substitute: Reopen connection upon “Error in the push function” from GnuTLS.

This works around an occasional issue where substitution stops abruptly
due to “Error in the push function” from GnuTLS, as reported at
<https://issues.guix.gnu.org/71238> by Richard Sent.

* guix/scripts/substitute.scm (call-with-cached-connection): Add
‘error/push-error’ and ‘error/pull-error’ to the list of gnutls-error
values for which the connection is reopened.

Change-Id: Icf079dd10b16739f62fee15bc3d90bab77110576

guix/scripts/substitute.scm

@@ -43,7 +43,11 @@ (define-module (guix scripts substitute)
                 #:select (uri-abbreviation nar-uri-abbreviation
                           (open-connection-for-uri
                            . guix:open-connection-for-uri)))
-  #:autoload   (gnutls) (error/invalid-session error/again error/interrupted)
+  #:autoload   (gnutls) (error/invalid-session
+                         error/again
+                         error/interrupted
+                         error/push-error
+                         error/pull-error)
   #:use-module (guix progress)
   #:use-module ((guix build syscalls)
                 #:select (set-thread-name))
@@ -426,6 +430,11 @@ (define (call-with-cached-connection uri proc)
                               (memq (first args)
                                     (list error/invalid-session
 
+                                          ;; "Error in the push function" is
+                                          ;; usually a transient error.
+                                          error/push-error
+                                          error/pull-error
+
                                           ;; XXX: These two are not properly handled in
                                           ;; GnuTLS < 3.7.3, in
                                           ;; 'write_to_session_record_port'; see