fix(distributor): relax content-type check

CHANGELOG.md

@@ -83,7 +83,7 @@
 * [BUGFIX] MQE: Fix deriv with histograms #10383
 * [BUGFIX] PromQL: Fix <aggr_over_time> functions with histograms https://github.com/prometheus/prometheus/pull/15711 #10400
 * [BUGFIX] MQE: Fix <aggr_over_time> functions with histograms #10400
-* [BUGFIX] Distributor: return HTTP status 415 Unsupported Media Type instead of 200 Success for Remote Write 2.0 until we support it. #10423
+* [BUGFIX] Distributor: return HTTP status 415 Unsupported Media Type instead of 200 Success for Remote Write 2.0 until we support it. #10423 #10916
 * [BUGFIX] Query-frontend: Add flag `-query-frontend.prom2-range-compat` and corresponding YAML to rewrite queries with ranges that worked in Prometheus 2 but are invalid in Prometheus 3. #10445 #10461 #10502
 * [BUGFIX] Distributor: Fix edge case at the HA-tracker with memberlist as KVStore, where when a replica in the KVStore is marked as deleted but not yet removed, it fails to update the KVStore. #10443
 * [BUGFIX] Distributor: Fix panics in `DurationWithJitter` util functions when computed variance is zero. #10507

pkg/distributor/push.go

@@ -251,7 +251,9 @@ func isRemoteWrite2(r *http.Request) (bool, error) {
 	}
 	parts := strings.Split(contentType, ";")
 	if parts[0] != appProtoContentType {
-		return false, fmt.Errorf("expected %v as the first (media) part, got %v content-type", appProtoContentType, contentType)
+		// We didn't use to check the content type so if someone wrote for
+		// example text/plain here, we'll accept and assume it is v1.
+		return false, nil
 	}
 
 	// Parse potential https://www.rfc-editor.org/rfc/rfc9110#parameter

pkg/distributor/push_test.go

@@ -57,6 +57,14 @@ func TestHandler_remoteWrite(t *testing.T) {
 	assert.Equal(t, 200, resp.Code)
 }
 
+func TestHandler_remoteWriteWithMalformedRequest(t *testing.T) {
+	req := createMalformedRW1Request(t, createPrometheusRemoteWriteProtobuf(t))
+	resp := httptest.NewRecorder()
+	handler := Handler(100000, nil, nil, false, false, validation.MockDefaultOverrides(), RetryConfig{}, verifyWritePushFunc(t, mimirpb.API), nil, log.NewNopLogger())
+	handler.ServeHTTP(resp, req)
+	assert.Equal(t, 200, resp.Code)
+}
+
 func TestOTelMetricsToMetadata(t *testing.T) {
 	otelMetrics := pmetric.NewMetrics()
 	rs := otelMetrics.ResourceMetrics().AppendEmpty()
@@ -525,6 +533,22 @@ func createRequest(t testing.TB, protobuf []byte) *http.Request {
 	return req
 }
 
+func createMalformedRW1Request(t testing.TB, protobuf []byte) *http.Request {
+	t.Helper()
+	inoutBytes := snappy.Encode(nil, protobuf)
+	req, err := http.NewRequest("POST", "http://localhost/", bytes.NewReader(inoutBytes))
+	require.NoError(t, err)
+	req.Header.Add("Content-Encoding", "snappy")
+	req.Header.Set("Content-Type", "text/plain")
+
+	const tenantID = "test"
+	req.Header.Set("X-Scope-OrgID", tenantID)
+	ctx := user.InjectOrgID(context.Background(), tenantID)
+	req = req.WithContext(ctx)
+
+	return req
+}
+
 func createPrometheusRemoteWriteProtobuf(t testing.TB) []byte {
 	t.Helper()
 	input := prompb.WriteRequest{