iisnode interceptor

interceptor.js

(function () {

	// refactor process.argv to determine the app entry point and remove the interceptor

	var appFile;
	var newArgs = [];
	process.argv.forEach(function (item, index) {
		if (index === 2)
			appFile = item;
		if (index !== 1)
			newArgs.push(item);
	});

	process.argv = newArgs;

	// intercept console.log to convert strings to uppercase

	var oldLog = console.log;
	console.log = function (thing) {
		if (typeof thing === 'string')
			oldLog(thing.toUpperCase());
		else
			oldLog.apply(this, arguments);
	};

	// run the original application entry point

	require(appFile);
})();

node.config

nodeProcessCommandLine: "c:\program files (x86)\nodejs\node.exe" "c:\program files\iisnode\www\helloworld\interceptor.js"

The scenario is to intercept invocations to console.* functions in node.js apps run under iisnode to redirect (or fork) the output to custom locations (e.g. specific files int the file system, cloud storage, web socket connection).

The design is following:

• Use the nodeProcessCommandLine iisnode configuration property to specify that iisnode should always run a predefined interceptor.js file instead of the actual application entry point; note that iisnode will still append the fully qualified application entry point file name as a command line parameter to nodeProcessCommandLine.
• Within interceptor.js, we intercept the console.* APIs we care about before running the original application entry point code. This means the application code will execute against the rigged version of console.* APIs, since native modules are cached globally by default.
• interceptor.js also fixes up the process.argv to remove itself from the list to ensure backwards compat with the edge case of iisnode hosted applications that rely on the order of parameters passed in.

The interceptor should overwrite require.main.filename to point to the one that is expected. It is used to figure out what module kicked off a process. In a web app, it is often used to find the root of the website.