Add defaults processor to set default field values (#7370)

plugins/processors/all/all.go

@@ -5,6 +5,7 @@ import (
 	_ "github.com/influxdata/telegraf/plugins/processors/converter"
 	_ "github.com/influxdata/telegraf/plugins/processors/date"
 	_ "github.com/influxdata/telegraf/plugins/processors/dedup"
+	_ "github.com/influxdata/telegraf/plugins/processors/defaults"
 	_ "github.com/influxdata/telegraf/plugins/processors/enum"
 	_ "github.com/influxdata/telegraf/plugins/processors/filepath"
 	_ "github.com/influxdata/telegraf/plugins/processors/override"

plugins/processors/defaults/README.md

@@ -0,0 +1,42 @@
+# Defaults Processor
+
+The *Defaults* processor allows you to ensure certain fields will always exist with a specified default value on your metric(s).
+
+There are three cases where this processor will insert a configured default field.
+
+1. The field is nil on the incoming metric
+1. The field is not nil, but its value is an empty string.
+1. The field is not nil, but its value is a string of one or more empty spaces.
+    
+### Configuration
+```toml
+## Set default fields on your metric(s) when they are nil or empty
+[[processors.defaults]]
+
+## This table determines what fields will be inserted in your metric(s)
+  [processors.defaults.fields]
+    field_1 = "bar"
+    time_idle = 0
+    is_error = true
+```
+
+### Example
+Ensure a _status\_code_ field with _N/A_ is inserted in the metric when one it's not set in the metric be default:
+
+```toml
+[[processors.defaults]]
+  [processors.defaults.fields]
+    status_code = "N/A"
+```
+
+```diff
+- lb,http_method=GET cache_status=HIT,latency=230
++ lb,http_method=GET cache_status=HIT,latency=230,status_code="N/A"
+```
+
+Ensure an empty string gets replaced by a default:
+
+```diff
+- lb,http_method=GET cache_status=HIT,latency=230,status_code=""
++ lb,http_method=GET cache_status=HIT,latency=230,status_code="N/A"
+```

plugins/processors/defaults/defaults.go

@@ -0,0 +1,72 @@
+package defaults
+
+import (
+	"github.com/influxdata/telegraf"
+	"github.com/influxdata/telegraf/plugins/processors"
+	"strings"
+)
+
+const sampleConfig = `
+  ## Ensures a set of fields always exists on your metric(s) with their 
+  ## respective default value.
+  ## For any given field pair (key = default), if it's not set, a field 
+  ## is set on the metric with the specified default.
+  ## 
+  ## A field is considered not set if it is nil on the incoming metric;
+  ## or it is not nil but its value is an empty string or is a string 
+  ## of one or more spaces.
+  ##   <target-field> = <value>
+  # [processors.defaults.fields]
+  #   field_1 = "bar"
+  #   time_idle = 0
+  #   is_error = true
+`
+
+// Defaults is a processor for ensuring certain fields always exist
+// on your Metrics with at least a default value.
+type Defaults struct {
+	DefaultFieldsSets map[string]interface{} `toml:"fields"`
+}
+
+// SampleConfig represents a sample toml config for this plugin.
+func (def *Defaults) SampleConfig() string {
+	return sampleConfig
+}
+
+// Description is a brief description of this processor plugin's behaviour.
+func (def *Defaults) Description() string {
+	return "Defaults sets default value(s) for specified fields that are not set on incoming metrics."
+}
+
+// Apply contains the main implementation of this processor.
+// For each metric in 'inputMetrics', it goes over each default pair.
+// If the field in the pair does not exist on the metric, the associated default is added.
+// If the field was found, then, if its value is the empty string or one or more spaces, it is replaced
+// by the associated default.
+func (def *Defaults) Apply(inputMetrics ...telegraf.Metric) []telegraf.Metric {
+	for _, metric := range inputMetrics {
+		for defField, defValue := range def.DefaultFieldsSets {
+			if maybeCurrent, isSet := metric.GetField(defField); !isSet {
+				metric.AddField(defField, defValue)
+			} else if trimmed, isStr := maybeTrimmedString(maybeCurrent); isStr && trimmed == "" {
+				metric.RemoveField(defField)
+				metric.AddField(defField, defValue)
+			}
+		}
+	}
+	return inputMetrics
+}
+
+func maybeTrimmedString(v interface{}) (string, bool) {
+	switch value := v.(type) {
+	case string:
+		return strings.TrimSpace(value), true
+	}
+	return "", false
+}
+
+func init() {
+	processors.Add("defaults", func() telegraf.Processor {
+		return &Defaults{}
+	})
+}

