feat(processors.defaults): Add support for specifying default tags (#16717)

Co-authored-by: Pieter Slabbert <pieter.slabbert@ilovezoona.com>

plugins/processors/defaults/README.md

@@ -1,14 +1,14 @@
 # Defaults Processor Plugin
 
-The _Defaults_ processor allows you to ensure certain fields will always exist
+The _Defaults_ processor allows you to ensure certain fields and tags will
-with a specified default value on your metric(s).
+always exist with a specified default value on your metric(s).
 
 There are three cases where this processor will insert a configured default
-field.
+field or tag.
 
-1. The field is nil on the incoming metric
+1. The field/tag is nil on the incoming metric
-1. The field is not nil, but its value is an empty string.
+1. The field/tag 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.
+1. The field/tag is not nil, but its value is a string of one or more empty spaces.
 
 Telegraf minimum version: Telegraf 1.15.0
 
@@ -24,11 +24,11 @@ See the [CONFIGURATION.md][CONFIGURATION.md] for more details.
 ## Configuration
 
 ```toml @sample.conf
-## Set default fields on your metric(s) when they are nil or empty
+## Set default fields and tags on your metric(s) when they are nil or empty
 [[processors.defaults]]
-  ## Ensures a set of fields always exists on your metric(s) with their
+  ## Ensures a set of fields or tags 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
+  ## For any given field/tag pair (key = default), if it's not set, a field/tag
   ## is set on the metric with the specified default.
   ##
   ## A field is considered not set if it is nil on the incoming metric;
@@ -39,6 +39,12 @@ See the [CONFIGURATION.md][CONFIGURATION.md] for more details.
     field_1 = "bar"
     time_idle = 0
     is_error = true
+  ## A tag is considered not set if it is nil on the incoming metric;
+  ## or it is not nil but it is empty string or a string of one or
+  ## more spaces.
+  ## <target-tag> = <value>
+  [processors.defaults.tags]
+    tag_1 = "foo"
 ```
 
 ## Example

plugins/processors/defaults/defaults.go

@@ -16,6 +16,7 @@ var sampleConfig string
 // on your Metrics with at least a default value.
 type Defaults struct {
 	DefaultFieldsSets map[string]interface{} `toml:"fields"`
+	DefaultTagsSets   map[string]string      `toml:"tags"`
 }
 
 func (*Defaults) SampleConfig() string {
@@ -37,6 +38,14 @@ func (def *Defaults) Apply(inputMetrics ...telegraf.Metric) []telegraf.Metric {
 				metric.AddField(defField, defValue)
 			}
 		}
+		for defTag, defValue := range def.DefaultTagsSets {
+			if maybeCurrent, isSet := metric.GetTag(defTag); !isSet {
+				metric.AddTag(defTag, defValue)
+			} else if trimmed := strings.TrimSpace(maybeCurrent); trimmed == "" {
+				metric.RemoveTag(defTag)
+				metric.AddTag(defTag, defValue)
+			}
+		}
 	}
 	return inputMetrics
 }

plugins/processors/defaults/defaults_test.go

@@ -133,6 +133,124 @@ func TestDefaults(t *testing.T) {
 	}
 }
 
+func TestTagDefaults(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{
+				DefaultTagsSets: map[string]string{
+					"wind_feel": "very chill",
+				},
+			},
+			input: testutil.MustMetric(
+				"CPU metrics",
+				map[string]string{
+					"wind_feel": "a dragon's breath",
+				},
+				map[string]interface{}{
+					"usage":   45,
+					"is_dead": false,
+				},
+				time.Unix(0, 0),
+			),
+			expected: []telegraf.Metric{
+				testutil.MustMetric(
+					"CPU metrics",
+					map[string]string{
+						"wind_feel": "a dragon's breath",
+					},
+					map[string]interface{}{
+						"usage":   45,
+						"is_dead": false,
+					},
+					time.Unix(0, 0),
+				),
+			},
+		},
+		{
+			name: "Tests that the missing tags are set on the metric",
+			defaults: &Defaults{
+				DefaultTagsSets: map[string]string{
+					"wind_feel": "Unknown",
+				},
+			},
+			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{
+						"wind_feel": "Unknown",
+					},
+					map[string]interface{}{
+						"usage":       45,
+						"temperature": 64,
+					},
+					time.Unix(0, 0),
+				),
+			},
+		},
+		{
+			name: "Tests that set but empty tags are replaced by specified defaults",
+			defaults: &Defaults{
+				DefaultTagsSets: map[string]string{
+					"wind_feel":     "Unknown",
+					"fan_loudness":  "Inaudible",
+					"boost_enabled": "false",
+				},
+			},
+			input: testutil.MustMetric(
+				"CPU metrics",
+				map[string]string{
+					"wind_feel":     " ",
+					"fan_loudness":  "         ",
+					"boost_enabled": "",
+				},
+				map[string]interface{}{
+					"max_clock_gz": 0,
+				},
+				time.Unix(0, 0),
+			),
+			expected: []telegraf.Metric{
+				testutil.MustMetric(
+					"CPU metrics",
+					map[string]string{
+						"wind_feel":     "Unknown",
+						"fan_loudness":  "Inaudible",
+						"boost_enabled": "false",
+					},
+					map[string]interface{}{
+						"max_clock_gz": 0,
+					},
+					time.Unix(0, 0),
+				),
+			},
+		},
+	}
+
+	for _, scenario := range scenarios {
+		t.Run(scenario.name, func(t *testing.T) {
+			defaults := scenario.defaults
+
+			resultMetrics := defaults.Apply(scenario.input)
+			require.Len(t, resultMetrics, 1)
+			testutil.RequireMetricsEqual(t, scenario.expected, resultMetrics)
+		})
+	}
+}
+
 func TestTracking(t *testing.T) {
 	inputRaw := []telegraf.Metric{
 		metric.New("foo", map[string]string{}, map[string]interface{}{"value": 42, "topic": "telegraf"}, time.Unix(0, 0)),

plugins/processors/defaults/sample.conf

@@ -1,8 +1,8 @@
-## Set default fields on your metric(s) when they are nil or empty
+## Set default fields and tags on your metric(s) when they are nil or empty
 [[processors.defaults]]
-  ## Ensures a set of fields always exists on your metric(s) with their
+  ## Ensures a set of fields or tags 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
+  ## For any given field/tag pair (key = default), if it's not set, a field/tag
   ## is set on the metric with the specified default.
   ##
   ## A field is considered not set if it is nil on the incoming metric;
@@ -13,3 +13,9 @@
     field_1 = "bar"
     time_idle = 0
     is_error = true
+  ## A tag is considered not set if it is nil on the incoming metric;
+  ## or it is not nil but it is empty string or a string of one or
+  ## more spaces.
+  ## <target-tag> = <value>
+  [processors.defaults.tags]
+    tag_1 = "foo"