Improve error handling for unescaping

runtime/mux.go

@@ -1,6 +1,7 @@
 package runtime
 
 import (
+	"errors"
 	"context"
 	"fmt"
 	"net/http"
@@ -14,7 +15,7 @@ import (
 	"google.golang.org/protobuf/proto"
 )
 
-// UnescapingMode defines the behavior of grpc-gateway for URL escaping.
+// UnescapingMode defines the behavior of ServeMux when unescaping path parameters.
 type UnescapingMode int
 
 const (
@@ -286,9 +287,13 @@ func (s *ServeMux) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 
 		pathParams, err := h.pat.MatchAndEscape(components, verb, s.unescapingMode)
 		if err != nil {
-			if err == ErrMalformedSequence {
+			var mse MalformedSequenceError
+			if ok := errors.As(err, &mse); ok {
 				_, outboundMarshaler := MarshalerForRequest(s, r)
-				s.routingErrorHandler(ctx, s, outboundMarshaler, w, r, http.StatusBadRequest)
+				s.errorHandler(ctx, s, outboundMarshaler, w, r, &HTTPStatusError{
+					HTTPStatus: http.StatusBadRequest,
+					Err:        mse,
+				})
 			}
 			continue
 		}
@@ -305,9 +310,13 @@ func (s *ServeMux) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		for _, h := range handlers {
 			pathParams, err := h.pat.MatchAndEscape(components, verb, s.unescapingMode)
 			if err != nil {
-				if err == ErrMalformedSequence {
+				var mse MalformedSequenceError
+				if ok := errors.As(err, &mse); ok {
 					_, outboundMarshaler := MarshalerForRequest(s, r)
-					s.routingErrorHandler(ctx, s, outboundMarshaler, w, r, http.StatusBadRequest)
+					s.errorHandler(ctx, s, outboundMarshaler, w, r, &HTTPStatusError{
+						HTTPStatus: http.StatusBadRequest,
+						Err:        mse,
+					})
 				}
 				continue
 			}

runtime/pattern.go

@@ -3,6 +3,7 @@ package runtime
 import (
 	"errors"
 	"fmt"
+	"strconv"
 	"strings"
 
 	"github.com/grpc-ecosystem/grpc-gateway/v2/utilities"
@@ -18,6 +19,12 @@ var (
 	ErrMalformedSequence = errors.New("malformed escape sequence")
 )
 
+type MalformedSequenceError string
+
+func (e MalformedSequenceError) Error() string {
+	return "malformed path escape " + strconv.Quote(string(e))
+}
+
 type op struct {
 	code    utilities.OpCode
 	operand int
@@ -180,7 +187,7 @@ func (p Pattern) MatchAndEscape(components []string, verb string, unescapingMode
 				}
 			} else if op.code == utilities.OpPush {
 				if c, err = unescape(c, unescapingMode, false); err != nil {
-					return nil, ErrMalformedSequence
+					return nil, err
 				}
 			}
 			stack = append(stack, c)
@@ -193,7 +200,7 @@ func (p Pattern) MatchAndEscape(components []string, verb string, unescapingMode
 			end -= p.tailLen
 			c := strings.Join(components[pos:end], "/")
 			if c, err = unescape(c, unescapingMode, true); err != nil {
-				return nil, ErrMalformedSequence
+				return nil, err
 			}
 			stack = append(stack, c)
 			pos = end
@@ -343,7 +350,7 @@ func unescape(s string, mode UnescapingMode, multisegment bool) (string, error)
 					s = s[:3]
 				}
 
-				return "", ErrMalformedSequence
+				return "", MalformedSequenceError(s)
 			}
 			i += 3
 		} else {