TCPConnection equivalent for listening for AIS client connections?

[nsands]

The TCPConnection class works when you want to connect to an AIS TCP server. However, our AIS service acts as a client and wants to initiate a connection to me.

Is there any equivalent class in pyais to cater for this?

I made the following class (a slightly modified copy of the TCPConnection class) which seems to work well for this purpose. At least it works well with our AIS service. However, I'd rather use an existing pyais class if it exists.

`class TCPListener(SocketStream):
"""
Read AIS data from a remote TCP client
https://en.wikipedia.org/wiki/NMEA_0183
"""

def recv(self) -> bytes:
    return self._fobj.recv(self.BUF_SIZE)

def __init__(
    self,
    host: str,
    port: int = 80,
    preprocessor: typing.Optional[PreprocessorProtocol] = None,
    tbq: typing.Optional[TagBlockQueue] = None
) -> None:
    sock: socket = socket(AF_INET, SOCK_STREAM)
    try:
        sock.bind((host, port))
        sock.listen()
        print(f"AIS TCP Listener listening on:  {host}:{port}")

        client_sock, client_address = sock.accept()
        print(f"Client has connected:  {client_address}")
    except ConnectionRefusedError as e:
        sock.close()
        raise ConnectionRefusedError(f"Failed to connect to {host}:{port}") from e
    super().__init__(client_sock, preprocessor=preprocessor, tbq=tbq)`

[M0r13n]

Hey @nsands,

you're referring to a TCP server that accepts a single remote connection, correct? Currently pyais does not include that functionality. I'm working on an implementation (see PR #189) that supports an arbitrary number of clients. Once it's production-ready, it should be a suitable replacement for your custom solution.

All the best

[nsands]

Yes, that’s correct. Thanks. I’ll look forward to the update.

[M0r13n]

@nsands After updating to v2.13.0 pyais comes with a built‑in class TCPServer capable of handling multiple concurrent client connections (see this example). Let me know if that works for you :)

All the best

[nsands]

Hey thanks for this. I've not installed the new version yet, but after a quick look at your code, I'm wondering if/how it handles timeouts from the TCP client AIS service?

I've had to update my own to the following, including timeouts, because the AIS service that I'm using periodically just times out altogether and stops sending messages (I've not idea why, and they won't tell me and won't allow me access to take a look at it). However, closing the TCP listener/server and re-opening a new one (ie, forcibly disconnecting the timed-out client) causes that client to reconnect, and continue sending messages again.

Will this TCPServer handle that situation ok?

Here's my updated TCPListener which handles the timeout. This will be reported to the calling script as a timeout exception, and the script can re-establish the server. Not sure if this is an appropriate way to do it for a multi-client service, though.

`class TCPListener(SocketStream):

def recv(self) -> bytes:
    return self._fobj.recv(self.BUF_SIZE)

def __init__(
    self,
    host: str,
    port: int = 80,
    preprocessor: typing.Optional[PreprocessorProtocol] = None,
    tbq: typing.Optional[TagBlockQueue] = None,
    timeout: int = None
) -> None:
    sock: socket = socket(AF_INET, SOCK_STREAM)
    sock.settimeout(timeout)
    try:
        sock.bind((host, port))
        sock.listen()
        print(f"AIS TCPListener listening on:  {host}:{port}")
        client_sock, client_address = sock.accept()
        print(f"AIS TCPListener client has connected:  {client_address}")
    except ConnectionRefusedError as e:
        sock.close()
        raise ConnectionRefusedError(f"AIS TCP Listener connection failed for:  {host}:{port}") from e
    super().__init__(client_sock, preprocessor=preprocessor, tbq=tbq)

`

[M0r13n]

Hey @nsands,

shouldn't you set the timeout on the client socket? In your example you set the timeout for the server socket. Thus, it is only used for bind(), listen() and accept(). However, your goal is to close stale connections (that were already established).

#190 is going to add the possibility to set a timeout for client connections. Stale connections will then be closed. And because the client supports an arbitrary number of clients, clients can re-establish a connection at any time - without the need to re-instantiate the server

[nsands]

Yes, you're correct - I should have also added the timeout to the client socket (and have done this now in my own code). I’m a mediocre coder, and this low-level networking stuff is outside of my comfort zone. 😊

Thanks for adding this server class and for planning to add the timeout for it.