Example of a Node HTTP server who's response body is 'stdout' of a `echo hello world` spawn.

spawn-response.js

var spawn = require('child_process').spawn;
var http = require('http');

http.createServer(function (request, response) {
  
  response.writeHead(200, {
    'Content-Type': 'text/plain',
    'Connection':'close',
    'Transfer-Encoding':'identity' // 'chunked' can't be used unfortunately
                                   // since the child_process won't know how
                                   // to do the encoding on it's own stdout
  });
  
  // Hack, to force Node to flush the HTTP response headers
  var flushed = response._send('');

  var callback = function() {  
    spawn('echo', ['hello', 'world'], {
      // Set the 'stdout' fd to the HTTP connection's fd.
      customFds: [-1, request.connection.fd, -1]
    });
    // stream.destroy() is optional, and should be called if you DO NOT
    // intend on sending additional data after the cp closes. IE the cp
    // ending will close the stream (the cp's stdout).
    request.connection.destroy();
  };

  // Wait until we're sure that the HTTP headers have been flushed
  // (this might not be necessary...)
  if (flushed) {
    callback();
  } else {
    request.connection.on('flush', callback);
  }

}).listen(8124);

console.log('Server running at http://127.0.0.1:8124/');