value: fix accessing array indexes with non-numeric values

Since libjson-c's json_object_get_int64() returns 0 for any input value
that has no integer representation, any kind of invalid array index
incorrectly yielded the first array element.

Fix this issue by explicitly converting string values and by rejecting
any other kind of value.

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

2 files changed, 36 insertions, 3 deletions

diff --git a/tests/03_bugs/09_reject_invalid_array_indexes b/tests/03_bugs/09_reject_invalid_array_indexes
new file mode 100644
index 0000000..a7e5272
--- /dev/null
+++ b/tests/03_bugs/09_reject_invalid_array_indexes
@@ -0,0 +1,25 @@
+Since libjson-c's json_object_get_int64() returns 0 for any input value
+that has no integer representation, any kind of invalid array index
+incorrectly yielded the first array element.
+
+-- Testcase --
+{%
+	x = [1, 2, 3];
+
+	print([
+		x[1],
+		x["1"],
+		x[1.0],
+		x[1.1],
+		x.foo,
+		x["foo"],
+		x["0abc"],
+		x[x],
+		x[{ foo: true }]
+	], "\n");
+%}
+-- End --
+
+-- Expect stdout --
+[ 2, 2, 2, null, null, null, null, null, null ]
+-- End --
diff --git a/value.c b/value.c
index 18b7a5e..4312135 100644
--- a/value.c
+++ b/value.c
@@ -205,6 +205,7 @@ uc_getval(json_object *scope, json_object *key)
 	const char *k;
 	int64_t idx;
 	double d;
+	char *e;
 
 	if (json_object_is_type(scope, json_type_array)) {
 		/* only consider doubles with integer values as array keys */
@@ -216,13 +217,20 @@ uc_getval(json_object *scope, json_object *key)
 			else
 				idx = -1;
 		}
-		else {
-			errno = 0;
+		else if (json_object_is_type(key, json_type_int)) {
 			idx = json_object_get_int64(key);
+		}
+		else if (json_object_is_type(key, json_type_string)) {
+			errno = 0;
+			k = json_object_get_string(key);
+			idx = strtoll(k, &e, 0);
 
-			if (errno != 0)
+			if (errno != 0 || e == k || *e != 0)
 				idx = -1;
 		}
+		else {
+			idx = -1;
+		}
 
 		if (idx >= 0 && idx < json_object_array_length(scope))
 			return json_object_get(json_object_array_get_idx(scope, idx));