Re: [Libexif-devel] Error handling: proposal

[Jan P. <pa...@pi...>]

Hi Lutz,

> On Wed, 2005-03-30 at 19:23 +0200, Jan Patera wrote:
>> should I understand it as you are strictly against completion codes
>> returned by exif functions?
>
> No, not at all. All I wanted to do is to make people aware of the limit=
s
> of error codes.
>
> Let's say we define EXIF_RESULT_OK, EXIF_RESULT_SOMEWHAT_OK and
> EXIF_RESULT_NOT_OK. What code should libexif return if it encounters an
> unknown tag or a wrong format on loading?

EXIF_RESULT_UNKNOWN_TAG and EXIF_RESULT_WRONG_TAG_FORMAT,
EXIF_RESULT_WRONG_SOMETHING_FORMAT and
EXIF_RESULT_WRONG_SOMETHING_ELSE_FORMAT. Depending on the situation.
There would be as many values as needed.

The values could be like SCODE/HRESULT in COM and similar interfaces:
some bits would indicate success/warning/error and some bits
what actually happened. There would be macros for simple checks
if (fatal) error or warning occured.

//  Values are 32 bit values layed out as follows:
//
//   3 3 2 2 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 1 1
//   1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0
//  +---+-+-+-----------------------+-------------------------------+
//  |Sev|   |     Facility          |               Code            |
//  +---+-+-+-----------------------+-------------------------------+
//
//  where
//      Sev - is the severity code
//          00 - Success
//          01 - Informational
//          10 - Warning
//          11 - Error
//      Facility - is the facility code
//      Code - is the facility's status code

#define EXIF_ERROR  0xC0000000
#define EXIF_WARN   0x80000000

Examples:
#define EXIF_FAILED(x)  (((x) & 0xC0000000) =3D=3D EXIF_ERROR) ? TRUE : F=
ALSE)
#define EXIF_ALMOST_OK(x) (((x) & 0xC0000000) =3D=3D EXIF_WARN) ? TRUE : =
FALSE)
#define EXIF_NO_MEMORY(x) (((x) & 0xFFFF) =3D=3D EXIF_CODE_NOMEMORY) ? TR=
UE :
FALSE)

// START of internal values
#define EXIF_CODE_NOMEMORY       1
#define EXIF_CODE_CANT_OPEN      2
#define EXIF_CODE_NO_DATA        3
#define EXIF_FAC_IFD      0x10000  // IFD parser
#define EXIF_FAC_LOADER   0x20000  // JPEG loader
#define EXIF_FAC_MNOTE    0x30000
// END of internal values

#define EX_MNOTE_NO_MEMORY   (EXIF_FAC_MNOTE | EXIF_EXIF_CODE_NOMEMORY)
#define EX_LOADER_NO_MEMORY  (EXIF_FAC_LOADER | EXIF_CODE_NOMEMORY)
#define EX_LOADER_NO_MEMORY_FATAL (EXIF_FAC_LOADER | EXIF_CODE_NOMEMORY |
EXIF_ERROR)
#define EX_CANNOT_OPEN_FILE  (EXIF_FAC_LOADER | EXIF_CODE_CANT_OPEN |
EXIF_ERROR)
#define EX_WRONG_TAG_FORMAT  (EXIF_WARN | EXIF_FAC_IFD |
EXIF_CODE_WRONG_FORMAT)
#define EX_WRONG_IFD_FORMAT  (EXIF_WARN | EXIF_FAC_LOADER |
EXIF_CODE_WRONG_FORMAT)
#define EX_WRONG_MNOTE_FORMAT (EXIF_WAR | EXIF_FAC_MNOTE |
EXIF_CODE_WRONG_FORMAT)
#define EX_NO_EXIF_DATA      (EXIF_WARN | EXIF_FAC_LOADER |
EXIF_CODE_NO_DATA)

Amd of course also this one ;-)
#define EX_OK     0

All relevant "returns;"'s would be replaced with appropriate
"return EX_CANNOT_OPEN_FILE;" or "return EX_WRONG_MNOTE_FORMAT;"

Quite powerfull bit-mask macros with mininum overhead in libEXIF
(just changed returns) giving lots of information.

 I hope you've got the idea ;-)
How do you (and also others) like it?

 --- Jan