Azure Functions Logging Provider

AzureFunctionsLoggingProvider.cs

public static class AzureFunctionsLoggerBuilderExtensions
{
    public static void AddAzureFunctions(this ILoggingBuilder logging, TraceWriter writer)
    {
        logging.Services.AddSingleton(writer);
        logging.Services.AddSingleton<ILoggerProvider, AzureFunctionsLoggerProvider>();
    }
}

public class AzureFunctionsLoggerProvider : ILoggerProvider
{
    private readonly TraceWriter _traceWriter;

    public AzureFunctionsLoggerProvider(TraceWriter traceWriter)
    {
        _traceWriter = traceWriter;
    }

    public ILogger CreateLogger(string categoryName)
    {
        return new AzureFunctionsLogger(categoryName, _traceWriter);
    }

    public void Dispose()
    {
    }

    private class AzureFunctionsLogger : ILogger, ISupportExternalScope
    {
        private readonly string _categoryName;
        private readonly TraceWriter _traceWriter;
        private IExternalScopeProvider _scopeProvider;

        public AzureFunctionsLogger(string categoryName, TraceWriter traceWriter)
        {
            _categoryName = categoryName;
            _traceWriter = traceWriter;
        }

        public IDisposable BeginScope<TState>(TState state)
        {
            return null;
        }

        public bool IsEnabled(LogLevel logLevel)
        {
            return true;
        }

        public void Log<TState>(LogLevel logLevel, EventId eventId, TState state, Exception exception, Func<TState, Exception, string> formatter)
        {
            var logLevelString = GetLogLevelString(logLevel);
            var builder = new StringBuilder();

            builder.AppendLine($"{logLevelString}: {_categoryName}[{eventId.Id}]");
            builder.Append($"      {formatter(state, exception)}");

            switch (logLevel)
            {
                case LogLevel.Trace:
                case LogLevel.Debug:
                    _traceWriter.Verbose(builder.ToString(), source: _categoryName);
                    break;
                case LogLevel.Warning:
                    _traceWriter.Warning(builder.ToString(), source: _categoryName);
                    break;
                case LogLevel.Error:
                case LogLevel.Critical:
                    _traceWriter.Error(builder.ToString(), source: _categoryName);
                    break;
                default:
                    _traceWriter.Info(builder.ToString(), source: _categoryName);
                    break;
            }
        }

        public void SetScopeProvider(IExternalScopeProvider scopeProvider)
        {
            _scopeProvider = scopeProvider;
        }
    }

    private static string GetLogLevelString(LogLevel logLevel)
    {
        switch (logLevel)
        {
            case LogLevel.Trace:
                return "trce";
            case LogLevel.Debug:
                return "dbug";
            case LogLevel.Information:
                return "info";
            case LogLevel.Warning:
                return "warn";
            case LogLevel.Error:
                return "fail";
            case LogLevel.Critical:
                return "crit";
            default:
                throw new ArgumentOutOfRangeException(nameof(logLevel));
        }
    }
}

MyFunction.cs

public static async Task<HttpResponseMessage> Run(..., TraceWriter log)
{
    var connection = new HubConnectionBuilder()
        .WithUrl("https://signalr-samples.azurewebsites.net/default")
        .ConfigureLogging(logging =>
        {
            // Register the logger provider using the AddAzureFunctions extension method,
            // passing in the TraceWriter instance.
            logging.AddAzureFunctions(log);
        })
        .Build();
}