Chunked Entities


This algebra provides vocabulary to describe endpoints whose requests or responses are streamed using the “chunked transfer-encoding” supported by HTTP1.1.

API documentation

The ChunkedEntities module enriches the Endpoints algebra with operations for defining request and responses entities carrying stream of values.

For instance, you can define an endpoint streaming a binary file as follows:

sourceval logo: Endpoint[Unit, Chunks[Array[Byte]]] =
  endpoint(get(path / "logo.png"), ok(bytesChunksResponse))

The return type, Endpoint[Unit, Chunks[Array[Byte]]], represents an endpoint whose request takes no parameter (Unit) and whose response produces a stream of Array[Byte] chunks.

Responses are streamed using the chunked transfer-encoding, which is supported by most HTTP 1.1 clients and servers.


API documentation

Clients and servers have to agree on the serialization format used by response chunks and WebSocket messages. The ChunkedJsonEntities module provides a jsonChunksRequest constructor and a jsonChunksResponse constructor for defining request entities and response entities carrying streams of values that are serialized into JSON. In addition, entity constructors must also be provided with an implementation of chunk framing, which is defined by the Framing module. This is required to compensate for the fact that the chunks of “chunked transfer-encoding” can be re-framed during transport, and thus cannot solely be relied on as a method of framing. The library provides the constructor for newLineDelimiterFraming, which delimits each frame by a new-line character:

sourcetrait JsonStreamingExample
    extends endpoints4s.algebra.Endpoints
    with endpoints4s.algebra.ChunkedJsonEntities
    with endpoints4s.algebra.JsonEntitiesFromSchemas {

  val ticks =
    endpoint(get(path / "ticks"), ok(jsonChunksResponse[Unit](newLineDelimiterFraming)))


This example uses the JsonEntitiesFromSchemas algebra to derive the JSON serialization format from a JSON schema, which can also be reused by the OpenAPI interpreter.

Eventually, mix a JsonEntitiesFromSchemas interpreter of your choice to turn the JSON schemas into proper JSON codecs. For instance, for Pekko-Http:

import endpoints4s.pekkohttp.server

object JsonStreamingExampleServer
    extends JsonStreamingExample
    with server.Endpoints
    with server.ChunkedJsonEntities
    with server.JsonEntitiesFromSchemas {

  val routes =
    ticks.implementedBy(_ => Source.tick(0.seconds, 1.second, ()))


Custom Serialization Format

Support for other serialization formats can be added by defining an operation returning a Chunks[A] value. For instance, the Protocol Buffers format would be supported as follows (using protoless):

import endpoints4s.algebra
import io.protoless.messages.{Decoder, Encoder}

trait ProtobufChunkedEntities extends algebra.ChunkedEntities {
  /** Streams containing values of type `A`, serialized with the given protobuf codec */
  def protobufChunksRequest[A : Encoder : Decoder]: RequestEntity[Chunks[A]]

And then, the protobufChunksRequest operation would have to be implemented on each interpreter.