Subject: bug#34102: [staging] Guix fails to download from TLSv1.3-enabled servers

From: Marius Bakke <[email-masked]>
Date: Wed, 16 Jan 2019 14:33:15 +0100

Hello!

On the staging branch (with GnuTLS 3.6), `guix download` will negotiate
TLSv1.3 with servers that support it, and fail shortly after the initial
handshake:

$ ./pre-inst-env guix download https://data.iana.org
Starting download of /tmp/guix-file.vJ4v7h
From https://data.iana.org...
Throw to key `gnutls-error' with args `(#<gnutls-error-enum Resource temporarily unavailable, try again.> read_from_session_record_port)'.
failed to download "/tmp/guix-file.vJ4v7h" from "https://data.iana.org"
guix download: error: https://data.iana.org: download failed

The GnuTLS maintainer have written a blog post about TLS 1.3 porting[0],
and I suspect the problem is that Guix (or the GnuTLS Guile bindings)
does not handle the "GNUTLS_E_REAUTH_REQUEST" error code; however my
attempts at catching it (or any error code) has been unfruitful.

This is an obvious merge blocker, help wanted!  Disabling TLS1.3 in the
priority string works as a last-resort workaround.

[0] https://nikmav.blogspot.com/2018/05/gnutls-and-tls-13.html