This is an explanation and partial implementation of RFC 3338: "Dual Stack Hosts Using BIA".
This RFC specifies a mechanism of dual stack hosts using a technique called "Bump-in-the-API" (BIA) which allows for the hosts to communicate with other IPv6 hosts using existing IPv4 applications. The goal of this mechanism is the same as that of the Bump-in-the- stack mechanism, but this mechanism provides the translation method between the IPv4 APIs and IPv6 APIs. Thus, the goal is simply achieved without IP header translation.
libbiased has been programmed 'literally' (with noweb). This means the source should be exceptionally readable. (agreed, this is not yet a very 'clean' literate program, but imho already much better than old-style C)