Re: [Qemu-devel] [PATCH 06/10] json-parser: fix handling of large whole number values

[Laszlo Ersek <lersek@redhat.com>]

On 05/10/13 04:20, Michael Roth wrote:
> Currently our JSON parser assumes that numbers lacking a mantissa are
> integers and attempts to store them as QInt/int64 values. This breaks in
> the case where the number overflows/underflows int64 values (which is
> still valid JSON)
> 
> Fix this by detecting such cases and using a QFloat to store the value
> instead.
> 
> Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
> ---
>  qobject/json-parser.c |   26 +++++++++++++++++++++++---
>  1 file changed, 23 insertions(+), 3 deletions(-)
> 
> diff --git a/qobject/json-parser.c b/qobject/json-parser.c
> index 05279c1..4d14e71 100644
> --- a/qobject/json-parser.c
> +++ b/qobject/json-parser.c
> @@ -640,9 +640,29 @@ static QObject *parse_literal(JSONParserContext *ctxt)
>      case JSON_STRING:
>          obj = QOBJECT(qstring_from_escaped_str(ctxt, token));
>          break;
> -    case JSON_INTEGER:
> -        obj = QOBJECT(qint_from_int(strtoll(token_get_value(token), NULL, 10)));
> -        break;
> +    case JSON_INTEGER: {
> +        /* A possibility exists that this is a whole-valued float where the
> +         * mantissa was left out due to being 0 (.0). It's not a big deal to
> +         * treat these as ints in the parser, so long as users of the
> +         * resulting QObject know to expect a QInt in place of a QFloat in
> +         * cases like these.
> +         *
> +         * However, in some cases these values will overflow/underflow a
> +         * QInt/int64 container, thus we should assume these are to be handled
> +         * as QFloats/doubles rather than silently changing their values.
> +         *
> +         * strtoll() indicates these instances by setting errno to ERANGE
> +         */
> +        int64_t value;
> +
> +        errno = 0; /* strtoll doesn't set errno on success */
> +        value = strtoll(token_get_value(token), NULL, 10);
> +        if (errno != ERANGE) {
> +            obj = QOBJECT(qint_from_int(value));
> +            break;
> +        }
> +        /* fall through to JSON_FLOAT */
> +    }
>      case JSON_FLOAT:
>          /* FIXME dependent on locale */
>          obj = QOBJECT(qfloat_from_double(strtod(token_get_value(token), NULL)));
> 

I wanted to correct you here and propose s/mantissa/fractional part/
everywhere in this patch (including commit message and patch body).

However <http://en.wiktionary.org/wiki/mantissa> tells me one meaning of
"mantissa" *is* "fractional part".

In that sense I won't try to "correct" you, but can you consider doing
the replacement still, in order not to confuse non-native speakers who
associate "mantissa" only with the third meaning Wiktionary gives, ie.
the significand in FP representation?

Otherwise the v2 series looks good to me (not R-b-ing it since you'll
post v3 to address Amos's note).

Thanks,
Laszlo