Added GladerFileHelpers IsFileLocked

Author: HelloKitty

src/Glader.Essentials.Common/File/GladerFileHelpers.cs

@@ -0,0 +1,46 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Text;
+
+namespace Glader.Essentials
+{
+	public static class GladerFileHelpers
+	{
+		/// <summary>
+		/// Indicates if the file is locked.
+		/// Returns false if the file doesn't even exist.
+		/// </summary>
+		/// <param name="path">Path to the file.</param>
+		/// <returns>True if the file appears to be locked.</returns>
+		public static bool IsFileLocked(string path)
+		{
+			if(!File.Exists(path))
+				return false;
+
+			try
+			{
+				using var stream = new FileStream(
+					path,
+					FileMode.Open,
+					FileAccess.ReadWrite,     // catch shares opened for write
+					FileShare.None);          // require exclusive access
+			}
+			catch(IOException ex) when(IsLockViolation(ex))
+			{
+				return true;
+			}
+
+			return false;
+		}
+
+		private static bool IsLockViolation(IOException ex)
+		{
+			// LOWORD of HResult is the Win32 error code:
+			var code = ex.HResult & 0xFFFF;
+			const int ERROR_SHARING_VIOLATION = 32;
+			const int ERROR_LOCK_VIOLATION = 33;
+			return code == ERROR_SHARING_VIOLATION || code == ERROR_LOCK_VIOLATION;
+		}
+	}
+}