[receiver/prometheusremotewrite] Parse labels (open-telemetry#35656)

#### Description
This PR builds on top of
open-telemetry#35535,
open-telemetry#35565
and
open-telemetry#35624.

Here we're parsing labels into resource/metric attributes. It's still
not great because resource attributes (with exception to
`service.namespace`, `service.name` and `service.name.id`) are encoded
into a special metric called `target_info`. Metrics related to specific
target infos may arrive in separate write requests, so it may be
impossible to build the full OTLP metric in a stateless way.

In this PR I'm ignoring this problem 😛, and transforming `job` and
`instance` labels into resource attributes, while all other labels
become scope attributes.

Please focus on the latest commit when reviewing this PR :) 
1c9ff80

---------

Signed-off-by: Arthur Silva Sens <[email protected]>

Author: ArthurSens

.chloggen/prwreceiver-parselabels.yaml

@@ -0,0 +1,27 @@
+# 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: receiver/prometheusremotewrite
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Parse labels from Prometheus Remote Write requests into Resource and Metric Attributes.
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [35656]
+
+# (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: Warning - The HTTP Server still doesn't pass metrics to the next consumer. The component is unusable for now.
+
+# 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/prometheusremotewritereceiver/go.mod

@@ -3,8 +3,10 @@ module github.com/open-telemetry/opentelemetry-collector-contrib/receiver/promet
 go 1.22.0
 
 require (
+	github.com/cespare/xxhash/v2 v2.3.0
 	github.com/gogo/protobuf v1.3.2
 	github.com/golang/snappy v0.0.4
+	github.com/open-telemetry/opentelemetry-collector-contrib/pkg/pdatatest v0.114.0
 	github.com/prometheus/prometheus v0.54.1
 	github.com/stretchr/testify v1.10.0
 	go.opentelemetry.io/collector/component v0.115.1-0.20241206185113-3f3e208e71b8
@@ -29,7 +31,6 @@ require (
 	github.com/alecthomas/units v0.0.0-20240626203959-61d1e3462e30 // indirect
 	github.com/aws/aws-sdk-go v1.54.19 // indirect
 	github.com/beorn7/perks v1.0.1 // indirect
-	github.com/cespare/xxhash/v2 v2.3.0 // indirect
 	github.com/davecgh/go-spew v1.1.2-0.20180830191138-d8f796af33cc // indirect
 	github.com/dennwc/varint v1.0.0 // indirect
 	github.com/felixge/httpsnoop v1.0.4 // indirect
@@ -56,6 +57,7 @@ require (
 	github.com/modern-go/reflect2 v1.0.2 // indirect
 	github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822 // indirect
 	github.com/mwitkow/go-conntrack v0.0.0-20190716064945-2f068394615f // indirect
+	github.com/open-telemetry/opentelemetry-collector-contrib/pkg/pdatautil v0.115.0 // indirect
 	github.com/pierrec/lz4/v4 v4.1.21 // indirect
 	github.com/pkg/browser v0.0.0-20240102092130-5ac0b6a4141c // indirect
 	github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2 // indirect
@@ -105,3 +107,9 @@ require (
 	k8s.io/klog/v2 v2.130.1 // indirect
 	k8s.io/utils v0.0.0-20230726121419-3b25d923346b // indirect
 )
+
+replace github.com/open-telemetry/opentelemetry-collector-contrib/pkg/pdatautil => ../../pkg/pdatautil
+
+replace github.com/open-telemetry/opentelemetry-collector-contrib/pkg/pdatatest => ../../pkg/pdatatest
+
+replace github.com/open-telemetry/opentelemetry-collector-contrib/pkg/golden => ../../pkg/golden

receiver/prometheusremotewritereceiver/receiver.go

@@ -12,13 +12,16 @@ import (
 	"strings"
 	"time"
 
+	"github.com/cespare/xxhash/v2"
 	"github.com/gogo/protobuf/proto"
 	promconfig "github.com/prometheus/prometheus/config"
+	"github.com/prometheus/prometheus/model/labels"
 	writev2 "github.com/prometheus/prometheus/prompb/io/prometheus/write/v2"
 	promremote "github.com/prometheus/prometheus/storage/remote"
 	"go.opentelemetry.io/collector/component"
 	"go.opentelemetry.io/collector/component/componentstatus"
 	"go.opentelemetry.io/collector/consumer"
+	"go.opentelemetry.io/collector/pdata/pcommon"
 	"go.opentelemetry.io/collector/pdata/pmetric"
 	"go.opentelemetry.io/collector/receiver"
 	"go.uber.org/zap/zapcore"
@@ -150,8 +153,113 @@ func (prw *prometheusRemoteWriteReceiver) parseProto(contentType string) (promco
 }
 
