request.on(readable) called twice for single request in nodejs - node.js

Question

I am new in nodejs and now days i am learnig http module.
I wrote a js program for node to check if content-type is application/json in request, then it should console at 'readable' event.
What happening is: on a single request 'readable' event called twice and print the value first time and second time it returns null.
Here is Code:
var connect = require('connect');
function jsonParse(req, res, next) {
if (req.headers['content-type'] == 'application/json' && req.method == 'POST') {
var readData = '';
req.on('readable', function() {
console.log('inside readable ' + req.read());
readData += req.read();
});
req.on('end', function() {
try {
req.body = JSON.parse(readData);
} catch (e) {
}
next();
})
} else {
next();
}
}
connect()
.use(jsonParse)
.use(function(req, res) {
if (req.body) {
res.end('JSON parsed !' + req.body);
} else {
res.end('no json detected !');
}
}).listen(3000);
I am calling this like:
output is :
inside readable {
"foo":"asdf"
}
inside readable null
Please guide me how can i handle this. Thanks in advance.

Answer 1

You should only read from the request when data is available, so when req.read() does not return null. You can check this with a while loop.
Replace:
var readData = '';
req.on('readable', function() {
console.log('inside readable ' + req.read());
readData += req.read();
});
With:
var readData = '';
req.on('readable', function(){
var chunk;
while (null !== (chunk = req.read())){
readData += chunk;
}
});