Methods for serving data include maintaining an incomplete version of an object at a server and at least one fragment at the server. In response to a request for the object from a client, the incomplete version of the object, an identifier for a fragment comprising a portion of the object, and a position for the fragment within the object are sent to the client. After receiving the incomplete version of the object, the identifier, and the position, the client requests the fragment from the server using the identifier. The object is constructed by including the fragment in the incomplete version of the object in a location specified by the position.