Calling SelectorSocketTransport.writelines with a very large payload doesn't get completely written to the socket #103462
Description
Bug report
As a consequence of the optimization introduced in #91166, when SelectorSocketTransport.writelines is used with a very large buffer which can't be written in one shot either by using socket.send or socket.sendmsg the remaining data in the buffer is never written to the socket.
The following example can be used to reproduce the error:
import asyncio
async def send_message(chunk_size: int, chunks: int):
await asyncio.sleep(1)
reader, writer = await asyncio.open_connection("127.0.0.1", 9898)
data = [bytes(chunk_size)] * chunks + [b"end"]
writer.writelines(data)
await writer.drain()
writer.close()
await writer.wait_closed()
async def handle_message(reader, writer):
data = await reader.read()
print(f"End marker: {data[-3:]!r}")
writer.close()
await writer.wait_closed()
async def run_server():
server = await asyncio.start_server(handle_message, "127.0.0.1", 9898)
async with server:
await server.serve_forever()
async def main():
await asyncio.gather(run_server(), send_message(6500, 100))
asyncio.run(main())The example above prints End marker: b'end' with python 3.11 but not with python 3.12.0a6+
Your environment
- CPython versions tested on:
3.12.0a7 - Operating system and architecture: macOS 13.2
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