Fine tune server candidate selection logic

DHCPv6 server info from ADVERTISE messages is inserted in the server
candidate list sorted according to the preference value (highest values
first in the list).
Server candidate list can only contain one entry from a given server.
Server with highest preference value is selected; in case the server
does not respond the next server is selected from the list.
When the server candidate list is empty and no servers responded;
the client restarts the DHCPv6 server discovery process

1 files changed, 100 insertions, 80 deletions

diff --git a/src/odhcp6c.c b/src/odhcp6c.c
index 460f230..c8d40f6 100644
--- a/src/odhcp6c.c
+++ b/src/odhcp6c.c
@@ -236,26 +236,53 @@ int main(_unused int argc, char* const argv[])
 		dhcpv6_set_ia_mode(ia_na_mode, ia_pd_mode);
 		bound = false;
 
-		// Server candidates need deep-delete
-		size_t cand_len;
-		struct dhcpv6_server_cand *cand = odhcp6c_get_state(STATE_SERVER_CAND, &cand_len);
-		for (size_t i = 0; i < cand_len / sizeof(*cand); ++i) {
-			free(cand[i].ia_na);
-			free(cand[i].ia_pd);
-		}
-		odhcp6c_clear_state(STATE_SERVER_CAND);
-
 		syslog(LOG_NOTICE, "(re)starting transaction on %s", ifname);
 
 		do_signal = 0;
-		int res = dhcpv6_request(DHCPV6_MSG_SOLICIT);
+		int mode = dhcpv6_request(DHCPV6_MSG_SOLICIT);
 		odhcp6c_signal_process();
 
-		if (res <= 0) {
-			continue; // Might happen if we got a signal
-		} else if (res == DHCPV6_STATELESS) { // Stateless mode
+		if (mode < 0)
+			continue;
+
+		do {
+			int res = dhcpv6_request(mode == DHCPV6_STATELESS ?
+					DHCPV6_MSG_INFO_REQ : DHCPV6_MSG_REQUEST);
+
+			odhcp6c_signal_process();
+			if (res > 0)
+				break;
+			else if (do_signal > 0) {
+				mode = -1;
+				break;
+			}
+
+			mode = dhcpv6_promote_server_cand();
+		} while (mode > DHCPV6_UNKNOWN);
+
+		if (mode < 0)
+			continue;
+
+		switch (mode) {
+		case DHCPV6_STATELESS:
+			bound = true;
+			syslog(LOG_NOTICE, "entering stateless-mode on %s", ifname);
+
 			while (do_signal == 0 || do_signal == SIGUSR1) {
 				do_signal = 0;
+				script_call("informed");					
+
+				int res = dhcpv6_poll_reconfigure();
+				odhcp6c_signal_process();
+
+				if (res > 0)
+					continue;
+
+				if (do_signal == SIGUSR1) {
+					do_signal = 0; // Acknowledged
+					continue;
+				} else if (do_signal > 0)
+					break;
 
 				res = dhcpv6_request(DHCPV6_MSG_INFO_REQ);
 				odhcp6c_signal_process();
@@ -263,84 +290,63 @@ int main(_unused int argc, char* const argv[])
 					continue;
 				else if (res < 0)
 					break;
-				else if (res > 0)
-					script_call("informed");
-
-				bound = true;
-				syslog(LOG_NOTICE, "entering stateless-mode on %s", ifname);
-
-				if (dhcpv6_poll_reconfigure() > 0)
-					script_call("informed");
 			}
+			break;
 
-			continue;
-		}
-
-		// Stateful mode
-		if (dhcpv6_request(DHCPV6_MSG_REQUEST) <= 0)
-			continue;
-
-		odhcp6c_signal_process();
-		script_call("bound");
-		bound = true;
-		syslog(LOG_NOTICE, "entering stateful-mode on %s", ifname);
+		case DHCPV6_STATEFUL:
+			script_call("bound");
+			bound = true;
+			syslog(LOG_NOTICE, "entering stateful-mode on %s", ifname);
 #ifdef EXT_BFD_PING
-		if (bfd_interval > 0)
-			bfd_start(ifname, bfd_loss, bfd_interval);
+			if (bfd_interval > 0)
+				bfd_start(ifname, bfd_loss, bfd_interval);
 #endif
 
