Error: Extensible error handling.
[Query Object Framework]

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Detailed Description

QofError supports the creation of new error codes (complete with error strings) along the lines of GdaError. Applications and backends can generate their own QofError values and register them with QofError. Any function can then set this error value and retrieve the error with qof_error_get_id or qof_error_get_message. The main advantage is that applications can set error states that are unrelated to the old QofBackendError values but retrieve all errors in the same manner.

• Use QofLog to record information for programmers and maintainers.
• Use QofError to communicate descriptive error messages to the user.

An error must be registered to be set. Registered errors can be set repeatedly into an error stack for the relevant session. Setting an error copies the registered error to the error stack and sets a time index in the copy.

Once an error has been unregistered, it cannot be set later. If the error has already been set on the error stack, the stack is not changed and the error remains readable.

Each error stack is specific to one QofSession.

Registered errors can be set in any session (if the QofErrorId is known) but most errors are specific to one session.

Applications can register new error values with qof_error_register passing the error message string, already marked for translation - a new QofErrorId will be returned. Error values are unregistered when the session ends or can be unregistered manually.

Each backend can also generate specific QofError values, in which case the translation is done within QOF.

Set an error by passing the QofErrorId (or the deprecated QofBackendError) to qof_error_set.

To check the error condition use qof_error_check - if an error has been set, qof_error_check returns the QofErrorId of that error without clearing the error from the stack.

To retrieve an error and clear it from the stack, use qof_error_get_id or qof_error_get_message.

Precise values of QofErrorId are not to be stored in applications as values (other than deprecated values) may change at any time.

There are no default errors - previous QofBackendError values are retained only as deprecated macros. Until libqof2, QofErrorId is guaranteed not to overlap a previous QofBackendError value but once deprecated code is removed in libqof2, any value can be used.

This deliberately makes it harder to re-use the same error time after time. The purpose is to encourage more detailed error reporting by supporting an unlimited number of error values.

Applications and backends can store the QofErrorId in a context or static values if the error must be set from multiple locations, otherwise an error can be registered and set locally.

If a subsystem or dependency generates an error message of it's own, this can also be passed to qof_error_register to generate a new error within the session, complete with the (translated) message direct from the subsystem. This increases the detail and clarity of the messages presented to the user. Programming errors and complex errors should still be logged using QofLog - QofError is for messages destined for the end user of the application using QOF.

Many applications already include message strings for the previous QofBackendError values but all are welcome to move to the new QofError strings.

QofError strings remain the property of QofError and should not be freed.

Since:

0.7.2

Files
file	qoferror.h
	Extensible error handling.
Defines
#define	QOF_MOD_ERROR   "qof-error-module"
#define	QOF_SUCCESS   0
#define	QOF_FATAL   -1
	general error value
Typedefs
typedef struct QofError_s	QofError
Functions
QofErrorId	qof_error_register (const gchar *err_message, gboolean use_file)
	Generate and register a new error.
void	qof_error_unregister (QofErrorId id)
	Unregister an error.
void	qof_error_set (QofSession *session, QofErrorId error)
	Add an error to the stack for this session.
void	qof_error_set_be (QofBackend *be, QofErrorId error)
void	qof_error_clear (QofSession *session)
	clear the error stack for the session.
QofErrorId	qof_error_check_be (QofBackend *be)
	Check for errors.
QofErrorId	qof_error_check (QofSession *session)
QofTime *	qof_error_get_time_be (QofBackend *be)
	Get the time of the most recent error.
QofTime *	qof_error_get_time (QofSession *session)
	Alternative for applications.
QofErrorId	qof_error_get_id_be (QofBackend *be)
	Pop the most recent error from the backend stack.
QofErrorId	qof_error_get_id (QofSession *session)
	Alternative for applications.
const gchar *	qof_error_get_message_be (QofBackend *be)
	Pop the most recent error and get the message.
const gchar *	qof_error_get_message (QofSession *session)
	Alternative for applications.

