Better logging if an NPM task exits with an error

Author: SteveSandersonMS

src/Microsoft.AspNetCore.SpaServices.Extensions/AngularCli/AngularCliBuilder.cs

@@ -3,9 +3,11 @@
 
 using Microsoft.AspNetCore.Builder;
 using Microsoft.AspNetCore.NodeServices.Npm;
+using Microsoft.AspNetCore.NodeServices.Util;
 using Microsoft.AspNetCore.SpaServices.Prerendering;
 using Microsoft.Extensions.Logging;
 using System;
+using System.IO;
 using System.Text.RegularExpressions;
 using System.Threading.Tasks;
 
@@ -58,9 +60,19 @@ internal Task StartAngularCliBuilderAsync(
                 "--watch");
             npmScriptRunner.AttachToLogger(logger);
 
-            return npmScriptRunner.StdOut.WaitForMatch(
-                new Regex("chunk"),
-                TimeoutMilliseconds);
+            using (var stdErrReader = new EventedStreamStringReader(npmScriptRunner.StdErr))
+            {
+                try
+                {
+                    return npmScriptRunner.StdOut.WaitForMatch(
+                        new Regex("chunk"),
+                        TimeoutMilliseconds);
+                }
+                catch (EndOfStreamException ex)
+                {
+                    throw new InvalidOperationException($"The NPM script '{npmScriptName}' exited without indicating success. Error output was: {stdErrReader.ReadAsString()}", ex);
+                }
+            }
         }
     }
 }

src/Microsoft.AspNetCore.SpaServices.Extensions/AngularCli/AngularCliMiddleware.cs

@@ -15,6 +15,8 @@
 using Microsoft.Extensions.Logging.Console;
 using System.Net.Sockets;
 using System.Net;
+using System.IO;
+using Microsoft.AspNetCore.NodeServices.Util;
 
 namespace Microsoft.AspNetCore.SpaServices.AngularCli
 {
@@ -126,9 +128,21 @@ private async Task<AngularCliServerInfo> StartAngularCliServerAsync(string npmSc
                 _sourcePath, npmScriptName, $"--port {portNumber}");
             npmScriptRunner.AttachToLogger(_logger);
 
-            var openBrowserLine = await npmScriptRunner.StdOut.WaitForMatch(
-                new Regex("open your browser on (http\\S+)"),
-                TimeoutMilliseconds);
+            Match openBrowserLine;
+            using (var stdErrReader = new EventedStreamStringReader(npmScriptRunner.StdErr))
+            {
+                try
+                {
+                    openBrowserLine = await npmScriptRunner.StdOut.WaitForMatch(
+                        new Regex("open your browser on (http\\S+)"),
+                        TimeoutMilliseconds);
+                }
+                catch (EndOfStreamException ex)
+                {
+                    throw new InvalidOperationException($"The NPM script '{npmScriptName}' exited without indicating that the Angular CLI was listening for requests. The error output was: {stdErrReader.ReadAsString()}", ex);
+                }
+            }
+
             var uri = new Uri(openBrowserLine.Groups[1].Value);
             var serverInfo = new AngularCliServerInfo { Port = uri.Port };
 

src/Microsoft.AspNetCore.SpaServices.Extensions/Npm/EventedStreamReader.cs

@@ -1,4 +1,7 @@
-using System;
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
 using System.IO;
 using System.Text;
 using System.Text.RegularExpressions;
@@ -11,9 +14,11 @@ class EventedStreamReader
     {
         public delegate void OnReceivedChunkHandler(ArraySegment<char> chunk);
         public delegate void OnReceivedLineHandler(string line);
+        public delegate void OnStreamClosedHandler();
 
         public event OnReceivedChunkHandler OnReceivedChunk;
         public event OnReceivedLineHandler OnReceivedLine;
+        public event OnStreamClosedHandler OnStreamClosed;
 
         private readonly StreamReader _streamReader;
         private readonly StringBuilder _linesBuffer;
@@ -31,6 +36,8 @@ public Task<Match> WaitForMatch(Regex regex, int timeoutMilliseconds = 0)
             var completionLock = new object();
 
             OnReceivedLineHandler onReceivedLineHandler = null;
+            OnStreamClosedHandler onStreamClosedHandler = null;
+
             onReceivedLineHandler = line =>
             {
                 var match = regex.Match(line);
@@ -41,13 +48,28 @@ public Task<Match> WaitForMatch(Regex regex, int timeoutMilliseconds = 0)
                         if (!tcs.Task.IsCompleted)
                         {
                             OnReceivedLine -= onReceivedLineHandler;
+                            OnStreamClosed -= onStreamClosedHandler;
                             tcs.SetResult(match);
                         }
                     }
                 }
             };
 
+            onStreamClosedHandler = () =>
+            {
+                lock (completionLock)
+                {
+                    if (!tcs.Task.IsCompleted)
+                    {
+                        OnReceivedLine -= onReceivedLineHandler;
+                        OnStreamClosed -= onStreamClosedHandler;
+                        tcs.SetException(new EndOfStreamException());
+                    }
+                }
+            };
+
             OnReceivedLine += onReceivedLineHandler;
+            OnStreamClosed += onStreamClosedHandler;
 
             if (timeoutMilliseconds > 0)
             {
@@ -59,6 +81,7 @@ public Task<Match> WaitForMatch(Regex regex, int timeoutMilliseconds = 0)
                         if (!tcs.Task.IsCompleted)
                         {
                             OnReceivedLine -= onReceivedLineHandler;
+                            OnStreamClosed -= onStreamClosedHandler;
                             tcs.SetCanceled();
                         }
                     }
@@ -76,6 +99,7 @@ private async Task Run()
                 var chunkLength = await _streamReader.ReadAsync(buf, 0, buf.Length);
                 if (chunkLength == 0)
                 {
+                    OnClosed();
                     break;
                 }
 
@@ -107,5 +131,11 @@ private void OnCompleteLine(string line)
             var dlg = OnReceivedLine;
             dlg?.Invoke(line);
         }
+
+        private void OnClosed()
+        {
+            var dlg = OnStreamClosed;
+            dlg?.Invoke();
+        }
     }
 }

src/Microsoft.AspNetCore.SpaServices.Extensions/Npm/EventedStreamStringReader.cs

@@ -0,0 +1,36 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using System.Text;
+
+namespace Microsoft.AspNetCore.NodeServices.Util
+{
+    class EventedStreamStringReader : IDisposable
+    {
+        private EventedStreamReader _eventedStreamReader;
+        private bool _isDisposed;
+        private StringBuilder _stringBuilder = new StringBuilder();
+
+        public EventedStreamStringReader(EventedStreamReader eventedStreamReader)
+        {
+            _eventedStreamReader = eventedStreamReader
+                ?? throw new ArgumentNullException(nameof(eventedStreamReader));
+            _eventedStreamReader.OnReceivedLine += OnReceivedLine;
+
+        }
+
+        public string ReadAsString() => _stringBuilder.ToString();
+
+        private void OnReceivedLine(string line) => _stringBuilder.AppendLine(line);
+
+        public void Dispose()
+        {
+            if (!_isDisposed)
+            {
+                _eventedStreamReader.OnReceivedLine -= OnReceivedLine;
+                _isDisposed = true;
+            }
+        }
+    }
+}