Add ensure2, which runs the finalizer even when constructing the effect throws an exception. Deprecate ensure.

Author: adamw

core/src/main/scala/sttp/monad/MonadError.scala

@@ -42,8 +42,17 @@ trait MonadError[F[_]] {
       case Failure(e) => error(e)
     }
 
+  /** Deprecated method which doesn't work properly when constructing the `f` effect itself throws exceptions - the
+    * finalizer `e` is not run in that case. Use `ensure2` instead, which uses a lazy-evaluated by-name parameter.
+    */
+  @deprecated(message = "Use ensure2 for proper exception handling", since = "1.5.0")
   def ensure[T](f: F[T], e: => F[Unit]): F[T]
 
+  /** Runs `f`, and ensures that `e` is always run afterwards, regardless of the outcome. `e` is run even when `f`
+    * throws exceptions during construction of the effect.
+    */
+  def ensure2[T](f: => F[T], e: => F[Unit]): F[T] = ensure(f, e)
+
   def blocking[T](t: => T): F[T] = eval(t)
 }
 
@@ -62,7 +71,7 @@ object syntax {
     def map[B](f: A => B)(implicit ME: MonadError[F]): F[B] = ME.map(r)(f)
     def flatMap[B](f: A => F[B])(implicit ME: MonadError[F]): F[B] = ME.flatMap(r)(f)
     def handleError[T](h: PartialFunction[Throwable, F[A]])(implicit ME: MonadError[F]): F[A] = ME.handleError(r)(h)
-    def ensure(e: => F[Unit])(implicit ME: MonadError[F]): F[A] = ME.ensure(r, e)
+    def ensure(e: => F[Unit])(implicit ME: MonadError[F]): F[A] = ME.ensure2(r, e)
     def flatTap[B](f: A => F[B])(implicit ME: MonadError[F]): F[A] = ME.flatTap(r)(f)
   }
 
@@ -98,13 +107,24 @@ object EitherMonad extends MonadError[Either[Throwable, *]] {
       case _                           => rt
     }
 
-  override def ensure[T](f: Either[Throwable, T], e: => Either[Throwable, Unit]): Either[Throwable, T] = {
+  override def ensure[T](f: Either[Throwable, T], e: => Either[Throwable, Unit]): Either[Throwable, T] = ensure2(f, e)
+
+  override def ensure2[T](f: => Either[Throwable, T], e: => Either[Throwable, Unit]): Either[Throwable, T] = {
     def runE =
       Try(e) match {
         case Failure(f) => Left(f)
         case Success(v) => v
       }
-    f match {
+
+    val ef =
+      try f
+      catch {
+        case t: Throwable =>
+          runE
+          throw t
+      }
+
+    ef match {
       case Left(f)  => runE.right.flatMap(_ => Left(f))
       case Right(v) => runE.right.map(_ => v)
     }
@@ -125,11 +145,22 @@ object TryMonad extends MonadError[Try] {
 
   override def fromTry[T](t: Try[T]): Try[T] = t
 
-  override def ensure[T](f: Try[T], e: => Try[Unit]): Try[T] =
-    f match {
+  override def ensure[T](f: Try[T], e: => Try[Unit]): Try[T] = ensure2(f, e)
+
+  override def ensure2[T](f: => Try[T], e: => Try[Unit]): Try[T] = {
+    val ef =
+      try f
+      catch {
+        case t: Throwable =>
+          e
+          throw t
+      }
+
+    ef match {
       case Success(v) => Try(e).flatten.map(_ => v)
       case Failure(f) => Try(e).flatten.flatMap(_ => Failure(f))
     }
+  }
 }
 class FutureMonad(implicit ec: ExecutionContext) extends MonadAsyncError[Future] {
   override def unit[T](t: T): Future[T] = Future.successful(t)
@@ -155,16 +186,23 @@ class FutureMonad(implicit ec: ExecutionContext) extends MonadAsyncError[Future]
     p.future
   }
 
