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From "Joscha Feth (JIRA)" <j...@apache.org>
Subject [jira] Commented: (COUCHDB-604) _changes feed with ?feed=continuous does not return valid JSON
Date Mon, 21 Dec 2009 13:00:18 GMT

    [ https://issues.apache.org/jira/browse/COUCHDB-604?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12793189#action_12793189
] 

Joscha Feth commented on COUCHDB-604:
-------------------------------------

Regarding the

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

just that it does not exist "in the wild" it does not neccessarily mean there isn't one -
we have a JSON Push Parser which can be compared to a SAX-like parser - it does not get a
reader, but uses a writer - and once data is written on that writer, the parser will do it's
work (and emit the above named events).
This Push Parser has now an extension to handle continous writes of distinct JSON objects
({}{}{}...) like the _changes feed delivers in continuous mode, but it might be different
with a different parser out there, which expects the feed to return valid JSON data.
That there is no end does not mean, that there might not be a parser which can not work with
the data.

Start Document
Starting seq
Starting id
Starting changes
Starting rev
Closing rev
...
... <-- lots of changes 
...
long time later
End Document <-- timeout of _changes feed happens here 

By the way, XMPP works the same - it basically has an infinitely long stream of XML elements
flowing - but still starts with a root node and ends with a closing one to be valid XML.

You might call it a feature request, but I think either the output should be valid JSON or
not. If you tell me the output is not valid JSON, okay, but I couldn't read this from the
docs, as all other _changes interfaces return valid JSON.

> _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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