PROPSAL: import Apple's mDNSResponder

[Ty Sarna <ty%sarna.org@localhost>]

I'd like to import Apple's mDNSResponder to the system. I think  
zeroconf is becoming more basic functionality, and is desirable across  
NetBSD's range of markets these days. Embedded devices and servers  
want to advertise services this way, and desktops want to access them.

There seem to be three potential choices out there for mDNS these  
days: Avahi, Apple's mDNSResponder, and the NetBSD SoC zeroconf.

Avahi is LGPL. mDNSResponder used to be APSL. Neither of those being  
acceptable, I believe that led to the SoC project. That project is  
still unfinished however, and in the meantime mDNSResponder has been  
relicensed in a combination of Apache2  (server) and BSD 3-clause  
(client library). As it is effectively the reference implementation,  
is externally maintained, and used in at least two other OSes (OS X of  
course, and it looks like OpenSolaris as well), it seems like the  
clear choice to me.


So, I would like to proceed as follows. There are a number of open  
questions or options.

1) Import mDNSResponder (currently 212.1, vs ancient 108 in pkgsrc) in  
src/external/apache2/dist. It will need a prepare-import.sh script to  
nuke the $Log$ lines in the sources (ugh!) and we can also prune out  
the Windows, OS X, MacOS 9, vxWorks, etc. sources.

2) Add reachover makefile for mdnsd. (QUESTION: do we want to call it  
mdnsd, which is how the supplied makefile builds it for  "posix", or  
mDNSResponder, which is what OS/X calls it? OpenSolaris went with mdnsd)

3) dnsetxd has yacc source that requires a feature not present in our  
current yacc (YYPARSE_PARAM), so it will not be built for now.

4) OPTION: the pkg currently installs some debugging tools like  
mDNSIdentify, mDNSClientPosix, etc. These don't ship in OS X. Do we  
reachover these as well? My feeling is no -- get them from pkgsrc if  
you need them.

5) Create a _mdnsd (_mdnsresponder?) user/group and get mdnsd to run  
under it. The issue is writing the socket and pid file in /var/run,  
which it doesn't have permissions to. Other than that it works fine.  
My idea is to create /var/run/mdnsd, owned by _mdnsd, and change the  
code to create the socket & pid file under there instead of in /var/run.

6) Create a rc.d script for it (QUESTION: does it default on or off?)

7) Supply client library functionality (QUESTION: separate libdns_sd,  
or include in libc a'la OS X? OpenSolaris went separate.)

8) I would like to reachover for dns-sd(1) as well, but that one file  
seems to still bear a APSL license. I will contact Apple about getting  
that relicensed.

9) Write a new nss_mdns plugin. The current pkgsrc one is a wrapper  
around one written for Linux, and it has issues. (OPTION: separate  
nss_mdns.so plugin, or if we build the client functionality into libc,  
do we build in the nss plugin too?) I have open questions about how  
this integrates with regular DNS-SD (a'la PR 32373 -- see David  
Young's message on tech-net from 20090303)