Re: [Qemu-devel] [PATCH 41/56] json: Nicer recovery from invalid leading zero

[Eric Blake]

On 08/08/2018 07:03 AM, Markus Armbruster wrote:
> For input 0123, the lexer produces the tokens
>
>      JSON_ERROR    01
>      JSON_INTEGER  23
>
> Reporting an error is correct; 0123 is invalid according to RFC 7159.
> But the error recovery isn't nice.
>
> Make the finite state machine eat digits before going into the error
> state.  The lexer now produces
>
>      JSON_ERROR    0123
>
> Signed-off-by: Markus Armbruster <address@hidden>
> ---
>   qobject/json-lexer.c | 7 ++++++-
>   1 file changed, 6 insertions(+), 1 deletion(-)

> @@ -158,10 +159,14 @@ static const uint8_t json_lexer[][256] =  {
>       /* Zero */
>       [IN_ZERO] = {
>           TERMINAL(JSON_INTEGER),
> -        ['0' ... '9'] = IN_ERROR,
> +        ['0' ... '9'] = IN_BAD_ZERO,
>           ['.'] = IN_MANTISSA,
>       },
>   
> +    [IN_BAD_ZERO] = {
> +        ['0' ... '9'] = IN_BAD_ZERO,
> +    },
> +

Should IN_BAD_ZERO also consume '.' and/or 'e' (after all, '01e2 is a 
valid C constant, but not a valid JSON literal)?  But I think your 
choice here is fine (again, add too much, and then the lexer has to 
track a lot of state; whereas this minimal addition catches the most 
obvious things with little effort).

Reviewed-by: Eric Blake <address@hidden>

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