[merp] Add API methods for getting hashcode/reason of last crash (#19901)

* [merp] Add API methods for getting hashcode/reason of last crash

* Add test

* Review feedback and cleanup

1 files changed, 38 insertions, 0 deletions

diff --git a/mcs/class/corlib/Mono/Runtime.cs b/mcs/class/corlib/Mono/Runtime.cs
index 13f1bad8d31..4a181f9721f 100644
--- a/mcs/class/corlib/Mono/Runtime.cs
+++ b/mcs/class/corlib/Mono/Runtime.cs
@@ -27,6 +27,7 @@
 //
 
 using System;
+using System.IO;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 
@@ -263,6 +264,43 @@ namespace Mono {
 			}
 		}
 
+		static string get_breadcrumb_value (string file_prefix, string directory_str, bool clear)
+		{
+			var allfiles = Directory.GetFiles (directory_str, $"{file_prefix}_*" );
+			if (allfiles.Length == 0)
+				return string.Empty;
+
+			if (allfiles.Length > 1) {
+				// it's impossible to tell which breadcrumb is the last one (let's not trust filesystem timestamps)
+				// delete the multiple files so at least next crash can make sense
+				try {
+					Array.ForEach (allfiles, f => File.Delete (f) );
+				} catch (Exception) { }
+
+				return string.Empty;
+			}
+
+			if (clear)
+				File.Delete (allfiles [0]);
+
+			var filename = Path.GetFileName (allfiles [0]);
+			return filename.Substring (file_prefix.Length + 1);
+		}
+
+		static long CheckCrashReportHash (string directory_str, bool clear)
+		{
+			var value = get_breadcrumb_value ("crash_hash", directory_str, clear);
+			if (value == string.Empty)
+				return 0;
+			else
+				return Convert.ToInt64 (value, 16);
+		}
+
+		static string CheckCrashReportReason (string directory_str, bool clear)
+		{
+			return get_breadcrumb_value ("crash_reason", directory_str, clear);
+		}
+
 		[MethodImplAttribute (MethodImplOptions.InternalCall)]
 		static extern void AnnotateMicrosoftTelemetry_internal (IntPtr key, IntPtr val);