快速上手MQTT

分类：基础知识篇 >> ESP32基础知识发布于 2024-05-16 341次阅读0点赞0收藏

原理

什么是MQTT
MQTT是一种网络通信协议

分为客户端、服务器
每个客户端可以接收数据（订阅）、发送数据（发布）
每个消息都由主题（topic）+消息内容（data）组成
MQTT大体过程
举例说明
假如客户端1向服务器订阅了led主题的信息，那么当服务器接收到来自任何一个客户端（3/5/6）的消息时，只要这个消息的主题是led，那么服务器就会将这个消息发送给客户端1

同理，如果除了客户端1之外还有其它的客户端（2/4）也订阅了led这个主题，那么服务器也会同时将这个消息送给客户端2、客户端4

MQTT服务器安装

自己电脑安装MQTT服务器

访问 https://www.emqx.io/zh 界面如下

找到上图中的立即下载，然后点击这个按钮，此时会跳转到新页面

在上图中选择自己电脑的操作系统版本，然后下载即可，我以Windows11为例

解压

注意查看是否是纯英文路径，如果不是请将解压后的整个文件夹复制到没有中文路径下，然后根据课件继续

此时弹出终端，界面如下

在上述界面中输入

emqx start

然后回车

测试安装效果

打开浏览器，输入http://localhost:18083/ 然后回车，会看到如下界面，表示安装MQTT服务器成功

登录成功后的样子如下

ESP32编写客户端程序

整体流程

esp32链接上wifi（注意与当前电脑链接到同一个局域网下，即同一个wifi路由器）
esp32上需要下载一个mqtt的库
我们自己编写一个.py文件调用上面第2步的mqtt库，从而使用mqtt实现客户端的功能
第2步骤的mqtt库文件，名字叫做umqttsimple.py，内容如下，不要做任何修改复制到esp32即可
```python
import usocket as socket
import ustruct as struct
from ubinascii import hexlify

class MQTTException(Exception):
pass

class MQTTClient:
def init(
self,
client_id,
server,
port=0,
user=None,
password=None,
keepalive=0,
ssl=False,
ssl_params={},
):
if port == 0:
port = 8883 if ssl else 1883
self.client_id = client_id
self.sock = None
self.server = server
self.port = port
self.ssl = ssl
self.ssl_params = ssl_params
self.pid = 0
self.cb = None
self.user = user
self.pswd = password
self.keepalive = keepalive
self.lw_topic = None
self.lw_msg = None
self.lw_qos = 0
self.lw_retain = False

def _send_str(self, s):
    self.sock.write(struct.pack("!H", len(s)))
    self.sock.write(s)

def _recv_len(self):
    n = 0
    sh = 0
    while 1:
        b = self.sock.read(1)[0]
        n |= (b & 0x7F) << sh
        if not b & 0x80:
            return n
        sh += 7

def set_callback(self, f):
    self.cb = f

def set_last_will(self, topic, msg, retain=False, qos=0):
    assert 0 <= qos <= 2
    assert topic
    self.lw_topic = topic
    self.lw_msg = msg
    self.lw_qos = qos
    self.lw_retain = retain

def connect(self, clean_session=True):
    self.sock = socket.socket()
    addr = socket.getaddrinfo(self.server, self.port)[0][-1]
    self.sock.connect(addr)
    if self.ssl:
        import ussl

        self.sock = ussl.wrap_socket(self.sock, **self.ssl_params)
    premsg = bytearray(b"\x10\0\0\0\0\0")
    msg = bytearray(b"\x04MQTT\x04\x02\0\0")

    sz = 10 + 2 + len(self.client_id)
    msg[6] = clean_session << 1
    if self.user is not None:
        sz += 2 + len(self.user) + 2 + len(self.pswd)
        msg[6] |= 0xC0
    if self.keepalive:
        assert self.keepalive < 65536
        msg[7] |= self.keepalive >> 8
        msg[8] |= self.keepalive & 0x00FF
    if self.lw_topic:
        sz += 2 + len(self.lw_topic) + 2 + len(self.lw_msg)
        msg[6] |= 0x4 | (self.lw_qos & 0x1) << 3 | (self.lw_qos & 0x2) << 3
        msg[6] |= self.lw_retain << 5

    i = 1
    while sz > 0x7F:
        premsg[i] = (sz & 0x7F) | 0x80
        sz >>= 7
        i += 1
    premsg[i] = sz

    self.sock.write(premsg, i + 2)
    self.sock.write(msg)
    # print(hex(len(msg)), hexlify(msg, ":"))
    self._send_str(self.client_id)
    if self.lw_topic:
        self._send_str(self.lw_topic)
        self._send_str(self.lw_msg)
    if self.user is not None:
        self._send_str(self.user)
        self._send_str(self.pswd)
    resp = self.sock.read(4)
