forward SDP between SIP and MNCC

We have added support for sending SDP via MNCC a long time ago, but so
far the SDP section remained empty. Now, implement actually forwarding
SDP codec information between SIP and MNCC.

The aim is to let the MSC know about all codec choices the remote SIP
call leg has to offer, so that finding a codec match between local and
remote call leg becomes possible.

Store any SDP info contained in incoming SIP and MNCC messages, and send
the stored SDP to the other call leg in all outgoing SIP and MNCC
messages.

In sdp_create_file(), we used to compose fixed SDP -- instead, take the
other call leg's SDP as-is, only make sure to modify the mode (e.g.
"a=sendrecv") to reflect the current call hold state.

The RTP address and codec info in the MNCC structures is now essentially
a redundant / possibly less accurate copy of the SDP info, but leave all
of that as-is, for backwards compat.

There is codec checking that may reject unexpected codecs. The
overall/future aim is to leave all codec checking up to the MSC, but so
far just leave current behaviour unchanged, until we notice problems.

Related: SYS#5066
Related: osmo-ttcn3-hacks Ib2ae8449e673f5027f01d428d3718c006f76d93e
Change-Id: I3df5d06f38ee2d122706a9ebffde7db4f2bd6bae

6 files changed, 199 insertions, 44 deletions

diff --git a/src/call.c b/src/call.c
index 9f593ea..3f7beb2 100644
--- a/src/call.c
+++ b/src/call.c
@@ -172,3 +172,20 @@ const char *call_leg_state(struct call_leg *leg)
 		return "Unknown call type";
 	}
 }
+
+void call_leg_rx_sdp(struct call_leg *leg, const char *rx_sdp)
+{
+	/* If no SDP was received, keep whatever SDP was previously seen. */
+	if (!rx_sdp || !*rx_sdp || !strncmp(leg->rx_sdp, rx_sdp, sizeof(leg->rx_sdp))) {
+		LOGP(DAPP, LOGL_DEBUG, "call(%u) leg(0x%p) no new SDP in %s\n", leg->call->id, leg,
+		     osmo_quote_str(rx_sdp, -1));
+		LOGP(DAPP, LOGL_DEBUG, "call(%u) leg(0x%p) keep stored SDP=%s\n", leg->call->id, leg,
+		     osmo_quote_str(leg->rx_sdp, -1));
+		return;
+	}
+	LOGP(DAPP, LOGL_DEBUG, "call(%u) leg(0x%p) received new SDP=%s\n", leg->call->id, leg, osmo_quote_str(rx_sdp, -1));
+	LOGP(DAPP, LOGL_DEBUG, "call(%u) leg(0x%p) replaced old SDP=%s\n", leg->call->id, leg,
+	     osmo_quote_str(leg->rx_sdp, -1));
+	OSMO_STRLCPY_ARRAY(leg->rx_sdp, rx_sdp);
+	leg->rx_sdp_changed = true;
+}
diff --git a/src/call.h b/src/call.h
index a835f71..cd8d630 100644
--- a/src/call.h
+++ b/src/call.h
@@ -62,7 +62,11 @@ struct call_leg {
 	/* SDP as received for this call leg. If this is an MNCC call leg, contains the SDP most recently received in an
 	 * MNCC message; if this is a SIP call leg, contains the SDP most recently received in a SIP message. If no SDP
 	 * was received yet, this string is empty. Otherwise a nul terminated string. */
-	char sdp[1024];
+	char rx_sdp[1024];
+	/* If the contents of rx_sdp[] changes, set rx_sdp_changed = true. When the other call leg transmits the next
+	 * message, it can decide whether to include SDP because there is new information, or whether to omit SDP
+	 * because it was already sent identically earlier. */
+	bool rx_sdp_changed;
 
 	/**
 	 * Remote started to ring/alert
@@ -167,6 +171,8 @@ void calls_init(void);
 
 struct call_leg *call_leg_other(struct call_leg *leg);
 
+void call_leg_rx_sdp(struct call_leg *cl, const char *rx_sdp);
+
 void call_leg_release(struct call_leg *leg);
 
 
diff --git a/src/mncc.c b/src/mncc.c
index 02ba2cc..ed36085 100644
--- a/src/mncc.c
+++ b/src/mncc.c
@@ -170,12 +170,14 @@ static int mncc_rtp_write(struct mncc_connection *conn, struct gsm_mncc_rtp *rtp
 	return rc;
 }
 
