[PATCH 1/1] sscanf: implement basic character sets

[PATCH 1/1] sscanf: implement basic character sets

[Jessica Yu]

Implement basic character sets for the '%[]' conversion specifier.

The '%[]' conversion specifier matches a nonempty sequence of characters
from the specified set of accepted (or with '^', rejected) characters
between the brackets. The substring matched is to be made up of characters
in (or not in) the set. This implementation differs from its glibc
counterpart in that it does not support character ranges (e.g., 'a-z' or
'0-9'), the hyphen '-' is *not* a special character, and the brackets
themselves cannot be matched.

Signed-off-by: Jessica Yu <jeyu@redhat.com>
---
 lib/vsprintf.c | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 525c8e1..6ee3e7f 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -2714,6 +2714,41 @@ int vsscanf(const char *buf, const char *fmt, va_list args)
 			num++;
 		}
 		continue;
+		case '[':
+		{
+			char *s = (char *)va_arg(args, char *);
+			char set[U8_MAX] = { 0 };
+			size_t (*op)(const char *str, const char *set);
+			size_t len = 0;
+			bool negate = (*(fmt) == '^');
+
+			if (field_width == -1)
+				field_width = SHRT_MAX;
+
+			op = negate ? &strcspn : &strspn;
+			if (negate)
+				fmt++;
+
+			len = strcspn(fmt, "]");
+			/* invalid format; stop here */
+			if (!len)
+				return num;
+
+			strncpy(set, fmt, len);
+			/* advance fmt past ']' */
+			fmt += len + 1;
+
+			len = (*op)(str, set);
+			/* no matches */
+			if (!len)
+				return num;
+
+			while (*str && len-- && field_width--)
+				*s++ = *str++;
+			*s = '\0';
+			num++;
+		}
+		continue;
 		case 'o':
 			base = 8;
 			break;
-- 
2.4.3

Re: [PATCH 1/1] sscanf: implement basic character sets

[Andy Shevchenko]

On Fri, 2016-02-19 at 20:22 -0500, Jessica Yu wrote:
> Implement basic character sets for the '%[]' conversion specifier.
> 
> The '%[]' conversion specifier matches a nonempty sequence of
> characters
> from the specified set of accepted (or with '^', rejected) characters
> between the brackets. The substring matched is to be made up of
> characters
> in (or not in) the set. This implementation differs from its glibc
> counterpart in that it does not support character ranges (e.g., 'a-z' 
> or
> '0-9'), the hyphen '-' is *not* a special character, and the brackets
> themselves cannot be matched.
> 
> Signed-off-by: Jessica Yu <jeyu@redhat.com>
> ---
>  lib/vsprintf.c | 35 +++++++++++++++++++++++++++++++++++
>  1 file changed, 35 insertions(+)
> 
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index 525c8e1..6ee3e7f 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -2714,6 +2714,41 @@ int vsscanf(const char *buf, const char *fmt,
> va_list args)
>  			num++;
>  		}
>  		continue;
> +		case '[':
> +		{
> +			char *s = (char *)va_arg(args, char *);
> +			char set[U8_MAX] = { 0 };

Hmm... 255 on stack, not the best idea.

> +			size_t (*op)(const char *str, const char
> *set);
> +			size_t len = 0;
> +			bool negate = (*(fmt) == '^');
> +
> +			if (field_width == -1)
> +				field_width = SHRT_MAX;
> +
> +			op = negate ? &strcspn : &strspn;
> +			if (negate)
> +				fmt++;
> +
> +			len = strcspn(fmt, "]");
> +			/* invalid format; stop here */
> +			if (!len)
> +				return num;
> +
> +			strncpy(set, fmt, len);

Perhaps here you may allocate memory on heap and copy the given set.
IIRC kstrndup() does this.

> +			/* advance fmt past ']' */
> +			fmt += len + 1;
> +
> +			len = (*op)(str, set);
> +			/* no matches */
> +			if (!len)
> +				return num;
> +
> +			while (*str && len-- && field_width--)
> +				*s++ = *str++;
> +			*s = '\0';
> +			num++;
> +		}
> +		continue;
>  		case 'o':
>  			base = 8;
>  			break;

-- 
Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Intel Finland Oy

Re: sscanf: implement basic character sets

[Jessica Yu]

+++ Andy Shevchenko [22/02/16 12:13 +0200]:
>On Fri, 2016-02-19 at 20:22 -0500, Jessica Yu wrote:
>> Implement basic character sets for the '%[]' conversion specifier.
>>
>> The '%[]' conversion specifier matches a nonempty sequence of
>> characters
>> from the specified set of accepted (or with '^', rejected) characters
>> between the brackets. The substring matched is to be made up of
>> characters
>> in (or not in) the set. This implementation differs from its glibc
>> counterpart in that it does not support character ranges (e.g., 'a-z'
>> or
>> '0-9'), the hyphen '-' is *not* a special character, and the brackets
>> themselves cannot be matched.
>>
>> Signed-off-by: Jessica Yu <jeyu@redhat.com>
>> ---
>>  lib/vsprintf.c | 35 +++++++++++++++++++++++++++++++++++
>>  1 file changed, 35 insertions(+)
>>
>> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
>> index 525c8e1..6ee3e7f 100644
>> --- a/lib/vsprintf.c
>> +++ b/lib/vsprintf.c
>> @@ -2714,6 +2714,41 @@ int vsscanf(const char *buf, const char *fmt,
>> va_list args)
>>  			num++;
>>  		}
>>  		continue;
>> +		case '[':
>> +		{
>> +			char *s = (char *)va_arg(args, char *);
>> +			char set[U8_MAX] = { 0 };
>
>Hmm... 255 on stack, not the best idea.
>
>> +			size_t (*op)(const char *str, const char
>> *set);
>> +			size_t len = 0;
>> +			bool negate = (*(fmt) == '^');
>> +
>> +			if (field_width == -1)
>> +				field_width = SHRT_MAX;
>> +
>> +			op = negate ? &strcspn : &strspn;
>> +			if (negate)
>> +				fmt++;
>> +
>> +			len = strcspn(fmt, "]");
>> +			/* invalid format; stop here */
>> +			if (!len)
>> +				return num;
>> +
>> +			strncpy(set, fmt, len);
>
>Perhaps here you may allocate memory on heap and copy the given set.
>IIRC kstrndup() does this.

Thanks for the comments Andy. I did in fact use kstrndup() originally,
but I was not sure about error handling. i.e., if kstrndup() fails we
normally return -ENOMEM, but in this case I suppose sscanf() could
just fail and return num?

Thanks,
Jessica