Returns a new empty instance.
Returns the nextChunk of data to output to the client.
This may return:
- A reference on a chunk of data (a hash, an array, etc..) - A string of bytes. This is usefull when you force using a binary writer (by using $req->requestedFormat('bin') in your handler) - undef if the end of the stream is reached.
Implement this in application specific subclasses (Or use one of the provided subclasses if your data source is compatible)