histogram: Expose #12305

Native histograms without a zero threshold aren't federated properly.

This adds a test to prove the specific failure mode, which is that
histograms with a zero threshold of zero are federated as classic
histograms.

The underlying reason is that the protobuf parser identifies a native
histogram by detecting a zero bucket or by detecting integer buckets.
Therefore, a float histogram with a zero threshold of zero and an
unpopulated zero bucket falls through the cracks (no integer buckets,
no zero bucket).

This commit also addse a test case for the latter.

Signed-off-by: beorn7 <beorn@grafana.com>

model/textparse/protobufparse_test.go

@@ -463,6 +463,24 @@ metric: <
   >
 >
 
+`,
+		`name: "test_float_histogram_with_zerothreshold_zero"
+help: "Test float histogram with a zero threshold of zero."
+type: HISTOGRAM
+metric: <
+  histogram: <
+    sample_count_float: 5.0
+    sample_sum: 12.1
+    schema: 3
+    positive_span: <
+      offset: 8
+      length: 2
+    >
+    positive_count: 2.0
+    positive_count: 3.0
+  >
+>
+
 `,
 		`name: "rpc_durations_seconds"
 help: "RPC latency distributions."
@@ -850,6 +868,30 @@ func TestProtobufParse(t *testing.T) {
 						"foo", "baz",
 					),
 				},
+				{
+					m:    "test_float_histogram_with_zerothreshold_zero",
+					help: "Test float histogram with a zero threshold of zero.",
+				},
+				{
+					m:   "test_float_histogram_with_zerothreshold_zero",
+					typ: MetricTypeHistogram,
+				},
+				{
+					m: "test_float_histogram_with_zerothreshold_zero",
+					fhs: &histogram.FloatHistogram{
+						Count:  5.0,
+						Sum:    12.1,
+						Schema: 3,
+						PositiveSpans: []histogram.Span{
+							{Offset: 8, Length: 2},
+						},
+						PositiveBuckets: []float64{2.0, 3.0},
+						NegativeSpans:   []histogram.Span{},
+					},
+					lset: labels.FromStrings(
+						"__name__", "test_float_histogram_with_zerothreshold_zero",
+					),
+				},
 				{
 					m:    "rpc_durations_seconds",
 					help: "RPC latency distributions.",
@@ -1550,14 +1592,38 @@ func TestProtobufParse(t *testing.T) {
 					),
 				},
 				{ // 67
+					m:    "test_float_histogram_with_zerothreshold_zero",
+					help: "Test float histogram with a zero threshold of zero.",
+				},
+				{ // 68
+					m:   "test_float_histogram_with_zerothreshold_zero",
+					typ: MetricTypeHistogram,
+				},
+				{ // 69
+					m: "test_float_histogram_with_zerothreshold_zero",
+					fhs: &histogram.FloatHistogram{
+						Count:  5.0,
+						Sum:    12.1,
+						Schema: 3,
+						PositiveSpans: []histogram.Span{
+							{Offset: 8, Length: 2},
+						},
+						PositiveBuckets: []float64{2.0, 3.0},
+						NegativeSpans:   []histogram.Span{},
+					},
+					lset: labels.FromStrings(
+						"__name__", "test_float_histogram_with_zerothreshold_zero",
+					),
+				},
+				{ // 70
 					m:    "rpc_durations_seconds",
 					help: "RPC latency distributions.",
 				},
-				{ // 68
+				{ // 71
 					m:   "rpc_durations_seconds",
 					typ: MetricTypeSummary,
 				},
-				{ // 69
+				{ // 72
 					m: "rpc_durations_seconds_count\xffservice\xffexponential",
 					v: 262,
 					lset: labels.FromStrings(
@@ -1565,7 +1631,7 @@ func TestProtobufParse(t *testing.T) {
 						"service", "exponential",
 					),
 				},
-				{ // 70
+				{ // 73
 					m: "rpc_durations_seconds_sum\xffservice\xffexponential",
 					v: 0.00025551262820703587,
 					lset: labels.FromStrings(
@@ -1573,7 +1639,7 @@ func TestProtobufParse(t *testing.T) {
 						"service", "exponential",
 					),
 				},
-				{ // 71
+				{ // 74
 					m: "rpc_durations_seconds\xffservice\xffexponential\xffquantile\xff0.5",
 					v: 6.442786329648548e-07,
 					lset: labels.FromStrings(
@@ -1582,7 +1648,7 @@ func TestProtobufParse(t *testing.T) {
 						"service", "exponential",
 					),
 				},
-				{ // 72
+				{ // 75
 					m: "rpc_durations_seconds\xffservice\xffexponential\xffquantile\xff0.9",
 					v: 1.9435742936658396e-06,
 					lset: labels.FromStrings(
@@ -1591,7 +1657,7 @@ func TestProtobufParse(t *testing.T) {
 						"service", "exponential",
 					),
 				},
-				{ // 73
+				{ // 76
 					m: "rpc_durations_seconds\xffservice\xffexponential\xffquantile\xff0.99",
 					v: 4.0471608667037015e-06,
 					lset: labels.FromStrings(
@@ -1600,22 +1666,22 @@ func TestProtobufParse(t *testing.T) {
 						"service", "exponential",
 					),
 				},
-				{ // 74
+				{ // 77
 					m:    "without_quantiles",
 					help: "A summary without quantiles.",
 				},
-				{ // 75
+				{ // 78
 					m:   "without_quantiles",
 					typ: MetricTypeSummary,
 				},
-				{ // 76
+				{ // 79
 					m: "without_quantiles_count",
 					v: 42,
 					lset: labels.FromStrings(
 						"__name__", "without_quantiles_count",
 					),
 				},
-				{ // 77
+				{ // 80
 					m: "without_quantiles_sum",
 					v: 1.234,
 					lset: labels.FromStrings(

