OpenThread: avoid hardcoded Golioth IPv6 address

Leverage the OpenThread DNS to synthesize the Golioth System Server
IPv6 address avoiding hardcoded IP address in applications.
NAT64 prefix used by the Thred Border Router is set while
synthesizing the address.

Signed-off-by: Marko Puric <[email protected]>

net/golioth/CMakeLists.txt

@@ -11,6 +11,7 @@ zephyr_library_sources_ifdef(CONFIG_GOLIOTH_RPC rpc.c)
 zephyr_library_sources_ifdef(CONFIG_GOLIOTH_SETTINGS settings.c)
 zephyr_library_sources_ifdef(CONFIG_GOLIOTH_SYSTEM_CLIENT system_client.c)
 zephyr_library_sources_ifdef(CONFIG_ZCBOR zcbor_utils.c)
+zephyr_library_sources_ifdef(CONFIG_NET_L2_OPENTHREAD ot_dns.c)
 
 if(CONFIG_GOLIOTH_AUTH_METHOD_CERT)
   set(path ${CONFIG_GOLIOTH_SYSTEM_CLIENT_CA_PATH})

net/golioth/ot_dns.c

@@ -0,0 +1,76 @@
+/*
+ * Copyright (c) 2024 Golioth, Inc.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <zephyr/logging/log.h>
+LOG_MODULE_REGISTER(golioth_openthread, CONFIG_GOLIOTH_SYSTEM_CLIENT_LOG_LEVEL);
+
+#include <openthread/nat64.h>
+#include <openthread/dns_client.h>
+#include <zephyr/net/openthread.h>
+#include <openthread/error.h>
+
+static otDnsQueryConfig dns_query;
+static char *golioth_ip6_addr;
+
+K_SEM_DEFINE(ot_dns_resolve, 0, 1);
+
+/* Callback for NAT64 IPv6 translated Golioth System Server address from the DNS query response */
+static void ot_dns_callback(otError aError, const otDnsAddressResponse *aResponse, void *aContext)
+{
+	otIp6Address golioth_addr;
+
+	if (aError != OT_ERROR_NONE) {
+		LOG_ERR("Golioth System Server DNS resolving error: %d", aError);
+		return;
+	}
+
+	if (otDnsAddressResponseGetAddress(aResponse, 0, &golioth_addr, NULL) == OT_ERROR_NONE) {
+		otIp6AddressToString(&golioth_addr,
+				     golioth_ip6_addr,
+				     OT_IP6_ADDRESS_STRING_SIZE);
+	}
+
+	k_sem_give(&ot_dns_resolve);
+}
+
+int synthesize_ip6_address(char *hostname, char *ip6_addr_buffer)
+{
+	int err = 0;
+	golioth_ip6_addr = ip6_addr_buffer;
+
+	struct openthread_context *ot_context = openthread_get_default_context();
+
+	otIp4Address dns_server_addr;
+
+	err = otIp4AddressFromString(CONFIG_DNS_SERVER1, &dns_server_addr);
+	if (err != OT_ERROR_NONE) {
+		LOG_ERR("DNS server IPv4 address error: %d", err);
+		return err;
+	}
+
+	err = otNat64SynthesizeIp6Address(ot_context->instance,
+					  &dns_server_addr,
+					  &dns_query.mServerSockAddr.mAddress);
+	if (err != OT_ERROR_NONE) {
+		LOG_ERR("Synthesize DNS server IPv6 address error: %d", err);
+		return err;
+	}
+
+	err = otDnsClientResolveIp4Address(ot_context->instance,
+					   hostname,
+					   ot_dns_callback,
+					   ot_context,
+					   &dns_query);
+	if (err != OT_ERROR_NONE) {
+		LOG_ERR("Golioth System Server address resolution DNS query error: %d", err);
+		return err;
+	}
+
+	k_sem_take(&ot_dns_resolve, K_FOREVER);
+
+	return 0;
+}
+

net/golioth/ot_dns.h

@@ -0,0 +1,24 @@
+/*
+ * Copyright (c) 2024 Golioth, Inc.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#ifndef __OT_DNS_H__
+#define __OT_DNS_H__
+
+/**
+ * @brief Synthesize the IPv6 address from a given host name
+ *
+ * Get the IPv6 address of Golioth Server to avoid hardcoding it in applications.
+ * NAT64 prefix used by the Thread Border Router is set while synthesizing the address.
+ *
+ * @param[in] hostname A pointer to the host name for which to querry the address
+ * @param[out] ip6_addr_buffer A buffer to char array to output the synthesized IPv6 address
+ *
+ * @retval 0 On success
+ * @retval <0 On failure
+ */
+int synthesize_ip6_address(char *hostname, char *ip6_addr_buffer);
+
+#endif /* __OT_DNS_GOL_H__ */

net/golioth/system_client.c

@@ -17,8 +17,12 @@ LOG_MODULE_REGISTER(golioth_system, CONFIG_GOLIOTH_SYSTEM_CLIENT_LOG_LEVEL);
 #include <zephyr/sys/atomic.h>
 #include <zephyr/sys/util.h>
 
+#include "ot_dns.h"
+
 #define RX_BUFFER_SIZE		CONFIG_GOLIOTH_SYSTEM_CLIENT_RX_BUF_SIZE
 
+static char golioth_system_server_host[40] = CONFIG_GOLIOTH_SYSTEM_SERVER_HOST;
+
 static const uint8_t tls_ca_crt[] = {
 #if defined(CONFIG_GOLIOTH_SYSTEM_CLIENT_CA_PATH)
 #include "golioth-systemclient-ca.inc"
@@ -244,11 +248,22 @@ SYS_INIT(golioth_system_init, APPLICATION,
 
 static int client_connect(struct golioth_client *client)
 {
-	int err;
+	int err = 0;
+
+#if defined(CONFIG_NET_L2_OPENTHREAD)
+
+	err = synthesize_ip6_address(golioth_system_server_host, golioth_system_server_host);
+	if (err) {
+		LOG_ERR("Failed to synthesize Golioth Server IPv6 address: %d", err);
+		return err;
+	}
+
+#endif
 
 	err = golioth_connect(client,
-			      CONFIG_GOLIOTH_SYSTEM_SERVER_HOST,
+			      golioth_system_server_host,
 			      CONFIG_GOLIOTH_SYSTEM_SERVER_PORT);
+
 	if (err) {
 		LOG_ERR("Failed to connect: %d", err);
 		return err;