asyncio.server: how to filter on remote IP-address

Question

I have a Tcp socket server class that is to run in CPython and MicroPython. It does, no problem there. Only I would like to extend its functionality with an IP filter. From an earlier version that still was a http server, I have a regular expression pattern to match the requesting IP-address. But where can I step in and inspect the remote address to accept or refuse the connection?

Note: the reader object in newConnection has no attribute '_transport' in microPython.

def log(*args, prio = 0):
    if prio >= 0:
        print(*args)



class TcpServer(SocketBase):
    
    def __init__(self, port=8888, requestHandler = None, ipMask = r"192.168.(\d+).(\d+)|localhost|127.0.0.1"):
        '''
        :param requestHandler: callable with parameters request, response
        '''
        super().__init__(host="0.0.0.0", port = port)
        self.requestHandler = requestHandler
        self.ipRange        = re.compile(ipMask)
        self.timeout        = TimeOut()

    
    async def start(self):
        self.server = await asyncio.start_server(self.newConnection, host=self.host, port=self.port)
        log("server started at ", (self.host, self.port), prio=1)
        
        while True:
            await asyncio.sleep(10)

    
    
    async def newConnection(self, reader, writer):
        log("Connected")

        self.connection = (reader, writer)
        self.timeout.extend(30)
        while not self.timeout.expired():
            if not await self.pollOpenConnection(reader, writer):
                # not data, then doze a while:
                await asyncio.sleep(1./25.)
                
        writer.close()
        log("Disconnected")

AFAIK it is not possible in a TCP server program to refuse a connection from banned IP addresses. The server could accept the connection, check the remote address and immediately reset the connection. It is not the same thing as refusing an incoming connection, but might be good enough. — VPfB
– VPfB, Commented Apr 24 at 19:29
The client will not know that the connection has been closed immediately, so it gets a 'connection reset'-error (localhost) or a timeout (network). It is good enough indeed for a private service. — resurrected user
– resurrected user, Commented Apr 25 at 15:12

Dave H. · Accepted Answer · 2025-04-24 13:50:46Z

2

In your connection handler you can find it from the stream writer:

remote_addr = writer.get_extra_info('peername')[0]

answered Apr 24 at 13:50

Dave H.

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2 Comments

resurrected user Apr 25 at 15:13

Spot on, thank you. I wonder how you figured that one out, all resources I found said to interrogate the reader, so I didn't even try the writer...

Dave H. Apr 26 at 19:01

I took the example from my own MicroPython web framework: github.com/DavesCodeMusings/thimble Where I first learned it, I don't remember. Possibly some helpful person on the MicroPython Github Discussion board: github.com/orgs/micropython/discussions

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