Control characters should be allowed in strings as part of control sequences

[ovidiu-munteanu]

According to the ECMA-404 standard (see section 9 String) control characters are allowed within JSON strings as long as they are escaped correctly.

Therefore, the string regex given in this implementation is incorrect as it excludes control characters that should be accepted. There are also some additional errors as the \ character should itself be escaped within a JSON string.

A correct definition for JSON strings is given below:

\\ Exclude the code points for the characters that should be escaped
valid_set_char = [^\u0000-\u001F\"\\]

\\ But allow them as part of a valid escape sequence
valid_escape_seq = \\\" | \\\\ | \\/ | \\b | \\f | \\n | \\r | \\r | \\t | (\\u([0-9a-fA-F]{4}))

\\ Therefore, a valid string consists of any number of valid characters or valid escape sequences
valid_character = {valid_set_char} | {valid_escape_seq}

[kimeshan]

Nice catch, feel free to submit a PR with the fix!