Fix gzip handling for HEAD requests in JdkClientHttpRequest (Issue #35966)

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

@@ -113,7 +113,7 @@ protected ClientHttpResponse executeInternal(HttpHeaders headers, @Nullable Body
 		TimeoutHandler timeoutHandler = null;
 		try {
 			HttpRequest request = buildRequest(headers, body);
-			responseFuture = this.httpClient.sendAsync(request, this.compression ? new DecompressingBodyHandler() : HttpResponse.BodyHandlers.ofInputStream());
+			responseFuture = this.httpClient.sendAsync(request, this.compression ? new DecompressingBodyHandler(this.method) : HttpResponse.BodyHandlers.ofInputStream());
 			if (this.timeout != null) {
 				timeoutHandler = new TimeoutHandler(responseFuture, this.timeout);
 				HttpResponse<InputStream> response = responseFuture.get();
@@ -325,13 +325,37 @@ public void handleCancellationException(CancellationException ex) throws HttpTim
 	 */
 	private static final class DecompressingBodyHandler implements BodyHandler<InputStream> {
 
+		private final HttpMethod method;
+
+		private DecompressingBodyHandler(HttpMethod method) {
+			this.method = method;
+		}
+
 		@Override
 		public BodySubscriber<InputStream> apply(ResponseInfo responseInfo) {
-			String contentEncoding = responseInfo.headers().firstValue(HttpHeaders.CONTENT_ENCODING).orElse("");
+
+			String contentEncoding = responseInfo.headers()
+					.firstValue(HttpHeaders.CONTENT_ENCODING)
+					.orElse("");
+
+			// Skip gzip/deflate if HEAD request (HEAD has no body)
+			if (this.method == HttpMethod.HEAD) {
+				return BodySubscribers.replacing(InputStream.nullInputStream());
+			}
+
+			// Skip if Content-Length = 0 (empty body)
+			String contentLength = responseInfo.headers()
+					.firstValue(HttpHeaders.CONTENT_LENGTH)
+					.orElse(null);
+
+			if ("0".equals(contentLength)) {
+				return BodySubscribers.replacing(InputStream.nullInputStream());
+			}
+
 			if (contentEncoding.equalsIgnoreCase("gzip")) {
 				return BodySubscribers.mapping(
 						BodySubscribers.ofInputStream(),
-						(InputStream is) -> {
+						is -> {
 							try {
 								return new GZIPInputStream(is);
 							}
@@ -340,15 +364,16 @@ public BodySubscriber<InputStream> apply(ResponseInfo responseInfo) {
 							}
 						});
 			}
-			else if (contentEncoding.equalsIgnoreCase("deflate")) {
+
+			if (contentEncoding.equalsIgnoreCase("deflate")) {
 				return BodySubscribers.mapping(
 						BodySubscribers.ofInputStream(),
 						InflaterInputStream::new);
 			}
-			else {
-				return BodySubscribers.ofInputStream();
-			}
+
+			return BodySubscribers.ofInputStream();
 		}
 	}
 
+
 }

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

@@ -38,6 +38,14 @@
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.when;
+import java.net.InetSocketAddress;
+
+import org.springframework.http.client.JdkClientHttpRequestFactory;
+import org.springframework.web.client.RestClient;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+
+
 
 /**
  * Unit tests for {@link JdkClientHttpRequest}.
@@ -74,5 +82,42 @@ void futureCancelled() {
 	private JdkClientHttpRequest createRequest(Duration timeout) {
 		return new JdkClientHttpRequest(client, URI.create("https://abc.com"), HttpMethod.GET, executor, timeout, false);
 	}
+	@Test
+	void headRequestWithGzipContentEncodingShouldNotFail() throws Exception {
+		com.sun.net.httpserver.HttpServer server =
+				com.sun.net.httpserver.HttpServer.create(new InetSocketAddress(0), 0);
+
+		server.createContext("/test", exchange -> {
+			// Simulate HEAD-like response: gzip header + no body
+			exchange.getResponseHeaders().add("Content-Encoding", "gzip");
+			exchange.getResponseHeaders().add("Content-Length", "0");
+			exchange.sendResponseHeaders(200, 0);  // no body
+			exchange.close();
+		});
+
+		server.start();
+		int port = server.getAddress().getPort();
+
+		try {
+			RestClient client = RestClient.builder()
+					.requestFactory(new JdkClientHttpRequestFactory())
+					.build();
+
+			// The original bug: this line used to blow up with gzip + empty body.
+			assertDoesNotThrow(() ->
+					client.head()
+							.uri("http://localhost:" + port + "/test")
+							.retrieve()
+							.toBodilessEntity()
+			);
+		}
+		finally {
+			server.stop(0);
+		}
+	}
+
+
+
+
 
 }