test(rw2): add nhcb testcases to remote write 2.0

Ref: https://github.com/prometheus/prometheus/issues/15021

Also modified spansToSpansProto to not allocate empty bucket spans array
when converting internal model to remote write model.
Otherwise the test TestDecodeWriteV2Request fails since empty array
is marshaled/unmarshaled as nil so we don't get back the exact same
thing.

Signed-off-by: György Krajcsovits <gyorgy.krajcsovits@grafana.com>

prompb/io/prometheus/write/v2/codec.go

@@ -196,6 +196,9 @@ func FromFloatHistogram(timestamp int64, fh *histogram.FloatHistogram) Histogram
 }
 
 func spansToSpansProto(s []histogram.Span) []BucketSpan {
+	if len(s) == 0 {
+		return nil
+	}
 	spans := make([]BucketSpan, len(s))
 	for i := 0; i < len(s); i++ {
 		spans[i] = BucketSpan{Offset: s[i].Offset, Length: s[i].Length}

storage/remote/codec_test.go

@@ -43,12 +43,12 @@ var (
 		Schema:          2,
 		ZeroThreshold:   1e-128,
 		ZeroCount:       0,
-		Count:           0,
+		Count:           3,
 		Sum:             20,
 		PositiveSpans:   []histogram.Span{{Offset: 0, Length: 1}},
 		PositiveBuckets: []int64{1},
 		NegativeSpans:   []histogram.Span{{Offset: 0, Length: 1}},
-		NegativeBuckets: []int64{-1},
+		NegativeBuckets: []int64{2},
 	}
 
 	writeRequestFixture = &prompb.WriteRequest{
@@ -90,6 +90,15 @@ var (
 		Help: "Test counter for test purposes",
 	}
 
+	testHistogramCustomBuckets = histogram.Histogram{
+		Schema:          histogram.CustomBucketsSchema,
+		Count:           16,
+		Sum:             20,
+		PositiveSpans:   []histogram.Span{{Offset: 1, Length: 2}},
+		PositiveBuckets: []int64{10, -4},     // Means 10 observations for upper bound 1.0 and 6 for upper bound +Inf.
+		CustomValues:    []float64{0.1, 1.0}, // +Inf is implied.
+	}
+
 	// writeV2RequestFixture represents the same request as writeRequestFixture,
 	// but using the v2 representation, plus includes writeV2RequestSeries1Metadata and writeV2RequestSeries2Metadata.
 	// NOTE: Use TestWriteV2RequestFixture and copy the diff to regenerate if needed.
@@ -106,7 +115,12 @@ var (
 				},
 				Samples:   []writev2.Sample{{Value: 1, Timestamp: 10}},
 				Exemplars: []writev2.Exemplar{{LabelsRefs: []uint32{11, 12}, Value: 1, Timestamp: 10}},
-				Histograms:       []writev2.Histogram{writev2.FromIntHistogram(10, &testHistogram), writev2.FromFloatHistogram(20, testHistogram.ToFloat(nil))},
+				Histograms: []writev2.Histogram{
+					writev2.FromIntHistogram(10, &testHistogram),
+					writev2.FromFloatHistogram(20, testHistogram.ToFloat(nil)),
+					writev2.FromIntHistogram(30, &testHistogramCustomBuckets),
+					writev2.FromFloatHistogram(40, testHistogramCustomBuckets.ToFloat(nil)),
+				},
 				CreatedTimestamp: 1, // CT needs to be lower than the sample's timestamp.
 			},
 			{
@@ -119,12 +133,38 @@ var (
 				},
 				Samples:   []writev2.Sample{{Value: 2, Timestamp: 20}},
 				Exemplars: []writev2.Exemplar{{LabelsRefs: []uint32{13, 14}, Value: 2, Timestamp: 20}},
-				Histograms: []writev2.Histogram{writev2.FromIntHistogram(30, &testHistogram), writev2.FromFloatHistogram(40, testHistogram.ToFloat(nil))},
+				Histograms: []writev2.Histogram{
+					writev2.FromIntHistogram(50, &testHistogram),
+					writev2.FromFloatHistogram(60, testHistogram.ToFloat(nil)),
+					writev2.FromIntHistogram(70, &testHistogramCustomBuckets),
+					writev2.FromFloatHistogram(80, testHistogramCustomBuckets.ToFloat(nil)),
+				},
 			},
 		},
 	}
 )
 
