Tracing Node's core modules? about njstrace

[ValYouW]

Hi!

Hmmm, this is not possible I'm afraid, at least not something I know of....
I went to check a bit on how these files are being used, and if I understood correctly, during build time (of node.exe) there is a script (tools/js2c.py) that embed all internal javascript code inside a c++ file (node_javascript.cc) that is then linked into node. Then inside node_native_module.cc they are being compiled (at runtime, method: LookupAndCompile), which means we can't touch this...

What you can do is "hijack" all the functions inside these modules and "trace" them, say you want to hikack fs, then after calling njsTrace.inject do this:

function wrapFunc(module, file, fname) {
	var orig = module[fname];
	module[fname] = function() {
		// note we dont really have line numbers for this method, use 0
		var __njsEntryData__ = __njsTraceEntry__({ file: file, name: fname, line: '0', args: arguments });
		var res = orig.apply(fs, arguments);
		__njsTraceExit__({ entryData: __njsEntryData__, exception: false, line: '0', returnValue: res });
		return res;
	}
}

var fs = require('fs');
var fsFuncs = Object.getOwnPropertyNames(fs).filter(x => typeof (fs[x]) === 'function');
for (let i = 0; i < fsFuncs.length; i++) {
	wrapFunc(fs, 'fs.js', fsFuncs[i]);
}

But since this is too "dangerous" I don't think it should be part of this library... try the above method and keep me posted, it's interesting :)

[christophschw]

Hey, thank you again for the explanation and especially for the code! That's my understanding too from what I read how Node handles the core modules.

Edit: My bad, I should learn to read my logs correctly 🤦‍♂️ This code works completely as intended in the whole context of teh app! 🎉
Big thank you! This is awesome!
Now, I will extend this for all core modules 😊

Edit 2:
Tracing almost all modules 😊

'use strict'
var coreModules = require('builtin-modules');
// Error due to events and zlib! Exclude others for performance reasons
var excludeModules = ['events', 'zlib', 'crypto', 'stream', 'util'];

// Wrap original function with tracer variables
// https://github.com/ValYouW/njsTrace/issues/18#issuecomment-575951138
function wrapFunc(module, file, fname) {
    var orig = module[fname];
    module[fname] = function () {
        // Note: we don't really have line numbers for this method, use 0
        var __njsEntryData__ = __njsTraceEntry__({ file: file, name: fname, line: '0', args: arguments });
        var res = orig.apply(module, arguments);
        __njsTraceExit__({ entryData: __njsEntryData__, exception: false, line: '0', returnValue: res });
        return res;
    }
}

for (let j = 0; j < coreModules.length; j++) {
    // Skip crypto module due to performance reasons
    if (!excludeModules.includes(coreModules[j])) {
        var coreModuleObj = require(coreModules[j])
        var coreModuleFuncs = Object.getOwnPropertyNames(coreModuleObj).filter(x => typeof (coreModuleObj[x]) === 'function');
        for (let i = 0; i < coreModuleFuncs.length; i++) {
            // Skip Buffer methods
            if (!coreModuleFuncs[i].includes('Buffer')) {
                wrapFunc(coreModuleObj, coreModules[j] + '.core', coreModuleFuncs[i]);
            }
        }
    }
}

[ValYouW]

Great!
BTW, one time I wanted to understand something in node so I just compiled it from source and debugged it (the c++ code). So you can always clone "node", modify the "libs" as you want and compile, you will have your own modified version of the libs....
Send a link to the paper when you are done with your project :)

[christophschw]

Yes, this is a very good idea.
Unfortunately, the overall report will be in German, but at least the abstract will be translated. I secretly hope that maybe my professor or someone at the chair will take the results publish it in english 😉 I'll keep you posted 😊
Thanks again!