prometheus/storage/remote/write_handler_test.go

// Copyright 2021 The Prometheus Authors
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package remote

import (
	"bytes"
	"context"
	"errors"
	"fmt"
	"io"
	"math"
	"net/http"
	"net/http/httptest"
	"strconv"
	"strings"
	"testing"
	"time"

	"github.com/gogo/protobuf/proto"
	"github.com/google/go-cmp/cmp"
	"github.com/prometheus/common/promslog"
	"github.com/stretchr/testify/require"

	"github.com/prometheus/prometheus/config"
	"github.com/prometheus/prometheus/model/exemplar"
	"github.com/prometheus/prometheus/model/histogram"
	"github.com/prometheus/prometheus/model/labels"
	"github.com/prometheus/prometheus/model/metadata"
	"github.com/prometheus/prometheus/prompb"
	writev2 "github.com/prometheus/prometheus/prompb/io/prometheus/write/v2"
	"github.com/prometheus/prometheus/storage"
	"github.com/prometheus/prometheus/tsdb"
	"github.com/prometheus/prometheus/util/compression"
	"github.com/prometheus/prometheus/util/testutil"
)

func TestRemoteWriteHandlerHeadersHandling_V1Message(t *testing.T) {
	payload, _, _, err := buildWriteRequest(nil, writeRequestFixture.Timeseries, nil, nil, nil, nil, "snappy")
	require.NoError(t, err)

	for _, tc := range []struct {
		name         string
		reqHeaders   map[string]string
		expectedCode int
	}{
		// Generally Prometheus 1.0 Receiver never checked for existence of the headers, so
		// we keep things permissive.
		{
			name: "correct PRW 1.0 headers",
			reqHeaders: map[string]string{
				"Content-Type":           remoteWriteContentTypeHeaders[config.RemoteWriteProtoMsgV1],
				"Content-Encoding":       compression.Snappy,
				RemoteWriteVersionHeader: RemoteWriteVersion20HeaderValue,
			},
			expectedCode: http.StatusNoContent,
		},
		{
			name: "missing remote write version",
			reqHeaders: map[string]string{
				"Content-Type":     remoteWriteContentTypeHeaders[config.RemoteWriteProtoMsgV1],
				"Content-Encoding": compression.Snappy,
			},
			expectedCode: http.StatusNoContent,
		},
		{
			name:         "no headers",
			reqHeaders:   map[string]string{},
			expectedCode: http.StatusNoContent,
		},
		{
			name: "missing content-type",
			reqHeaders: map[string]string{
				"Content-Encoding":       compression.Snappy,
				RemoteWriteVersionHeader: RemoteWriteVersion20HeaderValue,
			},
			expectedCode: http.StatusNoContent,
		},
		{
			name: "missing content-encoding",
			reqHeaders: map[string]string{
				"Content-Type":           remoteWriteContentTypeHeaders[config.RemoteWriteProtoMsgV1],
				RemoteWriteVersionHeader: RemoteWriteVersion20HeaderValue,
			},
			expectedCode: http.StatusNoContent,
		},
		{
			name: "wrong content-type",
			reqHeaders: map[string]string{
				"Content-Type":           "yolo",
				"Content-Encoding":       compression.Snappy,
				RemoteWriteVersionHeader: RemoteWriteVersion20HeaderValue,
			},
			expectedCode: http.StatusUnsupportedMediaType,
		},
		{
			name: "wrong content-type2",
			reqHeaders: map[string]string{
				"Content-Type":           appProtoContentType + ";proto=yolo",
				"Content-Encoding":       compression.Snappy,
				RemoteWriteVersionHeader: RemoteWriteVersion20HeaderValue,
			},
			expectedCode: http.StatusUnsupportedMediaType,
		},
		{
			name: "not supported content-encoding",
			reqHeaders: map[string]string{
				"Content-Type":           remoteWriteContentTypeHeaders[config.RemoteWriteProtoMsgV1],
				"Content-Encoding":       "zstd",
				RemoteWriteVersionHeader: RemoteWriteVersion20HeaderValue,
			},
			expectedCode: http.StatusUnsupportedMediaType,
		},
	} {
		t.Run(tc.name, func(t *testing.T) {
			req, err := http.NewRequest("", "", bytes.NewReader(payload))
			require.NoError(t, err)
			for k, v := range tc.reqHeaders {
				req.Header.Set(k, v)
			}

			appendable := &mockAppendable{}
			handler := NewWriteHandler(promslog.NewNopLogger(), nil, appendable, []config.RemoteWriteProtoMsg{config.RemoteWriteProtoMsgV1}, false)

			recorder := httptest.NewRecorder()
			handler.ServeHTTP(recorder, req)

			resp := recorder.Result()
			out, err := io.ReadAll(resp.Body)
			require.NoError(t, err)
			_ = resp.Body.Close()
			require.Equal(t, tc.expectedCode, resp.StatusCode, string(out))
		})
	}
}

func TestRemoteWriteHandlerHeadersHandling_V2Message(t *testing.T) {
	payload, _, _, err := buildV2WriteRequest(promslog.NewNopLogger(), writeV2RequestFixture.Timeseries, writeV2RequestFixture.Symbols, nil, nil, nil, "snappy")
	require.NoError(t, err)

