1  
 2     Three pieces of state need to be kept for each side of each option.
 3     (You need the localside, sending WILL/WONT & receiving DO/DONT, and
 4     the remoteside, sending DO/DONT and receiving WILL/WONT)
 5  
 6  	MY_STATE:	What state am I in?
 7  	WANT_STATE:	What state do I want?
 8  	WANT_RESP:	How many requests have I initiated?
 9  
10     Default values:
11  	MY_STATE = WANT_STATE = DONT
12  	WANT_RESP = 0
13  
14     The local setup will change based on the state of the Telnet
15     variables.  When we are the originator, we can either make the
16     local setup changes at option request time (in which case if
17     the option is denied we need to change things back) or when
18     the option is acknowledged.
19  
20     To initiate a switch to NEW_STATE:
21  
22  	if ((WANT_RESP == 0 && NEW_STATE == MY_STATE) ||
23  			WANT_STATE == NEW_STATE) {
24  	    do nothing;
25  	} else {
26  	    /*
27  	     * This is where the logic goes to change the local setup
28  	     * if we are doing so at request initiation
29  	     */
30  	    WANT_STATE = NEW_STATE;
31  	    send NEW_STATE;
32  	    WANT_RESP += 1;
33  	}
34  
35     When receiving NEW_STATE:
36  
37  	if (WANT_RESP) {
38  	    --WANT_RESP;
39  	    if (WANT_RESP && (NEW_STATE == MY_STATE))
40  		--WANT_RESP;
41  	}
42  	if (WANT_RESP == 0) {
43  	    if (NEW_STATE != WANT_STATE) {
44  		/*
45  		 * This is where the logic goes to decide if it is ok
46  		 * to switch to NEW_STATE, and if so, do any necessary
47  		 * local setup changes.
48  		 */
49  		if (ok_to_switch_to NEW_STATE)
50  		    WANT_STATE = NEW_STATE;
51  		else
52  		    WANT_RESP++;
53  *		if (MY_STATE != WANT_STATE)
54  		    reply with WANT_STATE;
55  	    } else {
56  		/*
57  		 * This is where the logic goes to change the local setup
58  		 * if we are doing so at request acknowledgment
59  		 */
60  	    }
61  	}
62  	MY_STATE = NEW_STATE;
63  
64  * This if() line is not needed, it should be ok to always do the
65    "reply with WANT_STATE".  With the if() line, asking to turn on
66    an option that the other side doesn't understand is:
67  		Send DO option
68  		Recv WONT option
69    Without the if() line, it is:
70  		Send DO option
71  		Recv WONT option
72  		Send DONT option
73    If the other side does not expect to receive the latter case,
74    but generates the latter case, then there is a potential for
75    option negotiation loops.  An implementation that does not expect
76    to get the second case should not generate it, an implementation
77    that does expect to get it may or may not generate it, and things
78    will still work.  Being conservative in what we send, we have the
79    if() statement in, but we expect the other side to generate the
80    last response.