Nginx(六)：配置解析之location解析

　　nginx成为非常流行的代理服务软件，最根本的原因也许是在于其强悍性能。但还有一些必要的条件，比如功能的完整，配置的易用，能够解决各种各样的实际需求问题，这些是一个好的软件的必备特性。

　　那么，今天我们就来看看nginx配置的部分原则和解析原理吧。我们只做location部分的细节解析，但其他配置道理基本相通，推一及二即可。

1. nginx配置的基本原则

　　nginx是支持高度配置化的，那么也许就会涉及许多部分的配置，要如何协调好这些配置，是个问题。比如是否将配置定义一个个独立的文件，或者其他。

　　然而，nginx使用一个统一的配置文件，管理起了所有的配置工作。即 nginx.conf, 其默认位置是 $NGINX_HOME/nginx.conf, 在这个主配置文件中，又可以包含其他任意多的配置文件，从而达到统一管理的作用。

　　其默认配置nginx.conf如下：

    
#user  nobody;
worker_processes  1;

#error_log  logs/error.log;
#error_log  logs/error.log  notice;
#error_log  logs/error.log  info;

#pid        logs/nginx.pid;


events {
    worker_connections  1024;
}


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       80;
        server_name  localhost;

        #charset koi8-r;

        #access_log  logs/host.access.log  main;

        location / {
            root   html;
            index  index.html index.htm;
        }

        #error_page  404              /404.html;

        # redirect server error pages to the static page /50x.html
        #
        error_page   500 502 503 504  /50x.html;
        location = /50x.html {
            root   html;
        }

        # proxy the PHP scripts to Apache listening on 127.0.0.1:80
        #
        #location ~ \.php$ {
        #    proxy_pass   http://127.0.0.1;
        #}

        # pass the PHP scripts to FastCGI server listening on 127.0.0.1:9000
        #
        #location ~ \.php$ {
        #    root           html;
        #    fastcgi_pass   127.0.0.1:9000;
        #    fastcgi_index  index.php;
        #    fastcgi_param  SCRIPT_FILENAME  /scripts$fastcgi_script_name;
        #    include        fastcgi_params;
        #}

        # deny access to .htaccess files, if Apache's document root
        # concurs with nginx's one
        #
        #location ~ /\.ht {
        #    deny  all;
        #}
    }


    # another virtual host using mix of IP-, name-, and port-based configuration
    #
    #server {
    #    listen       8000;
    #    listen       somename:8080;
    #    server_name  somename  alias  another.alias;

    #    location / {
    #        root   html;
    #        index  index.html index.htm;
    #    }
    #}


    # HTTPS server
    #
    #server {
    #    listen       443 ssl;
    #    server_name  localhost;

    #    ssl_certificate      cert.pem;
    #    ssl_certificate_key  cert.key;

    #    ssl_session_cache    shared:SSL:1m;
    #    ssl_session_timeout  5m;

    #    ssl_ciphers  HIGH:!aNULL:!MD5;
    #    ssl_prefer_server_ciphers  on;

    #    location / {
    #        root   html;
    #        index  index.html index.htm;
    #    }
    #}

}

　　这很明显不是什么标准语言语法，但其同样遵从一定的准则，从而让用户更易于理解配置。如：

　　　　1. 每一个细配置项，都使用一个’;’作为结束标识;
　　　　2. ‘#’ 代表该行被注释（这几乎是linux默认标准）;
　　　　3. 使用'{}’表示一个配置块，'{}’中代表其子项配置;
　　　　4. 使用include可以包含其他文件的配置，相当于将其中的配置项copy到当前位置，该包含路径可以是相对路径也可以是绝对路径;

　　因此，基本上，你只要按照这个标准来做配置，至少语法 是不会有误了。但是，具体应该如何配置呢？实际上这要依赖于某类操作的具体实现，比如 location 的 配置， user 的配置，都是有各自的含义的。如果想要具体了解各细节配置，则必须要查询官网的配置定义了。请参考： https://docs.nginx.com/nginx/admin-guide/basic-functionality/managing-configuration-files/

　　总体上来说，nginx有几个顶级配置: 

　　　　events – 连接类的配置，比如最大连接数配置
　　　　http – 重头戏，http模块配置，所有的代理服务http服务都在其子配置下
　　　　mail – 邮件配置
　　　　stream – TCP、UDP 底层通信协议配置，功能与http模块相仿
　　一般地我们接接触最多的应该就是http配置了，至于其他功能，没有实践就没有发言权，略去不说。

2. location的配置用例

　　location的本义是用于定位一个http请求匹配情况，用于确定某个路径的请求应该如何做转换处理。它是属于 http 模块下的 server 模块下的一个选项配置。即 nginx -> http -> server -> location {..} 是其配置体现。它拥有相当多的配置项，因为做反向代理或其他服务器时，往往都可以通过这个配置，将功能完成。

　　如下几个配置项，可供参考：

http {
    upstream backend {
        ip_hash;
        server backend1.example.com weight=5;
        server backend2.example.com;
        server 192.0.0.1 backup;
    }
    server {
        root /www/data;
        # 路径相等处理，优先级最高
        location = / {
            #...
        }
        # 根路径配置，优先级最低
        location / {
            root /data/www;
        }
        # 带前缀的配置，优先级其次
        location /images/ {
            root /data;
        }
        # 正则匹配的配置，优先级较高
        location ~ \.(gif|jpg|png)$ {
            root /data/images;
        }
        # 正则取反配置
        location ^~ \.(php)$ {
            root /data/other;
        }
        # 反向代理的配置，将请求转换给后端服务
        # 如果backend是一个 upstream 配置，则做为一个负载均衡器使用
        location /api1 {
            proxy_set_header Host $host;
            proxy_set_header X-Real-IP $remote_addr;
            proxy_pass http://backend;
        }
        location /api2 {
            proxy_pass http://www.abc.com;
        }
        # 路径重写
        location /users/ {
            rewrite ^/users/(.*)$ /show?user=$1 break;
        }
        # 带状态码的返回配置
        location /wrong/url {
            return 404;
            open_file_cache_errors off;
        }
        location /permanently/moved/url {
            return 301 http://www.example.com/moved/here;
        }
        # 响应内容替换
        location / {
            sub_filter     'href="http://127.0.0.1:8080/'    'href="https://$host/';
            sub_filter     'img src="http://127.0.0.1:8080/' 'img src="https://$host/';
            sub_filter_once on;
        }
    }
}

　　更多内容可查阅官网: https://docs.nginx.com/nginx/admin-guide/web-server/web-server/

　　总体上来说，location提供了可以配置如何查找本地文件，以及可以配置如何转发请求到其他服务器的方式。其中，还有很多附加的设置各种需求变量的实现，以辅助我们实现一些正常请求提供的内容。配置比较多，到真正使用时，按需配置即可。一般也是一次配置，永久使用，不会太费事。

3. location配置的解析

　　nginx有自己的一套配置方法，那么这些配置好了的语句，如何应用到具体的服务上呢？自然是需要先进行解析，然后放置到对应的内存空间变量中，然后在需要的时候进行读取判定，以及转换了。大体思路如此，但如何解析配置却并非易事。因为我们的配置是无数现有配置的任意组合，如何有效的放置到可理解的位置，应该需要单独的数据结构设计，以及解析步骤。实际上，这也相当于是一个简单的编译器或解析器，它需要将文本解析为认识的东西。

　　下面我们就一起来看看nginx都是如何解析这些配置的吧！（这自然是在启动时完成的工作）

// 首先，nginx会解析启动行命令，这里面可以指定配置文件
// core/nginx.c 
static ngx_int_t
ngx_get_options(int argc, char *const *argv)
{
    u_char     *p;
    ngx_int_t   i;

    for (i = 1; i < argc; i++) {

        p = (u_char *) argv[i];

        if (*p++ != '-') {
            ngx_log_stderr(0, "invalid option: \"%s\"", argv[i]);
            return NGX_ERROR;
        }

        while (*p) {

            switch (*p++) {

            case '?':
            case 'h':
                ngx_show_version = 1;
                ngx_show_help = 1;
                break;

            case 'v':
                ngx_show_version = 1;
                break;

            case 'V':
                ngx_show_version = 1;
                ngx_show_configure = 1;
                break;
            // -t 测试配置文件有效性
            case 't':
                ngx_test_config = 1;
                break;

            case 'T':
                ngx_test_config = 1;
                ngx_dump_config = 1;
                break;

            case 'q':
                ngx_quiet_mode = 1;
                break;

            case 'p':
                if (*p) {
                    ngx_prefix = p;
                    goto next;
                }

                if (argv[++i]) {
                    ngx_prefix = (u_char *) argv[i];
                    goto next;
                }

                ngx_log_stderr(0, "option \"-p\" requires directory name");
                return NGX_ERROR;
            // -c nginx.conf 指定nginx配置文件路径
            case 'c':
                if (*p) {
                    ngx_conf_file = p;
                    goto next;
                }

                if (argv[++i]) {
                    ngx_conf_file = (u_char *) argv[i];
                    goto next;
                }

                ngx_log_stderr(0, "option \"-c\" requires file name");
                return NGX_ERROR;

            case 'g':
                if (*p) {
                    ngx_conf_params = p;
                    goto next;
                }

                if (argv[++i]) {
                    ngx_conf_params = (u_char *) argv[i];
                    goto next;
                }

                ngx_log_stderr(0, "option \"-g\" requires parameter");
                return NGX_ERROR;
            // -s (stop|quit|reopen|reload) 向现有运行的nginx进程发起控制命令
            case 's':
                // 紧贴式给出命令: -sstop, -sreload
                if (*p) {
                    ngx_signal = (char *) p;

