Nginx(四)：http服务器静态文件查找的实现-轻识

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上一篇nginx的文章中，我们理解了整个http正向代理的运行流程原理，主要就是事件机制接入，header解析，body解析，然后遍历各种checker，直到处理成功为止。

我们以访问一个普通文件为例，nginx到底是如何找到这个文件并返回信息的呢？它会不会有些什么限制呢？

按我们自己的理解，它应该是uri栏里截取出相应的路径，然后对应到root下，查找到相应文件，返回即可。那么，它又是如何处理html和其他的各种不同格式的文件呢？

就让我们一起来探秘nginx文件的查找实现吧！

0. nginx 静态文件配置

要配置静态文件处理，只需在http server中配置root路径即可。（当然了，你可以根据前缀配置许多不同的root）

http {    include       mime.types;    default_type  application/octet-stream;
    #log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '    #                  '$status $body_bytes_sent "$http_referer" '    #                  '"$http_user_agent" "$http_x_forwarded_for"';
    #access_log  logs/access.log  main;
    sendfile        on;    #tcp_nopush     on;
    #keepalive_timeout  0;    keepalive_timeout  65;
    #gzip  on;
    server {        listen       8085;        server_name  localhost;
        #charset koi8-r;
        #access_log  logs/host.access.log  main;
        location /hello {            root   /www/hello;            index  index.html index.htm;        }
        location / {            root   html;            index  index.html index.htm;        }    }    # 后续可以添加无数个server 扩展}

配置简单吧，实际核心就两三行代码搞定：监听端口号 listen、访问域名 server_name、服务器根路径 root。明显这是nginx成功的原因之一。

本文要讨论的场景是，如果我访问 http://localhost:8085/1.txt?d=xxx, nginx将如何干成这件事？

1. checker的遍历回顾

我们先来回顾下，nginx是如何遍历各个checker的吧！

// http/ngx_http_core_module.c// 响应客户端操作, 多阶段式操作voidngx_http_core_run_phases(ngx_http_request_t *r){    ngx_int_t                   rc;    ngx_http_phase_handler_t   *ph;    ngx_http_core_main_conf_t  *cmcf;
    cmcf = ngx_http_get_module_main_conf(r, ngx_http_core_module);
    ph = cmcf->phase_engine.handlers;    // 依次调用各 checker, 直到有响应 OK 的checker为止    while (ph[r->phase_handler].checker) {        // 每次调用 checker 之后, 内部都会将 r->phase_handler++, 即迭代下一个        // 此处的 checker 非常之多, 是在各模块启动时, 自动向 ngx_http_core_module.main_conf 中进行注册的        /**          * 定义如下:        typedef enum {            NGX_HTTP_POST_READ_PHASE = 0,
            NGX_HTTP_SERVER_REWRITE_PHASE,
            NGX_HTTP_FIND_CONFIG_PHASE,            NGX_HTTP_REWRITE_PHASE,            NGX_HTTP_POST_REWRITE_PHASE,
            NGX_HTTP_PREACCESS_PHASE,
            NGX_HTTP_ACCESS_PHASE,            NGX_HTTP_POST_ACCESS_PHASE,
            NGX_HTTP_PRECONTENT_PHASE,
            NGX_HTTP_CONTENT_PHASE,
            NGX_HTTP_LOG_PHASE        } ngx_http_phases;
        // 注册方式        cmcf = ngx_http_conf_get_module_main_conf(cf, ngx_http_core_module);        h = ngx_array_push(&cmcf->phases[NGX_HTTP_ACCESS_PHASE].handlers);        *h = ngx_http_access_handler;        */        // 将请求信息和 handler 本身传入调用(不是面向, 只能这么做了)        rc = ph[r->phase_handler].checker(r, &ph[r->phase_handler]);        // 只要有一个处理成功, 则后续不再调用        if (rc == NGX_OK) {            return;        }    }}

