Add socket type (public/nat/private) to handshake and skip private nodes in NAT detection

src/etcp_connections.c

@@ -100,6 +100,7 @@ static void etcp_link_send_init(struct ETCP_LINK* link, uint8_t reset) {
     dgram->data[offset++] = link->local_link_id;
     dgram->data[offset++] = link->conn ? link->conn->sock_id : 0;
     dgram->data[offset++] = link->conn ? link->conn->only_local : 0;
+    dgram->data[offset++] = link->conn ? link->conn->type : CFG_SERVER_TYPE_UNKNOWN;
 
     // padding
     int s = rand() % (link->handshake_maxsize - link->handshake_minsize) + link->handshake_minsize;
@@ -1214,6 +1215,7 @@ void etcp_connections_read_callback_socket(socket_t sock, void* arg) {
         uint8_t link_id;
         uint8_t remote_socket_id;
         uint8_t only_local;
+        uint8_t type;
         uint8_t pubkey[SC_PUBKEY_SIZE];
         } *ack_hdr=(void*)&pkt->data[0];
     uint64_t peer_id = be64toh(*(uint64_t*)ack_hdr->id);
@@ -1358,6 +1360,7 @@ void etcp_connections_read_callback_socket(socket_t sock, void* arg) {
         link->remote_link_id = ack_hdr->link_id;
         link->remote_socket_id = ack_hdr->remote_socket_id;
         link->remote_only_local = ack_hdr->only_local;
+        link->remote_type = ack_hdr->type;
 
         // For CHANNEL_INIT (0x04): if link already initialized - no reset, otherwise reset
         // For INIT_REQUEST (0x02): always reset
@@ -1385,6 +1388,7 @@ void etcp_connections_read_callback_socket(socket_t sock, void* arg) {
         link->remote_link_id = ack_hdr->link_id;
         link->remote_socket_id = ack_hdr->remote_socket_id;
         link->remote_only_local = ack_hdr->only_local;
+        link->remote_type = ack_hdr->type;
 
         // For new links: check session_id to avoid false reinit
         if (conn->session_id != session_id) {
@@ -1410,6 +1414,7 @@ void etcp_connections_read_callback_socket(socket_t sock, void* arg) {
        uint8_t link_id;
         uint8_t remote_socket_id;
         uint8_t only_local;
+        uint8_t type;
         uint8_t peer_ipv4[4];
         uint8_t peer_port[2];
         } *ack_repl_hdr=(void*)&pkt->data[0];
@@ -1431,6 +1436,7 @@ void etcp_connections_read_callback_socket(socket_t sock, void* arg) {
     ack_repl_hdr->link_id = link->local_link_id;
     ack_repl_hdr->remote_socket_id = ack_hdr->remote_socket_id;
     ack_repl_hdr->only_local = e_sock->only_local;
+    ack_repl_hdr->type = e_sock->type;
     // Add client's IP:port (so client behind NAT can know its external address)
     if (addr.ss_family == AF_INET) {
         struct sockaddr_in *sin = (struct sockaddr_in*)&addr;
@@ -1537,9 +1543,10 @@ process_decrypted:
         link->remote_link_id = pkt->data[offset++];
         link->remote_socket_id = pkt->data[offset++];
         link->remote_only_local = pkt->data[offset++];
+        link->remote_type = pkt->data[offset++];
 
         // Parse NAT IP:port from response (new format includes 4+2 bytes)
-        if (pkt_len >= 23) {
+        if (pkt_len >= 24) {
             uint32_t new_nat_ip;
             memcpy(&new_nat_ip, &pkt->data[offset], 4);
             offset += 4;

src/etcp_connections.h

@@ -120,6 +120,7 @@ struct ETCP_LINK {
     uint8_t remote_link_id;         // id этого линка на peer (устанавливается в момент initialized)
     uint8_t remote_socket_id;       // socket id peer
     uint8_t remote_only_local;      // only_local flag from peer
+    uint8_t remote_type;            // CFG_SERVER_TYPE_* (type of peer's socket)
     uint8_t nat_type;               // NAT_TYPE_* (detected for this client link)
     uint8_t recv_keepalive;         // 1 - up, 0 - down (принимаются ли пакеты)
     uint8_t remote_keepalive;       // 1 - up, 0 - down (удаленная сторона сообщает - принимаются ли у нее пакеты)

src/route_bgp.c

@@ -586,7 +586,10 @@ static struct ETCP_CONN* route_bgp_find_third_node(struct ROUTE_BGP* bgp, struct
     struct ll_entry* e = bgp->senders_list->head;
     while (e) {
         struct ROUTE_BGP_CONN_ITEM* item = (struct ROUTE_BGP_CONN_ITEM*)e->data;
-        if (item && item->conn && item->conn != exclude && item->conn->links && item->conn->links->remote_only_local==0) return item->conn;
+        if (item && item->conn && item->conn != exclude && item->conn->links && item->conn->links->remote_only_local==0) {
+            // Skip nodes with private socket type - they can't help with NAT detection
+            if (item->conn->links->remote_type != CFG_SERVER_TYPE_PRIVATE) return item->conn;
+        }
         e = e->next;
     }
     return NULL;
@@ -609,6 +612,11 @@ static void route_bgp_extract_nat_addr(struct ETCP_CONN* conn, uint32_t* nat_ip,
 void route_bgp_start_link_nat_check(struct ROUTE_BGP* bgp, struct ETCP_LINK* link) {// проверяем тип нат для линка link
     if (!bgp || !link || !link->conn || !link->etcp) return;
     if (link->nat_check_status == NAT_CHECK_IN_PROGRESS) return;
+    // Skip NAT check for private sockets - they are not reachable from outside
+    if (link->conn->type == CFG_SERVER_TYPE_PRIVATE) {
+        DEBUG_DEBUG(DEBUG_CATEGORY_BGP, "skip nat check for private socket link");
+        return;
+    }
     // Find third node to send ping through
     struct ETCP_CONN* third_conn = route_bgp_find_third_node(bgp, link->etcp);
     if (!third_conn) {