refactor(cookies,encoding): move loop to it's dedicated function

internals/cookies/encoding.go

@@ -1,7 +1,7 @@
 package cookies
 
 import (
-	"errors"
+	e "errors"
 	"math/bits"
 	"net/http"
 	"reflect"
@@ -21,31 +21,22 @@ func Marshal[T any](c TypedCookie[T]) (http.Cookie, error) {
 	}
 
 	v := []string{}
-	for i := 0; i < rv.NumField(); i++ {
-		f := rv.Type().Field(i)
-		fv := rv.FieldByName(f.Name)
-
-		if fv.Kind() == reflect.Pointer {
-			fv = fv.Elem()
-		}
-
-		if !fv.IsValid() {
-			return http.Cookie{}, errors.New("No such field in object: " + f.Name)
-		}
-
-		t := f.Tag.Get("cookie")
+	err := forEachField(&rv, func(fv *reflect.Value, ft *reflect.StructField) error {
+		t := ft.Tag.Get("cookie")
 		if t == "" {
-			t = f.Name
+			t = ft.Name
 		}
 		tv := strings.Split(t, ",")
 
-		value, err := encodeString(fv)
+		value, err := encodeString(*fv)
 		if err != nil {
-			return http.Cookie{}, errors.Join(errors.New("Unsupportted type in struct: "+fv.Kind().String()), err)
+			return e.Join(e.New("Unsupported type in struct: "+fv.Kind().String()), err)
 		}
 
 		v = append(v, tv[0]+":"+value)
-	}
+
+		return nil
+	})
 
 	return http.Cookie{
 		Name:       c.Name,
@@ -58,19 +49,22 @@ func Marshal[T any](c TypedCookie[T]) (http.Cookie, error) {
 		Secure:     c.Secure,
 		HttpOnly:   c.HttpOnly,
 		SameSite:   c.SameSite,
-	}, nil
+	}, err
 }
 
 func Unmarshal[T any](data http.Cookie, v *TypedCookie[T]) error {
 	if reflect.ValueOf(v).Kind() != reflect.Pointer {
-		return errors.New("`v` is not a pointer: " + reflect.ValueOf(v).Kind().String())
+		return e.New("`v` is not a pointer: " + reflect.ValueOf(v).Kind().String())
+	}
+	if reflect.TypeOf(&v.TypedValue) == nil {
+		return e.New("TypedCookie.TypedValue is not a valid struct type")
 	}
 
 	m := make(map[string]string)
 	for _, pair := range strings.Split(data.Value, "|") {
 		pairV := strings.Split(pair, ":")
 		if len(pairV) == 0 {
-			return errors.New("Error trying to decode cookie value:\n" + data.Value + "\n\nMissing \":\" pair in first slice")
+			return e.New("Error trying to decode cookie value:\n" + data.Value + "\n\nMissing \":\" pair in first slice")
 		}
 
 		key := pairV[0]
@@ -85,55 +79,65 @@ func Unmarshal[T any](data http.Cookie, v *TypedCookie[T]) error {
 		m[key] = value
 	}
 
-	tt := reflect.TypeOf(&v.TypedValue)
 	tv := reflect.ValueOf(&v.TypedValue)
-	if tt == nil {
-		return errors.New("TypedCookie.TypedValue is not a valid struct{} type")
-	}
-
-	if tt.Kind() == reflect.Pointer {
-		tt = tt.Elem()
-	}
 	if tv.Kind() == reflect.Pointer {
 		tv = tv.Elem()
 	}
 
-	for i := 0; i < tt.NumField(); i++ {
-		f := tt.Field(i)
-		fv := tv.FieldByName(f.Name)
-		if fv.Kind() == reflect.Pointer {
-			fv = fv.Elem()
-		}
-
-		if !fv.IsValid() {
-			return errors.New("No such field in object: " + f.Name)
-		}
-		if !fv.CanSet() {
-			return errors.New("Cannot set value of such field in object: " + f.Name)
-		}
-
-		t := f.Tag.Get("cookie")
+	err := forEachField(&tv, func(fv *reflect.Value, ft *reflect.StructField) error {
+		t := ft.Tag.Get("cookie")
 		if t == "" {
-			t = f.Name
+			t = ft.Name
 		}
 		tk := strings.Split(t, ",")[0]
 
 		final, err := decodeString(m[tk], fv.Kind())
 		if err != nil {
-			return errors.Join(errors.New("Unsupportted type in struct: "+fv.Kind().String()), err)
+			return e.Join(e.New("Unsupported type in struct: "+fv.Kind().String()), err)
 		}
 
-		if strings.Contains(strings.ToLower(fv.Kind().String()), "complex") {
+		kStr := strings.ToLower(fv.Kind().String())
+		if strings.Contains(kStr, "complex") {
 			fv.SetComplex(final.(complex128))
-		} else if strings.Contains(strings.ToLower(fv.Kind().String()), "uint") {
+
+		} else if strings.Contains(kStr, "uint") {
 			fv.SetUint(final.(uint64))
-		} else if strings.Contains(strings.ToLower(fv.Kind().String()), "int") {
+
+		} else if strings.Contains(kStr, "int") {
 			fv.SetInt(final.(int64))
+
 		} else {
 			fv.Set(reflect.ValueOf(final))
 		}
+
+		return nil
+	})
+
+	return err
+}
+
+func forEachField(v *reflect.Value, callback func(fv *reflect.Value, ft *reflect.StructField) error) (err error) {
+	t := v.Type()
+
+	for i := 0; i < t.NumField(); i++ {
+		ft := t.Field(i)
+		fv := v.FieldByName(ft.Name)
+
+		if fv.Kind() == reflect.Pointer {
+			fv = fv.Elem()
+		}
+
+		if !fv.IsValid() {
+			return e.New("No such field: " + ft.Name)
+		}
+
+		err = callback(&fv, &ft)
+		if err != nil {
+			return e.Join(e.New("Error while looping through value"), err)
+		}
 	}
-	return nil
+
+	return err
 }
 
 func encodeString(v reflect.Value) (string, error) {
@@ -161,7 +165,7 @@ func encodeString(v reflect.Value) (string, error) {
 		return v.String(), nil
 
 	default:
-		return "", errors.ErrUnsupported
+		return "", e.ErrUnsupported
 	}
 }
 
@@ -209,7 +213,7 @@ func decodeString(v string, k reflect.Kind) (any, error) {
 		final = v
 
 	default:
-		return nil, errors.ErrUnsupported
+		return nil, e.ErrUnsupported
 	}
 
 	return final, err