Allow gzip compression without `Content-Length`

Ensure that gzip compression is applied when the `Content-Length` header
is not specified. Prior to this commit Tomcat and Jetty would compress a
response that didn't contain the header, but Undertow would not.

Fixes gh-4769

spring-boot/src/main/java/org/springframework/boot/context/embedded/undertow/UndertowEmbeddedServletContainer.java

@@ -36,6 +36,7 @@ import io.undertow.server.handlers.encoding.ContentEncodingRepository;
 import io.undertow.server.handlers.encoding.EncodingHandler;
 import io.undertow.server.handlers.encoding.GzipEncodingProvider;
 import io.undertow.servlet.api.DeploymentManager;
+import io.undertow.util.Headers;
 import io.undertow.util.HttpString;
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
@@ -161,7 +162,7 @@ public class UndertowEmbeddedServletContainer implements EmbeddedServletContaine
 
 	private Predicate[] getCompressionPredicates(Compression compression) {
 		List<Predicate> predicates = new ArrayList<Predicate>();
-		predicates.add(Predicates.maxContentSize(compression.getMinResponseSize()));
+		predicates.add(new MaxSizePredicate(compression.getMinResponseSize()));
 		predicates.add(new CompressibleMimeTypePredicate(compression.getMimeTypes()));
 		if (compression.getExcludedUserAgents() != null) {
 			for (String agent : compression.getExcludedUserAgents()) {
@@ -294,4 +295,25 @@ public class UndertowEmbeddedServletContainer implements EmbeddedServletContaine
 
 	}
 
+	/**
+	 * Predicate that returns true if the Content-Size of a request is above a given value
+	 * or is missing.
+	 */
+	private static class MaxSizePredicate implements Predicate {
+
+		private final Predicate maxContentSize;
+
+		public MaxSizePredicate(int size) {
+			this.maxContentSize = Predicates.maxContentSize(size);
+		}
+
+		@Override
+		public boolean resolve(HttpServerExchange value) {
+			if (value.getResponseHeaders().contains(Headers.CONTENT_LENGTH)) {
+				return this.maxContentSize.resolve(value);
+			}
+			return true;
+		}
+
+	}
 }

spring-boot/src/test/java/org/springframework/boot/context/embedded/AbstractEmbeddedServletContainerFactoryTests.java

@@ -360,7 +360,7 @@ public abstract class AbstractEmbeddedServletContainerFactoryTests {
 		ssl.setEnabled(false);
 		factory.setSsl(ssl);
 		this.container = factory.getEmbeddedServletContainer(
-				new ServletRegistrationBean(new ExampleServlet(true), "/hello"));
+				new ServletRegistrationBean(new ExampleServlet(true, false), "/hello"));
 		this.container.start();
 		SSLConnectionSocketFactory socketFactory = new SSLConnectionSocketFactory(
 				new SSLContextBuilder()
@@ -378,7 +378,7 @@ public abstract class AbstractEmbeddedServletContainerFactoryTests {
 		AbstractEmbeddedServletContainerFactory factory = getFactory();
 		factory.setSsl(getSsl(null, "password", "src/test/resources/test.jks"));
 		this.container = factory.getEmbeddedServletContainer(
-				new ServletRegistrationBean(new ExampleServlet(true), "/hello"));
+				new ServletRegistrationBean(new ExampleServlet(true, false), "/hello"));
 		this.container.start();
 		SSLConnectionSocketFactory socketFactory = new SSLConnectionSocketFactory(
 				new SSLContextBuilder()
@@ -658,6 +658,24 @@ public abstract class AbstractEmbeddedServletContainerFactoryTests {
 		assertFalse(doTestCompression(10000, null, new String[] { "testUserAgent" }));
 	}
 
+	@Test
+	public void compressionWithoutContentSizeHeader() throws Exception {
+		AbstractEmbeddedServletContainerFactory factory = getFactory();
+		Compression compression = new Compression();
+		compression.setEnabled(true);
+		factory.setCompression(compression);
+		this.container = factory.getEmbeddedServletContainer(
+				new ServletRegistrationBean(new ExampleServlet(false, true), "/hello"));
+		this.container.start();
+		TestGzipInputStreamFactory inputStreamFactory = new TestGzipInputStreamFactory();
+		Map<String, InputStreamFactory> contentDecoderMap = Collections
+				.singletonMap("gzip", (InputStreamFactory) inputStreamFactory);
+		getResponse(getLocalUrl("/hello"),
+				new HttpComponentsClientHttpRequestFactory(HttpClientBuilder.create()
+						.setContentDecoderRegistry(contentDecoderMap).build()));
+		assertThat(inputStreamFactory.wasCompressionUsed(), equalTo(true));
+	}
+
 	@Test
 	public void mimeMappingsAreCorrectlyConfigured() throws Exception {
 		AbstractEmbeddedServletContainerFactory factory = getFactory();
@@ -824,7 +842,7 @@ public abstract class AbstractEmbeddedServletContainerFactoryTests {
 	protected void assertForwardHeaderIsUsed(EmbeddedServletContainerFactory factory)
 			throws IOException, URISyntaxException {
 		this.container = factory.getEmbeddedServletContainer(
-				new ServletRegistrationBean(new ExampleServlet(true), "/hello"));
+				new ServletRegistrationBean(new ExampleServlet(true, false), "/hello"));
 		this.container.start();
 		assertThat(getResponse(getLocalUrl("/hello"), "X-Forwarded-For:140.211.11.130"),
 				containsString("remoteaddr=140.211.11.130"));

spring-boot/src/test/java/org/springframework/boot/context/embedded/ExampleServlet.java

@@ -20,9 +20,12 @@ import java.io.IOException;
 
 import javax.servlet.GenericServlet;
 import javax.servlet.ServletException;
+import javax.servlet.ServletOutputStream;
 import javax.servlet.ServletRequest;
 import javax.servlet.ServletResponse;
 
+import org.springframework.util.StreamUtils;
+
 /**
  * Simple example Servlet used for testing.
  *
@@ -33,12 +36,15 @@ public class ExampleServlet extends GenericServlet {
 
 	private final boolean echoRequestInfo;
 
+	private final boolean writeWithoutContentLength;
+
 	public ExampleServlet() {
-		this(false);
+		this(false, false);
 	}
 
-	public ExampleServlet(boolean echoRequestInfo) {
+	public ExampleServlet(boolean echoRequestInfo, boolean writeWithoutContentLength) {
 		this.echoRequestInfo = echoRequestInfo;
+		this.writeWithoutContentLength = writeWithoutContentLength;
 	}
 
 	@Override
@@ -49,7 +55,15 @@ public class ExampleServlet extends GenericServlet {
 			content += " scheme=" + request.getScheme();
 			content += " remoteaddr=" + request.getRemoteAddr();
 		}
-		response.getWriter().write(content);
+		if (this.writeWithoutContentLength) {
+			response.setContentType("text/plain");
+			ServletOutputStream outputStream = response.getOutputStream();
+			StreamUtils.copy(content.getBytes(), outputStream);
+			outputStream.flush();
+		}
+		else {
+			response.getWriter().write(content);
+		}
 	}
 
 }