ua: add support for hold+answer

- added ua_hold_answer() which will first put on-hold the active
  call (if exist) and then answer the new incoming call

fixes #50

include/baresip.h

@@ -511,6 +511,7 @@ int  ua_connect(struct ua *ua, struct call **callp,
 void ua_hangup(struct ua *ua, struct call *call,
 	       uint16_t scode, const char *reason);
 int  ua_answer(struct ua *ua, struct call *call);
+int  ua_hold_answer(struct ua *ua, struct call *call);
 int  ua_options_send(struct ua *ua, const char *uri,
 		     options_resp_h *resph, void *arg);
 int  ua_sipfd(const struct ua *ua);

modules/menu/menu.c

@@ -292,7 +292,7 @@ static int cmd_answer(struct re_printf *pf, void *unused)
 	(void)pf;
 	(void)unused;
 
-	ua_answer(uag_cur(), NULL);
+	ua_hold_answer(uag_cur(), NULL);
 
 	return 0;
 }

src/call.c

@@ -65,6 +65,7 @@ struct call {
 	time_t time_conn;         /**< Time when call initiated             */
 	time_t time_stop;         /**< Time when call stopped               */
 	bool got_offer;           /**< Got SDP Offer from Peer              */
+	bool on_hold;             /**< True if call is on hold              */
 	struct mnat_sess *mnats;  /**< Media NAT session                    */
 	bool mnat_wait;           /**< Waiting for MNAT to establish        */
 	struct menc_sess *mencs;  /**< Media encryption session state       */
@@ -779,8 +780,13 @@ int call_hold(struct call *call, bool hold)
 	if (!call || !call->sess)
 		return EINVAL;
 
+	if (hold == call->on_hold)
+		return 0;
+
 	info("call: %s %s\n", hold ? "hold" : "resume", call->peer_uri);
 
+	call->on_hold = hold;
+
 	FOREACH_STREAM
 		stream_hold(le->data, hold);
 
@@ -909,8 +915,10 @@ int call_info(struct re_printf *pf, const struct call *call)
 	if (!call)
 		return 0;
 
-	return re_hprintf(pf, "%H  %8s  %s", print_duration, call,
-			  state_name(call->state), call->peer_uri);
+	return re_hprintf(pf, "%H  %9s  %s  %s", print_duration, call,
+			  state_name(call->state),
+			  call->on_hold ? "(on hold)" : "         ",
+			  call->peer_uri);
 }
 
 
@@ -1654,3 +1662,9 @@ void call_set_xrtpstat(struct call *call)
 				  "X-RTP-Stat: %H\r\n",
 				  audio_print_rtpstat, call->audio);
 }
+
+
+bool call_is_onhold(const struct call *call)
+{
+	return call ? call->on_hold : false;
+}

src/core.h

@@ -171,6 +171,7 @@ int  call_notify_sipfrag(struct call *call, uint16_t scode,
 			 const char *reason, ...);
 int  call_af(const struct call *call);
 void call_set_xrtpstat(struct call *call);
+bool call_is_onhold(const struct call *call);
 
 
 /*

src/ua.c

@@ -249,6 +249,38 @@ static const char *translate_errorcode(uint16_t scode)
 }
 
 
+static struct call *ua_find_call_onhold(const struct ua *ua)
+{
+	struct le *le;
+
+	if (!ua)
+		return NULL;
+
+	for (le = ua->calls.tail; le; le = le->prev) {
+
+		struct call *call = le->data;
+
+		if (call_is_onhold(call))
+			return call;
+	}
+
+	return NULL;
+}
+
+
+static void resume_call(struct ua *ua)
+{
+	struct call *call;
+
+	call = ua_find_call_onhold(ua);
+	if (call) {
+		ua_printf(ua, "resuming previous call with '%s'\n",
+			  call_peeruri(call));
+		call_hold(call, false);
+	}
+}
+
+
 static void call_event_handler(struct call *call, enum call_event ev,
 			       const char *str, void *arg)
 {
@@ -328,6 +360,8 @@ static void call_event_handler(struct call *call, enum call_event ev,
 		}
 		ua_event(ua, UA_EVENT_CALL_CLOSED, call, str);
 		mem_deref(call);
+
+		resume_call(ua);
 		break;
 
 	case CALL_EVENT_TRANSFER:
@@ -770,6 +804,8 @@ void ua_hangup(struct ua *ua, struct call *call,
 	(void)call_hangup(call, scode, reason);
 
 	mem_deref(call);
+
+	resume_call(ua);
 }
 
 
@@ -792,14 +828,49 @@ int ua_answer(struct ua *ua, struct call *call)
 			return ENOENT;
 	}
 
-	/* todo: put previous call on-hold (if configured) */
-
 	ua->play = mem_deref(ua->play);
 
 	return call_answer(call, 200);
 }
 
 
+/**
+ * Put the current call on hold and answer the incoming call
+ *
+ * @param ua   User-Agent
+ * @param call Call to answer, or NULL for current call
+ *
+ * @return 0 if success, otherwise errorcode
+ */
+int ua_hold_answer(struct ua *ua, struct call *call)
+{
+	struct call *pcall;
+	int err;
+
+	if (!ua)
+		return EINVAL;
+
+	if (!call) {
+		call = ua_call(ua);
+		if (!call)
+			return ENOENT;
+	}
+
+	/* put previous call on-hold */
+	pcall = ua_prev_call(ua);
+	if (pcall) {
+		ua_printf(ua, "putting call with '%s' on hold\n",
+		     call_peeruri(pcall));
+
+		err = call_hold(pcall, true);
+		if (err)
+			return err;
+	}
+
+	return ua_answer(ua, call);
+}
+
+
 int ua_print_status(struct re_printf *pf, const struct ua *ua)
 {
 	struct le *le;