src/csharp/Grpc.Core/Marshaller.cs

#region Copyright notice and license

// Copyright 2015 gRPC authors.
//
// Licensed 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.

#endregion

using System;
using Grpc.Core.Utils;

namespace Grpc.Core
{
    /// <summary>
    /// Encapsulates the logic for serializing and deserializing messages.
    /// </summary>
    public class Marshaller<T>
    {
        readonly Func<T, byte[]> serializer;
        readonly Func<byte[], T> deserializer;

        readonly Action<T, SerializationContext> contextualSerializer;
        readonly Func<DeserializationContext, T> contextualDeserializer;

        /// <summary>
        /// Initializes a new marshaller from simple serialize/deserialize functions.
        /// </summary>
        /// <param name="serializer">Function that will be used to serialize messages.</param>
        /// <param name="deserializer">Function that will be used to deserialize messages.</param>
        public Marshaller(Func<T, byte[]> serializer, Func<byte[], T> deserializer)
        {
            this.serializer = GrpcPreconditions.CheckNotNull(serializer, nameof(serializer));
            this.deserializer = GrpcPreconditions.CheckNotNull(deserializer, nameof(deserializer));
            this.contextualSerializer = EmulateContextualSerializer;
            this.contextualDeserializer = EmulateContextualDeserializer;
        }

        /// <summary>
        /// Initializes a new marshaller from serialize/deserialize fuctions that can access serialization and deserialization
        /// context. Compared to the simple serializer/deserializer functions, using the contextual version provides more
        /// flexibility and can lead to increased efficiency (and better performance).
        /// Note: This constructor is part of an experimental API that can change or be removed without any prior notice.
        /// </summary>
        /// <param name="serializer">Function that will be used to serialize messages.</param>
        /// <param name="deserializer">Function that will be used to deserialize messages.</param>
        public Marshaller(Action<T, SerializationContext> serializer, Func<DeserializationContext, T> deserializer)
        {
            this.contextualSerializer = GrpcPreconditions.CheckNotNull(serializer, nameof(serializer));
            this.contextualDeserializer = GrpcPreconditions.CheckNotNull(deserializer, nameof(deserializer));
            // TODO(jtattermusch): once gRPC C# library switches to using contextual (de)serializer,
            // emulating the simple (de)serializer will become unnecessary.
            this.serializer = EmulateSimpleSerializer;
            this.deserializer = EmulateSimpleDeserializer;
        }

        /// <summary>
        /// Gets the serializer function.
        /// </summary>
        public Func<T, byte[]> Serializer => this.serializer;

        /// <summary>
        /// Gets the deserializer function.
        /// </summary>
        public Func<byte[], T> Deserializer => this.deserializer;

        /// <summary>
        /// Gets the serializer function.
        /// Note: experimental API that can change or be removed without any prior notice.
        /// </summary>
        public Action<T, SerializationContext> ContextualSerializer => this.contextualSerializer;

        /// <summary>
        /// Gets the serializer function.
        /// Note: experimental API that can change or be removed without any prior notice.
        /// </summary>
        public Func<DeserializationContext, T> ContextualDeserializer => this.contextualDeserializer;

        // for backward compatibility, emulate the simple serializer using the contextual one
        private byte[] EmulateSimpleSerializer(T msg)
        {
            // TODO(jtattermusch): avoid the allocation by passing a thread-local instance
            // This code will become unnecessary once gRPC C# library switches to using contextual (de)serializer.
            var context = new EmulatedSerializationContext();
            this.contextualSerializer(msg, context);
            return context.GetPayload();
        }

        // for backward compatibility, emulate the simple deserializer using the contextual one
        private T EmulateSimpleDeserializer(byte[] payload)
        {
            // TODO(jtattermusch): avoid the allocation by passing a thread-local instance
            // This code will become unnecessary once gRPC C# library switches to using contextual (de)serializer.
            var context = new EmulatedDeserializationContext(payload);
            return this.contextualDeserializer(context);
        }

        // for backward compatibility, emulate the contextual serializer using the simple one
        private void EmulateContextualSerializer(T message, SerializationContext context)
        {
            var payload = this.serializer(message);
            context.Complete(payload);
        }

        // for backward compatibility, emulate the contextual deserializer using the simple one
        private T EmulateContextualDeserializer(DeserializationContext context)
        {
            return this.deserializer(context.PayloadAsNewBuffer());
        }

        internal class EmulatedSerializationContext : SerializationContext
        {
            bool isComplete;
            byte[] payload;

            public override void Complete(byte[] payload)
            {
                GrpcPreconditions.CheckState(!isComplete);
                this.isComplete = true;
                this.payload = payload;
            }

            internal byte[] GetPayload()
            {
                return this.payload;
            }
        }

        internal class EmulatedDeserializationContext : DeserializationContext
        {
            readonly byte[] payload;
            bool alreadyCalledPayloadAsNewBuffer;

            public EmulatedDeserializationContext(byte[] payload)
            {
                this.payload = GrpcPreconditions.CheckNotNull(payload);
            }

            public override int PayloadLength => payload.Length;

            public override byte[] PayloadAsNewBuffer()
            {
                GrpcPreconditions.CheckState(!alreadyCalledPayloadAsNewBuffer);
                alreadyCalledPayloadAsNewBuffer = true;
                return payload;
            }
        }
    }

    /// <summary>
    /// Utilities for creating marshallers.
    /// </summary>
    public static class Marshallers
    {
        /// <summary>
        /// Creates a marshaller from specified serializer and deserializer.
        /// </summary>
        public static Marshaller<T> Create<T>(Func<T, byte[]> serializer, Func<byte[], T> deserializer)
        {
            return new Marshaller<T>(serializer, deserializer);
        }

        /// <summary>
        /// Creates a marshaller from specified contextual serializer and deserializer.
        /// Note: This method is part of an experimental API that can change or be removed without any prior notice.
        /// </summary>
        public static Marshaller<T> Create<T>(Action<T, SerializationContext> serializer, Func<DeserializationContext, T> deserializer)
        {
            return new Marshaller<T>(serializer, deserializer);
        }

        /// <summary>
        /// Returns a marshaller for <c>string</c> type. This is useful for testing.
        /// </summary>
        public static Marshaller<string> StringMarshaller
        {
            get
            {
                return new Marshaller<string>(System.Text.Encoding.UTF8.GetBytes,
                                              System.Text.Encoding.UTF8.GetString);
            }
        }
    }
}