Merge pull request #132 from Tetha/single_value_sum

Handled single-value .sum's gracefully.

master/lib/Munin/Master/GraphOld.pm

@@ -37,9 +37,10 @@ use strict;
 
 use Exporter;
 
-our (@ISA, @EXPORT);
+our (@ISA, @EXPORT, @EXPORT_OK);
 @ISA    = qw(Exporter);
 @EXPORT = qw(graph_startup graph_check_cron graph_main graph_config);
+@EXPORT_OK = qw(build_sum_cdef); # exportable for tests
 
 use IO::Socket;
 use IO::Handle;
@@ -599,6 +600,14 @@ sub get_stack_command {
     return munin_get($field, "stack");
 }
 
+sub build_sum_cdef {
+    if (@_ == 1) {
+        return "";
+    } else {
+        return "," . join(",$AddNAN,", @_[0 .. @_ - 2]) . ",$AddNAN";
+    }
+}
+
 sub expand_specials {
     my $service = shift;
     my $order   = shift;
@@ -723,9 +732,8 @@ sub expand_specials {
                 push(@spc_stack, $name);
                 push(@$preproc,  "$name=$pre");
             }
-            $service->{$last_name}->{"cdef"} .=
-		"," . join(",$AddNAN,", @spc_stack[0 .. @spc_stack - 2]) .
-		",$AddNAN";
+            $service->{$last_name}->{"cdef"} .= build_sum_cdef(@spc_stack);
+
 
             if (my $tc = munin_get($service->{$field}, "cdef", 0))
             {    # Oh bugger...

master/t/munin_master_graphold_sum_cdef.t

@@ -0,0 +1,32 @@
+# -*- cperl -*-
+# vim: ts=4 : sw=4 : et
+use warnings;
+use strict;
+
+use Test::More tests => 3;
+use Test::MockModule;
+
+my $mock = Test::MockModule->new('RRDs', no_auto => 1);
+$mock->mock('errors' => sub { });
+
+use_ok('Munin::Master::GraphOld', qw(build_sum_cdef));
+
+# It should be considered to move the RRDTool compatibility mechanisms into a centralized
+# module.
+my $AddNAN = "+";
+if ($RRDs::VERSION >= 1.3) {
+    $AddNAN = 'ADDNAN';
+}
+is(build_sum_cdef("a", "b", "c"), ",a,$AddNAN,b,$AddNAN", ".sum with >= 2 values");
+is(build_sum_cdef("a"), "", ".sum with = 1 value");
+
+# This test makes sure that both single value sums behave as expected (by
+# just returning that one value) and multiple value sums behave as before. 
+#
+# Rationale:
+#   Our hosts have multiple instances of the same service. Each instance has
+#   it's own status graph and we aggregate these status graphs into a single 
+#   host status graph.
+#   However, it is quite a pain to work around hosts with one instance of 
+#   a single instance, because "total.sum value_of_instance1" tended to output
+#   invalid CDEFs and thus, rrdtool balked.