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Re: HTTP/1.2 topics and beyond

From: Koen Holtman <koen@win.tue.nl>
Date: Mon, 29 Jul 1996 11:15:23 +0200 (MET DST)
Message-Id: <199607290915.LAA07648@wsooti04.win.tue.nl>
To: Martin Hamilton <martin@mrrl.lut.ac.uk>
Cc: http-wg%cuckoo.hpl.hp.com@hplb.hpl.hp.com
Martin Hamilton:
> Secondly, the number of MUSTs and SHOULDs (another 
>"entry cost") has gotten quite alarming -
>
>  % grep MUST draft-ietf-http-v11-spec-06.txt | wc -l
>       258
>
>  % grep SHOULD draft-ietf-http-v11-spec-06.txt | wc -l
>       189
>
>I'd argue that some of these do not, strictly speaking, belong in the 
>specification but have accumulated there over time because of the lack 
>of anywhere else that was particularly appropriate for them.  These are 
>the MUSTs and SHOULDs which are really guidelines for implementors 
>rather than basic requirements of the protocol.  It would be nice to 
>hive these off into a separate document, but this may turn out to be 
>unrealistic given the timescales involved...  have to wait and see.

I don't think that many MUST and SHOULDs are really guidelines for
implementors, so moving them into a separate document would not gain
you that much.  All in all, I don't think that the 1.1 spec can be
made much smaller by creating an implementation guide.  It can be made
more accessible, but not much smaller.  The 1.1 spec is a bit like a
monolithic OS kernel: there are so many interdependencies in the text
that you can't easily remove parts without breaking the whole.

My take on the MUSTs and SHOULDs in 1.1 is that most of them are of
the form `if you do this, only then MUST/SHOULD you ...'.  I estimate
that about half of the MUSTs and SHOULDs in 1.1 only apply to the
authors of proxy caches, not to user agent and origin server authors.

>One meta-comment: given that HTTP 1.1 requires so much from its 
>implementors, some sort of quick reference might be in order? 

Yes, I think a quick reference is definitely in order.  What we need
is a table that could serve as a reading guide: the table should give
information like `if you are a user agent author, do not bother to
read/understand section X.Y'.

At this point, I think that implementors wanting to upgrade their
software to 1.1 need a guide to deconstructing the HTTP/1.1 spec much
more than they need a guide to constructing HTTP/1.1 implementations.

> e.g. 
>listing the status of the various headers in clients' requests and 
>servers' responses (MUST? SHOULD?  MAY?) would be a good start.

Yes. I've been thinking about tables like the ones below.  I filled
these tables from memory, so re-use with caution.  `MUST IF' means
`MUST if particular conditions apply.'

Request header  generation  handling   generation  handling
                by user     by origin  by caching  by caching
(GET requests)  agent       server     proxy       proxy
---------------|-----------|----------|-----------|----------|

Accept            MAY        MAY          -          -
Accept-Charset    MAY        MAY          -          -
Accept-Encoding   MAY        MAY          -          MAY
Accept-Language   MAY        MAY          -          -
Authorization     MAY        MAY          -          -
Cache-Control     MAY        MUST         MAY        MUST
Connection        MAY        -            MAY        MUST?
rom              MUST IF    -            -          -
Host              MUST       MAY          MUST       -
If-Modified-Since MAY        MAY          MAY        MAY
If-Match          MAY        MAY          MAY        MAY
If-None-Match     MAY        MAY          MAY        MAY
If-Range          MAY        MAY          MAY        MAY
If-Unmodified-Since MAY      MAY          MAY        MAY
Max-Forwards      -          -            -          -
Pragma            MAY        -            MAY        MUST?
Proxy-Authorization MAY      -            MAY        MAY
    ..etc..


Response header handling    generation handling    generation
                by user     by origin  by caching  by caching
(GET responses) agent       server     proxy       proxy
---------------|-----------|----------|-----------|----------|

Accept-Ranges     MAY        MAY          MAY        MAY
Age               MAY        -            MUST       MUST
Allow             MAY        MAY          -          -
Cache-Control     MAY        MAY          MUST       -
   ..etc..
Vary              MAY        MUST IF      MUST       -
   ..etc..


>Martin

Koen.
Received on Monday, 29 July 1996 23:57:21 EDT

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