[syslog-ng] Writing a null character at the end of TCP payload

[Nicolas Fédou]

Yes, I am pretty sure as I have tested it (I posted the answer) :
http://serverfault.com/questions/591758/send-echo-message-to-graylog2-via-gelf-tcp-12201-port
After finding a clue in Graylog's issues :
https://github.com/Graylog2/graylog2-server/issues/127#issuecomment-17563306


Now, a function like template-escape() that may be called
"template-null-ending()" or any other may be easyer to deliver.
Gelf has mandatory fields, a compression option and seems to read only the
last GELF message per tcp frames as :
{ gelf 1 }\x0{ gelf 2 }\x0
Graylog shows only "gelf  2"
So, it forces the use of flush-lines(1).




2014-08-07 18:20 GMT+02:00 Balazs Scheidler <bazsi77 at gmail.com>:

> Hi,
>
> Adding a NUL via the template is difficult as the template compiler works
> with zero terminated string, and even though the lexer allows the use of
> \x0, this will indicate the end-of-the-string like you have seen it.
>
> Adding a zero byte would be possible by writing a template function
> $(format-gelf) and that probably could sit within the json module, reusing
> the infrastructure there.
>
> On the other hand, I've checked the GELF specification, and I can't see
> the NUL byte being required.
>
> http://graylog2.org/gelf#specs
>
> Are you sure this is the issue?
>
> Bazsi
>
>
> On Thu, Aug 7, 2014 at 11:09 AM, Nicolas Fédou <nicolas.fedou at gmail.com>
> wrote:
>
>> Hello,
>> I need to send a null character at the end of a message on a tcp output...
>> But this null is considered to be an end of string.
>>
>> My use case is sending a GELF message to a graylog's tcp input.
>> GELF message is a json syntax quite simple to comply with thanks to
>> format-json.
>> Graylog needs a null character at the end of a GELF message in TCP but
>> not in UDP.
>>
>> I tried many combination in the template with \x0, echo \x0,
>> `global_definition_of_null`, etc...
>> The matter is that null character when interpreted is an end of string,
>> and is not written in the tcp message.
>> I see truncated messages with ngrep.
>> Like "a\x0b" gives "a" according to ngrep.
>>
>> I did not find any option to actually write a null character.
>> Do you have any options ?
>>
>> As Graylog already have clients and librairies I belive they won't remove
>> the need for a null character.
>> Shall I open an issue on syslog-ng to ask for an option in templates or
>> in format-json ?
>>
>> Regards, Nicolas Fédou.
>>
>>
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>>
>
>
> --
> Bazsi
>
>
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