                } else if (argv[++i]) {
                    ngx_signal = argv[i];

                } else {
                    ngx_log_stderr(0, "option \"-s\" requires parameter");
                    return NGX_ERROR;
                }

                if (ngx_strcmp(ngx_signal, "stop") == 0
                    || ngx_strcmp(ngx_signal, "quit") == 0
                    || ngx_strcmp(ngx_signal, "reopen") == 0
                    || ngx_strcmp(ngx_signal, "reload") == 0)
                {
                    ngx_process = NGX_PROCESS_SIGNALLER;
                    goto next;
                }

                ngx_log_stderr(0, "invalid option: \"-s %s\"", ngx_signal);
                return NGX_ERROR;

            default:
                ngx_log_stderr(0, "invalid option: \"%c\"", *(p - 1));
                return NGX_ERROR;
            }
        }

    next:

        continue;
    }

    return NGX_OK;
}

　　以上，是对命令行参数的简单解析，解析出来的变量放入到各全局变量中：ngx_show_version|ngx_show_help|ngx_show_configure|ngx_test_config|ngx_dump_config|ngx_quiet_mode|ngx_prefix|ngx_conf_file|ngx_conf_params|ngx_signal.

　　以上，最重要的是两个参数：-c -s, 用于指定配置文件和操作现有nginx进程。当然，对于配置解析，自然最重要的是 -c 命令了。但对于一些没有指定的配置值，则使用系统的默认值。其处理如下：

// core/nginx.c
static ngx_int_t
ngx_process_options(ngx_cycle_t *cycle)
{
    u_char  *p;
    size_t   len;

    if (ngx_prefix) {
        len = ngx_strlen(ngx_prefix);
        p = ngx_prefix;

        if (len && !ngx_path_separator(p[len - 1])) {
            p = ngx_pnalloc(cycle->pool, len + 1);
            if (p == NULL) {
                return NGX_ERROR;
            }

            ngx_memcpy(p, ngx_prefix, len);
            p[len++] = '/';
        }

        cycle->conf_prefix.len = len;
        cycle->conf_prefix.data = p;
        cycle->prefix.len = len;
        cycle->prefix.data = p;

    } else {

#ifndef NGX_PREFIX

        p = ngx_pnalloc(cycle->pool, NGX_MAX_PATH);
        if (p == NULL) {
            return NGX_ERROR;
        }

        if (ngx_getcwd(p, NGX_MAX_PATH) == 0) {
            ngx_log_stderr(ngx_errno, "[emerg]: " ngx_getcwd_n " failed");
            return NGX_ERROR;
        }

        len = ngx_strlen(p);

        p[len++] = '/';

        cycle->conf_prefix.len = len;
        cycle->conf_prefix.data = p;
        cycle->prefix.len = len;
        cycle->prefix.data = p;

#else

#ifdef NGX_CONF_PREFIX
        // 默认路径前缀: conf/
        ngx_str_set(&cycle->conf_prefix, NGX_CONF_PREFIX);
#else
        ngx_str_set(&cycle->conf_prefix, NGX_PREFIX);
#endif
        ngx_str_set(&cycle->prefix, NGX_PREFIX);

#endif
    }

    if (ngx_conf_file) {
        cycle->conf_file.len = ngx_strlen(ngx_conf_file);
        cycle->conf_file.data = ngx_conf_file;

    } else {
        // 默认配置文件: conf/nginx.conf
        ngx_str_set(&cycle->conf_file, NGX_CONF_PATH);
    }

    if (ngx_conf_full_name(cycle, &cycle->conf_file, 0) != NGX_OK) {
        return NGX_ERROR;
    }

    for (p = cycle->conf_file.data + cycle->conf_file.len - 1;
         p > cycle->conf_file.data;
         p--)
    {
        if (ngx_path_separator(*p)) {
            cycle->conf_prefix.len = p - cycle->conf_file.data + 1;
            cycle->conf_prefix.data = cycle->conf_file.data;
            break;
        }
    }

    if (ngx_conf_params) {
        cycle->conf_param.len = ngx_strlen(ngx_conf_params);
        cycle->conf_param.data = ngx_conf_params;
    }

    if (ngx_test_config) {
        cycle->log->log_level = NGX_LOG_INFO;
    }

    return NGX_OK;
}

　　真正的配置文件解析是在初始化cycle的时候处理实现的：

// core/ngx_cycle.c
ngx_cycle_t *
ngx_init_cycle(ngx_cycle_t *old_cycle)
{
    void                *rv;
    char               **senv;
    ngx_uint_t           i, n;
    ngx_log_t           *log;
    ngx_time_t          *tp;
    ngx_conf_t           conf;
    ngx_pool_t          *pool;
    ngx_cycle_t         *cycle, **old;
    ngx_shm_zone_t      *shm_zone, *oshm_zone;
    ngx_list_part_t     *part, *opart;
    ngx_open_file_t     *file;
    ngx_listening_t     *ls, *nls;
    ngx_core_conf_t     *ccf, *old_ccf;
    ngx_core_module_t   *module;
    char                 hostname[NGX_MAXHOSTNAMELEN];

    ngx_timezone_update();

    /* force localtime update with a new timezone */

    tp = ngx_timeofday();
    tp->sec = 0;

    ngx_time_update();


    log = old_cycle->log;

    pool = ngx_create_pool(NGX_CYCLE_POOL_SIZE, log);
    if (pool == NULL) {
        return NULL;
    }
    pool->log = log;

    cycle = ngx_pcalloc(pool, sizeof(ngx_cycle_t));
    if (cycle == NULL) {
        ngx_destroy_pool(pool);
        return NULL;
    }

    cycle->pool = pool;
    cycle->log = log;
    cycle->old_cycle = old_cycle;

    cycle->conf_prefix.len = old_cycle->conf_prefix.len;
    cycle->conf_prefix.data = ngx_pstrdup(pool, &old_cycle->conf_prefix);
    if (cycle->conf_prefix.data == NULL) {
        ngx_destroy_pool(pool);
        return NULL;
    }

    cycle->prefix.len = old_cycle->prefix.len;
    cycle->prefix.data = ngx_pstrdup(pool, &old_cycle->prefix);
    if (cycle->prefix.data == NULL) {
        ngx_destroy_pool(pool);
        return NULL;
    }

    cycle->conf_file.len = old_cycle->conf_file.len;
    cycle->conf_file.data = ngx_pnalloc(pool, old_cycle->conf_file.len + 1);
    if (cycle->conf_file.data == NULL) {
        ngx_destroy_pool(pool);
        return NULL;
    }
    ngx_cpystrn(cycle->conf_file.data, old_cycle->conf_file.data,
                old_cycle->conf_file.len + 1);

    cycle->conf_param.len = old_cycle->conf_param.len;
    cycle->conf_param.data = ngx_pstrdup(pool, &old_cycle->conf_param);
    if (cycle->conf_param.data == NULL) {
        ngx_destroy_pool(pool);
        return NULL;
    }


    n = old_cycle->paths.nelts ? old_cycle->paths.nelts : 10;

    if (ngx_array_init(&cycle->paths, pool, n, sizeof(ngx_path_t *))
        != NGX_OK)
    {
        ngx_destroy_pool(pool);
        return NULL;
    }

    ngx_memzero(cycle->paths.elts, n * sizeof(ngx_path_t *));


    if (ngx_array_init(&cycle->config_dump, pool, 1, sizeof(ngx_conf_dump_t))
        != NGX_OK)
    {
        ngx_destroy_pool(pool);
        return NULL;
    }
    // 使用红黑树存放配置信息
    ngx_rbtree_init(&cycle->config_dump_rbtree, &cycle->config_dump_sentinel,
                    ngx_str_rbtree_insert_value);
    // 默认使用 20 个端口服务
    if (old_cycle->open_files.part.nelts) {
        n = old_cycle->open_files.part.nelts;
        for (part = old_cycle->open_files.part.next; part; part = part->next) {
            n += part->nelts;
        }

    } else {
        n = 20;
    }
    // 每个监听端口使用一个 open_files 表示
    if (ngx_list_init(&cycle->open_files, pool, n, sizeof(ngx_open_file_t))
        != NGX_OK)
    {
        ngx_destroy_pool(pool);
        return NULL;
    }


    if (old_cycle->shared_memory.part.nelts) {
        n = old_cycle->shared_memory.part.nelts;
        for (part = old_cycle->shared_memory.part.next; part; part = part->next)
        {
            n += part->nelts;
        }

    } else {
        n = 1;
    }

    if (ngx_list_init(&cycle->shared_memory, pool, n, sizeof(ngx_shm_zone_t))
        != NGX_OK)
    {
        ngx_destroy_pool(pool);
        return NULL;
    }

    n = old_cycle->listening.nelts ? old_cycle->listening.nelts : 10;

    if (ngx_array_init(&cycle->listening, pool, n, sizeof(ngx_listening_t))
        != NGX_OK)
    {
        ngx_destroy_pool(pool);
        return NULL;
    }

    ngx_memzero(cycle->listening.elts, n * sizeof(ngx_listening_t));


    ngx_queue_init(&cycle->reusable_connections_queue);


    cycle->conf_ctx = ngx_pcalloc(pool, ngx_max_module * sizeof(void *));
    if (cycle->conf_ctx == NULL) {
        ngx_destroy_pool(pool);
        return NULL;
    }

