Android客户端无法打开C服务器的套接字

Question

I couldn't find anything about this quite specific problem, but maybe someone else has done this.

I have a server program written in C (error checking removed for readability):

int main(int arc, char *argv[])
{
    int sockfd, newsockfd, portnum, cli_len, num_chars, n;

    char buffer[256];
    struct sockaddr_in serv_addr, cli_addr;

    // Set up the socket
    sockfd = socket(AF_INET, SOCK_STREAM, 0);

    // Set up our variables
    bzero((char *) &serv_addr, sizeof(serv_addr));
    portnum = atoi(argv[1]);
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(portnum); // Convert from host port to network port
    serv_addr.sin_addr.s_addr = INADDR_ANY;

    if(bind(sockfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) < 0)
        error("Socket could not be bound");

    listen(sockfd, 5); // Get ready to receive connections

    cli_len = sizeof(cli_addr);
    newsockfd = accept(sockfd, (struct sockaddr *) &cli_addr, &cli_len);

    // Message processing

    return 0;
}

Meanwhile, I have the Android client (Version 4.1.2):

private class ClientTask extends AsyncTask<String, Void, Void> {

        @Override
        protected Void doInBackground(String... params) {
            try {
                InetAddress a = InetAddress.getByAddress(new byte[] {(byte) 192, (byte) 168, 1, (byte) 102});
                sock = new Socket(a, 65053);
                BufferedReader inFromServer = new BufferedReader(new InputStreamReader(sock.getInputStream()));
                DataOutputStream outToServer = new DataOutputStream(sock.getOutputStream()); 

                // Message processing

            } catch (UnknownHostException e) {
                System.out.println("No address found for ");
            } catch (IOException e) {
                System.out.println("Failed to open socket");
            }
            return null;
        }
    }

The issue I have is that the socket can't be opened by the Android client. I always get "Failed to open socket" after the timeout. The android client works with a java server I have, and a java client I have at least makes the connection with the C server. I don't understand what could be wrong...

If you need more details or additional code, let me know.

Answer 1

You don't specify if you're running both devices (server and client) just under the same LAN, in which case you can discard connectivity problems. If not, this might be a test. If you're able to connect your client to your server under the same router, that means that otherwise (ie, using your public IPs) there's something blocking it, probably your router. Another issues could be antiviruses, OS ports blocking, router ports blocking...

If you're not able to connect both either under the same router connection, definitely it's a code issue. As you don't know where the culprit is, I'd suggest putting several Log.d() lines within the client code and printf() statements within the server code in the connectivity snippets on both sides and see where the bottleneck is, or use some debugging tool and put some breakpoints.

---- EDIT ----

Try connecting this way:

Socket socket;
final String host = "192.168.1.X";
final int port = 65053;
final int timeout = 30000;   // 30 seconds

try {
  socket = new Socket();
  socket.connect(new InetSocketAddress(host, port), timeout);
}
catch (UnknownHostException uhe) {
  Log.e("Sock", "I couldn't resolve the host you've provided!");
}
catch (SocketTimeoutException ste) {
  Log.e("Sock", "After a reasonable amount of time, I'm not able to connect!");
}
catch (IOException ioe) {
  Log.e("Sock", "Hmmm... Sudden disconnection, probably you should start again!");
} 

Answer 2

Whelp, it was a firewall issue, embarrassingly enough. Apparently Eclipse was let through my firewall, which is why the Java server worked, but I must've missed the prompt when I ran my C code through the command line. I disabled my firewall and it worked immediately.