可以说，它的各checker是非常复杂的，各模块都可以向其中注册处理器。这也是nginx灵活性的体现。不过我们不想关注太多。

文件的查找是在 static_module 中完成的，我们只需关注这个即可。

2. 静态文件模块的注册

静态文件模块主要就是负责静态文件的查找处理。几乎所有的http处理模块，都是先进行注册，然后再被调用的过程。static_module 自然不例外。

// http/modules/ngx_http_static_handler.c    static ngx_int_tngx_http_static_init(ngx_conf_t *cf){    ngx_http_handler_pt        *h;    ngx_http_core_main_conf_t  *cmcf;
    cmcf = ngx_http_conf_get_module_main_conf(cf, ngx_http_core_module);    // 获取http_core_module的配置    // 将ngx_http_static_handler 添加到 NGX_HTTP_CONTENT_PHASE 的handlers中    h = ngx_array_push(&cmcf->phases[NGX_HTTP_CONTENT_PHASE].handlers);    if (h == NULL) {        return NGX_ERROR;    }
    *h = ngx_http_static_handler;
    return NGX_OK;}
// 下面是一些nginx的模块暴露规范，只有这样，这个模块才会被接入到整个系统中static ngx_http_module_t  ngx_http_static_module_ctx = {    NULL,                                  /* preconfiguration */    ngx_http_static_init,                  /* postconfiguration */
    NULL,                                  /* create main configuration */    NULL,                                  /* init main configuration */
    NULL,                                  /* create server configuration */    NULL,                                  /* merge server configuration */
    NULL,                                  /* create location configuration */    NULL                                   /* merge location configuration */};

ngx_module_t  ngx_http_static_module = {    NGX_MODULE_V1,    &ngx_http_static_module_ctx,           /* module context */    NULL,                                  /* module directives */    NGX_HTTP_MODULE,                       /* module type */    NULL,                                  /* init master */    NULL,                                  /* init module */    NULL,                                  /* init process */    NULL,                                  /* init thread */    NULL,                                  /* exit thread */    NULL,                                  /* exit process */    NULL,                                  /* exit master */    NGX_MODULE_V1_PADDING};

3. 文件查找实现

经过前面的模块注册到 NGX_HTTP_CONTENT_PHASE 中，就会被nginx调用。前提是没有其他更合适的处理器的时候。而因为 static_module 是在 NGX_HTTP_CONTENT_PHASE 中，所以都会走content的处理器：

// http/ngx_http_core_module.c    ngx_int_tngx_http_core_content_phase(ngx_http_request_t *r,    ngx_http_phase_handler_t *ph){    size_t     root;    ngx_int_t  rc;    ngx_str_t  path;
    if (r->content_handler) {        r->write_event_handler = ngx_http_request_empty_handler;        ngx_http_finalize_request(r, r->content_handler(r));        return NGX_OK;    }
    ngx_log_debug1(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,                   "content phase: %ui", r->phase_handler);
    rc = ph->handler(r);    // 处理成功，则返回ok    if (rc != NGX_DECLINED) {        ngx_http_finalize_request(r, rc);        return NGX_OK;    }
    /* rc == NGX_DECLINED */
    ph++;
    if (ph->checker) {        r->phase_handler++;        return NGX_AGAIN;    }
    /* no content handler was found */
    if (r->uri.data[r->uri.len - 1] == '/') {
        if (ngx_http_map_uri_to_path(r, &path, &root, 0) != NULL) {            ngx_log_error(NGX_LOG_ERR, r->connection->log, 0,                          "directory index of \"%s\" is forbidden", path.data);        }
        ngx_http_finalize_request(r, NGX_HTTP_FORBIDDEN);        return NGX_OK;    }
    ngx_log_error(NGX_LOG_ERR, r->connection->log, 0, "no handler found");
    ngx_http_finalize_request(r, NGX_HTTP_NOT_FOUND);    return NGX_OK;}