 // translateV2 translates a v2 remote-write request into OTLP metrics.
-// For now translateV2 is not implemented and returns an empty metrics.
+// translate is not feature complete.
 // nolint
-func (prw *prometheusRemoteWriteReceiver) translateV2(_ context.Context, _ *writev2.Request) (pmetric.Metrics, promremote.WriteResponseStats, error) {
-	return pmetric.NewMetrics(), promremote.WriteResponseStats{}, nil
+func (prw *prometheusRemoteWriteReceiver) translateV2(_ context.Context, req *writev2.Request) (pmetric.Metrics, promremote.WriteResponseStats, error) {
+	var (
+		badRequestErrors error
+		otelMetrics      = pmetric.NewMetrics()
+		labelsBuilder    = labels.NewScratchBuilder(0)
+		stats            = promremote.WriteResponseStats{}
+		// Prometheus Remote-Write can send multiple time series with the same labels in the same request.
+		// Instead of creating a whole new OTLP metric, we just append the new sample to the existing OTLP metric.
+		// This cache is called "intra" because in the future we'll have a "interRequestCache" to cache resourceAttributes
+		// between requests based on the metric "target_info".
+		intraRequestCache = make(map[uint64]pmetric.ResourceMetrics)
+	)
+
+	for _, ts := range req.Timeseries {
+		ls := ts.ToLabels(&labelsBuilder, req.Symbols)
+
+		if !ls.Has(labels.MetricName) {
+			badRequestErrors = errors.Join(badRequestErrors, fmt.Errorf("missing metric name in labels"))
+			continue
+		} else if duplicateLabel, hasDuplicate := ls.HasDuplicateLabelNames(); hasDuplicate {
+			badRequestErrors = errors.Join(badRequestErrors, fmt.Errorf("duplicate label %q in labels", duplicateLabel))
+			continue
+		}
+
+		var rm pmetric.ResourceMetrics
+		hashedLabels := xxhash.Sum64String(ls.Get("job") + string([]byte{'\xff'}) + ls.Get("instance"))
+		intraCacheEntry, ok := intraRequestCache[hashedLabels]
+		if ok {
+			// We found the same time series in the same request, so we should append to the same OTLP metric.
+			rm = intraCacheEntry
+		} else {
+			rm = otelMetrics.ResourceMetrics().AppendEmpty()
+			parseJobAndInstance(rm.Resource().Attributes(), ls.Get("job"), ls.Get("instance"))
+			intraRequestCache[hashedLabels] = rm
+		}
+
+		switch ts.Metadata.Type {
+		case writev2.Metadata_METRIC_TYPE_COUNTER:
+			addCounterDatapoints(rm, ls, ts)
+		case writev2.Metadata_METRIC_TYPE_GAUGE:
+			addGaugeDatapoints(rm, ls, ts)
+		case writev2.Metadata_METRIC_TYPE_SUMMARY:
+			addSummaryDatapoints(rm, ls, ts)
+		case writev2.Metadata_METRIC_TYPE_HISTOGRAM:
+			addHistogramDatapoints(rm, ls, ts)
+		default:
+			badRequestErrors = errors.Join(badRequestErrors, fmt.Errorf("unsupported metric type %q for metric %q", ts.Metadata.Type, ls.Get(labels.MetricName)))
+		}
+	}
+
+	return otelMetrics, stats, badRequestErrors
+}
+
+// parseJobAndInstance turns the job and instance labels service resource attributes.
+// Following the specification at https://opentelemetry.io/docs/specs/otel/compatibility/prometheus_and_openmetrics/
+func parseJobAndInstance(dest pcommon.Map, job, instance string) {
+	if instance != "" {
+		dest.PutStr("service.instance.id", instance)
+	}
+	if job != "" {
+		parts := strings.Split(job, "/")
+		if len(parts) == 2 {
+			dest.PutStr("service.namespace", parts[0])
+			dest.PutStr("service.name", parts[1])
+			return
+		}
+		dest.PutStr("service.name", job)
+	}
+}
+
+func addCounterDatapoints(_ pmetric.ResourceMetrics, _ labels.Labels, _ writev2.TimeSeries) {
+	// TODO: Implement this function
+}
+
+func addGaugeDatapoints(rm pmetric.ResourceMetrics, ls labels.Labels, ts writev2.TimeSeries) {
+	// TODO: Cache metric name+type+unit and look up cache before creating new empty metric.
+	// In OTel name+type+unit is the unique identifier of a metric and we should not create
+	// a new metric if it already exists.
+
+	// TODO: Check if Scope is already present by comparing labels "otel_scope_name" and "otel_scope_version"
+	// with Scope.Name and Scope.Version. If it is present, we should append to the existing Scope.
+	m := rm.ScopeMetrics().AppendEmpty().Metrics().AppendEmpty().SetEmptyGauge()
+	addDatapoints(m.DataPoints(), ls, ts)
+}
+
+func addSummaryDatapoints(_ pmetric.ResourceMetrics, _ labels.Labels, _ writev2.TimeSeries) {
+	// TODO: Implement this function
+}
+
+func addHistogramDatapoints(_ pmetric.ResourceMetrics, _ labels.Labels, _ writev2.TimeSeries) {
+	// TODO: Implement this function
+}
+
+// addDatapoints adds the labels to the datapoints attributes.
+// TODO: We're still not handling several fields that make a datapoint complete, e.g. StartTimestamp,
+// Timestamp, Value, etc.
+func addDatapoints(datapoints pmetric.NumberDataPointSlice, ls labels.Labels, _ writev2.TimeSeries) {
+	attributes := datapoints.AppendEmpty().Attributes()
+
+	for _, l := range ls {
+		if l.Name == "instance" || l.Name == "job" || // Become resource attributes "service.name", "service.instance.id" and "service.namespace"
+			l.Name == labels.MetricName || // Becomes metric name
+			l.Name == "otel_scope_name" || l.Name == "otel_scope_version" { // Becomes scope name and version
+			continue
+		}
+		attributes.PutStr(l.Name, l.Value)
+	}
 }