    // 获取当前机器的hostname
    if (gethostname(hostname, NGX_MAXHOSTNAMELEN) == -1) {
        ngx_log_error(NGX_LOG_EMERG, log, ngx_errno, "gethostname() failed");
        ngx_destroy_pool(pool);
        return NULL;
    }

    /* on Linux gethostname() silently truncates name that does not fit */

    hostname[NGX_MAXHOSTNAMELEN - 1] = '\0';
    cycle->hostname.len = ngx_strlen(hostname);

    cycle->hostname.data = ngx_pnalloc(pool, cycle->hostname.len);
    if (cycle->hostname.data == NULL) {
        ngx_destroy_pool(pool);
        return NULL;
    }

    ngx_strlow(cycle->hostname.data, (u_char *) hostname, cycle->hostname.len);

    // 创建module内存空间
    if (ngx_cycle_modules(cycle) != NGX_OK) {
        ngx_destroy_pool(pool);
        return NULL;
    }

    // 让各模块依次进行配置
    for (i = 0; cycle->modules[i]; i++) {
        // NGINX_CORE_MODULE 可以进行配置文件处理
        // 即几套顶级模块, http,events,mail,...
        if (cycle->modules[i]->type != NGX_CORE_MODULE) {
            continue;
        }

        module = cycle->modules[i]->ctx;
        // 调用各模块的 create_conf 实现配置加载
        // 其中，以为的http模块会进行解析，其实却没有
        if (module->create_conf) {
            rv = module->create_conf(cycle);
            if (rv == NULL) {
                ngx_destroy_pool(pool);
                return NULL;
            }
            cycle->conf_ctx[cycle->modules[i]->index] = rv;
        }
    }


    senv = environ;


    ngx_memzero(&conf, sizeof(ngx_conf_t));
    /* STUB: init array ? */
    conf.args = ngx_array_create(pool, 10, sizeof(ngx_str_t));
    if (conf.args == NULL) {
        ngx_destroy_pool(pool);
        return NULL;
    }

    conf.temp_pool = ngx_create_pool(NGX_CYCLE_POOL_SIZE, log);
    if (conf.temp_pool == NULL) {
        ngx_destroy_pool(pool);
        return NULL;
    }


    conf.ctx = cycle->conf_ctx;
    conf.cycle = cycle;
    conf.pool = pool;
    conf.log = log;
    conf.module_type = NGX_CORE_MODULE;
    conf.cmd_type = NGX_MAIN_CONF;

#if 0
    log->log_level = NGX_LOG_DEBUG_ALL;
#endif

    if (ngx_conf_param(&conf) != NGX_CONF_OK) {
        environ = senv;
        ngx_destroy_cycle_pools(&conf);
        return NULL;
    }

    if (ngx_conf_parse(&conf, &cycle->conf_file) != NGX_CONF_OK) {
        environ = senv;
        ngx_destroy_cycle_pools(&conf);
        return NULL;
    }

    if (ngx_test_config && !ngx_quiet_mode) {
        ngx_log_stderr(0, "the configuration file %s syntax is ok",
                       cycle->conf_file.data);
    }

    for (i = 0; cycle->modules[i]; i++) {
        if (cycle->modules[i]->type != NGX_CORE_MODULE) {
            continue;
        }

        module = cycle->modules[i]->ctx;

        if (module->init_conf) {
            if (module->init_conf(cycle,
                                  cycle->conf_ctx[cycle->modules[i]->index])
                == NGX_CONF_ERROR)
            {
                environ = senv;
                ngx_destroy_cycle_pools(&conf);
                return NULL;
            }
        }
    }

    if (ngx_process == NGX_PROCESS_SIGNALLER) {
        return cycle;
    }

    ccf = (ngx_core_conf_t *) ngx_get_conf(cycle->conf_ctx, ngx_core_module);

    if (ngx_test_config) {

        if (ngx_create_pidfile(&ccf->pid, log) != NGX_OK) {
            goto failed;
        }

    } else if (!ngx_is_init_cycle(old_cycle)) {

        /*
         * we do not create the pid file in the first ngx_init_cycle() call
         * because we need to write the demonized process pid
         */

        old_ccf = (ngx_core_conf_t *) ngx_get_conf(old_cycle->conf_ctx,
                                                   ngx_core_module);
        if (ccf->pid.len != old_ccf->pid.len
            || ngx_strcmp(ccf->pid.data, old_ccf->pid.data) != 0)
        {
            /* new pid file name */

            if (ngx_create_pidfile(&ccf->pid, log) != NGX_OK) {
                goto failed;
            }

            ngx_delete_pidfile(old_cycle);
        }
    }


    if (ngx_test_lockfile(cycle->lock_file.data, log) != NGX_OK) {
        goto failed;
    }


    if (ngx_create_paths(cycle, ccf->user) != NGX_OK) {
        goto failed;
    }


    if (ngx_log_open_default(cycle) != NGX_OK) {
        goto failed;
    }

    /* open the new files */

    part = &cycle->open_files.part;
    file = part->elts;

    for (i = 0; /* void */ ; i++) {

        if (i >= part->nelts) {
            if (part->next == NULL) {
                break;
            }
            part = part->next;
            file = part->elts;
            i = 0;
        }

        if (file[i].name.len == 0) {
            continue;
        }

        file[i].fd = ngx_open_file(file[i].name.data,
                                   NGX_FILE_APPEND,
                                   NGX_FILE_CREATE_OR_OPEN,
                                   NGX_FILE_DEFAULT_ACCESS);

        ngx_log_debug3(NGX_LOG_DEBUG_CORE, log, 0,
                       "log: %p %d \"%s\"",
                       &file[i], file[i].fd, file[i].name.data);

        if (file[i].fd == NGX_INVALID_FILE) {
            ngx_log_error(NGX_LOG_EMERG, log, ngx_errno,
                          ngx_open_file_n " \"%s\" failed",
                          file[i].name.data);
            goto failed;
        }

#if !(NGX_WIN32)
        if (fcntl(file[i].fd, F_SETFD, FD_CLOEXEC) == -1) {
            ngx_log_error(NGX_LOG_EMERG, log, ngx_errno,
                          "fcntl(FD_CLOEXEC) \"%s\" failed",
                          file[i].name.data);
            goto failed;
        }
#endif
    }

    cycle->log = &cycle->new_log;
    pool->log = &cycle->new_log;


    /* create shared memory */

    part = &cycle->shared_memory.part;
    shm_zone = part->elts;

    for (i = 0; /* void */ ; i++) {

        if (i >= part->nelts) {
            if (part->next == NULL) {
                break;
            }
            part = part->next;
            shm_zone = part->elts;
            i = 0;
        }

        if (shm_zone[i].shm.size == 0) {
            ngx_log_error(NGX_LOG_EMERG, log, 0,
                          "zero size shared memory zone \"%V\"",
                          &shm_zone[i].shm.name);
            goto failed;
        }

        shm_zone[i].shm.log = cycle->log;

        opart = &old_cycle->shared_memory.part;
        oshm_zone = opart->elts;

        for (n = 0; /* void */ ; n++) {

            if (n >= opart->nelts) {
                if (opart->next == NULL) {
                    break;
                }
                opart = opart->next;
                oshm_zone = opart->elts;
                n = 0;
            }

            if (shm_zone[i].shm.name.len != oshm_zone[n].shm.name.len) {
                continue;
            }

            if (ngx_strncmp(shm_zone[i].shm.name.data,
                            oshm_zone[n].shm.name.data,
                            shm_zone[i].shm.name.len)
                != 0)
            {
                continue;
            }

            if (shm_zone[i].tag == oshm_zone[n].tag
                && shm_zone[i].shm.size == oshm_zone[n].shm.size
                && !shm_zone[i].noreuse)
            {
                shm_zone[i].shm.addr = oshm_zone[n].shm.addr;
#if (NGX_WIN32)
                shm_zone[i].shm.handle = oshm_zone[n].shm.handle;
#endif

                if (shm_zone[i].init(&shm_zone[i], oshm_zone[n].data)
                    != NGX_OK)
                {
                    goto failed;
                }

                goto shm_zone_found;
            }

            break;
        }

        if (ngx_shm_alloc(&shm_zone[i].shm) != NGX_OK) {
            goto failed;
        }

        if (ngx_init_zone_pool(cycle, &shm_zone[i]) != NGX_OK) {
            goto failed;
        }

        if (shm_zone[i].init(&shm_zone[i], NULL) != NGX_OK) {
            goto failed;
        }

    shm_zone_found:

        continue;
    }


    /* handle the listening sockets */

    if (old_cycle->listening.nelts) {
        ls = old_cycle->listening.elts;
        for (i = 0; i < old_cycle->listening.nelts; i++) {
            ls[i].remain = 0;
        }

        nls = cycle->listening.elts;
        for (n = 0; n < cycle->listening.nelts; n++) {

            for (i = 0; i < old_cycle->listening.nelts; i++) {
                if (ls[i].ignore) {
                    continue;
                }

                if (ls[i].remain) {
                    continue;
                }

                if (ls[i].type != nls[n].type) {
                    continue;
                }

                if (ngx_cmp_sockaddr(nls[n].sockaddr, nls[n].socklen,
                                     ls[i].sockaddr, ls[i].socklen, 1)
                    == NGX_OK)
                {
                    nls[n].fd = ls[i].fd;
                    nls[n].inherited = ls[i].inherited;
                    nls[n].previous = &ls[i];
                    ls[i].remain = 1;

                    if (ls[i].backlog != nls[n].backlog) {
                        nls[n].listen = 1;
                    }

