DATAMONGO-2230 - Decrement demand after emission in DataBufferPublisherAdapter.

We now decrement the demand and propagate exceptions from the adapter. Previously, we did not decrement the demand and kept emitting buffers although the subscriber demand was satisfied.

Original Pull Request: #693

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/gridfs/DataBufferPublisherAdapter.java

@@ -29,6 +29,7 @@ import java.util.concurrent.atomic.AtomicLongFieldUpdater;
 
 import org.reactivestreams.Publisher;
 import org.reactivestreams.Subscription;
+
 import org.springframework.core.io.buffer.DataBuffer;
 import org.springframework.core.io.buffer.DataBufferFactory;
 import org.springframework.core.io.buffer.DataBufferUtils;
@@ -74,11 +75,14 @@ class DataBufferPublisherAdapter {
 	@RequiredArgsConstructor
 	static class State {
 
-		private static final AtomicLongFieldUpdater<State> DEMAND = AtomicLongFieldUpdater.newUpdater(State.class, "demand");
+		private static final AtomicLongFieldUpdater<State> DEMAND = AtomicLongFieldUpdater.newUpdater(State.class,
+				"demand");
 
-		private static final AtomicIntegerFieldUpdater<State> STATE = AtomicIntegerFieldUpdater.newUpdater(State.class, "state");
+		private static final AtomicIntegerFieldUpdater<State> STATE = AtomicIntegerFieldUpdater.newUpdater(State.class,
+				"state");
 
-		private static final AtomicIntegerFieldUpdater<State> READ = AtomicIntegerFieldUpdater.newUpdater(State.class, "read");
+		private static final AtomicIntegerFieldUpdater<State> READ = AtomicIntegerFieldUpdater.newUpdater(State.class,
+				"read");
 
 		private static final int STATE_OPEN = 0;
 		private static final int STATE_CLOSED = 1;
@@ -123,6 +127,10 @@ class DataBufferPublisherAdapter {
 			return DEMAND.get(this);
 		}
 
+		boolean decrementDemand() {
+			return DEMAND.decrementAndGet(this) > 0;
+		}
+
 		void close() {
 			STATE.compareAndSet(this, STATE_OPEN, STATE_CLOSED);
 		}
@@ -141,7 +149,11 @@ class DataBufferPublisherAdapter {
 			DataBuffer dataBuffer = dataBufferFactory.allocateBuffer();
 			ByteBuffer intermediate = ByteBuffer.allocate(dataBuffer.capacity());
 
-			Mono.from(inputStream.read(intermediate)).subscribe(new BufferCoreSubscriber(sink, dataBuffer, intermediate));
+			try {
+				Mono.from(inputStream.read(intermediate)).subscribe(new BufferCoreSubscriber(sink, dataBuffer, intermediate));
+			} catch (Exception e) {
+				sink.error(e);
+			}
 		}
 
 		private class BufferCoreSubscriber implements CoreSubscriber<Integer> {
@@ -182,6 +194,7 @@ class DataBufferPublisherAdapter {
 				dataBuffer.write(intermediate);
 
 				sink.next(dataBuffer);
+				decrementDemand();
 
 				try {
 					if (bytes == -1) {

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/gridfs/DataBufferPublisherAdapterUnitTests.java

@@ -0,0 +1,55 @@
+/*
+ * Copyright 2019 the original author or authors.
+ *
+ * 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 org.springframework.data.mongodb.gridfs;
+
+import static org.mockito.Mockito.*;
+
+import reactor.core.publisher.Flux;
+import reactor.core.publisher.Mono;
+import reactor.test.StepVerifier;
+
+import org.junit.Test;
+
+import org.springframework.core.io.buffer.DataBuffer;
+import org.springframework.core.io.buffer.DataBufferFactory;
+import org.springframework.core.io.buffer.DefaultDataBufferFactory;
+
+/**
+ * Unit tests for {@link DataBufferPublisherAdapter}.
+ *
+ * @author Mark Paluch
+ */
+public class DataBufferPublisherAdapterUnitTests {
+
+	DataBufferFactory factory = new DefaultDataBufferFactory();
+
+	@Test // DATAMONGO-2230
+	public void adapterShouldPropagateErrors() {
+
+		AsyncInputStreamAdapter asyncInput = mock(AsyncInputStreamAdapter.class);
+
+		when(asyncInput.read(any())).thenReturn(Mono.just(1), Mono.error(new IllegalStateException()));
+		when(asyncInput.close()).thenReturn(Mono.empty());
+
+		Flux<DataBuffer> binaryStream = DataBufferPublisherAdapter.createBinaryStream(asyncInput, factory);
+
+		StepVerifier.create(binaryStream, 0) //
+				.thenRequest(1) //
+				.expectNextCount(1) //
+				.thenRequest(1) //
+				.verifyError(IllegalStateException.class);
+	}
+}