python实现 PUBLISH、PUBACK 报文（1）： 客户端能将消息发布到某个 Topic 之下。

好的，下面是Python实现PUBLISH和PUBACK报文的示例代码，用于客户端将消息发布到指定的Topic：

import struct

# 构建PUBLISH报文
def build_publish_packet(topic, message, qos, packet_id=None):
    packet_type = 0x30  # PUBLISH报文类型
    remaining_length = 2 + len(topic) + len(message)  # 剩余长度
    if qos > 0:
        remaining_length += 2
    # 构建payload数据
    payload = topic.encode('utf-8') + message.encode('utf-8')
    if qos > 0:
        payload = struct.pack("!H", packet_id) + payload

    # 构建固定报头
    fixed_header = struct.pack("!B", packet_type | ((qos & 0x03) << 1))

    return fixed_header + encode_remaining_length(remaining_length) + payload

# 构建PUBACK报文
def build_puback_packet(packet_id):
    packet_type = 0x40  # PUBACK报文类型
    remaining_length = 2  # 剩余长度
    # 构建payload数据
    payload = struct.pack("!H", packet_id)

    # 构建固定报头
    fixed_header = struct.pack("!B", packet_type)

    return fixed_header + encode_remaining_length(remaining_length) + payload

# 编码剩余长度
def encode_remaining_length(length):
    remaining_length = bytearray()
    while length > 0:
        digit = length % 128
        length //= 128
        if length > 0:
            digit |= 0x80
        remaining_length.append(digit)
    return remaining_length

# 测试代码
topic = "test/topic"
message = "Hello, MQTT!"
qos = 1
packet_id = 1
publish_packet = build_publish_packet(topic, message, qos, packet_id)
print("PUBLISH报文:", publish_packet.hex())

puback_packet = build_puback_packet(packet_id)
print("PUBACK报文:", puback_packet.hex())

上述代码中，`build_publish_packet()`函数用于构建PUBLISH报文，需要传入发布的主题、消息、QoS等级和报文标识符（如果QoS大于0）。`build_puback_packet()`函数用于构建PUBACK报文，需要传入报文标识符。

需要注意的是，MQTT协议中支持不同的QoS等级，具体可以参考MQTT协议文档。