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Main prints through craft-print, which runs `lp`; a Flatpak has no `lp`, so File › Print fails there. This keeps craft-print as the route wherever `lp` is on the path (and on Windows) and adds two more behind it: - `photocraft-ipp`, a pure-Rust IPP client (CUPS-Get-Printers/Classes/ Default, Print-Job over HTTP/1.1) that talks to CUPS over its socket or TCP; the Flatpak manifests grant --socket=cups for it. A `printServer` named in the request always takes this route. `file.print.printers` lists the queues. - The XDG Print portal as the app's spooler (`Session::print_spooler`), for a sandbox without the CUPS socket or a system without a printer: the system print dialog, seeded with copies, paper and orientation. PHOTOCRAFT_PRINT_PORTAL=1 prefers it, =0 removes it. A route that exists but fails (unknown printer, refused job) is an error; only a missing route moves on. Results gain `backend` (lp, windows, ipp, portal). docs/printing.md describes the routes.
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Printing
File › Print renders the flattened document onto one PDF page (paper size and orientation,
position and scale, crop and registration marks, labels, colour handling) and hands that page
to a printer. The rendering is print_cmds.rs in photocraft-engine, shared by the dialog, the
batch commands and automation (file.print, file.printOneCopy); this page is about the hand-off.
Routes to the printer
| Route | When | What the user sees |
|---|---|---|
craft-print (lp on CUPS, the Windows spooler) |
Whenever lp is on the path (macOS, Linux outside a sandbox) or on Windows |
Sent to the printer (request id is Office-42) |
CUPS over IPP (photocraft-ipp) |
No lp on the path (a Flatpak) and a print server answers: CUPS_SERVER, then /run/cups/cups.sock, /var/run/cups/cups.sock, /private/var/run/cupsd, then localhost:631; always for a printServer named in the request |
Sent to the printer (job 42 on Office) |
Print portal (org.freedesktop.portal.Print, desktop app on Linux) |
No print server reachable or no printer set up, or always with PHOTOCRAFT_PRINT_PORTAL=1 |
The system print dialog, seeded with the copies and paper; the outcome goes to the log |
| Print to PDF | output given (the Output field of the dialog) |
The file; nothing is spooled unless send is true |
A route that exists but fails (an unknown printer, a job the queue refuses) is an error; only a
missing route (no lp, no print server, no printer) moves on to the next one.
The IPP client is in-process, pure Rust (RFC 8010/8011: CUPS-Get-Printers, CUPS-Get-Classes,
CUPS-Get-Default, Print-Job with the PDF as the document), so no lp binary is needed. That
is what makes printing work in the Flatpak: the manifest grants --socket=cups, which mounts the
host's CUPS socket, and the sandbox has no lp. On a system without CUPS, or in a sandbox
without the socket, the app falls back to the print portal, whose dialog runs outside the sandbox.
Which printer
The dialog's Printer field, or "printer" in the command, names a queue (case-insensitively; a
CUPS class counts, as with lp -d).
Left empty, the server's default printer is used; without a default, the only printer; with
several and no default, the error names them. With no printer at all, the portal takes over when
it is available, otherwise the error says to add one in the system settings or print to PDF.
file.printers lists what the print server knows: {"printServer": "host[:port]|socket"}
is optional and defaults to the system's CUPS; the result is
{server, default, printers: [{name, info, state, acceptingJobs, default, class}]}, or an empty list
with a note when no server answers. "printServer" on file.print sends one job to a named
server; "dryRun": true renders the page and reports the equivalent lp command without
spooling.
Results
file.print returns sent, backend (lp, windows, ipp, portal), spooler (where the
job went) and pdf (the page's path, only when output named one).
Environment
| Variable | Effect |
|---|---|
CUPS_SERVER |
The print server, as CUPS itself reads it: host[:port] or a socket path |
PHOTOCRAFT_PRINT_PORTAL=1 |
Always use the system print dialog (the portal) instead of lp or CUPS directly |
PHOTOCRAFT_PRINT_PORTAL=0 |
Never use the portal; a missing print server is then an error |
Verification
crates/ipp/src/tests.rs: the client against a fake CUPS over TCP and a Unix socket: printer listing with state and default, the default printer and its absence,Print-Jobwith the document and the job id, chunked and content-length replies, HTTP and IPP error statuses, broken replies.crates/engine/src/print_cmds/tests.rs: printer resolution (requested, default, only one, several without a default, unknown, none); a completefile.printagainst a fake CUPS (printer URI, copies, job name, document format, the PDF itself) andfile.printers;lptaking the job when it is on the path; the IPP route when it is not (a child process with an empty path); the app's spooler when preferred, as the fallback without a printer, and skipped when a server is named; print to PDF untouched.apps/photocraft/src/print_portal.rs: the request path rule and the paper/copies seeding of the dialog (PWG names for the standard papers, millimetres for custom sizes).