Lazily test AsyncPredicate for 'and' and 'or' operations.

fixes gh-1571

spring-cloud-gateway-core/src/main/java/org/springframework/cloud/gateway/handler/AsyncPredicate.java

@@ -20,7 +20,6 @@ import java.util.function.Function;
 import java.util.function.Predicate;
 
 import org.reactivestreams.Publisher;
-import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
 
 import org.springframework.cloud.gateway.handler.predicate.GatewayPredicate;
@@ -106,8 +105,8 @@ public interface AsyncPredicate<T> extends Function<T, Publisher<Boolean>> {
 
 		@Override
 		public Publisher<Boolean> apply(T t) {
-			return Flux.zip(left.apply(t), right.apply(t))
-					.map(tuple -> tuple.getT1() && tuple.getT2());
+			return Mono.from(left.apply(t)).flatMap(
+					result -> !result ? Mono.just(false) : Mono.from(right.apply(t)));
 		}
 
 		@Override
@@ -133,8 +132,8 @@ public interface AsyncPredicate<T> extends Function<T, Publisher<Boolean>> {
 
 		@Override
 		public Publisher<Boolean> apply(T t) {
-			return Flux.zip(left.apply(t), right.apply(t))
-					.map(tuple -> tuple.getT1() || tuple.getT2());
+			return Mono.from(left.apply(t)).flatMap(
+					result -> result ? Mono.just(true) : Mono.from(right.apply(t)));
 		}
 
 		@Override

spring-cloud-gateway-core/src/test/java/org/springframework/cloud/gateway/handler/AsyncPredicateTest.java

@@ -0,0 +1,106 @@
+/*
+ * Copyright 2013-2019 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
+ *
+ *      https://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.cloud.gateway.handler;
+
+import java.util.function.Predicate;
+
+import org.junit.Assert;
+import org.junit.Test;
+import org.reactivestreams.Publisher;
+import reactor.core.publisher.Mono;
+import reactor.test.StepVerifier;
+
+public class AsyncPredicateTest {
+
+	@Test
+	public void andPredicateShouldNotTestRightOperatorIfLeftOperatorIsFalse() {
+		TestAsyncPredicate<Object> left = new TestAsyncPredicate<>(o -> false);
+		TestAsyncPredicate<Object> right = new TestAsyncPredicate<>(o -> true);
+		Publisher<Boolean> andTest = left.and(right).apply(new Object());
+
+		StepVerifier.create(andTest).expectNext(false).expectComplete().verify();
+
+		left.assertTested();
+		right.assertUntested();
+	}
+
+	@Test
+	public void andPredicateShouldTestRightOperatorIfLeftOperatorIsTrue() {
+		TestAsyncPredicate<Object> left = new TestAsyncPredicate<>(o -> true);
+		TestAsyncPredicate<Object> right = new TestAsyncPredicate<>(o -> false);
+		Publisher<Boolean> andTest = left.and(right).apply(new Object());
+
+		StepVerifier.create(andTest).expectNext(false).expectComplete().verify();
+
+		left.assertTested();
+		right.assertTested();
+	}
+
+	@Test
+	public void orPredicateShouldNotTestRightOperatorIfLeftOperatorIsTrue() {
+		TestAsyncPredicate<Object> left = new TestAsyncPredicate<>(o -> true);
+		TestAsyncPredicate<Object> right = new TestAsyncPredicate<>(o -> false);
+		Publisher<Boolean> orTest = left.or(right).apply(new Object());
+
+		StepVerifier.create(orTest).expectNext(true).expectComplete().verify();
+
+		left.assertTested();
+		right.assertUntested();
+	}
+
+	@Test
+	public void orPredicateShouldTestRightOperatorIfLeftOperatorIsFalse() {
+		TestAsyncPredicate<Object> left = new TestAsyncPredicate<>(o -> false);
+		TestAsyncPredicate<Object> right = new TestAsyncPredicate<>(o -> true);
+		Publisher<Boolean> orTest = left.or(right).apply(new Object());
+
+		StepVerifier.create(orTest).expectNext(true).expectComplete().verify();
+
+		left.assertTested();
+		right.assertTested();
+	}
+
+	/**
+	 * An AsyncPredicate decorator that records if the apply method was called.
+	 */
+	private final static class TestAsyncPredicate<T> implements AsyncPredicate<T> {
+
+		private final Predicate<T> delegate;
+
+		private boolean tested = false;
+
+		private TestAsyncPredicate(Predicate<T> predicate) {
+			this.delegate = predicate;
+		}
+
+		@Override
+		public Publisher<Boolean> apply(T t) {
+			tested = true;
+			return Mono.just(delegate.test(t));
+		}
+
+		public void assertTested() {
+			Assert.assertTrue("predicate must have been tested", tested);
+		}
+
+		public void assertUntested() {
+			Assert.assertFalse("predicate must not have been tested", tested);
+		}
+
+	}
+
+}