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;
  import java.util.Map;
  
  abstract class ExtensionSchema<T extends FieldSet.FieldDescriptorLite<T>> {
  
    /** Returns true for messages that support extensions. */
    abstract boolean hasExtensions(MessageLite prototype);
  
    /** Returns the extension {@link FieldSet} for the message instance. */
    abstract FieldSet<T> getExtensions(Object message);
  
    /** Replaces the extension {@link FieldSet} for the message instance. */
    abstract void setExtensions(Object message, FieldSet<T> extensions);
  
    /** Returns the extension {@link FieldSet} and ensures it's mutable. */
    abstract FieldSet<T> getMutableExtensions(Object message);
  
    /** Marks the extension {@link FieldSet} as immutable. */
    abstract void makeImmutable(Object message);
  
    /**
     * Parses an extension. Returns the passed-in unknownFields parameter if no unknown enum value is
     * found or a modified unknownFields (a new instance if the passed-in unknownFields is null)
     * containing unknown enum values found while parsing.
     *
     * @param <UT> The type used to store unknown fields. It's either UnknownFieldSet in full runtime
     *     or UnknownFieldSetLite in lite runtime.
     */
    abstract <UT, UB> UB parseExtension(
        Reader reader,
        Object extension,
        ExtensionRegistryLite extensionRegistry,
        FieldSet<T> extensions,
        UB unknownFields,
        UnknownFieldSchema<UT, UB> unknownFieldSchema)
        throws IOException;
  
    /** Gets the field number of an extension entry. */
    abstract int extensionNumber(Map.Entry<?, ?> extension);
  
    /** Serializes one extension entry. */
    abstract void serializeExtension(Writer writer, Map.Entry<?, ?> extension) throws IOException;
  
    /** Finds an extension by field number. */
    abstract Object findExtensionByNumber(
        ExtensionRegistryLite extensionRegistry, MessageLite defaultInstance, int number);
  
    /** Parses a length-prefixed MessageSet item from the reader. */
    abstract void parseLengthPrefixedMessageSetItem(
        Reader reader,
        Object extension,
        ExtensionRegistryLite extensionRegistry,
        FieldSet<T> extensions)
        throws IOException;
  
    /**
     * Parses the entire content of a {@link ByteString} as one MessageSet item. Unlike {@link
     * #parseLengthPrefixedMessageSetItem}, there isn't a length-prefix.
     */
    abstract void parseMessageSetItem(
        ByteString data,
        Object extension,
        ExtensionRegistryLite extensionRegistry,
        FieldSet<T> extensions)
        throws IOException;
  }
  