A printf wrapper, with loglevel support and timestamps

log.c

#include <stdio.h>
#include <stdarg.h>
#include <stdlib.h>
#include <time.h>
#include <libiberty/libiberty.h>
#include "log.h"
#include "config.h"

#define BUFSIZE		1024

#ifdef LOG_TIMESTAMPS

#define LOG_FORMAT	"%s [%s]: %s\n"  // timestamp loglevel: message\n

static char *gettimestamp() {
	int r;
	time_t t;
	char *res;
	struct tm *tmp;

	// In order to not waste space, the string is reallocated
	// later on. strftime(3) returns how many bytes have been put
	// into the buffer. If it does not fit into the buffer, it
	// errors out.
	res = xcalloc(1, BUFSIZE);

	t = time(NULL);
	tmp = localtime(&t);
	if (tmp == NULL) {
		perror("localtime(3)");
		exit(EXIT_FAILURE);
	}

	r = strftime(res, BUFSIZE, LOG_STRFTIME, tmp);
	if (r == 0) {
		fprintf(stderr, "strftime(3) failed\n");
		exit(EXIT_FAILURE);
	}

	// Reallocate to the actual size of the string.
	// It is not likely to fail, since we are freeing
	// memory here.
	return xrealloc(res, r);
}

static int __log(const char *level, const char *format, va_list args) {
	int len;
	char *timestamp;
	char *newformat;
	char *logformat = LOG_FORMAT;

	timestamp = gettimestamp();
	len = snprintf(NULL, 0, logformat, timestamp, level, format);
	len++;  // Trailing null byte.

	newformat = xmalloc(len);

	len = snprintf(newformat, len, logformat, timestamp, level, format);
	if (len < 0) {
		goto cleanup;
	}

	len = vprintf(newformat, args);

cleanup:
	free(timestamp);
	free(newformat);

	return len;
}

#else

#define LOG_FORMAT	"[%s]: %s\n"  // loglevel: message\n

static int __log(const char *level, const char *format, va_list args) {
	int len;
	char *newformat;
	char *logformat = LOG_FORMAT;

	len = snprintf(NULL, 0, logformat, level, format);
	len++;  // Trailing null byte.

	newformat = xmalloc(len);

	len = snprintf(newformat, len, logformat, level, format);
	if (len < 0) {
		goto cleanup;
	}

	len = vprintf(newformat, args);

cleanup:
	free(newformat);

	return len;
}
#endif

int debug(const char *format, ...) {
	int r;
	va_list ap;

	if (loglevel > DEBUG) {
		return -1;
	}

	va_start(ap, format);
	r = __log("DEBUG", format, ap);
	va_end(ap);

	return r;
}

int info(const char *format, ...) {
	int r;
	va_list ap;

	if (loglevel > INFO) {
		return -1;
	}

	va_start(ap, format);
	r = __log("INFO", format, ap);
	va_end(ap);

	return r;
}

int warning(const char *format, ...) {
	int r;
	va_list ap;

	if (loglevel > WARNING) {
		return -1;
	}

	va_start(ap, format);
	r = __log("WARNING", format, ap);
	va_end(ap);

	return r;
}

int error(const char *format, ...) {
	int r;
	va_list ap;

	if (loglevel > ERROR) {
		return -1;
	}

	va_start(ap, format);
	r = __log("ERROR", format, ap);
	va_end(ap);

	return r;
}

log.h

#pragma once

enum loglevel_t { DEBUG, INFO, WARNING, ERROR };
extern enum loglevel_t loglevel;

int debug(const char *format, ...);
int info(const char *format, ...);
int warning(const char *format, ...);
int error(const char *format, ...);