Adds gzip handler to JDK http client based on header

spring-web/src/main/java/org/springframework/http/client/JdkClientHttpRequest.java

@@ -24,10 +24,15 @@
 import java.net.http.HttpClient;
 import java.net.http.HttpRequest;
 import java.net.http.HttpResponse;
+import java.net.http.HttpResponse.BodyHandler;
+import java.net.http.HttpResponse.BodySubscriber;
+import java.net.http.HttpResponse.BodySubscribers;
+import java.net.http.HttpResponse.ResponseInfo;
 import java.net.http.HttpTimeoutException;
 import java.nio.ByteBuffer;
 import java.time.Duration;
 import java.util.Collections;
+import java.util.List;
 import java.util.Locale;
 import java.util.Set;
 import java.util.TreeSet;
@@ -37,6 +42,8 @@
 import java.util.concurrent.Executor;
 import java.util.concurrent.Flow;
 import java.util.concurrent.TimeUnit;
+import java.util.zip.GZIPInputStream;
+import java.util.zip.InflaterInputStream;
 
 import org.jspecify.annotations.Nullable;
 
@@ -59,6 +66,8 @@ class JdkClientHttpRequest extends AbstractStreamingClientHttpRequest {
 
 	private static final Set<String> DISALLOWED_HEADERS = disallowedHeaders();
 
+	private static final List<String> ALLOWED_ENCODINGS = List.of("gzip", "deflate");
+
 
 	private final HttpClient httpClient;
 
@@ -70,15 +79,18 @@ class JdkClientHttpRequest extends AbstractStreamingClientHttpRequest {
 
 	private final @Nullable Duration timeout;
 
+	private final boolean compressionEnabled;
+
 
 	public JdkClientHttpRequest(HttpClient httpClient, URI uri, HttpMethod method, Executor executor,
-			@Nullable Duration readTimeout) {
+			@Nullable Duration readTimeout, boolean compressionEnabled) {
 
 		this.httpClient = httpClient;
 		this.uri = uri;
 		this.method = method;
 		this.executor = executor;
 		this.timeout = readTimeout;
+		this.compressionEnabled = compressionEnabled;
 	}
 
 
@@ -98,7 +110,7 @@ protected ClientHttpResponse executeInternal(HttpHeaders headers, @Nullable Body
 		CompletableFuture<HttpResponse<InputStream>> responseFuture = null;
 		try {
 			HttpRequest request = buildRequest(headers, body);
-			responseFuture = this.httpClient.sendAsync(request, HttpResponse.BodyHandlers.ofInputStream());
+			responseFuture = this.httpClient.sendAsync(request, new DecompressingBodyHandler());
 
 			if (this.timeout != null) {
 				TimeoutHandler timeoutHandler = new TimeoutHandler(responseFuture, this.timeout);
@@ -141,6 +153,15 @@ else if (cause instanceof IOException ioEx) {
 	private HttpRequest buildRequest(HttpHeaders headers, @Nullable Body body) {
 		HttpRequest.Builder builder = HttpRequest.newBuilder().uri(this.uri);
 
+		// When compression is enabled and valid encoding is absent, we add gzip as standard encoding
+		if (this.compressionEnabled) {
+			if (headers.containsHeader(HttpHeaders.ACCEPT_ENCODING) &&
+					!ALLOWED_ENCODINGS.contains(headers.getFirst(HttpHeaders.ACCEPT_ENCODING))) {
+				headers.remove(HttpHeaders.ACCEPT_ENCODING);
+			}
+			headers.add(HttpHeaders.ACCEPT_ENCODING, "gzip");
+		}
+
 		headers.forEach((headerName, headerValues) -> {
 			if (!DISALLOWED_HEADERS.contains(headerName.toLowerCase(Locale.ROOT))) {
 				for (String headerValue : headerValues) {
@@ -226,7 +247,7 @@ public ByteBuffer map(byte[] b, int off, int len) {
 	/**
 	 * Temporary workaround to use instead of {@link HttpRequest.Builder#timeout(Duration)}
 	 * until <a href="https://bugs.openjdk.org/browse/JDK-8258397">JDK-8258397</a>
-	 * is fixed. Essentially, create a future wiht a timeout handler, and use it
+	 * is fixed. Essentially, create a future with a timeout handler, and use it
 	 * to close the response.
 	 * @see <a href="https://mail.openjdk.org/pipermail/net-dev/2021-October/016672.html">OpenJDK discussion thread</a>
 	 */
@@ -269,4 +290,39 @@ public void close() throws IOException {
 		}
 	}
 
