Make error message clearer if Node isn't installed (or not found on PATH). Fixesaspnet#527

Author: SteveSandersonMS

src/Microsoft.AspNetCore.NodeServices/HostingModels/OutOfProcessNodeInstance.cs

@@ -222,7 +222,7 @@ protected virtual ProcessStartInfo PrepareNodeProcessStartInfo(
 }
 else
 {
-debuggingArgs=string.Empty;
+debuggingArgs=string.Empty;
 }
 
 varthisProcessPid=Process.GetCurrentProcess().Id;
@@ -325,17 +325,26 @@ private static void SetEnvironmentVariable(ProcessStartInfo startInfo, string na
 
 privatestaticProcessLaunchNodeProcess(ProcessStartInfostartInfo)
 {
-varprocess=Process.Start(startInfo);
-
-// On Mac at least, a killed child process is left open as a zombie until the parent
-// captures its exit code. We don't need the exit code for this process, and don't want
-// to use process.WaitForExit() explicitly (we'd have to block the thread until it really
-// has exited), but we don't want to leave zombies lying around either. It's sufficient
-// to use process.EnableRaisingEvents so that .NET will grab the exit code and let the
-// zombie be cleaned away without having to block our thread.
-process.EnableRaisingEvents=true;
-
-returnprocess;
+try{
+varprocess=Process.Start(startInfo);
+
+// On Mac at least, a killed child process is left open as a zombie until the parent
+// captures its exit code. We don't need the exit code for this process, and don't want
+// to use process.WaitForExit() explicitly (we'd have to block the thread until it really
+// has exited), but we don't want to leave zombies lying around either. It's sufficient
+// to use process.EnableRaisingEvents so that .NET will grab the exit code and let the
+// zombie be cleaned away without having to block our thread.
+process.EnableRaisingEvents=true;
+
+returnprocess;
+}catch(Exceptionex){
+varmessage="Failed to start Node process. To resolve this:.\n\n"
++"[1] Ensure that Node.js is installed and can be found in one of the PATH directories.\n"
++$" Current PATH enviroment variable is: {Environment.GetEnvironmentVariable("PATH") }\n"
++" Make sure the Node executable is in one of those directories, or update your PATH.\n\n"
++"[2] See the InnerException for further details of the cause.";
+thrownewInvalidOperationException(message,ex);
+}
 }
 
 privatestaticstringUnencodeNewlines(stringstr)