Add a 'secret' probation strictrtp mode to handle delayed changes in RTP source

Often, Asterisk may realize that a change in the source of an RTP stream is
about to occur and ask that the RTP engine reset it's lock on the current RTP
source. In certain scenarios, it may take awhile for the new remote system to
send RTP packets, while the old remote system may continue providing RTP during
that time period. This causes Asterisk to re-lock onto the old source, thereby
rejecting the new source when the old source stops sending RTP and the new
source begins.

This patch prevents that by having a constant secondary, 'secret' probation
mode enabled when an RTP source has been chosen. RTP packets from other sources
are always considered, but never chosen unless the current RTP source stops
sending RTP.

Review: https://reviewboard.asterisk.org/r/2364

(closes issue AST-1124)
Reported by: John Bigelow
Tested by: John Bigelow

(closes issue AST-1125)
Reported by: John Bigelow
Tested by: John Bigelow
........

Merged revisions 382573 from http://svn.asterisk.org/svn/asterisk/branches/11


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@382589 65c4cc65-6c06-0410-ace0-fbb531ad65f3

1 files changed, 48 insertions, 60 deletions

diff --git a/res/res_rtp_asterisk.c b/res/res_rtp_asterisk.c
index fadace763..9e9a92c82 100644
--- a/res/res_rtp_asterisk.c
+++ b/res/res_rtp_asterisk.c
@@ -169,6 +169,12 @@ static int worker_terminate;
 #define COMPONENT_RTP 1
 #define COMPONENT_RTCP 2
 
+/*! \brief RTP learning mode tracking information */
+struct rtp_learning_info {
+	int max_seq;	/*!< The highest sequence number received */
+	int packets;	/*!< The number of remaining packets before the source is accepted */
+};
+
 /*! \brief RTP session description */
 struct ast_rtp {
 	int s;
@@ -233,14 +239,13 @@ struct ast_rtp {
 
 	enum strict_rtp_state strict_rtp_state; /*!< Current state that strict RTP protection is in */
 	struct ast_sockaddr strict_rtp_address;  /*!< Remote address information for strict RTP purposes */
-	struct ast_sockaddr alt_rtp_address; /*!<Alternate remote address information */
 
 	/*
 	 * Learning mode values based on pjmedia's probation mode.  Many of these values are redundant to the above,
 	 * but these are in place to keep learning mode sequence values sealed from their normal counterparts.
 	 */
-	uint16_t learning_max_seq;		/*!< Highest sequence number heard */
-	int learning_probation;		/*!< Sequential packets untill source is valid */
+	struct rtp_learning_info rtp_source_learn;	/* Learning mode track for the expected RTP source */
+	struct rtp_learning_info alt_source_learn;	/* Learning mode tracking for a new RTP source after one has been chosen */
 
 	struct rtp_red *red;
 
@@ -371,7 +376,6 @@ static struct ast_frame *ast_rtp_read(struct ast_rtp_instance *instance, int rtc
 static void ast_rtp_prop_set(struct ast_rtp_instance *instance, enum ast_rtp_property property, int value);
 static int ast_rtp_fd(struct ast_rtp_instance *instance, int rtcp);
 static void ast_rtp_remote_address_set(struct ast_rtp_instance *instance, struct ast_sockaddr *addr);
-static void ast_rtp_alt_remote_address_set(struct ast_rtp_instance *instance, struct ast_sockaddr *addr);
 static int rtp_red_init(struct ast_rtp_instance *instance, int buffer_time, int *payloads, int generations);
 static int rtp_red_buffer(struct ast_rtp_instance *instance, struct ast_frame *frame);
 static int ast_rtp_local_bridge(struct ast_rtp_instance *instance0, struct ast_rtp_instance *instance1);
@@ -1004,7 +1008,6 @@ static struct ast_rtp_engine asterisk_rtp_engine = {
 	.prop_set = ast_rtp_prop_set,
 	.fd = ast_rtp_fd,
 	.remote_address_set = ast_rtp_remote_address_set,
-	.alt_remote_address_set = ast_rtp_alt_remote_address_set,
 	.red_init = rtp_red_init,
 	.red_buffer = rtp_red_buffer,
 	.local_bridge = ast_rtp_local_bridge,
@@ -1021,7 +1024,7 @@ static struct ast_rtp_engine asterisk_rtp_engine = {
 #endif
 };
 
