Here is a list of all documented files with brief descriptions:

sofia-resolv
sres.h	Sofia DNS Resolver
sres_async.h	Asynchronous interface for Sofia DNS Resolver
sres_cache.h	Sofia DNS Resolver Cache
sres_config.h	Configuration for Sofia DNS Resolver
sres_record.h	Sofia DNS Resolver Records
sofia-sip
sres_sip.h	Asynchronous resolver for SIP
sresolv.h	Easy API for Sofia DNS Resolver