C语言日志处理

一、简介

zlog是一个高可靠性、高性能、线程安全、灵活、概念清晰的纯C日志函数库，在效率、功能、安全性上大大超过了log4c，并且是用c写成的，具有比较好的通用性。

二、安装

下载

https://github.com/HardySimpson/zlog

https://github.com/HardySimpson/zlog/archive/latest-stable.tar.gz
https://github.com/downloads/HardySimpson/zlog/zlog-latest-stable.tar.gz

三、实例

参考：

http://blog.itpub.net/26834829/viewspace-721002/
https://github.com/HardySimpson/zlog

源码目录:test,包括了大量使用示例，如下：

四、系统日志

参考：

http://blog.sina.com.cn/s/blog_5f70c7060100i4j5.html

示例：

#include <syslog.h>
int main(int argc, char **argv)
{
    openlog("MyMsgMARK", LOG_CONS | LOG_PID, 0);
    syslog(LOG_INFO,
           "This is a syslog test message generated by program '%s'\n",
           argv[0]);
    closelog();
    return 0;
}

编译

gcc -g -o test test.c

运行

五、Apache 日志处理分析

Apache通过调用ap_log_XXX函数进行日志记录，此处以ap_log_perror为例进行分析

Apache启动时通过httpd/modules/core/mod_so.c:load_module函数进行DSO模块加载，加载成功后将调用ap_log_perror函数记录模块加载日志

266     ap_log_perror(APLOG_MARK, APLOG_DEBUG, 0, cmd->pool, APLOGNO(01575)"loaded module %s from %s", modname, module_file);

ap_log_perror函数事实上是一个宏，定义在文件：/httpd/include/http_log.h，如下：

412 #define ap_log_perror ap_log_perror_

而ap_log_perror_函数实现在文件：httpd/server/log.c,代码如下：

1409 AP_DECLARE(void) ap_log_perror_(const char *file, int line, int module_index,
1410                                 int level, apr_status_t status, apr_pool_t *p,
1411                                 const char *fmt, ...)
1412 {
1413     va_list args;
1414
1415     va_start(args, fmt);
1416     log_error_core(file, line, module_index, level, status, NULL, NULL, NULL,
1417                    p, fmt, args);
1418     va_end(args);
1419 }

函数log_error_core，逻辑如下：

1、判断请求结构r是否为NULL，若不为空则：c = r->connection

2、判断服务器结构s是否为NULL，若为空则：logf = stderr_log，此处s为NULL

3、填充结构日志info

4、调用do_errorlog_default函数拼接要写入日志的内容并暂存在buf中，并返回相应长度len

5、调用write_logline函数进行实际的日志输出

6、运行日志钩子error_log

static void log_error_core(const char *file, int line, int module_index,
                           int level,
                           apr_status_t status, const server_rec *s,
                           const conn_rec *c,
                           const request_rec *r, apr_pool_t *pool,
                           const char *fmt, va_list args)
{
    char errstr[MAX_STRING_LEN];
    apr_file_t *logf = NULL;
    int level_and_mask = level & APLOG_LEVELMASK;
    const request_rec *rmain = NULL;
    core_server_config *sconf = NULL;
    ap_errorlog_info info;

    /* do we need to log once-per-req or once-per-conn info? */
    int log_conn_info = 0, log_req_info = 0;
    apr_array_header_t **lines = NULL;
    int done = 0;
    int line_number = 0;

    if (r)
    {
        AP_DEBUG_ASSERT(r->connection != NULL);
        c = r->connection;
    }

    if (s == NULL)
    {
        /*
         * If we are doing stderr logging (startup), don't log messages that are
         * above the default server log level unless it is a startup/shutdown
         * notice
         */
#ifndef DEBUG
        if ((level_and_mask != APLOG_NOTICE)
                && (level_and_mask > ap_default_loglevel))
        {
            return;
        }
#endif

        logf = stderr_log;
    }
    else
    {
        int configured_level = r ? ap_get_request_module_loglevel(r, module_index)        :
                               c ? ap_get_conn_server_module_loglevel(c, s, module_index) :
                               ap_get_server_module_loglevel(s, module_index);
        if (s->error_log)
        {
            /*
             * If we are doing normal logging, don't log messages that are
             * above the module's log level unless it is a startup/shutdown notice
             */
            if ((level_and_mask != APLOG_NOTICE)
                    && (level_and_mask > configured_level))
            {
            }
            else
            {
                /*
                 * If we are doing syslog logging, don't log messages that are
                 * above the module's log level (including a startup/shutdown notice)
                 */
                if (level_and_mask > configured_level)
                {

