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Date: Sun, 29 Nov 2009 22:41:20 +0000 (UTC)
From: "Glenn Rempe (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=12783495#action_12783495 ] 

Glenn Rempe commented on COUCHDB-583:
-------------------------------------

As a side note (this should probably be a discussion of its own though).  Has any thought been given to bolting WebMachine onto CouchDB as the primary HTTP interface?  I'm not sure how difficult it would be to retrofit, or if there are use cases that would preclude this, but doing so would seem to eliminate a lot of uncertainty (and possible errors) in making sure that the complexities of HTTP are properly handled?

I comment on it here since webmachine could in theory 'do the right thing' regarding handling content encoding, HTTP response codes, etc.

http://bitbucket.org/justin/webmachine/wiki/Home

Just a thought.  I'm curious if this has been discussed before.

> 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: 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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