// http/modules/ngx_http_static_handler.cstatic ngx_int_tngx_http_static_handler(ngx_http_request_t *r){    u_char                    *last, *location;    size_t                     root, len;    ngx_str_t                  path;    ngx_int_t                  rc;    ngx_uint_t                 level;    ngx_log_t                 *log;    ngx_buf_t                 *b;    ngx_chain_t                out;    ngx_open_file_info_t       of;    ngx_http_core_loc_conf_t  *clcf;    // 仅支持 get/head/post 方法进行静态文件处理    if (!(r->method & (NGX_HTTP_GET|NGX_HTTP_HEAD|NGX_HTTP_POST))) {        return NGX_HTTP_NOT_ALLOWED;    }    // 要求uri不能以'/'结尾，否则走其他协议    if (r->uri.data[r->uri.len - 1] == '/') {        return NGX_DECLINED;    }
    log = r->connection->log;
    /*     * ngx_http_map_uri_to_path() allocates memory for terminating '\0'     * so we do not need to reserve memory for '/' for possible redirect     */    // 解析文件路径到path中    last = ngx_http_map_uri_to_path(r, &path, &root, 0);    if (last == NULL) {        return NGX_HTTP_INTERNAL_SERVER_ERROR;    }
    path.len = last - path.data;
    ngx_log_debug1(NGX_LOG_DEBUG_HTTP, log, 0,                   "http filename: \"%s\"", path.data);
    clcf = ngx_http_get_module_loc_conf(r, ngx_http_core_module);    // 初始化文件实例    ngx_memzero(&of, sizeof(ngx_open_file_info_t));
    of.read_ahead = clcf->read_ahead;    of.directio = clcf->directio;    of.valid = clcf->open_file_cache_valid;    of.min_uses = clcf->open_file_cache_min_uses;    of.errors = clcf->open_file_cache_errors;    of.events = clcf->open_file_cache_events;
    if (ngx_http_set_disable_symlinks(r, clcf, &path, &of) != NGX_OK) {        return NGX_HTTP_INTERNAL_SERVER_ERROR;    }
    if (ngx_open_cached_file(clcf->open_file_cache, &path, &of, r->pool)        != NGX_OK)    {        switch (of.err) {
        case 0:            return NGX_HTTP_INTERNAL_SERVER_ERROR;
        case NGX_ENOENT:        case NGX_ENOTDIR:        case NGX_ENAMETOOLONG:
            level = NGX_LOG_ERR;            rc = NGX_HTTP_NOT_FOUND;            break;
        case NGX_EACCES:#if (NGX_HAVE_OPENAT)        case NGX_EMLINK:        case NGX_ELOOP:#endif
            level = NGX_LOG_ERR;            rc = NGX_HTTP_FORBIDDEN;            break;
        default:
            level = NGX_LOG_CRIT;            rc = NGX_HTTP_INTERNAL_SERVER_ERROR;            break;        }
        if (rc != NGX_HTTP_NOT_FOUND || clcf->log_not_found) {            ngx_log_error(level, log, of.err,                          "%s \"%s\" failed", of.failed, path.data);        }
        return rc;    }
    r->root_tested = !r->error_page;
    ngx_log_debug1(NGX_LOG_DEBUG_HTTP, log, 0, "http static fd: %d", of.fd);
    if (of.is_dir) {
        ngx_log_debug0(NGX_LOG_DEBUG_HTTP, log, 0, "http dir");
        ngx_http_clear_location(r);
        r->headers_out.location = ngx_list_push(&r->headers_out.headers);        if (r->headers_out.location == NULL) {            return NGX_HTTP_INTERNAL_SERVER_ERROR;        }
        len = r->uri.len + 1;
        if (!clcf->alias && r->args.len == 0) {            location = path.data + root;
            *last = '/';
        } else {            if (r->args.len) {                len += r->args.len + 1;            }
