[sr-dev] evapi buffer overflow?

[Alex Balashov]

Daniel,

Thank you for that clarification. I had considered that this might be a 
possible reason. However, the consumer is Node.js, so I figured that the 
high-level data read event that it presents might deal with this problem 
to provide chunked output to the implementor that was equal to the 
chunks sent.

Thanks, I will find a way to deal with it on the client side, and I'm 
sorry for prematurely assuming that it was some sort of bug.

-- Alex

On 01/09/2015 06:37 PM, Daniel-Constantin Mierla wrote:

> Hello,
>
> it looks like two jsons one after other, which is what happens over tcp
> stream. If you write them at the slow pace and the consumer reads
> constantly, then it is likely that it will read one document at a time.
> If you write faster than consumer reads, then it will get them
> accumulated in the tcp buffer, one after the other. The consumer needs
> to be a stream parser and detect when there first json document ends,
> process it, then read the next one.
>
> We do the same for sip, that's why the code for reading sip over tcp is
> rather complex, with lots of states (given there can be any kind of
> broken sip message).
>
> Alternative for evapi is to use the netstring encoding, which is easier
> to read a json document at once, because the size is given first.
>
> Cheers,
> Daniel
>
> On 09/01/15 22:01, Alex Balashov wrote:
>> Hi,
>>
>> I'm using evapi to emit JSON blobs to share presence event transitions
>> with a TCP client:
>>
>> loadmodule "evapi"
>>
>> modparam("evapi", "workers", 4)
>> modparam("evapi", "bind_addr", "0.0.0.0:8010")
>> modparam("evapi", "netstring_format", 0)
>>
>>
>>          if($hdr(Event) eq 'dialog' && $cl > 0) {
>>                  $xml(u=>doc) = $rb;
>>                  $var(state) =
>> $xml(u=>xpath:/di:dialog-info/di:dialog/di:state/text());
>>
>>                  evapi_relay("{ \"type\": \"state_transition\", "
>>                              "\"sip_user\": \"$(fU{s.escape.common})\", "
>>                              "\"sip_domain\":
>> \"$(fd{s.escape.common})\", "
>>                              "\"state\": \"$var(state)\" }");
>>          }
>>
>> Every once in a while, however, my consumer service's JSON.parse()
>> throws a parsing exception. There seems to be no particular pattern.
>> When I investigated the actual string being sent, I found two objects
>> concatenated:
>>
>> JSON parsing exception: SyntaxError: Unexpected token {
>> Raw received string was: { "type": "state_transition", "sip_user":
>> "6789540671", "sip_domain": "sip.evaristesys.com", "state": "" }{
>> "type": "state_transition", "sip_user": "6789540671", "sip_domain":
>> "sip.evaristesys.com", "state": "" }
>>
>> Any ideas as to why this might happen?
>>
>> Thanks,
>>
>> -- Alex
>>
>


-- 
Alex Balashov - Principal
Evariste Systems LLC
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