# Cyrus IMAP Server: prot layer

The prot layer, defined in `prot.h`, is a stdio replacement for network i/o. It does the standard buffering of input and output and allows certain operations especially suited for request/response protocols like IMAP.

## Events

The prot layer allows "events" to be associated with each prot stream. These events are trigger at the given time or after when the protstream is attempted to be read from.

An event is currently represented by the following datastructure:

    struct prot_waitevent;

    typedef struct prot_waitevent *prot_waiteventcallback_t(struct protstream *s,
                                struct prot_waitevent *ev,
                                void *rock);

    struct prot_waitevent {
        time_t mark;
        prot_waiteventcallback_t *proc;
        void *rock;
        struct prot_waitevent *next;
    };

The application is currently allowed to modify mark, proc, and rock as desired when there are no active calls to a prot function on the stream which this event is associated.

The API is as follows:

- Use `prot_addwaitevent()` to add an event callback onto the stream:

      extern struct prot_waitevent *prot_addwaitevent(struct protstream *s,
                              time_t mark,
                              prot_waiteventcallback_t *proc,
                              void *rock);

  where s is the stream to add the event to, mark is the time to trigger the event, proc is the callback to make, and rock is an opaque data item handed to the callback. It returns a pointer to the event structure; this is the pointer that must be used to remove the event or modify it in some way.

- Use `prot_removewaitevent()` to remove an event:

      extern void prot_removewaitevent(struct protstream *s,
                       struct prot_waitevent *event);

  It requires event to have been returned from `prot_addwaitevent()` previously. No further references are allowed to event or its fields. event->rock is not free'd nor examined in any way. This function may be called while inside the callback event->proc(). If an event is removed inside of its callback, that callback must return `NULL`.

Some common things to do with events:

- To reschedule an event ev, simply set ev->mark to the next time it should trigger. If currently in ev->proc(), it should return ev.

last modified: $Date: 2003/08/06 21:28:05 $