Compile regex at plugin level for time optimization

Signed-off-by: Lucas Thiesen <lucas.thiesen@zalando.de>

pkg/collector/hostname_collector.go

@@ -18,6 +18,7 @@ const (
 type HostnameCollectorPlugin struct {
 	metricName string
 	promPlugin CollectorPlugin
+	pattern    *regexp.Regexp
 }
 
 type HostnameCollector struct {
@@ -33,9 +34,15 @@ func NewHostnameCollectorPlugin(
 		return nil, fmt.Errorf("Failed to initialize hostname collector plugin, metric name was not defined")
 	}
 
+	p, err := regexp.Compile("^[a-zA-Z0-9.-]+$")
+	if err != nil {
+		return nil, fmt.Errorf("Failed to create regular expression to match hostname format")
+	}
+
 	return &HostnameCollectorPlugin{
 		metricName: metricName,
 		promPlugin: promPlugin,
+		pattern:    p,
 	}, nil
 }
 
@@ -56,13 +63,13 @@ func (p *HostnameCollectorPlugin) NewCollector(
 	if _, ok := config.Config["hostnames"]; !ok {
 		return nil, fmt.Errorf("Hostname is not specified, unable to create collector")
 	}
-	regex, err := regexp.Compile("^[a-zA-Z0-9.-]+$")
+
-	if err != nil {
-		return nil, fmt.Errorf("Failed to create regular expression to match hostname format")
-	}
 	hostnames := strings.Split(config.Config["hostnames"], ",")
+	if p.pattern == nil {
+		return nil, fmt.Errorf("Plugin did not specify hostname regex pattern, unable to create collector")
+	}
 	for _, h := range hostnames {
-		if ok := regex.MatchString(h); !ok {
+		if ok := p.pattern.MatchString(h); !ok {
 			return nil, fmt.Errorf(
 				"Invalid hostname format, unable to create collector: %s",
 				h,

pkg/collector/hostname_collector_test.go

@@ -2,6 +2,7 @@ package collector
 
 import (
 	"fmt"
+	"regexp"
 	"testing"
 	"time"
 
@@ -42,9 +43,13 @@ func TestHostnameCollectorPluginConstructor(tt *testing.T) {
 func TestHostnamePluginNewCollector(tt *testing.T) {
 	fakePlugin := &FakeCollectorPlugin{}
 
+	pattern, err := regexp.Compile("^[a-zA-Z0-9.-]+$")
+	require.Nil(tt, err, "Something is up, regex compiling failed.")
+
 	plugin := &HostnameCollectorPlugin{
 		metricName: "a_valid_one",
 		promPlugin: fakePlugin,
+		pattern:    pattern,
 	}
 	interval := time.Duration(42)
 
@@ -169,9 +174,12 @@ func TestHostnameCollectorGetMetrics(tt *testing.T) {
 func TestHostnameCollectorInterval(t *testing.T) {
 	interval := time.Duration(42)
 	fakePlugin := &FakeCollectorPlugin{}
+	pattern, err := regexp.Compile("^[a-zA-Z0-9.-]+$")
+	require.Nil(t, err, "Something is up, regex compiling failed.")
 	plugin := &HostnameCollectorPlugin{
 		metricName: "a_valid_one",
 		promPlugin: fakePlugin,
+		pattern:    pattern,
 	}
 	c, err := plugin.NewCollector(
 		&autoscalingv2.HorizontalPodAutoscaler{},
@@ -179,8 +187,8 @@ func TestHostnameCollectorInterval(t *testing.T) {
 		interval,
 	)
 
-	require.NotNil(t, c)
 	require.Nil(t, err)
+	require.NotNil(t, c)
 	require.Equal(t, interval, c.Interval())
 }