content: // Protocol Buffers - Google's data interchange format
  // Copyright 2008 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;
  
  import java.io.IOException;
  
  @ExperimentalApi
  abstract class UnknownFieldSchema<T, B> {
  
    /** Whether unknown fields should be dropped. */
    abstract boolean shouldDiscardUnknownFields(Reader reader);
  
    /** Adds a varint value to the unknown fields. */
    abstract void addVarint(B fields, int number, long value);
  
    /** Adds a fixed32 value to the unknown fields. */
    abstract void addFixed32(B fields, int number, int value);
  
    /** Adds a fixed64 value to the unknown fields. */
    abstract void addFixed64(B fields, int number, long value);
  
    /** Adds a length delimited value to the unknown fields. */
    abstract void addLengthDelimited(B fields, int number, ByteString value);
  
    /** Adds a group value to the unknown fields. */
    abstract void addGroup(B fields, int number, T subFieldSet);
  
    /** Create a new builder for unknown fields. */
    abstract B newBuilder();
  
    /** Returns an immutable instance of the field container. */
    abstract T toImmutable(B fields);
  
    /**
     * Sets the unknown fields into the message. Caller must take care of the mutability of the
     * fields.
     */
    abstract void setToMessage(Object message, T fields);
  
    /** Get the unknown fields from the message. */
    abstract T getFromMessage(Object message);
  
    /** Returns a builder for unknown fields in the message. */
    abstract B getBuilderFromMessage(Object message);
  
    /** Sets an unknown field builder into the message. */
    abstract void setBuilderToMessage(Object message, B builder);
  
    /** Marks unknown fields as immutable. */
    abstract void makeImmutable(Object message);
  
    /** Merges one field into the unknown fields. */
    final boolean mergeOneFieldFrom(B unknownFields, Reader reader) throws IOException {
      int tag = reader.getTag();
      int fieldNumber = WireFormat.getTagFieldNumber(tag);
      switch (WireFormat.getTagWireType(tag)) {
        case WireFormat.WIRETYPE_VARINT:
          addVarint(unknownFields, fieldNumber, reader.readInt64());
          return true;
        case WireFormat.WIRETYPE_FIXED32:
          addFixed32(unknownFields, fieldNumber, reader.readFixed32());
          return true;
        case WireFormat.WIRETYPE_FIXED64:
          addFixed64(unknownFields, fieldNumber, reader.readFixed64());
          return true;
        case WireFormat.WIRETYPE_LENGTH_DELIMITED:
          addLengthDelimited(unknownFields, fieldNumber, reader.readBytes());
          return true;
        case WireFormat.WIRETYPE_START_GROUP:
          final B subFields = newBuilder();
          int endGroupTag = WireFormat.makeTag(fieldNumber, WireFormat.WIRETYPE_END_GROUP);
          mergeFrom(subFields, reader);
          if (endGroupTag != reader.getTag()) {
            throw InvalidProtocolBufferException.invalidEndTag();
          }
          addGroup(unknownFields, fieldNumber, toImmutable(subFields));
          return true;
        case WireFormat.WIRETYPE_END_GROUP:
          return false;
        default:
          throw InvalidProtocolBufferException.invalidWireType();
      }
    }
  
    final void mergeFrom(B unknownFields, Reader reader) throws IOException {
      while (true) {
        if (reader.getFieldNumber() == Reader.READ_DONE
            || !mergeOneFieldFrom(unknownFields, reader)) {
          break;
        }
      }
    }
  
    abstract void writeTo(T unknownFields, Writer writer) throws IOException;
  
    abstract void writeAsMessageSetTo(T unknownFields, Writer writer) throws IOException;
  
    /** Merges {@code source} into {@code destination} and returns the merged instance. */
    abstract T merge(T destination, T source);
  
    /** Get the serialized size for message set serialization. */
    abstract int getSerializedSizeAsMessageSet(T message);
  
    abstract int getSerializedSize(T unknowns);
  }
  