The header mapper for spec 0.3

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

api/src/main/java/io/cloudevents/v03/http/BinaryFormatHeaderMapperImpl.java

@@ -0,0 +1,66 @@
+/**
+ * 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.v03.http;
+
+import static io.cloudevents.v02.http.BinaryFormatAttributeMapperImpl.HEADER_PREFIX;
+
+import java.util.Locale;
+import java.util.Map;
+import java.util.Objects;
+import java.util.AbstractMap.SimpleEntry;
+import java.util.Map.Entry;
+import java.util.stream.Collectors;
+
+import io.cloudevents.v03.ContextAttributes;
+
+/**
+ * 
+ * @author fabiojose
+ *
+ */
+public class BinaryFormatHeaderMapperImpl {
+	private BinaryFormatHeaderMapperImpl() {}
+
+	public static Map<String, Object> map(Map<String, String> attributes,
+			Map<String, String> extensions) {
+		Objects.requireNonNull(attributes);
+		Objects.requireNonNull(extensions);
+		
+		Map<String, Object> result = attributes.entrySet()
+			.stream()
+			.map(header -> new SimpleEntry<>(header.getKey()
+					.toLowerCase(Locale.US), header.getValue()))
+			.filter(header -> !header.getKey()
+					.equals(ContextAttributes.datacontenttype.name()))
+			.map(header -> new SimpleEntry<>(HEADER_PREFIX+header.getKey(),
+					header.getValue()))
+			.collect(Collectors.toMap(Entry::getKey, Entry::getValue));
+		
+		result.putAll(
+			extensions.entrySet()
+				.stream()
+				.map(header -> new SimpleEntry<>(HEADER_PREFIX+header.getKey(),
+						header.getValue()))
+				.collect(Collectors.toMap(Entry::getKey, Entry::getValue))
+		);
+		
+		result.put("Content-Type", attributes
+				.get(ContextAttributes.datacontenttype.name()));
+		
+		return result;
+	}
+
+}