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I am working on a project which contains two servers, one is written in python, the other in C. To maximize the capacity of the servers, we defined a binary proprietary protocol by which these two could talk to each other.

The protocol is defined in a C header file in the form of C struct. Usually, I would use VIM to do some substitutions to convert this file into Python code. But that means I have to manually do this every time the protocol is modified.

So, I believe a parser that could parse C header file would be a better choice. However, there are at least a dozen of Python parser generator. So I don't which one is more suitable for my particular task.

Any suggestion? Thanks a lot.

EDIT:

Of course I am ask anyone to write me the code....

The code is already finished. I converted the header file into Python code in the form that construct, a python library which could parse the binary data, could recognize.

I am also not looking for some already exist C parser. I am asking this question because a book I am reading talks a little about parser generator inspired me to learn how to use a real parser generator.

EDIT Again:

When we make the design of the system, I suggested to use Google Protocol Buffer, ZeroC ICE, or whatever multi-language network programming middleware to eliminate the task of implementing a protocol.

However, not every programmer could read English documents and would like to try new things, especially when they have plenty of experience of doing it in old and simple but a little clumsy way.

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  • So the question is: (1) recommend a python parser generator to work on C struct definitions and (2) write me the code? Just trying to clarify what you want. Commented Oct 19, 2010 at 14:24
  • possible duplicate of Extract the fields of a C struct Commented Oct 19, 2010 at 14:27
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    note that that's exactly the use case that prompted Google to create protocol buffers (code.google.com/p/protobuf), which had from the start Python, Java and C++ generators. i think now there are C bindings too. Commented Oct 19, 2010 at 14:30
  • I doubt that parsing binary formats in python would "maximize the capacity" Commented Oct 19, 2010 at 15:23

4 Answers 4

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As an alternative solution that might feel a bit over-ambitious from the beginning, but also might serve you very well in the long-term, is:

  • Redefine the protocol in some higher-level language, for instance some custom XML
  • Generate both the C struct definitions and any required Python versions from the same source.
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that's exactly what protocol buffers do
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I would personally use PLY:

http://www.dabeaz.com/ply/

And there is already a C parser written with PLY:

http://code.google.com/p/pycparser/

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If I were doing this, I would use IDL as the structure definition language. The main problem you will have with doing C structs is that C has pointers, particularly char* for strings. Using IDL restricts the data types and imposes some semantics.

Then you can do whatever you want. Most parser generators are going to have IDL as a sample grammar.

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A C struct is unlikely to be portable enough to be sending between machines. Different endian, different word-sizes, different compilers will all change the way the structure is mapped to bytes.

It would be better to use a properly portable binary format that is designed for communications.

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My colleagues are well trained to write code to handle endian translation, word size padding, etc.
Then the endian-defined padding-defined binary format is what you should be coding against. And the C-struct is just a temporary representation of that.

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