	for _, tc := range []struct {
		name          string
		reqHeaders    map[string]string
		expectedCode  int
		expectedError string
	}{
		{
			name: "correct PRW 2.0 headers",
			reqHeaders: map[string]string{
				"Content-Type":           remoteWriteContentTypeHeaders[config.RemoteWriteProtoMsgV2],
				"Content-Encoding":       compression.Snappy,
				RemoteWriteVersionHeader: RemoteWriteVersion20HeaderValue,
			},
			expectedCode: http.StatusNoContent,
		},
		{
			name: "missing remote write version",
			reqHeaders: map[string]string{
				"Content-Type":     remoteWriteContentTypeHeaders[config.RemoteWriteProtoMsgV2],
				"Content-Encoding": compression.Snappy,
			},
			expectedCode: http.StatusNoContent, // We don't check for now.
		},
		{
			name:          "no headers",
			reqHeaders:    map[string]string{},
			expectedCode:  http.StatusUnsupportedMediaType,
			expectedError: "prometheus.WriteRequest protobuf message is not accepted by this server; accepted [io.prometheus.write.v2.Request]",
		},
		{
			name: "missing content-type",
			reqHeaders: map[string]string{
				"Content-Encoding":       compression.Snappy,
				RemoteWriteVersionHeader: RemoteWriteVersion20HeaderValue,
			},
			// This only gives 415, because we explicitly only support 2.0. If we supported both
			// (default) it would be empty message parsed and ok response.
			// This is perhaps better, than 415 for previously working 1.0 flow with
			// no content-type.
			expectedCode:  http.StatusUnsupportedMediaType,
			expectedError: "prometheus.WriteRequest protobuf message is not accepted by this server; accepted [io.prometheus.write.v2.Request]",
		},
		{
			name: "missing content-encoding",
			reqHeaders: map[string]string{
				"Content-Type":           remoteWriteContentTypeHeaders[config.RemoteWriteProtoMsgV2],
				RemoteWriteVersionHeader: RemoteWriteVersion20HeaderValue,
			},
			expectedCode: http.StatusNoContent, // Similar to 1.0 impl, we default to Snappy, so it works.
		},
		{
			name: "wrong content-type",
			reqHeaders: map[string]string{
				"Content-Type":           "yolo",
				"Content-Encoding":       compression.Snappy,
				RemoteWriteVersionHeader: RemoteWriteVersion20HeaderValue,
			},
			expectedCode:  http.StatusUnsupportedMediaType,
			expectedError: "expected application/x-protobuf as the first (media) part, got yolo content-type",
		},
		{
			name: "wrong content-type2",
			reqHeaders: map[string]string{
				"Content-Type":           appProtoContentType + ";proto=yolo",
				"Content-Encoding":       compression.Snappy,
				RemoteWriteVersionHeader: RemoteWriteVersion20HeaderValue,
			},
			expectedCode:  http.StatusUnsupportedMediaType,
			expectedError: "got application/x-protobuf;proto=yolo content type; unknown remote write protobuf message yolo, supported: prometheus.WriteRequest, io.prometheus.write.v2.Request",
		},
		{
			name: "not supported content-encoding",
			reqHeaders: map[string]string{
				"Content-Type":           remoteWriteContentTypeHeaders[config.RemoteWriteProtoMsgV2],
				"Content-Encoding":       "zstd",
				RemoteWriteVersionHeader: RemoteWriteVersion20HeaderValue,
			},
			expectedCode:  http.StatusUnsupportedMediaType,
			expectedError: "zstd encoding (compression) is not accepted by this server; only snappy is acceptable",
		},
	} {
		t.Run(tc.name, func(t *testing.T) {
			req, err := http.NewRequest("", "", bytes.NewReader(payload))
			require.NoError(t, err)
			for k, v := range tc.reqHeaders {
				req.Header.Set(k, v)
			}

			appendable := &mockAppendable{}
			handler := NewWriteHandler(promslog.NewNopLogger(), nil, appendable, []config.RemoteWriteProtoMsg{config.RemoteWriteProtoMsgV2}, false)

			recorder := httptest.NewRecorder()
			handler.ServeHTTP(recorder, req)

			resp := recorder.Result()
			out, err := io.ReadAll(resp.Body)
			require.NoError(t, err)
			_ = resp.Body.Close()
			require.Equal(t, tc.expectedCode, resp.StatusCode, string(out))
			if tc.expectedCode/100 == 2 {
				return
			}

			// Invalid request case - no samples should be written.
			require.Equal(t, tc.expectedError, strings.TrimSpace(string(out)))
			require.Empty(t, appendable.samples)
			require.Empty(t, appendable.histograms)
			require.Empty(t, appendable.exemplars)
		})
	}

	t.Run("unsupported v1 request", func(t *testing.T) {
		payload, _, _, err := buildWriteRequest(promslog.NewNopLogger(), writeRequestFixture.Timeseries, nil, nil, nil, nil, "snappy")
		require.NoError(t, err)
		req, err := http.NewRequest("", "", bytes.NewReader(payload))
		require.NoError(t, err)
		for k, v := range map[string]string{
			"Content-Type":     remoteWriteContentTypeHeaders[config.RemoteWriteProtoMsgV1],
			"Content-Encoding": compression.Snappy,
		} {
			req.Header.Set(k, v)
		}

		appendable := &mockAppendable{}
		handler := NewWriteHandler(promslog.NewNopLogger(), nil, appendable, []config.RemoteWriteProtoMsg{config.RemoteWriteProtoMsgV2}, false)

		recorder := httptest.NewRecorder()
		handler.ServeHTTP(recorder, req)

		resp := recorder.Result()
		out, err := io.ReadAll(resp.Body)
		require.NoError(t, err)
		_ = resp.Body.Close()
		require.Equal(t, http.StatusUnsupportedMediaType, resp.StatusCode, string(out))

		require.Equal(t, "prometheus.WriteRequest protobuf message is not accepted by this server; accepted [io.prometheus.write.v2.Request]", strings.TrimSpace(string(out)))
		require.Empty(t, appendable.samples)
		require.Empty(t, appendable.histograms)
		require.Empty(t, appendable.exemplars)
	})
}

func TestRemoteWriteHandler_V1Message(t *testing.T) {
	payload, _, _, err := buildWriteRequest(nil, writeRequestFixture.Timeseries, nil, nil, nil, nil, "snappy")
	require.NoError(t, err)

	req, err := http.NewRequest("", "", bytes.NewReader(payload))
	require.NoError(t, err)

	// NOTE: Strictly speaking, even for 1.0 we require headers, but we never verified those
	// in Prometheus, so keeping like this to not break existing 1.0 clients.

	appendable := &mockAppendable{}
	handler := NewWriteHandler(promslog.NewNopLogger(), nil, appendable, []config.RemoteWriteProtoMsg{config.RemoteWriteProtoMsgV1}, false)

	recorder := httptest.NewRecorder()
	handler.ServeHTTP(recorder, req)

	resp := recorder.Result()
	require.Equal(t, http.StatusNoContent, resp.StatusCode)

	b := labels.NewScratchBuilder(0)
	i := 0
	j := 0
	k := 0
	for _, ts := range writeRequestFixture.Timeseries {
		labels := ts.ToLabels(&b, nil)
		for _, s := range ts.Samples {
			requireEqual(t, mockSample{labels, s.Timestamp, s.Value}, appendable.samples[i])
			i++
		}
		for _, e := range ts.Exemplars {
			exemplarLabels := e.ToExemplar(&b, nil).Labels
			requireEqual(t, mockExemplar{labels, exemplarLabels, e.Timestamp, e.Value}, appendable.exemplars[j])
			j++
		}
		for _, hp := range ts.Histograms {
			if hp.IsFloatHistogram() {
				fh := hp.ToFloatHistogram()
				requireEqual(t, mockHistogram{labels, hp.Timestamp, nil, fh}, appendable.histograms[k])
			} else {
				h := hp.ToIntHistogram()
				requireEqual(t, mockHistogram{labels, hp.Timestamp, h, nil}, appendable.histograms[k])
			}

