headless: expose OS-assigned control and audio listener ports

lib/socket_compat.c

@@ -246,3 +246,16 @@ uint16_t ss_get_port(const struct sockaddr_storage *addr) {
 
     return 0;
 }
+
+uint16_t socket_get_bound_port(socket_t sock) {
+    struct sockaddr_storage address; socklen_t size = sizeof(address);
+    if (getsockname(sock, (struct sockaddr*)&address, &size) != 0) {
+        DEBUG_ERROR(DEBUG_CATEGORY_SOCKET, "getsockname fd=%llu failed: %s",
+                    (unsigned long long)sock, socket_strerror(socket_get_error()));
+        return 0;
+    }
+    uint16_t port = ss_get_port(&address);
+    if (!port) DEBUG_ERROR(DEBUG_CATEGORY_SOCKET, "socket fd=%llu family=%d has no bound port",
+                           (unsigned long long)sock, address.ss_family);
+    return port;
+}