a.js

var buf = null;
var offset = 0;


stream.on('data', function(buf_) {
  assert(!buf);
  buf = buf_;
  stream.emit('readable');
  stream.pause();
});


stream.read = function(n) {
  if (!buf)
    return null;
    
  var left = buf.length - offset;
  if (left > n) {
    rv = buf.slice(offset, offset + n);
    offset += n;
  } else {
    rv = buf.slice(offset, offset + left);
    buf = null;
    offset = 0;
    stream.resume();
  }
  
  return buf;
}