C API to R connections?

Is it a public C API to R connection?  I couldn't find any.  Can I use
the *Rconnection in user C code?

Instead of straight fopen, I would like the ability to read in
compressed file (gz, bz2), remote file, etc, using the implementation
that R already has, with a uniformed interface.

Also it would be nice to open the file/connect in R and handle any
exceptions/errors in R but do the actually reading in C (I'm dealing
with a binary format).

Thanks,

Michael