new C# serialization API

src/csharp/Grpc.Core/DeserializationContext.cs

@@ -0,0 +1,49 @@
+#region Copyright notice and license
+
+// Copyright 2018 The 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
+
+namespace Grpc.Core
+{
+    /// <summary>
+    /// Provides access to the payload being deserialized when deserializing messages.
+    /// </summary>
+    public abstract class DeserializationContext
+    {
+        /// <summary>
+        /// Returns <c>true</c> if there is a payload to deserialize (= payload is not null), <c>false</c> otherwise.
+        /// </summary>
+        public virtual bool HasPayload => PayloadLength.HasValue;
+
+        /// <summary>
+        /// Get the total length of the payload in bytes or <c>null</c> if the payload is null.
+        /// </summary>
+        public abstract int? PayloadLength { get; }
+
+        /// <summary>
+        /// Gets the entire payload as a newly allocated byte array.
+        /// Once the byte array is returned, the byte array becomes owned by the caller and won't be ever accessed or reused by gRPC again.
+        /// NOTE: Obtaining the buffer as a newly allocated byte array is the simplest way of accessing the payload,
+        /// but it can have important consequences in high-performance scenarios.
+        /// In particular, using this method usually requires copying of the entire buffer one extra time.
+        /// Also, allocating a new buffer each time can put excessive pressure on GC, especially if
+        /// the payload is more than 86700 bytes large (which means the newly allocated buffer will be placed in LOH,
+        /// and LOH object can only be garbage collected via a full ("stop the world") GC run).
+        /// </summary>
+        /// <returns>byte array containing the entire payload or null if there is no payload.</returns>
+        public abstract byte[] PayloadAsNewBuffer();
+    }
+}

src/csharp/Grpc.Core/Marshaller.cs

@@ -29,36 +29,122 @@ namespace Grpc.Core
         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.
+        /// 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, "serializer");
-            this.deserializer = GrpcPreconditions.CheckNotNull(deserializer, "deserializer");
+            this.serializer = GrpcPreconditions.CheckNotNull(serializer, nameof(serializer));
+            this.deserializer = GrpcPreconditions.CheckNotNull(deserializer, nameof(deserializer));
+            this.contextualSerializer = EmulateContextualSerializer;
+            this.contextualDeserializer = EmulateContextualDeserializer;
         }
 
         /// <summary>
-        /// Gets the serializer function.
+        /// 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>
-        public Func<T, byte[]> Serializer
+        /// <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)
         {
-            get
-            {
-                return this.serializer;
-            }
+            this.contextualSerializer = GrpcPreconditions.CheckNotNull(serializer, nameof(serializer));
+            this.contextualDeserializer = GrpcPreconditions.CheckNotNull(deserializer, nameof(deserializer));
+            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
+        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)
         {
-            get
+            // TODO(jtattermusch): avoid the allocation by passing a thread-local instance
+            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
+            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;
+
+            public EmulatedDeserializationContext(byte[] payload)
+            {
+                this.payload = payload;
+            }
+
+            public override int? PayloadLength => payload?.Length;
+
+            public override byte[] PayloadAsNewBuffer()
             {
-                return this.deserializer;
+                return payload;
             }
         }
     }

src/csharp/Grpc.Core/SerializationContext.cs

@@ -0,0 +1,34 @@
+#region Copyright notice and license
+
+// Copyright 2018 The 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
+
+namespace Grpc.Core
+{
+    /// <summary>
+    /// Provides storage for payload when serializing a message.
+    /// </summary>
+    public abstract class SerializationContext
+    {
+        /// <summary>
+        /// Use the byte array as serialized form of current message and mark serialization process as complete.
+        /// Complete() can only be called once. By calling this method the caller gives up the ownership of the
+        /// payload which must not be accessed afterwards.
+        /// </summary>
+        /// <param name="payload">the serialized form of current message</param>
+        public abstract void Complete(byte[] payload);
+    }
+}