-  override def ensure[T](f: Future[T], e: => Future[Unit]): Future[T] = {
+  override def ensure[T](f: Future[T], e: => Future[Unit]): Future[T] = ensure2(f, e)
+
+  override def ensure2[T](f: => Future[T], e: => Future[Unit]): Future[T] = {
     val p = Promise[T]()
     def runE =
       Try(e) match {
         case Failure(f) => Future.failed(f)
         case Success(v) => v
       }
-    f.onComplete {
-      case Success(v) => runE.map(_ => v).onComplete(p.complete(_))
-      case Failure(f) => runE.flatMap(_ => Future.failed(f)).onComplete(p.complete(_))
+    try {
+      f.onComplete {
+        case Success(v) => runE.map(_ => v).onComplete(p.complete(_))
+        case Failure(f) => runE.flatMap(_ => Future.failed(f)).onComplete(p.complete(_))
+      }
+    } catch {
+      case t: Throwable =>
+        e.onComplete(_ => p.complete(Failure(t)))
     }
     p.future
   }
@@ -181,7 +219,8 @@ object IdentityMonad extends MonadError[Identity] {
       h: PartialFunction[Throwable, Identity[T]]
   ): Identity[T] = rt
   override def eval[T](t: => T): Identity[T] = t
-  override def ensure[T](f: Identity[T], e: => Identity[Unit]): Identity[T] =
+  override def ensure[T](f: Identity[T], e: => Identity[Unit]): Identity[T] = ensure2(f, e)
+  override def ensure2[T](f: => Identity[T], e: => Identity[Unit]): Identity[T] =
     try f
     finally e
 }

core/src/test/scala/sttp/monad/FutureMonadTest.scala

@@ -0,0 +1,23 @@
+package sttp.monad
+
+import org.scalatest.concurrent.ScalaFutures.convertScalaFuture
+import org.scalatest.flatspec.AnyFlatSpec
+import org.scalatest.matchers.should.Matchers
+
+import java.util.concurrent.atomic.AtomicBoolean
+import scala.concurrent.ExecutionContext.Implicits.global
+import scala.concurrent.Future
+
+class FutureMonadTest extends AnyFlatSpec with Matchers {
+  implicit val m: MonadError[Future] = new FutureMonad()
+
+  it should "ensure" in {
+    val ran = new AtomicBoolean(false)
+
+    intercept[RuntimeException] {
+      m.ensure2((throw new RuntimeException("boom!")): Future[Int], Future(ran.set(true))).futureValue
+    }
+
+    ran.get shouldBe true
+  }
+}

core/src/test/scala/sttp/monad/IdentityMonadTest.scala

@@ -0,0 +1,35 @@
+package sttp.monad
+
+import org.scalatest.flatspec.AnyFlatSpec
+import org.scalatest.matchers.should.Matchers
+
+import sttp.monad.syntax._
+import sttp.shared.Identity
+
+class IdentityMonadTest extends AnyFlatSpec with Matchers {
+  implicit val m: MonadError[Identity] = IdentityMonad
+
+  it should "map" in {
+    m.map(10)(_ + 2) shouldBe 12
+  }
+
+  it should "ensure" in {
+    var ran = false
+
+    intercept[RuntimeException] {
+      m.ensure2(m.error(new RuntimeException("boom!")), { ran = true })
+    }
+
+    ran shouldBe true
+  }
+
+  it should "ensure using syntax" in {
+    var ran = false
+
+    intercept[RuntimeException] {
+      m.error(new RuntimeException("boom!")).ensure({ ran = true })
+    }
+
+    ran shouldBe true
+  }
+}

ws/src/test/scala/sttp/ws/testing/WebSocketStubTests.scala

@@ -7,31 +7,15 @@ import sttp.monad.MonadError
 import sttp.ws.{WebSocketClosed, WebSocketFrame}
 