			k++
		}
	}
}

func expectHeaderValue(t testing.TB, expected int, got string) {
	t.Helper()

	require.NotEmpty(t, got)
	i, err := strconv.Atoi(got)
	require.NoError(t, err)
	require.Equal(t, expected, i)
}

func TestRemoteWriteHandler_V2Message(t *testing.T) {
	// V2 supports partial writes for non-retriable errors, so test them.
	for _, tc := range []struct {
		desc             string
		input            []writev2.TimeSeries
		expectedCode     int
		expectedRespBody string

		commitErr             error
		appendSampleErr       error
		appendCTZeroSampleErr error
		appendHistogramErr    error
		appendExemplarErr     error
		updateMetadataErr     error

		ingestCTZeroSample bool
	}{
		{
			desc:               "All timeseries accepted/ct_enabled",
			input:              writeV2RequestFixture.Timeseries,
			expectedCode:       http.StatusNoContent,
			ingestCTZeroSample: true,
		},
		{
			desc:         "All timeseries accepted/ct_disabled",
			input:        writeV2RequestFixture.Timeseries,
			expectedCode: http.StatusNoContent,
		},
		{
			desc: "Partial write; first series with invalid labels (no metric name)",
			input: append(
				// Series with test_metric1="test_metric1" labels.
				[]writev2.TimeSeries{{LabelsRefs: []uint32{2, 2}, Samples: []writev2.Sample{{Value: 1, Timestamp: 1}}}},
				writeV2RequestFixture.Timeseries...),
			expectedCode:     http.StatusBadRequest,
			expectedRespBody: "invalid metric name or labels, got {test_metric1=\"test_metric1\"}\n",
		},
		{
			desc: "Partial write; first series with invalid labels (empty metric name)",
			input: append(
				// Series with __name__="" labels.
				[]writev2.TimeSeries{{LabelsRefs: []uint32{1, 0}, Samples: []writev2.Sample{{Value: 1, Timestamp: 1}}}},
				writeV2RequestFixture.Timeseries...),
			expectedCode:     http.StatusBadRequest,
			expectedRespBody: "invalid metric name or labels, got {__name__=\"\"}\n",
		},
		{
			desc: "Partial write; first series with duplicate labels",
			input: append(
				// Series with __name__="test_metric1",test_metric1="test_metric1",test_metric1="test_metric1" labels.
				[]writev2.TimeSeries{{LabelsRefs: []uint32{1, 2, 2, 2, 2, 2}, Samples: []writev2.Sample{{Value: 1, Timestamp: 1}}}},
				writeV2RequestFixture.Timeseries...),
			expectedCode:     http.StatusBadRequest,
			expectedRespBody: "invalid labels for series, labels {__name__=\"test_metric1\", test_metric1=\"test_metric1\", test_metric1=\"test_metric1\"}, duplicated label test_metric1\n",
		},
		{
			desc: "Partial write; first series with odd number of label refs",
			input: append(
				[]writev2.TimeSeries{{LabelsRefs: []uint32{1, 2, 3}, Samples: []writev2.Sample{{Value: 1, Timestamp: 1}}}},
				writeV2RequestFixture.Timeseries...),
			expectedCode:     http.StatusBadRequest,
			expectedRespBody: "parsing labels for series [1 2 3]: invalid labelRefs length 3\n",
		},
		{
			desc: "Partial write; first series with out-of-bounds symbol references",
			input: append(
				[]writev2.TimeSeries{{LabelsRefs: []uint32{1, 999}, Samples: []writev2.Sample{{Value: 1, Timestamp: 1}}}},
				writeV2RequestFixture.Timeseries...),
			expectedCode:     http.StatusBadRequest,
			expectedRespBody: "parsing labels for series [1 999]: labelRefs 1 (name) = 999 (value) outside of symbols table (size 18)\n",
		},
		{
			desc: "Partial write; TimeSeries with only exemplars (no samples or histograms)",
			input: append(
				// Series with only exemplars, no samples or histograms.
				[]writev2.TimeSeries{{
					LabelsRefs: []uint32{1, 2},
					Exemplars: []writev2.Exemplar{{
						LabelsRefs: []uint32{},
						Value:      1.0,
						Timestamp:  1,
					}},
				}},
				writeV2RequestFixture.Timeseries...),
			expectedCode:     http.StatusBadRequest,
			expectedRespBody: "TimeSeries must contain at least one sample or histogram for series {__name__=\"test_metric1\"}\n",
		},
		{
			desc: "Partial write; first series with one OOO sample",
			input: func() []writev2.TimeSeries {
				f := proto.Clone(writeV2RequestFixture).(*writev2.Request)
				f.Timeseries[0].Samples = append(f.Timeseries[0].Samples, writev2.Sample{Value: 2, Timestamp: 0})
				return f.Timeseries
			}(),
			expectedCode:     http.StatusBadRequest,
			expectedRespBody: "out of order sample for series {__name__=\"test_metric1\", b=\"c\", baz=\"qux\", d=\"e\", foo=\"bar\"}\n",
		},
		{
			desc: "Partial write; first series with one dup sample",
			input: func() []writev2.TimeSeries {
				f := proto.Clone(writeV2RequestFixture).(*writev2.Request)
				f.Timeseries[0].Samples = append(f.Timeseries[0].Samples, f.Timeseries[0].Samples[0])
				return f.Timeseries
			}(),
			expectedCode:     http.StatusBadRequest,
			expectedRespBody: "duplicate sample for timestamp for series {__name__=\"test_metric1\", b=\"c\", baz=\"qux\", d=\"e\", foo=\"bar\"}\n",
		},
		{
			desc: "Partial write; first series with one OOO histogram sample",
			input: func() []writev2.TimeSeries {
				f := proto.Clone(writeV2RequestFixture).(*writev2.Request)
				f.Timeseries[0].Histograms = append(f.Timeseries[0].Histograms, writev2.FromFloatHistogram(1, testHistogram.ToFloat(nil)))
				return f.Timeseries
			}(),
			expectedCode:     http.StatusBadRequest,
			expectedRespBody: "out of order sample for series {__name__=\"test_metric1\", b=\"c\", baz=\"qux\", d=\"e\", foo=\"bar\"}\n",
		},
		{
			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[len(f.Timeseries[0].Histograms)-1])
				return f.Timeseries
			}(),
			expectedCode:     http.StatusBadRequest,
			expectedRespBody: "duplicate sample for timestamp for series {__name__=\"test_metric1\", b=\"c\", baz=\"qux\", d=\"e\", foo=\"bar\"}\n",
		},
		// Non retriable errors from various parts.
		{
			desc:            "Internal sample append error; rollback triggered",
			input:           writeV2RequestFixture.Timeseries,
			appendSampleErr: errors.New("some sample internal append error"),

