ESP32（DOIT DevKit）如何通过mDNS在同一LAN中找到另一个主机？

本文介绍了ESP32（DOIT DevKit）如何通过mDNS在同一LAN中找到另一个主机？的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

我有一个连接到我的Wifi局域网的Raspberry Pi，它以 mqtt-broker.local 的形式响应mDNS。

I have a Raspberry Pi connected to my Wifi LAN that responds to mDNS as mqtt-broker.local.

我可以使用以下命令在笔记本电脑上找到它：

I can find it on my laptop with this command:

$ avahi-resolve-host-name -4 mqtt-broker.local
mqtt-broker.local   192.168.XXX.YYY

我有一个ESP32 DOIT如果我使用IP地址 192.168.XXX.YYY 可以通过Wifi将消息发送到Raspberry Pi的DevKit设备，但是我希望ESP32使用mDNS解析主机。

I have an ESP32 DOIT DevKit device that can send messages to the Raspberry Pi via Wifi if I use the IP address 192.168.XXX.YYY, however I would like my ESP32 to resolve the host using mDNS.

我无法使mDNS正常运行，底部的代码显示：

I am not able to get the mDNS working, the code at the bottom prints:

Finding the mDNS details...
No services found...
Done finding the mDNS details...

此代码出了什么问题？

我应该把什么作为服务在 MDNS.queryService（ mqtt-broker， tcp）中？我什至尝试使用服务 mqtt 都没有运气，但是这没关系，无论Raspberry Pi（HTTP服务器，MQTT，FTP暴露了什么），mDNS东西都应该起作用等等...）

在这里检查信息不多这种服务和原型，而我对底层C / C ++不太熟悉，这些是什么？

What's wrong with this code?
What should I put as service in MDNS.queryService("mqtt-broker", "tcp")? I have tried even with service mqtt with no luck, however this shouldn't matter, the mDNS stuff should work regardless what's exposed from the Raspberry Pi (HTTP server, MQTT, FTP whatever...)
Checking here https://github.com/espressif/arduino-esp32/blob/master/libraries/ESPmDNS/src/ESPmDNS.h#L98 there is not that much information about this "service" and "proto", and I am not that much familiar with low-level C/C++, what are these things?

这是我正在使用的代码：

This is the code I am using:

// import the headers
#include <ESPmDNS.h>

void findMyPi() {
  Serial.println("Finding the mDNS details...");

  // make sure we are connected to the Wifi
  while (WiFi.status() != WL_CONNECTED) {
    delay(250);
    Serial.println("Not yet connected to Wifi...");
  }

  if (!MDNS.begin("whatever_this_could_be_anything")) {
    Serial.println("Error setting up MDNS responder!");
  }

  // what should I put in here as "service"?
  int n = MDNS.queryService("mqtt-broker", "tcp");
  if (n == 0) {
    Serial.println("No services found...");
  }
  else {
    for (int i = 0; i < n; ++i) {
      // Print details for each service found
      Serial.print("  ");
      Serial.print(i + 1);
      Serial.print(": ");
      Serial.print(MDNS.hostname(i)); // "mqtt-broker" ??? How can I find it???
      Serial.print(" (");
      Serial.print(MDNS.IP(i));
      Serial.print(":");
      Serial.print(MDNS.port(i));
      Serial.println(")");
    }
  }
  Serial.println("Done finding the mDNS details...");
}

此功能受以下示例启发：

This function has been inspired by this example:

推荐答案

最终使用与Espressif提供的mDNS库中的类不同的方法（ ESPmDNS.h ），组合形式：

Ended up using a different method from the class on that mDNS library provided by Espressif (ESPmDNS.h), a combination of:

IPAddress serverIp = MDNS.queryHost（mDnsHost）;

此检查的循环 serverIp.toString（）== 0.0.0.0

IPAddress serverIp = MDNS.queryHost(mDnsHost);
while loop on this check serverIp.toString() == "0.0.0.0"

这是将所有内容粘合在一起的代码：

This is the code that glues up all together:

// on my laptop (Ubuntu) the equivalent command is: `avahi-resolve-host-name -4 mqtt-broker.local`
String findMDNS(String mDnsHost) {
  // the input mDnsHost is e.g. "mqtt-broker" from "mqtt-broker.local"
  Serial.println("Finding the mDNS details...");
  // Need to make sure that we're connected to the wifi first
  while (WiFi.status() != WL_CONNECTED) {
    delay(250);
    Serial.print(".");
  }
  if (!MDNS.begin("esp32whatever")) {
    Serial.println("Error setting up MDNS responder!");
  } else {
    Serial.println("Finished intitializing the MDNS client...");
  }

  Serial.println("mDNS responder started");
  IPAddress serverIp = MDNS.queryHost(mDnsHost);
  while (serverIp.toString() == "0.0.0.0") {
    Serial.println("Trying again to resolve mDNS");
    delay(250);
    serverIp = MDNS.queryHost(mDnsHost);
  }
  Serial.print("IP address of server: ");
  Serial.println(serverIp.toString());
  Serial.println("Done finding the mDNS details...");
  return serverIp.toString();
}

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