plugins/processors/defaults/defaults_test.go

@@ -0,0 +1,131 @@
+package defaults
+
+import (
+	"testing"
+	"time"
+
+	"github.com/influxdata/telegraf"
+	"github.com/influxdata/telegraf/testutil"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestDefaults(t *testing.T) {
+	scenarios := []struct {
+		name     string
+		defaults *Defaults
+		input    telegraf.Metric
+		expected []telegraf.Metric
+	}{
+		{
+			name: "Test that no values are changed since they are not nil or empty",
+			defaults: &Defaults{
+				DefaultFieldsSets: map[string]interface{}{
+					"usage":     30,
+					"wind_feel": "very chill",
+					"is_dead":   true,
+				},
+			},
+			input: testutil.MustMetric(
+				"CPU metrics",
+				map[string]string{},
+				map[string]interface{}{
+					"usage":     45,
+					"wind_feel": "a dragon's breath",
+					"is_dead":   false,
+				},
+				time.Unix(0, 0),
+			),
+			expected: []telegraf.Metric{
+				testutil.MustMetric(
+					"CPU metrics",
+					map[string]string{},
+					map[string]interface{}{
+						"usage":     45,
+						"wind_feel": "a dragon's breath",
+						"is_dead":   false,
+					},
+					time.Unix(0, 0),
+				),
+			},
+		},
+		{
+			name: "Tests that the missing fields are set on the metric",
+			defaults: &Defaults{
+				DefaultFieldsSets: map[string]interface{}{
+					"max_clock_gz":  6,
+					"wind_feel":     "Unknown",
+					"boost_enabled": false,
+					"variance":      1.2,
+				},
+			},
+			input: testutil.MustMetric(
+				"CPU metrics",
+				map[string]string{},
+				map[string]interface{}{
+					"usage":       45,
+					"temperature": 64,
+				},
+				time.Unix(0, 0),
+			),
+			expected: []telegraf.Metric{
+				testutil.MustMetric(
+					"CPU metrics",
+					map[string]string{},
+					map[string]interface{}{
+						"usage":         45,
+						"temperature":   64,
+						"max_clock_gz":  6,
+						"wind_feel":     "Unknown",
+						"boost_enabled": false,
+						"variance":      1.2,
+					},
+					time.Unix(0, 0),
+				),
+			},
+		},
+		{
+			name: "Tests that set but empty fields are replaced by specified defaults",
+			defaults: &Defaults{
+				DefaultFieldsSets: map[string]interface{}{
+					"max_clock_gz":  6,
+					"wind_feel":     "Unknown",
+					"fan_loudness":  "Inaudible",
+					"boost_enabled": false,
+				},
+			},
+			input: testutil.MustMetric(
+				"CPU metrics",
+				map[string]string{},
+				map[string]interface{}{
+					"max_clock_gz": "",
+					"wind_feel":    " ",
+					"fan_loudness": "         ",
+				},
+				time.Unix(0, 0),
+			),
+			expected: []telegraf.Metric{
+				testutil.MustMetric(
+					"CPU metrics",
+					map[string]string{},
+					map[string]interface{}{
+						"max_clock_gz":  6,
+						"wind_feel":     "Unknown",
+						"fan_loudness":  "Inaudible",
+						"boost_enabled": false,
+					},
+					time.Unix(0, 0),
+				),
+			},
+		},
+	}
+
+	for _, scenario := range scenarios {
+		t.Run(scenario.name, func(t *testing.T) {
+			defaults := scenario.defaults
+
+			resultMetrics := defaults.Apply(scenario.input)
+			assert.Len(t, resultMetrics, 1)
+			testutil.RequireMetricsEqual(t, scenario.expected, resultMetrics)
+		})
+	}
+}