Just get one last value from socket

Question

I send data to socket on one side every second, but I can read that data on another side in any moment. Here's the writer:

from settings import Config

filename = Config.NAVIGATION_SOCKET_FILE

client = socket.socket(socket.AF_UNIX, socket.SOCK_DGRAM)
client.settimeout(None)
while True:
    try:
        client.connect(filename)
        break
    except Exception:
        continue
messages = ["$GPRMC,125504.049,A,5542.2389,N,03741.6063,E,0.06,25.82,200906,,,*17",
            "$GPRMC,155604.049,A,5542.2389,N,03741.6063,E,0.06,25.82,200906,,,*19",]
while True:
    msg = random.choice(messages)
    client.send(msg)
    print msg
    time.sleep(1)

And here's reader:

navigation_socket = socket.socket(socket.AF_UNIX, socket.SOCK_DGRAM)
if os.path.exists(app.config['NAVIGATION_SOCKET_FILE']):
        os.remove(app.config['NAVIGATION_SOCKET_FILE'])
navigation_socket.bind(app.config['NAVIGATION_SOCKET_FILE'])

class NavigationInfo(restful.Resource):
    def get(self):
        msg = navigation_socket.recv(1024)
        regex = re.compile(r"^\$GPRMC,(?P<time>\d{6}\.\d{3}),(?P<status>A|V),"
                           r"(?P<latitude>\d{4}\.\d{4}),(?P<lat_n_s>N|S),"
                           r"(?P<longitude>\d{5}\.\d{4}),(?P<long_e_w>E|W),"
                           r"(?P<hor_speed>\d+.\d+),(?P<track_angle>\d+.\d+),"
                           r"(?P<date>\d{6}),(?P<magnetic_declination>\d+\.\d+)?,"
                           r"(?P<magnetic_decl_direction>\d)?,"
                           r"(?P<mode>A|D|E|N)?\*(?P<checksum>\d\d)")
        result = regex.match(msg)
        navigation_info = result.groupdict()
        return navigation_info

So the first problem is that writer just stops writing data to socket when buffer is full (at least that's what I see) and when I request data on the other side, it's too old.

Can just I store one value in buffer and then rewrite it? Or maybe I'm getting it all wrong?

You may consider sleeping some seconds in your first while true, in case of an exception. (If connect raises, you'll stick at 100% CPU, for nothing). — Julien Palard, Jul 12 '14 at 16:43
@JulienPalard thanks. But the main problem for me here is that I'm not able to get fresh data from socket. — Dmitrii Mikhailov, Jul 12 '14 at 16:47

score 0 · Accepted Answer · answered Jul 12 '14 at 16:47

0

I think that you are using the solution in reverse.

Instead of pushing messaging, while not pulling messages ?

Your server may look like:

Wait for a connection
Give a random message
go to step 1

And your client may just connect to the server when he needs a message.

In your case, the connection is "opened all the time", in my solution the socket is opened only when needed. and closed right after the message is delivered.

answered Jul 12 '14 at 16:47

Julien Palard

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yw, don't hesitate to ask again if you're stuck. – Julien Palard Jul 12 '14 at 17:07
Could you provide any piece of code as example? I really don't now how to do that thing without using two unix sockets. And even if I have two, do I need to use threading to work with them concurrently? – Dmitrii Mikhailov Jul 13 '14 at 08:42
RTFM: https://docs.python.org/2/library/socketserver.html#socketserver-tcpserver-example (If you really want to stick to Unix Sockets, use UnixStreamServer but TCP is great too). – Julien Palard Jul 13 '14 at 09:05

Just get one last value from socket

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