gistfile1.c

#include <sys/uio.h>

#include <unistd.h>
#include <limits.h>
#include <stdio.h>
#include <string.h>
#include <error.h>

enum record_fields_type {
	RECORD_FIELD_TIME = 0,
	RECORD_FIELD_HOST,
	RECORD_FIELD_MSG,
	RECORD_FIELD_COUNTS,
};

#define RECORD_FIELD_REPEAT_MAX  5
#define RECORD_FIELDS_MAX        RECORD_FIELD_COUNTS * RECORD_FIELD_REPEAT_MAX
#define RECORDS_MAX              RECORD_FIELDS_MAX * 2 + 1

long int iov_max;

struct format {
	char line[LINE_MAX];
	struct iovec record[RECORDS_MAX];
	struct {
		enum record_fields_type source;
		struct iovec *destination;
	} rules[RECORD_FIELDS_MAX];
};

static void set_format_record(struct format *fmt, int i, char *s, size_t n)
{
	if (i >= iov_max)
		error(1, 0, "too many parts in the record format");
	fmt->record[i].iov_base = s;
	fmt->record[i].iov_len = n;
}

static void set_format_rule(struct format *fmt, int i,
		enum record_fields_type t, struct iovec *v)
{
	if (i >= RECORD_FIELDS_MAX)
		error(1, 0, "too many fields in the record");
	fmt->rules[i].source = t;
	fmt->rules[i].destination = v;
}

static void parse_format(struct format *fmt, char *line)
{
	char *cur, *ptr;
	int rec_nr, rule_nr, special;

	strncpy(fmt->line, line, LINE_MAX);
	memset(fmt->record, 0, sizeof(fmt->record[0]) * RECORDS_MAX);
	memset(fmt->rules, 0, sizeof(fmt->rules[0]) * RECORD_FIELDS_MAX);

	special = rec_nr = rule_nr = 0;
	cur = ptr = fmt->line;

	while (*ptr != '\0') {
		enum record_fields_type ruletype;

		if (special) {
			switch (*ptr) {
				case 't': ruletype = RECORD_FIELD_TIME; break;
				case 'h': ruletype = RECORD_FIELD_HOST; break;
				case 'm': ruletype = RECORD_FIELD_MSG;  break;
				case '%':
					special = 0;
					goto create_special;
				default:
					error(1, 0, "unexpected special: '%%%c'", *ptr);
			}
			special = 0;
			goto create_rule;

		} else if (*ptr == '%')
			special = 1;
next:
		ptr++;
		continue;
create_rule:
		set_format_record(fmt, rec_nr++, cur, (ptr - cur - 1));
		set_format_rule(fmt, rule_nr++, ruletype, fmt->record + rec_nr);
		set_format_record(fmt, rec_nr++, NULL, 0);
		cur = ptr + 1;
		goto next;
create_special:
		set_format_record(fmt, rec_nr++, cur, (ptr - cur - 1));
		cur = ptr;
		goto next;
	}

	if (special)
		error(1, 0, "unexpected '%%' at the end of line");

	if (cur != ptr)
		set_format_record(fmt, rec_nr++, cur, (ptr - cur));
}

static char *curtime = (char *) "May 2 12:34:56";
static char *curhost = (char *) "localhost";
static char *curmsg  = (char *) "TEST";

int main(int argc, char **argv)
{
	struct format fmt;

	iov_max = sysconf(_SC_IOV_MAX);

	printf("%s\n", argv[1]);

	parse_format(&fmt, argv[1]);

	for (int i = 0; i < RECORD_FIELDS_MAX; i++) {
		if (!fmt.rules[i].destination)
			continue;
		switch (fmt.rules[i].source) {
			case RECORD_FIELD_TIME:
				fmt.rules[i].destination->iov_base = curtime;
				fmt.rules[i].destination->iov_len = strlen(curtime);
				break;
			case RECORD_FIELD_HOST:
				fmt.rules[i].destination->iov_base = curhost;
				fmt.rules[i].destination->iov_len = strlen(curhost);
				break;
			case RECORD_FIELD_MSG:
				fmt.rules[i].destination->iov_base = curmsg;
				fmt.rules[i].destination->iov_len = strlen(curmsg);
				break;
			default:
				break;
		}
	}

	writev(STDOUT_FILENO, fmt.record, RECORDS_MAX);
	printf("\n");

	return 0;
}