Nginx-HTTP之静态网页访问流程分析二

11. HTTP 阶段执行

下面会依次执行以下阶段：

1. NGX_HTTP_SERVER_REWRITE_PHASE: 在将请求的 URI 与 location 表达式匹配前，修改请求的 URI （所谓重定向）是一个独立的 HTTP 阶段。
2. NGX_HTTP_FIND_CONFIG_PHASE：根据请求的 URI 寻找匹配的 location 表达式，这个阶段只能由 ngx_http_core_module 模块实现，不建议其他模块介入该阶段。
3. NGX_HTTP_REWRITE_PHASE：在 NGX_HTTP_FIND_CONFIG_PHASE 阶段寻找到匹配的 location 之后再修改请求的 URI。
4. NGX_HTTP_POST_REWRITE_PHASE：这一阶段是用于在 rewrite 重写 URL 后，防止错误的 nginx.conf 配置导致死循环（递归地修改 URI）。因此，这一阶段仅由 ngx_http_core_module 模块处理。目前，控制死循环的方式很简单，首先检查 rewrite 的次数，如果一个请求超过 10 次重定向，就认为进入了 rewrite 死循环，这时在 NGX_HTTP_POST_REWRITE_PHASE 阶段就会向用户返回 500，表示服务器内部错误.
5. NGX_HTTP_PREACCESS_PHASE：该阶段表示在处理 NGX_HTTP_ACCESS_PHASE 阶段决定请求的访问权限前，HTTP 模块可以介入的处理阶段。
6. NGX_HTTP_ACCESS_PHASE：这个阶段用于让 HTTP 模块判断是否允许这个请求访问 Nginx 服务器.
7. NGX_HTTP_POST_ACCESS_PHASE：在 NGX_HTTP_ACCESS_PAHSE 阶段中，当 HTTP 模块的 handler 处理函数返回不允许访问的错误码时（实际就是 NGX_HTTP_FORBIDDEN 或 NGX_HTTP_AUTHORIZED），这里将负责向用户发送拒绝服务的错误响应。因此，这个阶段实际上用于给 NGX_HTTP_ACCESS_PAHSE 阶段收尾.
8. NGX_HTTP_CONTENT_PHASE：该阶段用于处理 HTTP 请求内容的阶段，这是大部分 HTTP 模块最愿意介入的阶段。

11.1 NGX_HTTP_SERVER_REWRITE_PHASE

基于当前环境配置下，首先执行的第一个阶段为 NGX_HTTP_SERVER_REWRITE_PHASE，由前面 ngx_http_init_phase_handlers 函数知，该阶段实现了 checker 回调函数 ngx_http_core_rewrite_phase。因此会首先调用该 checker 函数，在 checker 函数中才会去调用 handler 方法。

ngx_http_core_rewrite_phase 源码如下：

ngx_int_t
ngx_http_core_rewrite_phase(ngx_http_request_t *r, ngx_http_phase_handler_t *ph)
{
    ngx_int_t  rc;

    ngx_log_debug1(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                   "rewrite phase: %ui", r->phase_handler);

    rc = ph->handler(r);

    /* 当前的 handler 执行完毕，按照顺序执行下一个 ngx_http_handler_pt 处理方法 */
    if (rc == NGX_DECLINED) {
        r->phase_handler++;
        return NGX_AGAIN;
    }

    /* 当前 ngx_http_handler_pt 处理方法尚未结束，这意味着该处理方法在当前阶段
     * 中有机会再次被调用，这里返回 NGX_OK，会使得 HTTP 框架立刻把控制权交还给
     * epoll 等事件模块，不再处理当前请求，唯有这个请求上的事件再次被触发时才会
     * 继续执行 */
    if (rc == NGX_DONE) {
        return NGX_OK;
    }

    /* NGX_OK, NGX_AGAIN, NGX_ERROR, NGX_HTTP_...  */

    ngx_http_finalize_request(r, rc);

    return NGX_OK;
}

对于 NGX_HTTP_SERVER_REWRITE_PHASE 阶段，当前 HTTP 框架仅有 ngx_http_rewrite_module 模块介入了该阶段，handler 函数为 ngx_http_rewrite_handler。

11.1.1 ngx_http_rewrite_handler

static ngx_int_t
ngx_http_rewrite_handler(ngx_http_request_t *r)
{
    ngx_int_t                     index;
    ngx_http_script_code_pt       code;
    ngx_http_script_engine_t     *e;
    ngx_http_core_srv_conf_t     *cscf;
    ngx_http_core_main_conf_t    *cmcf;
    ngx_http_rewrite_loc_conf_t  *rlcf;

    cmcf = ngx_http_get_module_main_conf(r, ngx_http_core_module);
    cscf = ngx_http_get_module_srv_conf(r, ngx_http_core_module);
    /*
     * 表示 NGX_HTTP_REWRITE_PHASE 阶段第 1 个 ngx_http_phase_handler_t 处理方法
     * 在 handlers 数组中的序号，用于在执行 HTTP 请求的任何阶段中快速跳转到
     * NGX_HTTP_REWRITE_PHASE 阶段处理请求
     */
    index = cmcf->phase_engine.location_rewrite_index;

    if (r->phase_handler == index && r->loc_conf == cscf->ctx->loc_conf) {
        /* skipping location rewrite phase for server null location */
        return NGX_DECLINED;
    }

    rlcf = ngx_http_get_module_loc_conf(r, ngx_http_rewrite_module);