+	/**
+	 * Custom BodyHandler that checks the Content-Encoding header and applies the appropriate decompression algorithm.
+	 * Supports Gzip and Deflate encoded responses.
+	 */
+	public static final class DecompressingBodyHandler implements BodyHandler<InputStream> {
+
+		@Override
+		public BodySubscriber<InputStream> apply(ResponseInfo responseInfo) {
+			String contentEncoding = responseInfo.headers().firstValue(HttpHeaders.CONTENT_ENCODING).orElse("");
+			if (contentEncoding.equalsIgnoreCase("gzip")) {
+				// If the content is gzipped, wrap the InputStream with a GZIPInputStream
+				return BodySubscribers.mapping(
+						BodySubscribers.ofInputStream(),
+						(InputStream is) -> {
+							try {
+								return new GZIPInputStream(is);
+							}
+							catch (IOException ex) {
+								throw new UncheckedIOException(ex); // Propagate IOExceptions
+							}
+						});
+			}
+			else if (contentEncoding.equalsIgnoreCase("deflate")) {
+				// If the content is encoded using deflate, wrap the InputStream with a InflaterInputStream
+				return BodySubscribers.mapping(
+						BodySubscribers.ofInputStream(),
+						InflaterInputStream::new);
+			}
+			else {
+				// Otherwise, return a standard InputStream BodySubscriber
+				return BodySubscribers.ofInputStream();
+			}
+		}
+	}
+
 }

spring-web/src/main/java/org/springframework/http/client/JdkClientHttpRequestFactory.java

@@ -43,6 +43,8 @@ public class JdkClientHttpRequestFactory implements ClientHttpRequestFactory {
 
 	private @Nullable Duration readTimeout;
 
+	private boolean compressionEnabled;
+
 
 	/**
 	 * Create a new instance of the {@code JdkClientHttpRequestFactory}
@@ -96,10 +98,18 @@ public void setReadTimeout(Duration readTimeout) {
 		this.readTimeout = readTimeout;
 	}
 
+	/**
+	 * Sets custom {@link BodyHandler} that can handle gzip encoded {@link HttpClient}'s response.
+	 * @param compressionEnabled to enable compression by default for all {@link HttpClient}'s requests.
+	 */
+	public void setCompressionEnabled(boolean compressionEnabled) {
+		this.compressionEnabled = compressionEnabled;
+	}
+
 
 	@Override
 	public ClientHttpRequest createRequest(URI uri, HttpMethod httpMethod) throws IOException {
-		return new JdkClientHttpRequest(this.httpClient, uri, httpMethod, this.executor, this.readTimeout);
+		return new JdkClientHttpRequest(this.httpClient, uri, httpMethod, this.executor, this.readTimeout, this.compressionEnabled);
 	}
 
 }

spring-web/src/test/java/org/springframework/http/client/AbstractMockWebServerTests.java

@@ -23,8 +23,14 @@
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
 
+import org.springframework.http.HttpHeaders;
 import org.springframework.util.StringUtils;
 
+import java.io.ByteArrayOutputStream;
+import java.nio.charset.StandardCharsets;
+import java.util.zip.DeflaterOutputStream;
+import java.util.zip.GZIPOutputStream;
+
 import static org.assertj.core.api.Assertions.assertThat;
 
