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Re: #445: Transfer-codings

From: Michael Sweet <msweet@apple.com>
Date: Fri, 04 Apr 2014 15:32:53 -0400
Cc: "ietf-http-wg@w3.org" <ietf-http-wg@w3.org>
Message-id: <EC20B04D-38FE-4FD7-89C0-AC91660D58EE@apple.com>
To: Matthew Kerwin <matthew@kerwin.net.au>
-1 on this.

First, why a separate flag when you can just look at a couple bytes in the DATA?

Second, what about all of the security considerations that have been brought up?

And finally, HTTP/2 is not supposed to introduce new semantics.  If you have TE: gzip/compress/zlib, then that needs to be proposed separately since it applies equally to HTTP/1.1 and HTTP/2.


On Apr 3, 2014, at 10:39 PM, Matthew Kerwin <matthew@kerwin.net.au> wrote:

> Here is my proposal for reintroducing transport-level compression:
> 
> 
> 6.1 DATA
> 
> New DATA Frame Payload:
> 
> ```
>  0                   1                   2                   3
>  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
>  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>  | Pad High? (8) |  Pad Low? (8) |
>  +---------------+---------------|
>  |        Encoding? (16)         |
>  +-------------------------------+-------------------------------+
>  |                            Data (*)                         ...
>  +---------------------------------------------------------------+
>  |                           Padding (*)                       ...
>  +---------------------------------------------------------------+
> ```
> 
> With the description:
> 
> ```
> Encoding: A 16 bit identifier which describes the encoding that has been applied to the Data field. This field is optional and is only present if the ENCODED flag is set.  A sender MUST NOT apply an encoding that has not first been advertised by the peer in a SETTINGS_ACCEPT_DATA_ENCODING settings frame, or was advertised with a rank of 0. Endpoints that receive a frame with an encoding identifier they do not support MUST treat this is a connection error of type PROTOCOL_ERROR.
> ```
> 
> And a new flag:
> 
> ```
> ENCODED (0x20): Bit 6 being set indicates that the Encoding field is present and describes the encoding that has been applied to the Data field.
> ```
> 
> This is intentionally designed to make it easy for people to, for example, detect the flag and immediately PROTOCOL_ERROR.  Hopefully it's not too much skin off anyone's nose.
> 
> 
> 
> 6.5.2 Defined SETTINGS Parameters
> 
> New parameter:
> 
> ```
> SETTINGS_ACCEPT_DATA_ENCODING (5): Indicates the sender's ability and willingness to receive DATA frames that are encoded using the scheme identified in the Value.
> 
> The Value field is further divided into two sub-fields, an unsigned 16 bit encoding identifier and an unsigned 16-bit rank.
> 
>  0                   1                   2                   3
>  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
>  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>  |         Encoding (16)         |           Rank (16)           |
>  +-------------------------------+-------------------------------+
> 
> The following encodings are defined:
> 
>   ENCODING_COMPRESS (1):
>    The "compress" coding is an adaptive Lempel-Ziv-Welch (LZW) coding that is commonly produced by the UNIX file compression program "compress".
> 
>   ENCODING_DEFLATE (2):
>    The "deflate" coding is a "zlib" data format [RFC1950] containing a "deflate" compressed data stream [RFC1951] that uses a combination of the Lempel-Ziv (LZ77) compression algorithm and Huffman coding.
> 
>   ENCODING_GZIP (3):
>    The "gzip" coding is an LZ77 coding with a 32 bit CRC that is commonly produced by the gzip file compression program [RFC1952].
> 
> An endpoint MAY ignore a SETTINGS_ACCEPT_DATA_ENCODING parameter with an encoding identifier it does not recognise or support.
> 
> The rank fulfils the same role as in the HTTP/1.1 TE header. The rank value is an integer in the range 0 through 65,535, where 1 is the least preferred and 65,535 is the most preferred; a value of 0 means "not acceptable".
> ```
> 
> The three encoding schemes are taken straight from HTTPbis-p1 section 4.2.  Again, it's designed specifically so that people can ignore it if they don't want to play along; but it grants us adventurous folk the chance to play.
> 
> 
> 8.1.3.5 Malformed Messages
> 
> Clarify the content-length:
> 
> ```
> A request or response that includes an entity body can include a content-length header field. A request or response is also malformed if the value of a content-length header field does not equal the sum of the DATA frame payload lengths, after any encoding is removed, that form the body.
> ```
> 
> Cheers
> -- 
>   Matthew Kerwin
>   http://matthew.kerwin.net.au/

_________________________________________________________
Michael Sweet, Senior Printing System Engineer, PWG Chair


Received on Friday, 4 April 2014 19:33:34 UTC

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