-static int mncc_rtp_send(struct mncc_connection *conn, uint32_t msg_type, uint32_t callref)
+static int mncc_rtp_send(struct mncc_connection *conn, uint32_t msg_type, uint32_t callref, const char *sdp)
 {
 	struct gsm_mncc_rtp mncc = { 0, };
 
 	mncc.msg_type = msg_type;
 	mncc.callref = callref;
+	if (sdp)
+		OSMO_STRLCPY_ARRAY(mncc.sdp, sdp);
 
 	return mncc_rtp_write(conn, &mncc);
 }
@@ -195,6 +197,10 @@ static bool send_rtp_connect(struct mncc_call_leg *leg, struct call_leg *other)
 	mncc.callref = leg->callref;
 	mncc.addr = other->addr;
 	mncc.payload_type = other->payload_type;
+
+	/* Forward whichever SDP was last received on the other call leg */
+	OSMO_STRLCPY_ARRAY(mncc.sdp, other->rx_sdp);
+
 	/*
 	 * FIXME: mncc.payload_msg_type should already be compatible.. but
 	 * payload_type should be different..
@@ -408,6 +414,8 @@ static void check_rtp_connect(struct mncc_connection *conn, const char *buf, int
 		return;
 	}
 
+	call_leg_rx_sdp(&leg->base, rtp->sdp);
+
 	/* extract information about where the RTP is */
 	if (rtp->addr.ss_family != AF_UNSPEC ||
 	    osmo_sockaddr_port((const struct sockaddr *)&rtp->addr) != 0 ||
@@ -446,6 +454,7 @@ static void check_rtp_create(struct mncc_connection *conn, const char *buf, int
 	leg->base.addr = rtp->addr;
 	leg->base.payload_type = rtp->payload_type;
 	leg->base.payload_msg_type = rtp->payload_msg_type;
+	call_leg_rx_sdp(&leg->base, rtp->sdp);
 
 	/* TODO.. now we can continue with the call */
 	LOGP(DMNCC, LOGL_INFO,
@@ -485,6 +494,8 @@ static void check_setup(struct mncc_connection *conn, const char *buf, int rc)
 	const struct gsm_mncc_number *called;
 	struct call *call;
 	struct mncc_call_leg *leg;
+	struct call_leg *other_leg;
+	const char *sdp = NULL;
 	struct osmo_gcr_parsed gcr;
 
 	if (rc < sizeof(*data)) {
@@ -557,6 +568,7 @@ static void check_setup(struct mncc_connection *conn, const char *buf, int rc)
 	memcpy(&leg->called, called, sizeof(leg->called));
 	memcpy(&leg->calling, &data->calling, sizeof(leg->calling));
 	memcpy(&leg->imsi, data->imsi, sizeof(leg->imsi));
+	call_leg_rx_sdp(&leg->base, data->sdp);
 
 	if (data->fields & MNCC_F_GCR) {
 		leg->base.call->gcr_present = true;
@@ -567,8 +579,14 @@ static void check_setup(struct mncc_connection *conn, const char *buf, int rc)
 		"Created call(%u) with MNCC leg(%u) IMSI(%.16s)\n",
 		call->id, leg->callref, data->imsi);
 
+	other_leg = call_leg_other(&leg->base);
+	if (other_leg && *other_leg->rx_sdp && other_leg->rx_sdp_changed) {
+		sdp = other_leg->rx_sdp;
+		other_leg->rx_sdp_changed = false;
+	}
+
 	start_cmd_timer(leg, MNCC_RTP_CREATE);
-	mncc_rtp_send(conn, MNCC_RTP_CREATE, data->callref);
+	mncc_rtp_send(conn, MNCC_RTP_CREATE, data->callref, sdp);
 }
 
 /*! Find MNCC Call leg by given MNCC message
@@ -672,6 +690,8 @@ static void check_stp_cmpl_ind(struct mncc_connection *conn, const char *buf, in
 	if (!leg)
 		return;
 
