[statsdreceiver] support simple tags (open-telemetry#29012)

dogstatsd supports two types of tags on metrics: simple and dimensional
tags[^1]. the former is just a key, the latter is a key and a value.

with the assumption that many users of the statsdreceiver are enabling
ingest of dogstatsd metrics, this makes the statsd parser more
optimistic, so it can handle tags w/o a value. this functionality is
gated behind a new `enable_simple_tags` flag.

when this happens, we set an attribute that has a zero value. so far as
i know, this is allowed in the opentelemetry spec. the decision of how
to handle attributes w/ zero values is best left to configuration w/in
the pipeline itself, as different users may have different opinions or
approaches that work best with their systems.

[^1]:
https://www.datadoghq.com/blog/the-power-of-tagged-metrics/#whats-a-metric-tag

**Testing:**

added coverage to unit tests to enable parsing simple tags.

---------

Co-authored-by: Alex Boten <aboten@lightstep.com>

.chloggen/statsd-support-simple-tags.yaml

@@ -0,0 +1,28 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: "enhancement"
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: "statsdreceiver"
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Add support for 'simple' tags that do not have a defined value, to accommodate DogStatsD metrics that may utilize these.
+
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [29012]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext: "This functionality is gated behind a new `enable_simple_tags` config boolean, as it is not part of the StatsD spec."
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: ['user']

receiver/statsdreceiver/README.md

@@ -33,6 +33,8 @@ The Following settings are optional:
 
 - `enable_metric_type: true`(default value is false): Enable the statsd receiver to be able to emit the metric type(gauge, counter, timer(in the future), histogram(in the future)) as a label.
 
+- `enable_simple_tags: true`(default value is false): Enable parsing tags that do not have a value, e.g. `#mykey` instead of `#mykey:myvalue`. DogStatsD supports such tagging.
+
 - `is_monotonic_counter` (default value is false): Set all counter-type metrics the statsd receiver received as monotonic.
 
 - `timer_histogram_mapping:`(default value is below): Specify what OTLP type to convert received timing/histogram data to.

receiver/statsdreceiver/config.go

@@ -19,6 +19,7 @@ type Config struct {
 	NetAddr               confignet.NetAddr                `mapstructure:",squash"`
 	AggregationInterval   time.Duration                    `mapstructure:"aggregation_interval"`
 	EnableMetricType      bool                             `mapstructure:"enable_metric_type"`
+	EnableSimpleTags      bool                             `mapstructure:"enable_simple_tags"`
 	IsMonotonicCounter    bool                             `mapstructure:"is_monotonic_counter"`
 	TimerHistogramMapping []protocol.TimerHistogramMapping `mapstructure:"timer_histogram_mapping"`
 }

receiver/statsdreceiver/internal/protocol/parser.go

@@ -12,7 +12,7 @@ import (
 
 // Parser is something that can map input StatsD strings to OTLP Metric representations.
 type Parser interface {
-	Initialize(enableMetricType bool, isMonotonicCounter bool, sendTimerHistogram []TimerHistogramMapping) error
+	Initialize(enableMetricType bool, enableSimpleTags bool, isMonotonicCounter bool, sendTimerHistogram []TimerHistogramMapping) error
 	GetMetrics() []BatchMetrics
 	Aggregate(line string, addr net.Addr) error
 }

receiver/statsdreceiver/internal/protocol/statsd_parser.go

@@ -79,6 +79,7 @@ var defaultObserverCategory = ObserverCategory{
 type StatsDParser struct {
 	instrumentsByAddress map[netAddr]*instruments
 	enableMetricType     bool
+	enableSimpleTags     bool
 	isMonotonicCounter   bool
 	timerEvents          ObserverCategory
 	histogramEvents      ObserverCategory
@@ -156,12 +157,13 @@ func (p *StatsDParser) resetState(when time.Time) {
 	p.instrumentsByAddress = make(map[netAddr]*instruments)
 }
 
