Truncate, don't delete files over threshold to keep permissions

Author: jjxtra

IPBanCore/Core/Utility/LogFileScanner.cs

@@ -259,17 +259,17 @@ public void Update()
                             Logger.Trace("Watched file {0} length has not changed", file.FileName);
                         }
 
-                        // if a max file size is specified and the file is over the max size, delete the file
+                        // if a max file size is specified and the file is over the max size, truncate the file
                         if (maxFileSize > 0 && len > maxFileSize)
                         {
                             try
                             {
-                                Logger.Warn("Deleting log file over max size: {0}", file.FileName);
-                                File.Delete(file.FileName);
+                                Logger.Warn("Truncating log file over max size: {0}", file.FileName);
+                                using var _ = new FileStream(file.FileName, FileMode.Truncate, FileAccess.Write, FileShare.ReadWrite);
                             }
                             catch
                             {
-                                // someone else might have it open, in which case we have no chance to delete
+                                // someone else might have it open, in which case we can try again later
                             }
                         }
                     }

IPBanTests/IPBanLogFileParserTests.cs

@@ -284,6 +284,28 @@ public void TestNormalizeGlob()
             ClassicAssert.Throws<ArgumentException>(() => LogFileScanner.NormalizeGlob("\\", out _, out _));
         }
 
+        /// <summary>
+        /// Ensure files are truncated to 0 bytes instead of deleted
+        /// </summary>
+        [Test]
+        public void TestTruncateFile()
+        {
+            var tempFile = Path.GetTempFileName();
+            try
+            {
+                using LogFileScanner scanner = new(tempFile, 4, 0);
+                scanner.Update();
+                File.AppendAllText(tempFile, "12345");
+                scanner.Update();
+                var bytes = File.ReadAllBytes(tempFile);
+                ClassicAssert.AreEqual(0, bytes.Length);
+            }
+            finally
+            {
+                File.Delete(tempFile);
+            }
+        }
+
         private LogFileScanner SetupLogFileScanner(string failureRegex = "",
             string failureRegexTimestampFormat = null,
             string successRegex = null,