mdedetrich / pekko-streams-circe   1.0.0

Apache License 2.0 GitHub

Pekko Streams support for JSON via Circe

Scala versions: 3.x 2.13 2.12

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Pekko Streams Circe Support

This library provides Json support for stream based applications using jawn as a parser. It supports all backends that jawn supports with support for circe provided as an example.

It is a fork of akka-streams-json built with Apache Pekko. akka-streams-json which is in itself a fork of


There are two main modules, pekko-stream-json and pekko-http-json. pekko-stream-json is the basis and provides the stream-based parser while pekko-http-json enabled support to use the desired json library as an Unmarshaller.

libraryDependencies ++= List(
  "org.mdedetrich" %% "pekko-stream-json" % <VERSION>,
  "org.mdedetrich" %% "pekko-http-json" % <VERSION>"

pekko-stream-circe is published for Scala 2.12, 2.13 and 3.3+.


The parser lives at

Use one of the constructor methods in the companion object to create the parser at various levels of abstraction, either a Stage, a Flow, or a Sink. You just add the jawn support facade of your choice, and you will can parsed into their respective Json AST.

For Http support, either import org.mdedetrich.pekko.http.JsonSupport._ or mixin ... with org.mdedetrich.pekko.http.JsonSupport.

Given an implicit jawn facade, this enables you to decode into the respective Json AST using the Pekko HTTP marshalling framework. As jawn is only about parsing and does not abstract over rendering, you'll only get an Unmarshaller.


libraryDependencies ++= List(
  "org.mdedetrich" %% "pekko-stream-circe" % "<VERSION>",
  "org.mdedetrich" %% "pekko-http-circe" % "<VERSION>"

(Using circe 0.14.x)

Adding support for a specific framework is quite easy.

These support modules allow you to directly marshall from/unmarshall into your data types using circe's Decoder and Encoder type classes.

Just mixin or import for Http or pipe your Source[ByteString, _].via([A]) to get a Source[A, _].

This flow even supports parsing multiple json documents in whatever fragmentation they may arrive, which is great for consuming stream/sse based APIs.

If there is an error in parsing the Json you can catch The exception provides Circe cursor history, current cursor and the type hint of the error.

Why jawn?

Jawn provides a nice interface for asynchronous parsing. Most other Json marshalling provider will consume the complete entity at first, convert it to a string and then start to parse. With jawn, the json is incrementally parsed with each arriving data chunk, using directly the underlying ByteBuffers without conversion.


This code is open source software licensed under the Apache 2.0 License.