binrep

binrep is a Haskell library for precisely modelling binary schemas, especially low-context byte-oriented file formats e.g. C enums, and working with them effectively and efficiently. Here's why it's useful:

• Explicit: Define Haskell data types with the binary schema "baked in". Use highly parameterized binary representation primitives including null-terminated data (e.g. C-style strings), Pascal-style data (length prefixed), sized explicit-endian machine integers, null-padded data.
• Low boilerplate: Free performant parsers and serializers via generics. (See Generic binary representation.)
• Easy validation: Use the strongweak library design pattern to define an unvalidated data type for easy internal transformation, and get validation code for free.
• Performant: Parsing and serialization is extremely fast, using bytezap and flatparse.

Usage

Dependencies

You need the ICU library. For running, you just need the runtime. For building, you need development files as well (headers etc). Alternatively, you may turn off the ICU features with a Cabal flag.

Philosophy

Modelling, not serializing

binrep is good at modelling binary data formats. It is not a plain "serialization" library, where the actual binary representation is hidden from the user (intentionally, with good reason). The binary and cereal libraries are great choices for that. They are interested in defining efficient binary codecs for Haskell data. However, their codec typeclasses hide representation decisions from the user. In cereal,

• machine integers are encoded with big endian
• bytestrings are written with an 8-byte length prefix

These are fine decisions. But they aren't accurate to the types. Endianness is an implementation decision.

binrep refuses to work with a machine integer unless it knows the endianness. Bytestrings are split into C-style (null-terminated) and Pascal-style (length-prefixed). This enforces careful consideration for the binary data being modelled.

Validation without boilerplate

A C-style bytestring must not contain any 0x00 null bytes. A Pascal-style bytestring must be short enough to be able to encode its length in the length prefix machine integer. But checking such invariants is tedious work. Am I really going to wrap everything in a bunch of newtypes and force users to call a bunch of checker functions every time?

Yes and no. Yes, binrep uses newtypes extensively, though most are type synonyms over the Refined newtype from Nikita Volkov's wonderful refined library. No, binrep doesn't want you to wrangle with these day-to-day. One solution is to define a simplified "weak" type, and convert between it and the binary-safe "strong" type. My strongweak library provides supporting definitions for this pattern, and generic derivers which will work with binrep's binary representation primitives.

Generic binary representation

(Generics are now handled by generic-data-functions. This info is largely the same, but the code is elsewhere.)

binrep includes powerful generics for automatically writing instances. They all work the same way:

• Constructors are encoded by sequentially encoding every enclosed field.
  • Empty constructors thus serialize to 0 bytes.
• For sum types, the constructor is disambiguated via a tag obtained from the constructor name.
  • Tags may be parsed on the type or term level.

Note that when parsing sum types, we compare tags sequentially. You may design your tag schema to have a more efficient approach. In such cases, consider using Generic.Data.FOnCstr from generic-data-functions.

As an example, you could encode constructor names as a null-terminated ASCII bytestring for a tag. (This is provided at Binrep.Generic.nullTermCstrPfxTag.) Alternatively, you may encode each constructor at a unique byte value, stated at the end of the constructor name.

Sum types (data types with multiple constructors) are handled by first encoding a "tag field", the value of which then indicates which constructor to use. You must provide a function to convert from a constructor name to a (unique) tag. You could encode them as a null-terminated ASCII bytestring (this is the default), or as a single byte. To ease this, you may consider putting the tag value in constructor names:

data BinarySumType = B1 | B2

getConstructorTag :: String -> Word8
getConstructorTag = read . drop 1

-- >>> getConstructorTag "B1"
-- 1

-- Or use our generic helper, which takes hex values:
--
-- >>> cSumTagHex @Word8 (drop . 1) "BFF"
-- 255

Similar projects

Kaitai Struct

Kaitai Struct is a wonderful declarative parser generator project. They bolt an expression language and a whole lot of binary cleverness on top of a nice YAML schema. It comes with an IDE, a visualizer, and you can compile schemas down to parsers for various different languages (no Haskell...).

Design principles like their fancy absolute offset handling and language neutrality have stunted serialization support. Though it's more like they have such powerful parsing that they can parse formats that can't be edited and re-serialized naively, like archives with file indexes. For proper handling, one should store a file table, and serialization generates the index. So in reverse, you would want to combine them. But it's a bit program-y. In binrep, you are in a programming language, so it's less of a problem... but I'm not sure if we can be very efficient at absolute offset stuff.

Realistically, Kaitai Struct is the best decision for fast iteration on reversing unknown data. binrep is useful for loading data straight into Haskell for further processing, especially converting between simpler formats.

Wuffs

Wuffs is a crazy exploration into safe low-level code via strong typing. You have to annotate every possibly dangerous statement with a proof of safety. It's a tedious, explicit, very safe and very fast imperative language for defining parsers and serializers.

Wuffs is more a codec engineer's tool than a reverse engineer's one. binrep isn't really interested in speed, and being a Haskell library we get to focus on defining types and their composition in a declarative & functional manner. As such, we get to define more useful things quicker using binrep. Though we share many core ideas, such as refinement types.

Check out Wuffs if you need to write a bunch of codecs and they really, really need to be both fast and safe. The trade-off is, of course, your time.

flat

https://hackage.haskell.org/package/flat

Cool, bit-oriented rather than byte-oriented.

License

Provided under the MIT license. See LICENSE for license text.