protobuf/src/ProtocolBuffers/GeneratedExtensionBase.cs

#region Copyright notice and license

// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc.  All rights reserved.
// http://github.com/jskeet/dotnet-protobufs/
// Original C++/Java/Python code:
// http://code.google.com/p/protobuf/
//
// 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.

#endregion

using System;
using System.Collections;
using System.Collections.Generic;
using System.Reflection;
using Google.ProtocolBuffers.Descriptors;

namespace Google.ProtocolBuffers
{
    /// <summary>
    /// Base type for all generated extensions.
    /// </summary>
    /// <remarks>
    /// The protocol compiler generates a static singleton instance of this
    /// class for each extension. For exmaple, imagine a .proto file with:
    /// <code>
    /// message Foo {
    ///   extensions 1000 to max
    /// }
    /// 
    /// extend Foo {
    ///   optional int32 bar;
    /// }
    /// </code>
    /// Then MyProto.Foo.Bar has type GeneratedExtensionBase&lt;MyProto.Foo,int&gt;.
    /// <para />
    /// In general, users should ignore the details of this type, and
    /// simply use the static singletons as parameters to the extension accessors
    /// in ExtendableMessage and ExtendableBuilder.
    /// The interface implemented by both GeneratedException and GeneratedRepeatException,
    /// to make it easier to cope with repeats separately.
    /// </remarks>
    public abstract class GeneratedExtensionBase<TExtension>
    {
        private readonly FieldDescriptor descriptor;
        private readonly IMessageLite messageDefaultInstance;

        protected GeneratedExtensionBase(FieldDescriptor descriptor, Type singularExtensionType)
        {
            if (!descriptor.IsExtension)
            {
                throw new ArgumentException("GeneratedExtension given a regular (non-extension) field.");
            }

            this.descriptor = descriptor;
            if (descriptor.MappedType == MappedType.Message)
            {
                PropertyInfo defaultInstanceProperty = singularExtensionType
                    .GetProperty("DefaultInstance", BindingFlags.Static | BindingFlags.Public);
                if (defaultInstanceProperty == null)
                {
                    throw new ArgumentException("No public static DefaultInstance property for type " +
                                                typeof(TExtension).Name);
                }

                messageDefaultInstance = (IMessageLite) defaultInstanceProperty.GetValue(null, null);
            }
        }

        public FieldDescriptor Descriptor
        {
            get { return descriptor; }
        }

        public int Number
        {
            get { return Descriptor.FieldNumber; }
        }

        /// <summary>
        /// Returns the default message instance for extensions which are message types.
        /// </summary>
        public IMessageLite MessageDefaultInstance
        {
            get { return messageDefaultInstance; }
        }

        public object SingularFromReflectionType(object value)
        {
            switch (Descriptor.MappedType)
            {
                case MappedType.Message:
                    if (value is TExtension)
                    {
                        return value;
                    }
                    else
                    {
                        // It seems the copy of the embedded message stored inside the
                        // extended message is not of the exact type the user was
                        // expecting.  This can happen if a user defines a
                        // GeneratedExtension manually and gives it a different type.
                        // This should not happen in normal use.  But, to be nice, we'll
                        // copy the message to whatever type the caller was expecting.
                        return MessageDefaultInstance.WeakCreateBuilderForType()
                            .WeakMergeFrom((IMessageLite) value).WeakBuild();
                    }
                case MappedType.Enum:
                    // Just return a boxed int - that can be unboxed to the enum
                    EnumValueDescriptor enumValue = (EnumValueDescriptor) value;
                    return enumValue.Number;
                default:
                    return value;
            }
        }

        /// <summary>
        /// Converts from the type used by the native accessors to the type
        /// used by reflection accessors. For example, the reflection accessors
        /// for enums use EnumValueDescriptors but the native accessors use
        /// the generated enum type.
        /// </summary>
        public object ToReflectionType(object value)
        {
            if (descriptor.IsRepeated)
            {
                if (descriptor.MappedType == MappedType.Enum)
                {
                    // Must convert the whole list.
                    IList<object> result = new List<object>();
                    foreach (object element in (IEnumerable) value)
                    {
                        result.Add(SingularToReflectionType(element));
                    }
                    return result;
                }
                else
                {
                    return value;
                }
            }
            else
            {
                return SingularToReflectionType(value);
            }
        }

        /// <summary>
        /// Like ToReflectionType(object) but for a single element.
        /// </summary>
        internal Object SingularToReflectionType(object value)
        {
            return descriptor.MappedType == MappedType.Enum
                       ? descriptor.EnumType.FindValueByNumber((int) value)
                       : value;
        }

        public abstract object FromReflectionType(object value);
    }
}