gzip: escape heap allocation (grafana#3922)

* add benchmark

* escape heap alloc

* rm bench test result

* fix lint: add error checking

Author: jungbumwoo

pkg/util/gziphandler/gzip.go

@@ -520,15 +520,22 @@ func handleContentType(contentTypes []parsedContentType, ct string) bool {
 func parseEncodings(s string) (codings, error) {
 	c := make(codings)
 	var e []string
+	var ss string
+	var found bool
 
-	for _, ss := range strings.Split(s, ",") {
+	for {
+		ss, s, found = strings.Cut(s, ",")
 		coding, qvalue, err := parseCoding(ss)
 
 		if err != nil {
 			e = append(e, err.Error())
 		} else {
 			c[coding] = qvalue
 		}
+
+		if !found {
+			break
+		}
 	}
 
 	// TODO (adammck): Use a proper multi-error struct, so the individual errors

pkg/util/gziphandler/gzip_test.go

@@ -15,6 +15,7 @@ import (
 	"net/url"
 	"os"
 	"strconv"
+	"strings"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -614,6 +615,17 @@ func TestContentTypes(t *testing.T) {
 	}
 }
 
+func BenchmarkParseEncodings(b *testing.B) {
+	req := httptest.NewRequest(http.MethodGet, "/whatever", nil)
+	req.Header.Set("Accept-Encoding", strings.Repeat(",", http.DefaultMaxHeaderBytes))
+	b.ReportAllocs()
+	b.ResetTimer()
+	for range b.N {
+		_, err := parseEncodings(req.Header.Get(acceptEncoding))
+		assert.Error(b, err)
+	}
+}
+
 // --------------------------------------------------------------------
 
 func BenchmarkGzipHandler_S2k(b *testing.B)   { benchmark(b, false, 2048) }