feat: receiver/prometheusremotewrite - Implement body unmarshaling (o…

…pen-telemetry#35624)

#### Description
This PR builds on top of open-telemetry#35535 and open-telemetry#35565. We're now making sure we're
able to unmarshal a remote write request, while also exercising the
decompression that is made by OTel's confighttp.

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

.chloggen/prwreceiver-bodyunmarshal.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: Implement body unmarshaling for Prometheus Remote Write requests
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [35624]
+
+# (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 do anything. It's just a placeholder 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: [api, user]

receiver/prometheusremotewritereceiver/go.mod

@@ -3,6 +3,8 @@ module github.com/open-telemetry/opentelemetry-collector-contrib/receiver/promet
 go 1.22.0
 
 require (
+	github.com/gogo/protobuf v1.3.2
+	github.com/golang/snappy v0.0.4
 	github.com/prometheus/prometheus v0.54.1
 	github.com/stretchr/testify v1.9.0
 	go.opentelemetry.io/collector/component v0.112.0
@@ -11,6 +13,7 @@ require (
 	go.opentelemetry.io/collector/confmap v1.18.0
 	go.opentelemetry.io/collector/consumer v0.112.0
 	go.opentelemetry.io/collector/consumer/consumertest v0.112.0
+	go.opentelemetry.io/collector/pdata v1.18.0
 	go.opentelemetry.io/collector/receiver v0.112.0
 	go.uber.org/goleak v1.3.0
 	go.uber.org/zap v1.27.0
@@ -26,16 +29,15 @@ require (
 	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
 	github.com/fsnotify/fsnotify v1.7.0 // indirect
 	github.com/go-kit/log v0.2.1 // indirect
 	github.com/go-logfmt/logfmt v0.6.0 // indirect
 	github.com/go-logr/logr v1.4.2 // indirect
 	github.com/go-logr/stdr v1.2.2 // indirect
 	github.com/go-viper/mapstructure/v2 v2.2.1 // indirect
-	github.com/gogo/protobuf v1.3.2 // indirect
 	github.com/golang-jwt/jwt/v5 v5.2.1 // indirect
-	github.com/golang/snappy v0.0.4 // indirect
 	github.com/google/uuid v1.6.0 // indirect
 	github.com/grafana/regexp v0.0.0-20240518133315-a468a5bfb3bc // indirect
 	github.com/jmespath/go-jmespath v0.4.0 // indirect
@@ -72,16 +74,17 @@ require (
 	go.opentelemetry.io/collector/consumer/consumerprofiles v0.112.0 // indirect
 	go.opentelemetry.io/collector/extension v0.112.0 // indirect
 	go.opentelemetry.io/collector/extension/auth v0.112.0 // indirect
-	go.opentelemetry.io/collector/pdata v1.18.0 // indirect
 	go.opentelemetry.io/collector/pdata/pprofile v0.112.0 // indirect
 	go.opentelemetry.io/collector/pipeline v0.112.0 // indirect
 	go.opentelemetry.io/collector/receiver/receiverprofiles v0.112.0 // indirect
+	go.opentelemetry.io/collector/semconv v0.112.0 // indirect
 	go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.56.0 // indirect
 	go.opentelemetry.io/otel v1.31.0 // indirect
 	go.opentelemetry.io/otel/metric v1.31.0 // indirect
 	go.opentelemetry.io/otel/sdk v1.31.0 // indirect
 	go.opentelemetry.io/otel/sdk/metric v1.31.0 // indirect
 	go.opentelemetry.io/otel/trace v1.31.0 // indirect
+	go.uber.org/atomic v1.11.0 // indirect
 	go.uber.org/multierr v1.11.0 // indirect
 	golang.org/x/crypto v0.28.0 // indirect
 	golang.org/x/net v0.30.0 // indirect

receiver/prometheusremotewritereceiver/receiver.go

@@ -7,14 +7,19 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"io"
 	"net/http"
 	"strings"
 	"time"
 
+	"github.com/gogo/protobuf/proto"
 	promconfig "github.com/prometheus/prometheus/config"
+	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/pmetric"
 	"go.opentelemetry.io/collector/receiver"
 	"go.uber.org/zap/zapcore"
 )
@@ -90,7 +95,28 @@ func (prw *prometheusRemoteWriteReceiver) handlePRW(w http.ResponseWriter, req *
 	// After parsing the content-type header, the next step would be to handle content-encoding.
 	// Luckly confighttp's Server has middleware that already decompress the request body for us.
 