#if (NGX_HAVE_DEFERRED_ACCEPT && defined SO_ACCEPTFILTER)

                    /*
                     * FreeBSD, except the most recent versions,
                     * could not remove accept filter
                     */
                    nls[n].deferred_accept = ls[i].deferred_accept;

                    if (ls[i].accept_filter && nls[n].accept_filter) {
                        if (ngx_strcmp(ls[i].accept_filter,
                                       nls[n].accept_filter)
                            != 0)
                        {
                            nls[n].delete_deferred = 1;
                            nls[n].add_deferred = 1;
                        }

                    } else if (ls[i].accept_filter) {
                        nls[n].delete_deferred = 1;

                    } else if (nls[n].accept_filter) {
                        nls[n].add_deferred = 1;
                    }
#endif

#if (NGX_HAVE_DEFERRED_ACCEPT && defined TCP_DEFER_ACCEPT)

                    if (ls[i].deferred_accept && !nls[n].deferred_accept) {
                        nls[n].delete_deferred = 1;

                    } else if (ls[i].deferred_accept != nls[n].deferred_accept)
                    {
                        nls[n].add_deferred = 1;
                    }
#endif

#if (NGX_HAVE_REUSEPORT)
                    if (nls[n].reuseport && !ls[i].reuseport) {
                        nls[n].add_reuseport = 1;
                    }
#endif

                    break;
                }
            }

            if (nls[n].fd == (ngx_socket_t) -1) {
                nls[n].open = 1;
#if (NGX_HAVE_DEFERRED_ACCEPT && defined SO_ACCEPTFILTER)
                if (nls[n].accept_filter) {
                    nls[n].add_deferred = 1;
                }
#endif
#if (NGX_HAVE_DEFERRED_ACCEPT && defined TCP_DEFER_ACCEPT)
                if (nls[n].deferred_accept) {
                    nls[n].add_deferred = 1;
                }
#endif
            }
        }

    } else {
        ls = cycle->listening.elts;
        for (i = 0; i < cycle->listening.nelts; i++) {
            ls[i].open = 1;
#if (NGX_HAVE_DEFERRED_ACCEPT && defined SO_ACCEPTFILTER)
            if (ls[i].accept_filter) {
                ls[i].add_deferred = 1;
            }
#endif
#if (NGX_HAVE_DEFERRED_ACCEPT && defined TCP_DEFER_ACCEPT)
            if (ls[i].deferred_accept) {
                ls[i].add_deferred = 1;
            }
#endif
        }
    }

    if (ngx_open_listening_sockets(cycle) != NGX_OK) {
        goto failed;
    }

    if (!ngx_test_config) {
        ngx_configure_listening_sockets(cycle);
    }


    /* commit the new cycle configuration */

    if (!ngx_use_stderr) {
        (void) ngx_log_redirect_stderr(cycle);
    }

    pool->log = cycle->log;

    if (ngx_init_modules(cycle) != NGX_OK) {
        /* fatal */
        exit(1);
    }


    /* close and delete stuff that lefts from an old cycle */

    /* free the unnecessary shared memory */

    opart = &old_cycle->shared_memory.part;
    oshm_zone = opart->elts;

    for (i = 0; /* void */ ; i++) {

        if (i >= opart->nelts) {
            if (opart->next == NULL) {
                goto old_shm_zone_done;
            }
            opart = opart->next;
            oshm_zone = opart->elts;
            i = 0;
        }

        part = &cycle->shared_memory.part;
        shm_zone = part->elts;

        for (n = 0; /* void */ ; n++) {

            if (n >= part->nelts) {
                if (part->next == NULL) {
                    break;
                }
                part = part->next;
                shm_zone = part->elts;
                n = 0;
            }

            if (oshm_zone[i].shm.name.len != shm_zone[n].shm.name.len) {
                continue;
            }

            if (ngx_strncmp(oshm_zone[i].shm.name.data,
                            shm_zone[n].shm.name.data,
                            oshm_zone[i].shm.name.len)
                != 0)
            {
                continue;
            }

            if (oshm_zone[i].tag == shm_zone[n].tag
                && oshm_zone[i].shm.size == shm_zone[n].shm.size
                && !oshm_zone[i].noreuse)
            {
                goto live_shm_zone;
            }

            break;
        }

        ngx_shm_free(&oshm_zone[i].shm);

    live_shm_zone:

        continue;
    }

old_shm_zone_done:


    /* close the unnecessary listening sockets */

    ls = old_cycle->listening.elts;
    for (i = 0; i < old_cycle->listening.nelts; i++) {

        if (ls[i].remain || ls[i].fd == (ngx_socket_t) -1) {
            continue;
        }

        if (ngx_close_socket(ls[i].fd) == -1) {
            ngx_log_error(NGX_LOG_EMERG, log, ngx_socket_errno,
                          ngx_close_socket_n " listening socket on %V failed",
                          &ls[i].addr_text);
        }

#if (NGX_HAVE_UNIX_DOMAIN)

        if (ls[i].sockaddr->sa_family == AF_UNIX) {
            u_char  *name;

            name = ls[i].addr_text.data + sizeof("unix:") - 1;

            ngx_log_error(NGX_LOG_WARN, cycle->log, 0,
                          "deleting socket %s", name);

            if (ngx_delete_file(name) == NGX_FILE_ERROR) {
                ngx_log_error(NGX_LOG_EMERG, cycle->log, ngx_socket_errno,
                              ngx_delete_file_n " %s failed", name);
            }
        }

#endif
    }


    /* close the unnecessary open files */

    part = &old_cycle->open_files.part;
    file = part->elts;

    for (i = 0; /* void */ ; i++) {

        if (i >= part->nelts) {
            if (part->next == NULL) {
                break;
            }
            part = part->next;
            file = part->elts;
            i = 0;
        }

        if (file[i].fd == NGX_INVALID_FILE || file[i].fd == ngx_stderr) {
            continue;
        }

        if (ngx_close_file(file[i].fd) == NGX_FILE_ERROR) {
            ngx_log_error(NGX_LOG_EMERG, log, ngx_errno,
                          ngx_close_file_n " \"%s\" failed",
                          file[i].name.data);
        }
    }

    ngx_destroy_pool(conf.temp_pool);

    if (ngx_process == NGX_PROCESS_MASTER || ngx_is_init_cycle(old_cycle)) {

        ngx_destroy_pool(old_cycle->pool);
        cycle->old_cycle = NULL;

        return cycle;
    }


    if (ngx_temp_pool == NULL) {
        ngx_temp_pool = ngx_create_pool(128, cycle->log);
        if (ngx_temp_pool == NULL) {
            ngx_log_error(NGX_LOG_EMERG, cycle->log, 0,
                          "could not create ngx_temp_pool");
            exit(1);
        }

        n = 10;

        if (ngx_array_init(&ngx_old_cycles, ngx_temp_pool, n,
                           sizeof(ngx_cycle_t *))
            != NGX_OK)
        {
            exit(1);
        }

        ngx_memzero(ngx_old_cycles.elts, n * sizeof(ngx_cycle_t *));

        ngx_cleaner_event.handler = ngx_clean_old_cycles;
        ngx_cleaner_event.log = cycle->log;
        ngx_cleaner_event.data = &dumb;
        dumb.fd = (ngx_socket_t) -1;
    }

    ngx_temp_pool->log = cycle->log;

    old = ngx_array_push(&ngx_old_cycles);
    if (old == NULL) {
        exit(1);
    }
    *old = old_cycle;

    if (!ngx_cleaner_event.timer_set) {
        ngx_add_timer(&ngx_cleaner_event, 30000);
        ngx_cleaner_event.timer_set = 1;
    }

    return cycle;


failed:

    if (!ngx_is_init_cycle(old_cycle)) {
        old_ccf = (ngx_core_conf_t *) ngx_get_conf(old_cycle->conf_ctx,
                                                   ngx_core_module);
        if (old_ccf->environment) {
            environ = old_ccf->environment;
        }
    }

    /* rollback the new cycle configuration */

    part = &cycle->open_files.part;
    file = part->elts;

    for (i = 0; /* void */ ; i++) {

        if (i >= part->nelts) {
            if (part->next == NULL) {
                break;
            }
            part = part->next;
            file = part->elts;
            i = 0;
        }

        if (file[i].fd == NGX_INVALID_FILE || file[i].fd == ngx_stderr) {
            continue;
        }

        if (ngx_close_file(file[i].fd) == NGX_FILE_ERROR) {
            ngx_log_error(NGX_LOG_EMERG, log, ngx_errno,
                          ngx_close_file_n " \"%s\" failed",
                          file[i].name.data);
        }
    }

