"git-credential-manager-core.exe diagnose" hangs when "git config --list" output is long

[wm1]

Repro:

• In a blank folder, git init and then modify .git\config to make the file bigger than 4K
• Run diagnose sub-command, it will hang at waiting for git config --list output.

[ OK ] Environment
[ OK ] File system
[ OK ] Networking
[ xxx ] Git

The underline issue is that GCM spawns a child process and redirects child's stdout. There is a size limit for the pipe buffer, and if the parent process does not read data out quickly, the child process will stall at writing to stdout.

A fix would be to add Process.OutputDataReceived to GitDiagnostic.RunInternalAsync.

I'd suggest reviewing all places that spawn child process for similar issue.

[wm1]

diff --git a/src/shared/Core/Diagnostics/GitDiagnostic.cs b/src/shared/Core/Diagnostics/GitDiagnostic.cs
index fe6a326..53486e2 100644
--- a/src/shared/Core/Diagnostics/GitDiagnostic.cs
+++ b/src/shared/Core/Diagnostics/GitDiagnostic.cs
@@ -8,6 +8,7 @@ namespace GitCredentialManager.Diagnostics
     public class GitDiagnostic : Diagnostic
     {
         private readonly IGit _git;
+        private StringBuilder _output = null;

         public GitDiagnostic(IGit git)
             : base("Git")
@@ -15,6 +16,7 @@ namespace GitCredentialManager.Diagnostics
             EnsureArgument.NotNull(git, nameof(git));

             _git = git;
+            _output = new StringBuilder();
         }

         protected override Task<bool> RunInternalAsync(StringBuilder log, IList<string> additionalFiles)
@@ -31,9 +33,20 @@ namespace GitCredentialManager.Diagnostics

             log.Append("Listing all Git configuration...");
             Process configProc = _git.CreateProcess("config --list --show-origin");
+
+            configProc.OutputDataReceived += new DataReceivedEventHandler((sender, e) =>
+            {
+                _output.Append(e.Data + "\n");
+            });
+
             configProc.Start();
+
+            // Asynchronously read the standard output of the spawned process.
+            // This raises OutputDataReceived events for each line of output.
+            configProc.BeginOutputReadLine();
+
             configProc.WaitForExit();
-            string gitConfig = configProc.StandardOutput.ReadToEnd().TrimEnd();
+            string gitConfig = _output.ToString();
             log.AppendLine(" OK");
             log.AppendLine("Git configuration:");
             log.AppendLine(gitConfig);