Mini-XML supports custom data types via global load and save callbacks. Only a single set of callbacks can be active at any time, however your callbacks can store additional information in order to support multiple custom data types as needed. The MXML_CUSTOM node type identifies custom data nodes.
The load callback receives a pointer to the current data node and a string of opaque character data from the XML source with character entities converted to the corresponding UTF-8 characters. For example, if we wanted to support a custom date/time type whose value is encoded as "yyyy-mm-ddThh:mm:ssZ" (ISO format), the load callback would look like the following:
typedef struct
{
unsigned year, /* Year */
month, /* Month */
day, /* Day */
hour, /* Hour */
minute, /* Minute */
second; /* Second */
time_t unix; /* UNIX time */
} iso_date_time_t;
int
load_custom(mxml_node_t *node,
const char *data)
{
iso_date_time_t *dt;
struct tm tmdata;
/*
* Allocate data structure...
*/
dt = calloc(1, sizeof(iso_date_time_t));
/*
* Try reading 6 unsigned integers from the
* data string...
*/
if (sscanf(data, "%u-%u-%uT%u:%u:%uZ",
&(dt->year), &(dt->month),
&(dt->day), &(dt->hour),
&(dt->minute),
&(dt->second)) != 6)
{
/*
* Unable to read numbers, free the data
* structure and return an error...
*/
free(dt);
return (-1);
}
/*
* Range check values...
*/
if (dt->month <1 || dt->month > 12 ||
dt->day <1 || dt->day > 31 ||
dt->hour <0 || dt->hour > 23 ||
dt->minute <0 || dt->minute > 59 ||
dt->second <0 || dt->second > 59)
{
/*
* Date information is out of range...
*/
free(dt);
return (-1);
}
/*
* Convert ISO time to UNIX time in
* seconds...
*/
tmdata.tm_year = dt->year - 1900;
tmdata.tm_mon = dt->month - 1;
tmdata.tm_day = dt->day;
tmdata.tm_hour = dt->hour;
tmdata.tm_min = dt->minute;
tmdata.tm_sec = dt->second;
dt->unix = gmtime(&tmdata);
/*
* Assign custom node data and destroy
* function pointers...
*/
node->value.custom.data = dt;
node->value.custom.destroy = free;
/*
* Return with no errors...
*/
return (0);
}
The function itself can return 0 on success or -1 if it is unable to decode the custom data or the data contains an error. Custom data nodes contain a void pointer to the allocated custom data for the node and a pointer to a destructor function which will free the custom data when the node is deleted.
The save callback receives the node pointer and returns an allocated string containing the custom data value. The following save callback could be used for our ISO date/time type:
char *
save_custom(mxml_node_t *node)
{
char data[255];
iso_date_time_t *dt;
dt = (iso_date_time_t *)node->custom.data;
snprintf(data, sizeof(data),
"%04u-%02u-%02uT%02u:%02u:%02uZ",
dt->year, dt->month, dt->day,
dt->hour, dt->minute, dt->second);
return (strdup(data));
}
You register the callback functions using the mxmlSetCustomHandlers() function:
mxmlSetCustomHandlers(load_custom,
save_custom);