    assert resp[0] == 0x20 and resp[1] == 0x02
    if resp[3] != 0:
        raise MQTTException(resp[3])
    return resp[2] & 1

def disconnect(self):
    self.sock.write(b"\xe0\0")
    self.sock.close()

def ping(self):
    self.sock.write(b"\xc0\0")

def publish(self, topic, msg, retain=False, qos=0):
    pkt = bytearray(b"\x30\0\0\0")
    pkt[0] |= qos << 1 | retain
    sz = 2 + len(topic) + len(msg)
    if qos > 0:
        sz += 2
    assert sz < 2097152
    i = 1
    while sz > 0x7F:
        pkt[i] = (sz & 0x7F) | 0x80
        sz >>= 7
        i += 1
    pkt[i] = sz
    # print(hex(len(pkt)), hexlify(pkt, ":"))
    self.sock.write(pkt, i + 1)
    self._send_str(topic)
    if qos > 0:
        self.pid += 1
        pid = self.pid
        struct.pack_into("!H", pkt, 0, pid)
        self.sock.write(pkt, 2)
    self.sock.write(msg)
    if qos == 1:
        while 1:
            op = self.wait_msg()
            if op == 0x40:
                sz = self.sock.read(1)
                assert sz == b"\x02"
                rcv_pid = self.sock.read(2)
                rcv_pid = rcv_pid[0] << 8 | rcv_pid[1]
                if pid == rcv_pid:
                    return
    elif qos == 2:
        assert 0

def subscribe(self, topic, qos=0):
    assert self.cb is not None, "Subscribe callback is not set"
    pkt = bytearray(b"\x82\0\0\0")
    self.pid += 1
    struct.pack_into("!BH", pkt, 1, 2 + 2 + len(topic) + 1, self.pid)
    # print(hex(len(pkt)), hexlify(pkt, ":"))
    self.sock.write(pkt)
    self._send_str(topic)
    self.sock.write(qos.to_bytes(1, "little"))
    while 1:
        op = self.wait_msg()
        if op == 0x90:
            resp = self.sock.read(4)
            # print(resp)
            assert resp[1] == pkt[2] and resp[2] == pkt[3]
            if resp[3] == 0x80:
                raise MQTTException(resp[3])
            return

# Wait for a single incoming MQTT message and process it.
# Subscribed messages are delivered to a callback previously
# set by .set_callback() method. Other (internal) MQTT
# messages processed internally.
def wait_msg(self):
    res = self.sock.read(1)
    self.sock.setblocking(True)
    if res is None:
        return None
    if res == b"":
        raise OSError(-1)
    if res == b"\xd0":  # PINGRESP
        sz = self.sock.read(1)[0]
        assert sz == 0
        return None
    op = res[0]
    if op & 0xF0 != 0x30:
        return op
    sz = self._recv_len()
    topic_len = self.sock.read(2)
    topic_len = (topic_len[0] << 8) | topic_len[1]
    topic = self.sock.read(topic_len)
    sz -= topic_len + 2
    if op & 6:
        pid = self.sock.read(2)
        pid = pid[0] << 8 | pid[1]
        sz -= 2
    msg = self.sock.read(sz)
    self.cb(topic, msg)
    if op & 6 == 2:
        pkt = bytearray(b"\x40\x02\0\0")
        struct.pack_into("!H", pkt, 2, pid)
        self.sock.write(pkt)
    elif op & 6 == 4:
        assert 0

# Checks whether a pending message from server is available.
# If not, returns immediately with None. Otherwise, does
# the same processing as wait_msg.
def check_msg(self):
    self.sock.setblocking(False)
    return self.wait_msg()

第3步要编写的自己的代码，文件名字MQTT客户端测试.py，内容如下
```python
import time
import network
from umqttsimple import MQTTClient


