node.js server handle request callback function ending before writing response - node.js

Question

I have an http server with a handleRequest callback that runs another script in vm.runInNewContext for each request. The script that runs inside vm.runInNewContext makes some asynchronous http post requests and writes the server response only after getting the responses from the posts.
As a result, the code of handleRequest callback ends before the server response is written.
Is it safe? or is there a way to avoid this situation?
Here is some code:
var server = http.createServer(handleRequest);
server.listen(8080);
var handleRequest = function (request, response) {
// get request data...
var context = {
ServerRequest : request,
ServerResponse : response
};
var stringScript = // a string with the script that posts data
var script = vm.createScript(stringScript);
script.runInNewContext({ context: context });
}
the script string does this:
var request = require('request');
var options = {....}
var req = request.get(options);
req.on('response', function (res) {
var chunks = [];
res.on('data', function(chunk) {
chunks.push(chunk);
});
res.on('end', function() {
var buffer = Buffer.concat(chunks);
var encoding = res.headers['content-encoding'];
if (encoding == 'gzip') {
zlib.gunzip(buffer, function(err, decoded) {
// set response headers and write the response
context.ServerResponse.end(decoded.toString());
});
} else if (encoding == 'deflate') {
zlib.inflate(buffer, function(err, decoded) {
// set response headers and write the response
context.ServerResponse.end(decoded.toString());
})
} else {
// set response headers and write the response
context.ServerResponse.end(buffer.toString());
}
});
});

Answer 1

Simple solution: Return a promise (e.g. use the Q-library) from the VM-script.
script.runInNewContext will return whatever you return from the VM-script. That way you have a "callback" for when the VM code finishes.
// Script for VM
// I simplified it. Just resolve or reject the promise whenever you are done with your work
'use strict';
var defer = q.defer();
doABarrelRoll(function() {
defer.resolve('RESULT');
});
defer.promise; // This line will return the promise.
When returning a value from a VM-script, you do not need any return construction. Just write the thing you want and let the magic happen.
// Script for current context
'use strict';
var server = http.createServer(handleRequest);
server.listen(8080);
var handleRequest = function (request, response) {
// get request data...
var context = {
ServerRequest : request,
ServerResponse : response
};
var stringScript = // a string with the script that posts data
var script = vm.createScript(stringScript);
var prom = script.runInNewContext({
context: context,
q: require('q'),
});
prom.done(function ($result) {
console.log('VM finished with result: ' + $result);
});
}