    /* 若没有在配置文件中对该模块的相应配置项进行设置，则这里直接返回
     * NGX_DECLINED，表示该 handler 执行完毕，依次指向下一个 handler */
    if (rlcf->codes == NULL) {
        return NGX_DECLINED;
    }

    e = ngx_pcalloc(r->pool, sizeof(ngx_http_script_engine_t));
    if (e == NULL) {
        return NGX_HTTP_INTERNAL_SERVER_ERROR;
    }

    e->sp = ngx_pcalloc(r->pool,
                        rlcf->stack_size * sizeof(ngx_http_variable_value_t));
    if (e->sp == NULL) {
        return NGX_HTTP_INTERNAL_SERVER_ERROR;
    }

    e->ip = rlcf->codes->elts;
    e->request = r;
    e->quote = 1;
    e->log = rlcf->log;
    e->status = NGX_DECLINED;

    while (*(uintptr_t *) e->ip) {
        code = *(ngx_http_script_code_pt *) e->ip;
        code(e);
    }

    if (e->status < NGX_HTTP_BAD_REQUEST) {
        return e->status;
    }

    if (r->err_status == 0) {
        return e->status;
    }

    return r->err_status;
}

11.2 NGX_HTTP_FIND_CONFIG_PHASE

该阶段是：根据请求的 URI 寻找匹配的 location 表达式，这个阶段只能由 ngx_http_core_module 模块实现，不建议其他模块介入该阶段

该阶段实现的 checker 方法为 ngx_http_core_find_config_phase。

ngx_int_t
ngx_http_core_find_config_phase(ngx_http_request_t *r,
    ngx_http_phase_handler_t *ph)
{
    u_char                    *p;
    size_t                     len;
    ngx_int_t                  rc;
    ngx_http_core_loc_conf_t  *clcf;

    /* content_handler:
     * 表示 NGX_HTTP_CONTENT_PHASE 阶段提供给 HTTP 模块处理请求的一种方式，
     * content_handler 指向 HTTP 模块实现的请求处理方法 */
    r->content_handler = NULL;
    /* 标志位，为 1 时表示 URL 发生过 rewrite 重写 */
    r->uri_changed = 0;

    rc = ngx_http_core_find_location(r);

    if (rc == NGX_ERROR) {
        ngx_http_finalize_request(r, NGX_HTTP_INTERNAL_SERVER_ERROR);
        return NGX_OK;
    }

    clcf = ngx_http_get_module_loc_conf(r, ngx_http_core_module);

    if (!r->internal && clcf->internal) {
        ngx_http_finalize_request(r, NGX_HTTP_NOT_FOUND);
        return NGX_OK;
    }

    ngx_log_debug2(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                   "using configuration \"%s%V\"",
                   (clcf->noname ? "*" : (clcf->exact_match ? "=" : "")),
                   &clcf->name);

    ngx_http_update_location_config(r);

    ngx_log_debug2(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                   "http cl:%O max:%O",
                   r->headers_in.content_length_n, clcf->client_max_body_size);

    if (r->headers_in.content_length_n != -1
        && !r->discard_body
        && clcf->client_max_body_size
        && clcf->client_max_body_size < r->headers_in.content_length_n)
    {
        ngx_log_error(NGX_LOG_ERR, r->connection->log, 0,
                      "client intended to send too large body: %O bytes",
                      r->headers_in.content_length_n);

        r->expect_tested = 1;
        (void) ngx_http_discard_request_body(r);
        ngx_http_finalize_request(r, NGX_HTTP_REQUEST_ENTITY_TOO_LARGE);
        return NGX_OK;
    }

    if (rc == NGX_DONE) {
        ngx_http_clear_location(r);

        r->headers_out.location = ngx_list_push(&r->headers_out.headers);
        if (r->headers_out.location == NULL) {
            ngx_http_finalize_request(r, NGX_HTTP_INTERNAL_SERVER_ERROR);
            return NGX_OK;
        }

        r->headers_out.location->hash = 1;
        ngx_str_set(&r->headers_out.location->key, "Location");

        if (r->args.len == 0) {
            r->headers_out.location->value = clcf->name;

        } else {
            len = clcf->name.len + 1 + r->args.len;
            p = ngx_pnalloc(r->pool, len);

            if (p == NULL) {
                ngx_http_clear_location(r);
                ngx_http_finalize_request(r, NGX_HTTP_INTERNAL_SERVER_ERROR);
                return NGX_OK;
            }

            r->headers_out.location->value.len = len;
            r->headers_out.location->value.data = p;

            p = ngx_cpymem(p, clcf->name.data, clcf->name.len);
            *p++ = '?';
            ngx_memcpy(p, r->args.data, r->args.len);
        }

        ngx_http_finalize_request(r, NGX_HTTP_MOVED_PERMANENTLY);
        return NGX_OK;
    }

    r->phase_handler++;
    return NGX_AGAIN;
}

11.2.1 ngx_http_core_find_location

/*
 * NGX_OK       - exact or regex match
 * NGX_DONE     - auto redirect
 * NGX_AGAIN    - inclusive match
 * NGX_ERROR    - regex error
 * NGX_DECLINED - no match
 */

static ngx_int_t
ngx_http_core_find_location(ngx_http_request_t *r)
{
    ngx_int_t                  rc;
    ngx_http_core_loc_conf_t  *pclcf;
#if (NGX_PCRE)
    ngx_int_t                  n;
    ngx_uint_t                 noregex;
    ngx_http_core_loc_conf_t  *clcf, **clcfp;

    noregex = 0;
#endif

    pclcf = ngx_http_get_module_loc_conf(r, ngx_http_core_module);

    rc = ngx_http_core_find_static_location(r, pclcf->static_locations);

    if (rc == NGX_AGAIN) {

#if (NGX_PCRE)
        clcf = ngx_http_get_module_loc_conf(r, ngx_http_core_module);

        noregex = clcf->noregex;
#endif

        /* look up nested locations */

        rc = ngx_http_core_find_location(r);
    }

    if (rc == NGX_OK || rc == NGX_DONE) {
        return rc;
    }

    /* rc == NGX_DECLINED or rc == NGX_AGAIN in nested location */

#if (NGX_PCRE)

    if (noregex == 0 && pclcf->regex_locations) {

        for (clcfp = pclcf->regex_locations; *clcfp; clcfp++) {

            ngx_log_debug1(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                           "test location: ~ \"%V\"", &(*clcfp)->name);

            n = ngx_http_regex_exec(r, (*clcfp)->regex, &r->uri);

            if (n == NGX_OK) {
                r->loc_conf = (*clcfp)->loc_conf;

