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1 office 1 MQTT client for lwIP
2  
3 Author: Erik Andersson
4  
5 Details of the MQTT protocol can be found at:
6 http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/os/mqtt-v3.1.1-os.html
7  
8 -----------------------------------------------------------------
9 1. Initial steps, reserve memory and make connection to server:
10  
11 1.1: Provide storage
12  
13 Static allocation:
14 mqtt_client_t static_client;
15 example_do_connect(&static_client);
16  
17 Dynamic allocation:
18 mqtt_client_t *client = mqtt_client_new();
19 if(client != NULL) {
20 example_do_connect(&client);
21 }
22  
23 1.2: Establish Connection with server
24  
25 void 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  
49 Connection to server can also be probed by calling mqtt_client_is_connected(client)
50  
51 -----------------------------------------------------------------
52 2. Implementing the connection status callback
53  
54  
55 static 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  
78 static 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 -----------------------------------------------------------------
87 3. 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 */
94 static int inpub_id;
95 static 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  
111 static 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 -----------------------------------------------------------------
136 4. Using outgoing publish
137  
138  
139 void 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 */
152 static 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 -----------------------------------------------------------------
160 5. Disconnecting
161  
162 Simply call mqtt_disconnect(client)