Support Accept-Encoding header weights with Compress middleware

pkg/middlewares/compress/acceptencoding.go

@@ -0,0 +1,137 @@
+package compress
+
+import (
+	"slices"
+	"strconv"
+	"strings"
+)
+
+const acceptEncodingHeader = "Accept-Encoding"
+
+const (
+	brotliName    = "br"
+	gzipName      = "gzip"
+	identityName  = "identity"
+	wildcardName  = "*"
+	notAcceptable = "not_acceptable"
+)
+
+type Encoding struct {
+	Type   string
+	Weight *float64
+}
+
+func getCompressionType(acceptEncoding []string, defaultType string) string {
+	if defaultType == "" {
+		// Keeps the pre-existing default inside Traefik.
+		defaultType = brotliName
+	}
+
+	encodings, hasWeight := parseAcceptEncoding(acceptEncoding)
+
+	if hasWeight {
+		if len(encodings) == 0 {
+			return identityName
+		}
+
+		encoding := encodings[0]
+
+		if encoding.Type == identityName && encoding.Weight != nil && *encoding.Weight == 0 {
+			return notAcceptable
+		}
+
+		if encoding.Type == wildcardName && encoding.Weight != nil && *encoding.Weight == 0 {
+			return notAcceptable
+		}
+
+		if encoding.Type == wildcardName {
+			return defaultType
+		}
+
+		return encoding.Type
+	}
+
+	for _, dt := range []string{brotliName, gzipName} {
+		if slices.ContainsFunc(encodings, func(e Encoding) bool { return e.Type == dt }) {
+			return dt
+		}
+	}
+
+	if slices.ContainsFunc(encodings, func(e Encoding) bool { return e.Type == wildcardName }) {
+		return defaultType
+	}
+
+	return identityName
+}
+
+func parseAcceptEncoding(acceptEncoding []string) ([]Encoding, bool) {
+	var encodings []Encoding
+	var hasWeight bool
+
+	for _, line := range acceptEncoding {
+		for _, item := range strings.Split(strings.ReplaceAll(line, " ", ""), ",") {
+			parsed := strings.SplitN(item, ";", 2)
+			if len(parsed) == 0 {
+				continue
+			}
+
+			switch parsed[0] {
+			case brotliName, gzipName, identityName, wildcardName:
+				// supported encoding
+			default:
+				continue
+			}
+
+			var weight *float64
+			if len(parsed) > 1 && strings.HasPrefix(parsed[1], "q=") {
+				w, _ := strconv.ParseFloat(strings.TrimPrefix(parsed[1], "q="), 64)
+
+				weight = &w
+				hasWeight = true
+			}
+
+			encodings = append(encodings, Encoding{
+				Type:   parsed[0],
+				Weight: weight,
+			})
+		}
+	}
+
+	slices.SortFunc(encodings, compareEncoding)
+
+	return encodings, hasWeight
+}
+
+func compareEncoding(a, b Encoding) int {
+	lhs, rhs := a.Weight, b.Weight
+
+	if lhs == nil && rhs == nil {
+		return 0
+	}
+
+	if lhs == nil && *rhs == 0 {
+		return -1
+	}
+
+	if lhs == nil {
+		return 1
+	}
+
+	if rhs == nil && *lhs == 0 {
+		return 1
+	}
+
+	if rhs == nil {
+		return -1
+	}
+
+	if *lhs < *rhs {
+		return 1
+	}
+
+	if *lhs > *rhs {
+		return -1
+	}
+
+	return 0
+}