Add override processor (#3773)

This plugin can perform the standard metric modifications using override semantics.

plugins/processors/all/all.go

@@ -1,5 +1,6 @@
 package all
 
 import (
+	_ "github.com/influxdata/telegraf/plugins/processors/override"
 	_ "github.com/influxdata/telegraf/plugins/processors/printer"
 )

plugins/processors/override/README.md

@@ -0,0 +1,30 @@
+# Override Processor Plugin
+
+The override processor plugin allows overriding all modifications that are
+supported by input plugins and aggregators:
+
+* name_override
+* name_prefix
+* name_suffix
+* tags
+
+All metrics passing through this processor will be modified accordingly. Values
+of *name_override*, *name_prefix*, *name_suffix* and already present *tags* with
+conflicting keys will be overwritten. Absent *tags* will be created.
+
+Use-case of this plugin encompass ensuring certain tags or naming conventions
+are adhered to irrespective of input plugin configurations, e.g. by
+`taginclude`.
+
+### Configuration:
+
+```toml
+# Add a global tag to all metrics
+[[processors.override]]
+  name_override = "new name_override"
+  name_prefix = "new name_prefix"
+  name_suffix = ":new name_suffix"
+  [processors.tags.add]
+    additional_tag = "tag_value"
+    existing_tag = "new tag_value"
+```

plugins/processors/override/override.go

@@ -0,0 +1,60 @@
+package override
+
+import (
+	"github.com/influxdata/telegraf"
+	"github.com/influxdata/telegraf/plugins/processors"
+)
+
+var sampleConfig = `
+## NOTE This processor will override names, name prefixes, name suffixes and
+## values of tags, that are already present in the metric passed through this
+## filter.
+
+## All modifications on inputs and aggregators can be overridden:
+# name_override = "new name"
+#	name_prefix = "new name_prefix"
+#	name_suffix = "new name_suffix"
+
+## Tags to be added (all values must be strings)
+# [processors.overide.tags]
+#   additional_tag = "tag_value"
+`
+
+type Override struct {
+	NameOverride string
+	NamePrefix   string
+	NameSuffix   string
+	Tags         map[string]string
+}
+
+func (p *Override) SampleConfig() string {
+	return sampleConfig
+}
+
+func (p *Override) Description() string {
+	return "Add all configured tags to all metrics that pass through this filter."
+}
+
+func (p *Override) Apply(in ...telegraf.Metric) []telegraf.Metric {
+	for _, metric := range in {
+		if len(p.NameOverride) > 0 {
+			metric.SetName(p.NameOverride)
+		}
+		if len(p.NamePrefix) > 0 {
+			metric.SetPrefix(p.NamePrefix)
+		}
+		if len(p.NameSuffix) > 0 {
+			metric.SetSuffix(p.NameSuffix)
+		}
+		for key, value := range p.Tags {
+			metric.AddTag(key, value)
+		}
+	}
+	return in
+}
+
+func init() {
+	processors.Add("override", func() telegraf.Processor {
+		return &Override{}
+	})
+}

plugins/processors/override/override_test.go

@@ -0,0 +1,80 @@
+package override
+
+import (
+	"testing"
+	"time"
+
+	"github.com/influxdata/telegraf"
+	"github.com/influxdata/telegraf/metric"
+	"github.com/stretchr/testify/assert"
+)
+
+func createTestMetric() telegraf.Metric {
+	metric, _ := metric.New("m1",
+		map[string]string{"metric_tag": "from_metric"},
+		map[string]interface{}{"value": int64(1)},
+		time.Now(),
+	)
+	return metric
+}
+
+func calculateProcessedTags(processor Override, metric telegraf.Metric) map[string]string {
+	processed := processor.Apply(metric)
+	return processed[0].Tags()
+}
+
+func TestRetainsTags(t *testing.T) {
+	processor := Override{}
+
+	tags := calculateProcessedTags(processor, createTestMetric())
+
+	value, present := tags["metric_tag"]
+	assert.True(t, present, "Tag of metric was not present")
+	assert.Equal(t, "from_metric", value, "Value of Tag was changed")
+}
+
+func TestAddTags(t *testing.T) {
+	processor := Override{Tags: map[string]string{"added_tag": "from_config", "another_tag": ""}}
+
+	tags := calculateProcessedTags(processor, createTestMetric())
+
+	value, present := tags["added_tag"]
+	assert.True(t, present, "Additional Tag of metric was not present")
+	assert.Equal(t, "from_config", value, "Value of Tag was changed")
+	assert.Equal(t, 3, len(tags), "Should have one previous and two added tags.")
+}
+
+func TestOverwritesPresentTagValues(t *testing.T) {
+	processor := Override{Tags: map[string]string{"metric_tag": "from_config"}}
+
+	tags := calculateProcessedTags(processor, createTestMetric())
+
+	value, present := tags["metric_tag"]
+	assert.True(t, present, "Tag of metric was not present")
+	assert.Equal(t, 1, len(tags), "Should only have one tag.")
+	assert.Equal(t, "from_config", value, "Value of Tag was not changed")
+}
+
+func TestOverridesName(t *testing.T) {
+	processor := Override{NameOverride: "overridden"}
+
+	processed := processor.Apply(createTestMetric())
+
+	assert.Equal(t, "overridden", processed[0].Name(), "Name was not overridden")
+}
+
+func TestNamePrefix(t *testing.T) {
+	processor := Override{NamePrefix: "Pre-"}
+
+	processed := processor.Apply(createTestMetric())
+
+	assert.Equal(t, "Pre-m1", processed[0].Name(), "Prefix was not applied")
+}
+
+func TestNameSuffix(t *testing.T) {
+	processor := Override{NameSuffix: "-suff"}
+
+	processed := processor.Apply(createTestMetric())
+
+	assert.Equal(t, "m1-suff", processed[0].Name(), "Suffix was not applied")
+}