                /* look up nested locations */

                rc = ngx_http_core_find_location(r);

                return (rc == NGX_ERROR) ? rc : NGX_OK;
            }

            if (n == NGX_DECLINED) {
                continue;
            }

            return NGX_ERROR;
        }
    }
#endif

    return rc;
}

11.2.2 ngx_http_core_find_static_location

/*
 * NGX_OK       - exact match
 * NGX_DONE     - auto redirect
 * NGX_AGAIN    - inclusive match
 * NGX_DECLINED - no match
 */

static ngx_int_t
ngx_http_core_find_static_location(ngx_http_request_t *r,
    ngx_http_location_tree_node_t *node)
{
    u_char     *uri;
    size_t      len, n;
    ngx_int_t   rc, rv;

    len = r->uri.len;
    uri = r->uri.data;

    rv = NGX_DECLINED;

    for ( ;; ) {

        if (node == NULL) {
            return rv;
        }

        ngx_log_debug2(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                       "test location: \"%*s\"",
                       (size_t) node->len, node->name);

        /* 以最小的长度为准 */
        n = (len <= (size_t) node->len) ? len : node->len;

        /* 比较这两个字符串的前 n 个字符是否相同，相同返回 0 */
        rc = ngx_filename_cmp(uri, node->name, n);

        if (rc != 0) {
            /* 当前节点不匹配 */
            node = (rc < 0) ? node->left : node->right;

            continue;
        }

        if (len > (size_t) node->len) {

            if (node->inclusive) {

                r->loc_conf = node->inclusive->loc_conf;
                rv = NGX_AGAIN;

                node = node->tree;
                uri += n;
                len -= n;

                continue;
            }

            /* exact only */

            node = node->right;

            continue;
        }

        if (len == (size_t) node->len) {

            if (node->exact) {
                r->loc_conf = node->exact->loc_conf;
                return NGX_OK;

            } else {
                r->loc_conf = node->inclusive->loc_conf;
                return NGX_AGAIN;
            }
        }

        /* len < node->len */

        if (len + 1 == (size_t) node->len && node->auto_redirect) {

            r->loc_conf = (node->exact) ? node->exact->loc_conf:
                                          node->inclusive->loc_conf;
            rv = NGX_DONE;
        }

        node = node->left;
    }
}

11.3 NGX_HTTP_REWRITE_PHASE

该阶段是：在 NGX_HTTP_FIND_CONFIG_PHASE 阶段寻找到匹配的 location 之后再修改请求的 URI。

该阶段实现的 checker 方法为 ngx_http_core_rewrite_phase，介入该阶段的模块也仅为 ngx_http_rewrite_module，handler 为 ngx_http_rewrite_handler。因此与 NGX_HTTP_SERVER_REWRITE_PHASE 阶段一样。具体可看该阶段的实现。

11.4 NGX_HTTP_POST_REWRITE_PHASE

这一阶段是用于在 rewrite 重写 URL 后，防止错误的 nginx.conf 配置导致死循环（递归地修改 URI）。因此，这一阶段仅由 ngx_http_core_module 模块处理。目前，控制死循环的方式很简单，首先检查 rewrite 的次数，如果一个请求超过 10 次重定向，就认为进入了 rewrite 死循环，这时在 NGX_HTTP_POST_REWRITE_PHASE 阶段就会向用户返回 500，表示服务器内部错误.

该阶段实现的 checker 方法为 ngx_http_core_post_rewrite_phase（不允许其他模块介入）:

ngx_int_t
ngx_http_core_post_rewrite_phase(ngx_http_request_t *r,
    ngx_http_phase_handler_t *ph)
{
    ngx_http_core_srv_conf_t  *cscf;

    ngx_log_debug1(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                   "post rewrite phase: %ui", r->phase_handler);

    /* 标志位，为 1 表示 URL 发生过 rewrite 重写 */
    if (!r->uri_changed) {
        /* 若没有发生过 rewrite 重写，phase_handler 加 1，按序执行下一个 handler */
        r->phase_handler++;
        return NGX_AGAIN;
    }

    ngx_log_debug1(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                   "uri changes: %d", r->uri_changes);

    /*
     * gcc before 3.3 compiles the broken code for
     *     if (r->uri_changes-- == 0)
     * if the r->uri_changes is defined as
     *     unsigned  uri_changes:4
     */

    r->uri_changes--;

    if (r->uri_changes == 0) {
        ngx_log_error(NGX_LOG_ERR, r->connection->log, 0,
                      "rewrite or internal redirection cycle "
                      "while processing \"%V\"", &r->uri);

        ngx_http_finalize_request(r, NGX_HTTP_INTERNAL_SERVER_ERROR);
        return NGX_OK;
    }

    r->phase_handler = ph->next;

    cscf = ngx_http_get_module_srv_conf(r, ngx_http_core_module);
    r->loc_conf = cscf->ctx->loc_conf;

    return NGX_AGAIN;
}

11.5 NGX_HTTP_PREACCESS_PHASE

该阶段表示在处理 NGX_HTTP_ACCESS_PHASE 阶段决定请求的访问权限前，HTTP 模块可以介入的处理阶段。

该阶段默认的 checker 方法为 ngx_http_core_generic_phase，该阶段分别有以下两个模块介入：

• ngx_http_limit_req_module: handler 为 ngx_http_limit_req_handler
• ngx_http_limit_conn_module: handler 为 ngx_http_limit_conn_handler

以下两个模块需要通过指定添加到 nginx 中才会在 ngx_modules 中有这里两个模块，否则默认无：

• ngx_http_degradation_module: handler 为 ngx_http_degradation_handler
• ngx_http_realip_module：handler 为 ngx_http_realip_handler

ngx_http_core_generic_phase 的实现如下：

ngx_int_t
ngx_http_core_generic_phase(ngx_http_request_t *r, ngx_http_phase_handler_t *ph)
{
    ngx_int_t  rc;

