语法: lua_need_request_body <on|off>
默认: off
环境: http, server, location, location if
阶段: depends on usage
在运行 rewrite/access/access_by_lua* 之前决定是否强制获取请求体数据。 Nginx 内部默认不读取客户端请求体，如果需要读取请求体数据，需要使用该指令设置为 on 或者在 Lua 代码中调用 ngx.req.read_body 函数。
为了读取请求体数据到$request_body变量，client_body_buffer_size必须要与client_max_body_size有同样的大小。因为内容大小超过client_body_buffer_size但是小于client_max_body_size时， Nginx 将把缓冲内存数据存到一个磁盘的临时文件上，这将导致$request_body变量是一个空值。
如果当前location包含 rewrite_by_lua 或 rewrite_by_lua_file 指令，请求体将在rewrite_by_lua 或 rewrite_by_lua_file代码运行之前（还是在rewrite阶段）被读取。如果只有content_by_lua指令，请求体直到内容生成的 Lua 代码执行时才会读取（既，请求体在处理生成返回数据阶段才回被读取）。
无论如何都非常推荐，使用ngx.req.read_body和ngx.req.discard_body函数，可以更好的控制请求体的读取过程。
这些也适用于 access_by_lua 和 access_by_lua_file。
English source:
syntax: lua_need_request_body <on|off>
default: off
context: http, server, location, location if
phase: depends on usage
Determines whether to force the request body data to be read before running rewrite/access/access_by_lua* or not. The Nginx core does not read the client request body by default and if request body data is required, then this directive should be turned on or the ngx.req.read_body function should be called within the Lua code.
To read the request body data within the $request_body variable, client_body_buffer_size must have the same value as client_max_body_size. Because when the content length exceeds client_body_buffer_size but less than client_max_body_size, Nginx will buffer the data into a temporary file on the disk, which will lead to empty value in the $request_body variable.
If the current location includes rewrite_by_lua or rewrite_by_lua_file directives,
then the request body will be read just before the rewrite_by_lua or rewrite_by_lua_file code is run (and also at the
rewrite phase). Similarly, if only content_by_lua is specified,
the request body will not be read until the content handler's Lua code is
about to run (i.e., the request body will be read during the content phase).
It is recommended however, to use the ngx.req.read_body and ngx.req.discard_body functions for finer control over the request body reading process instead.
This also applies to access_by_lua and access_by_lua_file.