logging: Clone array on log filters, prevent side-effects

Fixes https://caddy.community/t/is-caddy-mutating-header-content-from-logging-settings/20947

modules/logging/filters.go

@@ -26,6 +26,7 @@ import (
 	"strings"
 
 	"go.uber.org/zap/zapcore"
+	"golang.org/x/exp/slices"
 
 	"github.com/caddyserver/caddy/v2"
 	"github.com/caddyserver/caddy/v2/caddyconfig/caddyfile"
@@ -100,12 +101,15 @@ func (f *HashFilter) UnmarshalCaddyfile(d *caddyfile.Dispenser) error {
 // Filter filters the input field with the replacement value.
 func (f *HashFilter) Filter(in zapcore.Field) zapcore.Field {
 	if array, ok := in.Interface.(caddyhttp.LoggableStringArray); ok {
-		for i, s := range array {
-			array[i] = hash(s)
+		newArray := slices.Clone(array)
+		for i, s := range newArray {
+			newArray[i] = hash(s)
 		}
+		in.Interface = newArray
 	} else {
 		in.String = hash(in.String)
 	}
+
 	return in
 }
 
@@ -219,9 +223,11 @@ func (m *IPMaskFilter) Provision(ctx caddy.Context) error {
 // Filter filters the input field.
 func (m IPMaskFilter) Filter(in zapcore.Field) zapcore.Field {
 	if array, ok := in.Interface.(caddyhttp.LoggableStringArray); ok {
-		for i, s := range array {
-			array[i] = m.mask(s)
+		newArray := slices.Clone(array)
+		for i, s := range newArray {
+			newArray[i] = m.mask(s)
 		}
+		in.Interface = newArray
 	} else {
 		in.String = m.mask(in.String)
 	}
@@ -580,9 +586,11 @@ func (m *RegexpFilter) Provision(ctx caddy.Context) error {
 // Filter filters the input field with the replacement value if it matches the regexp.
 func (f *RegexpFilter) Filter(in zapcore.Field) zapcore.Field {
 	if array, ok := in.Interface.(caddyhttp.LoggableStringArray); ok {
-		for i, s := range array {
-			array[i] = f.regexp.ReplaceAllString(s, f.Value)
+		newArray := slices.Clone(array)
+		for i, s := range newArray {
+			newArray[i] = f.regexp.ReplaceAllString(s, f.Value)
 		}
+		in.Interface = newArray
 	} else {
 		in.String = f.regexp.ReplaceAllString(in.String, f.Value)
 	}