-func (p *StatsDParser) Initialize(enableMetricType bool, isMonotonicCounter bool, sendTimerHistogram []TimerHistogramMapping) error {
+func (p *StatsDParser) Initialize(enableMetricType bool, enableSimpleTags bool, isMonotonicCounter bool, sendTimerHistogram []TimerHistogramMapping) error {
 	p.resetState(timeNowFunc())
 
 	p.histogramEvents = defaultObserverCategory
 	p.timerEvents = defaultObserverCategory
 	p.enableMetricType = enableMetricType
+	p.enableSimpleTags = enableSimpleTags
 	p.isMonotonicCounter = isMonotonicCounter
 	// Note: validation occurs in ("../".Config).validate()
 	for _, eachMap := range sendTimerHistogram {
@@ -270,7 +272,7 @@ func (p *StatsDParser) observerCategoryFor(t MetricType) ObserverCategory {
 
 // Aggregate for each metric line.
 func (p *StatsDParser) Aggregate(line string, addr net.Addr) error {
-	parsedMetric, err := parseMessageToMetric(line, p.enableMetricType)
+	parsedMetric, err := parseMessageToMetric(line, p.enableMetricType, p.enableSimpleTags)
 	if err != nil {
 		return err
 	}
@@ -349,7 +351,7 @@ func (p *StatsDParser) Aggregate(line string, addr net.Addr) error {
 	return nil
 }
 
-func parseMessageToMetric(line string, enableMetricType bool) (statsDMetric, error) {
+func parseMessageToMetric(line string, enableMetricType bool, enableSimpleTags bool) (statsDMetric, error) {
 	result := statsDMetric{}
 
 	parts := strings.Split(line, "|")
@@ -410,11 +412,22 @@ func parseMessageToMetric(line string, enableMetricType bool) (statsDMetric, err
 
 			for _, tagSet := range tagSets {
 				tagParts := strings.SplitN(tagSet, ":", 2)
-				if len(tagParts) != 2 {
-					return result, fmt.Errorf("invalid tag format: %s", tagParts)
-				}
 				k := tagParts[0]
-				v := tagParts[1]
+				if k == "" {
+					return result, fmt.Errorf("invalid tag format: %q", tagSet)
+				}
+
+				// support both simple tags (w/o value) and dimension tags (w/ value).
+				// dogstatsd notably allows simple tags.
+				var v string
+				if len(tagParts) == 2 {
+					v = tagParts[1]
+				}
+
+				if v == "" && !enableSimpleTags {
+					return result, fmt.Errorf("invalid tag format: %q", tagSet)
+				}
+
 				kvs = append(kvs, attribute.String(k, v))
 			}
 		default:

receiver/statsdreceiver/internal/protocol/statsd_parser_test.go

@@ -53,8 +53,8 @@ func Test_ParseMessageToMetric(t *testing.T) {
 		},
 		{
 			name:  "invalid tag format",
-			input: "test.metric:42|c|#key1",
-			err:   errors.New("invalid tag format: [key1]"),
+			input: "test.metric:42|c|#:val1",
+			err:   errors.New("invalid tag format: \":val1\""),
 		},
 		{
 			name:  "unrecognized message part",
@@ -235,7 +235,7 @@ func Test_ParseMessageToMetric(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			got, err := parseMessageToMetric(tt.input, false)
+			got, err := parseMessageToMetric(tt.input, false, false)
 
 			if tt.err != nil {
 				assert.Equal(t, tt.err, err)
@@ -433,7 +433,66 @@ func Test_ParseMessageToMetricWithMetricType(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			got, err := parseMessageToMetric(tt.input, true)
+			got, err := parseMessageToMetric(tt.input, true, false)
+
+			if tt.err != nil {
+				assert.Equal(t, tt.err, err)
+			} else {
+				assert.NoError(t, err)
+				assert.Equal(t, tt.wantMetric, got)
+			}
+		})
+	}
+}
+
+func Test_ParseMessageToMetricWithSimpleTags(t *testing.T) {
+	tests := []struct {
+		name       string
+		input      string
+		wantMetric statsDMetric
+		err        error
+	}{
+		{
+			name:  "counter metric with sample rate and (dimensional) tag",
+			input: "test.metric:42|c|@0.1|#key:value",
+			wantMetric: testStatsDMetric(
+				"test.metric",
+				42,
+				false,
+				"c",
+				0.1,
+				[]string{"key"},
+				[]string{"value"}),
+		},
+		{
+			name:  "counter metric with sample rate and (simple) tag",
+			input: "test.metric:42|c|@0.1|#key",
+			wantMetric: testStatsDMetric(
+				"test.metric",
+				42,
+				false,
+				"c",
+				0.1,
+				[]string{"key"},
+				[]string{""}),
+		},
+		{
+			name:  "counter metric with sample rate and two (simple) tags",
+			input: "test.metric:42|c|@0.1|#key,key2",
+			wantMetric: testStatsDMetric(
+				"test.metric",
+				42,
+				false,
+				"c",
+				0.1,
+				[]string{"key", "key2"},
+				[]string{"", ""}),
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := parseMessageToMetric(tt.input, false, true)
 
