Simple and efficient file logger provider for .NET Core (.NET Core 2) without additional dependencies.

• very similar to standard ConsoleLogger but writes to a file
• can append to a file
• supports rolling file behaviour and can control total log size
• suitable for intensive concurrent usage: has internal message queue to avoid threads blocking

Add NReco.Logging.File package reference and initialize file logging provider:

Example of configuration section from 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
	}
}

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).

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).

Copyright 2017-2018 Vitaliy Fedorchenko

Distributed under the MIT license