asyncio.start_unix_server 和 redis 的套接字错误

Question

我正在尝试使用 asyncio 和 Unix 域套接字在 Python 中构建玩具内存 Redis 服务器。

我的最小示例只是 returns 每个请求的值 baz：

import asyncio


class RedisServer:
    def __init__(self):
        self.server_address = "/tmp/redis.sock"

    async def handle_req(self, reader, writer):
        await reader.readline()
        writer.write(b"\r\nbaz\r\n")
        await writer.drain()
        writer.close()
        await writer.wait_closed()

    async def main(self):
        server = await asyncio.start_unix_server(self.handle_req, self.server_address)
        async with server:
            await server.serve_forever()

    def run(self):
        asyncio.run(self.main())


RedisServer().run()

当我用 the redis client library 使用以下脚本测试两个连续的客户端请求时，它有效：

import time
import redis


r = redis.Redis(unix_socket_path="/tmp/redis.sock")

r.get("foo")
time.sleep(1)
r.get("bar")

但是，如果我删除 time.sleep(1)，有时它会起作用，有时第二个请求会失败：

Traceback (most recent call last):
  File "/tmp/env/lib/python3.8/site-packages/redis/connection.py", line 706, in send_packed_command
    sendall(self._sock, item)
  File "/tmp/env/lib/python3.8/site-packages/redis/_compat.py", line 9, in sendall
    return sock.sendall(*args, **kwargs)
BrokenPipeError: [Errno 32] Broken pipe

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "test.py", line 9, in <module>
    r.get("bar")
  File "/tmp/env/lib/python3.8/site-packages/redis/client.py", line 1606, in get
    return self.execute_command('GET', name)
  File "/tmp/env/lib/python3.8/site-packages/redis/client.py", line 900, in execute_command
    conn.send_command(*args)
  File "/tmp/env/lib/python3.8/site-packages/redis/connection.py", line 725, in send_command
    self.send_packed_command(self.pack_command(*args),
  File "/tmp/env/lib/python3.8/site-packages/redis/connection.py", line 717, in send_packed_command
    raise ConnectionError("Error %s while writing to socket. %s." %
redis.exceptions.ConnectionError: Error 32 while writing to socket. Broken pipe.

或：

Traceback (most recent call last):
  File "test.py", line 9, in <module>
    r.get("bar")
  File "/tmp/env/lib/python3.8/site-packages/redis/client.py", line 1606, in get
    return self.execute_command('GET', name)
  File "/tmp/env/lib/python3.8/site-packages/redis/client.py", line 901, in execute_command
    return self.parse_response(conn, command_name, **options)
  File "/tmp/env/lib/python3.8/site-packages/redis/client.py", line 915, in parse_response
    response = connection.read_response()
  File "/tmp/env/lib/python3.8/site-packages/redis/connection.py", line 739, in read_response
    response = self._parser.read_response()
  File "/tmp/env/lib/python3.8/site-packages/redis/connection.py", line 324, in read_response
    raw = self._buffer.readline()
  File "/tmp/env/lib/python3.8/site-packages/redis/connection.py", line 256, in readline
    self._read_from_socket()
  File "/tmp/env/lib/python3.8/site-packages/redis/connection.py", line 201, in _read_from_socket
    raise ConnectionError(SERVER_CLOSED_CONNECTION_ERROR)
redis.exceptions.ConnectionError: Connection closed by server.

我的实现似乎缺少客户端库期望的一些关键行为（可能是因为它是异步的）。我错过了什么？

Answer 1

如果你想在每次请求后关闭套接字，你需要使用 write_eof()，

Close the write end of the stream after the buffered write data is flushed.

见 docs.python.org -> write_eof

您的代码稍微修改后如下所示：

async def handle_req(self, reader, writer):
    await reader.readline()
    writer.write(b"\r\nbaz\r\n")
    await writer.drain()
    writer.write_eof()
    writer.close()
    await writer.wait_closed()

通常您不会在每次请求后关闭套接字。

以下示例仅供说明，旨在说明不需要关闭套接字。当然，你总是会读取一行，然后根据 Redis 协议解释数据。我们在这里知道发送了两个 GET 命令（每 5 行，具有 2 个元素的数组指示符，字符串指示符，字符串值 'GET' 以及字符串指示符和相应的值，即键）

async def handle_req(self, reader, writer):
    print("start")
    for i in range(0, 2):
        for x in range(0, 5):
            print(await reader.readline())
        writer.write(b"\r\nbaz\r\n")
        await writer.drain()
    writer.write_eof()
    writer.close()
    await writer.wait_closed()

客户端发送是这样完成的：

print(r.get("foo"))
print(r.get("bar"))
time.sleep(1)

最后一个time.sleep是保证客户端不会马上退出

控制台上的输出是：

start
b'*2\r\n'
b'\r\n'
b'GET\r\n'
b'\r\n'
b'foo\r\n'
b'*2\r\n'
b'\r\n'
b'GET\r\n'
b'\r\n'
b'bar\r\n'

注意start只输出一次，说明我们可以处理多个请求而不用马上关闭socket

asyncio.start_unix_server 和 redis 的套接字错误

Socket errors with asyncio.start_unix_server and redis

python

redis

python-3.x

redis-py

python-asyncio