    /*
     * generic phase checker,
     * used by the post read and pre-access phases
     */

    ngx_log_debug1(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                   "generic phase: %ui", r->phase_handler);

    rc = ph->handler(r);

    if (rc == NGX_OK) {
        r->phase_handler = ph->next;
        return NGX_AGAIN;
    }

    if (rc == NGX_DECLINED) {
        r->phase_handler++;
        return NGX_AGAIN;
    }

    if (rc == NGX_AGAIN || rc == NGX_DONE) {
        return NGX_OK;
    }

    /* rc == NGX_ERROR || rc == NGX_HTTP_...  */

    ngx_http_finalize_request(r, rc);

    return NGX_OK;
}

11.5.1 ngx_http_limit_req_handler

static ngx_int_t
ngx_http_limit_req_handler(ngx_http_request_t *r)
{
    uint32_t                     hash;
    ngx_str_t                    key;
    ngx_int_t                    rc;
    ngx_uint_t                   n, excess;
    ngx_msec_t                   delay;
    ngx_http_limit_req_ctx_t    *ctx;
    ngx_http_limit_req_conf_t   *lrcf;
    ngx_http_limit_req_limit_t  *limit, *limits;

    if (r->main->limit_req_set) {
        return NGX_DECLINED;
    }

    lrcf = ngx_http_get_module_loc_conf(r, ngx_http_limit_req_module);
    limits = lrcf->limits.elts;

    excess = 0;

    rc = NGX_DECLINED;

#if (NGX_SUPPRESS_WARN)
    limit = NULL;
#endif

    for (n = 0; n < lrcf->limits.nelts; n++) {

        ...
    }

    if (rc == NGX_DECLINED) {
        return NGX_DECLINED;
    }

    ...
}

对于当前配置文件，没有对该 ngx_http_limit_req_module 模块进行设置，因此该函数中会直接返回，不做其他处理。

11.5.2 ngx_http_limit_conn_handler

static ngx_int_t
ngx_stream_limit_conn_handler(ngx_stream_session_t *s)
{
    size_t                            n;
    uint32_t                          hash;
    ngx_str_t                         key;
    ngx_uint_t                        i;
    ngx_slab_pool_t                  *shpool;
    ngx_rbtree_node_t                *node;
    ngx_pool_cleanup_t               *cln;
    ngx_stream_limit_conn_ctx_t      *ctx;
    ngx_stream_limit_conn_node_t     *lc;
    ngx_stream_limit_conn_conf_t     *lccf;
    ngx_stream_limit_conn_limit_t    *limits;
    ngx_stream_limit_conn_cleanup_t  *lccln;

    lccf = ngx_stream_get_module_srv_conf(s, ngx_stream_limit_conn_module);
    limits = lccf->limits.elts;

    for (i = 0; i < lccf->limits.nelts; i++) {
        ...
    }

    return NGX_DECLINED;
}

该模块 ngx_http_limit_conn_module 没有进行相应配置，暂时忽略。

11.6 NGX_HTTP_ACCESS_PHASE

这个阶段用于让 HTTP 模块判断是否允许这个请求访问 Nginx 服务器.

该阶段实现的 checker 方法为 ngx_http_core_access_phase，介入的模块有：

• ngx_http_access_module：handler 为 ngx_http_access_handler
• ngx_http_auth_basic_module：handler 为 ngx_http_auth_basic_handler

该模块没有指定添加到 nginx 中进行：

• ngx_http_auth_request_module：handler 为 ngx_http_auth_request_handler

ngx_http_core_access_phase 的实现如下：

ngx_int_t
ngx_http_core_access_phase(ngx_http_request_t *r, ngx_http_phase_handler_t *ph)
{
    ngx_int_t                  rc;
    ngx_http_core_loc_conf_t  *clcf;

    /* 若当前请求 r 为子请求的话，直接返回 */
    if (r != r->main) {
        r->phase_handler = ph->next;
        return NGX_AGAIN;
    }

    ngx_log_debug1(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                   "access phase: %ui", r->phase_handler);

    rc = ph->handler(r);

    if (rc == NGX_DECLINED) {
        r->phase_handler++;
        return NGX_AGAIN;
    }

    if (rc == NGX_AGAIN || rc == NGX_DONE) {
        return NGX_OK;
    }

    clcf = ngx_http_get_module_loc_conf(r, ngx_http_core_module);

    if (clcf->satisfy == NGX_HTTP_SATISFY_ALL) {

        if (rc == NGX_OK) {
            r->phase_handler++;
            return NGX_AGAIN;
        }

    } else {
        if (rc == NGX_OK) {
            r->access_code = 0;

            if (r->headers_out.www_authenticate) {
                r->headers_out.www_authenticate->hash = 0;
            }

            r->phase_handler = ph->next;
            return NGX_AGAIN;
        }

        if (rc == NGX_HTTP_FORBIDDEN || rc == NGX_HTTP_UNAUTHORIZED) {
            if (r->access_code != NGX_HTTP_UNAUTHORIZED) {
                r->access_code = rc;
            }

            r->phase_handler++;
            return NGX_AGAIN;
        }
    }

    /* rc == NGX_ERROR || rc == NGX_HTTP_...  */

    ngx_http_finalize_request(r, rc);
    return NGX_OK;
}

11.6.1 ngx_http_access_handler

该 ngx_http_access_module 同样没有进行相应的配置，因此暂时不分析。

11.6.2 ngx_http_auth_basic_module

没有配置，暂不分析.

11.7 NGX_HTTP_POST_ACCESS_PHASE

在 NGX_HTTP_ACCESS_PAHSE 阶段中，当 HTTP 模块的 handler 处理函数返回不允许访问的错误码时（实际就是 NGX_HTTP_FORBIDDEN 或 NGX_HTTP_AUTHORIZED），这里将负责向用户发送拒绝服务的错误响应。因此，这个阶段实际上用于给 NGX_HTTP_ACCESS_PAHSE 阶段收尾.

