Python websockets send to client and keep connection alive
Solution 1
Presumably your function that processes the data is blocking, otherwise you'd simply await
it inside the coroutine. The straightforward approach is to use run_in_executor
to run it in another thread, and await
it in your handler coroutine:
async def hello(websocket, path):
loop = asyncio.get_event_loop()
await websocket.send("Hello Client! Please wait for your data.")
data = await loop.run_in_executor(None, get_data)
await websocket.send("Your data is here!")
await websocket.send(data)
def get_data():
# something that takes a long time to calculate
x = 19134702400093278081449423917**300000 % 256
return bytes([x])
Solution 2
To keep the connection open do not terminate the handler after processing the first message. For example, you can have an endless-loop that will keep processing the incoming messages until the connection is closed by the client:
async def hello(websocket, path):
while True:
try:
name = await websocket.recv()
except websockets.ConnectionClosed:
print(f"Terminated")
break
print(f"< {name}")
greeting = f"Hello {name}!"
await websocket.send(greeting)
print(f"> {greeting}")
In the async
fun you can then await
any long running operation as suggested here.
You will however need to adapt both server and client side in the similar way. Your client also terminates after receiving the first message.
Anton
Updated on June 28, 2022Comments
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Anton almost 2 years
I'm using python websockets: https://websockets.readthedocs.io/
They have a simple client/server example, where the server echoes the client's input back once. The code looks like this:
Client side:
# WS client example import asyncio import websockets async def hello(): async with websockets.connect( 'ws://localhost:8765') as websocket: name = input("What's your name? ") await websocket.send(name) print(f"> {name}") greeting = await websocket.recv() print(f"< {greeting}") asyncio.get_event_loop().run_until_complete(hello())
Server side:
# WS server example import asyncio import websockets async def hello(websocket, path): name = await websocket.recv() print(f"< {name}") greeting = f"Hello {name}!" await websocket.send(greeting) print(f"> {greeting}") start_server = websockets.serve(hello, 'localhost', 8765) asyncio.get_event_loop().run_until_complete(start_server) asyncio.get_event_loop().run_forever()
I want to adapt just the server side only, so that it does the following upon a socket connection:
- Send an acknowledgement message to the client. e.g.
Hello Client! Please wait for your data.
- Keep the connection alive.
- Process some data that takes some time.
- After the data has completed processing, notify the client on the existing websocket connection. e.g.
Your data is here!
The python websockets documentation doesn't have a code sample which does this.
- Send an acknowledgement message to the client. e.g.
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Ernest S Kirubakaran about 4 yearsCan you please tell how to write the same
hello
function for client?