 			if tt.err != nil {
 				assert.Equal(t, tt.err, err)
@@ -677,7 +736,7 @@ func TestStatsDParser_Aggregate(t *testing.T) {
 		t.Run(tt.name, func(t *testing.T) {
 			var err error
 			p := &StatsDParser{}
-			assert.NoError(t, p.Initialize(false, false, []TimerHistogramMapping{{StatsdType: "timer", ObserverType: "gauge"}, {StatsdType: "histogram", ObserverType: "gauge"}}))
+			assert.NoError(t, p.Initialize(false, false, false, []TimerHistogramMapping{{StatsdType: "timer", ObserverType: "gauge"}, {StatsdType: "histogram", ObserverType: "gauge"}}))
 			p.lastIntervalTime = time.Unix(611, 0)
 			addr, _ := net.ResolveUDPAddr("udp", "1.2.3.4:5678")
 			addrKey := newNetAddr(addr)
@@ -746,7 +805,7 @@ func TestStatsDParser_AggregateByAddress(t *testing.T) {
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			p := &StatsDParser{}
-			assert.NoError(t, p.Initialize(true, false, []TimerHistogramMapping{{StatsdType: "timer", ObserverType: "gauge"}, {StatsdType: "histogram", ObserverType: "gauge"}}))
+			assert.NoError(t, p.Initialize(true, false, false, []TimerHistogramMapping{{StatsdType: "timer", ObserverType: "gauge"}, {StatsdType: "histogram", ObserverType: "gauge"}}))
 			p.lastIntervalTime = time.Unix(611, 0)
 			for i, addr := range tt.addresses {
 				for _, line := range tt.input[i] {
@@ -814,7 +873,7 @@ func TestStatsDParser_AggregateWithMetricType(t *testing.T) {
 		t.Run(tt.name, func(t *testing.T) {
 			var err error
 			p := &StatsDParser{}
-			assert.NoError(t, p.Initialize(true, false, []TimerHistogramMapping{{StatsdType: "timer", ObserverType: "gauge"}, {StatsdType: "histogram", ObserverType: "gauge"}}))
+			assert.NoError(t, p.Initialize(true, false, false, []TimerHistogramMapping{{StatsdType: "timer", ObserverType: "gauge"}, {StatsdType: "histogram", ObserverType: "gauge"}}))
 			p.lastIntervalTime = time.Unix(611, 0)
 			addr, _ := net.ResolveUDPAddr("udp", "1.2.3.4:5678")
 			addrKey := newNetAddr(addr)
@@ -864,7 +923,7 @@ func TestStatsDParser_AggregateWithIsMonotonicCounter(t *testing.T) {
 		t.Run(tt.name, func(t *testing.T) {
 			var err error
 			p := &StatsDParser{}
-			assert.NoError(t, p.Initialize(false, true, []TimerHistogramMapping{{StatsdType: "timer", ObserverType: "gauge"}, {StatsdType: "histogram", ObserverType: "gauge"}}))
+			assert.NoError(t, p.Initialize(false, false, true, []TimerHistogramMapping{{StatsdType: "timer", ObserverType: "gauge"}, {StatsdType: "histogram", ObserverType: "gauge"}}))
 			p.lastIntervalTime = time.Unix(611, 0)
 			addr, _ := net.ResolveUDPAddr("udp", "1.2.3.4:5678")
 			addrKey := newNetAddr(addr)
@@ -986,7 +1045,7 @@ func TestStatsDParser_AggregateTimerWithSummary(t *testing.T) {
 		t.Run(tt.name, func(t *testing.T) {
 			var err error
 			p := &StatsDParser{}
-			assert.NoError(t, p.Initialize(false, false, []TimerHistogramMapping{{StatsdType: "timer", ObserverType: "summary"}, {StatsdType: "histogram", ObserverType: "summary"}}))
+			assert.NoError(t, p.Initialize(false, false, false, []TimerHistogramMapping{{StatsdType: "timer", ObserverType: "summary"}, {StatsdType: "histogram", ObserverType: "summary"}}))
 			addr, _ := net.ResolveUDPAddr("udp", "1.2.3.4:5678")
 			addrKey := newNetAddr(addr)
 			for _, line := range tt.input {
@@ -1003,7 +1062,7 @@ func TestStatsDParser_AggregateTimerWithSummary(t *testing.T) {
 
