Scala combinator library for working with binary data.
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.
The library uses Shapeless and is heavily influenced by scala.util.parsing.combinator.
This project is licensed under a 3-clause BSD license.
People are expected to follow the Typelevel Code of Conduct when discussing scodec on the Github page, Gitter channel, mailing list, or other venues.
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
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.
Many libraries have support for scodec:
There are various examples in the test directory, including codecs for:
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 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
See the releases page on the website.
This project uses sbt and requires node.js to be installed in order to run Scala.js tests. To build, run