How to handle NPM/Newman failure/hanging when executed via C# console

Question

I have the method created in C# (as below) which executes a few npm/newman commands via C# console-app. The current code handles if the cmd hangs/failed, but it does not handle the case if the nmp/newman execution hangs or fail.

Can you please help with this?

public string Runner ()
    {
        var psiNpm = new ProcessStartInfo
        {
            FileName = "cmd",
            RedirectStandardOutput = true,
            RedirectStandardInput = true,
            UseShellExecute = false
        };
        var pNpmRun = Process.Start(psiNpm);
        pNpmRun.StandardInput.WriteLine("npm install -g newman");
        pNpmRun.StandardInput.WriteLine("newman run " +
            "\"C:\\Postman\\Test.postman.json\" " +
            "--folder \"TestSearch\" " +
            "--environment \"C:\\Postman\\postman_environment.json\" " +
            "--disable-unicode");
        pNpmRun.StandardInput.WriteLine("exit");

          var tenMin = 10 * 60 * 1000;
          if(pNpmRun.WaitForExit(tenMin)) {
             return pNpmRun.StandardOutput.ReadToEnd();
          } else {
             pNpmRun.Kill();
             throw new TimeoutException("Command didn't complete in 10 minute timeout");
          }
    }

score 2 · Accepted Answer · answered Apr 10 '19 at 02:20

You can check the exit code of your npm and newman commands and return them to the calling process:

public string Runner ()
    {
        var psiNpm = new ProcessStartInfo
        {
            FileName = "cmd",
            RedirectStandardOutput = true,
            RedirectStandardInput = true,
            UseShellExecute = false
        };
        var pNpmRun = Process.Start(psiNpm);
        pNpmRun.StandardInput.WriteLine("npm install -g newman");

        pNpmRun.StandardInput.WriteLine("if not "%ERRORLEVEL%" == "0" exit 1");

        pNpmRun.StandardInput.WriteLine("newman run " +
            "\"C:\\Postman\\Test.postman.json\" " +
            "--folder \"TestSearch\" " +
            "--environment \"C:\\Postman\\postman_environment.json\" " +
            "--disable-unicode");

        pNpmRun.StandardInput.WriteLine("if not "%ERRORLEVEL%" == "0" exit 2");
        pNpmRun.StandardInput.WriteLine("exit 0");

          var tenMin = 10 * 60 * 1000;
          if(pNpmRun.WaitForExit(tenMin)) {
             var exitCode = pNpmRun.ExitCode;
             if(exitCode != 0) {
               throw new Exception("Command failed " + exitCode);
             }
             return pNpmRun.StandardOutput.ReadToEnd();
          } else {
             pNpmRun.Kill();
             throw new TimeoutException("Command didn't complete in 10 minute timeout");
          }
    }

After each command check the errorlevel, which is a "virtual environment variable", representing the exit code of the previous command. If it wasn't 0 (success, usually), then it exits the cmd process back to your C# code. Your C# code checks the ExitCode of the process, and if it isn't success (0), it throws an exception containing the ExitCode so you know which of the two commands failed. This relies on the npm and newman processes returning a non-zero exit code on failure.

That should handle "failure". Handling "hanging" would be more difficult. There isn't really any way to know if the process is ever going to return (read: halting problem (the one thing I learned at university)).

Thanks a lot @MarkPflug, for the example and detailed explanation! — KVN, Apr 10 '19 at 15:20
Sorry @MarkPflug, I think I need more help with using this one. If I use the code above as-it-is, then VS will complain on the syntax for "ERRORLEVEL does not exist in the current context" and also on the " == "0" exit" as "Syntax error, ',' expected" — KVN, Apr 10 '19 at 23:26
I missed escaping the quotes. It should read \"%ERRORLEVEL%\" — MarkPflug, Apr 11 '19 at 18:34

How to handle NPM/Newman failure/hanging when executed via C# console

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