Fix sliced string escaping

Author: tompng

java/src/json/ext/SWARBasicStringEncoder.java

@@ -27,9 +27,10 @@ void encode(ByteList src) throws IOException {
         // slice a string, the underlying byte array is the same, but the
         // begin index and real size are different. When reading from the ptrBytes
         // array, we need to always add ptr to the index.
-        ByteBuffer bb = ByteBuffer.wrap(ptrBytes, ptr, len);
+        ByteBuffer bb = ByteBuffer.wrap(ptrBytes, 0, ptr + len);
+
         while (pos + 8 <= len) {
-            long x = bb.getLong(pos);
+            long x = bb.getLong(ptr + pos);
             if (skipChunk(x)) {
                 pos += 8;
                 continue;
@@ -48,7 +49,7 @@ void encode(ByteList src) throws IOException {
         }
 
         if (pos + 4 <= len) {
-            int x = bb.getInt(pos);
+            int x = bb.getInt(ptr + pos);
             if (skipChunk(x)) {
                 pos += 4;
             }

test/json/json_encoding_test.rb

@@ -35,6 +35,8 @@ def test_generate_shared_string
     # Ref: https://github.com/ruby/json/issues/859
     s = "01234567890"
     assert_equal '"234567890"', JSON.dump(s[2..-1])
+    s = '01234567890123456789"a"b"c"d"e"f"g"h'
+    assert_equal '"\"a\"b\"c\"d\"e\"f\"g\""', JSON.dump(s[20, 15])
   end
 
   def test_unicode