[metricbeat] fix system/service filtering issues (#17415) (#17487)

* fix fitlering issues

* add changelog entry

* update tests

(cherry picked from commit d1a9176)

CHANGELOG.next.asciidoc

@@ -184,6 +184,7 @@ https://github.com/elastic/beats/compare/v7.0.0-alpha2...master[Check the HEAD d
 - Fix missing Accept header for Prometheus and OpenMetrics module. {issue}16870[16870] {pull}17291[17291]
 - Further revise check for bad data in docker/memory. {pull}17400[17400]
 - Combine cloudwatch aggregated metrics into single event. {pull}17345[17345]
+- Fix how we filter services by name in system/service {pull}17400[17400]
 - Fix cloudwatch metricset missing tags collection. {issue}17419[17419] {pull}17424[17424]
 - check if cpuOptions field is nil in DescribeInstances output in ec2 metricset. {pull}17418[17418]
 

metricbeat/module/system/service/service.go

@@ -20,6 +20,8 @@
 package service
 
 import (
+	"path/filepath"
+
 	"github.com/coreos/go-systemd/v22/dbus"
 	"github.com/mitchellh/mapstructure"
 	"github.com/pkg/errors"
@@ -86,7 +88,7 @@ func New(base mb.BaseMetricSet) (mb.MetricSet, error) {
 // of an error set the Error field of mb.Event or simply call report.Error().
 func (m *MetricSet) Fetch(report mb.ReporterV2) error {
 
-	units, err := m.unitList(m.conn, m.cfg.StateFilter, append([]string{"*.service"}, m.cfg.PatternFilter...))
+	units, err := m.unitList(m.conn, m.cfg.StateFilter, m.cfg.PatternFilter)
 	if err != nil {
 		return errors.Wrap(err, "error getting list of running units")
 	}
@@ -97,6 +99,16 @@ func (m *MetricSet) Fetch(report mb.ReporterV2) error {
 			continue
 		}
 
+		match, err := filepath.Match("*.service", unit.Name)
+		if err != nil {
+			m.Logger().Errorf("Error matching unit service %s: %s", unit.Name, err)
+			continue
+		}
+		// If we don't have a *.service, skip
+		if !match {
+			continue
+		}
+
 		props, err := getProps(m.conn, unit.Name)
 		if err != nil {
 			m.Logger().Errorf("error getting properties for service: %s", err)

metricbeat/module/system/service/service_test.go

@@ -29,6 +29,18 @@ import (
 	"github.com/elastic/beats/v7/libbeat/common"
 )
 
+var exampleUnits = []dbus.UnitStatus{
+	dbus.UnitStatus{
+		Name: "sshd.service",
+	},
+	dbus.UnitStatus{
+		Name: "metricbeat.service",
+	},
+	dbus.UnitStatus{
+		Name: "filebeat.service",
+	},
+}
+
 func TestFormProps(t *testing.T) {
 	testUnit := dbus.UnitStatus{
 		Name:        "test.service",
@@ -72,3 +84,23 @@ func TestFormProps(t *testing.T) {
 	assert.Equal(t, event.MetricSetFields["state_since"], testEvent["state_since"])
 	assert.NotEmpty(t, event.RootFields)
 }
+
+func TestFilterEmpty(t *testing.T) {
+
+	filtersBad := []string{
+		"asdf",
+	}
+	shouldNotMatch, err := matchUnitPatterns(filtersBad, exampleUnits)
+	assert.NoError(t, err)
+	assert.Empty(t, shouldNotMatch)
+}
+
+func TestFilterMatches(t *testing.T) {
+	filtersMatch := []string{
+		"ssh*",
+	}
+
+	shouldMatch, err := matchUnitPatterns(filtersMatch, exampleUnits)
+	assert.NoError(t, err)
+	assert.Len(t, shouldMatch, 1)
+}