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Re: Multiple Content-Location headers

From: Scott Lawrence <lawrence@agranat.com>
Date: Tue, 13 Jan 1998 08:52:54 -0500 (EST)
To: Jacob Palme <jpalme@dsv.su.se>
Cc: IETF working group on HTML in e-mail <mhtml@segate.sunet.se>, http-wg%cuckoo.hpl.hp.com@hplb.hpl.hp.com
Message-Id: <Pine.LNX.3.96.980112124128.24532D-100000@alice.agranat.com>

On Mon, 12 Jan 1998, Jacob Palme wrote:

> The MHTML group has decided to allow more than one Content-Location
> in the same message heading. This can be used, for example, if the
> same object can be located by several different URLs, and you want
> to specify all of them. A particular case is the following
> 
> Supposes a.gif and images/a.gif actually refer to the same image.
> And suppose the two HTML objects above have digital seals on them.
> Then, if you did not allow multiple Content-Location headers in
> the first body part, you would have to send the image twice, or
> you would have to modify the HTML invalidating the digital seals!

The usage of Content-Location within HTTP is specifically to allow the
specification of which one of some number of alternate versions of an
entity is in this response.  This would appear to me to be in conflict
with the use being suggested by MHTML.  I don't believe that this should
be changed at this late date, so I'd be carefull about assuming that
changes proposed by MHTML will apply to HTTP usage.

You describe the motivation for this as being a multipart message
containing multiple different references to the same entity.  For example,
message contains A, B, and C where A refers to C and B refers to D but D
is really another name for C.  Rather than adding an attribute to C to
give it the additional name (from the HTTP point of view overloading the
semantics of Content-Location), why not add another part to the message
that provides the equivalent of an HTTP redirect.  Something like (for
D):

Content-Type: mime/alternate-name
Location: C
Received on Tuesday, 13 January 1998 05:58:22 EST

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