receiver/prometheusremotewritereceiver/receiver_test.go

@@ -14,13 +14,38 @@ import (
 	"github.com/golang/snappy"
 	promconfig "github.com/prometheus/prometheus/config"
 	writev2 "github.com/prometheus/prometheus/prompb/io/prometheus/write/v2"
+	"github.com/prometheus/prometheus/storage/remote"
 	"github.com/stretchr/testify/assert"
 	"go.opentelemetry.io/collector/component/componenttest"
 	"go.opentelemetry.io/collector/consumer/consumertest"
+	"go.opentelemetry.io/collector/pdata/pmetric"
 	"go.opentelemetry.io/collector/receiver/receivertest"
+
+	"github.com/open-telemetry/opentelemetry-collector-contrib/pkg/pdatatest/pmetrictest"
 )
 
-func setupServer(t *testing.T) {
+var writeV2RequestFixture = &writev2.Request{
+	Symbols: []string{"", "__name__", "test_metric1", "job", "service-x/test", "instance", "107cn001", "d", "e", "foo", "bar", "f", "g", "h", "i", "Test gauge for test purposes", "Maybe op/sec who knows (:", "Test counter for test purposes"},
+	Timeseries: []writev2.TimeSeries{
+		{
+			Metadata:   writev2.Metadata{Type: writev2.Metadata_METRIC_TYPE_GAUGE},
+			LabelsRefs: []uint32{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, // Symbolized writeRequestFixture.Timeseries[0].Labels
+			Samples:    []writev2.Sample{{Value: 1, Timestamp: 1}},
+		},
+		{
+			Metadata:   writev2.Metadata{Type: writev2.Metadata_METRIC_TYPE_GAUGE},
+			LabelsRefs: []uint32{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, // Same series as first. Should use the same resource metrics.
+			Samples:    []writev2.Sample{{Value: 2, Timestamp: 2}},
+		},
+		{
+			Metadata:   writev2.Metadata{Type: writev2.Metadata_METRIC_TYPE_GAUGE},
+			LabelsRefs: []uint32{1, 2, 3, 9, 5, 10, 7, 8, 9, 10}, // This series has different label values for job and instance.
+			Samples:    []writev2.Sample{{Value: 2, Timestamp: 2}},
+		},
+	},
+}
+
+func setupMetricsReceiver(t *testing.T) *prometheusRemoteWriteReceiver {
 	t.Helper()
 
 	factory := NewFactory()
@@ -30,6 +55,13 @@ func setupServer(t *testing.T) {
 	assert.NoError(t, err)
 	assert.NotNil(t, prwReceiver, "metrics receiver creation failed")
 
