scodec

Scala combinator library for working with binary data.

Design Constraints

This library focuses on contract-first and pure functional encoding and decoding of binary data. The following design constraints are considered:

Binary structure should mirror protocol definitions and be self-evident under casual reading
Mapping binary structures to types should be statically verified
Encoding and decoding should be purely functional
Failures in encoding and decoding should provide descriptive errors
Compiler plugin should not be used

As a result, the library is implemented as a combinator based DSL. Performance is considered but yields to the above design constraints.

Acknowledgements

The library uses Shapeless and is heavily influenced by scala.util.parsing.combinator.

Administrative

This project is licensed under a 3-clause BSD license.

The scodec mailing list contains release announcements and is generally a good place to go for help. Also consider using the scodec tag on StackOverflow.

People are expected to follow the Typelevel Code of Conduct when discussing scodec on the Github page, Gitter channel, mailing list, or other venues.

Concerns or issues can be sent to Michael Pilquist (mpilquist@gmail.com) or to Typelevel.

Introduction

The primary abstraction is a Codec[A], which supports encoding a value of type A to a BitVector and decoding a BitVector to a value of type A.

The codecs package provides a number of predefined codecs and combinators.

    import scodec._
    import scodec.bits._
    import codecs._

    // Create a codec for an 8-bit unsigned int followed by an 8-bit unsigned int followed by a 16-bit unsigned int
    val firstCodec = uint8 ~ uint8 ~ uint16

    // Decode a bit vector using that codec
    val result: Attempt[DecodeResult[(Int ~ Int ~ Int)]] = firstCodec.decode(hex"102a03ff".bits)
    // Successful(DecodeResult(((16, 42), 1023), BitVector(empty)))

    // Sum the result
    val add3 = (_: Int) + (_: Int) + (_: Int)
    val sum: Attempt[DecodeResult[Int]] = result.map(_.map(add3))
    // Successful(DecodeResult(1081, BitVector(empty)))

Automatic case class binding is supported via Shapeless HLists:

    case class Point(x: Int, y: Int, z: Int)

    val pointCodec = (int8 :: int8 :: int8).as[Point]

    val encoded: Attempt[BitVector] = pointCodec.encode(Point(-5, 10, 1))
    // Successful(BitVector(24 bits, 0xfb0a01))

    val decoded: Attempt[DecodeResult[Point]] = pointCodec.decode(hex"0xfb0a01".bits)
    // Successful(DecodeResult(Point(-5, 10, 1), BitVector(empty)))

Codecs can also be implicitly resolved, resulting in usage like:

    // Assuming Codec[Point] is in implicit scope

    val encoded: Attempt[BitVector] = Codec.encode(Point(-5, 10, 1))
    // Successful(BitVector(24 bits, 0xfb0a01))

    val decoded: Attempt[DecodeResult[Point]] = Codec.decode[Point](hex"0xfb0a01".bits)
    // Successful(DecodeResult(Point(-5, 10, 1), BitVector(empty)))

Note: by default, scodec provides no implicit codecs. Many sensible defaults can be imported via import scodec.codecs.implicits._, including codecs for various primitive types and some immutable collections.

New codecs can be created by either implementing the Codec trait or by passing an encoder function and decoder function to the Codec apply method. Typically, new codecs are created by applying one or more combinators to existing codecs.

See the guide for detailed documentation. Also, see ScalaDoc. Especially:

Ecosystem

Many libraries have support for scodec:

Examples

There are various examples in the test directory, including codecs for:

The scodec-protocols has production quality codecs for the above examples.

The bitcoin-scodec library has a codec for the Bitcoin network protocol.

The scodec-msgpack library provides codecs for MessagePack.

The fs2-http project uses FS2, scodec, and shapeless to implement a minimal HTTP client and server.

Testing Your Own Codecs

If you're creating your own Codec instances scodec publishes some of its own test tooling in the scodec-testkit module.

Getting Binaries

See the releases page on the website.

Building

This project uses sbt and requires node.js to be installed in order to run Scala.js tests. To build, run sbt publish-local.

sirocchj/scodec