    /* free the newly created shared memory */

    part = &cycle->shared_memory.part;
    shm_zone = part->elts;

    for (i = 0; /* void */ ; i++) {

        if (i >= part->nelts) {
            if (part->next == NULL) {
                break;
            }
            part = part->next;
            shm_zone = part->elts;
            i = 0;
        }

        if (shm_zone[i].shm.addr == NULL) {
            continue;
        }

        opart = &old_cycle->shared_memory.part;
        oshm_zone = opart->elts;

        for (n = 0; /* void */ ; n++) {

            if (n >= opart->nelts) {
                if (opart->next == NULL) {
                    break;
                }
                opart = opart->next;
                oshm_zone = opart->elts;
                n = 0;
            }

            if (shm_zone[i].shm.name.len != oshm_zone[n].shm.name.len) {
                continue;
            }

            if (ngx_strncmp(shm_zone[i].shm.name.data,
                            oshm_zone[n].shm.name.data,
                            shm_zone[i].shm.name.len)
                != 0)
            {
                continue;
            }

            if (shm_zone[i].tag == oshm_zone[n].tag
                && shm_zone[i].shm.size == oshm_zone[n].shm.size
                && !shm_zone[i].noreuse)
            {
                goto old_shm_zone_found;
            }

            break;
        }

        ngx_shm_free(&shm_zone[i].shm);

    old_shm_zone_found:

        continue;
    }

    if (ngx_test_config) {
        ngx_destroy_cycle_pools(&conf);
        return NULL;
    }

    ls = cycle->listening.elts;
    for (i = 0; i < cycle->listening.nelts; i++) {
        if (ls[i].fd == (ngx_socket_t) -1 || !ls[i].open) {
            continue;
        }

        if (ngx_close_socket(ls[i].fd) == -1) {
            ngx_log_error(NGX_LOG_EMERG, log, ngx_socket_errno,
                          ngx_close_socket_n " %V failed",
                          &ls[i].addr_text);
        }
    }

    ngx_destroy_cycle_pools(&conf);

    return NULL;
}

　　nginx中设置了几个初始化的点，create_conf, init_conf, 供各模块实现各自的解析逻辑，以及使用一个全局的解析  ngx_conf_parse() 实现文件解析。

　　那么 http 作为独立的模块，其是否参与配置解析呢？我们看下其模块的配置即可：

// http 模块的配置简略
// http/ngx_http.c
static ngx_core_module_t  ngx_http_module_ctx = {
    ngx_string("http"),
    // 不做 create_conf 处理
    NULL,
    NULL
};

ngx_module_t  ngx_http_module = {
    NGX_MODULE_V1,
    &ngx_http_module_ctx,                  /* module context */
    ngx_http_commands,                     /* module directives */
    NGX_CORE_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
};

　　真正的解析工作在 ngx_conf_file.c 文件中进行， 有ngx_conf_param(), ngx_conf_parse() 完成具体的解析。

// core/ngx_conf_file.c
char *
ngx_conf_param(ngx_conf_t *cf)
{
    char             *rv;
    ngx_str_t        *param;
    ngx_buf_t         b;
    ngx_conf_file_t   conf_file;

    param = &cf->cycle->conf_param;

    if (param->len == 0) {
        return NGX_CONF_OK;
    }

    ngx_memzero(&conf_file, sizeof(ngx_conf_file_t));

    ngx_memzero(&b, sizeof(ngx_buf_t));

    b.start = param->data;
    b.pos = param->data;
    b.last = param->data + param->len;
    b.end = b.last;
    b.temporary = 1;

    conf_file.file.fd = NGX_INVALID_FILE;
    conf_file.file.name.data = NULL;
    conf_file.line = 0;

    cf->conf_file = &conf_file;
    cf->conf_file->buffer = &b;
    // 解析param信息，不解析配置文件
    rv = ngx_conf_parse(cf, NULL);

    cf->conf_file = NULL;

    return rv;
}

char *
ngx_conf_parse(ngx_conf_t *cf, ngx_str_t *filename)
{
    char             *rv;
    ngx_fd_t          fd;
    ngx_int_t         rc;
    ngx_buf_t         buf;
    ngx_conf_file_t  *prev, conf_file;
    enum {
        parse_file = 0,
        parse_block,
        parse_param
    } type;

#if (NGX_SUPPRESS_WARN)
    fd = NGX_INVALID_FILE;
    prev = NULL;
#endif
    // 如果给定配置文件，则解析
    if (filename) {

        /* open configuration file */
        // 打开配置文件
        fd = ngx_open_file(filename->data, NGX_FILE_RDONLY, NGX_FILE_OPEN, 0);

        if (fd == NGX_INVALID_FILE) {
            ngx_conf_log_error(NGX_LOG_EMERG, cf, ngx_errno,
                               ngx_open_file_n " \"%s\" failed",
                               filename->data);
            return NGX_CONF_ERROR;
        }

        prev = cf->conf_file;

        cf->conf_file = &conf_file;

        if (ngx_fd_info(fd, &cf->conf_file->file.info) == NGX_FILE_ERROR) {
            ngx_log_error(NGX_LOG_EMERG, cf->log, ngx_errno,
                          ngx_fd_info_n " \"%s\" failed", filename->data);
        }

        cf->conf_file->buffer = &buf;
        // NGX_CONF_BUFFER=1024
        buf.start = ngx_alloc(NGX_CONF_BUFFER, cf->log);
        if (buf.start == NULL) {
            goto failed;
        }

        buf.pos = buf.start;
        buf.last = buf.start;
        buf.end = buf.last + NGX_CONF_BUFFER;
        buf.temporary = 1;  // 初始化配置文件信息
        cf->conf_file->file.fd = fd;
        cf->conf_file->file.name.len = filename->len;
        cf->conf_file->file.name.data = filename->data;
        cf->conf_file->file.offset = 0;
        cf->conf_file->file.log = cf->log;
        cf->conf_file->line = 1;

        type = parse_file;

        if (ngx_dump_config
#if (NGX_DEBUG)
            || 1
#endif
           )
        {
            if (ngx_conf_add_dump(cf, filename) != NGX_OK) {
                goto failed;
            }

        } else {
            cf->conf_file->dump = NULL;
        }

    } else if (cf->conf_file->file.fd != NGX_INVALID_FILE) {

        type = parse_block;

    } else {
        type = parse_param;
    }

    // 此处实现真正的解析操作
    for ( ;; ) {
        // 重要1: 读取出一个个地token信息, 以pos, start等变量做标识起始
        rc = ngx_conf_read_token(cf);

        /*
         * ngx_conf_read_token() may return
         *
         *    NGX_ERROR             there is error
         *    NGX_OK                the token terminated by ";" was found
         *    NGX_CONF_BLOCK_START  the token terminated by "{" was found
         *    NGX_CONF_BLOCK_DONE   the "}" was found
         *    NGX_CONF_FILE_DONE    the configuration file is done
         */

        if (rc == NGX_ERROR) {
            goto done;
        }

        if (rc == NGX_CONF_BLOCK_DONE) {

            if (type != parse_block) {
                ngx_conf_log_error(NGX_LOG_EMERG, cf, 0, "unexpected \"}\"");
                goto failed;
            }

            goto done;
        }

        if (rc == NGX_CONF_FILE_DONE) {

            if (type == parse_block) {
                ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                                   "unexpected end of file, expecting \"}\"");
                goto failed;
            }

            goto done;
        }

        if (rc == NGX_CONF_BLOCK_START) {

            if (type == parse_param) {
                ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                                   "block directives are not supported "
                                   "in -g option");
                goto failed;
            }
        }

        /* rc == NGX_OK || rc == NGX_CONF_BLOCK_START */

        if (cf->handler) {

            /*
             * the custom handler, i.e., that is used in the http's
             * "types { ... }" directive
             */

            if (rc == NGX_CONF_BLOCK_START) {
                ngx_conf_log_error(NGX_LOG_EMERG, cf, 0, "unexpected \"{\"");
                goto failed;
            }

            rv = (*cf->handler)(cf, NULL, cf->handler_conf);
            if (rv == NGX_CONF_OK) {
                continue;
            }

            if (rv == NGX_CONF_ERROR) {
                goto failed;
            }

            ngx_conf_log_error(NGX_LOG_EMERG, cf, 0, "%s", rv);

            goto failed;
        }

　　　　 // 重要2: 将解析出的变量进行细致处理
        rc = ngx_conf_handler(cf, rc);

        if (rc == NGX_ERROR) {
            goto failed;
        }
    }

failed:

    rc = NGX_ERROR;

done:

    if (filename) {
        if (cf->conf_file->buffer->start) {
            ngx_free(cf->conf_file->buffer->start);
        }

        if (ngx_close_file(fd) == NGX_FILE_ERROR) {
            ngx_log_error(NGX_LOG_ALERT, cf->log, ngx_errno,
                          ngx_close_file_n " %s failed",
                          filename->data);
            rc = NGX_ERROR;
        }

        cf->conf_file = prev;
    }

    if (rc == NGX_ERROR) {
        return NGX_CONF_ERROR;
    }

    return NGX_CONF_OK;
}

// 读取一个个地 token 信息
static ngx_int_t
ngx_conf_read_token(ngx_conf_t *cf)
{
    u_char      *start, ch, *src, *dst;
    off_t        file_size;
    size_t       len;
    ssize_t      n, size;
    ngx_uint_t   found, need_space, last_space, sharp_comment, variable;
    ngx_uint_t   quoted, s_quoted, d_quoted, start_line;
    ngx_str_t   *word;
    ngx_buf_t   *b, *dump;

    found = 0;
    need_space = 0;
    last_space = 1;
    sharp_comment = 0;
    variable = 0;
    quoted = 0;
    s_quoted = 0;
    d_quoted = 0;

    cf->args->nelts = 0;
    b = cf->conf_file->buffer;
    dump = cf->conf_file->dump;
    start = b->pos;
    start_line = cf->conf_file->line;

    file_size = ngx_file_size(&cf->conf_file->file.info);

    for ( ;; ) {
        // last默认是最大buffer，pos默认为0，所以以下逻辑不一定走
        if (b->pos >= b->last) {

            if (cf->conf_file->file.offset >= file_size) {

                if (cf->args->nelts > 0 || !last_space) {

                    if (cf->conf_file->file.fd == NGX_INVALID_FILE) {
                        ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                                           "unexpected end of parameter, "
                                           "expecting \";\"");
                        return NGX_ERROR;
                    }

