RPM questions

[Joe Desbonnet <jdesbonnet@xxxxxxxxx>]

Some quick questions about RPMs:

1. What is the 'correct' method of arranging a set of update RPMs for
a given package in chronological order? I'm currently using the file
timestamp, but can I rely on mirror servers to preserve timestamps? At
first I thought sorting by file name would work until I encountered
kernel-2.6.9 and kernel-2.6.10 :)   I see there is a build date field
in the RPM header. Is that guaranteed to be in the correct order?

2. I need a quick and dirty way to get to calculate the payload offset
within an RPM. I'm developing in Java so I can't use the RPM
development libraries.

I'm currently using the following code (it's in Java -- but I think
it's obvious what's going on). At the end 'loc' holds the payload
offset. It works for all RPMs in the FC3 distribution, *but* I had to
fix the size of the signature structSize to 216 (a few RPMs reported
212 ?!). Obviously, despite working, I'm doing sometime wrong.


		// din is a InputStream for the RPM file. 
		// din.skip(n) skips forward n bytes.
		// din.read() reads a byte from the stream
		// din.readInt() reads a 32 bit int (4 bytes) from the stream
	
		// skip lead
		din.skip(96);
		int loc = 96;

		if (!((din.read() == 0x8e) && (din.read() == 0xad)
				&& (din.read() == 0xe8) && (din.read() == 0x01))) {
			System.err.println("start of signature magic not found");
			return -1;
		}

		din.skip(4);
		int nIndexEntries = din.readInt();
		int structSize = din.readInt();

		// TODO: why this?   <-- here is my problem: some rpms  reported
		// 212, but if I used this value it failed. If I fix structSize to 216 all
		// the RPMs in the FC3 distribution work !
		if (structSize==212) {
			structSize=216;
		}
		
		din.skip(nIndexEntries * 16 + structSize);
		loc += 16 + nIndexEntries * 16 + structSize;

		if (!((din.read() == 0x8e) && (din.read() == 0xad)
				&& (din.read() == 0xe8) && (din.read() == 0x01))) {
			System.err.println("start of header magic not found");
			return -1;
		}

		din.skip(4);
		nIndexEntries = din.readInt();
		structSize = din.readInt();

		din.skip(nIndexEntries * 16 + structSize);
		loc += 16 + nIndexEntries * 16 + structSize;

Thanks,
Joe.