如何移植MQTT物联网通信协议

摘要

本文简单介绍如何移植MQTT

适合群体

适用于润和Hi3861开发板的开发人员。

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。

已经移植好的MQTT源码：

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：

# 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"  ]}

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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：

#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 ms
", (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);}

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至此我们移植基本结束。

3、代码测试

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：

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",  ]}

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（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：

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();}

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（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。

#include #include #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 message
", msg_data->topicName->lenstring.len, msg_data->topicName->lenstring.data);
  printf("message is %.*s
", 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();}

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到这里就完成了代码部分，可以开始编译了。

4、编译

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。

我们选择这一个：

弄完后打开软件，按图操作：

此时我们去查看 我们电脑端的MQTT客户端软件，可以看到右边已经有接收MQTT信息了，主题未 ohospub，消息内容为 openharmony，说明实验成功。

电脑发送主题为ohossub，内容为123456，查看串口打印，可以看到也收到了数据。

本节移植MQTT的教程就到这里了，下一篇我们给大家分享：OneNET云接入，欢迎大家持续关注哦~

原文标题：OpenHarmony轻量系统开发【11】移植MQTT

文章出处：【微信公众号：HarmonyOS官方合作社区】欢迎添加关注！文章转载请注明出处。

审核编辑：汤梓红