Contextify : How to catch async errors

Question

I need to run unsafe JS script in node and be able to recover from errors. The script can use async functions so I use contextify instead of node built in VM module. The problem is that errors in async code in the script crash the node process.

Here is my test :

var contextify = require('contextify');
var context = {
    console:{
        log:function(msg){
            console.log('Contextify : '+msg);
        }
    },
    setTimeout:setTimeout
};
console.log("begin test");
contextify(context);
try{ // try to run unsafe script
    //context.run("console.log('Sync user script error');nonExistingFunction();"); // works
    context.run("setTimeout(function(){ console.log('Async user script error');nonExistingFunction(); },2000);"); // crash node process
}catch(err){
    console.log("Recover sync user script error"); 
}
console.log("end test");

How can I catch async errors ?

score 0 · Answer 1 · answered Sep 30 '14 at 10:21

I solved the problem by using child_process to create a thread for the script to execute in :

//main.js

var child_process = require('child_process');

var script = child_process.fork("scriptrunner.js");
script.on('error',function(err){
    console.log("Thread module error " + JSON.stringify(err));
});
script.on('exit',function(code,signal){
    if(code==null)
        console.log("Script crashed");
    else console.log("Script exited normally");
});
script.send("setTimeout(function(){ console.log('Async user script error');nonExistingFunction(); },2000);");

//scriptrunner.js

var contextify = require('contextify');

var context = {
    console:{
        log:function(msg){
            console.log('Contextify : '+msg);
        }
    },
    setTimeout:setTimeout
};
contextify(context);

process.on('message', function(js) {            
    try{        
        context.run(js);
    }catch(err){
        console.log("Catch sync user script error " + err);
    }
});

So now if the script crashes it crash its own process and not the main node process. The downside is that I can't pass complex object (such as my context) between my main process and the script's thread, I need to find a workaround for that.

I'm also using contextiy to run scripts. I have the opposite problem. How do I know when an async function inside a contextify instance finishes successfully and can return the result back to the parent process? Thanks in advance! — LPG, May 13 '16 at 22:14

Contextify : How to catch async errors

1 Answers1