res_phoneprov.c: Multihomed SERVER cache prevention

Phones moving between subnets on multi-homed server have their
initially connected interface IP cached in the SERVER variable,
even when it is not specified in the configuration files. This
prevents phones from obtaining the correct SERVER variable value
when they move to another subnet.

ASTERISK-30388 #close
Reported-by: cmaj

Change-Id: I1d18987a9d58e85556b4c4a6814ce7006524cc92

doc/CHANGES-staging/res_phoneprov_multihomed_server.txt

+Subject: res_phoneprov
+
+On multihomed Asterisk servers with dynamic SERVER template variables,
+reloading this module is no longer required when re-provisioning your
+phone to another interface address (e.g. when moving between VLANs.)

res/res_phoneprov.c

@@ -874,6 +874,8 @@ static int phoneprov_callback(struct ast_tcptls_session_instance *ser, const str
 	char path[PATH_MAX];
 	char *file = NULL;
 	char *server;
+	char *newserver = NULL;
+	struct extension *exten_iter;
 	int len;
 	int fd;
 	struct ast_str *http_header;
@@ -955,8 +957,7 @@ static int phoneprov_callback(struct ast_tcptls_session_instance *ser, const str
 			if ((res = getsockname(ast_iostream_get_fd(ser->stream), &name.sa, &namelen))) {
 				ast_log(LOG_WARNING, "Could not get server IP, breakage likely.\n");
 			} else {
-				struct extension *exten_iter;
-				const char *newserver = ast_inet_ntoa(name.sa_in.sin_addr);
+				newserver = ast_strdupa(ast_inet_ntoa(name.sa_in.sin_addr));
 
 				AST_LIST_TRAVERSE(&route->user->extensions, exten_iter, entry) {
 					AST_VAR_LIST_INSERT_TAIL(exten_iter->headp,
@@ -967,6 +968,21 @@ static int phoneprov_callback(struct ast_tcptls_session_instance *ser, const str
 
 		ast_str_substitute_variables_varshead(&tmp, 0, AST_LIST_FIRST(&route->user->extensions)->headp, file);
 
+		/* Do not retain dynamic SERVER address because next request from the phone might arrive on
+		 * different interface IP address eg. if this is a multi-homed server on multiple subnets */
+		if (newserver) {
+			struct ast_var_t *varns;
+			AST_LIST_TRAVERSE(&route->user->extensions, exten_iter, entry) {
+				AST_LIST_TRAVERSE_SAFE_BEGIN(exten_iter->headp, varns, entries) {
+					if (!strcmp(variable_lookup[AST_PHONEPROV_STD_SERVER], ast_var_name(varns))) {
+						AST_LIST_REMOVE_CURRENT(entries);
+						ast_var_delete(varns);
+					}
+				}
+				AST_LIST_TRAVERSE_SAFE_END
+			}
+		}
+
 		ast_free(file);
 
 		http_header = ast_str_create(80);