 /**
@@ -106,6 +112,26 @@ else if(request.getTarget().startsWith("/header/")) {
 					String headerName = request.getTarget().replace("/header/","");
 					return new MockResponse.Builder().body(headerName + ":" + request.getHeaders().get(headerName)).code(200).build();
 				}
+				else if(request.getTarget().startsWith("/compress/")) {
+					String encoding = request.getTarget().replace("/compress/","");
+					ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
+					if (encoding.equals("gzip")) {
+						try(GZIPOutputStream gzipOutputStream = new GZIPOutputStream(byteArrayOutputStream)) {
+							gzipOutputStream.write("Test Payload".getBytes());
+							gzipOutputStream.flush();
+						}
+					}
+					else if(encoding.equals("deflate")) {
+							try(DeflaterOutputStream deflaterOutputStream = new DeflaterOutputStream(byteArrayOutputStream)) {
+							deflaterOutputStream.write("Test Payload".getBytes());
+							deflaterOutputStream.flush();
+						}
+					} else {
+						byteArrayOutputStream.write("Test Payload".getBytes());
+					}
+					return new MockResponse.Builder().body(byteArrayOutputStream.toString(StandardCharsets.ISO_8859_1))
+							.code(200).setHeader(HttpHeaders.CONTENT_ENCODING, encoding).build();
+				}
 				return new MockResponse.Builder().code(404).build();
 			}
 			catch (Throwable ex) {

spring-web/src/test/java/org/springframework/http/client/JdkClientHttpRequestFactoryTests.java

@@ -108,6 +108,44 @@ void deleteRequestWithBody() throws Exception {
 		}
 	}
 
+	@Test
+	void compressionDisabled() throws IOException {
+		URI uri = URI.create(baseUrl + "/compress/");
+		ClientHttpRequest request = this.factory.createRequest(uri, HttpMethod.GET);
+		try (ClientHttpResponse response = request.execute()) {
+			assertThat(response.getStatusCode()).as("Invalid response status").isEqualTo(HttpStatus.OK);
+			assertThat(StreamUtils.copyToString(response.getBody(), StandardCharsets.ISO_8859_1))
+					.as("Invalid request body").isEqualTo("Test Payload");
+		}
+	}
+
+	@Test
+	void compressionGzip() throws IOException {
+		URI uri = URI.create(baseUrl + "/compress/gzip");
+		JdkClientHttpRequestFactory requestFactory = (JdkClientHttpRequestFactory) this.factory;
+		requestFactory.setCompressionEnabled(true);
+		ClientHttpRequest request = requestFactory.createRequest(uri, HttpMethod.GET);
+
+		try (ClientHttpResponse response = request.execute()) {
+			assertThat(response.getStatusCode()).as("Invalid response status").isEqualTo(HttpStatus.OK);
+			assertThat(StreamUtils.copyToString(response.getBody(), StandardCharsets.ISO_8859_1))
+					.as("Invalid request body").isEqualTo("Test Payload");
+		}
+	}
+
+	@Test
+	void compressionDeflate() throws IOException {
+		URI uri = URI.create(baseUrl + "/compress/deflate");
+		JdkClientHttpRequestFactory requestFactory = (JdkClientHttpRequestFactory) this.factory;
+		requestFactory.setCompressionEnabled(true);
+		ClientHttpRequest request = requestFactory.createRequest(uri, HttpMethod.GET);
+		try (ClientHttpResponse response = request.execute()) {
+			assertThat(response.getStatusCode()).as("Invalid response status").isEqualTo(HttpStatus.OK);
+			assertThat(StreamUtils.copyToString(response.getBody(), StandardCharsets.ISO_8859_1))
+					.as("Invalid request body").isEqualTo("Test Payload");
+		}
+	}
+
 	@Test // gh-34971
 	@EnabledForJreRange(min = JRE.JAVA_19) // behavior fixed in Java 19
 	void requestContentLengthHeaderWhenNoBody() throws Exception {