Learn Taiji Maker - mqtt Chapter 2 (IV) esp8266 reserved message application

Video link ：https://www.bilibili.com/video/BV1Ff4y1e7AB/?spm_id_from=autoNext&vd_source=b91967c499b23106586d7aa35af46413

The data link ：http://www.taichi-maker.com/homepage/esp8266-nodemcu-iot/iot-tuttorial/mqtt-tutorial/esp8266-retained-message/

Example 1 – Publish retention messages

/**********************************************************************  Project name /Project :  Zero basic introduction to the Internet of things   Program name /Program name : publish_retained_msg  The team /Team :  Taiji maker team  / Taichi-Maker (www.taichi-maker.com)  author /Author : CYNO Shuo   date /Date（YYYYMMDD） : 20201014  Purpose of procedure /Purpose :  The purpose of this program is to demonstrate how to use PubSubClient Library usage ESP8266 towards MQTT The server publishes reserved information .  This program is available at a_publish_ranye_url Based on the program . The key revision is publish Function added   The third parameter , Used to set whether the published information is reserved (retained msg) -----------------------------------------------------------------------  This sample program is made by Taiji maker team 《 Zero basic introduction to the Internet of things 》 Sample program in .  This tutorial is designed and produced by friends who are interested in the development of the Internet of things . For more information about this tutorial , Please refer to the following pages ： http://www.taichi-maker.com/homepage/esp8266-nodemcu-iot/iot-c/esp8266-nodemcu-web-client/http-request/ ***********************************************************************/
#include <ESP8266WiFi.h>
#include <PubSubClient.h>
 
//  Set up wifi Access information ( Please according to your WiFi Modify the information )
const char* ssid = "FAST_153C80";
const char* password = "123456798";
const char* mqttServer = "test.ranye-iot.net";
 
//  As above MQTT The server cannot connect normally , Please go to the following page to find a solution 
// http://www.taichi-maker.com/public-mqtt-broker/
 
WiFiClient wifiClient;
PubSubClient mqttClient(wifiClient);
 
void setup() {
    
  Serial.begin(9600);
 
  // Set up ESP8266 The working mode is wireless terminal mode 
  WiFi.mode(WIFI_STA);
  
  //  Connect WiFi
  connectWifi();
  
  //  Set up MQTT Server and port number 
  mqttClient.setServer(mqttServer, 1883);
 
  //  Connect MQTT The server 
  connectMQTTServer();
  
  if (mqttClient.connected()) {
     //  If the development board successfully connects to the server 
    pubRetMQTTmsg();               //  Publish the information  
  }
}
 
void loop() {
     
  mqttClient.loop();          //  Keep your heart beating 
}
 
void connectMQTTServer(){
    
  //  according to ESP8266 Of MAC Address generation client ID（ Avoid contact with other ESP8266 The client of ID The nuptial ）
  String clientId = "esp8266-" + WiFi.macAddress();
 
  //  Connect MQTT The server 
  if (mqttClient.connect(clientId.c_str())) {
     
    Serial.println("MQTT Server Connected.");
    Serial.println("Server Address: ");
    Serial.println(mqttServer);
    Serial.println("ClientId:");
    Serial.println(clientId);
  } else {
    
    Serial.print("MQTT Server Connect Failed. Client State:");
    Serial.println(mqttClient.state());
    delay(3000);
  }   
}
 
//  Publish the information 
void pubRetMQTTmsg(){
    
  //  Create a publishing theme . The title of the topic is Taichi-Maker- The prefix , The device is added later MAC Address .
  //  This is done to ensure that different users MQTT When information is released ,ESP8266 Client names vary ,
  String topicString = "Taichi-Maker-Ret-" + WiFi.macAddress();
  char publishTopic[topicString.length() + 1];  
  strcpy(publishTopic, topicString.c_str());
 
  //  Create an upcoming retention message . The message is "Retained Msg".
  String messageString = "Retained Msg"; 
  char publishMsg[messageString.length() + 1];   
  strcpy(publishMsg, messageString.c_str());
  
  //  Realization ESP8266 Post to topic retained Information 
  //  following publish The third parameter of the function is used to set the reserved information （retained message)
  if(mqttClient.publish(publishTopic, publishMsg, true)){
    
    Serial.println("Publish Topic:");Serial.println(publishTopic);
    Serial.println("Publish Retained message:");Serial.println(publishMsg);    
  } else {
    
    Serial.println("Message Publish Failed."); 
  }
}
 
// ESP8266 Connect wifi
void connectWifi(){
    
 
  WiFi.begin(ssid, password);
 
  // wait for WiFi Connect , Output success information after successful connection 
  while (WiFi.status() != WL_CONNECTED) {
    
    delay(1000);
    Serial.print(".");
  }
  Serial.println("");
  Serial.println("WiFi Connected!");  
  Serial.println(""); 
}

Let's verify the operation of the program .

First , Use the serial port monitor to see the output results .

next , We use MQTT.fx Software to subscribe to the news published by the development board . You can find , I received a message as soon as I subscribed .

below , Let's analyze the key content of this program .

//  Publish the information 
void pubRetMQTTmsg(){
    
  //  Create a publishing theme . The title of the topic is Taichi-Maker- The prefix , The device is added later MAC Address .
  //  This is done to ensure that different users MQTT When information is released ,ESP8266 Client names vary ,
  String topicString = "Taichi-Maker-Ret-" + WiFi.macAddress();
  char publishTopic[topicString.length() + 1];  
  strcpy(publishTopic, topicString.c_str());
 
  //  Create an upcoming retention message . The message is "Retained Msg".
  String messageString = "Retained Msg"; 
  char publishMsg[messageString.length() + 1];   
  strcpy(publishMsg, messageString.c_str());
  
  //  Realization ESP8266 Post to topic retained Information 
  //  following publish The third parameter of the function is used to set the reserved information （retained message)
  if(mqttClient.publish(publishTopic, publishMsg, true)){
    
    Serial.println("Publish Topic:");Serial.println(publishTopic);
    Serial.println("Publish Retained message:");Serial.println(publishMsg);    
  } else {
    
    Serial.println("Message Publish Failed."); 
  }
}

Be careful ,publish Function number 3、 ... and Parameters （true Just tell the server , This message is reserved , This parameter defaults to false） It is used to set retention information （retained message) Of .

Example 2 – Modify the reserved message

Just change the content of the message to be published .

Example 3 – Delete reserved messages

Just set the above message content to be published as empty .

  String messageString = ""; 

stay Serial port monitor end ,

stay MQTT.fx End ,