fix(otlp): Write status on error

go.mod

@@ -364,7 +364,7 @@ require (
 	golang.org/x/tools v0.23.0 // indirect
 	google.golang.org/genproto v0.0.0-20241113202542-65e8d215514f // indirect
 	google.golang.org/genproto/googleapis/api v0.0.0-20241104194629-dd2ea8efbc28 // indirect
-	google.golang.org/genproto/googleapis/rpc v0.0.0-20241113202542-65e8d215514f // indirect
+	google.golang.org/genproto/googleapis/rpc v0.0.0-20241113202542-65e8d215514f
 	gopkg.in/fsnotify/fsnotify.v1 v1.4.7 // indirect
 	gopkg.in/inf.v0 v0.9.1 // indirect
 	gopkg.in/tomb.v1 v1.0.0-20141024135613-dd632973f1e7 // indirect

pkg/distributor/http.go

@@ -19,38 +19,19 @@ import (
 
 // PushHandler reads a snappy-compressed proto from the HTTP body.
 func (d *Distributor) PushHandler(w http.ResponseWriter, r *http.Request) {
-	d.pushHandler(w, r, push.ParseLokiRequest)
+	d.pushHandler(w, r, push.ParseLokiRequest, push.HTTPError)
 }
 
 func (d *Distributor) OTLPPushHandler(w http.ResponseWriter, r *http.Request) {
-	interceptor := newOtelErrorHeaderInterceptor(w)
-	d.pushHandler(interceptor, r, push.ParseOTLPRequest)
+	d.pushHandler(w, r, push.ParseOTLPRequest, push.OTLPError)
 }
 
-// otelErrorHeaderInterceptor maps 500 errors to 503.
-// According to the OTLP specification, 500 errors are never retried on the client side, but 503 are.
-type otelErrorHeaderInterceptor struct {
-	http.ResponseWriter
-}
-
-func newOtelErrorHeaderInterceptor(w http.ResponseWriter) *otelErrorHeaderInterceptor {
-	return &otelErrorHeaderInterceptor{ResponseWriter: w}
-}
-
-func (i *otelErrorHeaderInterceptor) WriteHeader(statusCode int) {
-	if statusCode == http.StatusInternalServerError {
-		statusCode = http.StatusServiceUnavailable
-	}
-
-	i.ResponseWriter.WriteHeader(statusCode)
-}
-
-func (d *Distributor) pushHandler(w http.ResponseWriter, r *http.Request, pushRequestParser push.RequestParser) {
+func (d *Distributor) pushHandler(w http.ResponseWriter, r *http.Request, pushRequestParser push.RequestParser, errorWriter push.ErrorWriter) {
 	logger := util_log.WithContext(r.Context(), util_log.Logger)
 	tenantID, err := tenant.TenantID(r.Context())
 	if err != nil {
 		level.Error(logger).Log("msg", "error getting tenant id", "err", err)
-		http.Error(w, err.Error(), http.StatusBadRequest)
+		errorWriter(w, err.Error(), http.StatusBadRequest, logger)
 		return
 	}
 
@@ -70,7 +51,7 @@ func (d *Distributor) pushHandler(w http.ResponseWriter, r *http.Request, pushRe
 		}
 		d.writeFailuresManager.Log(tenantID, fmt.Errorf("couldn't parse push request: %w", err))
 
-		http.Error(w, err.Error(), http.StatusBadRequest)
+		errorWriter(w, err.Error(), http.StatusBadRequest, logger)
 		return
 	}
 
@@ -106,7 +87,7 @@ func (d *Distributor) pushHandler(w http.ResponseWriter, r *http.Request, pushRe
 				"err", body,
 			)
 		}
-		http.Error(w, body, int(resp.Code))
+		errorWriter(w, body, int(resp.Code), logger)
 	} else {
 		if d.tenantConfigs.LogPushRequest(tenantID) {
 			level.Debug(logger).Log(
@@ -115,7 +96,7 @@ func (d *Distributor) pushHandler(w http.ResponseWriter, r *http.Request, pushRe
 				"err", err.Error(),
 			)
 		}
-		http.Error(w, err.Error(), http.StatusInternalServerError)
+		errorWriter(w, err.Error(), http.StatusInternalServerError, logger)
 	}
 }
 

pkg/distributor/http_test.go

@@ -78,43 +78,11 @@ func TestRequestParserWrapping(t *testing.T) {
 	req, err := http.NewRequestWithContext(ctx, http.MethodPost, "fake-path", nil)
 	require.NoError(t, err)
 