            location = ngx_pnalloc(r->pool, len);            if (location == NULL) {                ngx_http_clear_location(r);                return NGX_HTTP_INTERNAL_SERVER_ERROR;            }
            last = ngx_copy(location, r->uri.data, r->uri.len);
            *last = '/';
            if (r->args.len) {                *++last = '?';                ngx_memcpy(++last, r->args.data, r->args.len);            }        }
        r->headers_out.location->hash = 1;        ngx_str_set(&r->headers_out.location->key, "Location");        r->headers_out.location->value.len = len;        r->headers_out.location->value.data = location;
        return NGX_HTTP_MOVED_PERMANENTLY;    }
#if !(NGX_WIN32) /* the not regular files are probably Unix specific */
    if (!of.is_file) {        ngx_log_error(NGX_LOG_CRIT, log, 0,                      "\"%s\" is not a regular file", path.data);
        return NGX_HTTP_NOT_FOUND;    }
#endif    // 真正到内容输出的时候，post又是不被允许的方法    if (r->method == NGX_HTTP_POST) {        return NGX_HTTP_NOT_ALLOWED;    }    // 静态文件处理，将会忽略所有请求body参数    rc = ngx_http_discard_request_body(r);
    if (rc != NGX_OK) {        return rc;    }    // 输出文件内容到客户端    log->action = "sending response to client";
    r->headers_out.status = NGX_HTTP_OK;    r->headers_out.content_length_n = of.size;    r->headers_out.last_modified_time = of.mtime;    // 设置 ETag header    if (ngx_http_set_etag(r) != NGX_OK) {        return NGX_HTTP_INTERNAL_SERVER_ERROR;    }    // content-type 设置，大概就是根据文件后缀找到相应的content-type 输出即可    if (ngx_http_set_content_type(r) != NGX_OK) {        return NGX_HTTP_INTERNAL_SERVER_ERROR;    }
    if (r != r->main && of.size == 0) {        return ngx_http_send_header(r);    }
    r->allow_ranges = 1;
    /* we need to allocate all before the header would be sent */
    b = ngx_calloc_buf(r->pool);    if (b == NULL) {        return NGX_HTTP_INTERNAL_SERVER_ERROR;    }
    b->file = ngx_pcalloc(r->pool, sizeof(ngx_file_t));    if (b->file == NULL) {        return NGX_HTTP_INTERNAL_SERVER_ERROR;    }    // 发送头信息，如果是 head 请求，则到此为止    // 该header响应会添加一些公共的请求头一并返回　　 // 其中content-type是根据文件类型做的映射返回，如txt文件映射为 text/plain　　 // 具体可以由用户指定，在 mime.types 中添加映射即可    // 使用一系列的filter过滤器链进行处理    // 当文件未发生变化时，会返回304, 即不再返回更多信息    /**        Accept-Ranges: bytes        Connection: keep-alive        Content-Length: 18        Content-Type: text/plain        Date: Wed, 07 Oct 2020 09:01:12 GMT        ETag: "5f66fc46-12"        Last-Modified: Sun, 20 Sep 2020 06:52:54 GMT        Server: nginx/1.19.2     */    rc = ngx_http_send_header(r);
    if (rc == NGX_ERROR || rc > NGX_OK || r->header_only) {        return rc;    }    // 封装要响应的文件描述符，输出响应    b->file_pos = 0;    b->file_last = of.size;
    b->in_file = b->file_last ? 1: 0;    b->last_buf = (r == r->main) ? 1: 0;    b->last_in_chain = 1;
    b->file->fd = of.fd;    b->file->name = path;    b->file->log = log;    b->file->directio = of.is_directio;
    out.buf = b;    out.next = NULL;    // 一系列的响应过滤器处理，响应body    /**     * range_filter     * copy_filter     * output_chain -> output_chain_copy_buf     */    return ngx_http_output_filter(r, &out);}

