Support zero-length chunked-encoded responses from XML services. (#2964)

The current code currently only considers responses with a content-length of zero as being empty. That isn't sufficient for chunk-encoded responses, which do not have a content-length. This change updates the logic to instead read a single byte off of the response stream to see if it's empty. This works for both zero content-length and empty chunked encoding streams.

Author: millems

.changes/next-release/bugfix-AWSSDKforJavav2-2c7120a.json

@@ -0,0 +1,6 @@
+{
+    "category": "AWS SDK for Java v2", 
+    "contributor": "", 
+    "type": "bugfix", 
+    "description": "Do not fail with a parsing error when receiving 0-length chunk-encoded responses for XML services."
+}

core/protocols/aws-xml-protocol/src/main/java/software/amazon/awssdk/protocols/xml/internal/unmarshall/XmlResponseParserUtils.java

@@ -15,8 +15,10 @@
 
 package software.amazon.awssdk.protocols.xml.internal.unmarshall;
 
-import static software.amazon.awssdk.http.Header.CONTENT_LENGTH;
-
+import java.io.BufferedInputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.UncheckedIOException;
 import java.util.Optional;
 import software.amazon.awssdk.annotations.SdkInternalApi;
 import software.amazon.awssdk.core.SdkField;
@@ -45,27 +47,42 @@ private XmlResponseParserUtils() {
      * @return A parsed XML document or an empty XML document if no payload/contents were found in the response.
      */
     public static XmlElement parse(SdkPojo sdkPojo, SdkHttpFullResponse response) {
-
         try {
             Optional<AbortableInputStream> responseContent = response.content();
 
-            // In some cases the responseContent is present but empty, so when we are not expecting a body we should
-            // not attempt to parse it even if the body appears to be present.
-            if ((!response.isSuccessful() || hasPayloadMembers(sdkPojo)) && responseContent.isPresent() &&
-                    !contentLengthZero(response) && !getBlobTypePayloadMemberToUnmarshal(sdkPojo).isPresent()) {
-                return XmlDomParser.parse(responseContent.get());
-            } else {
+            if (!responseContent.isPresent() ||
+                (response.isSuccessful() && !hasPayloadMembers(sdkPojo)) ||
+                getBlobTypePayloadMemberToUnmarshal(sdkPojo).isPresent()) {
+                return XmlElement.empty();
+            }
+
+            // Make sure there is content in the stream before passing it to the parser.
+            InputStream content = ensureMarkSupported(responseContent.get());
+            content.mark(2);
+            if (content.read() == -1) {
                 return XmlElement.empty();
             }
+            content.reset();
+
+            return XmlDomParser.parse(content);
+        } catch (IOException e) {
+            throw new UncheckedIOException(e);
         } catch (RuntimeException e) {
             if (response.isSuccessful()) {
                 throw e;
             }
-
             return XmlElement.empty();
         }
     }
 
+    private static InputStream ensureMarkSupported(AbortableInputStream content) {
+        if (content.markSupported()) {
+            return content;
+        }
+
+        return new BufferedInputStream(content);
+    }
+
     /**
      * Gets the Member which is a Payload and which is of Blob Type.
      * @param sdkPojo
@@ -85,10 +102,4 @@ private static boolean hasPayloadMembers(SdkPojo sdkPojo) {
         return sdkPojo.sdkFields().stream()
                       .anyMatch(f -> f.location() == MarshallLocation.PAYLOAD);
     }
-
-    private static boolean contentLengthZero(SdkHttpFullResponse response) {
-        return response.firstMatchingHeader(CONTENT_LENGTH).map(l -> Long.parseLong(l) == 0).orElse(false);
-    }
-
-
 }

services/s3/src/test/java/software/amazon/awssdk/services/s3/functionaltests/EmptyResponseTest.java

@@ -0,0 +1,49 @@
+/*
+ * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License").
+ * You may not use this file except in compliance with the License.
+ * A copy of the License is located at
+ *
+ *  http://aws.amazon.com/apache2.0
+ *
+ * or in the "license" file accompanying this file. This file 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 software.amazon.awssdk.services.s3.functionaltests;
+
+import static com.github.tomakehurst.wiremock.client.WireMock.aResponse;
+import static com.github.tomakehurst.wiremock.client.WireMock.anyUrl;
+import static com.github.tomakehurst.wiremock.client.WireMock.get;
+import static com.github.tomakehurst.wiremock.client.WireMock.stubFor;
+
+import com.github.tomakehurst.wiremock.junit.WireMockRule;
+import java.net.URI;
+import org.junit.Rule;
+import org.junit.Test;
+import software.amazon.awssdk.auth.credentials.AnonymousCredentialsProvider;
+import software.amazon.awssdk.regions.Region;
+import software.amazon.awssdk.services.s3.S3Client;
+
+public class EmptyResponseTest {
+    @Rule
+    public WireMockRule mockServer = new WireMockRule(0);
+
+    @Test
+    public void emptyChunkedEncodingResponseWorks() {
+        stubFor(get(anyUrl())
+                    .willReturn(aResponse().withStatus(200)
+                                           .withHeader("Transfer-Encoding", "chunked")));
+
+        S3Client client = S3Client.builder()
+                                  .endpointOverride(URI.create("http://localhost:" + mockServer.port()))
+                                  .region(Region.US_WEST_2)
+                                  .credentialsProvider(AnonymousCredentialsProvider.create())
+                                  .build();
+
+        client.listBuckets(); // Should not fail
+    }
+}