Add DelegatingServerHttpHeadersWriter

Servlet Spring Security has DelegatingRequestMatcherHeaderWriter
the reactive world of Spring Security was missing a class to
conditionally write headers.

Closes gh-11073

web/src/main/java/org/springframework/security/web/server/header/ServerWebExchangeDelegatingServerHttpHeadersWriter.java

@@ -0,0 +1,69 @@
+/*
+ * Copyright 2002-2022 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.security.web.server.header;
+
+import reactor.core.publisher.Mono;
+
+import org.springframework.security.web.server.util.matcher.ServerWebExchangeMatcher;
+import org.springframework.security.web.server.util.matcher.ServerWebExchangeMatcherEntry;
+import org.springframework.util.Assert;
+import org.springframework.web.server.ServerWebExchange;
+
+/**
+ * Delegates to a provided {@link ServerHttpHeadersWriter} if
+ * {@link ServerWebExchangeMatcher#matches(ServerWebExchange)} returns a match.
+ *
+ * @author David Herberth
+ * @since 5.8
+ */
+public final class ServerWebExchangeDelegatingServerHttpHeadersWriter implements ServerHttpHeadersWriter {
+
+	private final ServerWebExchangeMatcherEntry<ServerHttpHeadersWriter> headersWriter;
+
+	/**
+	 * Creates a new instance
+	 * @param headersWriter the {@link ServerWebExchangeMatcherEntry} holding a
+	 * {@link ServerWebExchangeMatcher} and the {@link ServerHttpHeadersWriter} to invoke
+	 * if the matcher returns a match.
+	 */
+	public ServerWebExchangeDelegatingServerHttpHeadersWriter(
+			ServerWebExchangeMatcherEntry<ServerHttpHeadersWriter> headersWriter) {
+		Assert.notNull(headersWriter, "headersWriter cannot be null");
+		this.headersWriter = headersWriter;
+	}
+
+	/**
+	 * Creates a new instance
+	 * @param webExchangeMatcher the {@link ServerWebExchangeMatcher} to use. If it
+	 * returns a match, the delegateHeadersWriter is invoked.
+	 * @param delegateHeadersWriter the {@link ServerHttpHeadersWriter} to invoke if the
+	 * {@link ServerWebExchangeMatcher} returns a match.
+	 */
+	public ServerWebExchangeDelegatingServerHttpHeadersWriter(ServerWebExchangeMatcher webExchangeMatcher,
+			ServerHttpHeadersWriter delegateHeadersWriter) {
+		Assert.notNull(webExchangeMatcher, "webExchangeMatcher cannot be null");
+		Assert.notNull(delegateHeadersWriter, "delegateHeadersWriter cannot be null");
+		this.headersWriter = new ServerWebExchangeMatcherEntry<>(webExchangeMatcher, delegateHeadersWriter);
+	}
+
+	@Override
+	public Mono<Void> writeHttpHeaders(ServerWebExchange exchange) {
+		return this.headersWriter.getMatcher().matches(exchange).filter(ServerWebExchangeMatcher.MatchResult::isMatch)
+				.flatMap((matchResult) -> this.headersWriter.getEntry().writeHttpHeaders(exchange));
+	}
+
+}

web/src/test/java/org/springframework/security/web/server/header/ServerWebExchangeDelegatingServerHttpHeadersWriterTests.java

@@ -0,0 +1,111 @@
+/*
+ * Copyright 2002-2022 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.security.web.server.header;
+
+import java.util.Collections;
+import java.util.Map;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+import reactor.core.publisher.Mono;
+
+import org.springframework.mock.http.server.reactive.MockServerHttpRequest;
+import org.springframework.mock.web.server.MockServerWebExchange;
+import org.springframework.security.web.server.util.matcher.ServerWebExchangeMatcher;
+import org.springframework.security.web.server.util.matcher.ServerWebExchangeMatcherEntry;
+import org.springframework.web.server.ServerWebExchange;
+
+import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
+import static org.mockito.BDDMockito.given;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
+
+/**
+ * @author David Herberth
+ */
+@ExtendWith(MockitoExtension.class)
+public class ServerWebExchangeDelegatingServerHttpHeadersWriterTests {
+
+	@Mock
+	private ServerWebExchangeMatcher matcher;
+
+	@Mock
+	private ServerHttpHeadersWriter delegate;
+
+	@Mock
+	private ServerWebExchangeMatcherEntry<ServerHttpHeadersWriter> matcherEntry;
+
+	private ServerWebExchange exchange;
+
+	private ServerWebExchangeDelegatingServerHttpHeadersWriter headerWriter;
+
+	@BeforeEach
+	public void setup() {
+		this.exchange = MockServerWebExchange.from(MockServerHttpRequest.get("/"));
+		this.headerWriter = new ServerWebExchangeDelegatingServerHttpHeadersWriter(this.matcher, this.delegate);
+	}
+
+	@Test
+	public void constructorNullWebExchangeMatcher() {
+		assertThatIllegalArgumentException()
+				.isThrownBy(() -> new ServerWebExchangeDelegatingServerHttpHeadersWriter(null, this.delegate));
+	}
+
+	@Test
+	public void constructorNullWebExchangeMatcherEntry() {
+		assertThatIllegalArgumentException()
+				.isThrownBy(() -> new ServerWebExchangeDelegatingServerHttpHeadersWriter(null));
+	}
+
+	@Test
+	public void constructorNullDelegate() {
+		assertThatIllegalArgumentException()
+				.isThrownBy(() -> new ServerWebExchangeDelegatingServerHttpHeadersWriter(this.matcher, null));
+	}
+
+	@Test
+	public void writeHeadersOnMatch() {
+		Map<String, Object> params = Collections.singletonMap("foo", "bar");
+		given(this.matcher.matches(this.exchange)).willReturn(ServerWebExchangeMatcher.MatchResult.match(params));
+		given(this.delegate.writeHttpHeaders(this.exchange)).willReturn(Mono.empty());
+		this.headerWriter.writeHttpHeaders(this.exchange).block();
+		verify(this.delegate).writeHttpHeaders(this.exchange);
+	}
+
+	@Test
+	public void writeHeadersOnNoMatch() {
+		given(this.matcher.matches(this.exchange)).willReturn(ServerWebExchangeMatcher.MatchResult.notMatch());
+		this.headerWriter.writeHttpHeaders(this.exchange).block();
+		verify(this.delegate, times(0)).writeHttpHeaders(this.exchange);
+	}
+
+	@Test
+	public void writeHeadersOnMatchWithServerWebExchangeMatcherEntry() {
+		this.headerWriter = new ServerWebExchangeDelegatingServerHttpHeadersWriter(this.matcherEntry);
+		given(this.matcherEntry.getMatcher()).willReturn(this.matcher);
+		given(this.matcherEntry.getEntry()).willReturn(this.delegate);
+		Map<String, Object> params = Collections.singletonMap("foo", "bar");
+		given(this.matcher.matches(this.exchange)).willReturn(ServerWebExchangeMatcher.MatchResult.match(params));
+		given(this.delegate.writeHttpHeaders(this.exchange)).willReturn(Mono.empty());
+		this.headerWriter.writeHttpHeaders(this.exchange).block();
+		verify(this.delegate).writeHttpHeaders(this.exchange);
+	}
+
+}