                }
            }

            /* the faked server_rec from mod_cgid does not have s->module_config */

            sconf = ap_get_core_module_config(s->module_config);
            if (c && !c->log_id)
            {
                add_log_id(c, NULL);
                if (sconf->error_log_conn && sconf->error_log_conn->nelts > 0)
                    log_conn_info = 1;
            }
            if (r)
            {
                if (r->main)
                    rmain = r->main;
                else
                    rmain = r;

                if (!rmain->log_id)
                {
                    /* XXX: do we need separate log ids for subrequests? */
                    if (sconf->error_log_req && sconf->error_log_req->nelts > 0)
                        log_req_info = 1;
                    /*
                     * XXX: potential optimization: only create log id if %L is
                     * XXX: actually used
                     */
                    add_log_id(c, rmain);
                }
            }
        }
    }

    info.s             = s;
    info.c             = c;
    info.pool          = pool;
    info.file          = NULL;
    info.line          = 0;
    info.status        = 0;
    info.using_syslog  = (logf == NULL);
    info.startup       = ((level & APLOG_STARTUP) == APLOG_STARTUP);
    info.format        = fmt;

    while (!done)
    {
        apr_array_header_t *log_format;
        int len = 0, errstr_start = 0, errstr_end = 0;
        /* XXX: potential optimization: format common prefixes only once */
        if (log_conn_info)
        {
            /* once-per-connection info */
            if (line_number == 0)
            {
                lines = (apr_array_header_t **)sconf->error_log_conn->elts;
                info.r = NULL;
                info.rmain = NULL;
                info.level = -1;
                info.module_index = APLOG_NO_MODULE;
            }

            log_format = lines[line_number++];

            if (line_number == sconf->error_log_conn->nelts)
            {
                /* this is the last line of once-per-connection info */
                line_number = 0;
                log_conn_info = 0;
            }
        }
        else if (log_req_info)
        {
            /* once-per-request info */
            if (line_number == 0)
            {
                lines = (apr_array_header_t **)sconf->error_log_req->elts;
                info.r = rmain;
                info.rmain = rmain;
                info.level = -1;
                info.module_index = APLOG_NO_MODULE;
            }

            log_format = lines[line_number++];

            if (line_number == sconf->error_log_req->nelts)
            {
                /* this is the last line of once-per-request info */
                line_number = 0;
                log_req_info = 0;
            }
        }
        else
        {
            /* the actual error message */
            info.r            = r;
            info.rmain        = rmain;
            info.level        = level_and_mask;
            info.module_index = module_index;
            info.file         = file;
            info.line         = line;
            info.status       = status;
            log_format = sconf ? sconf->error_log_format : NULL;
            done = 1;
        }

        /*
         * prepare and log one line
         */

        if (log_format && !info.startup)
        {
            len += do_errorlog_format(log_format, &info, errstr + len,
                                      MAX_STRING_LEN - len,
                                      &errstr_start, &errstr_end, fmt, args);
        }
        else
        {
            len += do_errorlog_default(&info, errstr + len, MAX_STRING_LEN - len,
                                       &errstr_start, &errstr_end, fmt, args);
        }

        if (!*errstr)
        {
            /*
             * Don't log empty lines. This can happen with once-per-conn/req
             * info if an item with AP_ERRORLOG_FLAG_REQUIRED is NULL.
             */
            continue;
        }
        write_logline(errstr, len, logf, level_and_mask);

        if (done)
        {
            /*
             * We don't call the error_log hook for per-request/per-conn
             * lines, and we only pass the actual log message, not the
             * prefix and suffix.
             */
            errstr[errstr_end] = '\0';
            ap_run_error_log(&info, errstr + errstr_start);
        }

