frontend: Expose query lookback delta

pkg/frontend/querymiddleware/codec.go

@@ -133,6 +133,8 @@ type MetricsQueryRequest interface {
 	// GetHints returns hints that could be optionally attached to the request to pass down the stack.
 	// These hints can be used to optimize the query execution.
 	GetHints() *Hints
+	// GetLookbackDelta returns the lookback delta for the request.
+	GetLookbackDelta() time.Duration
 	// WithID clones the current request with the provided ID.
 	WithID(id int64) (MetricsQueryRequest, error)
 	// WithStartEnd clone the current request with different start and end timestamp.

pkg/frontend/querymiddleware/model_extra.go

@@ -153,6 +153,10 @@ func (r *PrometheusRangeQueryRequest) GetHints() *Hints {
 	return r.hints
 }
 
+func (r *PrometheusRangeQueryRequest) GetLookbackDelta() time.Duration {
+	return r.lookbackDelta
+}
+
 // WithID clones the current `PrometheusRangeQueryRequest` with the provided ID.
 func (r *PrometheusRangeQueryRequest) WithID(id int64) (MetricsQueryRequest, error) {
 	newRequest := *r
@@ -345,6 +349,10 @@ func (r *PrometheusInstantQueryRequest) GetHints() *Hints {
 	return r.hints
 }
 
+func (r *PrometheusInstantQueryRequest) GetLookbackDelta() time.Duration {
+	return r.lookbackDelta
+}
+
 func (r *PrometheusInstantQueryRequest) WithID(id int64) (MetricsQueryRequest, error) {
 	newRequest := *r
 	newRequest.headers = cloneHeaders(r.headers)

pkg/frontend/querymiddleware/remote_read.go

@@ -11,6 +11,7 @@ import (
 	"net/http"
 	"net/url"
 	"strconv"
+	"time"
 
 	"github.com/golang/snappy"
 	"github.com/opentracing/opentracing-go"
@@ -285,6 +286,10 @@ func (r *remoteReadQueryRequest) GetHeaders() []*PrometheusHeader {
 	return nil
 }
 
+func (r *remoteReadQueryRequest) GetLookbackDelta() time.Duration {
+	return 0
+}
+
 func (r *remoteReadQueryRequest) WithID(_ int64) (MetricsQueryRequest, error) {
 	return nil, apierror.New(apierror.TypeInternal, "remoteReadQueryRequest.WithID not implemented")
 }