+	call_leg_rx_sdp(&leg->base, data->sdp);
+
 	LOGP(DMNCC, LOGL_INFO, "leg(%u) is now connected.\n", leg->callref);
 	stop_cmd_timer(leg, MNCC_SETUP_COMPL_IND);
 	leg->state = MNCC_CC_CONNECTED;
@@ -701,17 +721,28 @@ static void check_cnf_ind(struct mncc_connection *conn, const char *buf, int rc)
 {
 	const struct gsm_mncc *data;
 	struct mncc_call_leg *leg;
+	struct call_leg *other_leg;
+	const char *sdp = NULL;
 
 	leg = find_leg(conn, buf, rc, &data);
 	if (!leg)
 		return;
 
+	call_leg_rx_sdp(&leg->base, data->sdp);
+
+	/* Forward SDP received from the other side */
+	other_leg = call_leg_other(&leg->base);
+	if (other_leg && *other_leg->rx_sdp && other_leg->rx_sdp_changed) {
+		sdp = other_leg->rx_sdp;
+		other_leg->rx_sdp_changed = false;
+	}
+
 	LOGP(DMNCC, LOGL_DEBUG,
 		"leg(%u) confirmed. creating RTP socket.\n",
 		leg->callref);
 
 	start_cmd_timer(leg, MNCC_RTP_CREATE);
-	mncc_rtp_send(conn, MNCC_RTP_CREATE, data->callref);
+	mncc_rtp_send(conn, MNCC_RTP_CREATE, data->callref, sdp);
 }
 
 static void check_alrt_ind(struct mncc_connection *conn, const char *buf, int rc)
@@ -724,6 +755,8 @@ static void check_alrt_ind(struct mncc_connection *conn, const char *buf, int rc
 	if (!leg)
 		return;
 
+	call_leg_rx_sdp(&leg->base, data->sdp);
+
 	LOGP(DMNCC, LOGL_DEBUG,
 		"leg(%u) is alerting.\n", leg->callref);
 
@@ -802,6 +835,8 @@ static void check_stp_cnf(struct mncc_connection *conn, const char *buf, int rc)
 	if (!leg)
 		return;
 
+	call_leg_rx_sdp(&leg->base, data->sdp);
+
 	LOGP(DMNCC, LOGL_DEBUG, "leg(%u) setup completed\n", leg->callref);
 
 	other_leg = call_leg_other(&leg->base);
@@ -831,6 +866,8 @@ static void check_dtmf_start(struct mncc_connection *conn, const char *buf, int
 	if (!leg)
 		return;
 
+	call_leg_rx_sdp(&leg->base, data->sdp);
+
 	LOGP(DMNCC, LOGL_DEBUG, "leg(%u) DTMF key=%c\n", leg->callref, data->keypad);
 
 	other_leg = call_leg_other(&leg->base);
@@ -853,6 +890,8 @@ static void check_dtmf_stop(struct mncc_connection *conn, const char *buf, int r
 	if (!leg)
 		return;
 
+	call_leg_rx_sdp(&leg->base, data->sdp);
+
 	LOGP(DMNCC, LOGL_DEBUG, "leg(%u) DTMF key=%c\n", leg->callref, data->keypad);
 
 	mncc_fill_header(&out_mncc, MNCC_STOP_DTMF_RSP, leg->callref);
@@ -945,11 +984,17 @@ int mncc_create_remote_leg(struct mncc_connection *conn, struct call *call)
 		msgb_free(msg);
 	}
 
+	/* The call->initial leg is a SIP call leg that starts an MT call. There was SDP received in the SIP INVITE that
+	 * started this call. This here will be the call->remote, always forwarding the SDP that came in on
+	 * call->initial. */
+	if (call->initial && call->initial->rx_sdp_changed) {
+		OSMO_STRLCPY_ARRAY(mncc.sdp, call->initial->rx_sdp);
+		call->initial->rx_sdp_changed = false;
+	}
+
 	/*
 	 * TODO/FIXME:
-	 *  - Determine/request channel based on offered audio codecs
 	 *  - Screening, redirect?
-	 *  - Synth. the bearer caps based on codecs?
 	 */
 	rc = mncc_write(conn, &mncc);
 	if (rc != sizeof(mncc)) {
diff --git a/src/sdp.c b/src/sdp.c
index 6ef9656..7e632c3 100644
--- a/src/sdp.c
+++ b/src/sdp.c
@@ -124,6 +124,7 @@ bool sdp_screen_sdp(const sip_t *sip)
 	}
 
