Update http proxy to handle client disconnect scenario

src/WebJobs.Script.Grpc/Server/RetryProxyHandler.cs

@@ -37,6 +37,11 @@ protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage
                 {
                     return await base.SendAsync(request, cancellationToken);
                 }
+                catch (TaskCanceledException) when (cancellationToken.IsCancellationRequested)
+                {
+                    _logger.LogInformation("Request was canceled. Stopping retries.");
+                    break;
+                }
                 catch (HttpRequestException) when (attemptCount < MaxRetries)
                 {
                     _logger.LogWarning("Failed to proxy request to the worker. Retrying in {delay}ms. Attempt {attemptCount} of {maxRetries}.",
@@ -58,6 +63,9 @@ protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage
                 }
             }
 
+            // If the loop exits without returning, propagate the cancellation
+            cancellationToken.ThrowIfCancellationRequested();
+
             // This should never be reached.
             throw null;
         }

src/WebJobs.Script.WebHost/Middleware/SystemTraceMiddleware.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Diagnostics;
+using System.IO;
 using System.Linq;
 using System.Text;
 using System.Threading.Tasks;
@@ -36,6 +37,11 @@ public async Task Invoke(HttpContext context)
 
             await _next.Invoke(context);
 
+            if (context.RequestAborted.IsCancellationRequested)
+            {
+                context.Response.StatusCode = StatusCodes.Status499ClientClosedRequest;
+            }
+
             string identities = GetIdentities(context);
             _logger.ExecutedHttpRequest(requestId, identities, context.Response.StatusCode, (long)sw.GetElapsedTime().TotalMilliseconds);
         }