语法: ngx.req.init_body(buffer_size?)
环境: set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*
为当前请求创建一个新的空请求体并初始化缓冲区，为后续通过 ngx.req.append_body 和 ngx.req.finish_body API 写请求体数据做好准备。
如果设置了 buffer_size 参数，将设置该大小的内存缓冲区，用于后续的 ngx.req.append_body 写请求体数据。如果省略此参数，将使用 Nginx 标准指令 client_body_buffer_size 中设置的值作为缓冲区大小。
当请求体数据过大，不再能保存在内存缓冲区中时，数据将被写入一个临时文件，类似 Nginx 内核中的标准请求体处理方式。
需要强调的是，在当前请求的所有请求体被写入完成后，必须调用 ngx.req.finish_body 以结束写入。另外，当此函数与 ngx.req.socket 一起使用时，需要在执行此函数 之前 调用 ngx.req.socket，否则将会报 "request body already exists" (请求体已经存在) 错。
此函数典型用法如下：
ngx.req.init_body(128 * 1024) -- 缓冲区 128KB
for chunk in next_data_chunk() do
ngx.req.append_body(chunk) -- 每块可以是 4KB
end
ngx.req.finish_body()此函数可以与 ngx.req.append_body，ngx.req.finish_body，和 ngx.req.socket 一起，使用纯 Lua 语言实现高效的输入过滤器 (在 rewrite_by_lua* 或 access_by_lua* 环境中)，与其他 Nginx 内容处理程序或上游模块例如 ngx_http_proxy_module 和 ngx_http_fastcgi_module 配合使用。
这个函数在 v0.5.11 版本中首次引入。
English Source
syntax: ngx.req.init_body(buffer_size?)
context: set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*
Creates a new blank request body for the current request and inializes the buffer for later request body data writing via the ngx.req.append_body and ngx.req.finish_body APIs.
If the buffer_size argument is specified, then its value will be used for the size of the memory buffer for body writing with ngx.req.append_body. If the argument is omitted, then the value specified by the standard client_body_buffer_size directive will be used instead.
When the data can no longer be hold in the memory buffer for the request body, then the data will be flushed onto a temporary file just like the standard request body reader in the Nginx core.
It is important to always call the ngx.req.finish_body after all the data has been appended onto the current request body. Also, when this function is used together with ngx.req.socket, it is required to call ngx.req.socket before this function, or you will get the "request body already exists" error message.
The usage of this function is often like this:
ngx.req.init_body(128 * 1024) -- buffer is 128KB
for chunk in next_data_chunk() do
ngx.req.append_body(chunk) -- each chunk can be 4KB
end
ngx.req.finish_body()This function can be used with ngx.req.append_body, ngx.req.finish_body, and ngx.req.socket to implement efficient input filters in pure Lua (in the context of rewrite_by_lua* or access_by_lua*), which can be used with other Nginx content handler or upstream modules like ngx_http_proxy_module and ngx_http_fastcgi_module.
This function was first introduced in the v0.5.11 release.