The NetIO API is an abstraction layer for dealing with network I/O streams. This layer allows a great deal of control over how data is received from and sent on the network.
This layer was structured so that third-party modules could easily declare, or register, a set of custom I/O callbacks and put those callbacks into use as needed. To do this, there are seven callbacks available for modules' use and a structure representing a network I/O object.
The NetIO module developer should read the description of the network objects first, then the functions for working with these objects. There is also a development document that contains some suggestions and notes to keep in mind when devising one's own NetIO modules.