papyrium-advertiser-mdns

Announces Papyrium printers on the local network with multicast DNS, the way Bonjour and Avahi announce network printers, so senders such as a Centronics-to-network bridge can find them without being told an address.

A raw TCP printer is announced as a _pdl-datastream._tcp service, the type Apple's Bonjour Printing specification gives for raw port printing, so it appears like any other network printer. Its TXT record follows that specification's keys and says it is a Papyrium printer:

txtvers=1
qtotal=1
ty=Brother M-1109 (Papyrium)
product=(Brother M-1109)
note=Papyrium virtual printer
usb_MFG=Brother
usb_MDL=M-1109
usb_CMD=ESCP9
uuid=<the printer's UUID>

A client looking only for Papyrium printers can match "Papyrium" in ty or note, or in the instance name, and can recognise a particular printer by its uuid across renames and restarts.

There is no _papyrium DNS-SD subtype. python-zeroconf indexes a service under a single type, so a service registered under the subtype answers only browses for the subtype: once its announcements end, browsers of the plain _pdl-datastream._tcp type, such as printer dialogs and CUPS, no longer find it (python-zeroconf issues 1287 and 1093). Appearing as an ordinary printer matters more, so the plain type is used, and the TXT record is how a client tells Papyrium apart.

Only endpoints the network can reach are announced; an unspecified address stands for every address of its family on this machine except loopback. The services name their own host, papyrium-<8 hex digits>.local., so Papyrium never answers for the machine's own name. If the printer's name is taken, a free variant is chosen and the name actually registered is logged.

Registered as mdns on the papyrium.advertiser axis. It uses python-zeroconf, which is licensed LGPL-2.1-or-later, unmodified as an ordinary dependency; anyone distributing a bundle that includes it must meet the LGPL's terms for that library.