一個小巧的寫日誌文件的c實現

在看開源項目的twemproxy時，發現它的日誌系統寫的很小巧，稍微改改就可以變成自己的日誌系統，可以添加一個log.ini文件來配置日誌級別等等。

具體測試代碼如下：

#include <stdio.h>
#include <stdarg.h>
#include <sys/time.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <time.h>

struct logger {
    char *name;
    int  level;
    int  fd;
    int  nerror;
};

#define LOG_EMERG   0   /* system in unusable */
#define LOG_ALERT   1   /* action must be taken immediately */
#define LOG_CRIT    2   /* critical conditions */
#define LOG_ERR     3   /* error conditions */
#define LOG_WARN    4   /* warning conditions */
#define LOG_NOTICE  3   /* normal but significant condition (default) */
#define LOG_INFO    6   /* informational */
#define LOG_DEBUG   7   /* debug messages */
#define LOG_VERB    8   /* verbose messages */
#define LOG_VVERB   9   /* verbose messages on crack */
#define LOG_VVVERB  10  /* verbose messages on ganga */
#define LOG_PVERB   11  /* periodic verbose messages on crack */

#define LOG_MAX_LEN 256 /* max length of log message */

#define MIN(a, b)           ((a) < (b) ? (a) : (b))
#define MAX(a, b)           ((a) > (b) ? (a) : (b))

#define nc_scnprintf(_s, _n, ...)       \
    _scnprintf((char *)(_s), (size_t)(_n), __VA_ARGS__)

#define nc_vscnprintf(_s, _n, _f, _a)   \
    _vscnprintf((char *)(_s), (size_t)(_n), _f, _a)
#define nc_strftime(_s, _n, fmt, tm)        \
    (int)strftime((char *)(_s), (size_t)(_n), fmt, tm)

#define nc_write(_d, _b, _n)    \
    write(_d, _b, (size_t)(_n))

#define loga(...) do {                                                      \
    _log(__FILE__, __LINE__, 0, __VA_ARGS__);                               \
} while (0)

#define log_stderr(...) do {                                                \
    _log_stderr(__VA_ARGS__);                                               \
} while (0)

static struct logger logger;

int
log_init(int level, char *name)
{
    struct logger *l = &logger;

    l->level = MAX(LOG_EMERG, MIN(level, LOG_PVERB));
    l->name = name;
    if (name == NULL || !strlen(name)) {
        l->fd = STDERR_FILENO;
    } else {
        l->fd = open(name, O_WRONLY | O_APPEND | O_CREAT, 0644);
        if (l->fd < 0) {
            log_stderr("opening log file '%s' failed: %s", name,
                       strerror(errno));
            return -1;
        }
    }

    return 0;
}

int
_scnprintf(char *buf, size_t size, const char *fmt, ...)
{
    va_list args;
    int n;

    va_start(args, fmt);
    n = _vscnprintf(buf, size, fmt, args);
    va_end(args);

    return n;
}

int
_vscnprintf(char *buf, size_t size, const char *fmt, va_list args)
{
    int n;

    n = vsnprintf(buf, size, fmt, args);

    /*
     * The return value is the number of characters which would be written
     * into buf not including the trailing '\0'. If size is == 0 the
     * function returns 0.
     *
     * On error, the function also returns 0. This is to allow idiom such
     * as len += _vscnprintf(...)
     *
     * See: http://lwn.net/Articles/69419/
     */
    if (n <= 0) {
        return 0;
    }

    if (n < (int) size) {
        return n;
    }

    return (int)(size - 1);
}

void
_log(const char *file, int line, int panic, const char *fmt, ...)
{
    struct logger *l = &logger;
    int len, size, errno_save;
    char buf[LOG_MAX_LEN];
    va_list args;
    ssize_t n;
    struct timeval tv;

    if (l->fd < 0) {
        return;
    }

    errno_save = errno;
    len = 0;            /* length of output buffer */
    size = LOG_MAX_LEN; /* size of output buffer */

    gettimeofday(&tv, NULL);
    buf[len++] = '[';
    len += nc_strftime(buf + len, size - len, "%Y-%m-%d %H:%M:%S.", localtime(&tv.tv_sec));
    len += nc_scnprintf(buf + len, size - len, "%03ld", tv.tv_usec/1000);
    len += nc_scnprintf(buf + len, size - len, "] [pid:%d", getpid());
    len += nc_scnprintf(buf + len, size - len, "] %s:%d ", file, line);

    va_start(args, fmt);
    len += nc_vscnprintf(buf + len, size - len, fmt, args);
    va_end(args);

    buf[len++] = '\n';

    n = nc_write(l->fd, buf, len);
    if (n < 0) {
        l->nerror++;
    }

    errno = errno_save;

    if (panic) {
        abort();
    }
}

void
_log_stderr(const char *fmt, ...)
{
    struct logger *l = &logger;
    int len, size, errno_save;
    char buf[4 * LOG_MAX_LEN];
    va_list args;
    ssize_t n;

    errno_save = errno;
    len = 0;                /* length of output buffer */
    size = 4 * LOG_MAX_LEN; /* size of output buffer */

    va_start(args, fmt);
    len += nc_vscnprintf(buf, size, fmt, args);
    va_end(args);

    buf[len++] = '\n';

    n = nc_write(STDERR_FILENO, buf, len);
    if (n < 0) {
        l->nerror++;
    }

    errno = errno_save;
}

void
log_deinit(void)
{
    struct logger *l = &logger;

    if (l->fd < 0 || l->fd == STDERR_FILENO) {
        return;
    }

    close(l->fd);
}

int main(int argc, char *argv[])
{
    log_init(LOG_INFO, "a.log");
    loga("hello");
    loga("nihao");
    log_deinit();
    return 0;
}

運行後生成a.log文件，文件內容如下，具體輸出什麼格式的日誌可以自己定製：

[2019-08-06 01:12:04.984] [pid:38316] log.c:209 hello
[2019-08-06 01:12:04.985] [pid:38316] log.c:210 nihao