1MQTT client for lwIP 2 3Author: Erik Andersson 4 5Details of the MQTT protocol can be found at: 6http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/os/mqtt-v3.1.1-os.html 7 8----------------------------------------------------------------- 91. Initial steps, reserve memory and make connection to server: 10 111.1: Provide storage 12 13Static allocation: 14 mqtt_client_t static_client; 15 example_do_connect(&static_client); 16 17Dynamic allocation: 18 mqtt_client_t *client = mqtt_client_new(); 19 if(client != NULL) { 20 example_do_connect(&client); 21 } 22 231.2: Establish Connection with server 24 25void example_do_connect(mqtt_client_t *client) 26{ 27 struct mqtt_connect_client_info_t ci; 28 err_t err; 29 30 /* Setup an empty client info structure */ 31 memset(&ci, 0, sizeof(ci)); 32 33 /* Minimal amount of information required is client identifier, so set it here */ 34 ci.client_id = "lwip_test"; 35 36 /* Initiate client and connect to server, if this fails immediately an error code is returned 37 otherwise mqtt_connection_cb will be called with connection result after attempting 38 to establish a connection with the server. 39 For now MQTT version 3.1.1 is always used */ 40 41 err = mqtt_client_connect(client, ip_addr, MQTT_PORT, mqtt_connection_cb, 0, &ci); 42 43 /* For now just print the result code if something goes wrong 44 if(err != ERR_OK) { 45 printf("mqtt_connect return %d\n", err); 46 } 47} 48 49Connection to server can also be probed by calling mqtt_client_is_connected(client) 50 51----------------------------------------------------------------- 522. Implementing the connection status callback 53 54 55static void mqtt_connection_cb(mqtt_client_t *client, void *arg, mqtt_connection_status_t status) 56{ 57 err_t err; 58 if(status == MQTT_CONNECT_ACCEPTED) { 59 printf("mqtt_connection_cb: Successfully connected\n"); 60 61 /* Setup callback for incoming publish requests */ 62 mqtt_set_inpub_callback(client, mqtt_incoming_publish_cb, mqtt_incoming_data_cb, arg); 63 64 /* Subscribe to a topic named "subtopic" with QoS level 1, call mqtt_sub_request_cb with result */ 65 err = mqtt_subscribe(client, "subtopic", 1, mqtt_sub_request_cb, arg); 66 67 if(err != ERR_OK) { 68 printf("mqtt_subscribe return: %d\n", err); 69 } 70 } else { 71 printf("mqtt_connection_cb: Disconnected, reason: %d\n", status); 72 73 /* Its more nice to be connected, so try to reconnect */ 74 example_do_connect(client); 75 } 76} 77 78static void mqtt_sub_request_cb(void *arg, err_t result) 79{ 80 /* Just print the result code here for simplicity, 81 normal behaviour would be to take some action if subscribe fails like 82 notifying user, retry subscribe or disconnect from server */ 83 printf("Subscribe result: %d\n", result); 84} 85 86----------------------------------------------------------------- 873. Implementing callbacks for incoming publish and data 88 89/* The idea is to demultiplex topic and create some reference to be used in data callbacks 90 Example here uses a global variable, better would be to use a member in arg 91 If RAM and CPU budget allows it, the easiest implementation might be to just take a copy of 92 the topic string and use it in mqtt_incoming_data_cb 93*/ 94static int inpub_id; 95static void mqtt_incoming_publish_cb(void *arg, const char *topic, u32_t tot_len) 96{ 97 printf("Incoming publish at topic %s with total length %u\n", topic, (unsigned int)tot_len); 98 99 /* Decode topic string into a user defined reference */ 100 if(strcmp(topic, "print_payload") == 0) { 101 inpub_id = 0; 102 } else if(topic[0] == 'A') { 103 /* All topics starting with 'A' might be handled at the same way */ 104 inpub_id = 1; 105 } else { 106 /* For all other topics */ 107 inpub_id = 2; 108 } 109} 110 111static void mqtt_incoming_data_cb(void *arg, const u8_t *data, u16_t len, u8_t flags) 112{ 113 printf("Incoming publish payload with length %d, flags %u\n", len, (unsigned int)flags); 114 115 if(flags & MQTT_DATA_FLAG_LAST) { 116 /* Last fragment of payload received (or whole part if payload fits receive buffer 117 See MQTT_VAR_HEADER_BUFFER_LEN) */ 118 119 /* Call function or do action depending on reference, in this case inpub_id */ 120 if(inpub_id == 0) { 121 /* Don't trust the publisher, check zero termination */ 122 if(data[len-1] == 0) { 123 printf("mqtt_incoming_data_cb: %s\n", (const char *)data); 124 } 125 } else if(inpub_id == 1) { 126 /* Call an 'A' function... */ 127 } else { 128 printf("mqtt_incoming_data_cb: Ignoring payload...\n"); 129 } 130 } else { 131 /* Handle fragmented payload, store in buffer, write to file or whatever */ 132 } 133} 134 135----------------------------------------------------------------- 1364. Using outgoing publish 137 138 139void example_publish(mqtt_client_t *client, void *arg) 140{ 141 const char *pub_payload= "PubSubHubLubJub"; 142 err_t err; 143 u8_t qos = 2; /* 0 1 or 2, see MQTT specification */ 144 u8_t retain = 0; /* No don't retain such crappy payload... */ 145 err = mqtt_publish(client, "pub_topic", pub_payload, strlen(pub_payload), qos, retain, mqtt_pub_request_cb, arg); 146 if(err != ERR_OK) { 147 printf("Publish err: %d\n", err); 148 } 149} 150 151/* Called when publish is complete either with sucess or failure */ 152static void mqtt_pub_request_cb(void *arg, err_t result) 153{ 154 if(result != ERR_OK) { 155 printf("Publish result: %d\n", result); 156 } 157} 158 159----------------------------------------------------------------- 1605. Disconnecting 161 162Simply call mqtt_disconnect(client) 163