该阶段实现的 checker 方法为 ngx_http_core_post_access_phase，且没有 handler 方法，即不允许其他 HTTP 模块介入。

ngx_int_t
ngx_http_core_post_access_phase(ngx_http_request_t *r,
    ngx_http_phase_handler_t *ph)
{
    ngx_int_t  access_code;

    ngx_log_debug1(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                   "post access phase: %ui", r->phase_handler);

    access_code = r->access_code;

    if (access_code) {
        if (access_code == NGX_HTTP_FORBIDDEN) {
            ngx_log_error(NGX_LOG_ERR, r->connection->log, 0,
                          "access forbidden by rule");
        }

        r->access_code = 0;
        ngx_http_finalize_request(r, access_code);
        return NGX_OK;
    }

    r->phase_handler++;
    return NGX_AGAIN;
}

注：由于没有配置 try_files 配置项，因此直接跳过 NGX_HTTP_TRY_FILES_PHASE 阶段。

11.8 NGX_HTTP_CONTENT_PHASE

该阶段用于处理 HTTP 请求内容的阶段，这是大部分 HTTP 模块最愿意介入的阶段。

该阶段实现的 checker 方法为 ngx_http_core_content_phase，介入的模块有：

• ngx_http_index_module：handler 为 ngx_http_index_handler
• ngx_http_autoindex_module: handler 为 ngx_http_autoindex_handler
• ngx_http_dav_module：handler 为 ngx_http_dav_handler
• ngx_http_gzip_static_module：handler 为 ngx_http_gzip_static_handler
• ngx_http_random_index_module：handler 为 ngx_http_random_index_handler
• ngx_http_static_module：handler ngx_http_static_handler

ngx_http_core_content_phase 的实现如下：

ngx_int_t
ngx_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);

    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;
}

11.8.1 ngx_http_index_handler

/*
 * Try to open/test the first index file before the test of directory
 * existence because valid requests should prevail over invalid ones.
 * If open()/stat() of a file will fail then stat() of a directory
 * should be faster because kernel may have already cached some data.
 * Besides, Win32 may return ERROR_PATH_NOT_FOUND (NGX_ENOTDIR) at once.
 * Unix has ENOTDIR error; however, it's less helpful than Win32's one:
 * is only indicates that path points to a regular file, not a directory.
 */
static ngx_int_t
ngx_http_index_handler(ngx_http_request_t *r)
{
    ...

    /* 因为当前请求 uri 的最后一个字符不为 '/'，直接返回 */
    if (r->uri.data[r->uri.len - 1] != '/') {
        return NGX_DECLINED;
    }

    ...
}

11.8.2 ngx_http_autoindex_handler

static ngx_int_t
ngx_http_autoindex_handler(ngx_http_request_t *r)
{
    ...

    /* 由于当前请求 uri 的最后一个字节不为 '/'，因此直接返回 */
    if (r->uri.data[r->uri.len - 1] != '/') {
        return NGX_DECLINED;
    }

    ...
}

11.8.3 ngx_http_static_handler

static ngx_int_t
ngx_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;

    if (!(r->method & (NGX_HTTP_GET|NGX_HTTP_HEAD|NGX_HTTP_POST))) {
        return NGX_HTTP_NOT_ALLOWED;
    }

    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
     */

    /* 根据所访问文件的根目录和锁请求访问的静态文件，得出该文件的
     * 绝对路径，保存在 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);

    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;
    }

    /* 打开该文件并获取该文件的信息，同时设置当释放该内存池时调用的回调函数
     * 以便释放该文件的描述符 */
    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 && clcf->root_lengths == NULL && r->args.len == 0) {
            location = path.data + clcf->root.len;

            *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

    if (r->method == NGX_HTTP_POST) {
        return NGX_HTTP_NOT_ALLOWED;
    }

    /* 丢弃 HTTP 的请求包体，若本来就没有，则直接返回 */
    rc = ngx_http_discard_request_body(r);

    if (rc != NGX_OK) {
        return rc;
    }

    /* 下面将要执行的动作是发送响应给客户端 */
    log->action = "sending response to client";

    /* 设置响应的状态码 */
    r->headers_out.status = NGX_HTTP_OK;
    /* 设置响应的包体的大小 */
    r->headers_out.content_length_n = of.size;
    /* 该文件上一次修改时间（Unix时间戳） */
    r->headers_out.last_modified_time = of.mtime;

    /* 添加一个 ETag 响应头，ETag 对应实体内容的一个实体标签，与实体
     * 内容紧密相关，实体内容发生任何变化都会使这个头的值发生变化 */
    if (ngx_http_set_etag(r) != NGX_OK) {
        return NGX_HTTP_INTERNAL_SERVER_ERROR;
    }

    /* 实体头 Content-Type：服务器在返回内容时需要告诉浏览器本响应的内容是什么
     * 类型。HTTP 中把这种不同媒体类型的格式称为多媒体文件格式（MIME），而本实体
     * 头指出所传输实体内容的 MIME。由于 Web 服务器不知道所返回的的内容文件是
     * 哪种 MIME，所以需要通过对 Web 服务器进行设置，使文件扩展名与 MIME 之间进行
     * 映射。如 : Content-Type: text/html; */
    if (ngx_http_set_content_type(r) != NGX_OK) {
        return NGX_HTTP_INTERNAL_SERVER_ERROR;
    }

    /* 若当前请求为子请求 */
    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 */

    /* 为响应数据分配一个缓存 */
    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;
    }

    /* 该函数主要是调用 ngx_http_top_header_filter 链表中的函数，
     * 构造响应消息的消息报头，写入到 r->out 链表中 */
    rc = ngx_http_send_header(r);

    if (rc == NGX_ERROR || rc > NGX_OK || r->header_only) {
        return rc;
    }

    b->file_pos = 0;
    b->file_last = of.size;

    b->in_file = b->file_last ? 1: 0;
    /* 若当前请求为父请求，则表明这个最后一个 buf 了 */
    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;

    /* 接下来调用 ngx_http_top_body_filter 链表中的函数构造响应消息的响应正文 */
    return ngx_http_output_filter(r, &out);
}

11.8.3.1 ngx_http_map_uri_to_path

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) {

        /* 根目录路径的长度 */
        *root_length = clcf->root.len;

        /* 计算根目录的路径加上客户当访问的文件的长度 */
        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  clcf->root.data 中保存的静态文件的根目录拷贝到 path->data 中 */
        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;
        }
    }

    /* 若没有别名的话，这里拷贝的 last 为空字符串 */
    last = ngx_cpystrn(last, r->uri.data + alias, r->uri.len - alias + 1);

    return last;
}

11.8.3.2 ngx_open_cached_file

ngx_int_t
ngx_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;

    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;
        }

        /* 该接口用于对内存与其他资源文件的管理，从内存池里申请一块内存时，
         * 可能外部会附加一些其他资源（如打开的文件），这些资源的使用和申请的
         * 内存是绑定在一起的，那么在进行资源释放的时候，希望这些资源的释放
         * 能和内存池释放一起进行（通过 handler 回调函数），既能避免无意的
         * 资源泄露，又省得单独执行资源释放的麻烦. */
        cln = ngx_pool_cleanup_add(pool, sizeof(ngx_pool_cleanup_file_t));
        if (cln == NULL) {
            return NGX_ERROR;
        }

