Re: HTTP 'HASH' Method

trailer headers in chunks leads to a number of implementation 
difficulties especially for proxies.

It seems there are a few features in HTTP that primarily consider agents 
and servers, but not proxies, or specifically administrative 
requirements for proxies.

It makes it very difficult to make decisions based on header values, 
when the header itself may arrive a long time after the main headers of 
a response in some chunk down the line.

And it added a lot of complexity to header processing.

the options available to an administrator don't lend themselves to good 
user experiences. 

For instance a proxy administrator wishing to strictly enforce actions 
based on response header values has a big problem with trailers.  
Stripping any TE header in requests, or blocking responses from servers 
that indicate there will be trailers are about the only decent options.

The overall structure of a message seems to have been muddied with the 
addition of trailers - from a clear delineation between headers and 
resource, separated by 2 CRLF, we now no longer enjoy this clarity.  
Processing of "content" now has to be able to encounter and deal with 
new "headers".  This affects all resource processing, e.g caching, 
scanning etc.

It would be nice if the concept could be deprecated or re-thought before 
someone goes ahead and implements it, but I'm dreaming there I guess.




Henrik Nordstrom wrote:
> sön 2007-05-27 klockan 23:40 +0100 skrev Jamie Lokier:
>
>   
>> Where the trailers would be useful is in specifying the Vary header.
>> Currently, if the server can determine which requests headers are
>> prerequisites for the page, before it sends anything, it can put those
>> in the Vary header.  If not, it has to send "Vary: *".  If it worked
>> to put Vary in a trailer instead, it could be more accurate in those
>> cases.
>>     
>
> Should work, but only if the request indicates "TE: trailer" and the
> response a "Trailer: Vary". If "TE: trailer" is not seen then Vary is
> not allowed in the trailer. 3.6.1 Chunked transfer coding, and the fact
> that Vary can not be considered "optional" or safe to ignore while
> processing the response.
>
> A cache advertising "TE: trailer" and not handling Vary in the trailer
> is broken imho.
>
> Regards
> Henrik
>

Received on Monday, 28 May 2007 02:30:42 UTC