[sr-dev] evapi buffer overflow?

[Daniel-Constantin Mierla]

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
>

-- 
Daniel-Constantin Mierla
http://twitter.com/#!/miconda - http://www.linkedin.com/in/miconda