udp_unicast_join

Documentation
- Reference manual
- Packages
  - SWI-Prolog C-library
    - library(udp_broadcast): A UDP broadcast proxy
      - Caveats
        
        udp_broadcast_close/1
        
        udp_broadcast_initialize/2
        
        udp_peer_add/2
        
        udp_peer_del/2
        
        udp_peer/2
        
        udp_term_string_hook/3
        
        udp_unicast_join_hook/3

Availability::- use_module(library(udp_broadcast)).

[semidet,multifile]udp_unicast_join_hook(+Scope, +From, +Data)

This multifile hook is called if an UDP package is received on the port of the unicast network identified by Scope. From is the origin IP and port and Data is the message data that is deserialized as defined for the scope (see udp_term_string/3).

This hook is intended to initiate a new node joining the network of peers. We could in theory also omit the in-scope test and use a normal broadcast to join. Using a different channal however provides a basic level of security. A possibe implementation is below. The first fragment is a hook added to the server, the second is a predicate added to a client and the last initiates the request in the client. The excanged term (join(X)) can be used to exchange a welcome handshake.

:- multifile udp_broadcast:udp_unicast_join_hook/3.
udp_broadcast:udp_unicast_join_hook(Scope, From, join(welcome)) :-
    udp_peer_add(Scope, From),

join_request(Scope, Address, Reply) :-
    udp_peer_add(Scope, Address),
    broadcast_request(udp(Scope, join(X))).

?- join_request(myscope, "1.2.3.4":10001, Reply).
Reply = welcome.