Log4NetSoapExtension

Log4NetSoapExtension.cs

public class Log4NetSoapExtension : SoapExtension
{
    private static readonly ILog logger = LogManager.GetLogger("My Service");

    Stream oldStream;
    Stream newStream;

    public override Stream ChainStream(Stream stream)
    {
        oldStream = stream;
        newStream = new MemoryStream();
        return newStream;
    }

    public override object GetInitializer(LogicalMethodInfo methodInfo, SoapExtensionAttribute attribute)
    {
        return methodInfo.Name;
    }

    public override object GetInitializer(Type WebServiceType)
    {
        return WebServiceType.Name;
    }

    public override void Initialize(object initializer)
    {
    }

    public override void ProcessMessage(SoapMessage message)
    {
        switch (message.Stage)
        {
            case SoapMessageStage.BeforeSerialize:
                break;
            case SoapMessageStage.AfterSerialize:
                WriteOutput(message);
                break;
            case SoapMessageStage.BeforeDeserialize:
                WriteInput(message);
                break;
            case SoapMessageStage.AfterDeserialize:
                break;
        }
    }

    public void WriteOutput(SoapMessage message)
    {
        var soapString = (message is SoapServerMessage) ? "SoapResponse" : "SoapRequest";
        var header = soapString + ": " + message.MethodInfo.Name + "\n";
            
        if (message.Exception != null)
        {
            Log(header, newStream, message.Exception);
            return;
        }

        Log(header, newStream);

        Copy(newStream, oldStream);
    }

    public void WriteInput(SoapMessage message)
    {
        Copy(oldStream, newStream);
            
        string soapString = (message is SoapServerMessage) ? "SoapRequest" : "SoapResponse";
        var header = soapString + ": " + message.MethodInfo.Name + "\n";

        Log(header, newStream);
    }

    void Log(string header, Stream stream, Exception e = null)
    {
        var sb = new StringBuilder();
        var w = new StringWriter(sb);

        stream.Position = 0;
        Copy(stream, w);
        var msg = sb.ToString();
        try
        {
            //Since we're looking at SOAP, parse the XML so it gets formatted nicely.
            var log = header + XElement.Parse(msg.Trim()).ToString();
            if (e == null)
                logger.Info(log);
            else
                logger.Error(log, e);
        }
        catch (Exception) //message is not valid xml
        {
            if (e == null)
                logger.Info(header + msg);
            else
                logger.Error(header + msg, e);
        }
        if (e != null)
            Elmah.ErrorSignal.FromCurrentContext().Raise(e);

        stream.Position = 0;
    }

    void Copy(Stream from, TextWriter to)
    {
        var reader = new StreamReader(from);
        to.WriteLine(reader.ReadToEnd());
        to.Flush();
    }

    void Copy(Stream from, Stream to)
    {
        TextReader reader = new StreamReader(from);
        TextWriter writer = new StreamWriter(to);
        writer.WriteLine(reader.ReadToEnd());
        writer.Flush();
    }
}

[AttributeUsage(AttributeTargets.Method)]
public class Log4NetSoapExtensionAttribute : SoapExtensionAttribute
{
    public override Type ExtensionType
    {
        get { return typeof(Log4NetSoapExtension); }
    }

    public override int Priority { get; set; }
}

web.config

<configuration>
  <configSections>
    <section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler, log4net" />
  </configSections>
  <log4net>
    <appender name="FileAppender" type="log4net.Appender.FileAppender">
      <file type="log4net.Util.PatternString" value="c:\logs\log %date{dd MMM yyyy}.xml" />
      <appendToFile value="true" />
      <layout type="log4net.Layout.XmlLayoutSchemaLog4j">
        <locationInfo value="true" />
      </layout>
    </appender>
    <root>
      <level value="ALL" />
      <appender-ref ref="FileAppender" />
    </root>
  </log4net>
  <system.web>
    <webServices>
      <soapExtensionTypes>
        <add type="MyAssembly.Log4NetSoapExtension, MyAssembly" priority="1" group="1" />
      </soapExtensionTypes>
    </webServices>
  </system.web>
</configuration>

I had to remove message.MethodInfo.Name from the header string concatenation statement in the WriteInput method because message.MethodInfo throws an exception. Other than that works as advertised!