 	sdp_parser_free(parser);
+	/* FIXME: osmo-sip-connector should not interfere in codecs at all */
 	return false;
 
 success:
@@ -131,6 +132,9 @@ success:
 	return true;
 }
 
+/* Extract RTP address, port and payload type from SDP received in SIP message, in order to populate the legacy MNCC
+ * fields, for backwards compatibility. osmo-sip-connector now always sends the entire SDP info unchanged via MNCC,
+ * which obsoletes the legacy fields. But for backwards compatibility, still populate the legacy fields. */
 bool sdp_extract_sdp(struct sip_call_leg *leg, const sip_t *sip, bool any_codec)
 {
 	sdp_connection_t *conn;
@@ -191,7 +195,9 @@ bool sdp_extract_sdp(struct sip_call_leg *leg, const sip_t *sip, bool any_codec)
 			continue;
 
 		for (map = media->m_rtpmaps; map; map = map->rm_next) {
-			if (!any_codec && strcasecmp(map->rm_encoding, leg->wanted_codec) != 0)
+			if (!any_codec
+			    && leg->wanted_codec
+			    && strcasecmp(map->rm_encoding, leg->wanted_codec) != 0)
 				continue;
 
 			port = media->m_port;
@@ -208,6 +214,7 @@ bool sdp_extract_sdp(struct sip_call_leg *leg, const sip_t *sip, bool any_codec)
 		LOGP(DSIP, LOGL_ERROR, "leg(%p) did not find %d/%d\n",
 			leg, found_conn, found_map);
 		sdp_parser_free(parser);
+		/* FIXME: osmo-sip-connector should not interfere in codecs at all */
 		return false;
 	}
 
@@ -226,21 +233,43 @@ bool sdp_extract_sdp(struct sip_call_leg *leg, const sip_t *sip, bool any_codec)
 	return true;
 }
 
+/* One leg has sent a SIP or MNCC message, which is now translated/forwarded to the counterpart MNCC or SIP.
+ * Take as much from the source's SDP as possible, but make sure the connection mode reflects the 'mode' arg (sendrecv,
+ * recvonly, sendonly, inactive).
+ * For example, if the MSC sent an MNCC_SETUP_IND, the SDP from the MNCC is found in 'other', while 'leg' reflects the
+ * SIP side that should receive this SDP in the SIP Invite that is being composed by the caller of this function.
+ * \param leg  The target for which the returned SDP is intended.
+ * \param other  The source of which we are to reflect the SDP.
+ * \return  SDP string, using 'leg' as talloc ctx.
+ */
 char *sdp_create_file(struct sip_call_leg *leg, struct call_leg *other, sdp_mode_t mode)
 {
-	char *fmtp_str = NULL, *sdp;
-	char *mode_attribute;
-	char ip_addr[INET6_ADDRSTRLEN];
-	char ipv;
-
-	osmo_sockaddr_ntop((const struct sockaddr*)&other->addr, ip_addr);
-	ipv = other->addr.ss_family == AF_INET6 ? '6' : '4';
-	leg->wanted_codec = app_media_name(other->payload_msg_type);
-
-	if (strcmp(leg->wanted_codec, "AMR") == 0)
-		fmtp_str = talloc_asprintf(leg, "a=fmtp:%d octet-align=1\r\n", other->payload_type);
-
-	switch (mode) {
+	sdp_parser_t *parser;
+	sdp_session_t *sdp;
+	sdp_media_t *media;
+	const char *sdp_data;
+	sdp_printer_t *printer;
+	char buf[1024];
+	const char *sdp_str;
+	char *ret;
+
+	sdp_data = other->rx_sdp;
+
+	if (!*sdp_data) {
+		/* Legacy compat: We have not received any SDP from the other call leg. Compose some original SDP from
+		 * the RTP information we have. */
+		char *fmtp_str = NULL;
+		char *mode_attribute;
+		char ip_addr[INET6_ADDRSTRLEN];
+		char ipv;
+
+		osmo_sockaddr_ntop((const struct sockaddr *)&other->addr, ip_addr);
+		ipv = other->addr.ss_family == AF_INET6 ? '6' : '4';
+		leg->wanted_codec = app_media_name(other->payload_msg_type);
+		if (strcmp(leg->wanted_codec, "AMR") == 0)
+			fmtp_str = talloc_asprintf(leg, "a=fmtp:%d octet-align=1\r\n", other->payload_type);
+
+		switch (mode) {
 		case sdp_inactive:
 			mode_attribute = "a=inactive\r\n";
 			break;
@@ -256,25 +285,67 @@ char *sdp_create_file(struct sip_call_leg *leg, struct call_leg *other, sdp_mode
 		default:
 			OSMO_ASSERT(false);
 			break;
+		}
+
+		return talloc_asprintf(leg,
+				       "v=0\r\n"
+				       "o=Osmocom 0 0 IN IP%c %s\r\n"
+				       "s=GSM Call\r\n"
+				       "c=IN IP%c %s\r\n"
+				       "t=0 0\r\n"
+				       "m=audio %d RTP/AVP %d\r\n"
+				       "%s"
+				       "a=rtpmap:%d %s/8000\r\n"
+				       "%s",
+				       ipv, ip_addr, ipv, ip_addr,
+				       osmo_sockaddr_port((const struct sockaddr *)&other->addr),
+				       other->payload_type,
+				       fmtp_str ? fmtp_str : "",
+				       other->payload_type,
+				       leg->wanted_codec,
+				       mode_attribute);
+	}
+
+	/* We have received SDP from the other call leg. Forward this as-is, only apply the mode the caller requests:
+	 * parse SDP, set media mode, recompose. */
+	/* TODO: currently, we often detect the media mode from parsing SDP, and then forward the same SDP, applying the
+	 * same mode to it below. It may make sense to completely skip parsing and composition: the mode is usually
+	 * already in the received SDP.
+	 * However, there are some invocations of this function (sdp_create_file()) with hardcoded modes. Take a look if
+	 * that is really necessary, and if not, just drop below parsing + recomposition and use the sdp_data as is.
+	 */
+	parser = sdp_parse(NULL, sdp_data, strlen(sdp_data), 0);
+	if (!parser) {
+		LOGP(DSIP, LOGL_ERROR, "leg(%p) failed to parse SDP\n", other);
+		return talloc_strdup(leg, sdp_data);
 	}
 
