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Date: Wed, 9 Dec 2009 13:50:18 +0000 (UTC)
From: "Filipe Manana (JIRA)" <jira@apache.org>
To: dev@couchdb.apache.org
Subject: [jira] Commented: (COUCHDB-583) adding ?compression=(gzip|deflate)
 optional parameter to the attachment download API
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    [ https://issues.apache.org/jira/browse/COUCHDB-583?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12788090#action_12788090 ] 

Filipe Manana commented on COUCHDB-583:
---------------------------------------

Forgot to mention that in point 1), couchdb sends the response with the header "Content-Encoding: gzip".

For case 2) this header is missing (therefore the content encoding is identity - the attachment is sent in uncompressed form) if the request accepts identity encoding (either explicitly or by not having "*; q=0" or "identity; q=0" as part of the Accept-Encoding header value). Otherwise an HTTP error 406 is sent (as rfc 2616 recommends) - none of the specified encoding methods requested by the client are supported by the server.

> adding ?compression=(gzip|deflate) optional parameter to the attachment download API
> ------------------------------------------------------------------------------------
>
>                 Key: COUCHDB-583
>                 URL: https://issues.apache.org/jira/browse/COUCHDB-583
>             Project: CouchDB
>          Issue Type: New Feature
>          Components: HTTP Interface
>         Environment: CouchDB trunk revision 885240
>            Reporter: Filipe Manana
>         Attachments: couchdb-583-trunk-3rd-try.patch, jira-couchdb-583-1st-try-trunk.patch, jira-couchdb-583-2nd-try-trunk.patch
>
>   Original Estimate: 24h
>  Remaining Estimate: 24h
>
> The following new feature is added in the patch following this ticket creation.
> A new optional http query parameter "compression" is added to the attachments API.
> This parameter can have one of the values:  "gzip" or "deflate".
> When asking for an attachment (GET http request), if the query parameter "compression" is found, CouchDB will send the attachment compressed to the client (and sets the header Content-Encoding with gzip or deflate).
> Further, it adds a new config option "treshold_for_chunking_comp_responses" (httpd section) that specifies an attachment length threshold. If an attachment has a length >= than this threshold, the http response will be chunked (besides compressed).
> Note that using non chunked compressed  body responses requires storing all the compressed blocks in memory and then sending each one to the client. This is a necessary "evil", as we only know the length of the compressed body after compressing all the body, and we need to set the "Content-Length" header for non chunked responses. By sending chunked responses, we can send each compressed block immediately, without accumulating all of them in memory.
> Examples:
> $ curl http://localhost:5984/testdb/testdoc1/readme.txt?compression=gzip
> $ curl http://localhost:5984/testdb/testdoc1/readme.txt?compression=deflate
> $ curl http://localhost:5984/testdb/testdoc1/readme.txt   # attachment will not be compressed
> $ curl http://localhost:5984/testdb/testdoc1/readme.txt?compression=rar   # will give a 500 error code
> Etap test case included.
> Feedback would be very welcome.
> cheers

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