			expectedCode:     http.StatusInternalServerError,
			expectedRespBody: "some sample internal append error\n",
		},
		{
			desc:               "Internal histogram sample append error; rollback triggered",
			input:              writeV2RequestFixture.Timeseries,
			appendHistogramErr: errors.New("some histogram sample internal append error"),

			expectedCode:     http.StatusInternalServerError,
			expectedRespBody: "some histogram sample internal append error\n",
		},
		{
			desc:              "Partial write; skipped exemplar; exemplar storage errs are noop",
			input:             writeV2RequestFixture.Timeseries,
			appendExemplarErr: errors.New("some exemplar internal append error"),

			expectedCode: http.StatusNoContent,
		},
		{
			desc:              "Partial write; skipped metadata; metadata storage errs are noop",
			input:             writeV2RequestFixture.Timeseries,
			updateMetadataErr: errors.New("some metadata update error"),

			expectedCode: http.StatusNoContent,
		},
		{
			desc:      "Internal commit error; rollback triggered",
			input:     writeV2RequestFixture.Timeseries,
			commitErr: errors.New("storage error"),

			expectedCode:     http.StatusInternalServerError,
			expectedRespBody: "storage error\n",
		},
	} {
		t.Run(tc.desc, func(t *testing.T) {
			payload, _, _, err := buildV2WriteRequest(promslog.NewNopLogger(), tc.input, writeV2RequestFixture.Symbols, nil, nil, nil, "snappy")
			require.NoError(t, err)

			req, err := http.NewRequest("", "", bytes.NewReader(payload))
			require.NoError(t, err)

			req.Header.Set("Content-Type", remoteWriteContentTypeHeaders[config.RemoteWriteProtoMsgV2])
			req.Header.Set("Content-Encoding", compression.Snappy)
			req.Header.Set(RemoteWriteVersionHeader, RemoteWriteVersion20HeaderValue)

			appendable := &mockAppendable{
				commitErr:             tc.commitErr,
				appendSampleErr:       tc.appendSampleErr,
				appendCTZeroSampleErr: tc.appendCTZeroSampleErr,
				appendHistogramErr:    tc.appendHistogramErr,
				appendExemplarErr:     tc.appendExemplarErr,
				updateMetadataErr:     tc.updateMetadataErr,
			}
			handler := NewWriteHandler(promslog.NewNopLogger(), nil, appendable, []config.RemoteWriteProtoMsg{config.RemoteWriteProtoMsgV2}, tc.ingestCTZeroSample)

			recorder := httptest.NewRecorder()
			handler.ServeHTTP(recorder, req)

			resp := recorder.Result()
			require.Equal(t, tc.expectedCode, resp.StatusCode)
			respBody, err := io.ReadAll(resp.Body)
			require.NoError(t, err)
			require.Equal(t, tc.expectedRespBody, string(respBody))

			if tc.expectedCode == http.StatusInternalServerError {
				// We don't expect writes for partial writes with retry-able code.
				expectHeaderValue(t, 0, resp.Header.Get(rw20WrittenSamplesHeader))
				expectHeaderValue(t, 0, resp.Header.Get(rw20WrittenHistogramsHeader))
				expectHeaderValue(t, 0, resp.Header.Get(rw20WrittenExemplarsHeader))

				require.Empty(t, appendable.samples)
				require.Empty(t, appendable.histograms)
				require.Empty(t, appendable.exemplars)
				require.Empty(t, appendable.metadata)
				return
			}

			// 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, 8, resp.Header.Get(rw20WrittenHistogramsHeader))
			if tc.appendExemplarErr != nil {
				expectHeaderValue(t, 0, resp.Header.Get(rw20WrittenExemplarsHeader))
			} else {
				expectHeaderValue(t, 2, resp.Header.Get(rw20WrittenExemplarsHeader))
			}

			// Double check what was actually appended.
			var (
				b          = labels.NewScratchBuilder(0)
				i, j, k, m int
			)
			for _, ts := range writeV2RequestFixture.Timeseries {
				zeroHistogramIngested := false
				zeroFloatHistogramIngested := false
				ls, err := ts.ToLabels(&b, writeV2RequestFixture.Symbols)
				require.NoError(t, err)

				for _, s := range ts.Samples {
					if ts.CreatedTimestamp != 0 && tc.ingestCTZeroSample {
						requireEqual(t, mockSample{ls, ts.CreatedTimestamp, 0}, appendable.samples[i])
						i++
					}
					requireEqual(t, mockSample{ls, s.Timestamp, s.Value}, appendable.samples[i])
					i++
				}
				for _, hp := range ts.Histograms {
					if hp.IsFloatHistogram() {
						fh := hp.ToFloatHistogram()
						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 !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 {
						ex, err := e.ToExemplar(&b, writeV2RequestFixture.Symbols)
						require.NoError(t, err)
						exemplarLabels := ex.Labels
						requireEqual(t, mockExemplar{ls, exemplarLabels, e.Timestamp, e.Value}, appendable.exemplars[j])
						j++
					}
				}
				if tc.updateMetadataErr == nil {
					expectedMeta := ts.ToMetadata(writeV2RequestFixture.Symbols)
					requireEqual(t, mockMetadata{ls, expectedMeta}, appendable.metadata[m])
					m++
				}
			}
		})
	}
}

// NOTE: V2 Message is tested in TestRemoteWriteHandler_V2Message.
func TestOutOfOrderSample_V1Message(t *testing.T) {
	for _, tc := range []struct {
		Name      string
		Timestamp int64
	}{
		{
			Name:      "historic",
			Timestamp: 0,
		},
		{
			Name:      "future",
			Timestamp: math.MaxInt64,
		},
	} {
		t.Run(tc.Name, func(t *testing.T) {
			payload, _, _, err := buildWriteRequest(nil, []prompb.TimeSeries{{
				Labels:  []prompb.Label{{Name: "__name__", Value: "test_metric"}},
				Samples: []prompb.Sample{{Value: 1, Timestamp: tc.Timestamp}},
			}}, nil, nil, nil, nil, "snappy")
			require.NoError(t, err)

			req, err := http.NewRequest("", "", bytes.NewReader(payload))
			require.NoError(t, err)

			appendable := &mockAppendable{latestSample: map[uint64]int64{labels.FromStrings("__name__", "test_metric").Hash(): 100}}
			handler := NewWriteHandler(promslog.NewNopLogger(), nil, appendable, []config.RemoteWriteProtoMsg{config.RemoteWriteProtoMsgV1}, false)

			recorder := httptest.NewRecorder()
			handler.ServeHTTP(recorder, req)

			resp := recorder.Result()
			require.Equal(t, http.StatusBadRequest, resp.StatusCode)
		})
	}
}