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Define Documentation

#define QOF_FATAL   -1

general error value

Can be returned by any function handling QofErrorId to indicate a fatal error, e.g. g_return_val_if_fail

Definition at line 131 of file qoferror.h.

#define QOF_MOD_ERROR   "qof-error-module"

QofError log_module name.

Definition at line 121 of file qoferror.h.

#define QOF_SUCCESS   0

success value

Definition at line 124 of file qoferror.h.

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Typedef Documentation

typedef struct QofError_s QofError

opaque QofError type.

Definition at line 118 of file qoferror.h.

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Function Documentation

QofErrorId qof_error_check

(

QofSession *

session

)

alternative for applications.

Definition at line 227 of file qoferror.c.

{
    g_return_val_if_fail (session, QOF_FATAL);
    return qof_error_check_be (session->backend);
}

QofErrorId qof_error_check_be

(

QofBackend *

be

)

Check for errors.

Parameters:

be

The backend to check.

Returns:

QOF_SUCCESS if no errors have been set, otherwise the QofErrorId of the most recently set error.

Definition at line 234 of file qoferror.c.

{
    QofError * qerr;
    GList * first;

    if (!be)
        return QOF_FATAL;
    if (g_list_length (be->error_stack) == 0)
        return QOF_SUCCESS;
    first = g_list_first (be->error_stack);
    qerr = (QofError*)first->data;
    if (!qerr)
        return QOF_FATAL;
    return qerr->id;
}

void qof_error_clear

(

QofSession *

session

)

clear the error stack for the session.

Applications should clear the stack once errors have been presented to the user.

Definition at line 209 of file qoferror.c.

{
    g_return_if_fail (session);
    if (!session->backend)
        return;
    g_list_foreach (session->backend->error_stack, clear_list, NULL);
    g_list_free (session->backend->error_stack);
    session->backend->error_stack = NULL;
    if (session->error_message)
        g_free (session->error_message);
    session->error_message = NULL;
    session->last_err = QOF_SUCCESS;
#ifndef QOF_DISABLE_DEPRECATED
    session->backend->last_err = QOF_SUCCESS;
#endif
}

QofErrorId qof_error_get_id_be

(

QofBackend *

be

)

Pop the most recent error from the backend stack.

Returns and clears the most recently set error for this backend, if any.

Parameters:

be

The Backend that recorded the error.

Returns:

QOF_SUCCESS if no errors have been set, otherwise the QofErrorId of the most recently set error.

Definition at line 314 of file qoferror.c.

{
    QofError * qerr;
    GList * first;

    if (!be)
        return QOF_FATAL;
    if (g_list_length (be->error_stack) == 0)
        return QOF_SUCCESS;
    first = g_list_first (be->error_stack);
    qerr = (QofError*)first->data;
    if (!qerr)
        return QOF_FATAL;
    be->error_stack = 
        g_list_remove (be->error_stack, qerr);
#ifndef QOF_DISABLE_DEPRECATED
    set_previous_error (be);
#endif
    return qerr->id;
}

const gchar* qof_error_get_message_be

(

QofBackend *

be

)

Pop the most recent error and get the message.

Clears the most recently set error for this backend and returns the error message, if any.

Parameters:

be

The Backend that recorded the error.

Returns:

NULL if no errors have been set, otherwise the translated message for the most recently set error.

Definition at line 364 of file qoferror.c.

{
    QofError * qerr;
    GList * first;

    g_return_val_if_fail (be, NULL);
    if (g_list_length (be->error_stack) == 0)
    {
        DEBUG (" empty error stack");
        return NULL;
    }
    first = g_list_first (be->error_stack);
    qerr = (QofError*)first->data;
    if (!qerr)
    {
        DEBUG (" empty QofError value");
        return NULL;
    }
    DEBUG (" qerr->message=%s", qerr->message);
    be->error_stack = 
        g_list_remove (be->error_stack, qerr);
#ifndef QOF_DISABLE_DEPRECATED
    be->error_msg = qerr->message;
    set_previous_error (be);
#endif
    return qerr->message;
}

QofTime* qof_error_get_time_be

(

QofBackend *

be

)

Get the time of the most recent error.

