Invoking an asynchronous method inside a middleware in node-http-proxy - node.js

Question

I'm trying to create a proxy with node-http-proxy in Node.js that checks whether a request is authorized in a mongodb.
Basically, I created a middleware module for the node-http-proxy that I use like this:
httpProxy.createServer(
require('./example-middleware')(),
9005, 'localhost'
).listen(8005)
What the middleware module does is using mongojs to connect to mongodb and run a query to see if the user is authorized to access the resource:
module.exports = function(){
// Do something when first loaded!
console.log("Middleware loaded!");
return function (req, res, next) {
var record = extractCredentials(req);
var query = -- Db query --
//Debug:
log("Query result", query);
db.authList.find(query).sort({
"url.len": -1
}, function(err, docs){
console.log(docs);
// Return the creator for the longest matching path:
if(docs.length > 0) {
console.log("User confirmed!");
next();
} else {
console.log("User not confirmed!");
res.writeHead(403, {
'Content-Type': 'text/plain'
});
res.write('You are not allowed to access this resource...');
res.end();
}
});
}
}
Now the problem is that as soon as I add the asynchronous call to mongodb using mongojs the proxy hangs and never send the response back.
To clarify: on a "User not confirmed" everything works fine and the 403 is returned. On a "user confirmed" however I see the log but the browser then hangs forever and the request isn't proxied.
Now, if I remove the "user confirmed" and next() part outside of a callback it does work:
module.exports = function(){
// Do something when first loaded!
console.log("Middleware loaded!");
return function (req, res, next) {
var record = extractCredentials(req);
var query = --- query ---
console.log("User confirmed!");
next();
}
but I can't do that since the mongojs query is meant (rightfully I guess) to be executed asynchronously, the callback being triggered only when the db replied...
I also tried the version without using a middleware:
http.createServer(function (req, res) {
// run the async query here!
proxy.proxyRequest(req, res, {
host: 'localhost',
port: 9000
});
}).listen(8001);
But that did not help either...
Any clue? Note that I'm new to node.js so I suspect a misunderstanding on my side...

Answer 1

Found the answer, actually the catch is that the request needs to be buffered:
httpProxy.createServer(function (req, res, proxy) {
// ignore favicon
if (req.url === '/favicon.ico') {
res.writeHead(200, {
'Content-Type': 'image/x-icon'
} );
res.end();
console.log('favicon requested');
return;
}
var credentials = extractCredentials(req);
console.log(credentials);
var buffer = httpProxy.buffer(req);
checkRequest(credentials, function(user){
if(user == ...) {
console.log("Access granted!");
proxy.proxyRequest(req, res, {
host: 'localhost',
port: 9005,
buffer: buffer
});
} else {
console.log("Access denied!");
res.writeHead(403, {
"Content-Type": "text/plain"
});
res.write("You are not allowed to access this resource...");
res.end();
}
});
}).listen(8005);

Answer 2

Two problems:
You're not calling next(); in the else case of your sort callback.
The second parameter to your sort callback is a Cursor, not an array of documents. As such, docs.length > 0 is never true and the code always follows the else path.