tal: add tal_expand().

Helper to reallocate and append to an array.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

ccan/tal/tal.c

@@ -712,6 +712,37 @@ bool tal_resize_(tal_t **ctxp, size_t size, size_t count)
 	return true;
 }
 
+bool tal_expand_(tal_t **ctxp, const void *src, size_t size, size_t count)
+{
+	struct length *l;
+	bool ret = false;
+
+	l = find_property(debug_tal(to_tal_hdr(*ctxp)), LENGTH);
+
+	/* Check for additive overflow */
+	if (l->count + count < count) {
+		call_error("dup size overflow");
+		goto out;
+	}
+
+	/* Don't point src inside thing we're expanding! */
+	assert(src < *ctxp
+	       || (char *)src >= (char *)(*ctxp) + (size * l->count));
+
+	/* Note: updates l->count. */
+	if (!tal_resize_(ctxp, size, l->count + count))
+		goto out;
+
+	memcpy((char *)*ctxp + size * (l->count - count),
+	       src, count * size);
+	ret = true;
+
+out:
+	if (taken(src))
+		tal_free(src);
+	return ret;
+}
+
 void *tal_dup_(const tal_t *ctx, const void *p, size_t size,
 	       size_t n, size_t extra, bool add_count,
 	       const char *label)

ccan/tal/tal.h

@@ -305,6 +305,28 @@ void tal_set_backend(void *(*alloc_fn)(size_t size),
 		     void (*free_fn)(void *),
 		     void (*error_fn)(const char *msg));
 
+/**
+ * tal_expand - expand a tal array with contents.
+ * @a1p: a pointer to the tal array to expand.
+ * @a2: the second array (can be take()).
+ * @num2: the number of elements in the second array.
+ *
+ * Note that *@a1 and @a2 should be the same type.  tal_count(@a1) will
+ * be increased by @num2.
+ *
+ * Example:
+ *	int *arr1 = tal_arrz(NULL, int, 2);
+ *	int arr2[2] = { 1, 3 };
+ *
+ *	tal_expand(&arr1, arr2, 2);
+ *	assert(tal_count(arr1) == 4);
+ *	assert(arr1[2] == 1);
+ *	assert(arr1[3] == 3);
+ */
+#define tal_expand(a1p, a2, num2)				\
+	tal_expand_((void **)(a1p), (a2), sizeof**(a1p),	\
+		    (num2) + 0*sizeof(*(a1p) == (a2)))
+
 
 /**
  * tal_check - set the allocation or error functions to use
@@ -374,6 +396,7 @@ void *tal_dup_(const tal_t *ctx, const void *p, size_t size,
 tal_t *tal_steal_(const tal_t *new_parent, const tal_t *t);
 
 bool tal_resize_(tal_t **ctxp, size_t size, size_t count);
+bool tal_expand_(tal_t **ctxp, const void *src, size_t size, size_t count);
 
 bool tal_add_destructor_(const tal_t *ctx, void (*destroy)(void *me));
 bool tal_del_destructor_(const tal_t *ctx, void (*destroy)(void *me));

ccan/tal/test/run-expand.c

+#include <ccan/tal/tal.h>
+#include <ccan/tal/tal.c>
+#include <ccan/tap/tap.h>
+
+int main(void)
+{
+	int *a;
+	const int arr[] = { 1, 2 };
+
+	plan_tests(13);
+
+	a = tal_arrz(NULL, int, 1);
+	ok1(a);
+
+	ok1(tal_expand(&a, arr, 2));
+	ok1(tal_count(a) == 3);
+	ok1(a[0] == 0);
+	ok1(a[1] == 1);
+	ok1(a[2] == 2);
+
+	ok1(tal_expand(&a, take(tal_arrz(NULL, int, 1)), 1));
+	ok1(tal_count(a) == 4);
+	ok1(a[0] == 0);
+	ok1(a[1] == 1);
+	ok1(a[2] == 2);
+	ok1(a[3] == 0);
+	ok1(tal_first(NULL) == a && !tal_next(NULL, a));
+
+	tal_free(a);
+
+	return exit_status();
+}

ccan/tal/test/run-overflow.c

@@ -13,8 +13,9 @@ int main(void)
 {
 	void *p;
 	int *pi, *origpi;
+	char *cp;
 
-	plan_tests(26);
+	plan_tests(30);
 
 	tal_set_backend(NULL, NULL, NULL, my_error);
 
@@ -81,5 +82,17 @@ int main(void)
 	ok1(error_count == 1);
 	ok1(!tal_first(NULL));
 
+	/* Overflow on expand addition. */
+	cp = tal_arr(p, char, 100);
+	ok1(!tal_expand(&cp, NULL, (size_t)-99UL));
+	ok1(error_count == 2);
+	tal_free(cp);
+
+	/* Overflow when multiplied by size */
+	origpi = tal_arr(NULL, int, 100);
+	ok1(!tal_expand(&origpi, NULL, (size_t)-1UL / sizeof(int)));
+	ok1(error_count == 3);
+	tal_free(origpi);
+
 	return exit_status();
 }