// This test case currently aims to verify that the WriteHandler endpoint
// don't fail on exemplar ingestion errors since the exemplar storage is
// still experimental.
// NOTE: V2 Message is tested in TestRemoteWriteHandler_V2Message.
func TestOutOfOrderExemplar_V1Message(t *testing.T) {
	tests := []struct {
		Name      string
		Timestamp int64
	}{
		{
			Name:      "historic",
			Timestamp: 0,
		},
		{
			Name:      "future",
			Timestamp: math.MaxInt64,
		},
	}

	for _, tc := range tests {
		t.Run(tc.Name, func(t *testing.T) {
			payload, _, _, err := buildWriteRequest(nil, []prompb.TimeSeries{{
				Labels:    []prompb.Label{{Name: "__name__", Value: "test_metric"}},
				Exemplars: []prompb.Exemplar{{Labels: []prompb.Label{{Name: "foo", Value: "bar"}}, Value: 1, Timestamp: tc.Timestamp}},
			}}, nil, nil, nil, nil, "snappy")
			require.NoError(t, err)

			req, err := http.NewRequest("", "", bytes.NewReader(payload))
			require.NoError(t, err)

			appendable := &mockAppendable{latestSample: map[uint64]int64{labels.FromStrings("__name__", "test_metric").Hash(): 100}}
			handler := NewWriteHandler(promslog.NewNopLogger(), nil, appendable, []config.RemoteWriteProtoMsg{config.RemoteWriteProtoMsgV1}, false)

			recorder := httptest.NewRecorder()
			handler.ServeHTTP(recorder, req)

			resp := recorder.Result()
			// TODO: update to require.Equal(t, http.StatusConflict, resp.StatusCode) once exemplar storage is not experimental.
			require.Equal(t, http.StatusNoContent, resp.StatusCode)
		})
	}
}

// NOTE: V2 Message is tested in TestRemoteWriteHandler_V2Message.
func TestOutOfOrderHistogram_V1Message(t *testing.T) {
	for _, tc := range []struct {
		Name      string
		Timestamp int64
	}{
		{
			Name:      "historic",
			Timestamp: 0,
		},
		{
			Name:      "future",
			Timestamp: math.MaxInt64,
		},
	} {
		t.Run(tc.Name, func(t *testing.T) {
			payload, _, _, err := buildWriteRequest(nil, []prompb.TimeSeries{{
				Labels:     []prompb.Label{{Name: "__name__", Value: "test_metric"}},
				Histograms: []prompb.Histogram{prompb.FromIntHistogram(tc.Timestamp, &testHistogram), prompb.FromFloatHistogram(1, testHistogram.ToFloat(nil))},
			}}, nil, nil, nil, nil, "snappy")
			require.NoError(t, err)

			req, err := http.NewRequest("", "", bytes.NewReader(payload))
			require.NoError(t, err)

			appendable := &mockAppendable{latestSample: map[uint64]int64{labels.FromStrings("__name__", "test_metric").Hash(): 100}}
			handler := NewWriteHandler(promslog.NewNopLogger(), nil, appendable, []config.RemoteWriteProtoMsg{config.RemoteWriteProtoMsgV1}, false)

			recorder := httptest.NewRecorder()
			handler.ServeHTTP(recorder, req)

			resp := recorder.Result()
			require.Equal(t, http.StatusBadRequest, resp.StatusCode)
		})
	}
}

func BenchmarkRemoteWriteHandler(b *testing.B) {
	labelStrings := []string{
		"__name__", "test_metric",
		"test_label_name", "abcdefg'hijlmn234!@#$%^&*()_+~`\"{}[],./<>?hello0123hiOlá你好Dzieńdobry9Zd8ra765v4stvuyte",
	}
	v1Labels := prompb.FromLabels(labels.FromStrings(labelStrings...), nil)

	testCases := []struct {
		name        string
		payloadFunc func() ([]byte, error)
		protoFormat config.RemoteWriteProtoMsg
	}{
		{
			name: "V1 Write",
			payloadFunc: func() ([]byte, error) {
				buf, _, _, err := buildWriteRequest(nil, []prompb.TimeSeries{{
					Labels:     v1Labels,
					Histograms: []prompb.Histogram{prompb.FromIntHistogram(0, &testHistogram)},
				}}, nil, nil, nil, nil, "snappy")
				return buf, err
			},
			protoFormat: config.RemoteWriteProtoMsgV1,
		},
		{
			name: "V2 Write",
			payloadFunc: func() ([]byte, error) {
				buf, _, _, err := buildV2WriteRequest(promslog.NewNopLogger(), []writev2.TimeSeries{{
					LabelsRefs: []uint32{0, 1, 2, 3},
					Histograms: []writev2.Histogram{writev2.FromIntHistogram(0, &testHistogram)},
				}}, labelStrings,
					nil, nil, nil, "snappy")
				return buf, err
			},
			protoFormat: config.RemoteWriteProtoMsgV2,
		},
	}
	for _, tc := range testCases {
		b.Run(tc.name, func(b *testing.B) {
			appendable := &mockAppendable{}
			handler := NewWriteHandler(promslog.NewNopLogger(), nil, appendable, []config.RemoteWriteProtoMsg{tc.protoFormat}, false)
			b.ResetTimer()
			for i := 0; i < b.N; i++ {
				b.StopTimer()
				buf, err := tc.payloadFunc()
				require.NoError(b, err)
				req, err := http.NewRequest("", "", bytes.NewReader(buf))
				require.NoError(b, err)
				b.StartTimer()

				recorder := httptest.NewRecorder()
				handler.ServeHTTP(recorder, req)
			}
		})
	}
}

func TestCommitErr_V1Message(t *testing.T) {
	payload, _, _, err := buildWriteRequest(nil, writeRequestFixture.Timeseries, nil, nil, nil, nil, "snappy")
	require.NoError(t, err)

	req, err := http.NewRequest("", "", bytes.NewReader(payload))
	require.NoError(t, err)

	appendable := &mockAppendable{commitErr: errors.New("commit error")}
	handler := NewWriteHandler(promslog.NewNopLogger(), nil, appendable, []config.RemoteWriteProtoMsg{config.RemoteWriteProtoMsgV1}, false)

	recorder := httptest.NewRecorder()
	handler.ServeHTTP(recorder, req)

	resp := recorder.Result()
	body, err := io.ReadAll(resp.Body)
	require.NoError(t, err)
	require.Equal(t, http.StatusInternalServerError, resp.StatusCode)
	require.Equal(t, "commit error\n", string(body))
}