        /* 打开该文件并获取该文件的信息 */
        rc = ngx_open_and_stat_file(name, of, pool->log);

        /* 若该文件不是一个目录 */
        if (rc == NGX_OK && !of->is_dir) {
            /* 设置当释放该资源时，调用的回调函数 */
            cln->handler = ngx_pool_cleanup_file;
            clnf = cln->data;

            /* 该文件的打开描述符 */
            clnf->fd = of->fd;
            /* 客户端请求的文件的绝对路径名 */
            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;
}

11.8.3.3 ngx_pool_cleanup_add

ngx_pool_cleanup_t *
ngx_pool_cleanup_add(ngx_pool_t *p, size_t size)
{
    ngx_pool_cleanup_t  *c;

    c = ngx_palloc(p, sizeof(ngx_pool_cleanup_t));
    if (c == NULL) {
        return NULL;
    }

    if (size) {
        c->data = ngx_palloc(p, size);
        if (c->data == NULL) {
            return NULL;
        }

    } else {
        c->data = NULL;
    }

    c->handler = NULL;
    c->next = p->cleanup;

    p->cleanup = c;

    ngx_log_debug1(NGX_LOG_DEBUG_ALLOC, p->log, 0, "add cleanup: %p", c);

    return c;
}

11.8.3.4 ngx_open_and_stat_file

static ngx_int_t
ngx_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;

    /* 若该文件已经打开了 */
    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.
         */

        /* 使用只读且为非阻塞方法打开该文件 */
        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;
    }

    /* 调用 fstat 获取该文件的信息 */
    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;
    }

    /* 检测是否是一个目录 */
    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 {
        /* 否则为一个普通的文件 */
        of->fd = fd;

        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:

    /* 根据上面 stat 返回的文件信息初始化该文件 */
    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;
}

11.8.3.5 ngx_open_file_wrapper

static ngx_fd_t
ngx_open_file_wrapper(ngx_str_t *name, ngx_open_file_info_t *of,
    ngx_int_t mode, ngx_int_t create, ngx_int_t access, ngx_log_t *log)
{
    ngx_fd_t  fd;

#if !(NGX_HAVE_OPENAT)

    fd = ngx_open_file(name->data, mode, create, access);

    if (fd == NGX_INVALID_FILE) {
        of->err = ngx_errno;
        of->failed = ngx_open_file_n;
        return NGX_INVALID_FILE;
    }

    return fd;

#else

    u_char           *p, *cp, *end;
    ngx_fd_t          at_fd;
    ngx_str_t         at_name;

    if (of->disable_symlinks == NGX_DISABLE_SYMLINKS_OFF) {
        /* 调用 open 函数打开该文件 */
        fd = ngx_open_file(name->data, mode, create, access);

        if (fd == NGX_INVALID_FILE) {
            of->err = ngx_errno;
            of->failed = ngx_open_file_n;
            return NGX_INVALID_FILE;
        }

        /* 打开成功，则直接返回该文件描述符 */
        return fd;
    }

    p = name->data;
    end = p + name->len;

    at_name = *name;

    if (of->disable_symlinks_from) {

        cp = p + of->disable_symlinks_from;

        *cp = '\0';

        at_fd = ngx_open_file(p, NGX_FILE_SEARCH|NGX_FILE_NONBLOCK,
                              NGX_FILE_OPEN, 0);

        *cp = '/';

        if (at_fd == NGX_INVALID_FILE) {
            of->err = ngx_errno;
            of->failed = ngx_open_file_n;
            return NGX_INVALID_FILE;
        }

        at_name.len = of->disable_symlinks_from;
        p = cp + 1;

    } else if (*p == '/') {

        at_fd = ngx_open_file("/",
                              NGX_FILE_SEARCH|NGX_FILE_NONBLOCK,
                              NGX_FILE_OPEN, 0);

        if (at_fd == NGX_INVALID_FILE) {
            of->err = ngx_errno;
            of->failed = ngx_openat_file_n;
            return NGX_INVALID_FILE;
        }

        at_name.len = 1;
        p++;

    } else {
        at_fd = NGX_AT_FDCWD;
    }

    for ( ;; ) {
        cp = ngx_strlchr(p, end, '/');
        if (cp == NULL) {
            break;
        }

        if (cp == p) {
            p++;
            continue;
        }

        *cp = '\0';

        if (of->disable_symlinks == NGX_DISABLE_SYMLINKS_NOTOWNER) {
            fd = ngx_openat_file_owner(at_fd, p,
                                       NGX_FILE_SEARCH|NGX_FILE_NONBLOCK,
                                       NGX_FILE_OPEN, 0, log);

        } else {
            fd = ngx_openat_file(at_fd, p,
                           NGX_FILE_SEARCH|NGX_FILE_NONBLOCK|NGX_FILE_NOFOLLOW,
                           NGX_FILE_OPEN, 0);
        }

        *cp = '/';

        if (fd == NGX_INVALID_FILE) {
            of->err = ngx_errno;
            of->failed = ngx_openat_file_n;
            goto failed;
        }

        if (at_fd != NGX_AT_FDCWD && ngx_close_file(at_fd) == NGX_FILE_ERROR) {
            ngx_log_error(NGX_LOG_ALERT, log, ngx_errno,
                          ngx_close_file_n " \"%V\" failed", &at_name);
        }

        p = cp + 1;
        at_fd = fd;
        at_name.len = cp - at_name.data;
    }

    if (p == end) {

        /*
         * If pathname ends with a trailing slash, assume the last path
         * component is a directory and reopen it with requested flags;
         * if not, fail with ENOTDIR as per POSIX.
         *
         * We cannot rely on O_DIRECTORY in the loop above to check
         * that the last path component is a directory because
         * O_DIRECTORY doesn't work on FreeBSD 8.  Fortunately, by
         * reopening a directory, we don't depend on it at all.
         */

        fd = ngx_openat_file(at_fd, ".", mode, create, access);
        goto done;
    }

    if (of->disable_symlinks == NGX_DISABLE_SYMLINKS_NOTOWNER
        && !(create & (NGX_FILE_CREATE_OR_OPEN|NGX_FILE_TRUNCATE)))
    {
        fd = ngx_openat_file_owner(at_fd, p, mode, create, access, log);

