Merge pull request #1484 from fjmilens3/string_start_with

Bug in String#start_with? resulting from incorrect length determination

2 files changed, 8 insertions, 5 deletions

diff --git a/mrbgems/mruby-string-ext/src/string.c b/mrbgems/mruby-string-ext/src/string.c
index edebcecbc..33ed3095b 100644
--- a/mrbgems/mruby-string-ext/src/string.c
+++ b/mrbgems/mruby-string-ext/src/string.c
@@ -107,6 +107,7 @@ mrb_str_concat2(mrb_state *mrb, mrb_value self)
  *    # returns true if one of the prefixes matches.
  *    "hello".start_with?("heaven", "hell")     #=> true
  *    "hello".start_with?("heaven", "paradise") #=> false
+ *    "h".start_with?("heaven", "hell")         #=> false
  */
 static mrb_value
 mrb_str_start_with(mrb_state *mrb, mrb_value self)
@@ -116,13 +117,14 @@ mrb_str_start_with(mrb_state *mrb, mrb_value self)
   mrb_get_args(mrb, "*", &argv, &argc);
 
   for (i = 0; i < argc; i++) {
-    size_t len_l, len_r, len_cmp;
+    size_t len_l, len_r;
     len_l = RSTRING_LEN(self);
     len_r = RSTRING_LEN(argv[i]);
-    len_cmp = (len_l > len_r) ? len_r : len_l;
-    if (memcmp(RSTRING_PTR(self), RSTRING_PTR(argv[i]), len_cmp) == 0) {
-      return mrb_true_value();
-    }  
+    if (len_l >= len_r) {
+      if (memcmp(RSTRING_PTR(self), RSTRING_PTR(argv[i]), len_r) == 0) {
+        return mrb_true_value();
+      }
+    }
   }
   return mrb_false_value();
 }
diff --git a/mrbgems/mruby-string-ext/test/string.rb b/mrbgems/mruby-string-ext/test/string.rb
index 9eb6f6aaa..79e4360b5 100644
--- a/mrbgems/mruby-string-ext/test/string.rb
+++ b/mrbgems/mruby-string-ext/test/string.rb
@@ -104,6 +104,7 @@ end
 assert('String#start_with?') do
   assert_true "hello".start_with?("heaven", "hell")
   assert_true !"hello".start_with?("heaven", "paradise")
+  assert_true !"h".start_with?("heaven", "hell")
 end
 
 assert('String#end_with?') do