I needed to add logging functionality to an existing TypeScript application hosted on ASP.Net MVC.
Since I usually use log4net in C#, log4javascript was an obvious choice, as it provides a similar API.
First, I needed to declare the parts of the log4javascript API I use in TypeScript:
declare module log4javascript {
class Logger {
info(msg: string);
info(msg: string, value: any);
addAppender(app: AjaxAppender);
}
function getLogger(name: string): Logger;
function getNullLogger(): Logger;
class AjaxAppender {
constructor(url: string);
setSessionId(id: string);
setLayout(layout: JsonLayout);
addHeader(key: string, value: string);
}
class JsonLayout {
constructor(readable: boolean, combine: boolean);
}
}
In the logging class, I added logger and AjaxAppender. Depending on the data to log, I also configure a JsonLayout.
logger: log4javascript.Logger;
A non-logging logger instance is created using getNullLogger():
this.logger = log4javascript.getNullLogger();
Plain-text AjaxAppender
Use these statements to create an Ajax-based logger in TypeScript:
this.logger = log4javascript.getLogger("MyLoggerName");
var app = new log4javascript.AjaxAppender("http://myhost/myapp/mylogger");
this.logger.addAppender(app);
On the MVC side, the controller receives the parameters: logger, timestamp, level, url, message, sessionid, and layout. (Note that these parameter names can be changed using the setKeys() method)
The value for sessionid is set using
ajaxAppender.setSessionId(sessionId);
To log a string message, simply write
this.logger.info("my info log message");
The C# controller method stub therefore looks something like this:
[ValidateInput(false)]
[HttpPost]
public ActionResult Log(long? timestamp, string level, string sessionid, string message)
{
var ipaddr = Request.ServerVariables["HTTP_X_FORWARDED_FOR"];
if (string.IsNullOrEmpty(ipaddr))
ipaddr = Request.ServerVariables["REMOTE_ADDR"];
if (string.IsNullOrEmpty(ipaddr))
ipaddr = Request.UserHostAddress;
if (level == "INFO")
logger.Info(ipaddr + " " + sessionid + " " + message);
else
logger.Debug("[" + level + "] " + ipaddr + " " + sessionid + " " + message);
return Json(null);
}
where logger is an instance of log4net.Ilog.
JSON-formatted AjaxAppender
To change the appender’s data format to JSON, we set its layout to JsonLayout:
this.logger = log4javascript.getLogger("MyJsonLogger");
var app = new log4javascript.AjaxAppender("http://myhost/myapp/myjsonlogger");
app.setLayout(new log4javascript.JsonLayout(false, false));
app.addHeader("Content-Type", "application/json");
this.logger.addAppender(app);
The C# controller method receives a JSON array of log entries
[
{
"logger":"MyJsonLogger",
"timestamp":1448621329758,
"level":"INFO",
"url":"http://localhost/myapp/...",
"message":
[ "message1",
"message2", ...
]
}
]
where message1, message2, etc are the parameters of the logger’s debug/info/warn etc. calls.
We create a C# class containing the required properties
public class Data
{
public string logger;
public long? timestamp;
public string level;
public string url;
public string[] message;
}
and deserialize the HTTP request’s InputStream using JSON.Net:
[ValidateInput(false)]
[HttpPost]
public ActionResult Execute()
{
string inputContent;
using (var sr = new StreamReader(HttpContext.Request.InputStream))
{
inputContent = sr.ReadToEnd();
}
var data = JsonConvert.DeserializeObject<Data[]>(inputContent);
if (data != null)
{
foreach (var d in data)
{
if (d.level == "INFO")
logger.Info(d.message[0] + " " + d.message[1]);
else
logger.Debug("[" + d.level + "] " + d.message[0] + " " + d.message[1]);
}
}
return Json(null);
}
Again, logger is an instance of log4net.Ilog.
Posted by devio 
