recv() always returns -1 in android

Question

I need to send few strings on localhost via socket on android using native code (in C particularity) but I've faced weird problem - recv() function always returns -1 and eerno tells "Try again!"

Here is code responsible for initialization of socket and receiving response

void request() {

    struct sockaddr_in sa;
    memset(&sa, 0, sizeof(sa));
    sa.sin_family = AF_INET;
    //need to send string to localhost
    inet_aton("127.0.0.1", &(sa.sin_addr));
   
    int sock;
    char res[7];
    
    sock = socket(AF_INET, SOCK_STREAM, 0);
    sa.sin_port = htons(27042);
    int connection = connect(sock, (struct sockaddr *) &sa, sizeof sa);
    if (connection != -1) { //connection >= 0
        memset(res, 0, 7);

        send(sock, "\x00", 1, NULL);

        send(sock, "AUTH\r\n", 6, NULL);

        usleep(100); // Give it some time to answer

        int rec = recv(sock, res, 7, MSG_DONTWAIT);

        // rec is always -1 and errno says "Try again!"

    }

    close(sock);
}

There is an INTERNET permission in Manifest file.

I've tried to put recv(sock, res, 7, MSG_DONTWAIT) part in while loop to wait maybe it would return some data but no success. Maybe I need to call something like flush() after send()?

Does any one know where could be trouble?

UPD. This code runs in one android app (client) and tries to send string to other android app that runs on the same device (server).

Answer 1

Solution became pretty obvious - current "server" version can't process "AUTH" message that is why "client" app receive -1 response. I've tried older version and everything worked fine.