Stream from a mongodb cursor to Express response in node.js

Question

I am toying around with all the fancy node.js/mongodb/express platforms, and stumbled across a problem:

app.get('/tag/:tag', function(req, res){   var tag=req.params.tag;   console.log('got tag ' + tag + '.');   catalog.byTag(tag,function(err,cursor) {      if(err) {        console.dir(err);        res.end(err);      } else {        res.writeHead(200, { 'Content-Type': 'application/json'});         //this crashes        cursor.stream().pipe(res);       }   }); }); 

As you probably guessed, catalog.byTag(tag, callback) does a find() query to Mongodb and returns the cursor

This leads to an error:

TypeError: first argument must be a string or Buffer 

According to mongodb driver doc, I tried to pass this converter to stream():

function(obj) {return JSON.stringify(obj);} 

but that does not help.

Can anybody tell me how to correctly stream something to a response?

Or is the only solution a boilerplate to manually pump the data using the 'data' and 'end' events?

Answer 1

Use the cursor stream in combination with JSONStream to pipe it to your response object.

cursor.stream().pipe(JSONStream.stringify()).pipe(res);