ssh-ng: better way to keep SSH errors visible

A better fix than in 104448e75d87d03d2fb0b4ac96d4da72e1dae50d, hence a
revert + the fix.

It turns out that this commit has the side-effect that when having e.g.
`StrictHostKeyChecking=accept-new` for a remote builder, the warnings à la

    Warning: Permanently added 'builder' (ED25519) to the list of known hosts.

actually end up in the derivation's log whereas hostkey verification
errors don't, but only in the stderr of the `nix-build` invocation
(which was the motivation for the patch).

This change writes the stderr from the build-hook to

* the daemon's stderr, so that the SSH errors appear in the journal
  (which was the case before 104448e75d87d03d2fb0b4ac96d4da72e1dae50d)
* the client's stderr, as a log message
* NOT to the drv log (this is handled via `handleJSONLogMessage`)

I tried to fix the issue for legacy-ssh as well, but failed and
ultimately decided to not bother.

I know that we'll sooner or later replace the entire component, however
this is the part of the patch I have working for a while, so I figured I
might still submit it for the time being.

Change-Id: I21ca1aa0d8ae281d2eacddf26e0aa825272707e5

1 files changed, 1 insertions, 0 deletions

diff --git a/src/libstore/build/derivation-goal.cc b/src/libstore/build/derivation-goal.cc
index 7f72efa6a..96140e10b 100644
--- a/src/libstore/build/derivation-goal.cc
+++ b/src/libstore/build/derivation-goal.cc
@@ -1211,6 +1211,7 @@ HookReply DerivationGoal::tryBuildHook()
             else {
                 s += "\n";
                 writeLogsToStderr(s);
+                logger->log(lvlInfo, s);
             }
         }