Introduction to ZIO Schema Codecs

Once we generate a schema for a type, we can derive a codec for that type.

A codec is a utility that can encode/decode a value of some type A to/from some format (e.g. binary format, JSON, etc.)

Codec

Unlike codecs in other libraries, a codec in ZIO Schema has no type parameter:

trait Codec {
  def encoder[A](schema: Schema[A]): ZTransducer[Any, Nothing, A, Byte]
  def decoder[A](schema: Schema[A]): ZTransducer[Any, String, Byte, A]

  def encode[A](schema: Schema[A]): A => Chunk[Byte]
  def decode[A](schema: Schema[A]): Chunk[Byte] => Either[String, A]
}

The Codec trait has two basic methods:

• encode[A]: Given a Schema[A] it is capable of generating an Encoder[A] ( A => Chunk[Byte]) for any Schema.
• decode[A]: Given a Schema[A] it is capable of generating a Decoder[A] ( Chunk[Byte] => Either[String, A]) for any Schema.

Binary Codecs

The binary codecs are codecs that can encode/decode a value of some type A to/from binary format (e.g. Chunk[Byte]). In ZIO Schema, by having a BinaryCodec[A] instance, other than being able to encode/decode a value of type A to/from binary format, we can also encode/decode a stream of values of type A to/from a stream of binary format.

import zio.Chunk
import zio.stream.ZPipeline

trait Decoder[Whole, Element, +A] {
  def decode(whole: Whole): Either[DecodeError, A]
  def streamDecoder: ZPipeline[Any, DecodeError, Element, A]
}

trait Encoder[Whole, Element, -A] {
  def encode(value: A): Whole
  def streamEncoder: ZPipeline[Any, Nothing, A, Element]
}

trait Codec[Whole, Element, A] extends Encoder[Whole, Element, A] with Decoder[Whole, Element, A]

trait BinaryCodec[A] extends Codec[Chunk[Byte], Byte, A]

To make it simpler, we can think of a BinaryCodec[A] as the following trait:

import zio.Chunk
import zio.stream.ZPipeline

trait BinaryCodec[A] {
  def encode(value: A): Chunk[Byte]
  def decode(whole: Chunk[Byte]): Either[DecodeError, A]

  def streamEncoder: ZPipeline[Any, Nothing, A, Byte]
  def streamDecoder: ZPipeline[Any, DecodeError, Byte, A]
}

Example of possible codecs are:

• CSV Codec
• JSON Codec (already available)
• Apache Avro Codec (in progress)
• Apache Thrift Codec (in progress)
• XML Codec
• YAML Codec
• Protobuf Codec (already available)
• QueryString Codec
• etc.