-		while (do_signal == 0 || do_signal == SIGUSR1) {
-			// Renew Cycle
-			// Wait for T1 to expire or until we get a reconfigure
-			int res = dhcpv6_poll_reconfigure();
-			odhcp6c_signal_process();
-			if (res > 0) {
-				script_call("updated");
-				continue;
-			}
-
-			// Handle signal, if necessary
-			if (do_signal == SIGUSR1)
-				do_signal = 0; // Acknowledged
-			else if (do_signal > 0)
-				break; // Other signal type
-
-			size_t ia_pd_len, ia_na_len, ia_pd_new, ia_na_new;
-			odhcp6c_get_state(STATE_IA_PD, &ia_pd_len);
-			odhcp6c_get_state(STATE_IA_NA, &ia_na_len);
-
-			// If we have any IAs, send renew, otherwise request
-			int r;
-			if (ia_pd_len == 0 && ia_na_len == 0)
-				r = dhcpv6_request(DHCPV6_MSG_REQUEST);
-			else
-				r = dhcpv6_request(DHCPV6_MSG_RENEW);
-			odhcp6c_signal_process();
-			if (r > 0) { // Renew was succesfull
-				// Publish updates
-				script_call("updated");
-				continue; // Renew was successful
-			}
-
-			odhcp6c_clear_state(STATE_SERVER_ID); // Remove binding
+			while (do_signal == 0 || do_signal == SIGUSR1) {
+				// Renew Cycle
+				// Wait for T1 to expire or until we get a reconfigure
+				int res = dhcpv6_poll_reconfigure();
+				odhcp6c_signal_process();
+				if (res > 0) {
+					script_call("updated");
+					continue;
+				}
 
-			// If we have IAs, try rebind otherwise restart
-			res = dhcpv6_request(DHCPV6_MSG_REBIND);
-			odhcp6c_signal_process();
+				// Handle signal, if necessary
+				if (do_signal == SIGUSR1)
+					do_signal = 0; // Acknowledged
+				else if (do_signal > 0)
+					break; // Other signal type
 
-			odhcp6c_get_state(STATE_IA_PD, &ia_pd_new);
-			odhcp6c_get_state(STATE_IA_NA, &ia_na_new);
-			if (res <= 0 || (ia_pd_new == 0 && ia_pd_len) ||
-					(ia_na_new == 0 && ia_na_len))
-				break; // We lost all our IAs, restart
-			else if (res > 0)
-				script_call("rebound");
-		}
+				// If we have any IAs, send renew, otherwise request
+				res = dhcpv6_request(DHCPV6_MSG_RENEW);
+				odhcp6c_signal_process();
+				if (res > 0) { // Renew was succesfull
+					// Publish updates
+					script_call("updated");
+					continue; // Renew was successful
+				}
+				
+				odhcp6c_clear_state(STATE_SERVER_ID); // Remove binding
+
+				// If we have IAs, try rebind otherwise restart
+				res = dhcpv6_request(DHCPV6_MSG_REBIND);
+				odhcp6c_signal_process();
 
+				if (res > 0)
+					script_call("rebound");
+				else {
 #ifdef EXT_BFD_PING
-		bfd_stop();
+					bfd_stop();
 #endif
+					break;
+				}
+			}
+			break;
 
+		default:
+			break;
+		}
 
 		size_t ia_pd_len, ia_na_len, server_id_len;
 		odhcp6c_get_state(STATE_IA_PD, &ia_pd_len);
@@ -454,6 +460,20 @@ void odhcp6c_add_state(enum odhcp6c_state state, const void *data, size_t len)
 		memcpy(n, data, len);
 }
 
+void odhcp6c_insert_state(enum odhcp6c_state state, size_t offset, const void *data, size_t len)
+{
+	ssize_t len_after = state_len[state] - offset;
+	if (len_after < 0)
+		return;
+
+	uint8_t *n = odhcp6c_resize_state(state, len);
+	if (n) {
+		uint8_t *sdata = state_data[state];
+		
+		memmove(sdata + offset + len, sdata + offset, len_after);
+		memcpy(sdata + offset, data, len);
+	}
+}
 
 size_t odhcp6c_remove_state(enum odhcp6c_state state, size_t offset, size_t len)
 {