[KAFKA-7718] KIP-634 implementation

streams/src/main/java/org/apache/kafka/streams/header/Header.java

@@ -0,0 +1,30 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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 org.apache.kafka.streams.header;
+
+public interface Header {
+    /**
+     * The header's key, which is not necessarily unique within the set of headers on a Kafka message.
+     *
+     * @return the header's key; never null
+     */
+    String key();
+
+    byte[] value();
+
+    String valueAsUtf8();
+}

streams/src/main/java/org/apache/kafka/streams/header/Headers.java

@@ -0,0 +1,142 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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 org.apache.kafka.streams.header;
+
+import java.util.Iterator;
+
+public interface Headers extends Iterable<Header> {
+
+    /**
+     * Get the number of headers in this object.
+     *
+     * @return the number of headers; never negative
+     */
+    int size();
+
+    /**
+     * Determine whether this object has no headers.
+     *
+     * @return true if there are no headers, or false if there is at least one header
+     */
+    boolean isEmpty();
+
+    /**
+     * Get the collection of {@link Header} objects whose {@link Header#key() keys} all match the
+     * specified key.
+     *
+     * @param key the key; may not be null
+     * @return the iterator over headers with the specified key; may be null if there are no headers
+     * with the specified key
+     */
+    Iterator<Header> allWithName(final String key);
+
+    /**
+     * Return the last {@link Header} with the specified key.
+     *
+     * @param key the key for the header; may not be null
+     * @return the last Header, or null if there are no headers with the specified key
+     */
+    Header lastWithName(final String key);
+
+    boolean hasWithName(final String key);
+
+    /**
+     * Add the given {@link Header} to this collection.
+     *
+     * @param header the header; may not be null
+     * @return this object to facilitate chaining multiple methods; never null
+     */
+    Headers add(final Header header);
+
+    Headers add(final String key, final byte[] value);
+
+    Headers addUtf8(final String key, final String value);
+
+    /**
+     * Removes all {@link Header} objects whose {@link Header#key() key} matches the specified key.
+     *
+     * @param key the key; may not be null
+     * @return this object to facilitate chaining multiple methods; never null
+     */
+    Headers remove(final String key);
+
+    /**
+     * Removes all but the latest {@link Header} objects whose {@link Header#key() key} matches the
+     * specified key.
+     *
+     * @param key the key; may not be null
+     * @return this object to facilitate chaining multiple methods; never null
+     */
+    Headers retainLatest(final String key);
+
+    /**
+     * Removes all but the last {@link Header} object with each key.
+     *
+     * @return this object to facilitate chaining multiple methods; never null
+     */
+    Headers retainLatest();
+
+    /**
+     * Removes all headers from this object.
+     *
+     * @return this object to facilitate chaining multiple methods; never null
+     */
+    Headers clear();
+
+    /**
+     * Create a copy of this {@link Headers} object. The new copy will contain all of the same
+     * {@link Header} objects as this object.
+     *
+     * @return the copy; never null
+     */
+    Headers duplicate();
+
+    /**
+     * Get all {@link Header}s, apply the transform to each and store the result in place of the
+     * original.
+     *
+     * @param transform the transform to apply; may not be null
+     * @return this object to facilitate chaining multiple methods; never null
+     */
+    Headers apply(final Headers.HeaderTransform transform);
+
+    /**
+     * Get all {@link Header}s with the given key, apply the transform to each and store the result
+     * in place of the original.
+     *
+     * @param key       the header's key; may not be null
+     * @param transform the transform to apply; may not be null
+     * @return this object to facilitate chaining multiple methods; never null
+     */
+    Headers apply(final String key, final Headers.HeaderTransform transform);
+
+    /**
+     * A function to transform the supplied {@link Header}.
+     */
+    interface HeaderTransform {
+
+        /**
+         * Transform the given {@link Header} and return the updated {@link Header}.
+         *
+         * @param header the input header; never null
+         * @return the new header, or null if the supplied {@link Header} is to be removed
+         */
+        Header apply(final Header header);
+    }
+
+    org.apache.kafka.common.header.Headers unwrap();
+}

streams/src/main/java/org/apache/kafka/streams/header/StreamHeader.java

@@ -0,0 +1,58 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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 org.apache.kafka.streams.header;
+
+import java.util.Arrays;
+import org.apache.kafka.common.utils.Utils;
+
+public class StreamHeader implements Header {
+
+    final String key;
+    final byte[] value;
+
+    public StreamHeader(final String key, final byte[] value) {
+        this.key = key;
+        this.value = value;
+    }
+
+    public static StreamHeader wrap(final org.apache.kafka.common.header.Header header) {
+        return new StreamHeader(header.key(), header.value());
+    }
+
+    @Override
+    public String key() {
+        return key;
+    }
+
+    @Override
+    public byte[] value() {
+        return value;
+    }
+
+    @Override
+    public String valueAsUtf8() {
+        return Utils.utf8(value);
+    }
+
+    @Override
+    public String toString() {
+        return "StreamHeader(" +
+            "key='" + key + '\'' +
+            ",value=" + Arrays.toString(value) +
+            ')';
+    }
+}