Constant USER_AGENT 

pub const USER_AGENT: &'static str;

The user agent both paths send.

A tool-shaped agent (webfetch/0.1.x) is refused or challenged by a large share of CDNs, which turns an ordinary fetch into an empty page. The search path already sent a browser agent for exactly this reason; the fetch path did not, and the mismatch was the single most common cause of a 403.