[WASI] fix response header conversion and event loop

src/libraries/System.Net.Http/src/System/Net/Http/WasiHttpHandler/WasiHttpHandler.cs

@@ -54,15 +54,14 @@ public async Task<HttpResponseMessage> SendRequestAsync(HttpRequestMessage reque
                 cancellationToken.ThrowIfCancellationRequested();
 
                 var response = new HttpResponseMessage((HttpStatusCode)incomingResponse.Status());
-                WasiHttpInterop.ConvertResponseHeaders(incomingResponse, response);
-
 
                 // request body could be still streaming after response headers are received and started streaming response
                 // we will leave scope of this method
                 // we need to pass the ownership of the request and this wrapper to the response (via response content stream)
                 // unless we know that we are not streaming anymore
                 incomingStream = new WasiInputStream(this, incomingResponse.Consume());// passing self ownership, passing body ownership
                 response.Content = new StreamContent(incomingStream); // passing incomingStream ownership to SendAsync() caller
+                WasiHttpInterop.ConvertResponseHeaders(incomingResponse, response);
 
                 return response;
             }

src/libraries/System.Private.CoreLib/src/System/Threading/Wasi/WasiEventLoop.cs

@@ -14,6 +14,7 @@ internal static class WasiEventLoop
         // it will be leaked and stay in this list forever.
         // it will also keep the Pollable handle alive and prevent it from being disposed
         private static readonly List<PollableHolder> s_pollables = new();
+        private static bool s_tasksCanceled;
 
         internal static Task RegisterWasiPollableHandle(int handle, CancellationToken cancellationToken)
         {
@@ -35,6 +36,11 @@ internal static Task RegisterWasiPollable(Pollable pollable, CancellationToken c
         internal static void DispatchWasiEventLoop()
         {
             ThreadPoolWorkQueue.Dispatch();
+            if (s_tasksCanceled)
+            {
+                s_tasksCanceled = false;
+                return;
+            }
 
             var holders = new List<PollableHolder>(s_pollables.Count);
             var pending = new List<Pollable>(s_pollables.Count);
@@ -114,6 +120,11 @@ private static void CancelAndDispose(object? s)
                     return;
                 }
 
+                // Tell event loop to exit early, giving the application a
+                // chance to quit if the task(s) it is interested in have
+                // completed.
+                s_tasksCanceled = true;
+
                 // it will be removed from s_pollables on the next run
                 self.isDisposed = true;
                 self.pollable.Dispose();