etcp: exchange observed IPs on established TCP links

src/transport_layer/etcp_connections.c

@@ -1262,6 +1262,29 @@ void etcp_link_close(struct ETCP_LINK* link) {
 
 // ====== TCP link helpers ======
 
+/* По готовому STCP сообщает пиру его фактический IP; исходящий порт не является портом listener. */
+static void tcp_send_observed_ip(struct ETCP_LINK *link) {
+    struct UTUN_INSTANCE *inst = link->etcp->instance;
+    if (!link->tcp_link || (!link->is_server && inst->config && inst->config->global.socks_enabled)) return;
+    const struct sockaddr_storage *peer = stcp_link_get_peer_addr(link->tcp_link);
+    if (!peer) { DEBUG_WARN(DEBUG_CATEGORY_NAT, "TCP IP report cannot read peer socket=%s", link->etcp->log_name); return; }
+    struct ETCP_DGRAM *pkt = memory_pool_alloc(inst->pkt_pool);
+    if (!pkt) { DEBUG_ERROR(DEBUG_CATEGORY_NAT, "TCP IP report allocation failed peer=%s", link->etcp->log_name); return; }
+    pkt->link = link; pkt->data_len = 18; pkt->noencrypt_len = 0;
+    memset(pkt->data, 0, pkt->data_len); pkt->data[0] = ETCP_TCP_ADDRESS;
+    if (peer->ss_family == AF_INET) {
+        pkt->data[1] = 4; memcpy(pkt->data + 2, &((const struct sockaddr_in *)peer)->sin_addr, 4);
+    } else if (peer->ss_family == AF_INET6) {
+        pkt->data[1] = 6; memcpy(pkt->data + 2, &((const struct sockaddr_in6 *)peer)->sin6_addr, 16);
+    } else {
+        DEBUG_WARN(DEBUG_CATEGORY_NAT, "TCP IP report unsupported family=%d", peer->ss_family);
+        memory_pool_free(inst->pkt_pool, pkt); return;
+    }
+    DEBUG_DEBUG(DEBUG_CATEGORY_NAT, "TCP IP report peer=%s observed=%s", link->etcp->log_name, sockaddr_storage_to_str(peer).str);
+    if (etcp_encrypt_send(pkt) < 0) DEBUG_WARN(DEBUG_CATEGORY_NAT, "TCP IP report send failed");
+    memory_pool_free(inst->pkt_pool, pkt);
+}
+
 // Поднять TCP-линк в ready: синхронизация reset-эпохи (gop/rid), keepalive, ed25519,
 // mark initialized + link_status=1, уведомить коннект и loadbalancer.
 void etcp_link_enter_ready_tcp(struct ETCP_LINK *link) {
@@ -1297,6 +1320,7 @@ void etcp_link_enter_ready_tcp(struct ETCP_LINK *link) {
     DEBUG_INFO(DEBUG_CATEGORY_ETCP, "[%s] TCP link %d UP (mtu=%d init=%d up=%d tcp_links=%d)",
                etcp->log_name, link->local_link_id, link->mtu,
                etcp->initialized, etcp->links_up, etcp->tcp_link_count);
+    tcp_send_observed_ip(link);
 }
 
 // Повторная попытка STCP-подключения с экспоненциальным backoff (до 30 с).
@@ -2636,6 +2660,33 @@ int etcp_packet_decrypted(struct ETCP_SOCKET* e_sock, struct ETCP_DGRAM* pkt,
 
     uint8_t pkt_code = pkt->data[0];
 
+    if (pkt_code == ETCP_TCP_ADDRESS) {
+        struct UTUN_INSTANCE *inst = link->etcp->instance;
+        static const uint8_t zero[12];
+        if (!link->is_tcp || pkt->data_len != 18 ||
+            (pkt->data[1] != 4 && pkt->data[1] != 6) ||
+            (pkt->data[1] == 4 && memcmp(pkt->data + 6, zero, sizeof(zero)))) {
+            DEBUG_WARN(DEBUG_CATEGORY_NAT, "TCP IP report invalid transport/format peer=%s size=%u",
+                       link->etcp->log_name, pkt->data_len);
+            memory_pool_free(inst->pkt_pool, pkt); return 0;
+        }
+        if (!link->is_server && inst->config && inst->config->global.socks_enabled) {
+            DEBUG_DEBUG(DEBUG_CATEGORY_NAT, "TCP IP report ignored through SOCKS peer=%s", link->etcp->log_name);
+            memory_pool_free(inst->pkt_pool, pkt); return 0;
+        }
+        struct sockaddr_storage observed = {0};
+        if (pkt->data[1] == 4) {
+            observed.ss_family = AF_INET; memcpy(&((struct sockaddr_in *)&observed)->sin_addr, pkt->data + 2, 4);
+        } else {
+            observed.ss_family = AF_INET6; memcpy(&((struct sockaddr_in6 *)&observed)->sin6_addr, pkt->data + 2, 16);
+        }
+        link->local_as_seen_by_peer = observed;
+        const struct sockaddr_storage *local = stcp_link_get_local_addr(link->tcp_link);
+        if (local && inst->nat_det && link->conn) nat_detection_tcp_observed(inst->nat_det, link, local, &observed);
+        else if (!local) DEBUG_WARN(DEBUG_CATEGORY_NAT, "TCP IP report cannot read local socket peer=%s", link->etcp->log_name);
+        memory_pool_free(inst->pkt_pool, pkt); return 0;
+    }
+
 #ifdef UTUN_HAVE_STANDBY
     {
         char who[256];

src/transport_layer/etcp_connections.h

@@ -44,6 +44,7 @@ extern "C" {
 #define ETCP_PING               0x06
 #define ETCP_PONG               0x07
 #define ETCP_KEEPALIVE          0x08
+#define ETCP_TCP_ADDRESS        0x0d  // STCP control: code + family(4/6) + observed IP(16), без порта
 
 #define ETCP_PING_FLAG_WANT_RTT 0x01  // в PONG: хочу получить RTT от пингера
 #define ETCP_PING_FLAG_SEND_RTT 0x02  // в PING: несу RTT для получателя