--- /dev/null
+../../../licenses/BSD-MIT
\ No newline at end of file
--- /dev/null
+#include "config.h"
+#include <stdio.h>
+#include <string.h>
+
+/**
+ * tal/autoptr - automatic updates of pointers to tal objects.
+ *
+ * This code updates pointers when the pointed-to object is freed.
+ *
+ * Maintainer: Rusty Russell <rusty@rustcorp.com.au>
+ * License: BSD-MIT
+ * Example:
+ * #include <ccan/tal/autoptr/autoptr.h>
+ * #include <assert.h>
+ *
+ * static void *p;
+ *
+ * int main(void)
+ * {
+ * char *c = tal(NULL, char);
+ *
+ * // Sets p to point to c.
+ * autonull_set_ptr(NULL, &p, c);
+ * assert(p == c);
+ *
+ * // Automatically clears p.
+ * tal_free(c);
+ * assert(p == NULL);
+ * return 0;
+ * }
+ */
+int main(int argc, char *argv[])
+{
+ /* Expect exactly one argument */
+ if (argc != 2)
+ return 1;
+
+ if (strcmp(argv[1], "depends") == 0) {
+ printf("ccan/tal\n");
+ return 0;
+ }
+
+ return 1;
+}
--- /dev/null
+/* MIT (BSD) license - see LICENSE file for details */
+#include <ccan/tal/autoptr/autoptr.h>
+
+struct autonull {
+ void **pp;
+};
+
+static void autonull_remove(struct autonull *a);
+static void autonull_null_out(tal_t *p UNNEEDED, struct autonull *a)
+{
+ void **pp = a->pp;
+ tal_del_destructor(a, autonull_remove);
+ tal_free(a);
+ *pp = NULL;
+}
+
+static void autonull_remove(struct autonull *a)
+{
+ /* Don't NULL us out now. */
+ tal_del_destructor2(*a->pp, autonull_null_out, a);
+}
+
+struct autonull *autonull_set_ptr_(const tal_t *ctx, void *pp, const tal_t *p)
+{
+ struct autonull *a = tal(ctx, struct autonull);
+ a->pp = (void **)pp;
+ *a->pp = (void *)p;
+
+ /* If p is freed, NULL out a->pp */
+ tal_add_destructor2(*a->pp, autonull_null_out, a);
+
+ /* If they free autonull, it removes other destructor. */
+ tal_add_destructor(a, autonull_remove);
+ return a;
+}
--- /dev/null
+/* MIT (BSD) license - see LICENSE file for details */
+#ifndef CCAN_TAL_AUTOPTR_H
+#define CCAN_TAL_AUTOPTR_H
+#include <ccan/tal/tal.h>
+
+struct autonull;
+
+/**
+ * autonull_set_ptr - set a pointer, NULL it when pointer tal_free'd.
+ * @ctx: the tal context which owns this autonull.
+ * @pp: pointer to tal pointer
+ * @p: the tal pointer to set *@pp to.
+ *
+ * *@pp is set to @p. When @p is tal_free'd directly or indirectly, *@pp will
+ * be set to NULL. Or, if the returned object is freed, the callback is
+ * deactivated.
+ *
+ * Example:
+ * struct parent {
+ * struct child *c;
+ * };
+ * struct child {
+ * const char *name;
+ * };
+ *
+ * int main(void)
+ * {
+ * struct parent *p = tal(NULL, struct parent);
+ * struct child *c = tal(p, struct child);
+ * c->name = "Child";
+ *
+ * autonull_set_ptr(p, &p->c, c);
+ * assert(p->c == c);
+ *
+ * // Automatically clears p->c.
+ * tal_free(c);
+ * assert(p->c == NULL);
+ * return 0;
+ * }
+ *
+ */
+#define autonull_set_ptr(ctx, pp, p) \
+ autonull_set_ptr_((ctx), (pp) + 0*sizeof(*(pp) = (p)), (p))
+
+struct autonull *autonull_set_ptr_(const tal_t *ctx, void *pp, const tal_t *p);
+
+#endif /* CCAN_TAL_AUTOPTR_H */
--- /dev/null
+#include <ccan/tal/autoptr/autoptr.h>
+/* Include the C files directly. */
+#include <ccan/tal/autoptr/autoptr.c>
+#include <ccan/tap/tap.h>
+
+int main(void)
+{
+ char *p1, *p2, *p3;
+ struct autonull *a;
+
+ /* This is how many tests you plan to run */
+ plan_tests(8);
+
+ p1 = tal(NULL, char);
+
+ // Sets p1 to point to p2.
+ autonull_set_ptr(NULL, &p2, p1);
+ ok1(p2 == p1);
+ tal_free(p1);
+ ok1(p2 == NULL);
+
+ // Using p1 as the parent is the same. */
+ p1 = tal(NULL, char);
+ autonull_set_ptr(p1, &p2, p1);
+ ok1(p2 == p1);
+ tal_free(p1);
+ ok1(p2 == NULL);
+
+ // Freeing autodata deactivates it.
+ p1 = tal(NULL, char);
+ a = autonull_set_ptr(NULL, &p2, p1);
+ ok1(p2 == p1);
+ tal_free(a);
+ tal_free(p1);
+ ok1(p2 == p1);
+
+ // Making p3 the parent means freeing p3 deactivates it.
+ p3 = tal(NULL, char);
+ p1 = tal(NULL, char);
+ autonull_set_ptr(p3, &p2, p1);
+ ok1(p2 == p1);
+ tal_free(p3);
+ tal_free(p1);
+ ok1(p2 == p1);
+
+
+ /* This exits depending on whether all tests passed */
+ return exit_status();
+}