avast / grpc-json-bridge

Library for exposing gRPC endpoints via HTTP (JSON) API

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gRPC JSON Bridge

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This library allows to make a JSON encoded HTTP request to a gRPC service that is implemented in Java or Scala (using ScalaPB).

It provides an implementation-agnostic module for mapping to your favorite HTTP server (core, core-scalapb) as well as few implementations for direct usage in some well-known HTTP servers.

Standard GPB <-> JSON mapping is used.

The API is finally tagless (read more e.g. here) meaning it can use whatever F[_]: cats.effect.Effect (e.g. cats.effect.IO, monix.eval.Task).


compile 'com.avast.grpc:grpc-json-bridge-core_2.12:x.x.x'
libraryDependencies += "com.avast.grpc" %% "grpc-json-bridge-core" % "x.x.x"
syntax = "proto3";
package com.avast.grpc.jsonbridge.test;

service TestService {
    rpc Add (AddParams) returns (AddResponse) {}

message AddParams {
    int32 a = 1;
    int32 b = 2;

message AddResponse {
    int32 sum = 1;
import com.avast.grpc.jsonbridge.ReflectionGrpcJsonBridge

// for whole server
val grpcServer: io.grpc.Server = ???
val bridge = ReflectionGrpcJsonBridge.createFromServer[Task](grpcServer)

// or for selected services
val s1: ServerServiceDefinition = ???
val s2: ServerServiceDefinition = ???
val anotherBridge = ReflectionGrpcJsonBridge.createFromServices[Task](s1, s2)

// call a method manually, with a header specified
val jsonResponse = bridge.invoke("com.avast.grpc.jsonbridge.test.TestService/Add", """ { "a": 1, "b": 2} """, Map("My-Header" -> "value"))

This usage supposes that the project uses standard gRPC Java class generation, using protoc-gen-grpc-java.

If the project uses ScalaPB to generate the classes then following dependency should used instead:

compile 'com.avast.grpc:grpc-json-bridge-core-scalapb_2.12:x.x.x'
libraryDependencies += "com.avast.grpc" %% "grpc-json-bridge-core-scalapb" % "x.x.x"

And ScalaPBReflectionGrpcJsonBridge class must be used to create a new bridge.


compile 'com.avast.grpc:grpc-json-bridge-http4s_2.12:x.x.x'
libraryDependencies += "com.avast.grpc" %% "grpc-json-bridge-http4s" % "x.x.x"
import com.avast.grpc.jsonbridge.GrpcJsonBridge
import com.avast.grpc.jsonbridge.http4s.{Configuration, Http4s}
import org.http4s.HttpService

val bridge: GrpcJsonBridge[Task] = ???
val service: HttpService[Task] = Http4s(Configuration.Default)(bridge)


compile 'com.avast.grpc:grpc-json-bridge-akkahttp_2.12:x.x.x'
libraryDependencies += "com.avast.grpc" %% "grpc-json-bridge-akkahttp" % "x.x.x"
import com.avast.grpc.jsonbridge.GrpcJsonBridge
import com.avast.grpc.jsonbridge.akkahttp.{AkkaHttp, Configuration}
import akka.http.scaladsl.server.Route

val bridge: GrpcJsonBridge[Task] = ???
val route: Route = AkkaHttp(Configuration.Default)(bridge)

Calling the bridged service

List all available methods:

> curl -X GET http://localhost:9999/


List all methods from particular service:

> curl -X GET http://localhost:9999/com.avast.grpc.jsonbridge.test.TestService


Call a method (please note that POST and application/json must be always specified):

> curl -X POST -H "Content-Type: application/json" --data ""{\"a\":1, \"b\": 2 }"" http://localhost:9999/com.avast.grpc.jsonbridge.test.TestService/Add