Does Express.js support sending unbuffered progressively flushed responses?

Perl's Catalyst framework permitts you to send an progressively flushed response over an open connection. You could for instance use write_fh() on Catalyst::Response. I've begun using Node.js, and I can't find how to do the equivalent.

If I want to send a big CSV file, on the order of 200 megs is there a way to do that without buffering the whole CSV file in memory? Granted, the client will timeout if you don't send data in a certain amount of time, so a promise would be nice if -- but is there anyway to do this?

When I try to do a res.send(text) in a callback, I get

Express
500 Error: This socket has been ended by the other party

And, it doesn't seem that Express.js supports an explicit socket.close() or anything of the ilk.

Here is an example,

exports.foo = function (res) {                          
  var query = client.query("SELECT * FROM naics.codes");
  query.on('row', function(row) {                       
    //console.log(row);                                 
    res.write("GOT A ROW");                             
  });                                                   
  query.on('end', function() {                          
    res.end();                                          
    client.end();                                       
  });                                                   
};                                                      

I would expect for that to send "GOT A ROW" out for each row, until the call to client.end() signifying completion.

Express is built on the native HTTP module, which means res is an instance of http.ServerResponse, which inherits from the writable stream interface. That said, you can do this:

app.get('/', function(req, res) {
  var stream = fs.createReadStream('./file.csv');
  stream.pipe(res);

  // or use event handlers
  stream.on('data', function(data) {
    res.write(data);
  });

  stream.on('end', function() {
    res.end();
  });
});

The reason you can't use the res.send() method in Express for streams is because it will use res.close() automatically for you.