LocalSocket communication with Unix Domain in Android NDK

Question

I have Android application, which needs to establish unix domain socket connection with our C++ library (using Android NDK)

public static String SOCKET_ADDRESS = "your.local.socket.address"; // STRING

There is LocalSocket in java which accepts "string" (your.local.socket.address)

#define ADDRESS     "/tmp/unix.str" /* ABSOLUTE PATH */
  struct sockaddr_un saun, fsaun;
    if ((s = socket(AF_UNIX, SOCK_STREAM, 0)) < 0) {
        perror("server: socket");
        exit(1);
    }
    saun.sun_family = AF_UNIX;
    strcpy(saun.sun_path, ADDRESS);

But the unix domain socket which is at native layer accepts "absolute path". So how can these two parties communicate to each other?

Please share any example if possible

Answer 1

LocalSocket uses the Linux abstract namespace instead of the filesystem. In C these addresses are specified by prepending '\0' to the path.

const char name[] = "\0your.local.socket.address";
struct sockaddr_un addr;
addr.sun_family = AF_UNIX;

// size-1 because abstract socket names are *not* null terminated
memcpy(addr.sun_path, name, sizeof(name) - 1);

Also note that you should not pass sizeof(sockaddr_un) to bind or sendto because all bytes following the '\0' character are interpreted as the abstract socket name. Calculate and pass the real size instead:

int res = sendto(sock, &data, sizeof(data), 0,
                 (struct sockaddr const *) &addr,
                 sizeof(addr.sun_family) + sizeof(name) - 1);

Answer 2

Pro Android C++ with the NDK book, chapter 10 helped me to get started with the same.