                    ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                                  "unexpected end of file, "
                                  "expecting \";\" or \"}\"");
                    return NGX_ERROR;
                }

                return NGX_CONF_FILE_DONE;
            }
            // 默认两值相等，len为0
            len = b->pos - start;

            if (len == NGX_CONF_BUFFER) {
                cf->conf_file->line = start_line;

                if (d_quoted) {
                    ch = '"';

                } else if (s_quoted) {
                    ch = '\'';

                } else {
                    ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                                       "too long parameter \"%*s...\" started",
                                       10, start);
                    return NGX_ERROR;
                }

                ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                                   "too long parameter, probably "
                                   "missing terminating \"%c\" character", ch);
                return NGX_ERROR;
            }

            if (len) {
                ngx_memmove(b->start, start, len);
            }
            // 计算剩余大小
            size = (ssize_t) (file_size - cf->conf_file->file.offset);
            // 如果剩余大小超出当前缓冲的大小，则只能取当前缓冲剩余大小
            if (size > b->end - (b->start + len)) {
                size = b->end - (b->start + len);
            }
            // 从配置文件中读取size大小的数据出来，放到buf中备用，相当于尽量一次全部读取
            n = ngx_read_file(&cf->conf_file->file, b->start + len, size,
                              cf->conf_file->file.offset);

            if (n == NGX_ERROR) {
                return NGX_ERROR;
            }

            if (n != size) {
                ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                                   ngx_read_file_n " returned "
                                   "only %z bytes instead of %z",
                                   n, size);
                return NGX_ERROR;
            }
            // 交换各偏移信息
            b->pos = b->start + len;
            b->last = b->pos + n;
            start = b->start;

            if (dump) {
                dump->last = ngx_cpymem(dump->last, b->pos, size);
            }
        }
        // 从文件中读出一个字符用以判定，即如果假设文件已读取完，则相当于一个个字符取出判定
        ch = *b->pos++;
        // 遇到换行，line++，注释标识重置
        if (ch == LF) {
            cf->conf_file->line++;

            if (sharp_comment) {
                sharp_comment = 0;
            }
        }
        // 如果注释标识有效，则忽略当前段的字符，直到标识被清除
        if (sharp_comment) {
            continue;
        }
        // 引号闭合处理
        if (quoted) {
            quoted = 0;
            continue;
        }
        // 判断是否有新的语句开始，类似空格都可以
        if (need_space) {
            if (ch == ' ' || ch == '\t' || ch == CR || ch == LF) {
                last_space = 1;
                need_space = 0;
                continue;
            }
            // 遇到分号，当前解析结束，即得到一个独立语句，如 root /www;
            if (ch == ';') {
                return NGX_OK;
            }
            // 遇到块也结束当前解析，交由子处理器处理
            if (ch == '{') {
                return NGX_CONF_BLOCK_START;
            }

            if (ch == ')') {
                last_space = 1;
                need_space = 0;

            } else {
                ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                                   "unexpected \"%c\"", ch);
                return NGX_ERROR;
            }
        }

        if (last_space) {
            // 新语句开始，行号暂存
            start = b->pos - 1;
            start_line = cf->conf_file->line;
            // 忽略空格类字符
            if (ch == ' ' || ch == '\t' || ch == CR || ch == LF) {
                continue;
            }

            switch (ch) {

            case ';':
            case '{':
                if (cf->args->nelts == 0) {
                    ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                                       "unexpected \"%c\"", ch);
                    return NGX_ERROR;
                }
                // 语句结束，nelts 到底是啥？
                if (ch == '{') {
                    return NGX_CONF_BLOCK_START;
                }

                return NGX_OK;

            case '}':
                if (cf->args->nelts != 0) {
                    ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                                       "unexpected \"}\"");
                    return NGX_ERROR;
                }

                return NGX_CONF_BLOCK_DONE;

            case '#':
                sharp_comment = 1;
                continue;

            case '\\':  // 转义符
                quoted = 1;
                last_space = 0;
                continue;

            case '"':
                start++;
                d_quoted = 1;
                last_space = 0;
                continue;

            case '\'':
                start++;
                s_quoted = 1;
                last_space = 0;
                continue;

            case '$':    // 变量解析
                variable = 1;
                last_space = 0;
                continue;

            default:
                last_space = 0;
            }

        } else {
            // ${xxx} 变量
            if (ch == '{' && variable) {
                continue;
            }

            variable = 0;

            if (ch == '\\') {
                quoted = 1;
                continue;
            }

            if (ch == '$') {
                variable = 1;
                continue;
            }
            // 引号处理
            if (d_quoted) {
                if (ch == '"') {
                    d_quoted = 0;
                    need_space = 1;
                    found = 1;
                }

            } else if (s_quoted) {
                if (ch == '\'') {
                    s_quoted = 0;
                    need_space = 1;
                    found = 1;
                }

            } else if (ch == ' ' || ch == '\t' || ch == CR || ch == LF
                       || ch == ';' || ch == '{')
            {
                last_space = 1;
                found = 1; // 完整解析一个语句
            }

            if (found) { 
                word = ngx_array_push(cf->args);
                if (word == NULL) {
                    return NGX_ERROR;
                }

                word->data = ngx_pnalloc(cf->pool, b->pos - 1 - start + 1);
                if (word->data == NULL) {
                    return NGX_ERROR;
                }
                // 将解析出的语句赋值到 args 中
                for (dst = word->data, src = start, len = 0;
                     src < b->pos - 1;
                     len++)
                {
                    if (*src == '\\') {
                        switch (src[1]) {
                        case '"':
                        case '\'':
                        case '\\':
                            // 去除转义标识
                            src++; 
                            break;

                        case 't':
                            //  翻译转义
                            *dst++ = '\t';  
                            src += 2;
                            continue;

                        case 'r':
                            *dst++ = '\r';
                            src += 2;
                            continue;

                        case 'n':
                            *dst++ = '\n';
                            src += 2;
                            continue;
                        }

                    }
                    *dst++ = *src++;
                }
                *dst = '\0';
                word->len = len;

                if (ch == ';') {
                    return NGX_OK;
                }

                if (ch == '{') {
                    return NGX_CONF_BLOCK_START;
                }

                found = 0;
            }
        }
    }
}

　　大体原理是：读取一个个token，然后进行依次翻译，分小语句，大block,… 类型依次处理。将解析的结果放入cf->args中。其解析结果如 location ~ /api/.*go { ,如 listen 80 81;

　　还差一个细节，就是读取到token之后，又是如何传递给各模块的呢？实际就是上面的重点2： ngx_conf_handler() 处理。

static ngx_int_t
ngx_conf_handler(ngx_conf_t *cf, ngx_int_t last)
{
    char           *rv;
    void           *conf, **confp;
    ngx_uint_t      i, found;
    ngx_str_t      *name;
    ngx_command_t  *cmd;
    // 获取最后存入的配置变量名,elts是个神奇的变量，相当于数组末尾值, nelts 相当于数组长度
    name = cf->args->elts;

    found = 0;
    // 遍历模块的 commands 列表，依次调用进行处理, 比如 root /www 处理
    // location /api {..} 处理
    for (i = 0; cf->cycle->modules[i]; i++) {

        cmd = cf->cycle->modules[i]->commands;
        if (cmd == NULL) {
            continue;
        }

        for ( /* void */ ; cmd->name.len; cmd++) {
            // 名字不同必然不负责解析
            if (name->len != cmd->name.len) {
                continue;
            }

            if (ngx_strcmp(name->data, cmd->name.data) != 0) {
                continue;
            }

            found = 1;
            // 配置模块处理
            if (cf->cycle->modules[i]->type != NGX_CONF_MODULE
                && cf->cycle->modules[i]->type != cf->module_type)
            {
                continue;
            }

            /* is the directive's location right ? */
            // 变量类型判定
            if (!(cmd->type & cf->cmd_type)) {
                continue;
            }

            if (!(cmd->type & NGX_CONF_BLOCK) && last != NGX_OK) {
                ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                                  "directive \"%s\" is not terminated by \";\"",
                                  name->data);
                return NGX_ERROR;
            }

            if ((cmd->type & NGX_CONF_BLOCK) && last != NGX_CONF_BLOCK_START) {
                ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                                   "directive \"%s\" has no opening \"{\"",
                                   name->data);
                return NGX_ERROR;
            }

            /* is the directive's argument count right ? */
            // 参数个数匹配
            if (!(cmd->type & NGX_CONF_ANY)) {

                if (cmd->type & NGX_CONF_FLAG) {

                    if (cf->args->nelts != 2) {
                        goto invalid;
                    }

