slm: fix IPv6 only case

If ISP sends only IPv6 DNS records, pdn_dynamic_params_get was
failing. pdn_dynamic_params_get_v6 was implemented and used as
a fallback on the SLM's ppp.

DevZone Nordic Case ID: 336147

Signed-off-by: Oguzhan Turk <[email protected]>

Author: TaeZStkyoht

applications/serial_lte_modem/src/slm_ppp.c

@@ -213,7 +213,11 @@ static int ppp_start_internal(void)
 	ret = pdn_dynamic_params_get(PDP_CID, &ctx->ipcp.my_options.dns1_address,
 				     &ctx->ipcp.my_options.dns2_address, &mtu);
 	if (ret) {
-		return ret;
+		/* If any error happened on pdn getting with IPv4, try to parse with IPv6 */
+		ret = pdn_dynamic_params_get_v6(PDP_CID, NULL, NULL, &mtu);
+		if (ret) {
+			return ret;
+		}
 	}
 
 	if (mtu) {

doc/nrf/releases_and_maturity/releases/release-notes-changelog.rst

@@ -451,7 +451,9 @@ Security libraries
 Modem libraries
 ---------------
 
-|no_changes_yet_note|
+* :ref:`pdn_readme` library:
+
+  * Added the :c:func:`pdn_dynamic_params_get_v6` function to get PDN parameters for IPv6-only.
 
 Multiprotocol Service Layer libraries
 -------------------------------------

include/modem/pdn.h

@@ -193,6 +193,19 @@ int pdn_id_get(uint8_t cid);
 int pdn_dynamic_params_get(uint8_t cid, struct in_addr *dns4_pri,
 			   struct in_addr *dns4_sec, unsigned int *ipv4_mtu);
 
+/**
+ * @brief Retrieve dynamic parameters of a given PDP context.
+ *
+ * @param cid The PDP context ID.
+ * @param[out] dns6_pri The address of the primary IPv6 DNS server. Optional, can be NULL.
+ * @param[out] dns6_sec The address of the secondary IPv6 DNS server. Optional, can be NULL.
+ * @param[out] ipv6_mtu The IPv6 MTU. Optional, can be NULL.
+ *
+ * @return Zero on success or an error code on failure.
+ */
+int pdn_dynamic_params_get_v6(uint8_t cid, struct in6_addr *dns6_pri,
+			   struct in6_addr *dns6_sec, unsigned int *ipv6_mtu);
+
 /**
  * @brief Retrieve the default Access Point Name (APN).
  *

lib/pdn/pdn.c

@@ -659,6 +659,55 @@ int pdn_dynamic_params_get(uint8_t cid, struct in_addr *dns4_pri,
 	return 0;
 }
 
+int pdn_dynamic_params_get_v6(uint8_t cid, struct in6_addr *dns6_pri,
+			   struct in6_addr *dns6_sec, unsigned int *ipv6_mtu)
+{
+	int matched;
+	const char *fmt;
+	unsigned int mtu;
+	char dns6_pri_str[INET6_ADDRSTRLEN];
+	char dns6_sec_str[INET6_ADDRSTRLEN];
+	char at_cmd[sizeof("AT+CGCONTRDP=10")];
+
+	if (snprintf(at_cmd, sizeof(at_cmd), "AT+CGCONTRDP=%u", cid) >= sizeof(at_cmd)) {
+		return -E2BIG;
+	}
+	/* "+CGCONTRDP: 0,,"ims","","",
+	 *	"0000:0000:0000:0000:0000:0000:0000:0000",
+	 *	"0000:0000:0000:0000:0000:0000:0000:0000",,,,,1500"
+	 */
+	fmt = "+CGCONTRDP: %*u,,\"%*[^\"]\",\"\",\"\","
+		"\"%45[0-9A-Fa-f:]\",\"%45[0-9A-Fa-f:]\",,,,,%u";
+
+	/* If IPv6 is enabled, it will be the first response line. */
+	matched = nrf_modem_at_scanf(at_cmd, fmt, &dns6_pri_str, &dns6_sec_str, &mtu);
+	/* Need to match at least the two IP addresses, or there is an error */
+	if (matched < 2) {
+		return -EBADMSG;
+	}
+
+	if (dns6_pri) {
+		if (zsock_inet_pton(AF_INET6, dns6_pri_str, dns6_pri) != 1) {
+			return -EADDRNOTAVAIL;
+		}
+	}
+	if (dns6_sec) {
+		if (zsock_inet_pton(AF_INET6, dns6_sec_str, dns6_sec) != 1) {
+			return -EADDRNOTAVAIL;
+		}
+	}
+	if (ipv6_mtu) {
+		/* If we matched the MTU, copy it here, otherwise report zero */
+		if (matched == 3) {
+			*ipv6_mtu = mtu;
+		} else {
+			*ipv6_mtu = 0;
+		}
+	}
+
+	return 0;
+}
+
 int pdn_default_apn_get(char *buf, size_t len)
 {
 	int err;