-	// The next step in follow up PRs would be to decode the request body.
+	body, err := io.ReadAll(req.Body)
+	if err != nil {
+		prw.settings.Logger.Warn("Error decoding remote write request", zapcore.Field{Key: "error", Type: zapcore.ErrorType, Interface: err})
+		http.Error(w, err.Error(), http.StatusBadRequest)
+		return
+	}
+
+	var prw2Req writev2.Request
+	if err = proto.Unmarshal(body, &prw2Req); err != nil {
+		prw.settings.Logger.Warn("Error decoding remote write request", zapcore.Field{Key: "error", Type: zapcore.ErrorType, Interface: err})
+		http.Error(w, err.Error(), http.StatusBadRequest)
+		return
+	}
+
+	_, stats, err := prw.translateV2(req.Context(), &prw2Req)
+	stats.SetHeaders(w)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusBadRequest) // Following instructions at https://prometheus.io/docs/specs/remote_write_spec_2_0/#invalid-samples
+		return
+	}
+
+	w.WriteHeader(http.StatusNoContent)
 }
 
 // parseProto parses the content-type header and returns the version of the remote-write protocol.
@@ -122,3 +148,10 @@ func (prw *prometheusRemoteWriteReceiver) parseProto(contentType string) (promco
 	// No "proto=" parameter found, assume v1.
 	return promconfig.RemoteWriteProtoMsgV1, nil
 }
+
+// translateV2 translates a v2 remote-write request into OTLP metrics.
+// For now translateV2 is not implemented and returns an empty metrics.
+// nolint
+func (prw *prometheusRemoteWriteReceiver) translateV2(_ context.Context, _ *writev2.Request) (pmetric.Metrics, promremote.WriteResponseStats, error) {
+	return pmetric.NewMetrics(), promremote.WriteResponseStats{}, nil
+}

receiver/prometheusremotewritereceiver/receiver_test.go

@@ -4,19 +4,25 @@
 package prometheusremotewritereceiver // import "github.com/open-telemetry/opentelemetry-collector-contrib/receiver/prometheusremotewritereceiver"
 
 import (
+	"bytes"
 	"context"
 	"fmt"
 	"net/http"
 	"testing"
 
+	"github.com/gogo/protobuf/proto"
+	"github.com/golang/snappy"
 	promconfig "github.com/prometheus/prometheus/config"
+	writev2 "github.com/prometheus/prometheus/prompb/io/prometheus/write/v2"
 	"github.com/stretchr/testify/assert"
 	"go.opentelemetry.io/collector/component/componenttest"
 	"go.opentelemetry.io/collector/consumer/consumertest"
 	"go.opentelemetry.io/collector/receiver/receivertest"
 )
 
-func TestHandlePRWContentTypeNegotiation(t *testing.T) {
+func setupServer(t *testing.T) {
+	t.Helper()
+
 	factory := NewFactory()
 	cfg := factory.CreateDefaultConfig()
 
@@ -31,6 +37,10 @@ func TestHandlePRWContentTypeNegotiation(t *testing.T) {
 	t.Cleanup(func() {
 		assert.NoError(t, prwReceiver.Shutdown(ctx), "Must not error shutting down")
 	})
+}
+
+func TestHandlePRWContentTypeNegotiation(t *testing.T) {
+	setupServer(t)
 
 	for _, tc := range []struct {
 		name         string
@@ -60,18 +70,31 @@ func TestHandlePRWContentTypeNegotiation(t *testing.T) {
 		{
 			name:         "x-protobuf/v2 proto parameter",
 			contentType:  fmt.Sprintf("application/x-protobuf;proto=%s", promconfig.RemoteWriteProtoMsgV2),
-			extectedCode: http.StatusOK,
+			extectedCode: http.StatusNoContent,
 		},
 	} {
 		t.Run(tc.name, func(t *testing.T) {
-			req, err := http.NewRequest(http.MethodPost, "http://localhost:9090/api/v1/write", nil)
+			body := writev2.Request{}
+			pBuf := proto.NewBuffer(nil)
+			err := pBuf.Marshal(&body)
+			assert.NoError(t, err)
+
+			var compressedBody []byte
+			snappy.Encode(compressedBody, pBuf.Bytes())
+			req, err := http.NewRequest(http.MethodPost, "http://localhost:9090/api/v1/write", bytes.NewBuffer(compressedBody))
 			assert.NoError(t, err)
 
 			req.Header.Set("Content-Type", tc.contentType)
+			req.Header.Set("Content-Encoding", "snappy")
 			resp, err := http.DefaultClient.Do(req)
 			assert.NoError(t, err)
 
 			assert.Equal(t, tc.extectedCode, resp.StatusCode)
+			if tc.extectedCode == http.StatusNoContent { // We went until the end
+				assert.NotEmpty(t, resp.Header.Get("X-Prometheus-Remote-Write-Samples-Written"))
+				assert.NotEmpty(t, resp.Header.Get("X-Prometheus-Remote-Write-Histograms-Written"))
+				assert.NotEmpty(t, resp.Header.Get("X-Prometheus-Remote-Write-Exemplars-Written"))
+			}
 		})
 	}
 }