simple logger

log.c

#include <stdarg.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <pthread.h>
#include <time.h>


struct log {
	pthread_mutex_t mutex;

	char context[32];
	char message[128];
};

void log_init(struct log *self, const char fmt[], ...);
void log_printf(struct log *self, const char fmt[], ...);
void log_errorf(struct log *self, int number, const char fmt[], ...);


/*
 * log
 */
static char __datetime[32];
static pthread_mutex_t __datetime_mutex = PTHREAD_MUTEX_INITIALIZER;

static void
__cstr_copy(char dest[], size_t size, const char src[])
{
	size_t i = 0;
	for (; (i < size) && (src[i] != '\0'); i++)
		dest[i] = src[i];

	dest[i] = '\0';
}


static const char *
__datetime_now(char dest[], size_t size)
{
	size_t len = 0;
	time_t tm_raw;
	struct tm *tm;


	pthread_mutex_lock(&__datetime_mutex); /* LOCK */

	tm_raw = time(NULL);
	tm = localtime(&tm_raw);
	if (tm == NULL)
		goto out0;

	const char *const res = asctime(tm);
	if (res == NULL)
		goto out0;

	const size_t res_len = strlen(res);
	if (res_len == 0)
		goto out0;

	__cstr_copy(dest, size, res);
	len = res_len - 1;

out0:
	dest[len] = '\0';
	pthread_mutex_unlock(&__datetime_mutex); /* UNLOCK */
	return dest;
}


void
log_init(struct log *self, const char fmt[], ...)
{
	int ret;
	va_list va;
	const size_t size = sizeof(self->context);


	va_start(va, fmt);
	ret = vsnprintf(self->context, size, fmt, va);
	va_end(va);

	if (ret < 0)
		self->context[0] = '\0';

	if ((size_t)ret >= size)
		__cstr_copy(&self->context[size - 4], 4, "...");

	self->message[0] = '\0';

	pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
	self->mutex = mutex;
}


void
log_printf(struct log *self, const char fmt[], ...)
{
	int ret;
	va_list va;
	const size_t size = sizeof(self->message);


	pthread_mutex_lock(&self->mutex); /* LOCK */

	va_start(va, fmt);
	ret = vsnprintf(self->message, size, fmt, va);
	va_end(va);

	if (ret < 0)
		self->message[0] = '\0';

	if ((size_t)ret >= size)
		__cstr_copy(&self->message[size - 4], 4, "...");

	const char *const datetime_now = __datetime_now(__datetime, sizeof(__datetime));
	printf("%s: %s: %s\n", datetime_now, self->context, self->message);

	pthread_mutex_unlock(&self->mutex); /* UNLOCK */
}


void
log_errorf(struct log *self, int number, const char fmt[], ...)
{
	int ret;
	va_list va;
	const size_t size = sizeof(self->message);


	pthread_mutex_lock(&self->mutex); /* LOCK */

	va_start(va, fmt);
	ret = vsnprintf(self->message, size, fmt, va);
	va_end(va);

	if (ret < 0)
		self->message[0] = '\0';

	if ((size_t)ret >= size)
		__cstr_copy(&self->message[size - 4], 4, "...");

	const char *const datetime_now = __datetime_now(__datetime, sizeof(__datetime));
	if (number == 0) {
		fprintf(stderr, "%s: %s: %s\n", datetime_now, self->context,
			self->message);
	} else {
		fprintf(stderr, "%s: %s: %s: %s\n", datetime_now, self->context,
			self->message, strerror(abs(number)));
	}

	pthread_mutex_unlock(&self->mutex); /* UNLOCK */
}


/*
 * main
 */
int
main(void)
{
	struct log l;
	log_init(&l, "main a");
	log_printf(&l, "test aaa");
	log_errorf(&l, 1,"test bbb");

	struct log ll;
	log_init(&ll, "main b loooooooooooooooooooooooooooooooooooooooooooooong");
	log_printf(&ll, __func__);
	log_errorf(&ll, 1,
		   "test looooooooooooooooooooooooooooooooooooooooooooooooooooo"
		   "ooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo"
		   "ooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo"
		   "ooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo"
		   "ooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo"
		   "ooooooooooooooooooooooooooooooooooooooooooooooooooooooooong");
	log_printf(&ll, "test cccc");

	struct log lll;
	log_init(&lll, __FUNCTION__);
	log_printf(&lll, "test aaa");
	return 0;
}