$proxy_internal_body_length

Description

The `$proxy_internal_body_length` variable in NGINX is utilized within the context of proxying between servers, specifically when NGINX acts as a reverse proxy. This variable keeps track of the size of the body of the request that has been received from an upstream server. The value of this variable is set after NGINX processes the request coming from the upstream server, generally when the request is being forwarded or when a response is being received. This variable is particularly useful in configurations where the size of the body content needs to be monitored or manipulated. For example, if you're implementing content filtering, logging, or conditional processing based on body size, `$proxy_internal_body_length` provides an immediate and accurate way to retrieve the length of the incoming body data. The typical values for this variable will vary depending on the request and response scenarios, but it generally reflects the number of bytes present in the request body. In this scenario of proxying, when NGINX processes a request, it calculates the body length derived from the proxied content and sets it to this variable before handling further operations or directives where the size might be relevant.

Config Example

location /proxy {
    proxy_pass http://backend;
    access_log /var/log/nginx/proxy.log "$proxy_internal_body_length";
}