// Regression test for https://github.com/prometheus/prometheus/issues/17206
func TestHistogramValidationErrorHandling(t *testing.T) {
	testCases := []struct {
		desc     string
		hist     histogram.Histogram
		expected string
	}{
		{
			desc: "count mismatch",
			hist: histogram.Histogram{
				Schema:          2,
				ZeroThreshold:   1e-128,
				ZeroCount:       1,
				Count:           10,
				Sum:             20,
				PositiveSpans:   []histogram.Span{{Offset: 0, Length: 1}},
				PositiveBuckets: []int64{2},
				NegativeSpans:   []histogram.Span{{Offset: 0, Length: 1}},
				NegativeBuckets: []int64{3},
				// Total: 1 (zero) + 2 (positive) + 3 (negative) = 6, but Count = 10
			},
			expected: "histogram's observation count should equal",
		},
		{
			desc: "custom buckets zero count",
			hist: histogram.Histogram{
				Schema:          histogram.CustomBucketsSchema,
				Count:           10,
				Sum:             20,
				ZeroCount:       1, // Invalid: custom buckets must have zero count of 0
				PositiveSpans:   []histogram.Span{{Offset: 0, Length: 1}},
				PositiveBuckets: []int64{10},
				CustomValues:    []float64{1.0},
			},
			expected: "custom buckets: must have zero count of 0",
		},
	}

	for _, protoMsg := range []config.RemoteWriteProtoMsg{config.RemoteWriteProtoMsgV1, config.RemoteWriteProtoMsgV2} {
		protoName := "V1"
		if protoMsg == config.RemoteWriteProtoMsgV2 {
			protoName = "V2"
		}

		for _, tc := range testCases {
			testName := fmt.Sprintf("%s %s", protoName, tc.desc)
			t.Run(testName, func(t *testing.T) {
				dir := t.TempDir()
				opts := tsdb.DefaultOptions()

				db, err := tsdb.Open(dir, nil, nil, opts, nil)
				require.NoError(t, err)
				t.Cleanup(func() { require.NoError(t, db.Close()) })

				handler := NewWriteHandler(promslog.NewNopLogger(), nil, db.Head(), []config.RemoteWriteProtoMsg{protoMsg}, false)
				recorder := httptest.NewRecorder()

				var buf []byte
				if protoMsg == config.RemoteWriteProtoMsgV1 {
					ts := []prompb.TimeSeries{{
						Labels:     []prompb.Label{{Name: "__name__", Value: "test"}},
						Histograms: []prompb.Histogram{prompb.FromIntHistogram(1, &tc.hist)},
					}}
					buf, _, _, err = buildWriteRequest(nil, ts, nil, nil, nil, nil, "snappy")
				} else {
					st := writev2.NewSymbolTable()
					ts := []writev2.TimeSeries{{
						LabelsRefs: st.SymbolizeLabels(labels.FromStrings("__name__", "test"), nil),
						Histograms: []writev2.Histogram{writev2.FromIntHistogram(1, &tc.hist)},
					}}
					buf, _, _, err = buildV2WriteRequest(promslog.NewNopLogger(), ts, st.Symbols(), nil, nil, nil, "snappy")
				}
				require.NoError(t, err)

				req := httptest.NewRequest(http.MethodPost, "/api/v1/write", bytes.NewReader(buf))
				req.Header.Set("Content-Type", remoteWriteContentTypeHeaders[protoMsg])
				req.Header.Set("Content-Encoding", "snappy")

				handler.ServeHTTP(recorder, req)

				require.Equal(t, http.StatusBadRequest, recorder.Code)
				require.Contains(t, recorder.Body.String(), tc.expected)
			})
		}
	}
}

func TestCommitErr_V2Message(t *testing.T) {
	payload, _, _, err := buildV2WriteRequest(promslog.NewNopLogger(), writeV2RequestFixture.Timeseries, writeV2RequestFixture.Symbols, nil, nil, nil, "snappy")
	require.NoError(t, err)

	req, err := http.NewRequest("", "", bytes.NewReader(payload))
	require.NoError(t, err)

	req.Header.Set("Content-Type", remoteWriteContentTypeHeaders[config.RemoteWriteProtoMsgV2])
	req.Header.Set("Content-Encoding", compression.Snappy)
	req.Header.Set(RemoteWriteVersionHeader, RemoteWriteVersion20HeaderValue)

	appendable := &mockAppendable{commitErr: errors.New("commit error")}
	handler := NewWriteHandler(promslog.NewNopLogger(), nil, appendable, []config.RemoteWriteProtoMsg{config.RemoteWriteProtoMsgV2}, false)

	recorder := httptest.NewRecorder()
	handler.ServeHTTP(recorder, req)

	resp := recorder.Result()
	body, err := io.ReadAll(resp.Body)
	require.NoError(t, err)
	require.Equal(t, http.StatusInternalServerError, resp.StatusCode)
	require.Equal(t, "commit error\n", string(body))
}

func BenchmarkRemoteWriteOOOSamples(b *testing.B) {
	b.Skip("Not a valid benchmark (does not count to b.N)")
	dir := b.TempDir()

	opts := tsdb.DefaultOptions()
	opts.OutOfOrderCapMax = 30
	opts.OutOfOrderTimeWindow = 120 * time.Minute.Milliseconds()

	db, err := tsdb.Open(dir, nil, nil, opts, nil)
	require.NoError(b, err)

	b.Cleanup(func() {
		require.NoError(b, db.Close())
	})
	// TODO: test with other proto format(s)
	handler := NewWriteHandler(promslog.NewNopLogger(), nil, db.Head(), []config.RemoteWriteProtoMsg{config.RemoteWriteProtoMsgV1}, false)

	buf, _, _, err := buildWriteRequest(nil, genSeriesWithSample(1000, 200*time.Minute.Milliseconds()), nil, nil, nil, nil, "snappy")
	require.NoError(b, err)

