NReco.Logging.File

Simple and efficient file logger provider for .NET Core (any version) without additional dependencies.

• very similar to standard ConsoleLogger but writes to a file
• can append to existing file or overwrite log file on restart
• supports a 'rolling file' behaviour and can control total log size
• it is possible to change log file name on-the-fly
• suitable for intensive concurrent usage: has internal message queue to avoid threads blocking

How to use

Add NReco.Logging.File package reference and initialize a file logging provider in services.AddLogging (Startup.cs):

services.AddLogging(loggingBuilder => {
	loggingBuilder.AddFile("app.log", append:true);
});

or

services.AddLogging(loggingBuilder => {
	var loggingSection = Configuration.GetSection("Logging");
	loggingBuilder.AddFile(loggingSection);
});

Example of the configuration section in appsettings.json:

"Logging": {
	"LogLevel": {
	  "Default": "Debug",
	  "System": "Information",
	  "Microsoft": "Error"
	},
	"File": {
		"Path": "app.log",
		"Append": "True",
		"FileSizeLimitBytes": 0,  // use to activate rolling file behaviour
		"MaxRollingFiles": 0  // use to specify max number of log files
	}
}

Rolling File

This feature is activated with FileLoggerOptions properties: FileSizeLimitBytes and MaxRollingFiles. Lets assume that file logger is configured for "test.log":

• if only FileSizeLimitBytes is specified file logger will create "test.log", "test1.log", "test2.log" etc
• use MaxRollingFiles in addition to FileSizeLimitBytes to limit number of log files; for example, for value "3" file logger will create "test.log", "test1.log", "test2.log" and again "test.log", "test1.log" (old files will be overwritten).

Change log file name on-the-fly

It is possible to specify a custom log file name formatter with FileLoggerOptions property FormatLogFileName. Log file name may change in time - for example, to create a new log file per day:

services.AddLogging(loggingBuilder => {
	loggingBuilder.AddFile("app_{0:yyyy}-{0:MM}-{0:dd}.log", fileLoggerOpts => {
		fileLoggerOpts.FormatLogFileName = fName => {
			return String.Format(fName, DateTime.UtcNow);
		};
	});
});

Note that this handler is called on every log message 'write'; you may cache the log file name calculation in your handler to avoid any potential overhead in case of high-load logger usage.

Custom log entry formatting

You can specify FileLoggerProvider.FormatLogEntry handler to customize log entry content. For example, it is possible to write log entry as JSON array:

loggerFactory.AddProvider(new NReco.Logging.File.FileLoggerProvider("logs/app.js", true) {
	FormatLogEntry = (msg) => {
		var sb = new System.Text.StringBuilder();
		StringWriter sw = new StringWriter(sb);
		var jsonWriter = new Newtonsoft.Json.JsonTextWriter(sw);
		jsonWriter.WriteStartArray();
		jsonWriter.WriteValue(DateTime.Now.ToString("o"));
		jsonWriter.WriteValue(msg.LogLevel.ToString());
		jsonWriter.WriteValue(msg.EventId.Id);
		jsonWriter.WriteValue(msg.Message);
		jsonWriter.WriteValue(msg.Exception?.ToString());
		jsonWriter.WriteEndArray();
		return sb.ToString();
	}
});

(in case of .NET Core 2 use loggingBuilder.AddProvider instead of loggerFactory.AddProvider).

License

Copyright 2017-2020 Vitaliy Fedorchenko and contributors

Distributed under the MIT license