11.1 MQTT介绍
MQTT 是当前最主流的物联网通信协议，需要物联网云平台，例如华为云、阿里云、移动OneNET都支持mqtt。而Hi3861则是一款专为IoT应用场景打造的芯片。本节主要讲如何在鸿蒙系统中通过移植第3方软件包 paho mqtt去实现MQTT协议功能，最后会给出测试验证。为后续的物联网项目打好基础。
友情预告，本节内容较多，源码也贴出来了，大家最好先看一遍，然后再操作一次。
11.2 MQTT移植
如果不想要自己移植的，可以跳过本节
MQTT 全称为 Message Queuing Telemetry Transport（消息队列遥测传输）是一种基于发布/订阅范式的二进制“轻量级”消息协议，由IB公司发布。针对于网络受限和嵌入式设备而设计的一种数据传输协议。MQTT最大优点在于，可以以极少的代码和有限的带宽，为连接远程设备提供实时可靠的消息服务。作为一种低开销、低带宽占用的即时通讯协议，使其在物联网、小型设备、移动应用等方面有较广泛的应用。MQTT模型如图所示。
更多MQTT协议的介绍见这篇文章： MQTT 协议开发入门
1. 下载paho mqtt软件包，添加到鸿蒙代码中
paho mqtt-c 是基于C语言实现的MQTT客户端，非常适合用在嵌入式设备上。首先下载源码：
下载之后解压，会得到这么一个文件夹：
如何在鸿蒙系统中移植 Paho-MQTT 实现MQTT协议-鸿蒙HarmonyOS技术社区
我们在鸿蒙系统源码的 third_party 文件夹下创建一个 pahomqtt 文件夹，然后把解压后的所有文件都拷贝到 pahomqtt 文件夹下
下一步，我们在pahomqtt 文件夹下面新建BUILD.gn文件，用来构建编译。其内容如下：
代码语言：c复制# Copyright (c) 2020 Huawei Device Co., Ltd.
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import("//build/lite/config/component/lite_component.gni")
import("//build/lite/ndk/ndk.gni")
config("pahomqtt_config") {
include_dirs = [
"MQTTPacket/src",
"MQTTClient-C/src",
"MQTTClient-C/src/liteOS",
"//kernel/liteos_m/components/cmsis/2.0",
]
}
pahomqtt_sources = [
"MQTTClient-C/src/liteOS/MQTTLiteOS.c",
"MQTTClient-C/src/MQTTClient.c",
"MQTTPacket/src/MQTTConnectClient.c",
"MQTTPacket/src/MQTTConnectServer.c",
"MQTTPacket/src/MQTTDeserializePublish.c",
"MQTTPacket/src/MQTTFormat.c",
"MQTTPacket/src/MQTTPacket.c",
"MQTTPacket/src/MQTTSerializePublish.c",
"MQTTPacket/src/MQTTSubscribeClient.c",
"MQTTPacket/src/MQTTSubscribeServer.c",
"MQTTPacket/src/MQTTUnsubscribeClient.c",
"MQTTPacket/src/MQTTUnsubscribeServer.c",
]
lite_library("pahomqtt_static") {
target_type = "static_library"
sources = pahomqtt_sources
public_configs = [ ":pahomqtt_config" ]
}
lite_library("pahomqtt_shared") {
target_type = "shared_library"
sources = pahomqtt_sources
public_configs = [ ":pahomqtt_config" ]
}
ndk_lib("pahomqtt_ndk") {
if (board_name != "hi3861v100") {
lib_extension = ".so"
deps = [
":pahomqtt_shared"
]
} else {
deps = [
":pahomqtt_static"
]
}
head_files = [
"//third_party/pahomqtt"
]
}2. 移植
我们使用到的是MQTTClient-C的代码，该代码支持多线程。
（1）创建LiteOS文件夹
MQTT已经提供了Linux和freertos的移植，这里我们参考，新建文件夹：
third_partypahomqttMQTTClient-CsrcliteOS
里面存放两个文件：
MQTTLiteOS.c 和 MQTTLiteOS.h
内容如下：
代码语言：c复制#include "MQTTLiteOS.h"
//用来创建线程
int ThreadStart(Thread* thread, void (*fn)(void*), void* arg)
{
int rc = 0;
thread = thread;
osThreadAttr_t attr;
attr.name = "MQTTTask";
attr.attr_bits = 0U;
attr.cb_mem = NULL;
attr.cb_size = 0U;
attr.stack_mem = NULL;
attr.stack_size = 2048;
attr.priority = osThreadGetPriority(osThreadGetId());
rc = (int)osThreadNew((osThreadFunc_t)fn, arg, &attr);
return rc;
}
//定时器初始化
void TimerInit(Timer* timer)
{
timer->end_time = (struct timeval){0, 0};
}
char TimerIsExpired(Timer* timer)
{
struct timeval now, res;
gettimeofday(&now, NULL);
timersub(&timer->end_time, &now, &res);
return res.tv_sec < 0 || (res.tv_sec == 0 && res.tv_usec <= 0);
}
void TimerCountdownMS(Timer* timer, unsigned int timeout)
{