+	return prwReceiver.(*prometheusRemoteWriteReceiver)
+}
+
+func setupServer(t *testing.T) {
+	t.Helper()
+
+	prwReceiver := setupMetricsReceiver(t)
 	ctx, cancel := context.WithCancel(context.Background())
 	t.Cleanup(cancel)
 
@@ -98,3 +130,89 @@ func TestHandlePRWContentTypeNegotiation(t *testing.T) {
 		})
 	}
 }
+
+func TestTranslateV2(t *testing.T) {
+	prwReceiver := setupMetricsReceiver(t)
+	ctx, cancel := context.WithCancel(context.Background())
+	t.Cleanup(cancel)
+
+	for _, tc := range []struct {
+		name            string
+		request         *writev2.Request
+		expectError     string
+		expectedMetrics pmetric.Metrics
+		expectedStats   remote.WriteResponseStats
+	}{
+		{
+			name: "missing metric name",
+			request: &writev2.Request{
+				Symbols: []string{"", "foo", "bar"},
+				Timeseries: []writev2.TimeSeries{
+					{
+						LabelsRefs: []uint32{1, 2},
+						Samples:    []writev2.Sample{{Value: 1, Timestamp: 1}},
+					},
+				},
+			},
+			expectError: "missing metric name in labels",
+		},
+		{
+			name: "duplicate label",
+			request: &writev2.Request{
+				Symbols: []string{"", "__name__", "test"},
+				Timeseries: []writev2.TimeSeries{
+					{
+						LabelsRefs: []uint32{1, 2, 1, 2},
+						Samples:    []writev2.Sample{{Value: 1, Timestamp: 1}},
+					},
+				},
+			},
+			expectError: `duplicate label "__name__" in labels`,
+		},
+		{
+			name:    "valid request",
+			request: writeV2RequestFixture,
+			expectedMetrics: func() pmetric.Metrics {
+				expected := pmetric.NewMetrics()
+				rm1 := expected.ResourceMetrics().AppendEmpty()
+				rmAttributes1 := rm1.Resource().Attributes()
+				rmAttributes1.PutStr("service.namespace", "service-x")
+				rmAttributes1.PutStr("service.name", "test")
+				rmAttributes1.PutStr("service.instance.id", "107cn001")
+				sm1 := rm1.ScopeMetrics().AppendEmpty()
+				sm1Attributes := sm1.Metrics().AppendEmpty().SetEmptyGauge().DataPoints().AppendEmpty().Attributes()
+				sm1Attributes.PutStr("d", "e")
+				sm1Attributes.PutStr("foo", "bar")
+				// Since we don't check "scope_name" and "scope_version", we end up with duplicated scope metrics for repeated series.
+				// TODO: Properly handle scope metrics.
+				sm2 := rm1.ScopeMetrics().AppendEmpty()
+				sm2Attributes := sm2.Metrics().AppendEmpty().SetEmptyGauge().DataPoints().AppendEmpty().Attributes()
+				sm2Attributes.PutStr("d", "e")
+				sm2Attributes.PutStr("foo", "bar")
+
+				rm2 := expected.ResourceMetrics().AppendEmpty()
+				rmAttributes2 := rm2.Resource().Attributes()
+				rmAttributes2.PutStr("service.name", "foo")
+				rmAttributes2.PutStr("service.instance.id", "bar")
+				mAttributes2 := rm2.ScopeMetrics().AppendEmpty().Metrics().AppendEmpty().SetEmptyGauge().DataPoints().AppendEmpty().Attributes()
+				mAttributes2.PutStr("d", "e")
+				mAttributes2.PutStr("foo", "bar")
+
+				return expected
+			}(),
+			expectedStats: remote.WriteResponseStats{},
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			metrics, stats, err := prwReceiver.translateV2(ctx, tc.request)
+			if tc.expectError != "" {
+				assert.ErrorContains(t, err, tc.expectError)
+				return
+			}
+
+			assert.NoError(t, err)
+			assert.NoError(t, pmetrictest.CompareMetrics(tc.expectedMetrics, metrics))
+			assert.Equal(t, tc.expectedStats, stats)
+		})
+	}
+}