cleanup and simplify middleware implementations, refactor some other code

internal/net/http/middleware/modify_response.go

@@ -2,32 +2,19 @@ package middleware
 
 import (
 	"net/http"
-
-	E "github.com/yusing/go-proxy/internal/error"
 )
 
-type modifyResponse = modifyRequest
-
-var ModifyResponse = &Middleware{withOptions: NewModifyResponse}
-
-func NewModifyResponse(optsRaw OptionsRaw) (*Middleware, E.Error) {
-	mr := new(modifyResponse)
-	mr.m = &Middleware{
-		impl: mr,
-		before: func(next http.HandlerFunc, w ResponseWriter, r *Request) {
-			next(w, r)
-		},
-		modifyResponse: func(resp *Response) error {
-			mr.m.AddTraceResponse("before modify response", resp.Response)
-			mr.modifyHeaders(resp.OriginalRequest, resp, resp.Header)
-			mr.m.AddTraceResponse("after modify response", resp.Response)
-			return nil
-		},
-	}
-	err := Deserialize(optsRaw, &mr.modifyRequestOpts)
-	if err != nil {
-		return nil, err
-	}
-	mr.checkVarSubstitution()
-	return mr.m, nil
+type modifyResponse struct {
+	ModifyRequestOpts
+	*Tracer
+}
+
+var ModifyResponse = NewMiddleware[modifyResponse]()
+
+// modifyResponse implements ResponseModifier.
+func (mr *modifyResponse) modifyResponse(resp *http.Response) error {
+	mr.AddTraceResponse("before modify response", resp)
+	mr.modifyHeaders(resp.Request, resp, resp.Header)
+	mr.AddTraceResponse("after modify response", resp)
+	return nil
 }