Add OnFileRemoving life cycle hook #106

Author: Marcin_Osada

src/Serilog.Sinks.File/Sinks/File/FileLifecycleHooks.cs

@@ -35,5 +35,19 @@ public abstract class FileLifecycleHooks
         /// <param name="encoding">The encoding to use when reading/writing to the stream.</param>
         /// <returns>The <see cref="Stream"/> Serilog should use when writing events to the log file.</returns>
         public virtual Stream OnFileOpened(Stream underlyingStream, Encoding encoding) => underlyingStream;
+
+        /// <summary>
+        /// Method called on log files that were marked as obsolete (old) and by default would be deleted.
+        /// This can be used to move old logs to archive location or send to backup server
+        /// </summary>
+        /// <remarks>
+        /// Executing long synchronous operation may affect responsiveness of application
+        /// </remarks>
+        /// <param name="fullPath">Log file full path</param>
+        /// <returns>
+        /// Return if Serilog should delete file.
+        /// Warning: returning false and keeping file in same place will result in calling this method again in next scan for obsolete files
+        /// </returns>
+        public virtual bool OnFileRemoving(string fullPath) => true;
     }
 }

src/Serilog.Sinks.File/Sinks/File/RollingFileSink.cs

@@ -199,11 +199,12 @@ void ApplyRetentionPolicy(string currentFilePath)
                 var fullPath = Path.Combine(_roller.LogFileDirectory, obsolete);
                 try
                 {
-                    System.IO.File.Delete(fullPath);
+                    if (_hooks == null || _hooks.OnFileRemoving(fullPath))
+                        System.IO.File.Delete(fullPath);
                 }
                 catch (Exception ex)
                 {
-                    SelfLog.WriteLine("Error {0} while removing obsolete log file {1}", ex, fullPath);
+                    SelfLog.WriteLine("Error {0} while processing obsolete log file {1}", ex, fullPath);
                 }
             }
         }