	req, err := http.NewRequest("", "", bytes.NewReader(buf))
	require.NoError(b, err)

	recorder := httptest.NewRecorder()
	handler.ServeHTTP(recorder, req)
	require.Equal(b, http.StatusNoContent, recorder.Code)
	require.Equal(b, uint64(1000), db.Head().NumSeries())

	var bufRequests [][]byte
	for i := range 100 {
		buf, _, _, err = buildWriteRequest(nil, genSeriesWithSample(1000, int64(80+i)*time.Minute.Milliseconds()), nil, nil, nil, nil, "snappy")
		require.NoError(b, err)
		bufRequests = append(bufRequests, buf)
	}

	b.ResetTimer()
	for i := range 100 {
		req, err = http.NewRequest("", "", bytes.NewReader(bufRequests[i]))
		require.NoError(b, err)

		recorder = httptest.NewRecorder()
		handler.ServeHTTP(recorder, req)
		require.Equal(b, http.StatusNoContent, recorder.Code)
		require.Equal(b, uint64(1000), db.Head().NumSeries())
	}
}

func genSeriesWithSample(numSeries int, ts int64) []prompb.TimeSeries {
	var series []prompb.TimeSeries
	for i := range numSeries {
		s := prompb.TimeSeries{
			Labels:  []prompb.Label{{Name: "__name__", Value: fmt.Sprintf("test_metric_%d", i)}},
			Samples: []prompb.Sample{{Value: float64(i), Timestamp: ts}},
		}
		series = append(series, s)
	}

	return series
}

type mockAppendable struct {
	latestSample    map[uint64]int64
	samples         []mockSample
	latestExemplar  map[uint64]int64
	exemplars       []mockExemplar
	latestHistogram map[uint64]int64
	latestFloatHist map[uint64]int64
	histograms      []mockHistogram
	metadata        []mockMetadata

	// optional errors to inject.
	commitErr             error
	appendSampleErr       error
	appendCTZeroSampleErr error
	appendHistogramErr    error
	appendExemplarErr     error
	updateMetadataErr     error
}

type mockSample struct {
	l labels.Labels
	t int64
	v float64
}

type mockExemplar struct {
	l  labels.Labels
	el labels.Labels
	t  int64
	v  float64
}

type mockHistogram struct {
	l  labels.Labels
	t  int64
	h  *histogram.Histogram
	fh *histogram.FloatHistogram
}

type mockMetadata struct {
	l labels.Labels
	m metadata.Metadata
}

// Wrapper to instruct go-cmp package to compare a list of structs with unexported fields.
func requireEqual(t *testing.T, expected, actual any, msgAndArgs ...any) {
	t.Helper()

	testutil.RequireEqualWithOptions(t, expected, actual,
		[]cmp.Option{cmp.AllowUnexported(mockSample{}), cmp.AllowUnexported(mockExemplar{}), cmp.AllowUnexported(mockHistogram{}), cmp.AllowUnexported(mockMetadata{})},
		msgAndArgs...)
}

func (m *mockAppendable) Appender(context.Context) storage.Appender {
	if m.latestSample == nil {
		m.latestSample = map[uint64]int64{}
	}
	if m.latestHistogram == nil {
		m.latestHistogram = map[uint64]int64{}
	}
	if m.latestFloatHist == nil {
		m.latestFloatHist = map[uint64]int64{}
	}
	if m.latestExemplar == nil {
		m.latestExemplar = map[uint64]int64{}
	}
	return m
}

func (*mockAppendable) SetOptions(*storage.AppendOptions) {
	panic("unimplemented")
}

func (m *mockAppendable) Append(_ storage.SeriesRef, l labels.Labels, t int64, v float64) (storage.SeriesRef, error) {
	if m.appendSampleErr != nil {
		return 0, m.appendSampleErr
	}
	hash := l.Hash()
	latestTs := m.latestSample[hash]
	if t < latestTs {
		return 0, storage.ErrOutOfOrderSample
	}
	if t == latestTs {
		return 0, storage.ErrDuplicateSampleForTimestamp
	}

	if l.IsEmpty() {
		return 0, tsdb.ErrInvalidSample
	}
	if _, hasDuplicates := l.HasDuplicateLabelNames(); hasDuplicates {
		return 0, tsdb.ErrInvalidSample
	}

	m.latestSample[hash] = t
	m.samples = append(m.samples, mockSample{l, t, v})
	return storage.SeriesRef(hash), nil
}

func (m *mockAppendable) Commit() error {
	if m.commitErr != nil {
		_ = m.Rollback() // As per Commit method contract.
	}
	return m.commitErr
}

func (m *mockAppendable) Rollback() error {
	m.samples = m.samples[:0]
	m.exemplars = m.exemplars[:0]
	m.histograms = m.histograms[:0]
	m.metadata = m.metadata[:0]
	return nil
}

func (m *mockAppendable) AppendExemplar(ref storage.SeriesRef, l labels.Labels, e exemplar.Exemplar) (storage.SeriesRef, error) {
	if m.appendExemplarErr != nil {
		return 0, m.appendExemplarErr
	}

	latestTs := m.latestExemplar[uint64(ref)]
	if e.Ts < latestTs {
		return 0, storage.ErrOutOfOrderExemplar
	}
	if e.Ts == latestTs {
		return 0, storage.ErrDuplicateExemplar
	}

	m.latestExemplar[uint64(ref)] = e.Ts
	m.exemplars = append(m.exemplars, mockExemplar{l, e.Labels, e.Ts, e.Value})
	return ref, nil
}

func (m *mockAppendable) AppendHistogram(_ storage.SeriesRef, l labels.Labels, t int64, h *histogram.Histogram, fh *histogram.FloatHistogram) (storage.SeriesRef, error) {
	if m.appendHistogramErr != nil {
		return 0, m.appendHistogramErr
	}
	hash := l.Hash()
	var latestTs int64
	if h != nil {
		latestTs = m.latestHistogram[hash]
	} else {
		latestTs = m.latestFloatHist[hash]
	}
	if t < latestTs {
		return 0, storage.ErrOutOfOrderSample
	}
	if t == latestTs {
		return 0, storage.ErrDuplicateSampleForTimestamp
	}

	if l.IsEmpty() {
		return 0, tsdb.ErrInvalidSample
	}
	if _, hasDuplicates := l.HasDuplicateLabelNames(); hasDuplicates {
		return 0, tsdb.ErrInvalidSample
	}

	if h != nil {
		m.latestHistogram[hash] = t
	} else {
		m.latestFloatHist[hash] = t
	}
	m.histograms = append(m.histograms, mockHistogram{l, t, h, fh})
	return storage.SeriesRef(hash), nil
}

func (m *mockAppendable) AppendHistogramCTZeroSample(_ storage.SeriesRef, l labels.Labels, t, ct int64, h *histogram.Histogram, _ *histogram.FloatHistogram) (storage.SeriesRef, error) {
	if m.appendCTZeroSampleErr != nil {
		return 0, m.appendCTZeroSampleErr
	}

