review feedback

pkg/loghttp/query.go

@@ -38,6 +38,9 @@ type QueryStatus string
 const (
 	QueryStatusSuccess = "success"
 	QueryStatusFail    = "fail"
+	// How much stack space to allocate for unescaping JSON strings; if a string longer
+	// than this needs to be escaped, it will result in a heap allocation
+	unescapeStackBufSize = 64
 )
 
 // QueryResponse represents the http json response to a Loki range and instant query
@@ -55,7 +58,9 @@ func (q *QueryResponse) UnmarshalJSON(data []byte) error {
 		case "warnings":
 			var warnings []string
 			if _, err := jsonparser.ArrayEach(value, func(value []byte, dataType jsonparser.ValueType, offset int, err error) {
-				warnings = append(warnings, string(value))
+				if dataType == jsonparser.String {
+					warnings = append(warnings, unescapeJSONString(value))
+				}
 			}); err != nil {
 				return err
 			}
@@ -72,6 +77,16 @@ func (q *QueryResponse) UnmarshalJSON(data []byte) error {
 	})
 }
 
+func unescapeJSONString(b []byte) string {
+	var stackbuf [unescapeStackBufSize]byte // stack-allocated array for allocation-free unescaping of small strings
+	bU, err := jsonparser.Unescape(b, stackbuf[:])
+	if err != nil {
+		return ""
+	}
+
+	return string(bU)
+}
+
 // PushRequest models a log stream push but is unmarshalled to proto push format.
 type PushRequest struct {
 	Streams []LogProtoStream `json:"streams"`

pkg/logql/accumulator.go

@@ -4,6 +4,7 @@ import (
 	"container/heap"
 	"context"
 	"fmt"
+	"golang.org/x/exp/maps"
 	"sort"
 	"time"
 
@@ -355,10 +356,7 @@ func (acc *AccumulatedStreams) Result() []logqlmodel.Result {
 		)
 	}
 
-	warnings := make([]string, 0, len(acc.warnings))
-	for w := range acc.warnings {
-		warnings = append(warnings, w)
-	}
+	warnings := maps.Keys(acc.warnings)
 	sort.Strings(warnings)
 
 	res.Warnings = warnings

pkg/logqlmodel/metadata/context.go

@@ -7,6 +7,7 @@ package metadata
 import (
 	"context"
 	"errors"
+	"golang.org/x/exp/maps"
 	"sort"
 	"sync"
 
@@ -79,11 +80,7 @@ func (c *Context) Warnings() []string {
 	c.mtx.Lock()
 	defer c.mtx.Unlock()
 
-	warnings := make([]string, 0, len(c.warnings))
-	for warning := range c.warnings {
-		warnings = append(warnings, warning)
-	}
-
+	warnings := maps.Keys(c.warnings)
 	sort.Strings(warnings)
 
 	return warnings
@@ -121,6 +118,10 @@ func ExtendHeaders(dst map[string][]string, src []*definitions.PrometheusRespons
 }
 
 func AddWarnings(ctx context.Context, warnings ...string) error {
+	if len(warnings) == 0 {
+		return nil
+	}
+
 	context, ok := ctx.Value(metadataKey).(*Context)
 	if !ok {
 		return ErrNoCtxData

pkg/querier/queryrange/codec.go

@@ -6,6 +6,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"golang.org/x/exp/maps"
 	"io"
 	"net/http"
 	"net/url"
@@ -1992,10 +1993,7 @@ func mergeLokiResponse(responses ...queryrangebase.Response) *LokiResponse {
 		}
 	}
 
-	warnings := make([]string, 0, len(uniqueWarnings))
-	for w := range uniqueWarnings {
-		warnings = append(warnings, w)
-	}
+	warnings := maps.Keys(uniqueWarnings)
 	sort.Strings(warnings)
 
 	if len(warnings) == 0 {

pkg/querier/queryrange/queryrangebase/query_range.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"context"
 	"fmt"
+	"golang.org/x/exp/maps"
 	"io"
 	"math"
 	"net/http"
@@ -171,10 +172,7 @@ func (p prometheusCodec) MergeResponse(responses ...Response) (Response, error)
 		}
 	}
 
-	warnings := make([]string, 0, len(uniqueWarnings))
-	for w := range uniqueWarnings {
-		warnings = append(warnings, w)
-	}
+	warnings := maps.Keys(uniqueWarnings)
 	sort.Strings(warnings)
 
 	if len(warnings) == 0 {

pkg/querier/queryrange/querysharding.go

@@ -252,7 +252,6 @@ func (ast *astMapperware) Do(ctx context.Context, r queryrangebase.Request) (que
 		return nil, err
 	}
 
-	// TODO(tpatterson): add warnings to response
 	switch res.Data.Type() {
 	case parser.ValueTypeMatrix:
 		return &LokiPromResponse{

vendor/modules.txt

@@ -1633,6 +1633,7 @@ golang.org/x/crypto/sha3
 # golang.org/x/exp v0.0.0-20240325151524-a685a6edb6d8
 ## explicit; go 1.20
 golang.org/x/exp/constraints
+golang.org/x/exp/maps
 golang.org/x/exp/slices
 # golang.org/x/mod v0.16.0
 ## explicit; go 1.18