lib: make map_contains recongize null value

Without changing the interface, map_contains is able to tell whether the item exist in map or not.

More about the intension: module stats use map internally, metric with zero value is not being able to retrieve by stats_get since map_contains checks the return value against NULL.

lib/generic/map.c

@@ -118,24 +118,7 @@ static cb_data_t *cbt_make_data(map_t *map, const uint8_t *str, size_t len, void
return x;
}
-/*! Creates a new, empty critbit map */
-EXPORT map_t map_make(void)
-{
-	map_t map;
-	map.root = NULL;
-	map.malloc = &malloc_std;
-	map.free = &free_std;
-	map.baton = NULL;
-	return map;
-}
-
-/*! Returns non-zero if map contains str */
-EXPORT int map_contains(map_t *map, const char *str)
-{
-	return map_get(map, str) != NULL;
-}
-
-EXPORT void *map_get(map_t *map, const char *str)
+static int cbt_get(map_t *map, const char *str, void **value)
{
const uint8_t *ubytes = (void *)str;
const size_t ulen = strlen(str);
@@ -143,7 +126,7 @@ EXPORT void *map_get(map_t *map, const char *str)
cb_data_t *x = NULL;
if (p == NULL) {
-		return NULL;
+		return 0;
}
while (ref_is_internal(p)) {
@@ -161,10 +144,37 @@ EXPORT void *map_get(map_t *map, const char *str)
x = (cb_data_t *)p;
if (strcmp(str, (const char *)x->key) == 0) {
-		return x->value;
+		if (value != NULL) {
+			*value = x->value;
+		}
+		return 1;
}
-	return NULL;
+	return 0;
+}
+
+/*! Creates a new, empty critbit map */
+EXPORT map_t map_make(void)
+{
+	map_t map;
+	map.root = NULL;
+	map.malloc = &malloc_std;
+	map.free = &free_std;
+	map.baton = NULL;
+	return map;
+}
+
+/*! Returns non-zero if map contains str */
+EXPORT int map_contains(map_t *map, const char *str)
+{
+	return cbt_get(map, str, NULL);
+}
+
+EXPORT void *map_get(map_t *map, const char *str)
+{
+	void *v = NULL;
+	cbt_get(map, str, &v);
+	return v;
}
/*! Inserts str into map, returns 0 on success */