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

Scodec 1.x used Shapeless and is heavily influenced by scala.util.parsing.combinator. As of Scodec 2.x, the library only depends on the standard library.

Administrative

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

The scodec channel on Gitter is a good place to go for help. Also consider using the scodec tag on StackOverflow.

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 tuples:

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

    val pointCodec: Codec[Point] = (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(0xfb0a01)
    // Successful(DecodeResult(Point(-5, 10, 1), BitVector(empty)))

Codecs can also be derived, resulting in usage like:

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

    val encoded: Attempt[BitVector] = Codec.encode(Point(-5, 10, 1))
    // Successful(BitVector(96 bits, 0x000000fb0000000a00000001))

    val decoded: Attempt[DecodeResult[Point]] = Codec.decode[Point](0x000000fb0000000a00000001)
    // Successful(DecodeResult(Point(-5, 10, 1), BitVector(empty)))

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:

• Codec
• codecs package

Ecosystem

Many libraries have support for scodec:

• FS2
• Circe
• Refined

Examples

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

• UDP Datagrams
• MPEG Packets
• libpcap Files

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

The bmsg library has a codec for the Bitcoin Cash and Bitcoin Core 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.

The scodec-bson library implements BSON codecs and combinators.

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.

Code of Conduct

See the Code of Conduct.