Switch to ValueTask for async methods

We only have CompleteAsync and RunAsync on IWebSocketPipe, but since the underlying primitives we invoke on either the pipe reader/writer or websocket, all return ValueTask to avoid allocations, we might as well follow suit.

Background: https://devblogs.microsoft.com/dotnet/understanding-the-whys-whats-and-whens-of-valuetask/

Fixes #3

src/Tests/SimpleWebSocketPipeTests.cs

@@ -12,7 +12,7 @@ public record SimpleWebSocketPipeTests(ITestOutputHelper Output)
         public async Task WhenWebSocketNotOpen_ThenThrowsAsync()
         {
             IWebSocketPipe pipe = WebSocketPipe.Create(new ClientWebSocket());
-            await Assert.ThrowsAsync<InvalidOperationException>(() => pipe.RunAsync());
+            await Assert.ThrowsAsync<InvalidOperationException>(() => pipe.RunAsync().AsTask());
         }
 
         [Fact]
@@ -26,7 +26,7 @@ public async Task WhenConnected_ThenRuns()
             using var pipe = WebSocketPipe.Create(socket);
 
             await Task.WhenAll(
-                pipe.RunAsync(server.Cancellation.Token),
+                pipe.RunAsync(server.Cancellation.Token).AsTask(),
                 Task.Delay(100).ContinueWith(_ => server.Cancellation.Cancel()));
         }
 
@@ -41,7 +41,9 @@ public async Task WhenServerClosesWebSocket_ThenClientCompletesGracefully()
 
             await server.DisposeAsync();
 
-            Task.WaitAny(run, Task.Delay(100).ContinueWith(_ => throw new TimeoutException()));
+            Task.WaitAny(
+                run.AsTask(),
+                Task.Delay(100).ContinueWith(_ => throw new TimeoutException()));
         }
 
         [Fact]

src/Tests/WebSocketServer.cs

@@ -1,5 +1,4 @@
-using System.IO.Pipelines;
-using System.Net;
+using System.Net;
 using System.Net.WebSockets;
 using Xunit.Abstractions;
 
@@ -52,7 +51,7 @@ static WebSocketServer Create(Func<IWebSocketPipe, Task>? pipeBehavior, Func<Web
                     if (pipeBehavior != null)
                     {
                         using var pipe = WebSocketPipe.Create(websocket, options);
-                        await Task.WhenAll(pipeBehavior(pipe), pipe.RunAsync(cts.Token));
+                        await Task.WhenAll(pipeBehavior(pipe), pipe.RunAsync(cts.Token).AsTask());
                     }
                     else if (socketBehavior != null)
                     {

src/WebSocketPipe/IWebSocketPipe.cs

@@ -41,7 +41,7 @@ public interface IWebSocketPipe : IDuplexPipe, IDisposable
         /// <param name="closeStatusDescription">Optional close status description to use if the underlying 
         /// <see cref="WebSocket"/> is closed.</param>
         /// <returns></returns>
-        public Task CompleteAsync(WebSocketCloseStatus? closeStatus = null, string? closeStatusDescription = null);
+        public ValueTask CompleteAsync(WebSocketCloseStatus? closeStatus = null, string? closeStatusDescription = null);
 
         /// <summary>
         /// Starts populating the <see cref="IDuplexPipe.Input"/> with incoming data from the underlying 
@@ -54,6 +54,6 @@ public interface IWebSocketPipe : IDuplexPipe, IDisposable
         /// <see cref="IDuplexPipe.Output"/> are completed, or an explicit invocation of <see cref="CompleteAsync"/> 
         /// is executed.
         /// </returns>
-        public Task RunAsync(CancellationToken cancellation = default);
+        public ValueTask RunAsync(CancellationToken cancellation = default);
     }
 }

src/WebSocketPipe/SimpleWebSocketPipe.cs

@@ -41,7 +41,7 @@ public SimpleWebSocketPipe(WebSocket webSocket, WebSocketPipeOptions options)
 
         public string? SubProtocol => webSocket.SubProtocol;
 
-        public async Task RunAsync(CancellationToken cancellation = default)
+        public async ValueTask RunAsync(CancellationToken cancellation = default)
         {
             if (webSocket.State != WebSocketState.Open)
                 throw new InvalidOperationException($"WebSocket must be opened. State was {webSocket.State}");
@@ -51,10 +51,13 @@ public async Task RunAsync(CancellationToken cancellation = default)
 
             // NOTE: when both are completed, the CompleteAsync will be called automatically 
             // by both writing and reading, so we ensure CloseWhenCompleted is performed.
-            await Task.WhenAll(reading, writing);
+
+            // TODO: replace with ValueTask.WhenAll if/when it ships. 
+            // See https://github.com/dotnet/runtime/issues/23625
+            await Task.WhenAll(reading.AsTask(), writing.AsTask());
         }
 
-        public async Task CompleteAsync(WebSocketCloseStatus? closeStatus = null, string? closeStatusDescription = null)
+        public async ValueTask CompleteAsync(WebSocketCloseStatus? closeStatus = null, string? closeStatusDescription = null)
         {
             if (completed)
                 return;
@@ -87,7 +90,7 @@ async ValueTask CloseAsync(WebSocketCloseStatus closeStatus, string closeStatusD
             await Task.WhenAny(closeTask, Task.Delay(closeTimeout));
         }
 
-        async Task FillInputAsync(CancellationToken cancellation)
+        async ValueTask FillInputAsync(CancellationToken cancellation)
         {
             while (webSocket.State == WebSocketState.Open && !cancellation.IsCancellationRequested)
             {
@@ -126,7 +129,7 @@ ex is WebSocketException ||
             await CompleteAsync(webSocket.CloseStatus, webSocket.CloseStatusDescription);
         }
 
-        async Task SendOutputAsync(CancellationToken cancellation)
+        async ValueTask SendOutputAsync(CancellationToken cancellation)
         {
             while (webSocket.State == WebSocketState.Open && !cancellation.IsCancellationRequested)
             {