-	distributors[0].pushHandler(httptest.NewRecorder(), req, stubParser)
+	distributors[0].pushHandler(httptest.NewRecorder(), req, stubParser, push.HTTPError)
 
 	require.True(t, called)
 }
 
-func Test_OtelErrorHeaderInterceptor(t *testing.T) {
-	for _, tc := range []struct {
-		name         string
-		inputCode    int
-		expectedCode int
-	}{
-		{
-			name:         "500",
-			inputCode:    http.StatusInternalServerError,
-			expectedCode: http.StatusServiceUnavailable,
-		},
-		{
-			name:         "400",
-			inputCode:    http.StatusBadRequest,
-			expectedCode: http.StatusBadRequest,
-		},
-		{
-			name:         "204",
-			inputCode:    http.StatusNoContent,
-			expectedCode: http.StatusNoContent,
-		},
-	} {
-		t.Run(tc.name, func(t *testing.T) {
-			r := httptest.NewRecorder()
-			i := newOtelErrorHeaderInterceptor(r)
-
-			http.Error(i, "error", tc.inputCode)
-			require.Equal(t, tc.expectedCode, r.Code)
-		})
-	}
-}
-
 func stubParser(
 	_ string,
 	_ *http.Request,

pkg/loghttp/push/otlp_test.go

@@ -4,6 +4,8 @@ import (
 	"context"
 	"encoding/base64"
 	"fmt"
+	"net/http"
+	"net/http/httptest"
 	"testing"
 	"time"
 
@@ -13,6 +15,8 @@ import (
 	"github.com/stretchr/testify/require"
 	"go.opentelemetry.io/collector/pdata/pcommon"
 	"go.opentelemetry.io/collector/pdata/plog"
+	"google.golang.org/genproto/googleapis/rpc/status"
+	"google.golang.org/protobuf/proto"
 
 	"github.com/grafana/loki/pkg/push"
 
@@ -733,3 +737,41 @@ type fakeRetention struct{}
 func (f fakeRetention) RetentionPeriodFor(_ string, _ labels.Labels) time.Duration {
 	return time.Hour
 }
+
+func TestOtlpError(t *testing.T) {
+	for _, tc := range []struct {
+		name         string
+		msg          string
+		inCode       int
+		expectedCode int
+	}{
+		{
+			name:         "500 error maps 503",
+			msg:          "test error 500 to 503",
+			inCode:       http.StatusInternalServerError,
+			expectedCode: http.StatusServiceUnavailable,
+		},
+		{
+			name:         "other error",
+			msg:          "test error",
+			inCode:       http.StatusForbidden,
+			expectedCode: http.StatusForbidden,
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			logger := log.NewNopLogger()
+
+			r := httptest.NewRecorder()
+			OTLPError(r, tc.msg, tc.inCode, logger)
+
+			require.Equal(t, tc.expectedCode, r.Code)
+			require.Equal(t, "application/octet-stream", r.Header().Get("Content-Type"))
+
+			respStatus := &status.Status{}
+			require.NoError(t, proto.Unmarshal(r.Body.Bytes(), respStatus))
+
+			require.Equal(t, tc.msg, respStatus.Message)
+			require.EqualValues(t, 0, respStatus.Code)
+		})
+	}
+}

pkg/loghttp/push/push.go

@@ -16,17 +16,19 @@ import (
 
 	"github.com/dustin/go-humanize"
 	"github.com/go-kit/log"
+	"github.com/gogo/protobuf/proto"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/promauto"
 	"github.com/prometheus/prometheus/model/labels"
-
-	loki_util "github.com/grafana/loki/v3/pkg/util"
+	"google.golang.org/grpc/codes"
+	grpcstatus "google.golang.org/grpc/status"
 