    } else {
        fd = ngx_openat_file(at_fd, p, mode|NGX_FILE_NOFOLLOW, create, access);
    }

done:

    if (fd == NGX_INVALID_FILE) {
        of->err = ngx_errno;
        of->failed = ngx_openat_file_n;
    }

failed:

    if (at_fd != NGX_AT_FDCWD && ngx_close_file(at_fd) == NGX_FILE_ERROR) {
        ngx_log_error(NGX_LOG_ALERT, log, ngx_errno,
                      ngx_close_file_n " \"%V\" failed", &at_name);
    }

    return fd;
#endif
}

11.8.3.6 ngx_http_set_etag

ngx_int_t
ngx_http_set_etag(ngx_http_request_t *r)
{
    ngx_table_elt_t           *etag;
    ngx_http_core_loc_conf_t  *clcf;

    clcf = ngx_http_get_module_loc_conf(r, ngx_http_core_module);

    if (!clcf->etag) {
        return NGX_OK;
    }

    /* 将 ETag 头部放入到 headers_out.header 链表中 */
    etag = ngx_list_push(&r->headers_out.headers);
    if (etag == NULL) {
        return NGX_ERROR;
    }

    etag->hash = 1;
    ngx_str_set(&etag->key, "ETag");

    etag->value.data = ngx_pnalloc(r->pool, NGX_OFF_T_LEN + NGX_TIME_T_LEN + 3);
    if (etag->value.data == NULL) {
        etag->hash = 0;
        return NGX_ERROR;
    }

    /* 根据该文件的上一次修改时间和该文件的大小构成一个 ETag 头部的值 */
    etag->value.len = ngx_sprintf(etag->value.data, "\"%xT-%xO\"",
                                  r->headers_out.last_modified_time,
                                  r->headers_out.content_length_n)
                      - etag->value.data;

    r->headers_out.etag = etag;

    return NGX_OK;
}

11.8.3.7 ngx_http_set_content_type

ngx_int_t
ngx_http_set_content_type(ngx_http_request_t *r)
{
    u_char                     c, *exten;
    ngx_str_t                 *type;
    ngx_uint_t                 i, hash;
    ngx_http_core_loc_conf_t  *clcf;

    /* 若该 headers_out 中已经有 Content-Type 头了，则直接返回 */
    if (r->headers_out.content_type.len) {
        return NGX_OK;
    }

    clcf = ngx_http_get_module_loc_conf(r, ngx_http_core_module);

    /* 该请求文件的扩展名，如 "html" */
    if (r->exten.len) {

        hash = 0;

        for (i = 0; i < r->exten.len; i++) {
            c = r->exten.data[i];

            if (c >= 'A' && c <= 'Z') {

                exten = ngx_pnalloc(r->pool, r->exten.len);
                if (exten == NULL) {
                    return NGX_ERROR;
                }

                hash = ngx_hash_strlow(exten, r->exten.data, r->exten.len);

                r->exten.data = exten;

                break;
            }

            /* 生成一个哈希查找的 key */
            hash = ngx_hash(hash, c);
        }

        /* 在哈希表 types_hash 中根据 key（即 hash）查找与 r->exten.data 相同的项 */
        type = ngx_hash_find(&clcf->types_hash, hash,
                             r->exten.data, r->exten.len);

        if (type) {
            r->headers_out.content_type_len = type->len;
            /* 对于 html 类型的，这里对应的 Content-Type 为 "text/html" */
            r->headers_out.content_type = *type;

            return NGX_OK;
        }
    }

    r->headers_out.content_type_len = clcf->default_type.len;
    r->headers_out.content_type = clcf->default_type;

    return NGX_OK;
}

11.8.3.8 ngx_hash_find

/*
 * 返回散列表中关键字与 name、len 指定关键字完全相同的槽中，
 * ngx_hash_elt_t 结构体中 value 成员所指向的用户数据.
 */
void *
ngx_hash_find(ngx_hash_t *hash, ngx_uint_t key, u_char *name, size_t len)
{
    ngx_uint_t       i;
    ngx_hash_elt_t  *elt;

#if 0
    ngx_log_error(NGX_LOG_ALERT, ngx_cycle->log, 0, "hf:\"%*s\"", len, name);
#endif

    /* 对 key 取模得到对应的 hash 节点 */
    elt = hash->buckets[key % hash->size];

    if (elt == NULL) {
        return NULL;
    }

    /* 然后在该 hash 节点所对应的 bucket 里逐个（该 bucket 的实现类似数组，结束有
     * 哨兵保证）对于元素名称来找到唯一的那个实际元素，最后返回其 value 值
     * （比如，如果在 addr->hash 结构里找到对应的实际元素，返回的 value 就是
     * 其 ngx_http_core_srv_cnf_t 配置）*/
    while (elt->value) {
        if (len != (size_t) elt->len) {
            goto next;
        }

        for (i = 0; i < len; i++) {
            if (name[i] != elt->name[i]) {
                goto next;
            }
        }

        /* 将返回该名称和完成都相同的项 */
        return elt->value;

    next:

        elt = (ngx_hash_elt_t *) ngx_align_ptr(&elt->name[0] + elt->len,
                                               sizeof(void *));
        continue;
    }

    return NULL;
}

11.8.3.9 ngx_http_send_header

ngx_int_t
ngx_http_send_header(ngx_http_request_t *r)
{
    if (r->post_action) {
        return NGX_OK;
    }

    /* 标志位，为 1 表示该 header 已经发送了 */
    if (r->header_sent) {
        ngx_log_error(NGX_LOG_ALERT, r->connection->log, 0,
                      "header already sent");
        return NGX_ERROR;
    }

    /* 错误状态码 */
    if (r->err_status) {
        r->headers_out.status = r->err_status;
        r->headers_out.status_line.len = 0;
    }

