Treat response trailers as regular headers (#38)

Author: igor-vovk

README.md

@@ -13,7 +13,7 @@ Scala:
 
 * [ScalaPB](https://scalapb.github.io) services with `Future` monad
 * [fs2-grpc](https://github.com/typelevel/fs2-grpc), built on top of `cats-effect` and `fs2`
-* [ZIO gRPC](https://scalapb.github.io/zio-grpc/), built on top of `ZIO` monad (the most feature-rich implementation)
+* [ZIO gRPC](https://scalapb.github.io/zio-grpc/), built on top of `ZIO`
 
 *Note*: at the moment, only unary (non-streaming) methods are supported.
 
@@ -71,7 +71,7 @@ supports_message_receive_limit: false
 
 ## Usage
 
-Library is installed via SBT (you also need to install particular `http4s` server implementation):
+Installing with SBT (you also need to install particular `http4s` server implementation):
 
 ```scala
 libraryDependencies ++= Seq(
@@ -109,10 +109,10 @@ val httpServer: Resource[IO, org.http4s.server.Server] = {
 httpServer.use(_ => IO.never).unsafeRunSync()
 ```
 
-### Tip: GRPC OpenTelemetry integration
+### Hint: GRPC OpenTelemetry integration
 
 Since the library creates a separate "fake" GRPC server, traffic going through it won't be captured by the
-instrumentation of the main GRPC server.
+instrumentation of your main GRPC server (if any).
 
 Here is how you can integrate OpenTelemetry with the Connect-RPC server:
 
@@ -129,8 +129,11 @@ ConnectRouteBuilder.forServices[IO](grpcServices)
   .build
 ```
 
-This will make sure that all the traffic going through the Connect-RPC server will be captured by the same
-opentelemetry.
+### ZIO Interop
+
+Because the library uses the Tagless Final pattern, it is perfectly possible to use it with ZIO. You might check
+`zio_interop` branch, where conformance is implemented with `ZIO` and `ZIO-gRPC`.
+You can read [this](https://zio.dev/guides/interop/with-cats-effect/).
 
 ## Development
 
@@ -147,14 +150,14 @@ Diagnostic data from the server itself is written to the log file `out/out.log`.
 
 ### Conformance tests status
 
-Current status: 6/79 tests pass
+Current status: 11/79 tests pass.
 
 Known issues:
 
-* `fs2-grpc` server implementation doesn't support setting response headers (which is required by the tests): [#31](https://github.com/igor-vovk/connect-rpc-scala/issues/31)
-* `google.protobuf.Any` serialization doesn't follow Connect-RPC spec: [#32](https://github.com/igor-vovk/connect-rpc-scala/issues/32)
+* `google.protobuf.Any` serialization doesn't follow Connect-RPC
+  spec: [#32](https://github.com/igor-vovk/connect-rpc-scala/issues/32)
 
 ## Future improvements
 
-* Support GET-requests
-* Support non-unary (streaming) methods
+[x] Support GET-requests
+[ ] Support non-unary (streaming) methods

conformance/src/main/scala/org/ivovk/connect_rpc_scala/conformance/ConformanceServiceImpl.scala

@@ -75,7 +75,10 @@ class ConformanceServiceImpl[F[_] : Async] extends ConformanceServiceFs2GrpcTrai
         throw new StatusRuntimeException(status)
     }
 
-    val trailers = mkMetadata(responseDefinition.responseTrailers)
+    val trailers = mkMetadata(Seq.concat(
+      responseDefinition.responseHeaders,
+      responseDefinition.responseTrailers.map(h => h.copy(name = s"trailer-${h.name}")),
+    ))
 
     Async[F].sleep(Duration(responseDefinition.responseDelayMs, TimeUnit.MILLISECONDS)) *>
       Async[F].pure(UnaryHandlerResponse(

core/src/main/scala/org/ivovk/connect_rpc_scala/ConnectHandler.scala

@@ -27,6 +27,7 @@ class ConnectHandler[F[_] : Async](
   methodRegistry: MethodRegistry,
   channel: Channel,
   httpDsl: Http4sDsl[F],
+  treatTrailersAsHeaders: Boolean,
 ) {
 
   import httpDsl.*
@@ -119,12 +120,11 @@ class ConnectHandler[F[_] : Async](
             message
           )
         }).map { response =>
-          val headers = org.http4s.Headers.empty ++
-            responseHeaderMetadata.get.toHeaders ++
-            responseTrailerMetadata.get.toTrailingHeaders
+          val headers = responseHeaderMetadata.get.toHeaders() ++
+            responseTrailerMetadata.get.toHeaders(trailing = !treatTrailersAsHeaders)
 
           if (logger.isTraceEnabled) {
-            logger.trace(s"<<< Headers: ${headers.redactSensitive}")
+            logger.trace(s"<<< Headers: ${headers.redactSensitive()}")
           }
 
           Response(Ok, headers = headers).withEntity(response)

core/src/main/scala/org/ivovk/connect_rpc_scala/ConnectRouteBuilder.scala

@@ -35,6 +35,7 @@ case class ConnectRouteBuilder[F[_] : Async] private(
   channelConfigurator: Endo[ManagedChannelBuilder[_]] = identity,
   executor: Executor = ExecutionContext.global,
   waitForShutdown: Duration = 5.seconds,
+  treatTrailersAsHeaders: Boolean = true,
 ) {
 
   import Mappings.*
@@ -54,6 +55,17 @@ case class ConnectRouteBuilder[F[_] : Async] private(
   def withWaitForShutdown(duration: Duration): ConnectRouteBuilder[F] =
     copy(waitForShutdown = duration)
 
+  /**
+   * If enabled, trailers will be treated as headers (no "trailer-" prefix).
+   *
+   * Both `fs2-grpc` and `zio-grpc` support trailing headers only, so enabling this option is a single way to
+   * send headers from the server to the client.
+   *
+   * Enabled by default.
+   */
+  def withTreatTrailersAsHeaders(enabled: Boolean): ConnectRouteBuilder[F] =
+    copy(treatTrailersAsHeaders = enabled)
+
   /**
    * Method can be used if you want to add additional routes to the server.
    * Otherwise, it is preferred to use the [[build]] method.
@@ -86,6 +98,7 @@ case class ConnectRouteBuilder[F[_] : Async] private(
         methodRegistry,
         channel,
         httpDsl,
+        treatTrailersAsHeaders,
       )
 
       HttpRoutes.of[F] {

core/src/main/scala/org/ivovk/connect_rpc_scala/Mappings.scala

@@ -40,9 +40,12 @@ trait HeaderMappings {
       new Headers(b.result())
     }
 
-    def toHeaders: Headers = headers()
+    def toHeaders(trailing: Boolean = false): Headers = {
+      val prefix = if trailing then "trailer-" else ""
+
+      headers(prefix)
+    }
 
-    def toTrailingHeaders: Headers = headers("trailer-")
   }
 
 }