-static void rtp_learning_seq_init(struct ast_rtp *rtp, uint16_t seq);
+static void rtp_learning_seq_init(struct rtp_learning_info *info, uint16_t seq);
 
 static void ast_rtp_on_ice_complete(pj_ice_sess *ice, pj_status_t status)
 {
@@ -1032,7 +1035,7 @@ static void ast_rtp_on_ice_complete(pj_ice_sess *ice, pj_status_t status)
 	}
 
 	rtp->strict_rtp_state = STRICT_RTP_LEARN;
-	rtp_learning_seq_init(rtp, (uint16_t)rtp->seqno);
+	rtp_learning_seq_init(&rtp->rtp_source_learn, (uint16_t)rtp->seqno);
 }
 
 static void ast_rtp_on_ice_rx_data(pj_ice_sess *ice, unsigned comp_id, unsigned transport_id, void *pkt, pj_size_t size, const pj_sockaddr_t *src_addr, unsigned src_addr_len)
@@ -1592,13 +1595,13 @@ static int create_new_socket(const char *type, int af)
  * \brief Initializes sequence values and probation for learning mode.
  * \note This is an adaptation of pjmedia's pjmedia_rtp_seq_init function.
  *
- * \param rtp pointer to rtp struct used with the received rtp packet.
- * \param seq sequence number read from the rtp header
+ * \param info The learning information to track
+ * \param seq sequence number read from the rtp header to initialize the information with
  */
-static void rtp_learning_seq_init(struct ast_rtp *rtp, uint16_t seq)
+static void rtp_learning_seq_init(struct rtp_learning_info *info, uint16_t seq)
 {
-	rtp->learning_max_seq = seq - 1;
-	rtp->learning_probation = learning_min_sequential;
+	info->max_seq = seq - 1;
+	info->packets = learning_min_sequential;
 }
 
 /*!
@@ -1606,29 +1609,23 @@ static void rtp_learning_seq_init(struct ast_rtp *rtp, uint16_t seq)
  * \brief Updates sequence information for learning mode and determines if probation/learning mode should remain in effect.
  * \note This function was adapted from pjmedia's pjmedia_rtp_seq_update function.
  *
- * \param rtp pointer to rtp struct used with the received rtp packet.
+ * \param info Structure tracking the learning progress of some address
  * \param seq sequence number read from the rtp header
- * \return boolean value indicating if probation mode is active at the end of the function
+ * \retval 0 if probation mode should exit for this address
+ * \retval non-zero if probation mode should continue
  */
-static int rtp_learning_rtp_seq_update(struct ast_rtp *rtp, uint16_t seq)
+static int rtp_learning_rtp_seq_update(struct rtp_learning_info *info, uint16_t seq)
 {
-	int probation = 1;
-
-	ast_debug(1, "%p -- probation = %d, seq = %d\n", rtp, rtp->learning_probation, seq);
-
-	if (seq == rtp->learning_max_seq + 1) {
+	if (seq == info->max_seq + 1) {
 		/* packet is in sequence */
-		rtp->learning_probation--;
-		rtp->learning_max_seq = seq;
-		if (rtp->learning_probation == 0) {
-			probation = 0;
-		}
+		info->packets--;
 	} else {
-		rtp->learning_probation = learning_min_sequential - 1;
-		rtp->learning_max_seq = seq;
+		/* Sequence discontinuity; reset */
+		info->packets = learning_min_sequential - 1;
 	}
+	info->max_seq = seq;
 
-	return probation;
+	return (info->packets == 0);
 }
 
 static void rtp_add_candidates_to_ice(struct ast_rtp_instance *instance, struct ast_rtp *rtp, struct ast_sockaddr *addr, int port, int component,
@@ -1719,7 +1716,8 @@ static int ast_rtp_new(struct ast_rtp_instance *instance,
 	rtp->seqno = ast_random() & 0xffff;
 	rtp->strict_rtp_state = (strictrtp ? STRICT_RTP_LEARN : STRICT_RTP_OPEN);
 	if (strictrtp) {
-		rtp_learning_seq_init(rtp, (uint16_t)rtp->seqno);
+		rtp_learning_seq_init(&rtp->rtp_source_learn, (uint16_t)rtp->seqno);
+		rtp_learning_seq_init(&rtp->alt_source_learn, (uint16_t)rtp->seqno);
 	}
 
 	/* Create a new socket for us to listen on and use */
@@ -3552,34 +3550,36 @@ static struct ast_frame *ast_rtp_read(struct ast_rtp_instance *instance, int rtc
 
