Node.js JSON escaping issue

I been following this tutorial on creating a simple API with Node.js and MongoDB, however I've run into some issues with the formatting of the JSON post that I'm making.

The post is something along the lines of:

curl POST -d '{"test":"test"}' http://127.0.0.1:3000/add

However once in MongoDB it looks like the following:

{\"test\":\"test\"}":"","_id":"4ff725d6349fdf9c0d000004"}

My POST function is as follows:

app.post('/add', function(req, res){
   require('mongodb').connect(mongourl, function(err, conn){
    conn.collection('docs', function(err, coll){
      coll.insert( req.body, {safe:true}, function(err){
      res.writeHead(200, {
        "Content-Type": "application/json",
        "Access-Control-Allow-Origin": "*"
      });
      res.end(JSON.stringify(req.body));
      });
    });
  });
 });

Any ideas on how I can ensure the POST is processed correctly would be helpful!

Thanks in advance!