fix: move log retention out of EntryPoint.cs, redo retention behaviour for release

Dalamud/Logging/Retention/DebugRetentionBehaviour.cs

@@ -0,0 +1,15 @@
+using System.IO;
+
+namespace Dalamud.Logging.Retention;
+
+/// <summary>
+/// Class implementing log retention behaviour for debug builds.
+/// </summary>
+internal class DebugRetentionBehaviour : RetentionBehaviour
+{
+    /// <inheritdoc/>
+    public override void Apply(FileInfo logFile, FileInfo rolloverFile)
+    {
+        CullLogFile(logFile, 1 * 1024 * 1024, rolloverFile, 10 * 1024 * 1024);
+    }
+}

Dalamud/Logging/Retention/ReleaseRetentionBehaviour.cs

@@ -0,0 +1,15 @@
+using System.IO;
+
+namespace Dalamud.Logging.Retention;
+
+/// <summary>
+/// Class implementing log retention behaviour for release builds.
+/// </summary>
+internal class ReleaseRetentionBehaviour : RetentionBehaviour
+{
+    /// <inheritdoc/>
+    public override void Apply(FileInfo logFile, FileInfo rolloverFile)
+    {
+        CullLogFile(logFile, 0, rolloverFile, 10 * 1024 * 1024);
+    }
+}

Dalamud/Logging/Retention/RetentionBehaviour.cs

@@ -0,0 +1,91 @@
+using System;
+using System.IO;
+
+using Serilog;
+
+namespace Dalamud.Logging.Retention;
+
+/// <summary>
+/// Class implementing retention behaviour for log files.
+/// </summary>
+internal abstract class RetentionBehaviour
+{
+    /// <summary>
+    /// Apply the specified retention behaviour to log files.
+    /// </summary>
+    /// <param name="logFile">The regular log file path.</param>
+    /// <param name="rolloverFile">The rollover "old" log file path.</param>
+    public abstract void Apply(FileInfo logFile, FileInfo rolloverFile);
+    
+    /// <summary>
+    /// Trim existing log file to a specified length, and optionally move the excess data to another file.
+    /// </summary>
+    /// <param name="logFile">Target log file to trim.</param>
+    /// <param name="logMaxSize">Maximum size of target log file.</param>
+    /// <param name="oldFile">.old file to move excess data to.</param>
+    /// <param name="oldMaxSize">Maximum size of .old file.</param>
+    protected static void CullLogFile(FileInfo logFile, int logMaxSize, FileInfo oldFile, int oldMaxSize)
+    {
+        var targetFiles = new[]
+        {
+            (logFile, logMaxSize),
+            (oldFile, oldMaxSize),
+        };
+        var buffer = new byte[4096];
+
+        try
+        {
+            if (!logFile.Exists)
+                logFile.Create().Close();
+
+            // 1. Move excess data from logFile to oldFile
+            if (logFile.Length > logMaxSize)
+            {
+                using var reader = logFile.Open(FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
+                using var writer = oldFile.Open(FileMode.Append, FileAccess.Write, FileShare.ReadWrite);
+
+                var amountToMove = (int)Math.Min(logFile.Length - logMaxSize, oldMaxSize);
+                reader.Seek(-(logMaxSize + amountToMove), SeekOrigin.End);
+
+                for (var i = 0; i < amountToMove; i += buffer.Length)
+                    writer.Write(buffer, 0, reader.Read(buffer, 0, Math.Min(buffer.Length, amountToMove - i)));
+            }
+
+            // 2. Cull each of .log and .old files
+            foreach (var (file, maxSize) in targetFiles)
+            {
+                if (!file.Exists || file.Length <= maxSize)
+                    continue;
+
+                using var reader = file.Open(FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
+                using var writer = file.Open(FileMode.Open, FileAccess.Write, FileShare.ReadWrite);
+
+                reader.Seek(file.Length - maxSize, SeekOrigin.Begin);
+                for (int read; (read = reader.Read(buffer, 0, buffer.Length)) > 0;)
+                    writer.Write(buffer, 0, read);
+
+                writer.SetLength(maxSize);
+            }
+        }
+        catch (Exception ex)
+        {
+            if (ex is IOException)
+            {
+                foreach (var (file, _) in targetFiles)
+                {
+                    try
+                    {
+                        if (file.Exists)
+                            file.Delete();
+                    }
+                    catch (Exception ex2)
+                    {
+                        Log.Error(ex2, "Failed to delete {file}", file.FullName);
+                    }
+                }
+            }
+
+            Log.Error(ex, "Log cull failed");
+        }
+    }
+}