 	/* If strict RTP protection is enabled see if we need to learn the remote address or if we need to drop the packet */
 	if (rtp->strict_rtp_state == STRICT_RTP_LEARN) {
-		ast_debug(1, "%p -- start learning mode pass with addr = %s\n", rtp, ast_sockaddr_stringify(&addr));
+		ast_debug(1, "%p -- Probation learning mode pass with source address %s\n", rtp, ast_sockaddr_stringify(&addr));
 		/* For now, we always copy the address. */
 		ast_sockaddr_copy(&rtp->strict_rtp_address, &addr);
 
 		/* Send the rtp and the seqno from header to rtp_learning_rtp_seq_update to see whether we can exit or not*/
-		if (rtp_learning_rtp_seq_update(rtp, ntohl(rtpheader[0]))) {
-			ast_debug(1, "%p -- Condition for learning hasn't exited, so reject the frame.\n", rtp);
+		if (rtp_learning_rtp_seq_update(&rtp->rtp_source_learn, seqno)) {
+			ast_debug(1, "%p -- Probation at seq %d with %d to go; discarding frame\n",
+				rtp, rtp->rtp_source_learn.max_seq, rtp->rtp_source_learn.packets);
 			return &ast_null_frame;
 		}
 
-		ast_debug(1, "%p -- Probation Ended. Set strict_rtp_state to STRICT_RTP_CLOSED with address %s\n", rtp, ast_sockaddr_stringify(&addr));
+		ast_verb(4, "%p -- Probation passed - setting RTP source address to %s\n", rtp, ast_sockaddr_stringify(&addr));
 		rtp->strict_rtp_state = STRICT_RTP_CLOSED;
-	} else if (rtp->strict_rtp_state == STRICT_RTP_CLOSED) {
-		if (ast_sockaddr_cmp(&rtp->strict_rtp_address, &addr)) {
-			/* Hmm, not the strict addres. Perhaps we're getting audio from the alternate? */
-			if (!ast_sockaddr_cmp(&rtp->alt_rtp_address, &addr)) {
-				/* ooh, we did! You're now the new expected address, son! */
-				ast_sockaddr_copy(&rtp->strict_rtp_address,
-						  &addr);
-			} else  {
-				const char *real_addr = ast_strdupa(ast_sockaddr_stringify(&addr));
-				const char *expected_addr = ast_strdupa(ast_sockaddr_stringify(&rtp->strict_rtp_address));
-
-				ast_debug(1, "Received RTP packet from %s, dropping due to strict RTP protection. Expected it to be from %s\n",
-						real_addr, expected_addr);
-
+	}
+	if (rtp->strict_rtp_state == STRICT_RTP_CLOSED) {
+		if (!ast_sockaddr_cmp(&rtp->strict_rtp_address, &addr)) {
+			/* Always reset the alternate learning source */
+			rtp_learning_seq_init(&rtp->alt_source_learn, seqno);
+		} else {
+			/* Start trying to learn from the new address. If we pass a probationary period with
+			 * it, that means we've stopped getting RTP from the original source and we should
+			 * switch to it.
+			 */
+			if (rtp_learning_rtp_seq_update(&rtp->alt_source_learn, seqno)) {
+				ast_debug(1, "%p -- Received RTP packet from %s, dropping due to strict RTP protection. Will switch to it in %d packets\n",
+						rtp, ast_sockaddr_stringify(&addr), rtp->alt_source_learn.packets);
 				return &ast_null_frame;
 			}
+			ast_verb(4, "%p -- Switching RTP source address to %s\n", rtp, ast_sockaddr_stringify(&addr));
+			ast_sockaddr_copy(&rtp->strict_rtp_address, &addr);
 		}
 	}
 
@@ -3958,24 +3958,12 @@ static void ast_rtp_remote_address_set(struct ast_rtp_instance *instance, struct
 
 	if (strictrtp && rtp->strict_rtp_state != STRICT_RTP_OPEN) {
 		rtp->strict_rtp_state = STRICT_RTP_LEARN;
-		rtp_learning_seq_init(rtp, rtp->seqno);
+		rtp_learning_seq_init(&rtp->rtp_source_learn, rtp->seqno);
 	}
 
 	return;
 }
 
-static void ast_rtp_alt_remote_address_set(struct ast_rtp_instance *instance, struct ast_sockaddr *addr)
-{
-	struct ast_rtp *rtp = ast_rtp_instance_get_data(instance);
-
-	/* No need to futz with rtp->rtcp here because ast_rtcp_read is already able to adjust if receiving
-	 * RTCP from an "unexpected" source
-	 */
-	ast_sockaddr_copy(&rtp->alt_rtp_address, addr);
-
-	return;
-}
-
 /*! \brief Write t140 redundacy frame
  * \param data primary data to be buffered
  */