struct timeval now;
gettimeofday(&now, NULL);
struct timeval interval = {timeout / 1000, (timeout % 1000) * 1000};
timeradd(&now, &interval, &timer->end_time);
}
void TimerCountdown(Timer* timer, unsigned int timeout)
{
struct timeval now;
gettimeofday(&now, NULL);
struct timeval interval = {timeout, 0};
timeradd(&now, &interval, &timer->end_time);
}
int TimerLeftMS(Timer* timer)
{
struct timeval now, res;
gettimeofday(&now, NULL);
timersub(&timer->end_time, &now, &res);
//printf("left %d msn", (res.tv_sec < 0) ? 0 : res.tv_sec * 1000 res.tv_usec / 1000);
return (res.tv_sec < 0) ? 0 : res.tv_sec * 1000 res.tv_usec / 1000;
}
void MutexInit(Mutex* mutex)
{
mutex->sem = osSemaphoreNew(1, 1, NULL);
}
int MutexLock(Mutex* mutex)
{
return osSemaphoreAcquire(mutex->sem, LOS_WAIT_FOREVER);
}
int MutexUnlock(Mutex* mutex)
{
return osSemaphoreRelease(mutex->sem);
}
//接受数据
int ohos_read(Network* n, unsigned char* buffer, int len, int timeout_ms)
{
struct timeval interval = {timeout_ms / 1000, (timeout_ms % 1000) * 1000};
if (interval.tv_sec < 0 || (interval.tv_sec == 0 && interval.tv_usec <= 0))
{
interval.tv_sec = 0;
interval.tv_usec = 100;
}
setsockopt(n->my_socket, SOL_SOCKET, SO_RCVTIMEO, (char *)&interval, sizeof(struct timeval));
int bytes = 0;
while (bytes < len)
{
int rc = recv(n->my_socket, &buffer[bytes], (size_t)(len - bytes), 0);
if (rc == -1)
{
if (errno != EAGAIN && errno != EWOULDBLOCK)
bytes = -1;
break;
}
else if (rc == 0)
{
bytes = 0;
break;
}
else
bytes = rc;
}
return bytes;
}
//写数据
int ohos_write(Network* n, unsigned char* buffer, int len, int timeout_ms)
{
struct timeval tv;
tv.tv_sec = 0; /* 30 Secs Timeout */
tv.tv_usec = timeout_ms * 1000; // Not init'ing this can cause strange errors
setsockopt(n->my_socket, SOL_SOCKET, SO_SNDTIMEO, (char *)&tv,sizeof(struct timeval));
int rc = send(n->my_socket, buffer, len, 0);
return rc;
}
//网络初始化
void NetworkInit(Network* n)
{
n->my_socket = 0;
n->mqttread = ohos_read;
n->mqttwrite = ohos_write;
}
//网络连接
int NetworkConnect(Network* n, char* addr, int port)
{
int type = SOCK_STREAM;
struct sockaddr_in address;
int rc = -1;
sa_family_t family = AF_INET;
struct addrinfo *result = NULL;
struct addrinfo hints = {0, AF_UNSPEC, SOCK_STREAM, IPPROTO_TCP, 0, NULL, NULL, NULL};
if ((rc = getaddrinfo(addr, NULL, &hints, &result)) == 0)
{
struct addrinfo* res = result;
/* prefer ip4 addresses */
while (res)
{
if (res->ai_family == AF_INET)
{
result = res;
break;
}
res = res->ai_next;
}
if (result->ai_family == AF_INET)
{
address.sin_port = htons(port);
address.sin_family = family = AF_INET;
address.sin_addr = ((struct sockaddr_in*)(result->ai_addr))->sin_addr;
}
else
rc = -1;
freeaddrinfo(result);
}
if (rc == 0)
{
n->my_socket = socket(family, type, 0);
if (n->my_socket != -1)
rc = connect(n->my_socket, (struct sockaddr*)&address, sizeof(address));
else
rc = -1;
}
return rc;
}
void NetworkDisconnect(Network* n)
{
close(n->my_socket);
}至此我们移植基本结束
11.3 测试代码
测试代码比较好写。主要是3个文件，内容我都贴出来了：
