gnome-metadata

Gnome Library Reference Manual
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Description

One of the problems that a desktop environment faces is the fact that it is usually necessary to have a mechanism for storing information about a file's properties. For example, applications might want to bind an icon for a specific executable file or bind a small thumbnail image for a graphic produced by a graphics program. These icons should be semantically attached to the main file.

The GNOME metadata was implemented by Tom Tromey at Cygnus, given a number of design constraints and tradeoffs (described in detail in [TROMEY]).

Here is a list of the GNOME metadata features:

Binding the information on a per-file basis: This is a per-user setting and each user keeps track of his own bindings. System defaults apply on top of these.
Binding information by file content: Given the type of the file (using file signatures, similar to the Unix-file(1) command).
Binding information by a regular expression. For example, a default icon for gif files would be provided by a regular expression "*.\.gif$".
The metadata system is optimized to provide a coherent GUI solution, rather than as a compromise to kludging existing command line tools.
Most ordinary uses of files will continue to work without metadata, just as they do now.

There are a number of standard properties for file metadata in GNOME, for example: "View" stores the action for viewing the file contents; "Open" stores analogous action for editing; "Icon" which contains the icon used for displaying the file on the desktop. For a complete list of the existing keys see FIXME.

Details

enum GnomeMetadataError_t

typedef enum
{
	GNOME_METADATA_OK = 0,		   /* No error. */
	GNOME_METADATA_IO_ERROR,	   /* IO or other low-level
					      communications/storage
					      error.  */
	GNOME_METADATA_NOT_FOUND	   /* Information not found.  */
} GnomeMetadataError_t;

This describes the errors that can be returned by some gnome-metadata functions.

gnome_metadata_set ()

int         gnome_metadata_set              (const char *file,
                                             const char *name,
                                             int size,
                                             const char *data);

Sets metadata associated with file and name.

`file` :	File with which metadata will be associated
`name` :	Metadata key.
`size` :	Size in bytes of data
`data` :	Data to be stored.
Returns :	`0` on success or an error code.

gnome_metadata_remove ()

int         gnome_metadata_remove           (const char *file,
                                             const char *name);

Remove a piece of metadata associated with file.

`file` :	File name
`name` :	Metadata key.
Returns :	`0` on success, or an error code.

gnome_metadata_list ()

char**      gnome_metadata_list             (const char *file);

`file` :	File name.
Returns :	an array of all metadata keys associated with `file`. The array is `NULL` terminated. The result can be freed with g_strfreev(). This only returns keys for which there is a particular association with `file`. It will not return keys for which a regex or other match succeeds.

gnome_metadata_get ()

int         gnome_metadata_get              (const char *file,
                                             const char *name,
                                             int *size,
                                             char **buffer);

Get a piece of metadata associated with file. size and buffer are result parameters. *buffer is g_malloc()d.

`file` :	File name
`name` :	Metadata key
`size` :	Return parameter for size of data
`buffer` :	Return parameter for data
Returns :	`0`, or an error code. On error *`buffer` will be set to `NULL`.

gnome_metadata_get_fast ()

int         gnome_metadata_get_fast         (const char *file,
                                             const char *name,
                                             int *size,
                                             char **buffer);

Like gnome_metadata_get(), but won't run the `file' command to characterize the file type.

`file` :	File name
`name` :	Metadata key
`size` :	Return parameter for size of data
`buffer` :	Return parameter for data
Returns :	`0`, or an error code. On error *`buffer` will be set to `NULL`.

gnome_metadata_rename ()

int         gnome_metadata_rename           (const char *from,
                                             const char *to);

This function moves metadata associated with file from to file to. It should be called after a file is renamed.

`from` :	Source file name
`to` :	Destination file name
Returns :	`0` on success, or an error code.

gnome_metadata_copy ()

int         gnome_metadata_copy             (const char *from,
                                             const char *to);

This function copies metadata associated with file from to file to. It should be called after a file is copied.

`from` :	Source file name
`to` :	Destination file name
Returns :	`0` on success, or an error code.

gnome_metadata_delete ()

int         gnome_metadata_delete           (const char *file);

This function deletes all metadata associated with file. It should be called after a file is deleted.

`file` :	File name
Returns :	`0` on success, or an error code.

gnome_metadata_regex_add ()

void        gnome_metadata_regex_add        (const char *regex,
                                             const char *key,
                                             int size,
                                             const char *data);

Add a regular expression to the internal list. This regex is used when matching requests for the metadata key.

`regex` :	The regular expression.
`key` :	The metadata key.
`size` :	Size of data in bytes.
`data` :	The data.

gnome_metadata_regex_remove ()

void        gnome_metadata_regex_remove     (const char *regex,
                                             const char *key);

Remove the regular expression from the internal list.

`regex` :	The regular expression.
`key` :	The metadata key.

gnome_metadata_type_add ()

void        gnome_metadata_type_add         (const char *type,
                                             const char *key,
                                             int size,
                                             const char *data);

Add a file type to the internal list. This pairing is used when matching requests for the metadata key.

`type` :	File type
`key` :	The metadata key.
`size` :	Size of data in bytes.
`data` :	The data.

gnome_metadata_type_remove ()

void        gnome_metadata_type_remove      (const char *type,
                                             const char *key);

Remove a type/key pairing from the internal list.

`type` :	The file type.
`key` :	The metadata key.

gnome_metadata_lock ()

void        gnome_metadata_lock             (void);

Locks the metadata system. Used if you are going to invoke many metadata operations to speed up metadata access.

gnome_metadata_unlock ()

void        gnome_metadata_unlock           (void);

Unlocks the metadata system. Used if you are going to invoke many metadata operations to speed up metadata access.