content: // Protocol Buffers - Google's data interchange format
  // Copyright 2013 Google Inc.  All rights reserved.
  // https://developers.google.com/protocol-buffers/
  //
  // Redistribution and use in source and binary forms, with or without
  // modification, are permitted provided that the following conditions are
  // met:
  //
  //     * Redistributions of source code must retain the above copyright
  // notice, this list of conditions and the following disclaimer.
  //     * Redistributions in binary form must reproduce the above
  // copyright notice, this list of conditions and the following disclaimer
  // in the documentation and/or other materials provided with the
  // distribution.
  //     * Neither the name of Google Inc. nor the names of its
  // contributors may be used to endorse or promote products derived from
  // this software without specific prior written permission.
  //
  // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  
  package com.google.protobuf.nano;
  
  import java.io.IOException;
  
  /**
   * Base class of those Protocol Buffer messages that need to store unknown fields,
   * such as extensions.
   */
  public abstract class ExtendableMessageNano<M extends ExtendableMessageNano<M>>
          extends MessageNano {
      /**
       * A container for fields unknown to the message, including extensions. Extension fields can
       * can be accessed through the {@link #getExtension} and {@link #setExtension} methods.
       */
      protected FieldArray unknownFieldData;
  
      @Override
      protected int computeSerializedSize() {
          int size = 0;
          if (unknownFieldData != null) {
              for (int i = 0; i < unknownFieldData.size(); i++) {
                  FieldData field = unknownFieldData.dataAt(i);
                  size += field.computeSerializedSize();
              }
          }
          return size;
      }
  
      @Override
      public void writeTo(CodedOutputByteBufferNano output) throws IOException {
          if (unknownFieldData == null) {
              return;
          }
          for (int i = 0; i < unknownFieldData.size(); i++) {
              FieldData field = unknownFieldData.dataAt(i);
              field.writeTo(output);
          }
      }
  
      /**
       * Checks if there is a value stored for the specified extension in this
       * message.
       */
      public final boolean hasExtension(Extension<M, ?> extension) {
          if (unknownFieldData == null) {
              return false;
          }
          FieldData field = unknownFieldData.get(WireFormatNano.getTagFieldNumber(extension.tag));
          return field != null;
      }
  
      /**
       * Gets the value stored in the specified extension of this message.
       */
      public final <T> T getExtension(Extension<M, T> extension) {
          if (unknownFieldData == null) {
              return null;
          }
          FieldData field = unknownFieldData.get(WireFormatNano.getTagFieldNumber(extension.tag));
          return field == null ? null : field.getValue(extension);
      }
  
      /**
       * Sets the value of the specified extension of this message.
       */
      public final <T> M setExtension(Extension<M, T> extension, T value) {
          int fieldNumber = WireFormatNano.getTagFieldNumber(extension.tag);
          if (value == null) {
              if (unknownFieldData != null) {
                  unknownFieldData.remove(fieldNumber);
                  if (unknownFieldData.isEmpty()) {
                      unknownFieldData = null;
                  }
              }
          } else {
              FieldData field = null;
              if (unknownFieldData == null) {
                  unknownFieldData = new FieldArray();
              } else {
                  field = unknownFieldData.get(fieldNumber);
              }
              if (field == null) {
                  unknownFieldData.put(fieldNumber, new FieldData(extension, value));
              } else {
                  field.setValue(extension, value);
              }
          }
  
          @SuppressWarnings("unchecked") // Generated code should guarantee type safety
          M typedThis = (M) this;
          return typedThis;
      }
  
      /**
       * Stores the binary data of an unknown field.
       *
       * <p>Generated messages will call this for unknown fields if the store_unknown_fields
       * option is on.
       *
       * <p>Note that the tag might be a end-group tag (rather than the start of an unknown field) in
       * which case we do not want to add an unknown field entry.
       *
       * @param input the input buffer.
       * @param tag the tag of the field.
  
       * @return {@literal true} unless the tag is an end-group tag.
       */
      protected final boolean storeUnknownField(CodedInputByteBufferNano input, int tag)
              throws IOException {
          int startPos = input.getPosition();
          if (!input.skipField(tag)) {
              return false;  // This wasn't an unknown field, it's an end-group tag.
          }
          int fieldNumber = WireFormatNano.getTagFieldNumber(tag);
          int endPos = input.getPosition();
          byte[] bytes = input.getData(startPos, endPos - startPos);
          UnknownFieldData unknownField = new UnknownFieldData(tag, bytes);
  
          FieldData field = null;
          if (unknownFieldData == null) {
              unknownFieldData = new FieldArray();
          } else {
              field = unknownFieldData.get(fieldNumber);
          }
          if (field == null) {
              field = new FieldData();
              unknownFieldData.put(fieldNumber, field);
          }
          field.addUnknownField(unknownField);
          return true;
      }
  
      @Override
      public M clone() throws CloneNotSupportedException {
          M cloned = (M) super.clone();
          InternalNano.cloneUnknownFieldData(this, cloned);
          return cloned;
      }
  }
  