Treat an unset destination mbuffer as 'off' in checkBackupSet

When a backup set configures no mbuffer at all (neither the legacy 'mbuffer'
property nor a per-destination 'dst_X_mbuffer'), dst_X_mbuffer is left undef.
The check 'ne off' then evaluated undef ne 'off' as true, entering mbuffer
validation: it emitted uninitialized-value warnings and died with a bogus
"mbuffer size '' invalid".

Default an undef value to 'off' so such configurations are accepted. Add a
test exercising checkBackupSet with all mbuffer properties removed.

Author: moetiker

lib/ZnapZend/Config.pm

@@ -257,7 +257,8 @@ my $checkBackupSets = sub {
             }
 
             # mbuffer property set? check if executable is available on remote host
-            if ($backupSet->{$dst . '_mbuffer'} ne 'off') {
+            # (an undef value means no mbuffer was configured at all => treat as 'off')
+            if (($backupSet->{$dst . '_mbuffer'} // 'off') ne 'off') {
                 my ($mbuffer, $mbufferPort) = split /:/, $backupSet->{$dst . '_mbuffer'}, 2;
                 my ($remote, $dataset) = $splitHostDataSet->($backupSet->{$dst});
                 my $file = ($remote ? "$remote:" : '') . $mbuffer;

t/znapzend-lib-config-mbuffer.t

@@ -0,0 +1,47 @@
+#!/usr/bin/env perl
+
+# Test ZnapZend::Config::checkBackupSet() with a backup set that configures
+# no mbuffer at all (neither the legacy 'mbuffer' property nor a per-destination
+# 'dst_X_mbuffer'). Such a set leaves dst_X_mbuffer undefined; checkBackupSet
+# must treat that as "mbuffer off" and not fall into mbuffer validation (which
+# would emit uninitialized-value warnings and die with a bogus
+# "mbuffer size '' invalid").
+
+use strict;
+use warnings;
+
+use FindBin;
+$ENV{PATH} = $FindBin::RealBin . ':' . $ENV{PATH};
+my $buildDir;
+
+BEGIN {
+    $buildDir = shift @ARGV // $FindBin::RealBin . '/../';
+}
+
+use lib "$FindBin::RealBin/../lib";
+use lib "$buildDir/thirdparty/lib/perl5";
+
+use Test::More;
+use Test::Exception;
+use Mojo::Log;
+
+use_ok 'ZnapZend::Config';
+
+my $zLog = Mojo::Log->new(level => 'fatal');
+my $cfg = ZnapZend::Config->new(zLog => $zLog, debug => 0);
+isa_ok($cfg, 'ZnapZend::Config');
+
+my $bs = $cfg->getBackupSet(0, 0, 'tank/source')->[0];
+ok($bs && $bs->{src} eq 'tank/source', 'got backup set for tank/source');
+
+# Simulate a configuration that does not use mbuffer anywhere:
+# drop the legacy 'mbuffer'/'mbuffer_size' and every per-destination
+# mbuffer property, leaving dst_X_mbuffer to default to undef.
+delete $bs->{$_} for grep { /mbuffer/ } keys %$bs;
+
+lives_ok { $cfg->checkBackupSet($bs) }
+    'checkBackupSet tolerates a backup set without any mbuffer configuration';
+
+done_testing;
+
+1;

test.sh

@@ -15,3 +15,5 @@ perl -I./thirdparty/lib/perl5 \
   -MDevel::Cover=+ignore,thirdparty ./t/autoscrub.t
 perl -I./thirdparty/lib/perl5 \
   -MDevel::Cover=+ignore,thirdparty ./t/znapzend-lib-splitter.t
+perl -I./thirdparty/lib/perl5 \
+  -MDevel::Cover=+ignore,thirdparty ./t/znapzend-lib-config-mbuffer.t