From a66f0b54751e95a83c5c2d50cee375b5411d36fb Mon Sep 17 00:00:00 2001
From: Calle Pettersson <cpettsson@gmail.com>
Date: Sat, 4 Mar 2017 12:44:47 +0100
Subject: [PATCH] Add [defaults] placeholder support to collectors.enabled

---
 exporter.go      | 27 ++++++++++++++++++++++----
 exporter_test.go | 49 ++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 72 insertions(+), 4 deletions(-)
 create mode 100644 exporter_test.go

diff --git a/exporter.go b/exporter.go
index e5837752..190b0274 100644
--- a/exporter.go
+++ b/exporter.go
@@ -25,8 +25,9 @@ type WmiCollector struct {
 }
 
 const (
-	defaultCollectors = "cpu,cs,logical_disk,net,os,service,system"
-	serviceName       = "wmi_exporter"
+	defaultCollectors            = "cpu,cs,logical_disk,net,os,service,system"
+	defaultCollectorsPlaceholder = "[defaults]"
+	serviceName                  = "wmi_exporter"
 )
 
 var (
@@ -90,9 +91,27 @@ func execute(name string, c collector.Collector, ch chan<- prometheus.Metric) {
 	scrapeDurations.WithLabelValues(name, result).Observe(duration.Seconds())
 }
 
+func expandEnabledCollectors(enabled string) []string {
+	expanded := strings.Replace(enabled, defaultCollectorsPlaceholder, defaultCollectors, -1)
+	separated := strings.Split(expanded, ",")
+	unique := map[string]bool{}
+	for _, s := range separated {
+		if s != "" {
+			unique[s] = true
+		}
+	}
+	result := make([]string, 0, len(unique))
+	for s, _ := range unique {
+		result = append(result, s)
+	}
+	return result
+}
+
 func loadCollectors(list string) (map[string]collector.Collector, error) {
 	collectors := map[string]collector.Collector{}
-	for _, name := range strings.Split(list, ",") {
+	enabled := expandEnabledCollectors(list)
+
+	for _, name := range enabled {
 		fn, ok := collector.Factories[name]
 		if !ok {
 			return nil, fmt.Errorf("collector '%s' not available", name)
@@ -115,7 +134,7 @@ func main() {
 		showVersion       = flag.Bool("version", false, "Print version information.")
 		listenAddress     = flag.String("telemetry.addr", ":9182", "host:port for WMI exporter.")
 		metricsPath       = flag.String("telemetry.path", "/metrics", "URL path for surfacing collected metrics.")
-		enabledCollectors = flag.String("collectors.enabled", filterAvailableCollectors(defaultCollectors), "Comma-separated list of collectors to use.")
+		enabledCollectors = flag.String("collectors.enabled", filterAvailableCollectors(defaultCollectors), "Comma-separated list of collectors to use. Use '[default]' as a placeholder for all the collectors enabled by default")
 		printCollectors   = flag.Bool("collectors.print", false, "If true, print available collectors and exit.")
 	)
 	flag.Parse()
diff --git a/exporter_test.go b/exporter_test.go
new file mode 100644
index 00000000..475e09a1
--- /dev/null
+++ b/exporter_test.go
@@ -0,0 +1,49 @@
+package main
+
+import (
+	"sort"
+	"strings"
+	"testing"
+)
+
+type expansionTestCase struct {
+	input          string
+	expectedOutput []string
+}
+
+func TestExpandEnabled(t *testing.T) {
+	expansionTests := []expansionTestCase{
+		{"", []string{}},
+		// Default case
+		{"cs,os", []string{"cs", "os"}},
+		// Placeholder expansion
+		{defaultCollectorsPlaceholder, strings.Split(defaultCollectors, ",")},
+		// De-duplication
+		{"cs,cs", []string{"cs"}},
+		// De-duplicate placeholder
+		{defaultCollectorsPlaceholder + "," + defaultCollectorsPlaceholder, strings.Split(defaultCollectors, ",")},
+		// Composite case
+		{"foo," + defaultCollectorsPlaceholder + ",bar", append(strings.Split(defaultCollectors, ","), "foo", "bar")},
+	}
+
+	for _, testCase := range expansionTests {
+		output := expandEnabledCollectors(testCase.input)
+		sort.Strings(output)
+
+		success := true
+		if len(output) != len(testCase.expectedOutput) {
+			success = false
+		} else {
+			sort.Strings(testCase.expectedOutput)
+			for idx := range output {
+				if output[idx] != testCase.expectedOutput[idx] {
+					success = false
+					break
+				}
+			}
+		}
+		if !success {
+			t.Error("For", testCase.input, "expected", testCase.expectedOutput, "got", output)
+		}
+	}
+}