Support IObservable input/output (#236)

Author: mgravell

src/protobuf-net.Grpc/Configuration/ServerBinder.cs

@@ -52,7 +52,7 @@ public int Bind(object state, Type serviceType, BinderConfiguration? binderConfi
                 var bindCtx = new ServiceBindContext(serviceContract, serviceType, state, binderConfiguration.Binder);
                 foreach (var op in ContractOperation.FindOperations(binderConfiguration, serviceContract, this))
                 {
-                    if (ServerInvokerLookup.TryGetValue(op.MethodType, op.Context, op.Result, op.Void, out var invoker)
+                    if (ServerInvokerLookup.TryGetValue(op.MethodType, op.Context, op.Arg, op.Result, op.Void, out var invoker)
                         && AddMethod(op.From, op.To, op.Name, op.Method, op.MethodType, invoker, bindCtx,
                         serviceContractSimplifiedExceptions || op.Method.IsDefined(typeof(SimpleRpcExceptionsAttribute))
                         ))

src/protobuf-net.Grpc/Internal/ContractOperation.cs

@@ -73,9 +73,10 @@ internal void SetTrailers(RpcException fault)
             }
         }
 
-        internal void SetTrailers<T>(T call, Func<T, Status> getStatus, Func<T, Metadata> getMetadata)
+        internal void SetTrailers<T>(T? call, Func<T, Status> getStatus, Func<T, Metadata> getMetadata)
             where T : class
         {
+            if (call is null) return;
             try
             {
                 _trailers = getMetadata(call) ?? Metadata.Empty;
@@ -88,10 +89,15 @@ internal void SetTrailers<T>(T call, Func<T, Status> getStatus, Func<T, Metadata
             }
         }
 
-        internal ValueTask SetHeadersAsync(Task<Metadata> headers)
+        internal ValueTask SetHeadersAsync(Task<Metadata>? headers)
         {
+            if (headers is null) return default;
             var tcs = Interlocked.CompareExchange(ref _headersTaskOrSource, headers, null) as TaskCompletionSource<Metadata>;
-            if (headers.RanToCompletion())
+            if (tcs is null)
+            {
+                return new ValueTask(headers);
+            }
+            else if (headers.RanToCompletion())
             {
                 // headers are sync; update TCS if one
                 tcs?.TrySetResult(headers.Result);
@@ -103,11 +109,11 @@ internal ValueTask SetHeadersAsync(Task<Metadata> headers)
                 return Awaited(this, tcs, headers);
             }
 
-            static async ValueTask Awaited(MetadataContext context, TaskCompletionSource<Metadata>? tcs, Task<Metadata> headers)
+            static async ValueTask Awaited(MetadataContext context, TaskCompletionSource<Metadata> tcs, Task<Metadata> headers)
             {
                 try
                 {
-                    tcs?.TrySetResult(await headers.ConfigureAwait(false));
+                    tcs.TrySetResult(await headers.ConfigureAwait(false));
                 }
                 catch (RpcException fault)
                 {