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Some randomness concerning chunked encoding.

From: <hallam@w3.org>
Date: Sat, 02 Mar 96 15:22:47 -0500
Message-Id: <9603022022.AA21404@zorch.w3.org>
To: http-wg%cuckoo.hpl.hp.com@hplb.hpl.hp.com

Hi,

	I'm just looking into the chunked encoding stuff and writing 
a little code. I had an idea which may save us a compatibility problem 
at a later date but which could probably be implemented now without
difficulty:-

	The point is that in future we may want to have attributes
associated with each chunk, eg a running message digest or the like.
There is also the question of multiplexing channels. forget for the
moment the issue of client/server compatibility but consider the action
of a gateway. We may wish to avoid having to upgrade proxies etc if
we incorporate channel type features into the spec.

The spec at present is for chunks of the following form:-


1A
abcdefghijklmnopqrstuvwxyz
10
0123456789
0
Footer: foo


What I would like to do is to require parsers to be tolerant of 
additional garbage on the chunk size line:-


1A ajwiuwenbq3iuy3ig23==
abcdefghijklmnopqrstuvwxyz
10 This will be ignored but might be an MD5 of the chunk
0123456789
0
Footer: foo


The 1.1 spec would not define semantics for the additional parameters but
would require parsers to be tolerant.

This effectively means that the parser needs to introduce a "throw
away data loop" into the FSM:-

Start 	-- hex --> 	Number
Number	-- hex -->	Number
Number	-- CR -->	GotCR
Number	-- LF -->	Start	[If NUMBER > 0]
			Footer	[Otherwise]

# We add the following transitions :

Number  -- SP -->	Junk
Junk	-- CR -->	GotCR
Junk	-- ANY -->	Junk


Naturally no 1.1 compliant generator would generate such data.


For the price of three extra transitions in the state table of the
parse we get a really big win. Is there anyone who would get trodden
on if we went this route?


This raises another problem. If I want to release a product that has
a subset of 1.1 implemented what do I report in the protocol? If I
report 1.0 this may be wrong because I may have used a non 1.0 feature.
If I report 1.1 then this may also be wrong.


		Phill
Received on Saturday, 2 March 1996 12:24:41 EST

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