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Re: checksums on http transfers?

From: Joe Orton <joe_at_manyfish.co.uk>
Date: 2001-11-07 22:07:08 CET

On Wed, Nov 07, 2001 at 02:06:25PM -0500, Kevin Pilch-Bisson wrote:
...
> In light of this, I thought I would bring this subject up again. I was
> wondering does http have an md5sum header or something, and how would we
> go about making mod_dav_svn generate and send this header, and have
> neon verify it. gstein, joe, any pointers? I'd be willing to take on
> this challenge, just to make sure I don't get any more wonky working copies
> if my ISP's NAT goes flaky again.

Yup, this could be done with the Content-MD5 header (section 14.15 of
RFC 2616, just a base64 of the MD5 digest as you'd expect). Sending the
header and picking it up in ra_dav would be easy: getting the checksum
value is the problem. Choices I can see:

- the checksum is stored in the repository (or cheaply accessible from it)
- before sending the file, read it through once to precompute the checksum
- force the file to be sent using chunked transfer-encoding, calculate
the digest while sending it, and send the header in a chunked
response trailer

(the last option probably requires a PhD in Apache 2.0 filters ;)

joe

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Received on Sat Oct 21 14:36:48 2006

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