Subject: [bug#27704] [PATCH] daemon: Show actual rather than collateral error when export fails.

From: [email-masked] (Ludovic Courtès)
Date: Mon, 17 Jul 2017 11:47:04 +0200

Hello,

Jan Nieuwenhuizen <[email-masked]> skribis:

> Having the wrong permissions on /etc/guix/signing-key.sec gives
>
>     guix-daemon: nix/libutil/serialise.cc:15: virtual nix::BufferedSink::~BufferedSink(): Assertion `!bufPos' failed.
>
> this patch changes that to
>
>     guix-daemon: error: file `/etc/guix/signing-key.sec' should be secret (inaccessible to everybody else)!
>
> * nix/nix-daemon/nix-daemon.cc (performOp): Catch any exportPath exception,
> report and exit on that.  Fixes failing later with uninformative collateral error.

Good catch!

> --- a/nix/nix-daemon/nix-daemon.cc
> +++ b/nix/nix-daemon/nix-daemon.cc
> @@ -436,7 +436,13 @@ static void performOp(bool trusted, unsigned int clientVersion,
>          bool sign = readInt(from) == 1;
>          startWork();
>          TunnelSink sink(to);
> -        store->exportPath(path, sign, sink);
> +        try {
> +            store->exportPath(path, sign, sink);
> +        }
> +        catch (std::exception &e) {
> +            fprintf (stderr, "guix-daemon: error: %s\n", e.what ());
> +            exit (EXIT_FAILURE);

I think we should simply do:

  sink.flush();
  throw e;

in the ‘catch’ handler.

That way, we won’t have the assertion failure, and yet the error will
correctly propagate to the client without forcing a disconnect.

Could you check if that works as expected?

Thank you!

Ludo’.