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: 1. specify the location of fields in the packet 2. allow for bit fields 3. conditionals: a flag (bit field) = true means that data can appear at a later location in the packet 4. 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

How about C# itself?

eg

class MySimplePDLData {
  // format: name (or blank if padding), bit length, value (or blank if data),
  // name of presence flag field (or blank if no presence flag), C# type
  // one packet type per string, fields separated by pipes (|)
  string[] pdl = {

// MY-SIMPLE-PDL-START

  ",8,0xf8,|version,8,,Int32|type,8,,Int32|id1,64,,Int64",
  ...

// MY-SIMPLE-PDL-END

  };
}

If the data is already in memory, you don't need to do IO on a file format. From here you can either dynamically interpret packes or generate the necessary C# source code for packet recognition/pack/unpack, again using C# itself.

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.