feat: add SetOnResponse cfg

README.md

@@ -18,7 +18,13 @@ To choose a Rule you have to fill the `Type` field with one of the following:
 - 'RewriteValueRule': to rewrite header values
 - 'Set'             : to Set a header
 
-Each Rule can be named with the `Name` field
+Each Rule can be named with the `Name` field.
+
+Each Rule can also be configured to change headers on the request or the
+response by using the `SetOnResponse` configuration.
+If `SetOnResponse` is set to `true`, the header will be changed on the response.
+Otherwise, it will be changed on the request.
+Its default value is `false`.
 
 ### Rename
 
@@ -177,6 +183,7 @@ Foo: X-Test
 # Modified header:
 Foo: Y-Test
 ```
+
 ### Careful
 
 The rules will be evaluated in the order of definition

pkg/handler/deleter/delete.go

@@ -10,6 +10,12 @@ func Validate(rule types.Rule) error {
 	return nil
 }
 
-func Handle(_ http.ResponseWriter, req *http.Request, rule types.Rule) {
+func Handle(rw http.ResponseWriter, req *http.Request, rule types.Rule) {
+	if rule.SetOnResponse {
+		rw.Header().Del(rule.Name)
+
+		return
+	}
+
 	req.Header.Del(rule.Header)
 }

pkg/handler/deleter/delete_test.go

@@ -82,7 +82,6 @@ func TestValidation(t *testing.T) {
 		{
 			name: "valid rule",
 			rule: types.Rule{
-				Name:   "Delete Rule",
 				Header: "not-empty",
 				Type:   types.Delete,
 			},

pkg/handler/join/join.go

@@ -15,7 +15,7 @@ func Validate(rule types.Rule) error {
 	return nil
 }
 
-func Handle(_ http.ResponseWriter, req *http.Request, rule types.Rule) {
+func Handle(rw http.ResponseWriter, req *http.Request, rule types.Rule) {
 	val, ok := req.Header[rule.Header]
 	if !ok {
 		return
@@ -26,6 +26,12 @@ func Handle(_ http.ResponseWriter, req *http.Request, rule types.Rule) {
 		newHeaderVal += rule.Sep + getValue(value, rule.HeaderPrefix, req)
 	}
 
+	if rule.SetOnResponse {
+		rw.Header().Set(rule.Name, newHeaderVal)
+
+		return
+	}
+
 	req.Header.Set(rule.Header, newHeaderVal)
 }
 

pkg/handler/rename/rename.go

@@ -20,16 +20,24 @@ func Validate(rule types.Rule) error {
 	return nil
 }
 
-func Handle(_ http.ResponseWriter, req *http.Request, rule types.Rule) {
+func Handle(rw http.ResponseWriter, req *http.Request, rule types.Rule) {
 	for headerName, headerValues := range req.Header {
 		if matched := rule.Regexp.Match([]byte(headerName)); !matched {
 			continue
 		}
 
-		req.Header.Del(headerName)
+		if rule.SetOnResponse {
+			rw.Header().Del(headerName)
+		} else {
+			req.Header.Del(headerName)
+		}
 
 		for _, val := range headerValues {
-			req.Header.Set(rule.Value, val)
+			if rule.SetOnResponse {
+				rw.Header().Set(rule.Value, val)
+			} else {
+				req.Header.Set(rule.Value, val)
+			}
 		}
 	}
 }

pkg/handler/rewrite/rewrite.go

@@ -25,21 +25,34 @@ func Validate(rule types.Rule) error {
 	return nil
 }
 
-func Handle(_ http.ResponseWriter, req *http.Request, rule types.Rule) {
-	for headerName, headerValues := range req.Header {
+func Handle(rw http.ResponseWriter, req *http.Request, rule types.Rule) {
+	headers := req.Header
+	if rule.SetOnResponse {
+		headers = rw.Header()
+	}
+
+	for headerName, headerValues := range headers {
 		if matched := rule.Regexp.Match([]byte(headerName)); !matched {
 			continue
 		}
 
-		req.Header.Del(headerName)
+		if rule.SetOnResponse {
+			rw.Header().Del(headerName)
+		} else {
+			req.Header.Del(headerName)
+		}
 
 		for _, headerValue := range headerValues {
 			replacedHeaderValue := rule.ValueReplace
 			ruleValueRegexp := regexp.MustCompile(rule.Value)
 			captures := ruleValueRegexp.FindStringSubmatch(headerValue)
 
 			if len(captures) == 0 || captures[0] == "" {
-				req.Header.Add(headerName, headerValue)
+				if rule.SetOnResponse {
+					rw.Header().Set(rule.Header, replacedHeaderValue)
+				} else {
+					req.Header.Set(headerName, headerValue)
+				}
 
 				continue
 			}
@@ -49,7 +62,11 @@ func Handle(_ http.ResponseWriter, req *http.Request, rule types.Rule) {
 				replacedHeaderValue = strings.ReplaceAll(replacedHeaderValue, placeholder, capture)
 			}
 
-			req.Header.Add(headerName, replacedHeaderValue)
+			if rule.SetOnResponse {
+				rw.Header().Set(rule.Header, replacedHeaderValue)
+			} else {
+				req.Header.Set(headerName, replacedHeaderValue)
+			}
 		}
 	}
 }

pkg/handler/set/set.go

@@ -15,5 +15,11 @@ func Validate(rule types.Rule) error {
 }
 
 func Handle(_ http.ResponseWriter, req *http.Request, rule types.Rule) {
+	if rule.SetOnResponse {
+		req.Header.Set(rule.Header, rule.Value)
+
+		return
+	}
+
 	req.Header.Set(rule.Header, rule.Value)
 }

pkg/types/types.go

@@ -32,6 +32,8 @@ type Rule struct {
 	Value        string         `yaml:"Value"`
 	ValueReplace string         `yaml:"ValueReplace"` // value used as replacement in rewrite
 	Values       []string       `yaml:"Values"`       // values to join
+	// if SetOnResponse is true, the header will be changed on the response. It will be on the request otherwise (default).
+	SetOnResponse bool `yaml:"SetOnRequest"`
 }
 
 var ErrMissingRequiredFields = errors.New("missing required fields")