rtp_proxy: add RTP_LOOPBACK mode for local loop back

This will echo back all voice received on the socket back to the same
socket/subscriber.

If we mark a socket as LOOPBACK at the BSC, we don't yet know a priori
which source IP/port the BTS side of the socket will have, so we can
only bind our local IP+port.  Only once the first message from the
BTS arrives at the BSC rtp_proxy, we know the source and should do a
connect() to that remote address.

The rtp_proxy has no idea when a call is disconnected, so the loopback
mode only works for the first call, but no subsequent calls.

This patch compares IP/PORT of the BTS side of the RTP flow and issues a
new connect only if it is not the current remote address.

3 files changed, 62 insertions, 3 deletions

diff --git a/openbsc/include/openbsc/rtp_proxy.h b/openbsc/include/openbsc/rtp_proxy.h
index 9d8d5832e..f9a55ebb0 100644
--- a/openbsc/include/openbsc/rtp_proxy.h
+++ b/openbsc/include/openbsc/rtp_proxy.h
@@ -38,6 +38,7 @@ enum rtp_rx_action {
 	RTP_NONE,
 	RTP_PROXY,
 	RTP_RECV_UPSTREAM,
+	RTP_LOOPBACK
 };
 
 enum rtp_tx_action {
@@ -85,6 +86,7 @@ int rtp_socket_bind(struct rtp_socket *rs, uint32_t ip);
 int rtp_socket_bind_port(struct rtp_socket *rs, uint32_t ip, uint16_t port);
 int rtp_socket_connect(struct rtp_socket *rs, uint32_t ip, uint16_t port);
 int rtp_socket_proxy(struct rtp_socket *this, struct rtp_socket *other);
+int rtp_socket_loopback(struct rtp_socket *s);
 int rtp_socket_upstream(struct rtp_socket *this, struct gsm_network *net, uint32_t callref);
 int rtp_socket_free(struct rtp_socket *rs);
 int rtp_send_frame(struct rtp_socket *rs, struct gsm_data_frame *frame);
diff --git a/openbsc/src/libtrau/rtp_proxy.c b/openbsc/src/libtrau/rtp_proxy.c
index 693a57a91..f00b1656b 100644
--- a/openbsc/src/libtrau/rtp_proxy.c
+++ b/openbsc/src/libtrau/rtp_proxy.c
@@ -392,11 +392,15 @@ static int rtp_socket_read(struct rtp_socket *rs, struct rtp_sub_socket *rss)
 	struct msgb *msg = msgb_alloc(RTP_ALLOC_SIZE, "RTP/RTCP");
 	struct msgb *new_msg;
 	struct rtp_sub_socket *other_rss;
+	struct sockaddr_in src_addr;
+	socklen_t src_addrlen;
 
 	if (!msg)
 		return -ENOMEM;
 
-	rc = read(rss->bfd.fd, msg->data, RTP_ALLOC_SIZE);
+	src_addrlen = sizeof(src_addr);
+	rc = recvfrom(rss->bfd.fd, msg->data, RTP_ALLOC_SIZE, 0,
+			(struct sockaddr *)&src_addr, &src_addrlen);
 	if (rc <= 0) {
 		rss->bfd.when &= ~BSC_FD_READ;
 		return rc;
@@ -405,6 +409,20 @@ static int rtp_socket_read(struct rtp_socket *rs, struct rtp_sub_socket *rss)
 	msgb_put(msg, rc);
 
 	switch (rs->rx_action) {
+	case RTP_LOOPBACK:
+		/* if this socket is not connected yet to a remote
+		 * address, do so now */
+		if (rss->sin_local.sin_addr.s_addr != src_addr.sin_addr.s_addr ||
+		    rss->sin_local.sin_port != src_addr.sin_port) {
+			LOGP(DLMUX, LOGL_INFO, "connecting loopback socket\n");
+			rc = rtp_socket_connect(rs,
+					   ntohl(src_addr.sin_addr.s_addr),
+					   ntohs(src_addr.sin_port));
+		}
+		/* FIXME: Do we need RTCP mangling here? */
+		msgb_enqueue(&rss->tx_queue, msg);
+		rss->bfd.when |= BSC_FD_WRITE;
+		break;
 	case RTP_PROXY:
 		if (!rs->proxy.other_sock) {
 			rc = -EIO;
@@ -724,6 +742,16 @@ int rtp_socket_proxy(struct rtp_socket *this, struct rtp_socket *other)
 	return 0;
 }
 
+/*! \brief put socket into loopback mode, echong back all data
+ *  \param[in] RTP socket to be put in loopback mode
+ */
+int rtp_socket_loopback(struct rtp_socket *s)
+{
+	s->rx_action = RTP_LOOPBACK;
+
+	return 0;
+}
+
 /*! \brief bind RTP/RTCP socket to application, disabling proxy
  *  \param[in] this RTP socket
  *  \param[in] net gsm_network argument to trau_tx_to_mncc()
diff --git a/openbsc/src/libtrau/rtp_proxy_main.c b/openbsc/src/libtrau/rtp_proxy_main.c
index afb245364..87d6b7723 100644
--- a/openbsc/src/libtrau/rtp_proxy_main.c
+++ b/openbsc/src/libtrau/rtp_proxy_main.c
@@ -143,6 +143,29 @@ static struct vty_app_info vty_info = {
 	.is_config_node	= bsc_vty_is_config_node,
 };
 
+static int create_socket_loop(uint16_t port)
+{
+	struct rtp_socket *s;
+	int rc;
+
+	s = rtp_socket_create();
+	if (!s)
+		return -EIO;
+
+	rc = rtp_socket_bind_port(s, INADDR_ANY, port);
+	if (rc < 0)
+		goto err_free_s;
+
+	rc = rtp_socket_loopback(s);
+	if (rc < 0)
+		goto err_free_s;
+
+	return 0;
+err_free_s:
+	rtp_socket_free(s);
+	return -EIO;
+}
+
 static int create_socket_pair(uint16_t port1, uint16_t port2)
 {
 	struct rtp_socket *a, *b;
@@ -225,15 +248,21 @@ int main(int argc, char **argv)
 	osmo_init_ignore_signals();
 
 	/* hard-wire map CIC 1->33, 2->33, ... */
-	for (i = 1; i <= 4; i++) {
+	for (i = 1; i <= 8; i++) {
 		uint16_t port1, port2;
 		port1 = PORT_BY_CIC(0, i);
 		port2 = PORT_BY_CIC(1, i);
-		printf("Creating UDP port mapping %u -> %u\n", port1, port2);
+		printf("Creating UDP port mapping (%u,%u:%u) -> (%u,%u:%u)\n",
+			0,i,1,i,port1, port2);
 		rc = create_socket_pair(port1, port2);
 		if (rc < 0)
 			exit(1);
 	}
+	printf("Creating loopback CIC (%u,%u:%u)\n",
+		0, 16, PORT_BY_CIC(0, 16));
+	rc = create_socket_loop(PORT_BY_CIC(0,16));
+	if (rc < 0)
+		exit(1);
 
 	if (daemonize) {
 		rc = osmo_daemonize();