Merge pull request #270 from eriksjolund/check_num_remaining_bytes_of_escaped_json_character

Check num remaining bytes of escaped json character

c++/src/capnp/compat/json-test.c++

@@ -410,6 +410,7 @@ KJ_TEST("basic json decoding") {
     KJ_EXPECT_THROW_MESSAGE("Unexpected input", json.decodeRaw("a", root));
     KJ_EXPECT_THROW_MESSAGE("ends prematurely", json.decodeRaw("[", root));
     KJ_EXPECT_THROW_MESSAGE("ends prematurely", json.decodeRaw("{", root));
+    KJ_EXPECT_THROW_MESSAGE("ends prematurely", json.decodeRaw("\"\\u\"", root));
     KJ_EXPECT_THROW_MESSAGE("Unexpected input", json.decodeRaw("[}", root));
     KJ_EXPECT_THROW_MESSAGE("Unexpected input", json.decodeRaw("{]", root));
     KJ_EXPECT_THROW_MESSAGE("Unexpected input", json.decodeRaw("[}]", root));

c++/src/capnp/compat/json.c++

@@ -616,6 +616,7 @@ public:
           case 't' : decoded.add('\t'); advance(); break;
           case 'u' :
             advance();  // consume 'u'
+            KJ_REQUIRE(remaining.size() >= 4, "JSON message ends prematurely.");
             unescapeAndAppend(kj::arrayPtr(remaining.begin(), 4), decoded);
             advance(4);
             break;