+func TestHistogramFixtureValid(t *testing.T) {
+	for _, ts := range writeRequestFixture.Timeseries {
+		for _, h := range ts.Histograms {
+			if h.IsFloatHistogram() {
+				require.NoError(t, h.ToFloatHistogram().Validate())
+			} else {
+				require.NoError(t, h.ToIntHistogram().Validate())
+			}
+		}
+	}
+	for _, ts := range writeV2RequestFixture.Timeseries {
+		for _, h := range ts.Histograms {
+			if h.IsFloatHistogram() {
+				require.NoError(t, h.ToFloatHistogram().Validate())
+			} else {
+				require.NoError(t, h.ToIntHistogram().Validate())
+			}
+		}
+	}
+}
+
 func TestWriteV2RequestFixture(t *testing.T) {
 	// Generate dynamically writeV2RequestFixture, reusing v1 fixture elements.
 	st := writev2.NewSymbolTable()
@@ -143,7 +183,12 @@ func TestWriteV2RequestFixture(t *testing.T) {
 				},
 				Samples:   []writev2.Sample{{Value: 1, Timestamp: 10}},
 				Exemplars: []writev2.Exemplar{{LabelsRefs: exemplar1LabelRefs, Value: 1, Timestamp: 10}},
-				Histograms:       []writev2.Histogram{writev2.FromIntHistogram(10, &testHistogram), writev2.FromFloatHistogram(20, testHistogram.ToFloat(nil))},
+				Histograms: []writev2.Histogram{
+					writev2.FromIntHistogram(10, &testHistogram),
+					writev2.FromFloatHistogram(20, testHistogram.ToFloat(nil)),
+					writev2.FromIntHistogram(30, &testHistogramCustomBuckets),
+					writev2.FromFloatHistogram(40, testHistogramCustomBuckets.ToFloat(nil)),
+				},
 				CreatedTimestamp: 1,
 			},
 			{
@@ -155,7 +200,12 @@ func TestWriteV2RequestFixture(t *testing.T) {
 				},
 				Samples:   []writev2.Sample{{Value: 2, Timestamp: 20}},
 				Exemplars: []writev2.Exemplar{{LabelsRefs: exemplar2LabelRefs, Value: 2, Timestamp: 20}},
-				Histograms: []writev2.Histogram{writev2.FromIntHistogram(30, &testHistogram), writev2.FromFloatHistogram(40, testHistogram.ToFloat(nil))},
+				Histograms: []writev2.Histogram{
+					writev2.FromIntHistogram(50, &testHistogram),
+					writev2.FromFloatHistogram(60, testHistogram.ToFloat(nil)),
+					writev2.FromIntHistogram(70, &testHistogramCustomBuckets),
+					writev2.FromFloatHistogram(80, testHistogramCustomBuckets.ToFloat(nil)),
+				},
 			},
 		},
 		Symbols: st.Symbols(),

storage/remote/write_handler_test.go

@@ -391,7 +391,7 @@ func TestRemoteWriteHandler_V2Message(t *testing.T) {
 			desc: "Partial write; first series with one dup histogram sample",
 			input: func() []writev2.TimeSeries {
 				f := proto.Clone(writeV2RequestFixture).(*writev2.Request)
-				f.Timeseries[0].Histograms = append(f.Timeseries[0].Histograms, f.Timeseries[0].Histograms[1])
+				f.Timeseries[0].Histograms = append(f.Timeseries[0].Histograms, f.Timeseries[0].Histograms[len(f.Timeseries[0].Histograms)-1])
 				return f.Timeseries
 			}(),
 			expectedCode:     http.StatusBadRequest,
@@ -483,7 +483,7 @@ func TestRemoteWriteHandler_V2Message(t *testing.T) {
 			// Double check mandatory 2.0 stats.
 			// writeV2RequestFixture has 2 series with 1 sample, 2 histograms, 1 exemplar each.
 			expectHeaderValue(t, 2, resp.Header.Get(rw20WrittenSamplesHeader))
-			expectHeaderValue(t, 4, resp.Header.Get(rw20WrittenHistogramsHeader))
+			expectHeaderValue(t, 8, resp.Header.Get(rw20WrittenHistogramsHeader))
 			if tc.appendExemplarErr != nil {
 				expectHeaderValue(t, 0, resp.Header.Get(rw20WrittenExemplarsHeader))
 			} else {
@@ -496,6 +496,8 @@ func TestRemoteWriteHandler_V2Message(t *testing.T) {
 				i, j, k, m int
 			)
 			for _, ts := range writeV2RequestFixture.Timeseries {
+				zeroHistogramIngested := false
+				zeroFloatHistogramIngested := false
 				ls := ts.ToLabels(&b, writeV2RequestFixture.Symbols)
 
 				for _, s := range ts.Samples {
@@ -509,21 +511,27 @@ func TestRemoteWriteHandler_V2Message(t *testing.T) {
 				for _, hp := range ts.Histograms {
 					if hp.IsFloatHistogram() {
 						fh := hp.ToFloatHistogram()
-						if ts.CreatedTimestamp != 0 && tc.ingestCTZeroSample {
+						if !zeroFloatHistogramIngested && ts.CreatedTimestamp != 0 && tc.ingestCTZeroSample {
 							requireEqual(t, mockHistogram{ls, ts.CreatedTimestamp, nil, &histogram.FloatHistogram{}}, appendable.histograms[k])
 							k++
+							zeroFloatHistogramIngested = true
 						}
 						requireEqual(t, mockHistogram{ls, hp.Timestamp, nil, fh}, appendable.histograms[k])
 					} else {
 						h := hp.ToIntHistogram()
-						if ts.CreatedTimestamp != 0 && tc.ingestCTZeroSample {
+						if !zeroHistogramIngested && ts.CreatedTimestamp != 0 && tc.ingestCTZeroSample {
 							requireEqual(t, mockHistogram{ls, ts.CreatedTimestamp, &histogram.Histogram{}, nil}, appendable.histograms[k])
 							k++
+							zeroHistogramIngested = true
 						}
 						requireEqual(t, mockHistogram{ls, hp.Timestamp, h, nil}, appendable.histograms[k])
 					}
 					k++
 				}
+				if ts.CreatedTimestamp != 0 && tc.ingestCTZeroSample {
+					require.True(t, zeroHistogramIngested)
+					require.True(t, zeroFloatHistogramIngested)
+				}
 				if tc.appendExemplarErr == nil {
 					for _, e := range ts.Exemplars {
 						exemplarLabels := e.ToExemplar(&b, writeV2RequestFixture.Symbols).Labels