Respect narrowed buffers when parsing JSON (bug#77325)

* src/json.c (Fjson_insert): Simplify 'memcpy' argument.
(Fjson_parse_buffer): Only read to ZV, not all the way to Z.
* test/src/json-tests.el (with-all-gap-positions-in-temp-buffer):
New macro.
(json-parse-buffer/restricted): New test.

1 files changed, 26 insertions, 0 deletions

diff --git a/test/src/json-tests.el b/test/src/json-tests.el
index 94b6cfcffca..1cb667ddeac 100644
--- a/test/src/json-tests.el
+++ b/test/src/json-tests.el
@@ -315,6 +315,32 @@ Test with both unibyte and multibyte strings."
     (should-not (bobp))
     (should (looking-at-p (rx " [456]" eos)))))
 
+(defmacro with-all-gap-positions-in-temp-buffer (string &rest body)
+  "Create a temporary buffer containing STRING, and evaluate BODY
+with each possible gap position.
+See also `with-temp-buffer'."
+  `(with-temp-buffer
+     (insert ,string)
+     (dotimes (i (- (point-max) (point-min)))
+       (goto-char (- (point-max) i))
+       (insert "X")
+       (delete-region (1- (point)) (point))
+       ,@body)))
+
+(ert-deftest json-parse-buffer/restricted ()
+  (with-all-gap-positions-in-temp-buffer
+   "[123] [456] [789]"
+   (pcase-dolist (`((,beg . ,end) ,result)
+                  '(((7 . 12) [456])
+                    ((1 . 6) [123])
+                    ((13 . 18) [789])))
+     (goto-char beg)
+     (narrow-to-region beg end)
+     (should (equal (json-parse-buffer) result))
+     (should (= (point) end))
+     (should-error (json-parse-buffer) :type 'json-end-of-file)
+     (widen))))
+
 (ert-deftest json-parse-with-custom-null-and-false-objects ()
   (let* ((input
           "{ \"abc\" : [9, false] , \"def\" : null }")