stcp: fix memory leaks and cleanup architecture

- stcp_conn_do_close: always deferred free for allocated conns (was else-if)
- stcp_link_on_stcp_close: don't null link->conn (close_impl needs it for rx_queue)
- stcp_link_close_impl: free rx_queue/tx_queue before close, null conn after cleanup
- stcp_client_connect: return NULL on derive_session failure (was returning dead cli)
- stcp_frame_decrypt/stcp_recv_try: dedup CRC check into stcp_check_crc helper
- test_stcp: add test8_srv_recv_close (error-recv close chain)

src/transport_layer/stcp.c

@@ -39,6 +39,18 @@ void stcp_conn_free(struct stcp_conn *c) {
     if (c->allocated) u_free(c);
 }
 
+static int stcp_check_crc(const uint8_t *data, size_t data_len) {
+    uint32_t recv_crc = ((uint32_t)data[data_len]) | ((uint32_t)data[data_len + 1] << 8) |
+                        ((uint32_t)data[data_len + 2] << 16) | ((uint32_t)data[data_len + 3] << 24);
+    uint32_t calc_crc = crc32_calc(data, data_len);
+    if (recv_crc != calc_crc) {
+        DEBUG_ERROR(DEBUG_CATEGORY_ETCP, "stcp CRC mismatch recv=%08x calc=%08x data_len=%zu",
+                    recv_crc, calc_crc, data_len);
+        return -1;
+    }
+    return 0;
+}
+
 int stcp_frame_encrypt(struct stcp_conn *c, const uint8_t *data, size_t data_len, uint8_t *output, size_t *output_len) {
     uint32_t crc = crc32_calc(data, data_len);
     output[0] = (uint8_t)(data_len >> 0);
@@ -64,13 +76,7 @@ int stcp_frame_decrypt(uint8_t *data, size_t len, struct sc_stream_state *stream
         return -1;
     }
     size_t data_len = len - SC_CRC32_SIZE;
-    uint32_t recv_crc = ((uint32_t)data[data_len]) | ((uint32_t)data[data_len + 1] << 8) |
-                        ((uint32_t)data[data_len + 2] << 16) | ((uint32_t)data[data_len + 3] << 24);
-    uint32_t calc_crc = crc32_calc(data, data_len);
-    if (recv_crc != calc_crc) {
-        DEBUG_ERROR(DEBUG_CATEGORY_ETCP, "stcp_frame_decrypt CRC mismatch recv=%08x calc=%08x", recv_crc, calc_crc);
-        return -1;
-    }
+    if (stcp_check_crc(data, data_len) != 0) return -1;
     *out_len = data_len;
     return 0;
 }
@@ -249,13 +255,7 @@ void stcp_recv_try(struct stcp_conn *c) {
 
         size_t data_len = (size_t)c->recv_msg_size;
         uint8_t *plain = c->recv_buf + 2;
-        uint32_t recv_crc = ((uint32_t)plain[data_len]) | ((uint32_t)plain[data_len + 1] << 8) |
-                            ((uint32_t)plain[data_len + 2] << 16) | ((uint32_t)plain[data_len + 3] << 24);
-        uint32_t calc_crc = crc32_calc(plain, data_len);
-        if (recv_crc != calc_crc) {
-            DEBUG_ERROR(DEBUG_CATEGORY_ETCP, "stcp_recv_try CRC mismatch recv=%08x calc=%08x data_len=%zu", recv_crc, calc_crc, data_len);
-            stcp_conn_do_close(c, 5); return;
-        }
+        if (stcp_check_crc(plain, data_len) != 0) { stcp_conn_do_close(c, 5); return; }
 
         if (c->recv_on_chunk) c->recv_on_chunk(c, plain, data_len);
         if (c->state == STCP_STATE_CLOSED || c->state == STCP_STATE_ERROR) return;
@@ -301,7 +301,8 @@ void stcp_conn_do_close(struct stcp_conn *c, int err) {
         void (*cb)(struct stcp_conn*, int, void*) = c->on_close;
         c->on_close = NULL;
         cb(c, err, c->close_arg);
-    } else if (c->allocated) {
+    }
+    if (c->allocated) {
         uasync_call_soon(c->ua, c, stcp_conn_deferred_free);
     }
 }

src/transport_layer/stcp_client.c

@@ -183,7 +183,7 @@ struct stcp_client *stcp_client_connect(struct UASYNC *ua, const char *addr, uin
         c->socket_id = uasync_add_socket_t(ua, c->sock, client_conn_read_cb, stcp_write_cb, NULL, c);
         if (!c->socket_id) { socket_close_wrapper(c->sock); u_free(cli); return NULL; }
         c->hs_timer = uasync_set_timeout(ua, STCP_CONNECT_TIMEOUT, c, hs_timeout_cb, "stcp_hs");
-        if (client_derive_session(c, cli->peer_pubkey)) { stcp_conn_do_close(c, 1); return cli; }
+        if (client_derive_session(c, cli->peer_pubkey)) { stcp_conn_do_close(c, 1); u_free(cli); return NULL; }
         client_send_handshake(c, cli->peer_pubkey, cli->my_ed25519_pubkey);
         stcp_recv_set(c, SC_PUBKEY_ENC_SIZE + STCP_HS_ENC_SERVER, 0, client_hs_cb);
     }