web/federate_test.go

@@ -335,18 +335,41 @@ func TestFederationWithNativeHistograms(t *testing.T) {
 		},
 		NegativeBuckets: []int64{1, 1, -1, 0},
 	}
+	histWithoutZeroBucket := &histogram.Histogram{
+		Count:  20,
+		Sum:    99.23,
+		Schema: 1,
+		PositiveSpans: []histogram.Span{
+			{Offset: 0, Length: 2},
+			{Offset: 1, Length: 2},
+		},
+		PositiveBuckets: []int64{2, 2, -2, 0},
+		NegativeSpans: []histogram.Span{
+			{Offset: 0, Length: 2},
+			{Offset: 1, Length: 2},
+		},
+		NegativeBuckets: []int64{2, 2, -2, 0},
+	}
 	app := db.Appender(context.Background())
 	for i := 0; i < 6; i++ {
 		l := labels.FromStrings("__name__", "test_metric", "foo", fmt.Sprintf("%d", i))
 		expL := labels.FromStrings("__name__", "test_metric", "instance", "", "foo", fmt.Sprintf("%d", i))
-		if i%3 == 0 {
+		switch i {
+		case 0, 3:
 			_, err = app.Append(0, l, 100*60*1000, float64(i*100))
 			expVec = append(expVec, promql.Sample{
 				T:      100 * 60 * 1000,
 				F:      float64(i * 100),
 				Metric: expL,
 			})
-		} else {
+		case 4:
+			_, err = app.AppendHistogram(0, l, 100*60*1000, histWithoutZeroBucket.Copy(), nil)
+			expVec = append(expVec, promql.Sample{
+				T:      100 * 60 * 1000,
+				H:      histWithoutZeroBucket.ToFloat(),
+				Metric: expL,
+			})
+		default:
 			hist.ZeroCount++
 			_, err = app.AppendHistogram(0, l, 100*60*1000, hist.Copy(), nil)
 			expVec = append(expVec, promql.Sample{