【rt-thread网络】第1篇：通过paho-mqtt软件包入门rt-thread的sal
一、paho-mqtt软件包程序流程
1.1 paho_mqtt_start
在rt_wlan_register_event_handler函数注册好RT_WLAN_EVT_READY的回调函数paho_mqtt_start，当wifi准备好后调用mq_start启动mqtt。在mq_start中，初始化MQTTClient结构体，设置mqtt连接的参数：mqtt的uri、mqtt的用户名（username）和密码（password）、mqtt发布和订阅的主题Topic、消息质量等级QoS，最后调用paho_mqtt_start创建处理mqtt的线程paho_mqtt_thread。
static void mq_start(void)
{
/* init condata param by using MQTTPacket_connectData_initializer */
MQTTPacket_connectData condata = MQTTPacket_connectData_initializer;
static char cid[20] = { 0 };
static int is_started = 0;
if (is_started)
{
return;
}
/* config MQTT context param */
{
client.isconnected = 0;
client.uri = MQTT_URI;
/* generate the random client ID */
rt_snprintf(cid, sizeof(cid), "rtthread%d", rt_tick_get());
/* config connect param */
memcpy(&client.condata, &condata, sizeof(condata));
client.condata.clientID.cstring = cid;
client.condata.keepAliveInterval = 60;
client.condata.cleansession = 1;
client.condata.username.cstring = MQTT_USERNAME;
client.condata.password.cstring = MQTT_PASSWORD;
/* config MQTT will param. */
client.condata.willFlag = 1;
client.condata.will.qos = 1;
client.condata.will.retained = 0;
client.condata.will.topicName.cstring = MQTT_PUBTOPIC;
client.condata.will.message.cstring = MQTT_WILLMSG;
/* malloc buffer. */
client.buf_size = client.readbuf_size = 1024;
client.buf = malloc(client.buf_size);
client.readbuf = malloc(client.readbuf_size);
if (!(client.buf && client.readbuf))
{
LOG_E("no memory for MQTT client buffer!");
goto _exit;
}
/* set event callback function */
client.connect_callback = mqtt_connect_callback;
client.online_callback = mqtt_online_callback;
client.offline_callback = mqtt_offline_callback;
/* set subscribe table and event callback */
client.messageHandlers[0].topicFilter = MQTT_SUBTOPIC;
client.messageHandlers[0].callback = mqtt_sub_callback;
client.messageHandlers[0].qos = QOS1;
/* set default subscribe event callback */
client.defaultMessageHandler = mqtt_sub_default_callback;
}
/* run mqtt client */
paho_mqtt_start(&client);
is_started = 1;
_exit:
return;
}
rt_wlan_register_event_handler(RT_WLAN_EVT_READY, (void (*)(int, struct rt_wlan_buff *, void *))mq_start, RT_NULL);
1.2 paho_mqtt_thread
在paho_mqtt_thread中调用paho-mqtt提供的接口和rt-thread的sal的接口完成与mqtt服务器的交互，包括以下几个方面：与服务器的连接、订阅主题、向服务器发送心跳包、处理服务器发送下来的消息（CONNACK、PUBACK、SUBACK、PUBLISH、PUBREC、PUBCOMP、PINGRESP）、回环服务器通过topic发送下来的消息。
static void paho_mqtt_thread(void *param)
{
MQTTClient *c = (MQTTClient *)param;
int i, rc, len;
int rc_t = 0;
c->pub_sock = socket(AF_INET, SOCK_DGRAM, 0);
if (c->pub_sock == -1)
{
debug_printf("create pub_sock error!\n");
goto _mqtt_exit;
}
/* bind publish socket. */
{
struct sockaddr_in pub_server_addr;
c->pub_port = pub_port;
pub_port ++;
pub_server_addr.sin_family = AF_INET;
pub_server_addr.sin_port = htons((c->pub_port));
pub_server_addr.sin_addr.s_addr = INADDR_ANY;
memset(&(pub_server_addr.sin_zero), 0, sizeof(pub_server_addr.sin_zero));
rc = bind(c->pub_sock, (struct sockaddr *)&pub_server_addr, sizeof(struct sockaddr));
if (rc == -1)
{
debug_printf("pub_sock bind error!\n");
goto _mqtt_exit;
}
}
_mqtt_start:
if (c->connect_callback)
{
c->connect_callback(c);
}
rc = net_connect(c);
if (rc != 0)
{
goto _mqtt_restart;
}
rc = MQTTConnect(c);
if (rc != 0)
{
goto _mqtt_restart;
}
for (i = 0; i < MAX_MESSAGE_HANDLERS; i++)
{
const char *topic = c->messageHandlers[i].topicFilter;
if(topic == RT_NULL)
continue;
rc = MQTTSubscribe(c, topic, QOS2);
debug_printf("Subscribe #%d %s %s!\n", i, topic, (rc < 0) ? ("fail") : ("OK"));
if (rc != 0)
{
goto _mqtt_disconnect;
}
}
if (c->online_callback)
{
c->online_callback(c);
}
c->tick_ping = rt_tick_get();
while (1)
{
int res;
rt_tick_t tick_now;
fd_set readset;
struct timeval timeout;
tick_now = rt_tick_get();
if (((tick_now - c->tick_ping) / RT_TICK_PER_SECOND) > (c->keepAliveInterval - 5))