        *errstr = '\0';
    }
}

do_errorlog_default函数拼接要写入日志的内容并暂存在buf中，并返回相应长度len，此处拼接出的日志的内容如下：

[Sat Jun 20 22:08:19.506426 2015] [so:debug] [pid 3826] mod_so.c(266): AH01575: loaded module unixd_module from /app/HRP/lib/mod_unixd.so

do_errorlog_default函数实现在文件：httpd/server/log.c,代码如下：

static int do_errorlog_default(const ap_errorlog_info *info, char *buf,
                               int buflen, int *errstr_start, int *errstr_end,
                               const char *errstr_fmt, va_list args)
{
    int len = 0;
    int field_start = 0;
    int item_len;
#ifndef AP_UNSAFE_ERROR_LOG_UNESCAPED
    char scratch[MAX_STRING_LEN];
#endif

    if (!info->using_syslog && !info->startup)
    {
        buf[len++] = '[';
        len += log_ctime(info, "u", buf + len, buflen - len);
        buf[len++] = ']';
        buf[len++] = ' ';
    }

    if (!info->startup)
    {
        buf[len++] = '[';
        len += log_module_name(info, NULL, buf + len, buflen - len);
        buf[len++] = ':';
        len += log_loglevel(info, NULL, buf + len, buflen - len);
        len += cpystrn(buf + len, "] [pid ", buflen - len);

        len += log_pid(info, NULL, buf + len, buflen - len);
#if APR_HAS_THREADS
        field_start = len;
        len += cpystrn(buf + len, ":tid ", buflen - len);
        item_len = log_tid(info, NULL, buf + len, buflen - len);
        if (!item_len)
            len = field_start;
        else
            len += item_len;
#endif
        buf[len++] = ']';
        buf[len++] = ' ';
    }

    if (info->level >= APLOG_DEBUG)
    {
        item_len = log_file_line(info, NULL, buf + len, buflen - len);
        if (item_len)
        {
            len += item_len;
            len += cpystrn(buf + len, ": ", buflen - len);
        }
    }

    if (info->status)
    {
        item_len = log_apr_status(info, NULL, buf + len, buflen - len);
        if (item_len)
        {
            len += item_len;
            len += cpystrn(buf + len, ": ", buflen - len);
        }
    }

    /*
     * useragent_ip/client_ip can be client or backend server. If we have
     * a scoreboard handle, it is likely a client.
     */
    if (info->r)
    {
        len += apr_snprintf(buf + len, buflen - len,
                            info->r->connection->sbh ? "[client %s:%d] " : "[remote %s:%d] ",
                            info->r->useragent_ip,
                            info->r->useragent_addr ? info->r->useragent_addr->port : 0);
    }
    else if (info->c)
    {
        len += apr_snprintf(buf + len, buflen - len,
                            info->c->sbh ? "[client %s:%d] " : "[remote %s:%d] ",
                            info->c->client_ip,
                            info->c->client_addr ? info->c->client_addr->port : 0);
    }

    /* the actual error message */
    *errstr_start = len;
#ifndef AP_UNSAFE_ERROR_LOG_UNESCAPED
    if (apr_vsnprintf(scratch, MAX_STRING_LEN, errstr_fmt, args))
    {
        len += ap_escape_errorlog_item(buf + len, scratch,
                                       buflen - len);

    }
#else
    len += apr_vsnprintf(buf + len, buflen - len, errstr_fmt, args);
#endif
    *errstr_end = len;

    field_start = len;
    len += cpystrn(buf + len, ", referer: ", buflen - len);
    item_len = log_header(info, "Referer", buf + len, buflen - len);
    if (item_len)
        len += item_len;
    else
        len = field_start;

    return len;
}

write_logline函数实现在文件：httpd/server/log.c,代码如下：

static void write_logline(char *errstr, apr_size_t len, apr_file_t *logf,
                          int level)
{
    /* NULL if we are logging to syslog */
    if (logf)
    {
        /* Truncate for the terminator (as apr_snprintf does) */
        if (len > MAX_STRING_LEN - sizeof(APR_EOL_STR))
        {
            len = MAX_STRING_LEN - sizeof(APR_EOL_STR);
        }
        strcpy(errstr + len, APR_EOL_STR);
        apr_file_puts(errstr, logf);
        apr_file_flush(logf);
    }
#ifdef HAVE_SYSLOG
    else
    {
        syslog(level < LOG_PRIMASK ? level : APLOG_DEBUG, "%.*s",
               (int)len, errstr);
    }
#endif
}