Protobuf: Enhance textual content-types detection (#444)

- Move content-type introspection in a separate support class.
- Add unit tests to ensure introspection is correct.

Signed-off-by: Day, Jeremy(jday) <jday@paypal.com>

formats/protobuf/src/main/java/io/cloudevents/protobuf/ProtoSerializer.java

@@ -77,15 +77,6 @@ public static CloudEvent toProto(io.cloudevents.CloudEvent ce) throws InvalidPro
         }
     }
 
-    // The proto spec says all text data should go into the text field. It is really difficult to figure out every case
-    // of text data based on the media type though, so I am just going to check for some common cases.
-    private static boolean isTextType(String type) {
-        if (type == null) {
-            return false;
-        }
-        return type.startsWith("text/") || "application/json".equals(type) || "application/xml".equals(type);
-    }
-
     /**
      * Defines a {@link CloudEventContextWriter} that will allow setting the attributes within a Protobuf object.
      */
@@ -272,9 +263,16 @@ public CloudEvent end(CloudEventData data) throws CloudEventRWException {
                             throw CloudEventRWException.newDataConversion(e, "byte[]", "com.google.protobuf.Any");
                         }
                         protoBuilder.setProtoData(dataAsAny);
-                    } else if (isTextType(dataContentType)) {
+                    } else if (ProtoSupport.isTextContent(dataContentType)) {
+                        /**
+                         * The protobuf format specification states that textual data must
+                         * be carried in the 'text_data' field.
+                         */
                         protoBuilder.setTextDataBytes(ByteString.copyFrom(data.toBytes()));
                     } else {
+                        /**
+                         * All other content is assumed to be binary.
+                         */
                         ByteString byteString = ByteString.copyFrom(data.toBytes());
                         protoBuilder.setBinaryData(byteString);
                     }

formats/protobuf/src/main/java/io/cloudevents/protobuf/ProtoSupport.java

@@ -0,0 +1,47 @@
+/*
+ * Copyright 2018-Present The CloudEvents Authors
+ * <p>
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * <p>
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * <p>
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License 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 io.cloudevents.protobuf;
+
+/**
+ * General support functions.
+ */
+
+final class ProtoSupport {
+
+    // Prevent Instantiation
+    private ProtoSupport() {
+    }
+
+    /**
+     * Determine if the given content type indicates that
+     * content is textual.
+     */
+    static boolean isTextContent(String contentType) {
+
+        if (contentType == null) {
+            return false;
+        }
+
+        return contentType.startsWith("text/")
+            || "application/json".equals(contentType)
+            || "application/xml".equals(contentType)
+            || contentType.endsWith("+json")
+            || contentType.endsWith("+xml")
+            ;
+    }
+}

formats/protobuf/src/test/java/io/cloudevents/protobuf/ProtoSupportTest.java

@@ -0,0 +1,49 @@
+/*
+ * Copyright 2018-Present The CloudEvents Authors
+ * <p>
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * <p>
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * <p>
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License 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 io.cloudevents.protobuf;
+
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+
+import java.io.IOException;
+import java.util.stream.Stream;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class ProtoSupportTest {
+
+    @ParameterizedTest
+    @MethodSource("textContentArguments")
+    public void serialize(String contentType, boolean isText) throws IOException {
+
+        assertThat(isText).isEqualTo(ProtoSupport.isTextContent(contentType));
+    }
+
+    // Test Data set for contentType text determination.
+    public static Stream<Arguments> textContentArguments() {
+        return Stream.of(
+            Arguments.of("application/json", true),
+            Arguments.of("application/xml", true),
+            Arguments.of("text/plain", true),
+            Arguments.of("application/protobuf", false),
+            Arguments.of("application/fubar+xml", true),
+            Arguments.of("application/fubar+json", true)
+        );
+    }
+}