buffer: fix UCS2 indexOf for odd buffer length

Fix `buffer.indexOf` for the case that the haystack has odd length
and the needle is not found in it. `StringSearch()` would return
the length of the buffer in multiples of `sizeof(uint16_t)`, but
checking that against `haystack_length` would not work if the latter
one was odd.

PR-URL: #6511
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Trevor Norris <trev.norris@gmail.com>

src/node_buffer.cc

@@ -994,7 +994,9 @@ void IndexOfString(const FunctionCallbackInfo<Value>& args) {
   bool is_forward = args[4]->IsTrue();
 
   const char* haystack = ts_obj_data;
-  const size_t haystack_length = ts_obj_length;
+  // Round down to the nearest multiple of 2 in case of UCS2.
+  const size_t haystack_length = (enc == UCS2) ?
+      ts_obj_length &~ 1 : ts_obj_length;  // NOLINT(whitespace/operators)
 
   const size_t needle_length =
       StringBytes::Size(args.GetIsolate(), needle, enc);

test/parallel/test-buffer-indexof.js

@@ -228,6 +228,9 @@ assert.strictEqual(Buffer.from('aaaa').indexOf('a'.repeat(4), 'ucs2'), -1);
 assert.strictEqual(Buffer.from('aaaa').indexOf('a'.repeat(4), 'utf8'), 0);
 assert.strictEqual(Buffer.from('aaaa').indexOf('你好', 'ucs2'), -1);
 
+// Haystack has odd length, but the needle is UCS2.
+assert.strictEqual(Buffer.from('aaaaa').indexOf('b', 'ucs2'), -1);
+
 {
   // Find substrings in Utf8.
   const lengths = [1, 3, 15];  // Single char, simple and complex.