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Apache Pekko gRPC - Support for building streaming gRPC servers and clients on top of Pekko Streams.
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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * license agreements; and to You under the Apache License, version 2.0:
 *
 *   https://www.apache.org/licenses/LICENSE-2.0
 *
 * This file is part of the Apache Pekko project, which was derived from Akka.
 */

/*
 * Copyright (C) 2009-2021 Lightbend Inc. 
 */

package org.apache.pekko.grpc.internal

import java.util.concurrent.CompletionStage

import org.apache.pekko
import pekko.annotation.InternalApi
import pekko.dispatch.ExecutionContexts
import pekko.grpc.GrpcSingleResponse
import pekko.util.FutureConverters._
import pekko.util.OptionVal
import io.grpc._

import scala.concurrent.{ Future, Promise }

/**
 * gRPC Netty based client listener transforming callbacks into a future response
 *
 * INTERNAL API
 */
@InternalApi
private[pekko] final class UnaryCallAdapter[Res] extends ClientCall.Listener[Res] {
  private val responsePromise = Promise[Res]()

  override def onMessage(message: Res): Unit =
    // close over var and make final
    if (!responsePromise.trySuccess(message)) {
      throw Status.INTERNAL.withDescription("More than one value received for unary call").asRuntimeException()
    }

  override def onClose(status: Status, trailers: Metadata): Unit =
    if (status.isOk) {
      if (!responsePromise.isCompleted)
        // No value received so mark the future as an error
        responsePromise.tryFailure(
          Status.INTERNAL.withDescription("No value received for unary call").asRuntimeException(trailers))
    } else {
      responsePromise.tryFailure(status.asRuntimeException(trailers))
    }

  def future: Future[Res] = responsePromise.future
  def cs: CompletionStage[Res] = future.asJava
}

/**
 * gRPC Netty based client listener transforming callbacks into a future response
 *
 * INTERNAL API
 */
// needs to be a separate class because of CompletionStage error handling not bubbling
// exceptions like Scala Futures do ;( flip side is that it saves some garbage
@InternalApi
private[pekko] final class UnaryCallWithMetadataAdapter[Res] extends ClientCall.Listener[Res] {
  private val responsePromise = Promise[GrpcSingleResponse[Res]]()
  private var headers: OptionVal[Metadata] = OptionVal.None
  private val trailerPromise = Promise[Metadata]()

  // always invoked before message
  override def onHeaders(headers: Metadata): Unit =
    this.headers = OptionVal.Some(headers)

  override def onMessage(message: Res): Unit = {
    val responseWithMetadata = new GrpcSingleResponse[Res] {
      // close over var and make final
      private val headersOnMessage = UnaryCallWithMetadataAdapter.this.headers match {
        case OptionVal.Some(h) => h
        case OptionVal.None    => throw new RuntimeException("Never got headers, this should not happen")
      }

      override def value: Res = message
      override def getValue(): Res = message

      private lazy val sMetadata: pekko.grpc.scaladsl.Metadata =
        MetadataImpl.scalaMetadataFromGoogleGrpcMetadata(headersOnMessage)
      private lazy val jMetadata: pekko.grpc.javadsl.Metadata =
        MetadataImpl.javaMetadataFromGoogleGrpcMetadata(headersOnMessage)
      override def headers = sMetadata
      override def getHeaders() = jMetadata

      private lazy val sTrailer =
        trailerPromise.future.map(MetadataImpl.scalaMetadataFromGoogleGrpcMetadata)(ExecutionContexts.parasitic)
      private lazy val jTrailer =
        trailerPromise.future.map(MetadataImpl.javaMetadataFromGoogleGrpcMetadata)(ExecutionContexts.parasitic).asJava

      def trailers = sTrailer
      def getTrailers() = jTrailer
    }
    if (!responsePromise.trySuccess(responseWithMetadata)) {
      throw Status.INTERNAL.withDescription("More than one value received for unary call").asRuntimeException()
    }
  }

  override def onClose(status: Status, trailers: Metadata): Unit =
    if (status.isOk) {
      if (!responsePromise.isCompleted)
        // No value received so mark the future as an error
        responsePromise.tryFailure(
          Status.INTERNAL.withDescription("No value received for unary call").asRuntimeException(trailers))
      trailerPromise.success(trailers)
    } else {
      responsePromise.tryFailure(status.asRuntimeException(trailers))
      trailerPromise.success(trailers)
    }

  def future: Future[GrpcSingleResponse[Res]] = responsePromise.future
  def cs: CompletionStage[GrpcSingleResponse[Res]] = future.asJava
}