                } else if (cmd->type & NGX_CONF_1MORE) {

                    if (cf->args->nelts < 2) {
                        goto invalid;
                    }

                } else if (cmd->type & NGX_CONF_2MORE) {

                    if (cf->args->nelts < 3) {
                        goto invalid;
                    }

                } else if (cf->args->nelts > NGX_CONF_MAX_ARGS) {

                    goto invalid;

                } else if (!(cmd->type & argument_number[cf->args->nelts - 1]))
                {
                    goto invalid;
                }
            }

            /* set up the directive's configuration context */

            conf = NULL;
            // 找不同的配置级别位置存储（这指针用得6啊）
            if (cmd->type & NGX_DIRECT_CONF) {
                conf = ((void **) cf->ctx)[cf->cycle->modules[i]->index];

            } else if (cmd->type & NGX_MAIN_CONF) {
                conf = &(((void **) cf->ctx)[cf->cycle->modules[i]->index]);

            } else if (cf->ctx) {
                confp = *(void **) ((char *) cf->ctx + cmd->conf);

                if (confp) {
                    conf = confp[cf->cycle->modules[i]->ctx_index];
                }
            }
            // 调用各命令的set方法，处理配置语义
            // 实际上就涉及到内嵌套解析问题了
            // 同样不会很简单哦
            rv = cmd->set(cf, cmd, conf);

            if (rv == NGX_CONF_OK) {
                return NGX_OK;
            }

            if (rv == NGX_CONF_ERROR) {
                return NGX_ERROR;
            }

            ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                               "\"%s\" directive %s", name->data, rv);

            return NGX_ERROR;
        }
    }
    // 配置使用错误
    if (found) {
        ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                           "\"%s\" directive is not allowed here", name->data);

        return NGX_ERROR;
    }

    ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                       "unknown directive \"%s\"", name->data);

    return NGX_ERROR;

invalid:

    ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                       "invalid number of arguments in \"%s\" directive",
                       name->data);

    return NGX_ERROR;
}

　　将解析出的配置信息接入到各子模块之后，才算是真正意义上的解析成功，也才能被各子模块使用。

　　下面我们再来看个样例，子模块如何解析配置，http location ….

 　　listen 80; 的解析比较简单些，有兴趣可查看：

static char *
ngx_http_core_listen(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
{
    ngx_http_core_srv_conf_t *cscf = conf;

    ngx_str_t              *value, size;
    ngx_url_t               u;
    ngx_uint_t              n;
    ngx_http_listen_opt_t   lsopt;

    cscf->listen = 1;

    value = cf->args->elts;

    ngx_memzero(&u, sizeof(ngx_url_t));

    u.url = value[1];
    u.listen = 1;
    u.default_port = 80;

    if (ngx_parse_url(cf->pool, &u) != NGX_OK) {
        if (u.err) {
            ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                               "%s in \"%V\" of the \"listen\" directive",
                               u.err, &u.url);
        }

        return NGX_CONF_ERROR;
    }

    ngx_memzero(&lsopt, sizeof(ngx_http_listen_opt_t));

    lsopt.backlog = NGX_LISTEN_BACKLOG;
    lsopt.rcvbuf = -1;
    lsopt.sndbuf = -1;
#if (NGX_HAVE_SETFIB)
    lsopt.setfib = -1;
#endif
#if (NGX_HAVE_TCP_FASTOPEN)
    lsopt.fastopen = -1;
#endif
#if (NGX_HAVE_INET6)
    lsopt.ipv6only = 1;
#endif
    // 更多参数解析，见官方文档说明
    for (n = 2; n < cf->args->nelts; n++) {

        if (ngx_strcmp(value[n].data, "default_server") == 0
            || ngx_strcmp(value[n].data, "default") == 0)
        {
            lsopt.default_server = 1;
            continue;
        }

        if (ngx_strcmp(value[n].data, "bind") == 0) {
            lsopt.set = 1;
            lsopt.bind = 1;
            continue;
        }

#if (NGX_HAVE_SETFIB)
        if (ngx_strncmp(value[n].data, "setfib=", 7) == 0) {
            lsopt.setfib = ngx_atoi(value[n].data + 7, value[n].len - 7);
            lsopt.set = 1;
            lsopt.bind = 1;

            if (lsopt.setfib == NGX_ERROR) {
                ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                                   "invalid setfib \"%V\"", &value[n]);
                return NGX_CONF_ERROR;
            }

            continue;
        }
#endif

#if (NGX_HAVE_TCP_FASTOPEN)
        if (ngx_strncmp(value[n].data, "fastopen=", 9) == 0) {
            lsopt.fastopen = ngx_atoi(value[n].data + 9, value[n].len - 9);
            lsopt.set = 1;
            lsopt.bind = 1;

            if (lsopt.fastopen == NGX_ERROR) {
                ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                                   "invalid fastopen \"%V\"", &value[n]);
                return NGX_CONF_ERROR;
            }

            continue;
        }
#endif

        if (ngx_strncmp(value[n].data, "backlog=", 8) == 0) {
            lsopt.backlog = ngx_atoi(value[n].data + 8, value[n].len - 8);
            lsopt.set = 1;
            lsopt.bind = 1;

            if (lsopt.backlog == NGX_ERROR || lsopt.backlog == 0) {
                ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                                   "invalid backlog \"%V\"", &value[n]);
                return NGX_CONF_ERROR;
            }

            continue;
        }

        if (ngx_strncmp(value[n].data, "rcvbuf=", 7) == 0) {
            size.len = value[n].len - 7;
            size.data = value[n].data + 7;

            lsopt.rcvbuf = ngx_parse_size(&size);
            lsopt.set = 1;
            lsopt.bind = 1;

            if (lsopt.rcvbuf == NGX_ERROR) {
                ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                                   "invalid rcvbuf \"%V\"", &value[n]);
                return NGX_CONF_ERROR;
            }

            continue;
        }

        if (ngx_strncmp(value[n].data, "sndbuf=", 7) == 0) {
            size.len = value[n].len - 7;
            size.data = value[n].data + 7;

            lsopt.sndbuf = ngx_parse_size(&size);
            lsopt.set = 1;
            lsopt.bind = 1;

            if (lsopt.sndbuf == NGX_ERROR) {
                ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                                   "invalid sndbuf \"%V\"", &value[n]);
                return NGX_CONF_ERROR;
            }

            continue;
        }

        if (ngx_strncmp(value[n].data, "accept_filter=", 14) == 0) {
#if (NGX_HAVE_DEFERRED_ACCEPT && defined SO_ACCEPTFILTER)
            lsopt.accept_filter = (char *) &value[n].data[14];
            lsopt.set = 1;
            lsopt.bind = 1;
#else
            ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                               "accept filters \"%V\" are not supported "
                               "on this platform, ignored",
                               &value[n]);
#endif
            continue;
        }

        if (ngx_strcmp(value[n].data, "deferred") == 0) {
#if (NGX_HAVE_DEFERRED_ACCEPT && defined TCP_DEFER_ACCEPT)
            lsopt.deferred_accept = 1;
            lsopt.set = 1;
            lsopt.bind = 1;
#else
            ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                               "the deferred accept is not supported "
                               "on this platform, ignored");
#endif
            continue;
        }

        if (ngx_strncmp(value[n].data, "ipv6only=o", 10) == 0) {
#if (NGX_HAVE_INET6 && defined IPV6_V6ONLY)
            if (ngx_strcmp(&value[n].data[10], "n") == 0) {
                lsopt.ipv6only = 1;

            } else if (ngx_strcmp(&value[n].data[10], "ff") == 0) {
                lsopt.ipv6only = 0;

            } else {
                ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                                   "invalid ipv6only flags \"%s\"",
                                   &value[n].data[9]);
                return NGX_CONF_ERROR;
            }

            lsopt.set = 1;
            lsopt.bind = 1;

            continue;
#else
            ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                               "ipv6only is not supported "
                               "on this platform");
            return NGX_CONF_ERROR;
#endif
        }

        if (ngx_strcmp(value[n].data, "reuseport") == 0) {
#if (NGX_HAVE_REUSEPORT)
            lsopt.reuseport = 1;
            lsopt.set = 1;
            lsopt.bind = 1;
#else
            ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                               "reuseport is not supported "
                               "on this platform, ignored");
#endif
            continue;
        }

        if (ngx_strcmp(value[n].data, "ssl") == 0) {
#if (NGX_HTTP_SSL)
            lsopt.ssl = 1;
            continue;
#else
            ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                               "the \"ssl\" parameter requires "
                               "ngx_http_ssl_module");
            return NGX_CONF_ERROR;
#endif
        }

        if (ngx_strcmp(value[n].data, "http2") == 0) {
#if (NGX_HTTP_V2)
            lsopt.http2 = 1;
            continue;
#else
            ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                               "the \"http2\" parameter requires "
                               "ngx_http_v2_module");
            return NGX_CONF_ERROR;
#endif
        }

        if (ngx_strcmp(value[n].data, "spdy") == 0) {
            ngx_conf_log_error(NGX_LOG_WARN, cf, 0,
                               "invalid parameter \"spdy\": "
                               "ngx_http_spdy_module was superseded "
                               "by ngx_http_v2_module");
            continue;
        }

        if (ngx_strncmp(value[n].data, "so_keepalive=", 13) == 0) {

            if (ngx_strcmp(&value[n].data[13], "on") == 0) {
                lsopt.so_keepalive = 1;

