Feature or Bugfix

• Bugfix

Purpose

• If an SSLError occurs following an HTTP HEAD operation, it seems unlikely that a subsequent HTTP GET will succeed, so don't attempt one.

Detail

• The SSLError exception that can be raised by requests is a subclass of ConnectionError, so our logic to handle HTTP HEAD request failures has allowed an HTTP GET to occur as a fallback.
• My understanding is that TLS operates at a protocol layer below HTTP, and so if there is a TLS-related error from a host, it seems unlikely that retrying with a different higher-layer protocol request (HTTP GET instead of HTTP HEAD) could succeed.
• We shouldn't make additional HTTP requests that we do not believe will succeed.

Relates

• Partially addresses Linkcheck shouldn't retry on SSL errors #9592.
• See also Linkcheck Reports Broken Link when Remote Server Closes on HEAD Request #9306 (could invalidate this approach?).