Support for the Ruby 2.2 series has ended. See here for reference.
Raw Strings are JSON Objects (the raw bytes are stored in an array for the key “raw”). The Ruby String can be created by this module method.
static VALUE mString_Extend_json_create(VALUE self, VALUE o) { VALUE ary; Check_Type(o, T_HASH); ary = rb_hash_aref(o, rb_str_new2("raw")); return rb_funcall(ary, i_pack, 1, rb_str_new2("C*")); }