应该如何在RabbitMQ标头中传递字符串值

import pika

# 创建RabbitMQ连接和通道
connection = pika.BlockingConnection(pika.ConnectionParameters('localhost'))
channel = connection.channel()

# 定义消息
message = 'Hello RabbitMQ!'
headers = {'header_key': 'string_value'}

# 设置消息的属性headers
properties = pika.BasicProperties(headers=headers)

# 发送消息到队列
channel.basic_publish(exchange='', routing_key='my_queue', body=message, properties=properties)

# 关闭连接
connection.close()

import pika

# 创建RabbitMQ连接和通道
connection = pika.BlockingConnection(pika.ConnectionParameters('localhost'))
channel = connection.channel()

# 定义回调函数来处理接收到的消息
def callback(ch, method, properties, body):
    # 读取消息的属性headers
    headers = properties.headers
    # 获取字符串值
    string_value = headers.get('header_key')

    # 处理消息
    print(f'Received message: {body}')
    print(f'String value: {string_value}')

# 声明队列并绑定回调函数
channel.queue_declare(queue='my_queue')
channel.basic_consume(queue='my_queue', on_message_callback=callback, auto_ack=True)

# 开始消费消息
channel.start_consuming()