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# echo-server.py
import trio
from itertools import count
# Port is arbitrary, but:
# - must be in between 1024 and 65535
# - can't be in use by some other program on your computer
# - must match what we set in our echo client
PORT = 12345
CONNECTION_COUNTER = count()
async def echo_server(server_stream):
# Assign each connection a unique number to make our debug prints easier
# to understand when there are multiple simultaneous connections.
ident = next(CONNECTION_COUNTER)
print(f"echo_server {ident}: started")
try:
async for data in server_stream:
print(f"echo_server {ident}: received data {data!r}")
await server_stream.send_all(data)
print(f"echo_server {ident}: connection closed")
# FIXME: add discussion of (Base)ExceptionGroup to the tutorial, and use
# exceptiongroup.catch() here. (Not important in this case, but important
# if the server code uses nurseries internally.)
except Exception as exc:
# Unhandled exceptions will propagate into our parent and take
# down the whole program. If the exception is KeyboardInterrupt,
# that's what we want, but otherwise maybe not...
print(f"echo_server {ident}: crashed: {exc!r}")
async def main():
await trio.serve_tcp(echo_server, PORT)
# We could also just write 'trio.run(trio.serve_tcp, echo_server, PORT)', but real
# programs almost always end up doing other stuff too and then we'd have to go
# back and factor it out into a separate function anyway. So it's simplest to
# just make it a standalone function from the beginning.
trio.run(main)
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