W3C home > Mailing lists > Public > ietf-http-wg-old@w3.org > January to April 1998

Re: FW: Digest mess

From: John Franks <john@math.nwu.edu>
Date: Wed, 31 Dec 1997 13:39:48 -0600 (CST)
To: Yaron Goland <yarong@microsoft.com>
Cc: "'ietf-http-wg@w3.org'" <ietf-http-wg@w3.org>, http-wg%cuckoo.hpl.hp.com@hplb.hpl.hp.com
Message-Id: <Pine.LNX.3.96.971231131126.2684A-100000@hopf.math.nwu.edu>
> > 
> > The main thing I hate about Digest is:
> > 
> > A) Can't digest arbitrary headers.
> > 
> > This is a big deal for groups like WebDAV where new headers are being
> > introduced which contain critical command information. For example the
> > depth header specifies if a command applies to a single resource or a
> > collection of resources. The destination header specifies the destination
> > of a move or copy. Changing these headers would have a profound effect on
> > the meaning of the method.
> > 


As you probably know from the discussion in this group the difficulty
with digesting headers is that proxies may modify them.  Proxies
may add headers which were not originally present, may change them,
or may "canonicalize" them.  All of these features would ruin a
digest.

It has proven difficult if not impossible to have the specification
require that proxies not change all the headers people would like
digested.  My guess is that it is futile to try to specify a set of
headers which must always be digested and must not be changed by
proxies.  At least the discussion so far has not shown anything like a
consensus on this.

On the other hand I agree that digesting arbitrary headers is highly
desirable.  Painful though it may be in terms of bandwidth, the only
way I think this can be done is by replicating all the relevant origin
server headers in a field of the Authentication-info header.  Proxies
are required not to touch the Authentication-info header.

This "origin-header" field would have a value which is a quoted string
consisting of the concatenation (with some separator) of the complete
headers which the sender wants digested.  This string would be included
in the material digested to form the entity-digest.

This would have the advantage of being extensible as any new headers
are added.

I am not sure what a good separator would be; colon might not work
too well.  Also I don't know what to do about headers containing
quotation marks.  Perhaps something like %-escapes for colons, quotes
and percents in the headers being concatenated and colon as separator?

John Franks
john@math.nwu.edu
Received on Monday, 5 January 1998 17:09:38 EST

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