def do_connect():
    wlan = network.WLAN(network.STA_IF)
    wlan.active(True)
    if not wlan.isconnected():
        print('connecting to network...')
        wlan.connect('dongfeiqiu', 'wangmingdong1225')
        i = 1
        while not wlan.isconnected():
            print("正在链接...{}".format(i))
            i += 1
            time.sleep(1)
    print('network config:', wlan.ifconfig())


def sub_cb(topic, msg): # 回调函数，收到服务器消息后会调用这个函数
    print(topic, msg)


# 1. 联网
do_connect()
# 2. 创建mqt
c = MQTTClient("umqtt_client", "192.168.31.54")  # 建立一个MQTT客户端
c.set_callback(sub_cb)  # 设置回调函数
c.connect()  # 建立连接
c.subscribe(b"ledctl")  # 监控ledctl这个通道，接收控制命令
while True:
    c.check_msg()
    time.sleep(1)

电脑通过MQTT控制ESP32上LED灯

在电脑上安装MQTT客户端

安装、运行
访问 https://mqttx.app/zh ，点击下图标记的“下载”按钮

此时会下载一个exe程序

双击这个exe，然后安装即可（注意最好不要安装到有中文路径中，防止意外）
安装成功之后，双击软件图标，运行后的效果如下

链接MQTT服务器

注意
首先要确保MQTT服务器是运行的，如果电脑重启，那么上次运行的MQTT服务器就不会自动运行，需要用上节课相同的方式将MQTT服务器运行起来，所以先用浏览器方式http://localhost:18083/看看能否打开，如果打开就说明MQTT服务器运行正常，否则需要手动开启MQTT服务器
创建新链接

填写信息（192.168.31.54是你运行MQTT服务器的电脑的ip）

点击链接

链接成功

在http://localhost:18083/#/connections中可以看到链接成功

ESP32运行新的客户端程序

import time
from machine import Pin  # ---- 添加 --------
import network
from umqttsimple import MQTTClient


def do_connect():
    wlan = network.WLAN(network.STA_IF)
    wlan.active(True)
    if not wlan.isconnected():
        print('connecting to network...')
        wlan.connect('dongfeiqiu', 'wangmingdong1225')
        i = 1
        while not wlan.isconnected():
            print("正在链接...{}".format(i))
            i += 1
            time.sleep(1)
    print('network config:', wlan.ifconfig())


def sub_cb(topic, msg): # 回调函数，收到服务器消息后会调用这个函数
    print(topic, msg)
    # ---- 添加 --------
    if topic.decode("utf-8") == "ledctl" and msg.decode("utf-8") == "on":
        led_pin.value(1)
    elif topic.decode("utf-8") == "ledctl" and msg.decode("utf-8") == "off":
        led_pin.value(0)
    # ---- 添加 --------


# 1. 联网
do_connect()

# 2. 创建mqt
c = MQTTClient("umqtt_client", "192.168.31.54")  # 建立一个MQTT客户端
c.set_callback(sub_cb)  # 设置回调函数
c.connect()  # 建立连接
c.subscribe(b"ledctl")  # 监控ledctl这个通道，接收控制命令

# ---- 添加 --------
# 3. 创建LED对应Pin对象
led_pin = Pin(2, Pin.OUT)
# ---- 添加 --------

while True:
    c.check_msg()
    time.sleep(1)

运行上述代码

会在MQTT服务器中看到链接成功

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