CONFIGFILE(3)

NAME
configfile, config_read, config_delete, config_renewed, config_length, config_issub, config_isatom, config_isstring - generic configuration file functions

SYNOPSIS
#include <configfile.h>
config_t *config_read(const char *file, int flags, config_t *cfg)
void config_delete(config_t *cfg)
int config_renewed(config_t *cfg)
size_t config_length(config_t *cfg)
int config_issub(config_t *cfg)
int config_isatom(config_t *cfg)
int config_isstring(config_t *cfg)

DESCRIPTION
The configfile routines operate on a generic configuration file that follows the syntax described in configfile(5).

The interface presented by the functions above uses the following type and definitions from <configfile.h>:

typedef const struct config {
	config_t	*next;	/* Next configuration file thing. */
	config_t	*list;	/* For a { sublist }. */
	const char	*file;	/* File and line where this is found. */
	unsigned	line;
	int	flags;	/* Special flags. */
	char	word[];	/* Payload. */
} config_t;
#define	CFG_CLONG	0x0001	/* strtol(word, &end, 0) is valid. */
#define	CFG_OLONG	0x0002	/* strtol(word, &end, 010). */
#define	CFG_DLONG	0x0004	/* strtol(word, &end, 10). */
#define	CFG_XLONG	0x0008	/* strtol(word, &end, 0x10). */
#define	CFG_CULONG	0x0010	/* strtoul(word, &end, 0). */
#define	CFG_OULONG	0x0020	/* strtoul(word, &end, 010). */
#define	CFG_DULONG	0x0040	/* strtoul(word, &end, 10). */
#define	CFG_XULONG	0x0080	/* strtoul(word, &end, 0x10). */
#define	CFG_STRING	0x0100	/* The word is enclosed in quotes. */
#define	CFG_SUBLIST	0x0200	/* This is a sublist, so no word. */
#define	CFG_ESCAPED	0x0400	/* Escapes are still marked with \. */

In memory a configuration file is represented as a list of config_t cells linked together with the next field ending with a null pointer. A sublist between braces is attached to a cell at the list field. Words and strings are put in the word field, a null terminated string. The flags field records the type and features of a cell. The CFG_*LONG flags are set if a word is a number according to one of the strtol or strtoul calls. Purely a number, no quotes or trailing garbage. The CFG_STRING flag is set if the object was enclosed in double quotes. Lastly CFG_SUBLIST tells if the cell is only a pointer to a sublist in braces.

Characters in a word or string may have been formed with the \ escape character. They have been parsed and expanded, but the \ is still present if CFG_ESCAPED is set. The word array may be changed, as long as it doesn't grow longer, so one may remove the \s like this:

    if (cfg->flags & CFG_ESCAPED) {
    	char *p, *q;
    	p= q= cfg->word;
    	for (;;) {
    		if ((*q = *p) == '\\') *q = *++p;
    		if (*q == 0) break;
    		p++;
    		q++;
    	}
    }

The low level syntax of a config file is checked when it is read. If an error is encountered a message is printed and the program exits with exit code 1. What the data means is not checked, that should be done by the program using the data. Only the atom include at the beginning of a list is special. It should be followed by a string. The string is seen as the name of a file, that is opened, read, and inserted in place of the include. Unless the name of the file starts with a /, it is sought relative to the directory the current file is found in. Nonexistent files are treated as being empty.

The file and line fields in each cell tell where the cell was read.

  Functions
A configuration file is read with config_read. The first argument is the file to read. The second is either 0 or CFG_ESCAPED to tell whether \ escapes should be fully expanded without leaving a trace, or if they should still be marked with a \ so that the caller knows where the excapes are. The third argument, cfg, should be a null pointer on the first call. If you want to reread a config file that may have changed then cfg should be what you previously read.

With config_delete one can free up the memory that has been acquired with malloc(3) to hold the contents of the configuration file.

To determine if the contents of configuration file has changed when reread one uses config_renewed after config_read. It returns a "changed" flag that is set when the configuration file changed and then clears that flag. It returns true on the very first call. For the function to work you need to feed the old data back into config_read, not delete and reread.

The length of a series of config structures is told by config_length. It follows the next fields, so a sublist between braces counts as one extra.

The config_issub, config_isatom and config_isstring functions are just pretty macros to test if a cell references a sublist, is a word/string, or is just a string. CFG_SUBLIST and CFG_STRING tell the same story.

FILES

*/etc/*.conf
    Several files in several etc directories.

SEE ALSO
configfile(5).

NOTES
The syntax of a config file puts some constraints on what you find in memory. The top level list consists entirely of sublist cells. These point to lists that start with at least an atom, followed by a mix of atoms and sublist cells. These sublists in turn point to a list of only sublist cells (recurse now.)

The struct config shown above is not exactly proper C to aid readability, read <configfile.h> itself to see why.

AUTHOR
Kees J. Bot (kjb@cs.vu.nl)