[avahi] Advertizing a service only on the local machine

[Till Kamppeter]

Hi,

I am leading the OpenPrinting project and currently I am working on 
driverless (IPP Everywhere, AirPrint) printing.

Driverless means that not driver is needed on the client. As driver we 
consider any kind of printer-model-specific software or data.

Driverless printers advertise themselves by Bonjour and are accessible 
via IPP. IPP is used as the client can poll capability information from 
the printer, so that no printer-model-specific data (the printer's 
capabilities) is needed. The printer also works with at least one known 
Page Description Language (PDL) so that no printer-model-specific 
software (filter for proprietary PDL) is needed.

This works fine in a network. I have made cups-browsed (part of 
cups-filters which I am maintaining) listening to Bonjour broadcasts of 
driverless printers to automatically set up print queues for them.

Now there are also IPP-over-USB printers. These printers have IPP 
implemented via USB, so that they can get queried for driverless 
printing like IPP network printers, and one can use the printer's web 
administration interface. I am maintaining ippusbxd which is a simple 
daemon mapping the the input and output to and from the printer to 
localhost:60000 (or other ports). With this one can set up the 
IPP-over-USB printer like an IPP network printer and also driverless 
printing works.

What is missing is that the IPP-over-USB printer gets advertised to the 
local cups-browsed for automatic print queue setup, as the printer is 
not Bonjour-broadcasting. So I tried to fire up an appropriate Avahi 
service from ippusbxd. What I need is that the service's address is 
"localhost:6000" and/or "127.0.0.1:60000" and that service is only 
advertised on the local machine, not on other machines on the local 
network, because the printer is only accessible from the local machine.

I have tried to add the service via

avahi_entry_group_add_service_strlst(bonjour_data->ipp_ref,
                                        AVAHI_IF_UNSPEC,
				       AVAHI_PROTO_UNSPEC, 0,
				       dnssd_name,
				       "_ipp._tcp", NULL,
                                        NULL, port,
				       ipp_txt);

and then the service gets advertised in the whole local network with the 
network IP and host name of my computer. The remote machines are not 
able to access the printer.

With

avahi_entry_group_add_service_strlst(bonjour_data->ipp_ref,
                                        AVAHI_IF_UNSPEC,
				       AVAHI_PROTO_UNSPEC, 0,
				       dnssd_name,
				       "_ipp._tcp", NULL,
                                        "localhost", port,
				       ipp_txt);

I get a host name error (-3).

With

avahi_entry_group_add_service_strlst(bonjour_data->ipp_ref,
                                        AVAHI_IF_UNSPEC,
				       AVAHI_PROTO_UNSPEC, 0,
				       dnssd_name,
				       "_ipp._tcp", NULL,
                                        "localhost.local", port,
				       ipp_txt);

the service gets broadcasted, but it apperas also on remote machines 
(see output of avahi-discover) but when one clicks on the list entry in 
avahi-discover, the details do not get shown. One gets a timeout after 
some seconds.

How do I have to proceed? I do not want to create D-Bus communication 
between ippusbxd and cups-browsed, nor do I want to build ippusbxd into 
cups-browsed.

    Till