Packet IO built an abstraction of network IO devices.
Session Manager has a hash table for tracking sessions. The caller feeds packets to the session manager and may return triggered session events.
Plugin Manager loads C/Lua plugins and manages per-plugin, per-session context. When the caller feeds an event to the plugin manager, it invokes plugin callbacks.
Protocol Decoders are libraries that parse and extract information from the packet payload.
Active Queue Management is queue management algorithm libraries that schedule packets by buffering, forwarding, marking, or dropping. A plugin creates a queue instance and enqueues packets as its needs.
- Question: Who consumes the dequeue events?

Concepts

Session is an abstract of Layer 4-7 connection, i.e., TCP Session, HTTP Session, DNS Session.

A session can derive child sessions.
All session has three states, which are Opening, Active, Closing.
State changes generate session events.

Event is something happened in a session, i.e., TCP OPENING, HTTP Request, Session Extra Data updates.

Session Extra Data is a developer defined data structure that attached to a session, it's lifetime is same as the session.

Packet IO Library

struct stellar_packet;

packet_io_loop()
{
  packet_io_device_rx(&rx_pkt)
  //ingress processing: Tunnel decoding, IP defragmentation
  session_manager();
  plugin_manager();
  //egress processing: AMQ
  rl_group_id=pkt_get_group_id(rx_pkt);
  void *raw_pkt=pkt_get_raw(rx_pkt);
  AMQ_enqueue(group_id[], raw_pkt, pkt_sz);

}

Plugin Manager

Plugin Management APIs

/*
 * The pm_session_dettach_me just sets the flag to disable this plugin and no longer call this event callback.
 * Before calling pm_session_dettach_me, the current plugin must release related resources for the current session.
 */
pm_session_dettach_me(session);

/*
 * The current plugin(cb2) takes over the current session, the pm_session_take_over setting flag disables other plugins,
 * and the current session does not call other plugins except for the SESSION_EVENT_CLOSING event.
 *
 *                               +-----+   +-----+   +-----+   +-----+
 * Plugin runtime callback list: | cb1 |-->| cb2 |-->| cb3 |-->| cb4 |
 *                               +-----+   +-----+   +-----+   +-----+
 *                                           /|\
 *                                            |
 *                         plugin cb2 run pm_session_take_over
 * 
 * A plugin(cb1/cb3/cb4) that is taken over, if the plugin was called before being taken over and has a registered SESSION_EVENT_CLOSING event,
 * it will be called again when the SESSION_EVENT_CLOSING event comes. Otherwise, the plugin will not be called.
 */
pm_session_take_over(session);

Session Manager

Session Management APIs

session_drop_current_packet(session);
session_set_ratelimit_group(session, rl_group_id);
session_set_metadata(session, const char *key, void *value, size_t val_sz, free_callback);
session_get_metadata(session, const char *key, void **value, size_t *val_sz);
session_del_metadata(session, key)
session_lock(session, plug_id);
session_unlock(session, plug_id);

Plugin Example

plugin_entry(session, ctx)
{
  session_get_metadata(session, "fw_action", value);
  if(value==INTERCEPT)
  {
    //pm_session_dettach_me(session);
    return;
  }
  ret=check_security_policy(session);
  if(ret==INTERCEPT)
  {
    pm_session_take_over(session);
  }
  else if(ret==RATE_LIMIT)
  {
    group_id=security_policy_id;
    amq_group_create(group_id, CIR, CBS);
    session_set_ratelimit_group(session, group_id);
  }
}