usockets: follow the whole adopted-socket chain when re-deriving the live socket

packages/bun-usockets/src/eventing/libuv.c

@@ -44,11 +44,7 @@ int us_internal_libuv_peer_reset_probe(LIBUS_SOCKET_DESCRIPTOR fd) {
 }
 
 static struct us_socket_t *us_internal_poll_cb_adopted_socket(struct us_poll_t *wp) {
-  struct us_socket_t *s = (struct us_socket_t *)wp;
-  if (s->flags.adopted && s->prev) {
-    s = s->prev;
-  }
-  return s;
+  return us_internal_socket_follow_adopted((struct us_socket_t *)wp);
 }
 
 static int us_internal_poll_cb_socket_is_probeable(struct us_poll_t *wp) {

packages/bun-usockets/src/internal/internal.h

@@ -343,6 +343,21 @@ struct us_socket_t {
 _Static_assert(sizeof(struct us_socket_flags) == 1, "us_socket_flags grew");
 #endif
 
+/* us_socket_adopt relocates a socket whose ext grows and retires the old block
+ * (is_closed + adopted, prev -> replacement; freed by the outermost tick's
+ * us_internal_free_closed_sockets, so it is still readable mid-dispatch). A
+ * callback may adopt more than once before returning, retiring each block in
+ * turn, so walk the whole chain rather than one link: one link can land on a
+ * block that is itself retired. The walk ends on the live block, which never
+ * has adopted set (the copy is taken before the source is flagged). Tolerates
+ * NULL, which callbacks may return. */
+static inline struct us_socket_t *us_internal_socket_follow_adopted(struct us_socket_t *s) {
+    while (s && s->flags.adopted && s->prev) {
+        s = s->prev;
+    }
+    return s;
+}
+
 struct us_connecting_socket_t {
     alignas(LIBUS_EXT_ALIGNMENT) struct addrinfo_request *addrinfo_req;
     struct us_socket_group_t *group;

packages/bun-usockets/src/loop.c

@@ -555,9 +555,7 @@ void us_internal_dispatch_ready_poll(struct us_poll_t *p, int error, int eof, in
                             us_dispatch_open(s, 0, bsd_addr_get_ip(&addr), bsd_addr_get_ip_length(&addr));
                         }
                         /* After socket adoption, track the new socket; the old one becomes invalid */
-                        if(s && s->flags.adopted && s->prev) {
-                            s = s->prev;
-                        }
+                        s = us_internal_socket_follow_adopted(s);
 
                         /* When the kernel deferred the accept until data arrived (TCP_DEFER_ACCEPT
                          * on Linux, SO_ACCEPTFILTER on FreeBSD), the request/ClientHello is already
@@ -583,9 +581,7 @@ void us_internal_dispatch_ready_poll(struct us_poll_t *p, int error, int eof, in
             /* We should only use s, no p after this point */
             struct us_socket_t *s = (struct us_socket_t *) p;
             /* After socket adoption, track the new socket; the old one becomes invalid */
-            if(s && s->flags.adopted && s->prev) {
-                s = s->prev;
-            }
+            s = us_internal_socket_follow_adopted(s);
             /* The group can change after calling a callback but the loop is always the same */
             struct us_loop_t* loop = s->group->loop;
             if (events & LIBUS_SOCKET_WRITABLE && !error) {
@@ -601,9 +597,7 @@ void us_internal_dispatch_ready_poll(struct us_poll_t *p, int error, int eof, in
 
                 s = s->ssl ? us_internal_ssl_on_writable(s) : us_dispatch_writable(s);
                 /* After socket adoption, track the new socket; the old one becomes invalid */
-                if(s && s->flags.adopted && s->prev) {
-                    s = s->prev;
-                }
+                s = us_internal_socket_follow_adopted(s);
 
                 if (!s || us_socket_is_closed(s)) {
                     return;
@@ -724,9 +718,7 @@ void us_internal_dispatch_ready_poll(struct us_poll_t *p, int error, int eof, in
                         s = s->ssl ? us_internal_ssl_on_data(s, loop->data.recv_buf + LIBUS_RECV_BUFFER_PADDING, length)
                                    : us_dispatch_data(s, loop->data.recv_buf + LIBUS_RECV_BUFFER_PADDING, length);
                         /* After socket adoption, track the new socket; the old one becomes invalid */
-                        if(s && s->flags.adopted && s->prev) {
-                            s = s->prev;
-                        }
+                        s = us_internal_socket_follow_adopted(s);
                         read_any = 1;
                         // loop->num_ready_polls isn't accessible on Windows.
                         #ifndef WIN32