[Qemu-devel] Re: ANN: QEMU Monitor Protocol git tree

[Avi Kivity <avi@redhat.com>]

On 09/23/2009 04:40 PM, Paolo Bonzini wrote:
> On 09/23/2009 12:57 PM, Avi Kivity wrote:
>> On 09/23/2009 12:57 PM, Daniel P. Berrange wrote:
>>>> Ignoring the dos-ism, since you can parse JSON with a regexp, why 
>>>> do we
>>>> need explicit message boundaries?
>>> I think it would be nice to be able to assume that each JSON message
>>> will not cross a line-end boundary. Whether we use CRLF, just CR or
>>> just LF I don't mind. Its much easier to search for a message boundary
>>> by just doing strchr('\n') than having to actually parse the JSON or
>>> use a regexp at that point.
>>
>> A good parser will consume exactly enough characters to make up an
>> object or let you know if it needs more. I don't think using a regexp is
>> warranted.
>
> Agreed, regexes are unnecessary.  Also because a regex cannot parse 
> JSON; it can only detect _some_ invalid JSON inputs, and then only if 
> you're given an already complete input.
>
> In other words, there are Javascript JSON parsers that are just "match 
> a regexp and run eval on the input", but the actual parsing is done by 
> the Javascript interpreter using eval.  The regexp is just avoiding 
> the security problems that are inherent in eval.

On the other hand, the two parsers I looked at only accept a string as 
input, not a stream (strangely, one of them internally converts the 
string to a stream, but doesn't expose the stream interface), so record 
termination might be helpful to parsers.  Would be best not to rely on 
it in the server, though.

-- 
error compiling committee.c: too many arguments to function