sbuf(9) functions in userspace

Hello,

as part of the GSoc project I'm working on the ipfw code,
and I need some functions similar to the sbuf(9) family but
working in userspace.
There is something like that already available for userland?

Otherwise I could use the following library:

    http://info.iet.unipi.it/~luigi/FreeBSD/#dynstring

that works like the sbuf(9) functions and it is ready to be used
in userland.

thanks, marta