Upload progress with Node.js Restify

I'm uploading a file to a Node.js Restify server and I'm trying to send back some progress information to the client.

In my example below the file uploads successfully but the progress dots (.) don't show up until the entire file has been uploaded and res.end() has been sent.

Is it possible to write to the response stream and have status information sent back to the client?

var restify = require('restify');
var fs = require('fs');


function uploadFile(req, res, next) {
    var path = req.params.devicename;
    var filename = req.params.filename;

    console.log("Upload file");
    var writeStream = fs.createWriteStream(path + "/" + filename);
    var r = req.pipe(writeStream);

    res.writeHead(200, {"Content-type":"text/plain"});

    r.on("drain", function() {
            res.write(".", "ascii");
    });

    r.on("finish", function () {
            console.log("Upload complete");
            res.write("Upload complete");
            res.end();
    });

    next();
}

// *************** start Restify server *********************
var server = restify.createServer();
server.post('/api/uploadfile/:devicename/:filename', uploadFile);
server.listen(8080, function() {
  console.log('%s listening at %s', server.name, server.url);
});

Thanks