quick and dirty header and body echo in node.js and express.js

Having some problem getting a client to Post JSON properly, so for diagnostics I came up with the following node.js:

Here's showpost.js:

var express = require('express');
var app = express();

app.use (function(req, res, next) {
    var data='';
    req.setEncoding('utf8');
    req.on('data', function(chunk) {
       data += chunk;
    });

    req.on('end', function() {
        req.body = data;
        next();
    });
});

app.get('/', function (req, res) {
   res.sendfile(__dirname + '/index.html');
});

app.post("/peek",function(req,res){
   console.log("HEADERS:");
    console.log(JSON.stringify(req.headers,null," "));
   console.log("BODY:");
    console.log(req.body);
   
    res.send(req.headers);
   
});
app.listen(3001);
console.log('Listening on port 3001');

Here's index.html in the same directory:
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js" type="text/javascript"></script>
<script>
function check(){
   
    var url = "/peek";
    var payload = JSON.stringify({"foo":"bar","hoo":["ha","ver"]});
   
    $.ajax({
        url: url,
        type: "post",
        data: payload,
        dataType: "json",
        contentType:"application/json",
        success: function(response) {
            $(".out").text(JSON.stringify(response,null," "));
        },
        error: function(e){
            alert(JSON.stringify(e));
        }
    });
   
}
</script>
<input type="button" value="peek" onClick="check();">
<pre class="out"></pre>

package.json is something like
{
  "name": "peek",
  "description": "quick and dirty post peeker",
  "version": "0.1.0",
  "private": true,
  "dependencies": {
    "express": "3.x"
  }
}

copy these files in a directory, run "npm install" then "nodemon showpost.json" (or plain old "node"). Then localhost:3001/ will have a button to press, or you can post to localhost:3001/peek