    /* ngx_http_top_header_filter 是个全局函数指针，由各个HTTP模块
     * 共同构造的一个单链表，存放的是各个 HTTP 模块在此阶段介入的
     * 处理 */
    return ngx_http_top_header_filter(r);
}

11.3.8.10 ngx_http_output_filter

ngx_int_t
ngx_http_output_filter(ngx_http_request_t *r, ngx_chain_t *in)
{
    ngx_int_t          rc;
    ngx_connection_t  *c;

    c = r->connection;

    ngx_log_debug2(NGX_LOG_DEBUG_HTTP, c->log, 0,
                   "http output filter \"%V?%V\"", &r->uri, &r->args);

    /* ngx_http_top_body_filter 是一个由各个 HTTP 模块构造的函数链表，
     * 保存的是各个 HTTP 模块想要在响应消息的响应正文中做的处理 */
    rc = ngx_http_top_body_filter(r, in);

    if (rc == NGX_ERROR) {
        /* NGX_ERROR may be returned by any filter */
        c->error = 1;
    }

    return rc;
}

11.3.8.11 ngx_http_finalize_request

void
ngx_http_finalize_request(ngx_http_request_t *r, ngx_int_t rc)
{
    ngx_connection_t          *c;
    ngx_http_request_t        *pr;
    ngx_http_core_loc_conf_t  *clcf;

    c = r->connection;

    ngx_log_debug5(NGX_LOG_DEBUG_HTTP, c->log, 0,
                   "http finalize request: %i, \"%V?%V\" a:%d, c:%d",
                   rc, &r->uri, &r->args, r == c->data, r->main->count);

    if (rc == NGX_DONE) {
        ngx_http_finalize_connection(r);
        return;
    }

    if (rc == NGX_OK && r->filter_finalize) {
        c->error = 1;
    }

    if (rc == NGX_DECLINED) {
        r->content_handler = NULL;
        r->write_event_handler = ngx_http_core_run_phases;
        ngx_http_core_run_phases(r);
        return;
    }

    if (r != r->main && r->post_subrequest) {
        rc = r->post_subrequest->handler(r, r->post_subrequest->data, rc);
    }

    if (rc == NGX_ERROR
        || rc == NGX_HTTP_REQUEST_TIME_OUT
        || rc == NGX_HTTP_CLIENT_CLOSED_REQUEST
        || c->error)
    {
        if (ngx_http_post_action(r) == NGX_OK) {
            return;
        }

        ngx_http_terminate_request(r, rc);
        return;
    }

    if (rc >= NGX_HTTP_SPECIAL_RESPONSE
        || rc == NGX_HTTP_CREATED
        || rc == NGX_HTTP_NO_CONTENT)
    {
        if (rc == NGX_HTTP_CLOSE) {
            ngx_http_terminate_request(r, rc);
            return;
        }

        if (r == r->main) {
            if (c->read->timer_set) {
                ngx_del_timer(c->read);
            }

            if (c->write->timer_set) {
                ngx_del_timer(c->write);
            }
        }

        c->read->handler = ngx_http_request_handler;
        c->write->handler = ngx_http_request_handler;

        ngx_http_finalize_request(r, ngx_http_special_response_handler(r, rc));
        return;
    }

    if (r != r->main) {
        clcf = ngx_http_get_module_loc_conf(r, ngx_http_core_module);

        if (r->background) {
            if (!r->logged) {
                if (clcf->log_subrequest) {
                    ngx_http_log_request(r);
                }

                r->logged = 1;

            } else {
                ngx_log_error(NGX_LOG_ALERT, c->log, 0,
                              "subrequest: \"%V?%V\" logged again",
                              &r->uri, &r->args);
            }

            r->done = 1;
            ngx_http_finalize_connection(r);
            return;
        }

        if (r->buffered || r->postponed) {

            if (ngx_http_set_write_handler(r) != NGX_OK) {
                ngx_http_terminate_request(r, 0);
            }

            return;
        }

        pr = r->parent;

        if (r == c->data) {

            r->main->count--;

            if (!r->logged) {
                if (clcf->log_subrequest) {
                    ngx_http_log_request(r);
                }

                r->logged = 1;

            } else {
                ngx_log_error(NGX_LOG_ALERT, c->log, 0,
                              "subrequest: \"%V?%V\" logged again",
                              &r->uri, &r->args);
            }

            r->done = 1;

            if (pr->postponed && pr->postponed->request == r) {
                pr->postponed = pr->postponed->next;
            }

            c->data = pr;

        } else {

            ngx_log_debug2(NGX_LOG_DEBUG_HTTP, c->log, 0,
                           "http finalize non-active request: \"%V?%V\"",
                           &r->uri, &r->args);

            r->write_event_handler = ngx_http_request_finalizer;

            if (r->waited) {
                r->done = 1;
            }
        }

        if (ngx_http_post_request(pr, NULL) != NGX_OK) {
            r->main->count++;
            ngx_http_terminate_request(r, 0);
            return;
        }

        ngx_log_debug2(NGX_LOG_DEBUG_HTTP, c->log, 0,
                       "http wake parent request: \"%V?%V\"",
                       &pr->uri, &pr->args);

        return;
    }

    if (r->buffered || c->buffered || r->postponed) {

        if (ngx_http_set_write_handler(r) != NGX_OK) {
            ngx_http_terminate_request(r, 0);
        }

        return;
    }

    if (r != c->data) {
        ngx_log_error(NGX_LOG_ALERT, c->log, 0,
                      "http finalize non-active request: \"%V?%V\"",
                      &r->uri, &r->args);
        return;
    }

    /* 标志位，为 1 表示当前请求结束 */
    r->done = 1;

    r->read_event_handler = ngx_http_block_reading;
    r->write_event_handler = ngx_http_request_empty_handler;

    if (!r->post_action) {
        /* 为 1 表示当前请求已经完全处理完 */
        r->request_complete = 1;
    }

    if (ngx_http_post_action(r) == NGX_OK) {
        return;
    }

    if (c->read->timer_set) {
        ngx_del_timer(c->read);
    }

    if (c->write->timer_set) {
        c->write->delayed = 0;
        ngx_del_timer(c->write);
    }

    if (c->read->eof) {
        ngx_http_close_request(r, 0);
        return;
    }

    ngx_http_finalize_connection(r);
}