 import scala.util.{Failure, Success}
+import sttp.monad.IdentityMonad
 
 class WebSocketStubTests extends AnyFlatSpec with Matchers with ScalaFutures {
-  type Identity[X] = X
-  object IdMonad extends MonadError[Identity] {
-    override def unit[T](t: T): Identity[T] = t
-    override def map[T, T2](fa: Identity[T])(f: T => T2): Identity[T2] = f(fa)
-    override def flatMap[T, T2](fa: Identity[T])(f: T => Identity[T2]): Identity[T2] = f(fa)
-
-    override def error[T](t: Throwable): Identity[T] = throw t
-    override protected def handleWrappedError[T](rt: Identity[T])(
-        h: PartialFunction[Throwable, Identity[T]]
-    ): Identity[T] = rt
-
-    override def eval[T](t: => T): Identity[T] = t
-    override def ensure[T](f: Identity[T], e: => Identity[Unit]): Identity[T] =
-      try f
-      finally e
-  }
-
   class MyException extends Exception
 
   "web socket stub" should "return initial Incoming frames on 'receive'" in {
     val frames = List("a", "b", "c").map(WebSocketFrame.text)
     val webSocketStub = WebSocketStub.initialReceive(frames)
-    val ws = webSocketStub.build(IdMonad)
+    val ws = webSocketStub.build(IdentityMonad)
 
     ws.receive() shouldBe WebSocketFrame.text("a")
     ws.receive() shouldBe WebSocketFrame.text("b")
@@ -42,7 +26,7 @@ class WebSocketStubTests extends AnyFlatSpec with Matchers with ScalaFutures {
     val okFrame = WebSocketFrame.text("abc")
     val exception = new MyException
     val webSocketStub = WebSocketStub.initialReceiveWith(List(Success(okFrame), Failure(exception)))
-    val ws = webSocketStub.build(IdMonad)
+    val ws = webSocketStub.build(IdentityMonad)
 
     ws.receive() shouldBe WebSocketFrame.text("abc")
     assertThrows[MyException](ws.receive())
@@ -59,7 +43,7 @@ class WebSocketStubTests extends AnyFlatSpec with Matchers with ScalaFutures {
         case `expectedFrame` => List(secondFrame, thirdFrame)
         case _               => List.empty
       }
-    val ws = webSocketStub.build(IdMonad)
+    val ws = webSocketStub.build(IdentityMonad)
 
     ws.receive() shouldBe WebSocketFrame.text("No. 1")
     assertThrows[IllegalStateException](ws.receive()) // no more stubbed messages
@@ -76,7 +60,7 @@ class WebSocketStubTests extends AnyFlatSpec with Matchers with ScalaFutures {
 
     val webSocketStub = WebSocketStub.noInitialReceive
       .thenRespondWith(_ => List(Success(ok), Failure(exception)))
-    val ws = webSocketStub.build(IdMonad)
+    val ws = webSocketStub.build(IdentityMonad)
 
     ws.send(WebSocketFrame.text("let's add responses"))
     ws.receive() shouldBe WebSocketFrame.text("ok")
@@ -87,7 +71,7 @@ class WebSocketStubTests extends AnyFlatSpec with Matchers with ScalaFutures {
     val ok = WebSocketFrame.text("ok")
     val closeFrame = WebSocketFrame.Close(500, "internal error")
     val webSocketStub = WebSocketStub.initialReceive(List(closeFrame, ok))
-    val ws = webSocketStub.build(IdMonad)
+    val ws = webSocketStub.build(IdentityMonad)
 
     ws.send(WebSocketFrame.text("let's add responses"))
     ws.receive() shouldBe closeFrame
@@ -100,7 +84,7 @@ class WebSocketStubTests extends AnyFlatSpec with Matchers with ScalaFutures {
       .thenRespondS(0) { case (counter, _) =>
         (counter + 1, List(WebSocketFrame.text(s"No. $counter")))
       }
-    val ws = webSocketStub.build(IdMonad)
+    val ws = webSocketStub.build(IdentityMonad)
 
     ws.send(WebSocketFrame.text("a"))
     ws.send(WebSocketFrame.text("b"))