bepin/BepInEx/Logging/LoggerTraceListener.cs

using System;
using System.Diagnostics;
using System.Linq;
using System.Reflection;
using Harmony;

namespace BepInEx.Logging
{
	/// <summary>
	/// A trace listener that writes to an underlying <see cref="BaseLogger"/> instance.
	/// </summary>
	/// <inheritdoc cref="TraceListener"/>
    public class LoggerTraceListener : TraceListener
    {
		/// <summary>
		/// The logger instance that is being written to.
		/// </summary>
        public BaseLogger Logger { get; }

        static LoggerTraceListener()
        {
            try
            {
                TraceFixer.ApplyFix();
            }
            catch { } //ignore everything, if it's thrown an exception, we're using an assembly that has already fixed this
        }
		
		/// <param name="logger">The logger instance to write to.</param>
        public LoggerTraceListener(BaseLogger logger)
        {
            Logger = logger;
        }
		
		/// <summary>
		/// Writes a message to the underlying <see cref="BaseLogger"/> instance.
		/// </summary>
		/// <param name="message">The message to write.</param>
        public override void Write(string message)
        {
            Logger.Write(message);
        }
		
	    /// <summary>
	    /// Writes a message and a newline to the underlying <see cref="BaseLogger"/> instance.
	    /// </summary>
	    /// <param name="message">The message to write.</param>
        public override void WriteLine(string message)
        {
            Logger.WriteLine(message);
        }

        public override void TraceEvent(TraceEventCache eventCache, string source, TraceEventType eventType, int id, string format, params object[] args)
            => TraceEvent(eventCache, source, eventType, id, string.Format(format, args));

        public override void TraceEvent(TraceEventCache eventCache, string source, TraceEventType eventType, int id, string message)
        {
            LogLevel level;

            switch (eventType)
            {
                case TraceEventType.Critical:
                    level = LogLevel.Fatal;
                    break;
                case TraceEventType.Error:
                    level = LogLevel.Error;
                    break;
                case TraceEventType.Warning:
                    level = LogLevel.Warning;
                    break;
                case TraceEventType.Information:
                    level = LogLevel.Info;
                    break;
                case TraceEventType.Verbose:
                default:
                    level = LogLevel.Debug;
                    break;
            }

            Logger.Log(level, $"{source} : {message}");
        }

		/// <summary>
		/// This exists because the Mono implementation of <see cref="Trace"/> is/was broken, and would call Write directly instead of calling TraceEvent. This class fixes that with a <see cref="Harmony"/> hook.
		/// </summary>
        private static class TraceFixer
        {
            private static Type TraceImplType;
            
            private static object ListenersSyncRoot;
            private static TraceListenerCollection Listeners;
            private static PropertyInfo prop_AutoFlush;

            private static bool AutoFlush => (bool)prop_AutoFlush.GetValue(null, null);


            public static void ApplyFix()
            {
                TraceImplType = AppDomain.CurrentDomain.GetAssemblies()
                    .First(x => x.GetName().Name == "System")
                    .GetTypes()
                    .First(x => x.Name == "TraceImpl");

                
                ListenersSyncRoot = AccessTools.Property(TraceImplType, "ListenersSyncRoot").GetValue(null, null);
                
                Listeners = (TraceListenerCollection)AccessTools.Property(TraceImplType, "Listeners").GetValue(null, null);
                
                prop_AutoFlush = AccessTools.Property(TraceImplType, "AutoFlush");



                HarmonyInstance instance = HarmonyInstance.Create("com.bepis.bepinex.tracefix");

                instance.Patch(
                    typeof(Trace).GetMethod("DoTrace", BindingFlags.Static | BindingFlags.NonPublic),
                    new HarmonyMethod(typeof(TraceFixer).GetMethod(nameof(DoTraceReplacement), BindingFlags.Static | BindingFlags.Public)),
                    null);
            }


            public static bool DoTraceReplacement(string kind, Assembly report, string message)
            {
                string arg = string.Empty;
                try
                {
                    arg = report.GetName().Name;
                }
                catch (MethodAccessException) { }

                TraceEventType type = (TraceEventType)Enum.Parse(typeof(TraceEventType), kind);

                lock (ListenersSyncRoot)
                {
                    foreach (object obj in Listeners)
                    {
                        TraceListener traceListener = (TraceListener)obj;
                        traceListener.TraceEvent(new TraceEventCache(), arg, type, 0, message);

                        if (AutoFlush)
                        {
                            traceListener.Flush();
                        }
                    }
                }

                return false;
            }
        }
    }
}