 	"github.com/grafana/loki/v3/pkg/analytics"
 	"github.com/grafana/loki/v3/pkg/loghttp"
 	"github.com/grafana/loki/v3/pkg/logproto"
 	"github.com/grafana/loki/v3/pkg/logql/syntax"
 	"github.com/grafana/loki/v3/pkg/util"
+	loki_util "github.com/grafana/loki/v3/pkg/util"
 	"github.com/grafana/loki/v3/pkg/util/constants"
 	"github.com/grafana/loki/v3/pkg/util/unmarshal"
 	unmarshal2 "github.com/grafana/loki/v3/pkg/util/unmarshal/legacy"
@@ -86,6 +88,7 @@ func (EmptyLimits) DiscoverServiceName(string) []string {
 type (
 	RequestParser        func(userID string, r *http.Request, tenantsRetention TenantsRetention, limits Limits, tracker UsageTracker, logPushRequestStreams bool, logger log.Logger) (*logproto.PushRequest, *Stats, error)
 	RequestParserWrapper func(inner RequestParser) RequestParser
+	ErrorWriter          func(w http.ResponseWriter, error string, code int, logger log.Logger)
 )
 
 type Stats struct {
@@ -307,3 +310,62 @@ func RetentionPeriodToString(retentionPeriod time.Duration) string {
 	}
 	return retentionHours
 }
+
+// OTLPError writes an OTLP-compliant error response to the given http.ResponseWriter.
+//
+// According to the OTLP spec: https://opentelemetry.io/docs/specs/otlp/#failures-1
+// Re. the error response format
+// > If the processing of the request fails, the server MUST respond with appropriate HTTP 4xx or HTTP 5xx status code.
+// > The response body for all HTTP 4xx and HTTP 5xx responses MUST be a Protobuf-encoded Status message that describes the problem.
+// > This specification does not use Status.code field and the server MAY omit Status.code field.
+// > The clients are not expected to alter their behavior based on Status.code field but MAY record it for troubleshooting purposes.
+// > The Status.message field SHOULD contain a developer-facing error message as defined in Status message schema.
+//
+// Re. retryable errors
+// > The requests that receive a response status code listed in following table SHOULD be retried.
+// > All other 4xx or 5xx response status codes MUST NOT be retried
+// > 429 Too Many Requests
+// > 502 Bad Gateway
+// > 503 Service Unavailable
+// > 504 Gateway Timeout
+// In loki, we expect clients to retry on 500 errors, so we map 500 errors to 503.
+func OTLPError(w http.ResponseWriter, error string, code int, logger log.Logger) {
+	// Map 500 errors to 503. 500 errors are never retried on the client side, but 503 are.
+	if code == http.StatusInternalServerError {
+		code = http.StatusServiceUnavailable
+	}
+
+	// As per the OTLP spec, we send the status code on the http header.
+	w.WriteHeader(code)
+
+	// Status 0 because we omit the Status.code field.
+	status := grpcstatus.New(0, error).Proto()
+	respBytes, err := proto.Marshal(status)
+	if err != nil {
+		level.Error(logger).Log("msg", "failed to marshal error response", "error", err)
+		writeResponseFailedBody, _ := proto.Marshal(grpcstatus.New(
+			codes.Internal,
+			fmt.Sprintf("failed to marshal error response. original error: %s", err.Error()),
+		).Proto())
+		_, _ = w.Write(writeResponseFailedBody)
+		return
+	}
+
+	w.Header().Set(contentType, "application/octet-stream")
+	if _, err = w.Write(respBytes); err != nil {
+		level.Error(logger).Log("msg", "failed to write error response", "error", err)
+		writeResponseFailedBody, _ := proto.Marshal(grpcstatus.New(
+			codes.Internal,
+			fmt.Sprintf("failed write error. original error: %s", err.Error()),
+		).Proto())
+		_, _ = w.Write(writeResponseFailedBody)
+	}
+}
+
+var _ ErrorWriter = OTLPError
+
+func HTTPError(w http.ResponseWriter, error string, code int, _ log.Logger) {
+	http.Error(w, error, code)
+}
+
+var _ ErrorWriter = HTTPError