整体可以简单用一句话说明，根据uri路径，结合root路径配置，得到文件信息，响应客户端。只处理 get/head请求，对文件内容无变化情况将会返回304。上面更多的是，只限于c语言的表达能力问题，做的许多变化，无须多看。

对于静态文件的处理，后续所有给定的参数都将被忽略掉。当然了也不是完全无用，不同参数也是有意义的，它用于检测文件是否发生变化。至于是html文件还是pdf或者txt，nginx并没有做特别的处理，它只是负责将内容返回给浏览器，浏览器做进一步解析从而达到html展现的效果。

另外，再次需要说明的一点是，nginx的性能优势是在于其巧妙地利用系统的非阻塞io，从而提升了处理能力，而且其扩展能力非常强，配置也非常友好。但其整体流程，与其他http服务器并无二致。

对于想要了解更多细节的同学，可以点开下面的代码，查看C语言的实现细节。

// http/ngx_http_core_module.c// 解析文件路径到path中u_char *ngx_http_map_uri_to_path(ngx_http_request_t *r, ngx_str_t *path,    size_t *root_length, size_t reserved){    u_char                    *last;    size_t                     alias;    ngx_http_core_loc_conf_t  *clcf;
    clcf = ngx_http_get_module_loc_conf(r, ngx_http_core_module);
    alias = clcf->alias;
    if (alias && !r->valid_location) {        ngx_log_error(NGX_LOG_ALERT, r->connection->log, 0,                      "\"alias\" cannot be used in location \"%V\" "                      "where URI was rewritten", &clcf->name);        return NULL;    }
    if (clcf->root_lengths == NULL) {
        *root_length = clcf->root.len;
        path->len = clcf->root.len + reserved + r->uri.len - alias + 1;
        path->data = ngx_pnalloc(r->pool, path->len);        if (path->data == NULL) {            return NULL;        }        // 将root根目录赋值给 path        last = ngx_copy(path->data, clcf->root.data, clcf->root.len);
    } else {
        if (alias == NGX_MAX_SIZE_T_VALUE) {            reserved += r->add_uri_to_alias ? r->uri.len + 1 : 1;
        } else {            reserved += r->uri.len - alias + 1;        }
        if (ngx_http_script_run(r, path, clcf->root_lengths->elts, reserved,                                clcf->root_values->elts)            == NULL)        {            return NULL;        }
        if (ngx_get_full_name(r->pool, (ngx_str_t *) &ngx_cycle->prefix, path)            != NGX_OK)        {            return NULL;        }
        *root_length = path->len - reserved;        last = path->data + *root_length;
        if (alias == NGX_MAX_SIZE_T_VALUE) {            if (!r->add_uri_to_alias) {                *last = '\0';                return last;            }
            alias = 0;        }    }    // 将uri的相对路径拼接到 path 中    last = ngx_copy(last, r->uri.data + alias, r->uri.len - alias);    *last = '\0';
    return last;}
// http/ngx_http_core_module.cngx_int_tngx_http_set_disable_symlinks(ngx_http_request_t *r,    ngx_http_core_loc_conf_t *clcf, ngx_str_t *path, ngx_open_file_info_t *of){#if (NGX_HAVE_OPENAT)    u_char     *p;    ngx_str_t   from;
    of->disable_symlinks = clcf->disable_symlinks;
    if (clcf->disable_symlinks_from == NULL) {        return NGX_OK;    }
    if (ngx_http_complex_value(r, clcf->disable_symlinks_from, &from)        != NGX_OK)    {        return NGX_ERROR;    }
    if (from.len == 0        || from.len > path->len        || ngx_memcmp(path->data, from.data, from.len) != 0)    {        return NGX_OK;    }
    if (from.len == path->len) {        of->disable_symlinks = NGX_DISABLE_SYMLINKS_OFF;        return NGX_OK;    }
    p = path->data + from.len;
    if (*p == '/') {        of->disable_symlinks_from = from.len;        return NGX_OK;    }
    p--;
    if (*p == '/') {        of->disable_symlinks_from = from.len - 1;    }#endif
    return NGX_OK;}

