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Content-Transfer-Encoding "packet"

From: Roy Fielding <fielding@beach.w3.org>
Date: Sun, 23 Jul 1995 00:03:39 -0400
Message-Id: <199507230403.AAA10044@beach.w3.org>
To: http-wg%cuckoo.hpl.hp.com@hplb.hpl.hp.com
Hi all,

To get the ball rolling again on the features of HTTP/1.1,
I'd like to get a firm definition of the packetized transfer
encoding.  The packet CTE will be used to safely delimit the
size of dynamically generated response messages and (if the
server is known to be 1.1 or above) requests with content.

The last time I posted my notes regarding the format, I referred
to it as being basically the same as that proposed by Dan Connolly
way back in<9409271503.AA27488@austin2.hal.com> on www-talk.
I'd like to change that now, before we get products out on the
street that use the sucker.

After investigating the needs of the security/authentication folks
regarding the desire to sign the content of a message after it
is generated, Phill Hallam-Baker has proposed adding a footer to
the format that would contain post-generation Entity-Header fields.

Also, I've been playing around with various formats and have
found that the optimum for most transfers uses a simple one-byte
prefix to encode the length of each packet, with a zero byte
indicating end-of-packets.

So, without further ado, here's the format:

Content-Transfer-Encoding: packet

    Entity-Body = *( packet ) NUL
                  footer
                  CRLF

    NUL         = <octet 0>

    packet      = packet-size packet-data

    packet-size = <OCTET, excluding octet 0, representing
                   the unsigned integer (1-255)>

    packet-data = packet-size(OCTET)

    footer      = *( Entity-Header )

Note that the footer is terminated by an empty line (just like the
headers) and is optional.  The semantics of a footer are as if the
given Entity-Header fields are part of the message headers.

The un-packetizer algorithm is fairly simple.

    length := 0
    packet-size := read-byte
    while (packet-size > 0) do
    {
        read input until amt-read == packet-size
        write buffer to BODY
        length := length + packet-size
        packet-size := read-byte
    }
    line := read-line
    while (line is not empty) do
    {
        process Entity-Header
        append header to HEADERS
    }
    replace Content-Length value with length.

In other words, the result looks like a normal message, with
the Content-Length computed by the unpacketizer.  In actuality,
it is often faster to read packet-size + 1 bytes, slurping in
the next packet-size as part of the prior packet read.

So, is that enough detail for discussion?  I will try to get
the updated 1.0 spec done this week, with the 1.1 spec soon
after that.


 ....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 Sunday, 23 July 1995 10:36:58 EDT

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