 func TestStatsDParser_Initialize(t *testing.T) {
 	p := &StatsDParser{}
-	assert.NoError(t, p.Initialize(true, false, []TimerHistogramMapping{{StatsdType: "timer", ObserverType: "gauge"}, {StatsdType: "histogram", ObserverType: "gauge"}}))
+	assert.NoError(t, p.Initialize(true, false, false, []TimerHistogramMapping{{StatsdType: "timer", ObserverType: "gauge"}, {StatsdType: "histogram", ObserverType: "gauge"}}))
 	teststatsdDMetricdescription := statsDMetricDescription{
 		name:       "test",
 		metricType: "g",
@@ -1022,7 +1081,7 @@ func TestStatsDParser_Initialize(t *testing.T) {
 
 func TestStatsDParser_GetMetricsWithMetricType(t *testing.T) {
 	p := &StatsDParser{}
-	assert.NoError(t, p.Initialize(true, false, []TimerHistogramMapping{{StatsdType: "timer", ObserverType: "gauge"}, {StatsdType: "histogram", ObserverType: "gauge"}}))
+	assert.NoError(t, p.Initialize(true, false, false, []TimerHistogramMapping{{StatsdType: "timer", ObserverType: "gauge"}, {StatsdType: "histogram", ObserverType: "gauge"}}))
 	instrument := newInstruments(nil)
 	instrument.gauges[testDescription("statsdTestMetric1", "g",
 		[]string{"mykey", "metric_type"}, []string{"myvalue", "gauge"})] = buildGaugeMetric(testStatsDMetric("testGauge1", 1, false, "g", 0, []string{"mykey", "metric_type"}, []string{"myvalue", "gauge"}), time.Unix(711, 0))
@@ -1095,7 +1154,7 @@ func TestStatsDParser_Mappings(t *testing.T) {
 		t.Run(tc.name, func(t *testing.T) {
 			p := &StatsDParser{}
 
-			assert.NoError(t, p.Initialize(false, false, tc.mapping))
+			assert.NoError(t, p.Initialize(false, false, false, tc.mapping))
 
 			addr, _ := net.ResolveUDPAddr("udp", "1.2.3.4:5678")
 			assert.NoError(t, p.Aggregate("H:10|h", addr))
@@ -1129,7 +1188,7 @@ func TestStatsDParser_ScopeIsIncluded(t *testing.T) {
 	}
 	testAddress, _ := net.ResolveUDPAddr("udp", "1.2.3.4:5678")
 
-	err := p.Initialize(true, false,
+	err := p.Initialize(true, false, false,
 		[]TimerHistogramMapping{
 			{StatsdType: "timer", ObserverType: "summary"},
 			{StatsdType: "histogram", ObserverType: "histogram"},
@@ -1399,7 +1458,7 @@ func TestStatsDParser_AggregateTimerWithHistogram(t *testing.T) {
 		t.Run(tt.name, func(t *testing.T) {
 			var err error
 			p := &StatsDParser{}
-			assert.NoError(t, p.Initialize(false, false, tt.mapping))
+			assert.NoError(t, p.Initialize(false, false, false, tt.mapping))
 			addr, _ := net.ResolveUDPAddr("udp", "1.2.3.4:5678")
 			for _, line := range tt.input {
 				err = p.Aggregate(line, addr)

receiver/statsdreceiver/receiver.go

@@ -91,6 +91,7 @@ func (r *statsdReceiver) Start(ctx context.Context, host component.Host) error {
 	ticker := time.NewTicker(r.config.AggregationInterval)
 	err = r.parser.Initialize(
 		r.config.EnableMetricType,
+		r.config.EnableSimpleTags,
 		r.config.IsMonotonicCounter,
 		r.config.TimerHistogramMapping,
 	)