From aa41d4cdd90259ea3eb0216d3ff5dc2853d304b4 Mon Sep 17 00:00:00 2001
From: Alexander Borisov <alexander.borisov@nginx.com>
Date: Tue, 16 Jul 2019 17:32:12 +0300
Subject: [PATCH] Fixed String.prototype.substring() with empty substring.

---
 njs/njs_string.c         | 4 ++--
 njs/test/njs_unit_test.c | 3 +++
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/njs/njs_string.c b/njs/njs_string.c
index e4ddd128..f2b65740 100644
--- a/njs/njs_string.c
+++ b/njs/njs_string.c
@@ -1357,10 +1357,10 @@ njs_string_slice_string_prop(njs_string_prop_t *dst,
         p = start;
         n = length;
 
-        do {
+        while (n != 0 && p < end) {
             p = nxt_utf8_next(p, end);
             n--;
-        } while (n != 0 && p < end);
+        }
 
         size = p - start;
         length -= n;
diff --git a/njs/test/njs_unit_test.c b/njs/test/njs_unit_test.c
index 860ab5a9..94be56d7 100644
--- a/njs/test/njs_unit_test.c
+++ b/njs/test/njs_unit_test.c
@@ -4822,6 +4822,9 @@ static njs_unit_test_t  njs_test[] =
     { nxt_string("'abcdefgh'.substring(100, 120)"),
       nxt_string("") },
 
+    { nxt_string("'α'.repeat(32).substring(32)"),
+      nxt_string("") },
+
     { nxt_string("'abcdefghijklmno'.slice(NaN, 5)"),
       nxt_string("abcde") },
 
-- 
2.47.3