net: mqtt: Add SOCKS5 proxy support

This commits adds a new MQTT transport. The purpose is to be able to
connect to a MQTT broker through a SOCKS5 proxy.

Signed-off-by: Tomasz Gorochowik <tgorochowik@antmicro.com>

include/net/mqtt.h

@@ -348,6 +348,11 @@ enum mqtt_transport_type {
 	MQTT_TRANSPORT_SECURE,
 #endif /* CONFIG_MQTT_LIB_TLS */
 
+#if defined(CONFIG_MQTT_LIB_SOCKS)
+	/** Use SOCKS5 proxy for MQTT connection. */
+	MQTT_TRANSPORT_SOCKS,
+#endif /* CONFIG_MQTT_LIB_SOCKS */
+
 	/** Shall not be used as a transport type.
 	 *  Indicator of maximum transport types possible.
 	 */
@@ -381,6 +386,18 @@ struct mqtt_transport {
 			struct mqtt_sec_config config;
 		} tls;
 #endif /* CONFIG_MQTT_LIB_TLS */
+
+#if defined(CONFIG_MQTT_LIB_SOCKS)
+		/* SOCKS5 proxy transport for MQTT */
+		struct {
+			/** Socket descriptor. */
+			int sock;
+
+			/** SOCKS5 proxy address. */
+			struct sockaddr_storage *proxy;
+		} socks5;
+#endif /* CONFIG_MQTT_LIB_SOCKS */
+
 	};
 };
 

subsys/net/lib/mqtt/CMakeLists.txt

@@ -12,3 +12,7 @@ zephyr_library_sources(
 zephyr_library_sources_ifdef(CONFIG_MQTT_LIB_TLS
   mqtt_transport_socket_tls.c
   )
+
+zephyr_library_sources_ifdef(CONFIG_MQTT_LIB_SOCKS
+  mqtt_transport_socks.c
+  )

subsys/net/lib/mqtt/Kconfig

@@ -32,4 +32,10 @@ config MQTT_LIB_TLS
 	help
 	  Enable TLS support for socket MQTT Library
 
+config MQTT_LIB_SOCKS
+	bool "SOCKS proxy support for socket MQTT Library"
+	select SOCKS
+	help
+	  Enable SOCKS proxy support for socket MQTT Library
+
 endif # MQTT_LIB

subsys/net/lib/mqtt/mqtt_transport.c

@@ -29,6 +29,11 @@ extern int mqtt_client_tls_read(struct mqtt_client *client, u8_t *data,
 extern int mqtt_client_tls_disconnect(struct mqtt_client *client);
 #endif /* CONFIG_MQTT_LIB_TLS */
 
+#if defined(CONFIG_MQTT_LIB_SOCKS)
+/* Transport handler functions for SOCKS5 proxy socket transport. */
+extern int mqtt_client_socks5_connect(struct mqtt_client *client);
+#endif /* CONFIG_MQTT_LIB_SOCKS */
+
 /**@brief Function pointer array for TCP/TLS transport handlers. */
 const struct transport_procedure transport_fn[MQTT_TRANSPORT_NUM] = {
 	{
@@ -43,8 +48,16 @@ const struct transport_procedure transport_fn[MQTT_TRANSPORT_NUM] = {
 		mqtt_client_tls_write,
 		mqtt_client_tls_read,
 		mqtt_client_tls_disconnect,
-	}
+	},
 #endif /* CONFIG_MQTT_LIB_TLS */
+#if defined(CONFIG_MQTT_LIB_SOCKS)
+	{
+		mqtt_client_socks5_connect,
+		mqtt_client_tcp_write,
+		mqtt_client_tcp_read,
+		mqtt_client_tcp_disconnect,
+	},
+#endif /* CONFIG_MQTT_LIB_SOCKS */
 };
 
 int mqtt_transport_connect(struct mqtt_client *client)

subsys/net/lib/mqtt/mqtt_transport_socks.c

@@ -0,0 +1,47 @@
+/*
+ * Copyright (c) 2019 Antmicro Ltd
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/** @file mqtt_transport_socks.c
+ *
+ * @brief Internal functions to handle transport over SOCKS5 proxy.
+ */
+
+#include <logging/log.h>
+LOG_MODULE_REGISTER(net_mqtt_socks, CONFIG_MQTT_LOG_LEVEL);
+
+#include <errno.h>
+#include <net/socket.h>
+#include <net/socks.h>
+#include <net/mqtt.h>
+
+#include "mqtt_os.h"
+
+/**@brief Handles connect request for TCP socket transport.
+ *
+ * @param[in] client Identifies the client on which the procedure is requested.
+ *
+ * @retval 0 or an error code indicating reason for failure.
+ */
+int mqtt_client_socks5_connect(struct mqtt_client *client)
+{
+	const struct sockaddr *broker = client->broker;
+	const struct sockaddr *proxy =
+		(struct sockaddr *)client->transport.socks5.proxy;
+
+	if (proxy == NULL || broker == NULL) {
+		return -EINVAL;
+	}
+
+	client->transport.socks5.sock =
+		socks5_client_tcp_connect(proxy, broker);
+
+	if (client->transport.socks5.sock < 0) {
+		return client->transport.socks5.sock;
+	}
+
+	MQTT_TRC("Connect completed");
+	return 0;
+}