将字节从 asyncio StreamReader 泵入文件描述符

Question

我有一个 Python 函数（用 C++ 实现），它从文件描述符（在 C++ 端包装在 FILE* 中）读取，我需要从 asyncio.StreamReader.具体来说，reader 是 HTTP 响应的内容：aiohttp.ClientResponse.content.

我想我可能 open a pipe, pass the read-end to the C++ function and connect the write-end 到 asyncio 的事件循环。但是，如何通过适当的流量控制和尽可能少的复制将数据从流 reader 移动到管道？

缺少部分的代码框架如下：

# obtain the StreamReader from aiohttp
content = aiohttp_client_response.content
# create a pipe
(pipe_read_fd, pipe_write_fd) = os.pipe()

# now I need a suitable protocol to manage the pipe transport
protocol = ?
(pipe_transport, __) = loop.connect_write_pipe(lambda: protocol, pipe_write_fd)

# the protocol should start reading from `content` and writing into the pipe
return pipe_read_fd

Answer 1

我通过使用 ThreadPoolExecutor 并阻止调用 os.write:

解决了这个问题

(read_fd, write_fd) = os.pipe()
task_1 = loop.create_task(pump_bytes_into_fd(write_fd))
task_2 = loop.run_in_executor(executor_1, parse_bytes_from_fd(read_fd))

async def pump_bytes_into_fd(write_fd):
    while True:
        chunk = await stream.read(CHUNK_SIZE)
        if chunk is None: break
        # process the chunk
        await loop.run_in_executor(executor_2, os.write, write_fd, chunk)

使用两个不同的执行器来阻塞读写以避免死锁是至关重要的。

Answer 2

来自 subprocess_attach_write_pipe asyncio 示例：

rfd, wfd = os.pipe()
pipe = open(wfd, 'wb', 0)
transport, _ = await loop.connect_write_pipe(asyncio.Protocol, pipe)
transport.write(b'data')

编辑 - 对于写入流量控制，请参阅以下方法：

这是一个可能的 FlowControl 实现，灵感来自 StreamWriter.drain:

class FlowControl(asyncio.streams.FlowControlMixin):
    async def drain(self):
        await self._drain_helper()

用法：

transport, protocol = await loop.connect_write_pipe(FlowControl, pipe)
transport.write(b'data')
await protocol.drain()

将字节从 asyncio StreamReader 泵入文件描述符

Pump bytes from asyncio StreamReader into a file descriptor

python

python-asyncio

aiohttp