Current Path : /usr/src/crypto/heimdal/appl/telnet/ |
FreeBSD hs32.drive.ne.jp 9.1-RELEASE FreeBSD 9.1-RELEASE #1: Wed Jan 14 12:18:08 JST 2015 root@hs32.drive.ne.jp:/sys/amd64/compile/hs32 amd64 |
Current File : //usr/src/crypto/heimdal/appl/telnet/telnet.state |
Three pieces of state need to be kept for each side of each option. (You need the localside, sending WILL/WONT & receiving DO/DONT, and the remoteside, sending DO/DONT and receiving WILL/WONT) MY_STATE: What state am I in? WANT_STATE: What state do I want? WANT_RESP: How many requests have I initiated? Default values: MY_STATE = WANT_STATE = DONT WANT_RESP = 0 The local setup will change based on the state of the Telnet variables. When we are the originator, we can either make the local setup changes at option request time (in which case if the option is denied we need to change things back) or when the option is acknowledged. To initiate a switch to NEW_STATE: if ((WANT_RESP == 0 && NEW_STATE == MY_STATE) || WANT_STATE == NEW_STATE) { do nothing; } else { /* * This is where the logic goes to change the local setup * if we are doing so at request initiation */ WANT_STATE = NEW_STATE; send NEW_STATE; WANT_RESP += 1; } When receiving NEW_STATE: if (WANT_RESP) { --WANT_RESP; if (WANT_RESP && (NEW_STATE == MY_STATE)) --WANT_RESP; } if (WANT_RESP == 0) { if (NEW_STATE != WANT_STATE) { /* * This is where the logic goes to decide if it is ok * to switch to NEW_STATE, and if so, do any necessary * local setup changes. */ if (ok_to_switch_to NEW_STATE) WANT_STATE = NEW_STATE; else WANT_RESP++; * if (MY_STATE != WANT_STATE) reply with WANT_STATE; } else { /* * This is where the logic goes to change the local setup * if we are doing so at request acknowledgment */ } } MY_STATE = NEW_STATE; * This if() line is not needed, it should be ok to always do the "reply with WANT_STATE". With the if() line, asking to turn on an option that the other side doesn't understand is: Send DO option Recv WONT option Without the if() line, it is: Send DO option Recv WONT option Send DONT option If the other side does not expect to receive the latter case, but generates the latter case, then there is a potential for option negotiation loops. An implementation that does not expect to get the second case should not generate it, an implementation that does expect to get it may or may not generate it, and things will still work. Being conservative in what we send, we have the if() statement in, but we expect the other side to generate the last response.