Support CIDR blocks in NO_PROXY env variable

[melkouri]

Is your feature request related to a problem? Please describe.

We have use cases where we would like to block all private IPs, hostnames using the NO_PROXY env variable. We want to specify whole CIDR blocks rather than whitelist each single IP, for example (NO_PROXY=172.16.0.0/12, 192.168.0.0/16).

Today the library only supports the NO_PROXY to be a list of single IPs (NO_PROXY=172.16.0.10, 192.168.0.10) and checks the host we're reaching against the list.

Describe the solution you'd like

• Add NO_PROXY parsing to get the host_ip and the mask for each element.
• Check if the targeted IP falls in the IP range of the CIDR.
  Implementation (fix: support CIDR blocks in no_proxy env variable #2876)

In other languages

• Golang: according to the documentation for http.ProxyFromEnvironment, the NO_PROXY environment variable does not natively support CIDR blocks. Instead, it only supports exact hostnames or IP addresses (optionally including ports).
• C-core supports using CIDR blocks in NO_PROXY(implementation) (doc)

[murgatroid99]

This feature is now available in version 1.13.x.