features: Add no answer option to Bridge.

Adds the n "no answer" option to the Bridge application
so that answer supervision can not automatically
be provided when Bridge is executed.

Additionally, a mechanism (dialplan variable)
is added to prevent bridge targets (typically the
target of a masquerade) from answering the channel
when they enter the bridge.

ASTERISK-30223 #close

Change-Id: I76f73fcd8e403bcd18f2abb40c658f537ac1ba6d

doc/CHANGES-staging/features_bridge_noanswer.txt

+Subject: features
+
+The Bridge application now has the n "no answer" option
+that can be used to prevent the channel from being
+automatically answered prior to bridging.

main/features.c

@@ -164,6 +164,12 @@
 							</variable>
 						</variablelist>
 					</option>
+					<option name="n">
+						<para>Do not answer the channel automatically before bridging.</para>
+						<para>Additionally, to prevent a bridged channel (the target of the Bridge application)
+						from answering, the <literal>BRIDGE_NOANSWER</literal> variable can be set to inhibit
+						answering.</para>
+					</option>
 					<option name="S(x)">
 						<para>Hang up the call after <replaceable>x</replaceable> seconds *after* the called party has answered the call.</para>
 					</option>
@@ -525,7 +531,7 @@ static void bridge_failed_peer_goto(struct ast_channel *chan, struct ast_channel
 }
 
 static int pre_bridge_setup(struct ast_channel *chan, struct ast_channel *peer, struct ast_bridge_config *config,
-		struct ast_bridge_features *chan_features, struct ast_bridge_features *peer_features)
+		struct ast_bridge_features *chan_features, struct ast_bridge_features *peer_features, int noanswer)
 {
 	int res;
 	SCOPE_TRACE(1, "%s Peer: %s\n", ast_channel_name(chan), ast_channel_name(peer));
@@ -553,7 +559,10 @@ static int pre_bridge_setup(struct ast_channel *chan, struct ast_channel *peer,
 
 	res = 0;
 
-	if (ast_channel_state(chan) != AST_STATE_UP) {
+	if (noanswer) {
+		ast_debug(1, "Skipping answer on %s due to no answer directive\n", ast_channel_name(chan));
+	} else if (ast_channel_state(chan) != AST_STATE_UP) {
+		ast_debug(1, "Answering channel for bridge: %s\n", ast_channel_name(chan));
 		res = ast_raw_answer_with_stream_topology(chan, config->answer_topology);
 		if (res != 0) {
 			return -1;
@@ -627,6 +636,8 @@ int ast_bridge_call_with_flags(struct ast_channel *chan, struct ast_channel *pee
 	struct ast_bridge *bridge;
 	struct ast_bridge_features chan_features;
 	struct ast_bridge_features *peer_features;
+	const char *value;
+	int noanswer;
 	SCOPE_TRACE(1, "%s Peer: %s\n", ast_channel_name(chan), ast_channel_name(peer));
 
 	/* Setup features. */
@@ -639,7 +650,12 @@ int ast_bridge_call_with_flags(struct ast_channel *chan, struct ast_channel *pee
 		return -1;
 	}
 
-	if (pre_bridge_setup(chan, peer, config, &chan_features, peer_features)) {
+	ast_channel_lock(chan);
+	value = pbx_builtin_getvar_helper(chan, "BRIDGE_NOANSWER");
+	noanswer = !ast_strlen_zero(value) ? 1 : 0;
+	ast_channel_unlock(chan);
+
+	if (pre_bridge_setup(chan, peer, config, &chan_features, peer_features, noanswer)) {
 		ast_bridge_features_destroy(peer_features);
 		ast_bridge_features_cleanup(&chan_features);
 		bridge_failed_peer_goto(chan, peer);
@@ -848,6 +864,7 @@ enum {
 	OPT_CALLER_PARK = (1 << 10),
 	OPT_CALLEE_KILL = (1 << 11),
 	OPT_CALLEE_GO_ON = (1 << 12),
+	OPT_NOANSWER = (1 << 13),
 };
 
 enum {
@@ -866,6 +883,7 @@ AST_APP_OPTIONS(bridge_exec_options, BEGIN_OPTIONS
 	AST_APP_OPTION('k', OPT_CALLEE_PARK),
 	AST_APP_OPTION('K', OPT_CALLER_PARK),
 	AST_APP_OPTION_ARG('L', OPT_DURATION_LIMIT, OPT_ARG_DURATION_LIMIT),
+	AST_APP_OPTION('n', OPT_NOANSWER),
 	AST_APP_OPTION_ARG('S', OPT_DURATION_STOP, OPT_ARG_DURATION_STOP),
 	AST_APP_OPTION('t', OPT_CALLEE_TRANSFER),
 	AST_APP_OPTION('T', OPT_CALLER_TRANSFER),
@@ -1012,6 +1030,7 @@ static int bridge_exec(struct ast_channel *chan, const char *data)
 	struct ast_bridge_features *peer_features;
 	struct ast_bridge *bridge;
 	struct ast_features_xfer_config *xfer_cfg;
+	int noanswer;
 
 	AST_DECLARE_APP_ARGS(args,
 		AST_APP_ARG(dest_chan);
@@ -1066,6 +1085,7 @@ static int bridge_exec(struct ast_channel *chan, const char *data)
 		ast_set_flag(&(bconfig.features_callee), AST_FEATURE_PARKCALL);
 	if (ast_test_flag(&opts, OPT_CALLER_PARK))
 		ast_set_flag(&(bconfig.features_caller), AST_FEATURE_PARKCALL);
+	noanswer = ast_test_flag(&opts, OPT_NOANSWER);
 
 	/* Setup after bridge goto location. */
 	if (ast_test_flag(&opts, OPT_CALLEE_GO_ON)) {
@@ -1096,7 +1116,7 @@ static int bridge_exec(struct ast_channel *chan, const char *data)
 		goto done;
 	}
 
-	if (pre_bridge_setup(chan, current_dest_chan, &bconfig, &chan_features, peer_features)) {
+	if (pre_bridge_setup(chan, current_dest_chan, &bconfig, &chan_features, peer_features, noanswer)) {
 		ast_bridge_features_destroy(peer_features);
 		ast_bridge_features_cleanup(&chan_features);
 		goto done;