lib: extend length() to handle objects

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

2 files changed, 28 insertions, 3 deletions

diff --git a/README.md b/README.md
index 1a2051f..97fbe94 100644
--- a/README.md
+++ b/README.md
@@ -637,10 +637,23 @@ if the given argument is no object.
 Convert the given string to lowercase and return the resulting string.
 Returns `null` if the given argument could not be converted to a string.
 
-#### 6.18. `length(arr_or_str)`
+#### 6.18. `length(x)`
 
-Return the length of the given array or string. Returns `null` if the given
-argument is neither an array, nor a string.
+Return the length of the given object, array or string. Returns `null` if
+the given argument is neither an object, array, nor a string.
+
+For objects, the length is defined as the number of keys within the object,
+for arrays the length specifies the amount of contained items and for strings
+it represents the number of contained bytes.
+
+```javascript
+length("test")                             // 4
+length([true, false, null, 123, "test"])   // 5
+length({foo: true, bar: 123, baz: "test"}) // 3
+length({})                                 // 0
+length(true)                               // null
+length(10.0)                               // null
+```
 
 #### 6.19. `log(x)`
 
diff --git a/lib.c b/lib.c
index f878d5c..af94e9a 100644
--- a/lib.c
+++ b/lib.c
@@ -368,8 +368,20 @@ static struct json_object *
 ut_length(struct ut_state *s, uint32_t off, struct json_object *args)
 {
 	struct json_object *arg = json_object_array_get_idx(args, 0);
+	size_t len;
 
 	switch (json_object_get_type(arg)) {
+	case json_type_object:
+		len = 0;
+
+		json_object_object_foreach(arg, k, v) {
+			(void)k;
+			(void)v;
+			len++;
+		}
+
+		return xjs_new_int64(len);
+
 	case json_type_array:
 		return xjs_new_int64(json_object_array_length(arg));