核心常量 -------- **环境:** *init_by_lua*\**, set_by_lua*\**, rewrite_by_lua*\**, access_by_lua*\**, content_by_lua*\**, header_filter_by_lua*\**, body_filter_by_lua, *\**log_by_lua*\**, ngx.timer.*\* ```lua ngx.OK (0) ngx.ERROR (-1) ngx.AGAIN (-2) ngx.DONE (-4) ngx.DECLINED (-5) ``` 请注意，这些常量中只有三个可以被 [Nginx API for Lua](#nginx-api-for-lua) 使用 (即 [ngx.exit](#ngxexit) 只接受 `NGX_OK`, `NGX_ERROR`, 和 `NGX_DECLINED` 作为输入)。 ```lua ngx.null ``` `ngx.null` 常量是一个 `NULL` 的[轻量用户数据](http://www.lua.org/pil/28.5.html)，一般被用来表达 Lua table 等里面的 nil (空) 值，类似于 [lua-cjson](http://www.kyne.com.au/~mark/software/lua-cjson.php) 库中的 `cjson.null` 常量。在`v0.5.0rc5` 版本中首次引入这个常量。 `ngx.DECLINED` 这个常量在`v0.5.0rc19`版本中首次引入。 > English Source **context:** *init_by_lua*\**, set_by_lua*\**, rewrite_by_lua*\**, access_by_lua*\**, content_by_lua*\**, header_filter_by_lua*\**, body_filter_by_lua, *\**log_by_lua*\**, ngx.timer.*\* ```lua ngx.OK (0) ngx.ERROR (-1) ngx.AGAIN (-2) ngx.DONE (-4) ngx.DECLINED (-5) ``` Note that only three of these constants are utilized by the [Nginx API for Lua](#nginx-api-for-lua) (i.e., [ngx.exit](#ngxexit) accepts `NGX_OK`, `NGX_ERROR`, and `NGX_DECLINED` as input). ```lua ngx.null ``` The `ngx.null` constant is a `NULL` light userdata usually used to represent nil values in Lua tables etc and is similar to the [lua-cjson](http://www.kyne.com.au/~mark/software/lua-cjson.php) library's `cjson.null` constant. This constant was first introduced in the `v0.5.0rc5` release. The `ngx.DECLINED` constant was first introduced in the `v0.5.0rc19` release. [返回目录](#nginx-api-for-lua)