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Re: [libvirt] [PATCH] json: add stream parser



On Thu, Mar 14, 2013 at 12:55:15PM +0400, Dmitry Guryanov wrote:
> Add function virJSONValueFromStream, which reads data from
> a stream and passes it to json parser. When end of the object
> is reached, it returns this object.
> To avoid reading from the stream by single bytes it reads to
> a buffer (in a structure virJSONStreamParserState), which should
> be passed to a consequent call of this function. So if the end
> of one object and the beginning of the next object have been
> read by a single system call - virJSONValueFromStream handle
> it correctly.
> 
> example of usage:
> 
> virJSONValuePtr v;
> virJSONStreamParserState state;
> 
> memset(&state, 0, sizeof(state));
> 
> while (1) {
>     v = virJSONValueFromStream(mon->fd, &state);
>     if (v == (void *)-1)
>         /* error */
>         break;
> 
>     if (v == NULL)
>         /* file descriptor has been closed */
>         break;
> 
>     /* handle object 'v' */
> }
> 
> I need such function for the parallels driver. It caches info
> about domains and needs some mechanism to update this cache.
> There is a "prlsrvctl monitor" command which waits for events
> forever and prints info about events to stdout in json format.
> So parallels driver could start separate thread which will
> read from prlsrvctl's stdout and update cache accordingly.
> 
> There is the same task in qemu_monitor_json, but each json object
> is printed in a separate line there. It's not possible in my case,
> because some fields could have line endings.

Even QEMU could output multi-line JSON if you set the 'pretty' flag,
so this would be useful for QEMU driver too at some point.

> 
> Signed-off-by: Dmitry Guryanov <dguryanov parallels com>
> ---
>  src/util/virjson.c |  110 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>  src/util/virjson.h |    8 ++++
>  2 files changed, 118 insertions(+), 0 deletions(-)

Since this is reasonably complex code can you also add
some more test cases to the tests/jsontest.c  file to
cover this functionality.

Daniel
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