1. A method of performing message payload processing functions in a network element on behalf of an application, the method comprising the computer-implemented steps of: receiving user-specified input at the network element; receiving one or more data packets at the network element; determining, based on the one or more data packets, a particular message classification indicated in the user-specified input; and processing at least a portion of an application layer message contained in one or more payload portions of the one or more data packets by performing, relative to the portion of the message, one or more actions that are (a) specified in the user-specified input and (b) associated with the particular message classification; wherein the message is directed to the application, and wherein the actions are performed on behalf of the application.