// core/ngx_open_file_cache.c// 尝试使用缓存文件ngx_int_tngx_open_cached_file(ngx_open_file_cache_t *cache, ngx_str_t *name,    ngx_open_file_info_t *of, ngx_pool_t *pool){    time_t                          now;    uint32_t                        hash;    ngx_int_t                       rc;    ngx_file_info_t                 fi;    ngx_pool_cleanup_t             *cln;    ngx_cached_open_file_t         *file;    ngx_pool_cleanup_file_t        *clnf;    ngx_open_file_cache_cleanup_t  *ofcln;
    of->fd = NGX_INVALID_FILE;    of->err = 0;    // 没有缓存，则重新打开文件    if (cache == NULL) {
        if (of->test_only) {
            if (ngx_file_info_wrapper(name, of, &fi, pool->log)                == NGX_FILE_ERROR)            {                return NGX_ERROR;            }
            of->uniq = ngx_file_uniq(&fi);            of->mtime = ngx_file_mtime(&fi);            of->size = ngx_file_size(&fi);            of->fs_size = ngx_file_fs_size(&fi);            of->is_dir = ngx_is_dir(&fi);            of->is_file = ngx_is_file(&fi);            of->is_link = ngx_is_link(&fi);            of->is_exec = ngx_is_exec(&fi);
            return NGX_OK;        }
        cln = ngx_pool_cleanup_add(pool, sizeof(ngx_pool_cleanup_file_t));        if (cln == NULL) {            return NGX_ERROR;        }        // 打开文件        rc = ngx_open_and_stat_file(name, of, pool->log);        // 找到对应文件，设置 handler 为 ngx_pool_cleanup_file        if (rc == NGX_OK && !of->is_dir) {            cln->handler = ngx_pool_cleanup_file;            clnf = cln->data;
            clnf->fd = of->fd;            clnf->name = name->data;            clnf->log = pool->log;        }
        return rc;    }
    cln = ngx_pool_cleanup_add(pool, sizeof(ngx_open_file_cache_cleanup_t));    if (cln == NULL) {        return NGX_ERROR;    }
    now = ngx_time();
    hash = ngx_crc32_long(name->data, name->len);
    file = ngx_open_file_lookup(cache, name, hash);
    if (file) {
        file->uses++;
        ngx_queue_remove(&file->queue);
        if (file->fd == NGX_INVALID_FILE && file->err == 0 && !file->is_dir) {
            /* file was not used often enough to keep open */
            rc = ngx_open_and_stat_file(name, of, pool->log);
            if (rc != NGX_OK && (of->err == 0 || !of->errors)) {                goto failed;            }
            goto add_event;        }
        if (file->use_event            || (file->event == NULL                && (of->uniq == 0 || of->uniq == file->uniq)                && now - file->created < of->valid#if (NGX_HAVE_OPENAT)                && of->disable_symlinks == file->disable_symlinks                && of->disable_symlinks_from == file->disable_symlinks_from#endif            ))        {            if (file->err == 0) {
                of->fd = file->fd;                of->uniq = file->uniq;                of->mtime = file->mtime;                of->size = file->size;
                of->is_dir = file->is_dir;                of->is_file = file->is_file;                of->is_link = file->is_link;                of->is_exec = file->is_exec;                of->is_directio = file->is_directio;
                if (!file->is_dir) {                    file->count++;                    ngx_open_file_add_event(cache, file, of, pool->log);                }
            } else {                of->err = file->err;#if (NGX_HAVE_OPENAT)                of->failed = file->disable_symlinks ? ngx_openat_file_n                                                    : ngx_open_file_n;#else                of->failed = ngx_open_file_n;#endif            }
            goto found;        }
        ngx_log_debug4(NGX_LOG_DEBUG_CORE, pool->log, 0,                       "retest open file: %s, fd:%d, c:%d, e:%d",                       file->name, file->fd, file->count, file->err);
