higherkindness.mu.MonixAdapters.scala Maven / Gradle / Ivy

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mu RPC is a purely functional library for building RPC endpoint based services with support for RPC and HTTP/2
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/*
 * Copyright 2017-2020 47 Degrees, LLC. 
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package higherkindness.mu
package rpc
package internal

import cats.~>
import cats.instances.future._
import io.grpc.stub.StreamObserver
import monix.execution.Ack.{Continue, Stop}
import monix.execution.{Ack, Scheduler}
import monix.reactive.Observable.Operator
import monix.reactive.observers.Subscriber
import org.reactivestreams.{Subscriber => RSubscriber}

import scala.concurrent.Future

trait MonixAdapters {

  def monixSubscriber2StreamObserver: Subscriber ~> StreamObserver =
    new (Subscriber ~> StreamObserver) {

      override def apply[A](fa: Subscriber[A]): StreamObserver[A] = new StreamObserver[A] {

        override def onError(t: Throwable): Unit = fa.onError(t)
        override def onCompleted(): Unit         = fa.onComplete()
        override def onNext(value: A): Unit = {
          fa.onNext(value)
          (): Unit
        }
      }
    }

  def reactiveSubscriber2StreamObserver: RSubscriber ~> StreamObserver =
    new (RSubscriber ~> StreamObserver) {

      override def apply[A](fa: RSubscriber[A]): StreamObserver[A] = new StreamObserver[A] {

        override def onError(t: Throwable): Unit = fa.onError(t)
        override def onCompleted(): Unit         = fa.onComplete()
        override def onNext(value: A): Unit      = fa.onNext(value)
      }
    }

  def streamObserver2MonixSubscriber(implicit S: Scheduler): StreamObserver ~> Subscriber =
    new (StreamObserver ~> Subscriber) {

      override def apply[A](fa: StreamObserver[A]): Subscriber[A] = new Subscriber[A] {

        override implicit val scheduler: Scheduler = S
        override def onError(ex: Throwable): Unit  = fa.onError(ex)
        override def onComplete(): Unit            = fa.onCompleted()
        override def onNext(elem: A): Future[Ack] =
          catsStdInstancesForFuture(S).handleError[Ack] {
            fa.onNext(elem)
            Continue
          } { t: Throwable =>
            fa.onError(t)
            Stop
          }
      }
    }

}

object converters extends MonixAdapters {

  private[internal] implicit class SubscriberOps[A](private val subscriber: Subscriber[A])
      extends AnyVal {
    def toStreamObserver: StreamObserver[A] = monixSubscriber2StreamObserver(subscriber)
  }

  private[internal] implicit class RSubscriberOps[A](private val rSubscriber: RSubscriber[A])
      extends AnyVal {
    def toStreamObserver: StreamObserver[A] = reactiveSubscriber2StreamObserver(rSubscriber)
  }

  private[internal] implicit class StreamObserverOps[A](private val observer: StreamObserver[A])
      extends AnyVal {
    def toSubscriber(implicit S: Scheduler): Subscriber[A] =
      streamObserver2MonixSubscriber.apply(observer)
  }

  private[internal] def StreamObserver2MonixOperator[Req, Res](
      op: StreamObserver[Res] => StreamObserver[Req]
  ): Operator[Req, Res] =
    (outputSubscriber: Subscriber[Res]) =>
      op(outputSubscriber.toStreamObserver).toSubscriber(outputSubscriber.scheduler)

}