refactor(querytee): move response comparator files to dedicated package

This change relocates response comparator logic to its own package to
prevent cyclic imports and improve code organization.
No functional changes.

Author: jnewbigin

cmd/querytee/main.go

@@ -9,6 +9,7 @@ import (
 	"github.com/grafana/dskit/log"
 	"github.com/grafana/dskit/server"
 	"github.com/grafana/dskit/tracing"
+	"github.com/grafana/loki/v3/tools/querytee/response_comparator"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/collectors"
 
@@ -85,7 +86,7 @@ func exit(code int) {
 }
 
 func lokiReadRoutes(cfg Config) []querytee.Route {
-	samplesComparator := querytee.NewSamplesComparator(querytee.SampleComparisonOptions{
+	samplesComparator := response_comparator.NewSamplesComparator(response_comparator.SampleComparisonOptions{
 		Tolerance:         cfg.ProxyConfig.ValueComparisonTolerance,
 		UseRelativeError:  cfg.ProxyConfig.UseRelativeError,
 		SkipRecentSamples: cfg.ProxyConfig.SkipRecentSamples,

tools/querytee/proxy.go

@@ -19,6 +19,7 @@ import (
 	"github.com/gorilla/mux"
 	"github.com/grafana/dskit/flagext"
 	"github.com/grafana/dskit/middleware"
+	"github.com/grafana/loki/v3/tools/querytee/response_comparator"
 	"github.com/pkg/errors"
 	"github.com/prometheus/client_golang/prometheus"
 
@@ -71,7 +72,7 @@ type Route struct {
 	Path               string
 	RouteName          string
 	Methods            []string
-	ResponseComparator ResponsesComparator
+	ResponseComparator response_comparator.ResponsesComparator
 }
 
 type Proxy struct {
@@ -240,7 +241,7 @@ func (p *Proxy) Start() error {
 
 	// register read routes
 	for _, route := range p.readRoutes {
-		var comparator ResponsesComparator
+		var comparator response_comparator.ResponsesComparator
 		if p.cfg.CompareResponses {
 			comparator = route.ResponseComparator
 		}

tools/querytee/proxy_endpoint.go

@@ -14,22 +14,14 @@ import (
 	"github.com/go-kit/log"
 	"github.com/go-kit/log/level"
 	"github.com/grafana/loki/v3/tools/querytee/goldfish"
+	"github.com/grafana/loki/v3/tools/querytee/response_comparator"
 )
 
-type ResponsesComparator interface {
-	Compare(expected, actual []byte, queryEvaluationTime time.Time) (*ComparisonSummary, error)
-}
-
-type ComparisonSummary struct {
-	skipped        bool
-	missingMetrics int
-}
-
 type ProxyEndpoint struct {
 	backends   []*ProxyBackend
 	metrics    *ProxyMetrics
 	logger     log.Logger
-	comparator ResponsesComparator
+	comparator response_comparator.ResponsesComparator
 
 	instrumentCompares bool
 
@@ -43,7 +35,7 @@ type ProxyEndpoint struct {
 	goldfishManager *goldfish.Manager
 }
 
-func NewProxyEndpoint(backends []*ProxyBackend, routeName string, metrics *ProxyMetrics, logger log.Logger, comparator ResponsesComparator, instrumentCompares bool) *ProxyEndpoint {
+func NewProxyEndpoint(backends []*ProxyBackend, routeName string, metrics *ProxyMetrics, logger log.Logger, comparator response_comparator.ResponsesComparator, instrumentCompares bool) *ProxyEndpoint {
 	hasPreferredBackend := false
 	for _, backend := range backends {
 		if backend.preferred {
@@ -195,12 +187,12 @@ func (p *ProxyEndpoint) executeBackendRequests(r *http.Request, resCh chan *Back
 					"route-name", p.routeName,
 					"query", r.URL.RawQuery, "err", err)
 				result = comparisonFailed
-			} else if summary != nil && summary.skipped {
+			} else if summary != nil && summary.Skipped {
 				result = comparisonSkipped
 			}
 
 			if p.instrumentCompares && summary != nil {
-				p.metrics.missingMetrics.WithLabelValues(p.backends[i].name, p.routeName, result, issuer).Observe(float64(summary.missingMetrics))
+				p.metrics.missingMetrics.WithLabelValues(p.backends[i].name, p.routeName, result, issuer).Observe(float64(summary.MissingMetrics))
 			}
 			p.metrics.responsesComparedTotal.WithLabelValues(p.backends[i].name, p.routeName, result, issuer).Inc()
 		}
@@ -275,9 +267,9 @@ func (p *ProxyEndpoint) waitBackendResponseForDownstream(resCh chan *BackendResp
 	return responses[0]
 }
 
-func (p *ProxyEndpoint) compareResponses(expectedResponse, actualResponse *BackendResponse, queryEvalTime time.Time) (*ComparisonSummary, error) {
+func (p *ProxyEndpoint) compareResponses(expectedResponse, actualResponse *BackendResponse, queryEvalTime time.Time) (*response_comparator.ComparisonSummary, error) {
 	if expectedResponse.err != nil {
-		return &ComparisonSummary{skipped: true}, nil
+		return &response_comparator.ComparisonSummary{Skipped: true}, nil
 	}
 
 	if actualResponse.err != nil {
@@ -286,7 +278,7 @@ func (p *ProxyEndpoint) compareResponses(expectedResponse, actualResponse *Backe
 
 	// compare response body only if we get a 200
 	if expectedResponse.status != 200 {
-		return &ComparisonSummary{skipped: true}, nil
+		return &response_comparator.ComparisonSummary{Skipped: true}, nil
 	}
 
 	if actualResponse.status != 200 {

tools/querytee/proxy_endpoint_test.go

@@ -15,6 +15,7 @@ import (
 	"github.com/go-kit/log"
 	"github.com/grafana/loki/v3/pkg/goldfish"
 	querytee_goldfish "github.com/grafana/loki/v3/tools/querytee/goldfish"
+	"github.com/grafana/loki/v3/tools/querytee/response_comparator"
 	"github.com/pkg/errors"
 	"github.com/prometheus/client_golang/prometheus"
 	prom_testutil "github.com/prometheus/client_golang/prometheus/testutil"
@@ -425,8 +426,8 @@ func Test_BackendResponse_statusCode(t *testing.T) {
 
 type mockComparator struct{}
 
-func (c *mockComparator) Compare(_, _ []byte, _ time.Time) (*ComparisonSummary, error) {
-	return &ComparisonSummary{missingMetrics: 12}, nil
+func (c *mockComparator) Compare(_, _ []byte, _ time.Time) (*response_comparator.ComparisonSummary, error) {
+	return &response_comparator.ComparisonSummary{MissingMetrics: 12}, nil
 }
 
 func Test_endToEnd_traceIDFlow(t *testing.T) {

tools/querytee/proxy_test.go

@@ -13,6 +13,7 @@ import (
 
 	"github.com/go-kit/log"
 	"github.com/gorilla/mux"
+	"github.com/grafana/loki/v3/tools/querytee/response_comparator"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
@@ -25,7 +26,9 @@ var testWriteRoutes = []Route{}
 
 type testComparator struct{}
 
-func (testComparator) Compare(_, _ []byte, _ time.Time) (*ComparisonSummary, error) { return nil, nil }
+func (testComparator) Compare(_, _ []byte, _ time.Time) (*response_comparator.ComparisonSummary, error) {
+	return nil, nil
+}
 
 func Test_NewProxy(t *testing.T) {
 	cfg := ProxyConfig{}