All QofError values are timestamped at the moment that the error is set.

Parameters:

be

The Backend where the error was set.

Returns:

NULL if no error exists, otherwise the QofTime that the error was set.

Definition at line 251 of file qoferror.c.

{
    QofError * qerr;
    GList * first;

    if (g_list_length(be->error_stack) == 0)
        return NULL;
    first = g_list_first (be->error_stack);
    qerr = (QofError*)first->data;
    return qerr->qt;
}

QofErrorId qof_error_register	(	const gchar *	err_message,
		gboolean	use_file
	)

Generate and register a new error.

Parameters:

	err_message	The user-friendly string to add as an error, already marked for translation.
	use_file	TRUE if the session filename should be substituted in the string - err_message must contain a bare string format specifier: s. Note that flags, width, precision or size specifiers are not accepted and the filename is output in full, complete with the access_method. e.g. file:/home/user/app/data.xml

To use a different presentation of the filename or other customised strings, prepare the error message before registering it with QofError.

Registered errors are cleared when the session is destroyed.

Applications need to plan the use of locally registered error codes so that the same errors are not repeatedly registered.

Returns:

The QofErrorId of this error.

Definition at line 91 of file qoferror.c.

{
    QofError * qerr;

    ENTER (" ");
    qerr = g_new0 (QofError, 1);
    count++;
#ifndef QOF_DISABLE_DEPRECATED
    count += ERR_LAST;
#endif
    qerr->id = count;
    if (use_file)
    {
        gchar * spec;

        spec = g_strrstr (err_message, "%s");
        use_file = (spec) ? TRUE : FALSE;
    }
    qerr->use_file = use_file;
    qerr->message = g_strdup (err_message);
    g_hash_table_insert (error_table, GINT_TO_POINTER(qerr->id), qerr);
    LEAVE (" ");
    return qerr->id;
}

void qof_error_set	(	QofSession *	session,
		QofErrorId	error
	)

Add an error to the stack for this session.

Parameters:

	session	The session that raised the error.
	error	The QofErrorId of the error to be recorded.

Definition at line 133 of file qoferror.c.

{
    QofError * qerr, * set;

    g_return_if_fail (session);
    if (error == QOF_SUCCESS)
    {
        DEBUG (" passed success, not error.");
        return;
    }
    qerr = g_hash_table_lookup (error_table, GINT_TO_POINTER(error));
    if (!qerr)
    {
        DEBUG (" failed hash table lookup");
        return;
    }
    session->last_err = error;
    if (session->error_message)
        g_free (session->error_message);
    if (qerr->use_file)
        session->error_message = g_strdup_printf (qerr->message,
            qof_session_get_url (session));
    else
        session->error_message = g_strdup (qerr->message);
    if (!session->backend)
        return;
    /* create a new error for the list */
    set = g_new0 (QofError, 1);
    if (qerr->use_file)
        set->message = g_strdup_printf (qerr->message,
            qof_session_get_file_path (session));
    else
        set->message = g_strdup (qerr->message);
    set->id = error;
    set->qt = qof_time_get_current ();
    session->backend->error_stack = 
        g_list_prepend (session->backend->error_stack, set);
#ifndef QOF_DISABLE_DEPRECATED
    session->backend->last_err = error;
#endif
}

void qof_error_unregister

(

QofErrorId

id

)

Unregister an error.

Registered errors are normally freed when the session ends. Errors can also be unregistered (and freed) directly.

An unregistered error can not be set later.

Definition at line 117 of file qoferror.c.

{
    QofError * qerr;
    gboolean result;

    ENTER (" ");
    qerr = g_hash_table_lookup (error_table, GINT_TO_POINTER(id));
    qof_error_free (qerr);
    result = g_hash_table_remove (error_table, 
        GINT_TO_POINTER(id));
    if (!result)
        LEAVE ("unable to remove registered error.");
    LEAVE (" ok.");
}

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