	// Created Timestamp can't be higher than the original sample's timestamp.
	if ct > t {
		return 0, storage.ErrOutOfOrderSample
	}
	hash := l.Hash()
	var latestTs int64
	if h != nil {
		latestTs = m.latestHistogram[hash]
	} else {
		latestTs = m.latestFloatHist[hash]
	}
	if ct < latestTs {
		return 0, storage.ErrOutOfOrderSample
	}
	if ct == latestTs {
		return 0, storage.ErrDuplicateSampleForTimestamp
	}

	if l.IsEmpty() {
		return 0, tsdb.ErrInvalidSample
	}

	if _, hasDuplicates := l.HasDuplicateLabelNames(); hasDuplicates {
		return 0, tsdb.ErrInvalidSample
	}

	if h != nil {
		m.latestHistogram[hash] = ct
		m.histograms = append(m.histograms, mockHistogram{l, ct, &histogram.Histogram{}, nil})
	} else {
		m.latestFloatHist[hash] = ct
		m.histograms = append(m.histograms, mockHistogram{l, ct, nil, &histogram.FloatHistogram{}})
	}
	return storage.SeriesRef(hash), nil
}

func (m *mockAppendable) UpdateMetadata(ref storage.SeriesRef, l labels.Labels, mp metadata.Metadata) (storage.SeriesRef, error) {
	if m.updateMetadataErr != nil {
		return 0, m.updateMetadataErr
	}

	m.metadata = append(m.metadata, mockMetadata{l: l, m: mp})
	return ref, nil
}

func (m *mockAppendable) AppendCTZeroSample(_ storage.SeriesRef, l labels.Labels, t, ct int64) (storage.SeriesRef, error) {
	if m.appendCTZeroSampleErr != nil {
		return 0, m.appendCTZeroSampleErr
	}

	// Created Timestamp can't be higher than the original sample's timestamp.
	if ct > t {
		return 0, storage.ErrOutOfOrderSample
	}
	hash := l.Hash()
	latestTs := m.latestSample[hash]
	if ct < latestTs {
		return 0, storage.ErrOutOfOrderSample
	}
	if ct == latestTs {
		return 0, storage.ErrDuplicateSampleForTimestamp
	}

	if l.IsEmpty() {
		return 0, tsdb.ErrInvalidSample
	}
	if _, hasDuplicates := l.HasDuplicateLabelNames(); hasDuplicates {
		return 0, tsdb.ErrInvalidSample
	}

	m.latestSample[hash] = ct
	m.samples = append(m.samples, mockSample{l, ct, 0})
	return storage.SeriesRef(hash), nil
}

var (
	highSchemaHistogram = &histogram.Histogram{
		Schema: 10,
		PositiveSpans: []histogram.Span{
			{
				Offset: -1,
				Length: 2,
			},
		},
		PositiveBuckets: []int64{1, 2},
		NegativeSpans: []histogram.Span{
			{
				Offset: 0,
				Length: 1,
			},
		},
		NegativeBuckets: []int64{1},
	}
	reducedSchemaHistogram = &histogram.Histogram{
		Schema: 8,
		PositiveSpans: []histogram.Span{
			{
				Offset: 0,
				Length: 1,
			},
		},
		PositiveBuckets: []int64{4},
		NegativeSpans: []histogram.Span{
			{
				Offset: 0,
				Length: 1,
			},
		},
		NegativeBuckets: []int64{1},
	}
)

func TestHistogramsReduction(t *testing.T) {
	for _, protoMsg := range []config.RemoteWriteProtoMsg{config.RemoteWriteProtoMsgV1, config.RemoteWriteProtoMsgV2} {
		t.Run(string(protoMsg), func(t *testing.T) {
			appendable := &mockAppendable{}
			handler := NewWriteHandler(promslog.NewNopLogger(), nil, appendable, []config.RemoteWriteProtoMsg{protoMsg}, false)

			var (
				err     error
				payload []byte
			)

			if protoMsg == config.RemoteWriteProtoMsgV1 {
				payload, _, _, err = buildWriteRequest(nil, []prompb.TimeSeries{
					{
						Labels:     []prompb.Label{{Name: "__name__", Value: "test_metric1"}},
						Histograms: []prompb.Histogram{prompb.FromIntHistogram(1, highSchemaHistogram)},
					},
					{
						Labels:     []prompb.Label{{Name: "__name__", Value: "test_metric2"}},
						Histograms: []prompb.Histogram{prompb.FromFloatHistogram(2, highSchemaHistogram.ToFloat(nil))},
					},
				}, nil, nil, nil, nil, "snappy")
			} else {
				payload, _, _, err = buildV2WriteRequest(promslog.NewNopLogger(), []writev2.TimeSeries{
					{
						LabelsRefs: []uint32{0, 1},
						Histograms: []writev2.Histogram{writev2.FromIntHistogram(1, highSchemaHistogram)},
					},
					{
						LabelsRefs: []uint32{0, 2},
						Histograms: []writev2.Histogram{writev2.FromFloatHistogram(2, highSchemaHistogram.ToFloat(nil))},
					},
				}, []string{"__name__", "test_metric1", "test_metric2"},
					nil, nil, nil, "snappy")
			}
			require.NoError(t, err)

			req, err := http.NewRequest("", "", bytes.NewReader(payload))
			require.NoError(t, err)

			req.Header.Set("Content-Type", remoteWriteContentTypeHeaders[protoMsg])

			recorder := httptest.NewRecorder()
			handler.ServeHTTP(recorder, req)

			resp := recorder.Result()
			body, err := io.ReadAll(resp.Body)
			require.NoError(t, err)
			require.Equal(t, http.StatusNoContent, resp.StatusCode)
			require.Empty(t, body)

			require.Len(t, appendable.histograms, 2)
			require.Equal(t, int64(1), appendable.histograms[0].t)
			require.Equal(t, reducedSchemaHistogram, appendable.histograms[0].h)
			require.Equal(t, int64(2), appendable.histograms[1].t)
			require.Equal(t, reducedSchemaHistogram.ToFloat(nil), appendable.histograms[1].fh)
		})
	}
}