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From Keyur Shah <keyu...@gmail.com>
Subject RE: Trailer header and tomcat
Date Wed, 05 Aug 2009 22:35:14 GMT

Martin - I can verify that my ETag implementation meets the spec
requirements. Both buffered and streaming impls. yield the same ETag. With
the buffered implementation tomcat does include the ETag header in the
response. With the streaming impl. it does not (even though I set Trailer:
ETag)

--Keyur


mgainty wrote:
> 
> 
> coding needs to conform to the spec's requirement for [weak]opaque-tag
> 
> entity-tag = [ weak ] opaque-tag
>       weak       = "W/"
>       opaque-tag = quoted-string
> 
>    
> A "strong entity tag" MAY be shared by two entities of a resource
>    only if they are equivalent by octet equality.(i interpret this as byte
> for byte equivalence)
> 
> 
> 
>    A "weak entity tag," indicated by the "W/" prefix, MAY be shared by
>    two entities of a resource only if the entities are equivalent and
>    could be substituted for each other with no significant change in
>    semantics. A weak entity tag can only be used for weak comparison.
> 
> E-Tags are generally used for transmission of sizable resources such as
> blobs/jpgs
> 
> http://www.w3.org/Protocols/rfc2616/rfc2616-sec3.html#sec3.11
> 
> Martin Gainty 
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> 
> 
>> Date: Wed, 5 Aug 2009 14:55:35 -0700
>> From: keyurva@gmail.com
>> To: users@tomcat.apache.org
>> Subject: Re: Trailer header and tomcat
>> 
>> 
>> Thanks Filip. Buffering is what I do right now and that is what I'm
>> trying to
>> avoid. With a large number of concurrent users, the buffering is proving
>> to
>> be a performance bottleneck and is causing frequent GC sweeps.
>> 
>> I think what I'm trying to do with the Trailer header is valid http usage
>> (correct me if that's wrong). And I was hoping tomcat supports this
>> usage.
>> 
>> --Keyur
>> 
>> 
>> Filip Hanik - Dev Lists wrote:
>> > 
>> > On 08/05/2009 02:14 PM, Keyur Shah wrote:
>> >> Tomcat by default sends chunked responses => 
>> Transfer-Encoding:chunked
>> >>
>> >> I'm calculating the ETag for the response dynamically as the content
>> is
>> >> being
>> >> written to the response stream. Since I'll know the final value of the
>> >> ETag
>> >> only
>> >> when the stream is closed, I indicate that using the Trailer header =>
>> >> Trailer:
>> >> ETag
>> >>
>> >> I'm ensuring that just before the stream is closed, I set the ETag
>> header
>> >> =>
>> >> ETag: SomeETagValue
>> >>
>> >> However, when I look at the response on the client, the ETag header
>> was
>> >> never
>> >> written.
>> >>
>> >> Is this a tomcat specific bug or am I doing something wrong?
>> >>    
>> > When you write, after you have filled up the buffer, tomcat will commit 
>> > the response.
>> > You will need to not write any of your response until you have the tag, 
>> > so buffer your response,
>> > calculate your tag, set the header, write the response
>> > 
>> > Filip
>> >> Thanks,
>> >> Keyur
>> >>    
>> > 
>> > 
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>> > 
>> > 
>> 
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> 
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