-	sdp = talloc_asprintf(leg,
-				"v=0\r\n"
-				"o=Osmocom 0 0 IN IP%c %s\r\n"
-				"s=GSM Call\r\n"
-				"c=IN IP%c %s\r\n"
-				"t=0 0\r\n"
-				"m=audio %d RTP/AVP %d\r\n"
-				"%s"
-				"a=rtpmap:%d %s/8000\r\n"
-				"%s",
-				ipv, ip_addr, ipv, ip_addr,
-				osmo_sockaddr_port((const struct sockaddr *)&other->addr),
-				other->payload_type,
-				fmtp_str ? fmtp_str : "",
-				other->payload_type,
-				leg->wanted_codec,
-				mode_attribute);
-	talloc_free(fmtp_str);
-	return sdp;
+	sdp = sdp_session(parser);
+	if (!sdp) {
+		LOGP(DSIP, LOGL_ERROR, "leg(%p) no sdp session\n", other);
+		sdp_parser_free(parser);
+		return talloc_strdup(leg, sdp_data);
+	}
+
+	for (media = sdp->sdp_media; media; media = media->m_next)
+		media->m_mode = mode;
+
+	printer = sdp_print(NULL, sdp, buf, sizeof(buf), sdp_f_mode_always);
+	if (!printer) {
+		LOGP(DSIP, LOGL_ERROR, "leg(%p) failed to print SDP\n", other);
+		sdp_parser_free(parser);
+		return talloc_strdup(leg, sdp_data);
+	}
+
+	sdp_str = sdp_message(printer);
+	if (!sdp_str) {
+		LOGP(DSIP, LOGL_ERROR, "leg(%p) failed to print SDP: %s\n", other, sdp_printing_error(printer));
+		sdp_str = sdp_data;
+	}
+
+	ret = talloc_strdup(leg, sdp_str);
+
+	sdp_parser_free(parser);
+	sdp_printer_free(printer);
+	return ret;
 }
diff --git a/src/sdp.h b/src/sdp.h
index 8e4e314..dae2e96 100644
--- a/src/sdp.h
+++ b/src/sdp.h
@@ -11,5 +11,4 @@ struct call_leg;
 bool sdp_get_sdp_mode(const sip_t *sip, sdp_mode_t *mode);
 bool sdp_screen_sdp(const sip_t *sip);
 bool sdp_extract_sdp(struct sip_call_leg *leg, const sip_t *sip, bool any_codec);
-
-char *sdp_create_file(struct sip_call_leg *, struct call_leg *, sdp_mode_t mode);
+char *sdp_create_file(struct sip_call_leg *leg, struct call_leg *other, sdp_mode_t mode);
diff --git a/src/sip.c b/src/sip.c
index 61c7cbd..0c8130f 100644
--- a/src/sip.c
+++ b/src/sip.c
@@ -46,6 +46,12 @@ static void sip_dtmf_call(struct call_leg *_leg, int keypad);
 static void sip_hold_call(struct call_leg *_leg);
 static void sip_retrieve_call(struct call_leg *_leg);
 