        if (file->is_dir) {
            /*             * chances that directory became file are very small             * so test_dir flag allows to use a single syscall             * in ngx_file_info() instead of three syscalls             */
            of->test_dir = 1;        }
        of->fd = file->fd;        of->uniq = file->uniq;
        rc = ngx_open_and_stat_file(name, of, pool->log);
        if (rc != NGX_OK && (of->err == 0 || !of->errors)) {            goto failed;        }
        if (of->is_dir) {
            if (file->is_dir || file->err) {                goto update;            }
            /* file became directory */
        } else if (of->err == 0) {  /* file */
            if (file->is_dir || file->err) {                goto add_event;            }
            if (of->uniq == file->uniq) {
                if (file->event) {                    file->use_event = 1;                }
                of->is_directio = file->is_directio;
                goto update;            }
            /* file was changed */
        } else { /* error to cache */
            if (file->err || file->is_dir) {                goto update;            }
            /* file was removed, etc. */        }
        if (file->count == 0) {
            ngx_open_file_del_event(file);
            if (ngx_close_file(file->fd) == NGX_FILE_ERROR) {                ngx_log_error(NGX_LOG_ALERT, pool->log, ngx_errno,                              ngx_close_file_n " \"%V\" failed", name);            }
            goto add_event;        }
        ngx_rbtree_delete(&cache->rbtree, &file->node);
        cache->current--;
        file->close = 1;
        goto create;    }
    /* not found */
    rc = ngx_open_and_stat_file(name, of, pool->log);
    if (rc != NGX_OK && (of->err == 0 || !of->errors)) {        goto failed;    }
create:
    if (cache->current >= cache->max) {        ngx_expire_old_cached_files(cache, 0, pool->log);    }
    file = ngx_alloc(sizeof(ngx_cached_open_file_t), pool->log);
    if (file == NULL) {        goto failed;    }
    file->name = ngx_alloc(name->len + 1, pool->log);
    if (file->name == NULL) {        ngx_free(file);        file = NULL;        goto failed;    }
    ngx_cpystrn(file->name, name->data, name->len + 1);
    file->node.key = hash;
    ngx_rbtree_insert(&cache->rbtree, &file->node);
    cache->current++;
    file->uses = 1;    file->count = 0;    file->use_event = 0;    file->event = NULL;
add_event:
    ngx_open_file_add_event(cache, file, of, pool->log);
update:
    file->fd = of->fd;    file->err = of->err;#if (NGX_HAVE_OPENAT)    file->disable_symlinks = of->disable_symlinks;    file->disable_symlinks_from = of->disable_symlinks_from;#endif
    if (of->err == 0) {        file->uniq = of->uniq;        file->mtime = of->mtime;        file->size = of->size;
        file->close = 0;
        file->is_dir = of->is_dir;        file->is_file = of->is_file;        file->is_link = of->is_link;        file->is_exec = of->is_exec;        file->is_directio = of->is_directio;
        if (!of->is_dir) {            file->count++;        }    }
    file->created = now;
found:
    file->accessed = now;
    ngx_queue_insert_head(&cache->expire_queue, &file->queue);
    ngx_log_debug5(NGX_LOG_DEBUG_CORE, pool->log, 0,                   "cached open file: %s, fd:%d, c:%d, e:%d, u:%d",                   file->name, file->fd, file->count, file->err, file->uses);
    if (of->err == 0) {
        if (!of->is_dir) {            cln->handler = ngx_open_file_cleanup;            ofcln = cln->data;
            ofcln->cache = cache;            ofcln->file = file;            ofcln->min_uses = of->min_uses;            ofcln->log = pool->log;        }
        return NGX_OK;    }
    return NGX_ERROR;
failed:
