node js http server request body as stream readabl

I'm writing a http server using node.js and having trouble isolating the request body as a stream readable. Here is a basic sample of my code:

var http = require('http')
  , fs = require('fs');

http.createServer(function(req, res) {
  if ( req.method.toLowerCase() == 'post') {
    req.pipe(fs.createWriteStream('out.txt'));
    req.on('end', function() {
      res.writeHead(200, {'content-type': 'text/plain'})
      res.write('Upload Complete!\n');
      res.end();
    });
  }
}).listen(8182);
console.log('listening on port 8182');

According to node's documentation the a request param is an instance of http.IncomingObject which implements node's readable stream interface. The problem with just using stream.pipe() as I did above is the readable stream includes the plain text of the request headers along with the request body. Is there a way to isolate only the request body as a readable stream?

I'm aware that there are frameworks for file uploads such as formidable. My ultimate goal is not to create an upload server but to act as a proxy and stream the request body to another web service.

thanks in advance.

Edit>> working server for "Content-type: multipart/form-data" using busboy

var http = require('http')
  , fs = require('fs')
  , Busboy = require('busboy');

http.createServer(function(req, res) {
  if ( req.method.toLowerCase() == 'post') {
    var busboy = new Busboy({headers: req.headers});
    busboy.on('file', function(fieldname, file, filename, encoding, mimetype) {
      file.pipe(fs.createWriteStream('out.txt'));
    });
    req.pipe(busboy);
    req.on('end', function() {
      res.writeHead(200, 'Content-type: text/plain');
      res.write('Upload Complete!\n');
      res.end();
    });
  }
}).listen(8182);
console.log('listening on port 8182');

Check your req.headers['content-type']. If it's multipart/form-data then you could use a module like busboy to parse the request for you and give you readable streams for file parts (and plain strings for non-file parts if they exist).

If the content-type is some other multipart/* type, then you could use dicer, which is the underlying module that busboy uses for parsing multipart.