深入理解Paho-MQTT多级通配符订阅：#字符使用规范解析

import paho.mqtt.client as mqtt
import time

# MQTT Broker 配置
BROKER_ADDRESS = "broker.hivemq.com" # 使用公共测试Broker
PORT = 1883
CLIENT_ID = "paho_mqtt_tutorial_client_" + str(time.time())

# 连接回调函数
def on_connect(client, userdata, flags, rc):
    if rc == 0:
        print("连接到 MQTT Broker 成功！")
        # 尝试订阅
        subscribe_topics(client)
    else:
        print(f"连接失败，返回码: {rc}")

# 消息接收回调函数
def on_message(client, userdata, msg):
    print(f"收到消息 - 主题: {msg.topic}, 内容: {msg.payload.decode()}")

def subscribe_topics(client):
    # ---------------------------------------------------
    # 1. 错误的订阅尝试：多级通配符 # 未在末尾
    # 这将导致 ValueError
    print("\n--- 尝试订阅无效的多级通配符主题 ---")
    invalid_topics_list = [('A/#/B', 1), ('A/#/C', 1), ('A/#/D', 1)]
    try:
        client.subscribe(invalid_topics_list)
        print("（错误）成功订阅了无效主题 - 这不应该发生！")
    except ValueError as e:
        print(f"捕获到预期的错误: {e}")
        print("原因：多级通配符 '#' 必须是主题过滤器的最后一个字符。")
    except Exception as e:
        print(f"捕获到其他错误: {e}")

    # ---------------------------------------------------
    # 2. 正确的订阅尝试：单级通配符 +
    print("\n--- 尝试订阅有效的单级通配符主题 ---")
    valid_single_level_topics = [('A/+/B', 1), ('A/+/C', 1), ('A/+/D', 1)]
    try:
        client.subscribe(valid_single_level_topics)
        print(f"成功订阅了单级通配符主题: {valid_single_level_topics}")
    except Exception as e:
        print(f"订阅单级通配符主题失败: {e}")

    # ---------------------------------------------------
    # 3. 正确的订阅尝试：多级通配符 # 在末尾
    print("\n--- 尝试订阅有效的多级通配符主题 (# 在末尾) ---")
    valid_multi_level_topic_1 = 'A/#'
    valid_multi_level_topic_2 = 'sport/tennis/#'
    try:
        client.subscribe(valid_multi_level_topic_1)
        client.subscribe(valid_multi_level_topic_2)
        print(f"成功订阅了多级通配符主题: '{valid_multi_level_topic_1}', '{valid_multi_level_topic_2}'")
    except Exception as e:
        print(f"订阅多级通配符主题失败: {e}")

# 创建 MQTT 客户端实例
client = mqtt.Client(client_id=CLIENT_ID)
client.on_connect = on_connect
client.on_message = on_message

# 连接到 Broker
print(f"尝试连接到 Broker: {BROKER_ADDRESS}:{PORT}")
client.connect(BROKER_ADDRESS, PORT, 60)

# 启动循环以处理网络流量、回调等
client.loop_start()

# 保持运行一段时间以便接收消息
try:
    while True:
        time.sleep(1)
except KeyboardInterrupt:
    print("\n程序终止。")
finally:
    client.loop_stop()
    client.disconnect()
    print("客户端断开连接。")