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From "Filipe Manana (JIRA)" <j...@apache.org>
Subject [jira] Created: (COUCHDB-583) adding ?compression=(gzip|deflate) optional parameter to the attachment download API
Date Sun, 29 Nov 2009 15:43:20 GMT
adding ?compression=(gzip|deflate) optional parameter to the attachment download API
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                 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


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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