Protocol Definition Language

Question

What protocol definition do you recommend? I evaluated Google's protocol buffers, but it does not allow me to control the placement of fields in the packet being built. I assume the same is true for Thrift. My requirements are:

2. specify the location of fields in the packet
3. allow for bit fields
4. conditionals: a flag (bit field) = true means that data can appear at a later location in the packet
5. ability to define a packet structure by referring to another packet definition

Thank you.

("Flavor" on SourceForge, used for defining MPEG-4 might be a candidate, but I am looking for something that seems to have more of a community and preferably works in a .NET environment.)

Answer 1

Have a look to ASN.1 http://es.wikipedia.org/wiki/ASN.1

FooProtocol DEFINITIONS ::= BEGIN

FooQuestion ::= SEQUENCE {
    trackingNumber INTEGER,
    question       IA5String
}

FooAnswer ::= SEQUENCE {
    questionNumber INTEGER,
    answer         BOOLEAN
}

END

It seems to cover your main requirements:

- Bit detail
- ordered content
- type references
- not sure, about conditions

Is widely used, and you can find some implementations on java and python

Answer 2

I'd be interested in the reasons for your requirements. Why do you need to control the position of the fields? Why are bitfields important? Conditionals?

It sounds like you have a (more or less) fixed wire format for which you need to write a parser for, and in that case none of the existing popular protocol/serialization formats (Protobufs, Thrift, JSON, Yaml, etc.) will work for you.

A somewhat unorthodox approach is to use Erlang or Haskell, both of which have good support for parsing binary protocols.