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From "Robert Newson (JIRA)" <j...@apache.org>
Subject [jira] Commented: (COUCHDB-604) _changes feed with ?feed=continuous does not return valid JSON
Date Mon, 21 Dec 2009 12:35:18 GMT

    [ https://issues.apache.org/jira/browse/COUCHDB-604?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12793177#action_12793177
] 

Robert Newson commented on COUCHDB-604:
---------------------------------------


The feed format used to be as you wish it, and still is for non-continuous mode. Consider
the uses of continuous mode, though, and this makes sense. Continuous mode is for continuous
replication and for external indexers (e.g, couchdb-lucene but also many others). If the response
is a single JSON object, then those users would have to wait for the end of the response before
they can parse the result, and there is no end to a continuous feed in general.

If there exists a SAX-style json parser, then that might be another approach, but I'm not
aware of one.

This programming model seems so trivial that even if one did exist, I can't imagine it would
be easier;

while (read(line) != EOF) {
  change=parse(line);
  apply(change);
}



> _changes feed with ?feed=continuous does not return valid JSON
> --------------------------------------------------------------
>
>                 Key: COUCHDB-604
>                 URL: https://issues.apache.org/jira/browse/COUCHDB-604
>             Project: CouchDB
>          Issue Type: Bug
>          Components: HTTP Interface
>    Affects Versions: 0.10
>            Reporter: Joscha Feth
>
> When using the _changes interface via ?feed=continuous the JSON returned is rather 
> a stream of JSON documents than a valid JSON file itself:
> {"seq":38,"id":"f473fe61a8a53778d91c38b23ed6e20f","changes":[{"rev":"9-d3e71c7f5f991b26fe014d884a27087f"}]}
> {"seq":68,"id":"2a574814d61d9ec8a0ebbf43fa03d75b","changes":[{"rev":"6-67179f215e42d63092dc6b2199a3bf51"}],"deleted":true}
> {"seq":70,"id":"75dbdacca8e475f5909e3cc298905ef8","changes":[{"rev":"1-0dee261a2bd4c7fb7f2abd811974d3f8"}]}
> {"seq":71,"id":"09fb03236f80ea0680a3909c2d788e43","changes":[{"rev":"1-a9646389608c13a5c26f4c14c6863753"}]}
> to be valid there needs to be a root element (and then an array with commata) like in
the non-continuous feed:
> {"results":[
> {"seq":38,"id":"f473fe61a8a53778d91c38b23ed6e20f","changes":[{"rev":"9-d3e71c7f5f991b26fe014d884a27087f"}]},
> {"seq":68,"id":"2a574814d61d9ec8a0ebbf43fa03d75b","changes":[{"rev":"6-67179f215e42d63092dc6b2199a3bf51"}],"deleted":true},
> {"seq":70,"id":"75dbdacca8e475f5909e3cc298905ef8","changes":[{"rev":"1-0dee261a2bd4c7fb7f2abd811974d3f8"}]},
> {"seq":71,"id":"09fb03236f80ea0680a3909c2d788e43","changes":[{"rev":"1-a9646389608c13a5c26f4c14c6863753"}]},
> in short this means that if someone does not parse the change events in an object like
manner (e.g. waiting for a line-ending and then parsing the line), but using a SAX-like parser
(throwing events of each new object, etc.) and expecting the response to be JSON (which it
is not, because its not {x:[{},{},{}]} but {}{}{} which is not valid) there is an error thrown.
> I can see, that people doing this line by line might be okay with the above approach,
but the response is not valid JSON and it would be nice if there were a flag to make the response
valid JSON.

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