（1）BUILD.gn文件内容：
代码语言：c复制static_library("mqtt_test") {
sources = [
"mqtt_test.c",
"mqtt_entry.c"
]
include_dirs = [
"//utils/native/lite/include",
"//kernel/liteos_m/components/cmsis/2.0",
"//base/iot_hardware/interfaces/kits/wifiiot_lite",
"//vendor/hisi/hi3861/hi3861/third_party/lwip_sack/include",
"//foundation/communication/interfaces/kits/wifi_lite/wifiservice",
"//third_party/pahomqtt/MQTTPacket/src",
"//third_party/pahomqtt/MQTTClient-C/src",
"//third_party/pahomqtt/MQTTClient-C/src/liteOS",
]
#表示需要a_myparty 软件包
deps = [
"//third_party/pahomqtt:pahomqtt_static",
]
}（2）mqtt_entry.c文件
主要是进行热点连接，因为我们要使用MQTT需要用到网络。热点连接的代码之前在第9章已经讲说，这里就不完全贴了，代码仓库也有，主要的代码部分：
代码语言：c复制void wifi_sta_task(void *arg)
{
arg = arg;
//连接热点
hi_wifi_start_sta();
while(wifi_ok_flg == 0)
{
usleep(30000);
}
usleep(2000000);
//开始进入MQTT测试
mqtt_test();
}（3）mqtt_test.c 文件则是编写了一个简单的MQTT测试代码
其中测试用的mqtt服务器是我自己的服务器：5.196.95.208
大家也可以改成自己的。
代码语言：c复制#include <stdio.h>
#include <unistd.h>
#include "ohos_init.h"
#include "cmsis_os2.h"
#include "hi_wifi_api.h"
#include "lwip/ip_addr.h"
#include "lwip/netifapi.h"
#include "lwip/sockets.h"
#include "MQTTClient.h"
static MQTTClient mq_client;
unsigned char *onenet_mqtt_buf;
unsigned char *onenet_mqtt_readbuf;
int buf_size;
Network n;
MQTTPacket_connectData data = MQTTPacket_connectData_initializer;
//消息回调函数
void mqtt_callback(MessageData *msg_data)
{
size_t res_len = 0;
uint8_t *response_buf = NULL;
char topicname[45] = { "$crsp/" };
LOS_ASSERT(msg_data);
printf("topic %.*s receive a messagern", msg_data->topicName->lenstring.len, msg_data->topicName->lenstring.data);
printf("message is %.*srn", msg_data->message->payloadlen, msg_data->message->payload);
}
int mqtt_connect(void)
{
int rc = 0;
NetworkInit(&n);
NetworkConnect(&n, "5.196.95.208", 1883);
buf_size = 2048;
onenet_mqtt_buf = (unsigned char *) malloc(buf_size);
onenet_mqtt_readbuf = (unsigned char *) malloc(buf_size);
if (!(onenet_mqtt_buf && onenet_mqtt_readbuf))
{
printf("No memory for MQTT client buffer!");
return -2;
}
MQTTClientInit(&mq_client, &n, 1000, onenet_mqtt_buf, buf_size, onenet_mqtt_readbuf, buf_size);
MQTTStartTask(&mq_client);
data.keepAliveInterval = 30;
data.cleansession = 1;
data.clientID.cstring = "ohos_hi3861";
data.username.cstring = "123456";
data.password.cstring = "222222";
data.keepAliveInterval = 10;
data.cleansession = 1;
mq_client.defaultMessageHandler = mqtt_callback;
//连接服务器
rc = MQTTConnect(&mq_client, &data);
//订阅消息，并设置回调函数
MQTTSubscribe(&mq_client, "ohossub", 0, mqtt_callback);
while(1)
{
MQTTMessage message;
message.qos = QOS1;
message.retained = 0;
message.payload = (void *)"openharmony";
message.payloadlen = strlen("openharmony");
//发送消息
if (MQTTPublish(&mq_client, "ohospub", &message) < 0)
{
return -1;
}
}
return 0;
}
void mqtt_test(void)
{
mqtt_connect();
}到这里就完成了代码部分，可以开始编译了。
11.4 实验
这里我们需要先下载一个 Windows电脑端的 MQTT客户端，这样我们就可以用电脑订阅开发板的MQTT主题信息了。
写在最后
如果你觉得这篇内容对你还蛮有帮助，我想邀请你帮我三个小忙：
- 点赞，转发，有你们的 『点赞和评论』，才是我创造的动力；
- 关注小编，同时可以期待后续文章ing
