Merge pull request #107 from nogard111/OnFileRemovingHook

Add OnFileRemoving life cycle hook #106

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

@@ -19,6 +19,7 @@ namespace Serilog.Sinks.File
 {
     /// <summary>
     /// Enables hooking into log file lifecycle events.
+    /// Hooks run synchronously and therefore may affect responsiveness of the application if long operations are performed.
     /// </summary>
     public abstract class FileLifecycleHooks
     {
@@ -35,5 +36,12 @@ 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>
+        /// Called before an obsolete (rolling) log file is deleted.
+        /// This can be used to copy old logs to an archive location or send to a backup server.
+        /// </summary>
+        /// <param name="path">The full path to the file being deleted.</param>
+        public virtual void OnFileDeleting(string path) {}
     }
 }

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

@@ -199,11 +199,12 @@ void ApplyRetentionPolicy(string currentFilePath)
                 var fullPath = Path.Combine(_roller.LogFileDirectory, obsolete);
                 try
                 {
+                    _hooks?.OnFileDeleting(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);
                 }
             }
         }

test/Serilog.Sinks.File.Tests/RollingFileSinkTests.cs

@@ -71,6 +71,28 @@ public void WhenRetentionCountIsSetOldFilesAreDeleted()
                 });
         }
 
+        [Fact]
+        public void WhenRetentionCountAndArchivingHookIsSetOldFilesAreCopiedAndOriginalDeleted()
+        {
+            const string archiveDirectory = "OldLogs";
+            LogEvent e1 = Some.InformationEvent(),
+                    e2 = Some.InformationEvent(e1.Timestamp.AddDays(1)),
+                    e3 = Some.InformationEvent(e2.Timestamp.AddDays(5));
+
+            TestRollingEventSequence(
+                (pf, wt) => wt.File(pf, retainedFileCountLimit: 2, rollingInterval: RollingInterval.Day, hooks: new ArchiveOldLogsHook(archiveDirectory)),
+                new[] {e1, e2, e3},
+                files =>
+                {
+                    Assert.Equal(3, files.Count);
+                    Assert.True(!System.IO.File.Exists(files[0]));
+                    Assert.True(System.IO.File.Exists(files[1]));
+                    Assert.True(System.IO.File.Exists(files[2]));
+
+                    Assert.True(System.IO.File.Exists(ArchiveOldLogsHook.AddTopDirectory(files[0], archiveDirectory)));
+                });
+        }
+
         [Fact]
         public void WhenSizeLimitIsBreachedNewFilesCreated()
         {

test/Serilog.Sinks.File.Tests/Support/ArchiveOldLogsHook.cs

@@ -0,0 +1,35 @@
+using System;
+using System.IO;
+using System.Text;
+
+namespace Serilog.Sinks.File.Tests.Support
+{
+    internal class ArchiveOldLogsHook : FileLifecycleHooks
+    {
+        private readonly string _relativeArchiveDir;
+
+        public ArchiveOldLogsHook(string relativeArchiveDir)
+        {
+            _relativeArchiveDir = relativeArchiveDir;
+        }
+
+        public override void OnFileDeleting(string path)
+        {
+            base.OnFileDeleting(path);
+            var newFile = AddTopDirectory(path, _relativeArchiveDir, true);
+            System.IO.File.Copy(path, newFile, false);
+        }
+
+        public static string AddTopDirectory(string path, string directoryToAdd, bool createOnNonExist = false)
+        {
+            string file = Path.GetFileName(path);
+            string directory = Path.Combine(Path.GetDirectoryName(path) ?? throw new InvalidOperationException(), directoryToAdd);
+
+            if (createOnNonExist && !Directory.Exists(directory))
+            {
+                Directory.CreateDirectory(directory);
+            }
+            return Path.Combine(directory, file);
+        }
+    }
+}