            } else if (ngx_strcmp(&value[n].data[13], "off") == 0) {
                lsopt.so_keepalive = 2;

            } else {

#if (NGX_HAVE_KEEPALIVE_TUNABLE)
                u_char     *p, *end;
                ngx_str_t   s;

                end = value[n].data + value[n].len;
                s.data = value[n].data + 13;

                p = ngx_strlchr(s.data, end, ':');
                if (p == NULL) {
                    p = end;
                }

                if (p > s.data) {
                    s.len = p - s.data;

                    lsopt.tcp_keepidle = ngx_parse_time(&s, 1);
                    if (lsopt.tcp_keepidle == (time_t) NGX_ERROR) {
                        goto invalid_so_keepalive;
                    }
                }

                s.data = (p < end) ? (p + 1) : end;

                p = ngx_strlchr(s.data, end, ':');
                if (p == NULL) {
                    p = end;
                }

                if (p > s.data) {
                    s.len = p - s.data;

                    lsopt.tcp_keepintvl = ngx_parse_time(&s, 1);
                    if (lsopt.tcp_keepintvl == (time_t) NGX_ERROR) {
                        goto invalid_so_keepalive;
                    }
                }

                s.data = (p < end) ? (p + 1) : end;

                if (s.data < end) {
                    s.len = end - s.data;

                    lsopt.tcp_keepcnt = ngx_atoi(s.data, s.len);
                    if (lsopt.tcp_keepcnt == NGX_ERROR) {
                        goto invalid_so_keepalive;
                    }
                }

                if (lsopt.tcp_keepidle == 0 && lsopt.tcp_keepintvl == 0
                    && lsopt.tcp_keepcnt == 0)
                {
                    goto invalid_so_keepalive;
                }

                lsopt.so_keepalive = 1;

#else

                ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                                   "the \"so_keepalive\" parameter accepts "
                                   "only \"on\" or \"off\" on this platform");
                return NGX_CONF_ERROR;

#endif
            }

            lsopt.set = 1;
            lsopt.bind = 1;

            continue;

#if (NGX_HAVE_KEEPALIVE_TUNABLE)
        invalid_so_keepalive:

            ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                               "invalid so_keepalive value: \"%s\"",
                               &value[n].data[13]);
            return NGX_CONF_ERROR;
#endif
        }

        if (ngx_strcmp(value[n].data, "proxy_protocol") == 0) {
            lsopt.proxy_protocol = 1;
            continue;
        }

        ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                           "invalid parameter \"%V\"", &value[n]);
        return NGX_CONF_ERROR;
    }
    // 将监听端口加入列表
    for (n = 0; n < u.naddrs; n++) {
        lsopt.sockaddr = u.addrs[n].sockaddr;
        lsopt.socklen = u.addrs[n].socklen;
        lsopt.addr_text = u.addrs[n].name;
        lsopt.wildcard = ngx_inet_wildcard(lsopt.sockaddr);

        if (ngx_http_add_listen(cf, cscf, &lsopt) != NGX_OK) {
            return NGX_CONF_ERROR;
        }
    }

    return NGX_CONF_OK;
}

View Code

　　location 的解析则肯定会复杂很多，因为它是一个块级的配置，内部将会有很多复杂的配置，想想这必然又涉及到递归解析了。

// location /xx {..} 的解析
static char *
ngx_http_core_location(ngx_conf_t *cf, ngx_command_t *cmd, void *dummy)
{
    char                      *rv;
    u_char                    *mod;
    size_t                     len;
    ngx_str_t                 *value, *name;
    ngx_uint_t                 i;
    ngx_conf_t                 save;
    ngx_http_module_t         *module;
    ngx_http_conf_ctx_t       *ctx, *pctx;
    ngx_http_core_loc_conf_t  *clcf, *pclcf;

    ctx = ngx_pcalloc(cf->pool, sizeof(ngx_http_conf_ctx_t));
    if (ctx == NULL) {
        return NGX_CONF_ERROR;
    }

    pctx = cf->ctx;
    ctx->main_conf = pctx->main_conf;
    ctx->srv_conf = pctx->srv_conf;

    ctx->loc_conf = ngx_pcalloc(cf->pool, sizeof(void *) * ngx_http_max_module);
    if (ctx->loc_conf == NULL) {
        return NGX_CONF_ERROR;
    }
    // 嵌套解析
    for (i = 0; cf->cycle->modules[i]; i++) {
        if (cf->cycle->modules[i]->type != NGX_HTTP_MODULE) {
            continue;
        }

        module = cf->cycle->modules[i]->ctx;

        if (module->create_loc_conf) {
            // 将解析的值放入 ctx 中，备用
            ctx->loc_conf[cf->cycle->modules[i]->ctx_index] =
                                                   module->create_loc_conf(cf);
            if (ctx->loc_conf[cf->cycle->modules[i]->ctx_index] == NULL) {
                return NGX_CONF_ERROR;
            }
        }
    }

    clcf = ctx->loc_conf[ngx_http_core_module.ctx_index];
    clcf->loc_conf = ctx->loc_conf;

    value = cf->args->elts;

    if (cf->args->nelts == 3) {

        len = value[1].len;
        mod = value[1].data;
        name = &value[2];
        // 疏松写法
        // uri 模式匹配
        if (len == 1 && mod[0] == '=') {

            clcf->name = *name;
            clcf->exact_match = 1;

        } else if (len == 2 && mod[0] == '^' && mod[1] == '~') {

            clcf->name = *name;
            clcf->noregex = 1;

        } else if (len == 1 && mod[0] == '~') {

            if (ngx_http_core_regex_location(cf, clcf, name, 0) != NGX_OK) {
                return NGX_CONF_ERROR;
            }

        } else if (len == 2 && mod[0] == '~' && mod[1] == '*') {

            if (ngx_http_core_regex_location(cf, clcf, name, 1) != NGX_OK) {
                return NGX_CONF_ERROR;
            }

        } else {
            ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                               "invalid location modifier \"%V\"", &value[1]);
            return NGX_CONF_ERROR;
        }

    } else {

        name = &value[1];
        // 紧密写法
        if (name->data[0] == '=') {

            clcf->name.len = name->len - 1;
            clcf->name.data = name->data + 1;
            clcf->exact_match = 1;

        } else if (name->data[0] == '^' && name->data[1] == '~') {

            clcf->name.len = name->len - 2;
            clcf->name.data = name->data + 2;
            clcf->noregex = 1;

        } else if (name->data[0] == '~') {

            name->len--;
            name->data++;

            if (name->data[0] == '*') {

                name->len--;
                name->data++;

                if (ngx_http_core_regex_location(cf, clcf, name, 1) != NGX_OK) {
                    return NGX_CONF_ERROR;
                }

            } else {
                if (ngx_http_core_regex_location(cf, clcf, name, 0) != NGX_OK) {
                    return NGX_CONF_ERROR;
                }
            }

        } else {

            clcf->name = *name;

            if (name->data[0] == '@') {
                clcf->named = 1;
            }
        }
    }

    pclcf = pctx->loc_conf[ngx_http_core_module.ctx_index];

    if (cf->cmd_type == NGX_HTTP_LOC_CONF) {

        /* nested location */

#if 0
        clcf->prev_location = pclcf;
#endif

        if (pclcf->exact_match) {
            ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                               "location \"%V\" cannot be inside "
                               "the exact location \"%V\"",
                               &clcf->name, &pclcf->name);
            return NGX_CONF_ERROR;
        }

        if (pclcf->named) {
            ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                               "location \"%V\" cannot be inside "
                               "the named location \"%V\"",
                               &clcf->name, &pclcf->name);
            return NGX_CONF_ERROR;
        }

        if (clcf->named) {
            ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                               "named location \"%V\" can be "
                               "on the server level only",
                               &clcf->name);
            return NGX_CONF_ERROR;
        }

        len = pclcf->name.len;

#if (NGX_PCRE)
        if (clcf->regex == NULL
            && ngx_filename_cmp(clcf->name.data, pclcf->name.data, len) != 0)
#else
        if (ngx_filename_cmp(clcf->name.data, pclcf->name.data, len) != 0)
#endif
        {
            ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                               "location \"%V\" is outside location \"%V\"",
                               &clcf->name, &pclcf->name);
            return NGX_CONF_ERROR;
        }
    }
    // 添加到location列表中，备用
    if (ngx_http_add_location(cf, &pclcf->locations, clcf) != NGX_OK) {
        return NGX_CONF_ERROR;
    }

    save = *cf;
    cf->ctx = ctx;
    cf->cmd_type = NGX_HTTP_LOC_CONF;
    // 递归解析
    rv = ngx_conf_parse(cf, NULL);

    *cf = save;

    return rv;
}

　　同样，它会遍历其http模块下有哪些可以解析的命令，然后交其处理，然后再处理自身的逻辑。从而完成整个块的配置解析。

 　　解析后的location信息添加到全局变更信息中， 这由 ngx_http_add_location() 完成并维护，实际上就是放到 loc_conf对应的模块变量下，以链表的形式保存起来，后续配置读取由其完成。

4. location配置的应用

 　　上一节已经解析出location的各项配置了，那么它是如何运用到实际中呢？实际上，就是在需要的时候，从相应配置变量中取出来使用判定即可。

　　或者参考我之前的文章：正反向代理的实现： https://www.cnblogs.com/yougewe/p/13778108.html

　　欲知后事如何，且听下回分解。