[tech] Integrity checks for Gemini pages

[Stephane Bortzmeyer]

On Sun, May 30, 2021 at 01:38:54PM +0200,
 Almaember <almaember@disroot.org> wrote 
 a message of 21 lines which said:

> The web however has a Length header in HTTP. The point isn't to perform
> overly complicated checks, but to be able to somewhat tell if the whole file
> got transferred successfully.

Since Gemini requires TLS, the proper solution is to require an
explicit TLS close
<https://gitlab.com/gemini-specification/protocol/-/issues/2>.