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Re: Content-Transfer-Encoding "packet"

From: Roy Fielding <fielding@beach.w3.org>
Date: Mon, 24 Jul 1995 21:58:35 -0400
Message-Id: <199507250158.VAA02048@beach.w3.org>
To: Jeffrey Mogul <mogul@pa.dec.com>
Cc: http-wg%cuckoo.hpl.hp.com@hplb.hpl.hp.com
>Although I strongly favor the use of ASCII encodings of "packet"
>lengths (perhaps we could use a term besides "packet", which will
>cause untold confusion for years to come), I agree that it might
>be nice to use an encoding that occupies a fixed number of bytes.

We could call it "chunky" if you like... I prefer that over "chunks",
though I'm sure we could have no end of amusement talking about
blowing chunks across the network.  ;-)

>Note also that if we use a simple ASCII encoding, you need
>to parse the input stream to figure out where the end of
>the "packet" length string is.  If we use an encoding that
>takes a fixed number of columns, then you don't need to parse
>anything, you just grab a bunch of bytes.

Good point -- I prefer that as well (in fact, knowing the size of
the size ahead of time was one of the main reasons to do a 256chunk).

>Since I also don't see any reason to limit the "packet" size
>to just 256 bytes, or to any small value, I recommend that the
>length field be fairly large.  For example, suppose that the
>standard says "use 6 digits + CR + LF".  Then this leaves
>the following data nicely aligned (even for 64-bit machines),
>and allows almost a million bytes per "packet".  Better yet,
>use a hexadecimal encoding; this allows >16 million bytes, and
>is much easier to encode and decode.

Hmmm, fixed hex sounds reasonable, but 6 digits is a bit overboard.
And why would we need the CRLF if the size is fixed?  It does not
improve readability (aside from the first chunk).

How about four hex bytes:

	0 0 0 8
	eight bytes of data
	F F F F
	65,535 bytes of data
	0 0 0 0 CR LF
	<footer>
	CR LF

I would still prefer to see some hard data on the performance
differences.  Unlike the rest of HTTP/1.1, this has to be right
the first time its distributed in beta code.

 ....Roy T. Fielding  Department of ICS, University of California, Irvine USA
                      Visiting Scholar, MIT/LCS + World-Wide Web Consortium
                      (fielding@w3.org)                (fielding@ics.uci.edu)
Received on Monday, 24 July 1995 19:07:59 EDT

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