> It would be nice if I could easily compute the hash if I know the > message-id --- I assume I can just run it through sha1. This would > allow me to shorten commit URLs, which would be a win for GMail.
Now that I look closer, Magnus' example shows that this proposal is underspecified: exactly how would the message-ID be rendered before being fed into sha1? In particular it's not clear from this whether "@" should be spelled "@" or "%40". The existing archive website is quite forgiving about that, you can write either --- but the sha1 transform would be utterly unforgiving. Instead of opaque hash X you'd get opaque hash Y, and there'd be no way even to see what caused the mismatch.
It should always be @. The %40 is a sideeffect of @ not being allowed in an URL.
(BTW, after some experimentation I'm totally unable to reproduce Magnus' example using sha1sum(1) and base64(1), so that is not the only underspecified point here.)
The problem is that sha1sum generates a hex version of the sum, not the binary version. You also need to be careful about the newlines.