An ActiveEntry represents a url that is currently being loaded. The url load may be successful or it may fail, but, at some point it is an ActiveEntry, receiving cycles.
An ActiveEntry maintains all the data required by various steps throughout the netlib url loading process. When NET_GetURL() is called for a url, an ActiveEntry is created for that url. At this point, the ActiveEntry is initialized to hold the url itself (URL_Struct), the exit routine to be called when the load is complete (Net_GEtUrlExitFunc*), the window id to associate the load with a given window (MWContext*), the url type (int), and the output format (FO_Present_Types). The ActiveEntry is then placed in the netlib net_EntryList. Once it is determined that the url is not in the cache, the ActiveEntries protocol implementation pointer is set to the protocol implementation for the given scheme/protocol, and that protocol implementation's initialize member is called, with the current ActiveEntry as an argument.
A protocol implementation's initialization member then sets the ActiveEntries connection data (TCP_ConData) which maintains info such as the current state of the load (see netlib State Machines), the file descriptor/socket, long with other connection related information. Before the initialization member returns, it makes an initial call the protocol implementation's process routine (see netlib Process function) to initiate the actual load. Who knows, perhaps the load can complete in one call to the process function.
So, after a successful call to NET_GetURL(), an ActiveEntry for the url passed into NET_GetURL() resides in the global netlib net_EntryList. The net_EntryList is global to all of netlib, so it is accessible to all the various protocol implementations. At this point the url load has begun. An active entry exists with information about a url and the connection it's going to use to send/receive data.
In order for the load to continue, the front end must call NET_ProcessNet() continuously until all url loads are complete. One of NET_ProcessNet()'s arguments is a file descriptor. NET_ProcessNet() matches this file descriptor up with whichever active entry has the same file descriptor and calls that active entries protocol implementation's process member.
Once processing is complete the ActiveEntry is deallocated and removed from the netlib net_EntryList. This step can be part of the protocol implementation's process routine or by a call to the implementation's cleanup member.
Judson Valeski, 1998