Function cargo::util::network::proxy::http_proxy_exists

pub fn http_proxy_exists(http: &CargoHttpConfig, gctx: &GlobalContext) -> bool

Determine if an http proxy exists.

Checks the following for existence, in order:

• Cargo’s http.proxy
• Git’s http.proxy
• http_proxy env var
• HTTP_PROXY env var
• https_proxy env var
• HTTPS_PROXY env var