+static const char *sip_get_sdp(const sip_t *sip)
+{
+	if (!sip || !sip->sip_payload)
+		return NULL;
+	return sip->sip_payload->pl_data;
+}
 
 /* Find a SIP Call leg by given nua_handle */
 static struct sip_call_leg *sip_find_leg(nua_handle_t *nh)
@@ -196,6 +202,8 @@ static void new_call(struct sip_agent *agent, nua_handle_t *nh,
 	nua_handle_bind(nh, leg);
 	leg->sdp_payload = talloc_strdup(leg, sip->sip_payload->pl_data);
 
+	call_leg_rx_sdp(&leg->base, sip_get_sdp(sip));
+
 	app_route_call(call,
 			talloc_strdup(leg, from),
 			talloc_strdup(leg, to));
@@ -236,6 +244,8 @@ static void sip_handle_reinvite(struct sip_call_leg *leg, nua_handle_t *nh, cons
 	     osmo_sockaddr_ntop((struct sockaddr*)&prev_addr, ip_addr),
 	     osmo_sockaddr_port((struct sockaddr*)&prev_addr));
 
+	call_leg_rx_sdp(&leg->base, sip_get_sdp(sip));
+
 	if (mode == sdp_sendonly) {
 		/* SIP side places call on HOLD */
 		sdp = sdp_create_file(leg, other, sdp_recvonly);
@@ -355,6 +365,8 @@ void nua_callback(nua_event_t event, int status, char const *phrase, nua_t *nua,
 		struct sip_call_leg *leg;
 		leg = (struct sip_call_leg *) hmagic;
 
+		call_leg_rx_sdp(&leg->base, sip_get_sdp(sip));
+
 		/* MT call is moving forward */
 
 		/* The dialogue is now confirmed */
@@ -396,8 +408,10 @@ void nua_callback(nua_event_t event, int status, char const *phrase, nua_t *nua,
 		 * respond to the re-INVITE query. */
 		if (sip->sip_payload && sip->sip_payload->pl_data) {
 			struct sip_call_leg *leg = sip_find_leg(nh);
-			if (leg)
+			if (leg) {
+				call_leg_rx_sdp(&leg->base, sip_get_sdp(sip));
 				sip_handle_reinvite(leg, nh, sip);
+			}
 		}
 	} else if (event == nua_r_bye || event == nua_r_cancel) {
 		/* our bye or hang up is answered */
@@ -423,10 +437,12 @@ void nua_callback(nua_event_t event, int status, char const *phrase, nua_t *nua,
 
 		if (status == 100) {
 			struct sip_call_leg *leg = sip_find_leg(nh);
-			if (leg)
+			if (leg) {
+				call_leg_rx_sdp(&leg->base, sip_get_sdp(sip));
 				sip_handle_reinvite(leg, nh, sip);
-			else
+			} else {
 				new_call((struct sip_agent *) magic, nh, sip);
+			}
 		}
 	} else if (event == nua_i_cancel) {
 		struct sip_call_leg *leg;
@@ -521,6 +537,7 @@ static void sip_ring_call(struct call_leg *_leg)
 	OSMO_ASSERT(_leg->type == CALL_TYPE_SIP);
 	leg = (struct sip_call_leg *) _leg;
 
+	/* 180 Ringing should not contain any SDP. */
 	nua_respond(leg->nua_handle, SIP_180_RINGING, TAG_END());
 }