via mDNS/DNS-SD (Avahi/AirPrint).
- Keep runtime configuration (printer address, protocol, queue name) in
environment variables.
- Document the supported client matrix.
## Capabilities
### New Capabilities
- `printserver/cups`: Containerised CUPS print server which shares the Brother
HL-4150CDN over IPP/AirPrint and prints by sending PostScript (BR-Script3)
directly to the printer.
### Modified Capabilities
None
## Impact
- Containerfile plus supporting `cupsd.conf` and `entrypoint.sh` in the
repository root.
- Uses `assets/Brother HL-4150CDN/ppd/BR4150_2.PPD`.
- Runtime ports: CUPS/IPP (631/tcp), mDNS/DNS-SD (5353/udp).
- No 32-bit runtime libraries; the image no longer depends on the host CPU
architecture.
- Windows clients install Brother's own BR-Script3 Windows driver client-side.
- The unused Brother Linux `.deb` packages previously under
`assets/Brother HL-4150CDN/` have been removed.