Follow standard REST-JSON content-type handling

Update the REST-JSON marshalling logic to conform to the standard expected
behavior WRT to the `Content-Type` of the request.

Author: dagnir

.changes/next-release/bugfix-AWSSDKforJavav2-47e105f.json

@@ -0,0 +1,6 @@
+{
+    "category": "AWS SDK for Java v2", 
+    "contributor": "", 
+    "type": "bugfix", 
+    "description": "Update the REST-JSON marshalling logic to conform to the standard expected behavior WRT to the `Content-Type` of the request."
+}

core/protocols/aws-json-protocol/src/main/java/software/amazon/awssdk/protocols/json/DefaultJsonContentTypeResolver.java

@@ -23,6 +23,7 @@
  */
 @SdkProtectedApi
 public class DefaultJsonContentTypeResolver implements JsonContentTypeResolver {
+    private static final String REST_JSON_CONTENT_TYPE = "application/json";
 
     private final String prefix;
 
@@ -32,7 +33,9 @@ public DefaultJsonContentTypeResolver(String prefix) {
 
     @Override
     public String resolveContentType(AwsJsonProtocolMetadata protocolMetadata) {
-        //Changing this to 'application/json' may break clients expecting 'application/x-amz-json-1.1'
+        if (AwsJsonProtocol.REST_JSON.equals(protocolMetadata.protocol())) {
+            return REST_JSON_CONTENT_TYPE;
+        }
         return prefix + protocolMetadata.protocolVersion();
     }
 }

core/protocols/aws-json-protocol/src/main/java/software/amazon/awssdk/protocols/json/internal/marshall/JsonProtocolMarshaller.java

@@ -16,7 +16,6 @@
 package software.amazon.awssdk.protocols.json.internal.marshall;
 
 import static software.amazon.awssdk.core.internal.util.Mimetype.MIMETYPE_EVENT_STREAM;
-import static software.amazon.awssdk.core.protocol.MarshallingType.DOCUMENT;
 import static software.amazon.awssdk.http.Header.CHUNKED;
 import static software.amazon.awssdk.http.Header.CONTENT_LENGTH;
 import static software.amazon.awssdk.http.Header.CONTENT_TYPE;
@@ -176,25 +175,30 @@ private void startMarshalling() {
     void doMarshall(SdkPojo pojo) {
         for (SdkField<?> field : pojo.sdkFields()) {
             Object val = field.getValueOrDefault(pojo);
-            if (isBinary(field, val)) {
-                request.contentStreamProvider(((SdkBytes) val)::asInputStream);
-            } else if (isDocumentType(field) && val != null) {
-                marshalDocumentType(field, val);
-            } else {
-                if (val != null && field.containsTrait(PayloadTrait.class)) {
-                    jsonGenerator.writeStartObject();
-                    doMarshall((SdkPojo) val);
-                    jsonGenerator.writeEndObject();
-                } else {
-                    MARSHALLER_REGISTRY.getMarshaller(field.location(), field.marshallingType(), val)
-                                       .marshall(val, marshallerContext, field.locationName(), (SdkField<Object>) field);
+            if (isExplicitBinaryPayload(field)) {
+                if (val != null) {
+                    request.contentStreamProvider(((SdkBytes) val)::asInputStream);
+                }
+            } else if (isExplicitPayloadMember(field)) {
+                // Explicit JSON payloads are always marshalled as an object,
+                // even if they're null, in which case it's an empty object.
+                jsonGenerator.writeStartObject();
+                if (val != null) {
+                    if (field.marshallingType().equals(MarshallingType.DOCUMENT)) {
+                        marshallField(field, val);
+                    } else {
+                        doMarshall((SdkPojo) val);
+                    }
                 }
+                jsonGenerator.writeEndObject();
+            } else {
+                marshallField(field, val);
             }
         }
     }
 
-    private boolean isBinary(SdkField<?> field, Object val) {
-        return isExplicitPayloadMember(field) && val instanceof SdkBytes;
+    private boolean isExplicitBinaryPayload(SdkField<?> field) {
+        return isExplicitPayloadMember(field) && MarshallingType.SDK_BYTES.equals(field.marshallingType());
     }
 
     private boolean isExplicitPayloadMember(SdkField<?> field) {
@@ -243,27 +247,16 @@ private SdkHttpFullRequest finishMarshalling() {
                 }
                 request.removeHeader(CONTENT_LENGTH);
                 request.putHeader(TRANSFER_ENCODING, CHUNKED);
-            } else if (contentType != null && !hasStreamingInput && request.contentStreamProvider() != null) {
+            } else if (contentType != null && !hasStreamingInput && request.headers().containsKey(CONTENT_LENGTH)) {
                 request.putHeader(CONTENT_TYPE, contentType);
             }
         }
 
         return request.build();
     }
 
-    private boolean isDocumentType(SdkField<?> field) {
-        return DOCUMENT.equals(field.marshallingType());
-    }
-
-    private void marshalDocumentType(SdkField<?> field, Object val) {
-        boolean isExplicitPayloadField = hasExplicitPayloadMember && field.containsTrait(PayloadTrait.class);
-        if (isExplicitPayloadField) {
-            jsonGenerator.writeStartObject();
-        }
+    private void marshallField(SdkField<?> field, Object val) {
         MARSHALLER_REGISTRY.getMarshaller(field.location(), field.marshallingType(), val)
                            .marshall(val, marshallerContext, field.locationName(), (SdkField<Object>) field);
-        if (isExplicitPayloadField) {
-            jsonGenerator.writeEndObject();
-        }
     }
 }

test/codegen-generated-classes-test/src/test/java/software/amazon/awssdk/services/documenttype/DocumentTypeTest.java

@@ -223,7 +223,7 @@ public void explicitDocumentOnlyNullPayload() {
         WithExplicitDocumentPayloadResponse response =
             jsonClient.withExplicitDocumentPayload(c -> c.myDocument(null).accept(AcceptHeader.IMAGE_JPEG));
         String syncRequest = getSyncRequestBody();
-        assertThat(syncRequest).isEmpty();
+        assertThat(syncRequest).isEqualTo("{}");
         SdkHttpRequest sdkHttpRequest = getSyncRequest();
         assertThat(sdkHttpRequest.firstMatchingHeader("accept").get()).contains(AcceptHeader.IMAGE_JPEG.toString());
         assertThat(response.myDocument()).isNull();
@@ -236,7 +236,7 @@ public void explicitDocumentOnlyEmptyPayload() {
         WithExplicitDocumentPayloadResponse response =
             jsonClient.withExplicitDocumentPayload(c -> c.myDocument(null).accept(AcceptHeader.IMAGE_JPEG));
         String syncRequest = getSyncRequestBody();
-        assertThat(syncRequest).isEmpty();
+        assertThat(syncRequest).isEqualTo("{}");
         SdkHttpRequest sdkHttpRequest = getSyncRequest();
         assertThat(sdkHttpRequest.firstMatchingHeader("accept").get()).contains(AcceptHeader.IMAGE_JPEG.toString());
         assertThat(response.myDocument()).isNull();

test/protocol-tests-core/src/main/resources/software/amazon/awssdk/protocol/suites/cases/rest-json-input.json

@@ -59,7 +59,7 @@
     }
   },
   {
-    "description": "Explicit payload member and no parameters marshalls into an empty request body",
+    "description": "Explicit payload member and no parameters marshalls into an empty JSON object",
     "given": {
       "input": {
       }
@@ -71,7 +71,7 @@
     "then": {
       "serializedAs": {
         "body": {
-          "equals": ""
+          "jsonEquals": "{}"
         }
       }
     }