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From "Robert Newson (JIRA)" <>
Subject [jira] Commented: (COUCHDB-604) _changes feed with ?feed=continuous does not return valid JSON
Date Mon, 21 Dec 2009 14:48:18 GMT


Robert Newson commented on COUCHDB-604:

continuous mode used to return valid JSON, and clients were expected to clip out valid lines
(using the newline hints) if they wanted to parse each change as it happened. It was deliberately
changed to this behavior to allow clients to more easily handle _changes, since all consumers
of _changes at that time needed to do the same logic.

Changing it back will make it "correct" but harder to use (every consumer will have to add
hackish logic to parse part of the response). Since the request format is predicated on "Sax-style
json parsers" which apparently don't exist, it feels like purism for its own sake, practicality
taking a step down.

Perhaps it suffices to change the returned content-type to multipart/related where each part
is a valid JSON response?

That said, I would hope it suffices to document the returned format for continuous mode with
the expectation that it will be the preferred format for developers that write external indexers
(which is the reason it was changed to the current format in the first place).

> _changes feed with ?feed=continuous does not return valid JSON
> --------------------------------------------------------------
>                 Key: COUCHDB-604
>                 URL:
>             Project: CouchDB
>          Issue Type: Improvement
>          Components: HTTP Interface
>    Affects Versions: 0.10
>            Reporter: Joscha Feth
>            Priority: Trivial
> 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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