{
timeout.tv_sec = 1;
//debug_printf("tick close to ping.\n");
}
else
{
timeout.tv_sec = c->keepAliveInterval - 10 - (tick_now - c->tick_ping) / RT_TICK_PER_SECOND;
//debug_printf("timeount for ping: %d\n", timeout.tv_sec);
}
timeout.tv_usec = 0;
FD_ZERO(&readset);
FD_SET(c->sock, &readset);
FD_SET(c->pub_sock, &readset);
/* int select(maxfdp1, readset, writeset, exceptset, timeout); */
res = select(((c->pub_sock > c->sock) ? c->pub_sock : c->sock) + 1,
&readset, RT_NULL, RT_NULL, &timeout);
if (res == 0)
{
len = MQTTSerialize_pingreq(c->buf, c->buf_size);
rc = sendPacket(c, len);
if (rc != 0)
{
debug_printf("[%d] send ping rc: %d \n", rt_tick_get(), rc);
goto _mqtt_disconnect;
}
/* wait Ping Response. */
timeout.tv_sec = 5;
timeout.tv_usec = 0;
FD_ZERO(&readset);
FD_SET(c->sock, &readset);
res = select(c->sock + 1, &readset, RT_NULL, RT_NULL, &timeout);
if (res <= 0)
{
debug_printf("[%d] wait Ping Response res: %d\n", rt_tick_get(), res);
goto _mqtt_disconnect;
}
} /* res == 0: timeount for ping. */
if (res < 0)
{
debug_printf("select res: %d\n", res);
goto _mqtt_disconnect;
}
if (FD_ISSET(c->sock, &readset))
{
//debug_printf("sock FD_ISSET\n");
rc_t = MQTT_cycle(c);
//debug_printf("sock FD_ISSET rc_t : %d\n", rc_t);
if (rc_t < 0) goto _mqtt_disconnect;
continue;
}
if (FD_ISSET(c->pub_sock, &readset))
{
struct sockaddr_in pub_client_addr;
uint32_t addr_len = sizeof(struct sockaddr);
MQTTMessage *message;
MQTTString topic = MQTTString_initializer;
//debug_printf("pub_sock FD_ISSET\n");
len = recvfrom(c->pub_sock, c->readbuf, c->readbuf_size, MSG_DONTWAIT,
(struct sockaddr *)&pub_client_addr, &addr_len);
if (pub_client_addr.sin_addr.s_addr != *((uint32_t *)(&netif_default->ip_addr)))
{
#if 1
char client_ip_str[16]; /* ###.###.###.### */
strcpy(client_ip_str,
inet_ntoa(*((struct in_addr *) & (pub_client_addr.sin_addr))));
debug_printf("pub_sock recvfrom len: %s, skip!\n", client_ip_str);
#endif
continue;
}
if (len < sizeof(MQTTMessage))
{
c->readbuf[len] = '\0';
debug_printf("pub_sock recv %d byte: %s\n", len, c->readbuf);
if (strcmp((const char *)c->readbuf, "DISCONNECT") == 0)
{
debug_printf("DISCONNECT\n");
goto _mqtt_disconnect_exit;
}
continue;
}
message = (MQTTMessage *)c->readbuf;
message->payload = c->readbuf + sizeof(MQTTMessage);
topic.cstring = (char *)c->readbuf + sizeof(MQTTMessage) + message->payloadlen;
//debug_printf("pub_sock topic:%s, payloadlen:%d\n", topic.cstring, message->payloadlen);
len = MQTTSerialize_publish(c->buf, c->buf_size, 0, message->qos, message->retained, message->id,
topic, (unsigned char *)message->payload, message->payloadlen);
if (len <= 0)
{
debug_printf("MQTTSerialize_publish len: %d\n", len);
goto _mqtt_disconnect;
}
if ((rc = sendPacket(c, len)) != PAHO_SUCCESS) // send the subscribe packet
{
debug_printf("MQTTSerialize_publish sendPacket rc: %d\n", rc);
goto _mqtt_disconnect;
}
} /* pbulish sock handler. */
} /* while (1) */
_mqtt_disconnect:
MQTTDisconnect(c);
_mqtt_restart:
if (c->offline_callback)
{
c->offline_callback(c);
}
net_disconnect(c);
rt_thread_delay(RT_TICK_PER_SECOND * 5);
debug_printf("restart!\n");
goto _mqtt_start;
_mqtt_disconnect_exit:
MQTTDisconnect(c);
net_disconnect(c);
_mqtt_exit:
debug_printf("thread exit\n");
return;
}
二、关键业务分析
2.1 讲解两个socket
MQTTClient结构体中有两个socket，一个是基于tcp的负责控制与服务器连接的sock，另一个是基于udp协议的负责消息发布的pub_sock。
2.1.1 sock
- 连接：在net_connect调用socket、connet函数建立与服务器的tcp连接。
- 处理：sock接收到服务器的数据后，在MQTT_cycle中处理来自服务器的CONNACK、PUBACK、SUBACK、PUBLISH、PUBREC、PUBCOMP、PINGRESP消息。
- 断开连接：在net_disconnect函数中调用closesocket关闭与服务器的tcp连接。
2.1.1 pub_sock
- 连接：分为pub_sock的绑定和mqtt连接的建立
1、调用socket创建pub_sock，之后调用bind绑定pub_sock到udp端口。
2、在MQTTConnect函数中，通过sock发送connect消息给服务器，建立mqtt连接。 - 处理：先recvfrom将接受的数据拷贝到MQTTClient的readbuf，再将数据回环发布到服务器。
- 断开连接：通过sock向服务器发送DISCONNECT消息，断开mqtt连接。