add mapping function support for rsocket metadata; known use case for routed/brokered rsocket messages

Author: kbahr

RSocket.Rpc.Core/RSocketService.Metadata.cs

@@ -6,7 +6,7 @@ namespace RSocket.RPC
 {
 	partial class RSocketService
 	{
-		public struct RemoteProcedureCallMetadata           //SPEC: https://github.com/rsocket/rsocket-rpc-java/blob/master/rsocket-rpc-core/src/main/java/io/rsocket/rpc/frames/Metadata.java
+        public struct RemoteProcedureCallMetadata           //SPEC: https://github.com/rsocket/rsocket-rpc-java/blob/master/rsocket-rpc-core/src/main/java/io/rsocket/rpc/frames/Metadata.java
 		{
 			public const UInt16 VERSION = 1;
 
@@ -35,6 +35,11 @@ public RemoteProcedureCallMetadata(ReadOnlySequence<byte> metadata)
 				Metadata = reader.Sequence.Slice(reader.Position, reader.Remaining);
 			}
 
+            public static RemoteProcedureCallMetadata create(ReadOnlySequence<byte> metadata)
+            {
+                return new RemoteProcedureCallMetadata(metadata);
+            }
+
 			public static implicit operator ReadOnlySequence<byte>(RemoteProcedureCallMetadata _)
 			{
 				var memory = new Memory<byte>(new byte[_.Length]);      //FUTURE PERFORMANCE: Someday, maybe use a buffer pool instead of allocating. These are presumed small, but the string scan adds some overhead.

RSocket.Rpc.Core/RSocketService.cs

@@ -19,8 +19,7 @@ public abstract partial class RSocketService
 
 		public RSocketService(RSocket socket) { Socket = socket; }
 
-
-		protected Task __RequestFireAndForget<TMessage>(TMessage message, Func<TMessage, byte[]> messagemapper, 
+        protected Task __RequestFireAndForget<TMessage>(TMessage message, Func<TMessage, byte[]> messagemapper, 
 			ReadOnlySequence<byte> metadata = default, ReadOnlySequence<byte> tracing = default, string service = default, [CallerMemberName]string method = default)
 			=> __RequestFireAndForget(new ReadOnlySequence<byte>(messagemapper(message)), metadata, tracing, service: service, method: method);
 
@@ -88,23 +87,24 @@ private protected IAsyncEnumerable<T> __RequestChannel<TMessage, T>(IAsyncEnumer
 
 		static System.Collections.Concurrent.ConcurrentDictionary<string, IRSocketService> Services = new System.Collections.Concurrent.ConcurrentDictionary<string, IRSocketService>();
 
-		static public void Register(RSocket socket, IRSocketService service)
+        static public void Register(RSocket socket, IRSocketService service, Func<ReadOnlySequence<byte>, RSocketService.RemoteProcedureCallMetadata> metadataMapper = null)
 		{
 			Services[service.ServiceName] = service;
 
-			//TODO Need to ensure that this really only happens once per Socket.
+            metadataMapper = metadataMapper ?? RemoteProcedureCallMetadata.create;
+            //TODO Need to ensure that this really only happens once per Socket.
 
-			socket.Respond(message => (RPC: new RSocketService.RemoteProcedureCallMetadata(message.Metadata), message.Data),
+            socket.Respond(message => (RPC: metadataMapper(message.Metadata), message.Data),
 				request => Dispatch(request.Data, request.RPC.Service, request.RPC.Method, request.RPC.Tracing, request.RPC.Metadata),
 				result => (Data: result, Metadata: default));
 
 			//TODO This looks data/metadata backwards?
-			socket.Stream(message => (RPC: new RSocketService.RemoteProcedureCallMetadata(message.Metadata), message.Data),
+			socket.Stream(message => (RPC: metadataMapper(message.Metadata), message.Data),
 				request => Dispatch(request.Data, request.RPC.Service, request.RPC.Method, request.RPC.Tracing, request.RPC.Metadata),
 				result => (Data: result, Metadata: default));
 
 			socket.Channel((request, messages) => Dispatch(request.Data, request.RPC.Service, request.RPC.Method, request.RPC.Tracing, request.RPC.Metadata, messages.ToAsyncEnumerable()),
-				message => (RPC: new RSocketService.RemoteProcedureCallMetadata(message.Metadata), message.Data),
+				message => (RPC: metadataMapper(message.Metadata), message.Data),
 				incoming => incoming.Data,
 				result => (Data: result, Metadata: default));
 		}