src/transport_layer/stcp_link.c

@@ -84,7 +84,7 @@ static void link_rx_cb(struct ll_queue *q, void *arg) {
 static void stcp_link_on_stcp_close(struct stcp_conn *conn, int err, void *arg) {
     struct stcp_link *link = (struct stcp_link *)arg;
     (void)conn; (void)err;
-    link->conn = NULL; link->ready = 0;
+    link->ready = 0;
     if (link->etcp_link) { link->etcp_link->recv_keepalive = 0; link->etcp_link->link_status = 0; }
     if (link->on_close_cb) link->on_close_cb(link, err, link->close_arg);
 }
@@ -210,13 +210,18 @@ struct stcp_link *stcp_link_connect(struct stcp_link_config *cfg) {
 
 static void stcp_link_close_impl(void *arg) {
     struct stcp_link *link = (struct stcp_link *)arg;
+
     if (link->cli) {
+        struct stcp_conn *c = stcp_client_get_conn(link->cli);
+        if (c && c->rx_queue) queue_free(c->rx_queue);
+        if (link->tx_queue) queue_free(link->tx_queue);
         stcp_client_destroy(link->cli);
     } else if (link->conn) {
-        if (link->conn->rx_queue) queue_free(link->conn->rx_queue);
-        if (link->tx_queue) queue_free(link->tx_queue);
-        stcp_conn_do_close(link->conn, 0);
-        stcp_conn_free(link->conn);
+        struct stcp_conn *conn = link->conn;
+        if (conn->rx_queue) { queue_free(conn->rx_queue); conn->rx_queue = NULL; }
+        if (link->tx_queue) { queue_free(link->tx_queue); link->tx_queue = NULL; }
+        stcp_conn_do_close(conn, 0);
+        link->conn = NULL;
     }
     u_free(link);
 }

tests/test_stcp.c

@@ -7,6 +7,7 @@
 #include "../lib/ll_queue.h"
 #include "../lib/debug_config.h"
 #include "../lib/mem.h"
+#include "../lib/socket_compat.h"
 #include <stdio.h>
 #include <string.h>
 #include <stdlib.h>
@@ -373,6 +374,36 @@ static int test7_bulk_4mb(void) {
     return 0;
 }
 
+// ======================= test 8: server recv error → close chain (allocated=1 + on_close + deferred free) =======================
+
+static int test8_srv_recv_close(void) {
+    struct UASYNC *ua = uasync_create(); TASSERT(ua);
+    struct test_peer srv = {0}, cli = {0};
+    uint16_t port = BASE_PORT + 8;
+
+    struct stcp_server *ss = stcp_server_create(ua, port, &s_keys, NULL, server_connect_cb, &srv, peer_close_cb, &srv, AF_INET); TASSERT(ss);
+    struct stcp_client *sc = stcp_client_connect(ua, "127.0.0.1", port, &c_keys, s_keys.public_key, NULL, client_ready_cb, &cli, peer_close_cb, &cli); TASSERT(sc);
+
+    int ticks = 0;
+    while ((!srv.ready || !cli.ready) && ticks < 200) { uasync_poll(ua, 10); ticks++; }
+    TASSERT(srv.ready && cli.ready);
+
+    socket_close_wrapper(cli.conn->sock); cli.conn->sock = SOCKET_INVALID;
+
+    ticks = 0;
+    while (!srv.closed && ticks < 200) { uasync_poll(ua, 10); ticks++; }
+    TASSERT(srv.closed);
+
+    // server conn freed via deferred free (allocated=1 + on_close=peer_close_cb)
+    srv.conn = NULL;   // prevent explicit stcp_conn_free double-free
+    srv.ready = 0;
+
+    peer_cleanup(&srv); peer_cleanup(&cli);
+    stcp_client_destroy(sc); stcp_server_destroy(ss);
+    uasync_destroy(ua, 1);  // flush deferred → stcp_conn_free(srv_conn)
+    return 0;
+}
+
 // ======================= main =======================
 
 int main(void) {
@@ -393,6 +424,7 @@ int main(void) {
     TRUN(test5_multi);
     TRUN(test6_interleaved);
     TRUN(test7_bulk_4mb);
+    TRUN(test8_srv_recv_close);
 
     DEBUG_INFO(DEBUG_CATEGORY_GENERAL, "============================================");
     DEBUG_INFO(DEBUG_CATEGORY_GENERAL, "Results: %d/%d passed", tests_passed, tests_total);