F# – Imitating Erlang’s bit syntax for easier binary protocol implementation

Bit Syntax in Erlang

One of the often under-appreciated features of Erlang is its Bit Syntax for parsing and pattern matching binary data at a bit level. For instance, to pare TCP segments you can write something along the line of:

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The same capability can be applied to anything binary protocols, such as video encoding, imaging, or UDP.

 

Imitating with F# Computation Expressions

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Whilst this capability is not built into F#, or any other language that I know of for that matter, we do have a very powerful, and robust feature in F# in Computation Expressions.

With computation expressions, I was able to create a small library that allows you to write and read data to and from a stream at a bit level. With the bitWriter and bitReader workflows you will be able to write and parse TCP headers with code like the following:

 

The library is available via Nuget:

please give it a try, and let me know if you find any bugs here.

 

p.s. there is still much work to be done on the library. For instance, it’s allocating a new buffer array for each workflow rather than using a buffer pool. If you find this library useful and in need for greater performance, please feel free to contribute and help improve the performance of this library.

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  • Eirik Tsarpalis

    Interesting library, I was wondering if you have thought about using the type system to check if the two workflows (write/read) match. I wrote a snippet some time ago (http://fssnip.net/jL) but it would be interesting to see if there is any practical application to this.

  • Yan Cui

    That’s a great idea, I hadn’t thought of that. I imagine it’ll be useful in any .Net-to-.Net client server scenarios, the type safety it provides will be pretty awesome :-)

    My original motivation for this library was to make it easier for us to integrate our .Net code with our Erlang code which takes advantage of its bit syntax to make more socket protocols more compact (e.g. using 3 bits to represent a number instead of 8 for instance).

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