[Nagiosplug-devel] NRPE Protocol

[Hiren Patel]

Michael Wyraz wrote:
> Hi,
> 
> because I wanted to integrate some of our own monitoring tasks to 
> nagios, I spent some time with the NRPE protocol. Since it's almost 
> impossible to find some documentation, I gathered my informations from 
> the source.
> 
> Here's what I found out about it:
> - any numbers are stored in big-endian notation (highest bytes first)
> - a packet consists of exactly 1036 Bytes
>   - 2 byte integer: version of the protocol (currently 1,2,3)
>   - 2 byte integer: type of the packet (1=request, 2=response)
>   - 4 byte long integer: crc32 checksum of the message
>   - 2 byte integer: return code of the remote command (in requests it's 
> filled with a random number)
>   - 1024 byte data: the command or response text, filled with zero-bytes
>   - 2 byte of garbage: this is because the c structure is sent "as it 
> is" over the wire. When creating messages, it's fine to set it to zero.
> - the crc32 checksum is calculated from the whole message (including the 
> 2 bytes of garbage). the 4 bytes reserved for the crc are set to zero 
> for calculation the crc. The default crc32 algorithm is used.
> 

out of interest, where do you determine that there is 2 bytes of 
garbage? I've had a peak at nrpe, I don't clearly see why this is the case.

regarding your suggestion on http://hessian.caucho.com/, is this not 
more of a web orientated protocol. what made you pick this, curious.

I like your ideas around a variable length plugin output, moving the 
checksum to the end and HMAC.