    if (file) {        ngx_rbtree_delete(&cache->rbtree, &file->node);
        cache->current--;
        if (file->count == 0) {
            if (file->fd != NGX_INVALID_FILE) {                if (ngx_close_file(file->fd) == NGX_FILE_ERROR) {                    ngx_log_error(NGX_LOG_ALERT, pool->log, ngx_errno,                                  ngx_close_file_n " \"%s\" failed",                                  file->name);                }            }
            ngx_free(file->name);            ngx_free(file);
        } else {            file->close = 1;        }    }
    if (of->fd != NGX_INVALID_FILE) {        if (ngx_close_file(of->fd) == NGX_FILE_ERROR) {            ngx_log_error(NGX_LOG_ALERT, pool->log, ngx_errno,                          ngx_close_file_n " \"%V\" failed", name);        }    }
    return NGX_ERROR;}
// core/ngx_open_file_cache.c// 打开文件static ngx_int_tngx_open_and_stat_file(ngx_str_t *name, ngx_open_file_info_t *of,    ngx_log_t *log){    ngx_fd_t         fd;    ngx_file_info_t  fi;
    if (of->fd != NGX_INVALID_FILE) {
        if (ngx_file_info_wrapper(name, of, &fi, log) == NGX_FILE_ERROR) {            of->fd = NGX_INVALID_FILE;            return NGX_ERROR;        }
        if (of->uniq == ngx_file_uniq(&fi)) {            goto done;        }
    } else if (of->test_dir) {
        if (ngx_file_info_wrapper(name, of, &fi, log) == NGX_FILE_ERROR) {            of->fd = NGX_INVALID_FILE;            return NGX_ERROR;        }
        if (ngx_is_dir(&fi)) {            goto done;        }    }
    if (!of->log) {
        /*         * Use non-blocking open() not to hang on FIFO files, etc.         * This flag has no effect on a regular files.         */        // 使用非阻塞io打开文件        fd = ngx_open_file_wrapper(name, of, NGX_FILE_RDONLY|NGX_FILE_NONBLOCK,                                   NGX_FILE_OPEN, 0, log);
    } else {        fd = ngx_open_file_wrapper(name, of, NGX_FILE_APPEND,                                   NGX_FILE_CREATE_OR_OPEN,                                   NGX_FILE_DEFAULT_ACCESS, log);    }
    if (fd == NGX_INVALID_FILE) {        of->fd = NGX_INVALID_FILE;        return NGX_ERROR;    }    // 检测文件有效性    if (ngx_fd_info(fd, &fi) == NGX_FILE_ERROR) {        ngx_log_error(NGX_LOG_CRIT, log, ngx_errno,                      ngx_fd_info_n " \"%V\" failed", name);
        if (ngx_close_file(fd) == NGX_FILE_ERROR) {            ngx_log_error(NGX_LOG_ALERT, log, ngx_errno,                          ngx_close_file_n " \"%V\" failed", name);        }
        of->fd = NGX_INVALID_FILE;
        return NGX_ERROR;    }
    if (ngx_is_dir(&fi)) {        if (ngx_close_file(fd) == NGX_FILE_ERROR) {            ngx_log_error(NGX_LOG_ALERT, log, ngx_errno,                          ngx_close_file_n " \"%V\" failed", name);        }
        of->fd = NGX_INVALID_FILE;
    } else {        of->fd = fd;        // 如果文件过大，则先预读取部分数据        if (of->read_ahead && ngx_file_size(&fi) > NGX_MIN_READ_AHEAD) {            if (ngx_read_ahead(fd, of->read_ahead) == NGX_ERROR) {                ngx_log_error(NGX_LOG_ALERT, log, ngx_errno,                              ngx_read_ahead_n " \"%V\" failed", name);            }        }
        if (of->directio <= ngx_file_size(&fi)) {            if (ngx_directio_on(fd) == NGX_FILE_ERROR) {                ngx_log_error(NGX_LOG_ALERT, log, ngx_errno,                              ngx_directio_on_n " \"%V\" failed", name);
            } else {                of->is_directio = 1;            }        }    }
done:    // 复制文件信息返回    of->uniq = ngx_file_uniq(&fi);    of->mtime = ngx_file_mtime(&fi);    of->size = ngx_file_size(&fi);    of->fs_size = ngx_file_fs_size(&fi);    of->is_dir = ngx_is_dir(&fi);    of->is_file = ngx_is_file(&fi);    of->is_link = ngx_is_link(&fi);    of->is_exec = ngx_is_exec(&fi);
    return NGX_OK;}