语法: ngx.exit(status)
环境: rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua*, ngx.timer.*
当 status >= 200 (即 ngx.HTTP_OK 及以上) 时，本函数中断当前请求执行并返回状态值给 nginx。
当 status == 0 (即 ngx.OK) 时，本函数退出当前的“处理阶段句柄” (或当使用 content_by_lua 指令时的“内容句柄”) ，继续执行当前请求的下一个阶段 (如果有)。
status 参数可以是 status argument can be ngx.OK, ngx.ERROR, ngx.HTTP_NOT_FOUND, ngx.HTTP_MOVED_TEMPORARILY 或其它 HTTP status constants。
要返回一个自定义内容的错误页，使用类似下面的代码：
ngx.status = ngx.HTTP_GONE
ngx.say("This is our own content")
-- 退出整个请求而不是当前处理阶段
ngx.exit(ngx.HTTP_OK)实际效果:
$ curl -i http://localhost/test
HTTP/1.1 410 Gone
Server: nginx/1.0.6
Date: Thu, 15 Sep 2011 00:51:48 GMT
Content-Type: text/plain
Transfer-Encoding: chunked
Connection: keep-alive
This is our own content可以直接使用数字作为参数，例如：
ngx.exit(501)请注意，虽然此方法接受所有 HTTP status constants 作为输入，但在 core constants 中仅支持 NGX_OK 和 NGX_ERROR 作为输入。
同时请注意，因为调用此方法会中断当前请求处理，所以建议代码风格是与 return 语句一起调用此方法，即，使用 return ngx.exit(...) 来强调请求处理过程已经中断。
当使用在 header_filter_by_lua 环境中时，ngx.exit() 是一个异步操作，会立即返回。这个行为在未来版本中可能会改变，所以建议用户一直使用上述与 returen 同时使用的代码风格。
English Source
syntax: ngx.exit(status)
context: rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua*, ngx.timer.*
When status >= 200 (i.e., ngx.HTTP_OK and above), it will interrupt the execution of the current request and return status code to nginx.
When status == 0 (i.e., ngx.OK), it will only quit the current phase handler (or the content handler if the content_by_lua directive is used) and continue to run later phases (if any) for the current request.
The status argument can be ngx.OK, ngx.ERROR, ngx.HTTP_NOT_FOUND,
ngx.HTTP_MOVED_TEMPORARILY, or other HTTP status constants.
To return an error page with custom contents, use code snippets like this:
ngx.status = ngx.HTTP_GONE
ngx.say("This is our own content")
-- to cause quit the whole request rather than the current phase handler
ngx.exit(ngx.HTTP_OK)The effect in action:
$ curl -i http://localhost/test
HTTP/1.1 410 Gone
Server: nginx/1.0.6
Date: Thu, 15 Sep 2011 00:51:48 GMT
Content-Type: text/plain
Transfer-Encoding: chunked
Connection: keep-alive
This is our own contentNumber literals can be used directly as the argument, for instance,
ngx.exit(501)Note that while this method accepts all HTTP status constants as input, it only accepts NGX_OK and NGX_ERROR of the core constants.
Also note that this method call terminates the processing of the current request and that it is recommended that a coding style that combines this method call with the return statement, i.e., return ngx.exit(...) be used to reinforce the fact that the request processing is being terminated.
When being used in the context of header_filter_by_lua, ngx.exit() is an asynchronous operation and will return immediately. This behavior may change in future and it is recommended that users always use return in combination as suggested above.