Turns a map o extensions into instances of ExtensionFormat

Signed-off-by: Fabio José <fabiojose@gmail.com>

api/src/main/java/io/cloudevents/fun/ExtensionUmarshaller.java

@@ -0,0 +1,38 @@
+/**
+ * Copyright 2019 The CloudEvents Authors
+ *
+ * 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
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * 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.fun;
+
+import java.util.Map;
+import java.util.Optional;
+
+import io.cloudevents.extensions.ExtensionFormat;
+
+/**
+ * 
+ * @author fabiojose
+ *
+ */
+@FunctionalInterface
+public interface ExtensionUmarshaller {
+
+	/**
+	 * Unmarshals the map of extensions into {@link ExtensionFormat}
+	 * @param extensions
+	 * @return
+	 */
+	Optional<ExtensionFormat> unmarshal(Map<String, String> extensions);
+	
+}