This is a RPM binary format reader implementation written in PHP as a proof of concept, and as study project, and now released under the GPLv2.

This library contains the following files:

RPMDefines.php : RPM tag type and constants definitions
RPMIO.php : Used to read the RPM header information, and interpret its binary types propery
RPMLead.php : Reads in the RPM lead information (mostly depreciated info, use header info instead)
RPMSignature.php : Reads the signature of the RPM
RPMIndex.php : RPM index reading & parsing
RPMIndexEntry : Class instanced by RPMIndex
RPMHeader.php : RPM Header reading & parsing
RPM.php : demo file, change /path/to/some/file.rpm to a real rpm file, and run to see all the info collected

You can download the library here: phpRPMlib-1.0.tar.gz and here: http://phprpmlib.googlecode.com/files/phpRPMlib-1.0.tar.gz
Google code project page: http://code.google.com/p/phprpmlib/
Subversion repository: http://phprpmlib.googlecode.com/svn/trunk/