Re: [Qemu-devel] [PATCH 28/56] json: Fix \uXXXX for surrogate pairs

[Eric Blake]

On 08/08/2018 07:03 AM, Markus Armbruster wrote:
> The JSON parser treats each half of a surrogate pair as unpaired
> surrogate.  Fix it to recognize surrogate pairs.
>
> Signed-off-by: Markus Armbruster <address@hidden>
> ---
>   qobject/json-parser.c | 16 +++++++++++++++-
>   tests/check-qjson.c   |  3 +--
>   2 files changed, 16 insertions(+), 3 deletions(-)

> @@ -168,6 +170,18 @@ static QString *parse_string(JSONParserContext *ctxt, 
> JSONToken *token)
>                       cp |= hex2decimal(*ptr);
>                   }
>   
> +                if (cp >= 0xD800 && cp <= 0xDBFF && !leading_surrogate
> +                    && ptr[1] == '\\' && ptr[2] == 'u') {
> +                    ptr += 2;
> +                    leading_surrogate = cp;
> +                    goto hex;
> +                }
> +                if (cp >= 0xDC00 && cp <= 0xDFFF && leading_surrogate) {
> +                    cp &= 0x3FF;
> +                    cp |= (leading_surrogate & 0x3FF) << 10;
> +                    cp += 0x010000;
> +                }
> +
>                   if (mod_utf8_encode(utf8_buf, sizeof(utf8_buf), cp) < 0) {
>                       parse_error(ctxt, token,
>                                   "\\u%.4s is not a valid Unicode character",

Consider "\\udbff\\udfff" - a valid surrogate pair (in terms of being in 
range), but which decodes to u+10ffff.  Since is_valid_codepoint() (part 
of mod_utf8_encode()) rejects it due to (codepoint & 0xfffe) == 0xfffe, 
it means we end up printing this error message, but only using the 
second half of the surrogate pair.  Is that okay?

Otherwise,
Reviewed-by: Eric Blake <address@hidden>

--
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org