Log4net

The SimpleW.Helper.Log4net package provides a bridge between the SimpleW internal logging system and log4net.

It allows all logs emitted through SimpleW.Observability.Log to be automatically forwarded to a log4net ILog instance.

This integration keeps the SimpleW logging API lightweight and allocation-friendly, while letting developers use the mature log4net ecosystem (appenders, layouts, filters, etc.).

Features

It allows you to :

• Forward all SimpleW logs to log4net
• Automatically detect the minimum logging level from the provided log4net logger
• Preserve TraceId / SpanId from System.Diagnostics.Activity
• Attach the SimpleW log source as a log4net property
• Add custom enrichers

Requirements

• .NET 8.0
• SimpleW (core server)
• Log4net (>= 3.2)

Installation

$ dotnet add package SimpleW.Helper.Log4net --version 26.0.0-rc.20260202-1339

Configuration options

Option	Default	Description
MinimumLevel	auto	Overrides the SimpleW global minimum log level. When null, the level is automatically detected from the provided log4net logger.
Mode	SinkMode.Add	Determines how the log4net bridge is attached. Add chains the sink with existing SimpleW sinks. Replace replaces the current SimpleW sink entirely.
IncludeSource	true	When enabled, the SimpleW log source (entry.Source) is attached to the log4net context properties.
IncludeTraceAndSpan	true	When an active System.Diagnostics.Activity exists, the bridge adds trace_id and span_id properties to the log event.
SourcePropertyName	"simplew_source"	Name of the log4net property used to store the SimpleW log source.
TraceIdPropertyName	"trace_id"	Name of the property used to store the Activity.TraceId.
SpanIdPropertyName	"span_id"	Name of the property used to store the Activity.SpanId.
Enricher	null	Optional callback allowing custom enrichment of the log4net properties for each log entry. Receives (IDictionary<string, object?> properties, LogEntry entry).

Minimal Example

Configure a simple log4net console logger in code :

using log4net;
using log4net.Appender;
using log4net.Layout;
using log4net.Repository.Hierarchy;
using SimpleW.Helper.Log4net;

var hierarchy = (Hierarchy)LogManager.GetRepository();

var layout = new PatternLayout("%date %-5level %message%newline");
layout.ActivateOptions();

var consoleAppender = new ConsoleAppender {
    Layout = layout
};
consoleAppender.ActivateOptions();

hierarchy.Root.AddAppender(consoleAppender);
hierarchy.Root.Level = log4net.Core.Level.Info;
hierarchy.Configured = true;

ILog logger = LogManager.GetLogger(typeof(Program));

Install the bridge :

var bridge = SimpleWLog4NetBridge.Install(logger, configure: options => {
    options.IncludeSource = true;
});

Once installed, every log emitted via :

Log.Info("MySource", "Hello world");

will be forwarded to Log4net.

Automatic Minimum Level Detection

When installing the bridge, SimpleW automatically detects the minimum level enabled in the log4net logger.

Example :

hierarchy.Root.Level = log4net.Core.Level.Warn;

The bridge will automatically configure:

SimpleW.Log.MinimumLevel = Warning

This ensures that disabled log levels are filtered before log creation, preserving the performance characteristics of SimpleW logging.

Replace vs Add Sink

By default the bridge adds a sink.

options.Mode = SinkMode.Add;

This allows multiple logging targets.

Example :

SimpleW
 ├─ Console sink
 └─ log4net  bridge

If you want Log4net to be the only logging target, replace the sink:

SimpleWLog4netBridge.Install(logger, replaceExistingSink: true);

Activity / Distributed Tracing

When a System.Diagnostics.Activity is active (for example when using OpenTelemetry), the bridge automatically attaches :

trace_id
span_id

These properties are stored in log4net LogicalThreadContext properties, allowing layouts such as :

%date %-5level %property{trace_id} %property{span_id} %message%newline

This allows log4net logs to correlate with distributed traces.

SimpleW telemetry is based on System.Diagnostics.Activity and integrates naturally with the OpenTelemetry ecosystem.