From 42416d13e7d81a45a4c6487989d084c35357c249 Mon Sep 17 00:00:00 2001
From: Jason Streifling <jason@streifling.com>
Date: Thu, 17 Oct 2024 21:27:54 +0200
Subject: [PATCH] Bring back proper extensionAttributes

---
 commonAttributes.go   | 20 ++++++++++----------
 extensionAttribute.go | 27 +++++++++++++++++++++++++++
 2 files changed, 37 insertions(+), 10 deletions(-)
 create mode 100644 extensionAttribute.go

diff --git a/commonAttributes.go b/commonAttributes.go
index f5641cf..5833c78 100644
--- a/commonAttributes.go
+++ b/commonAttributes.go
@@ -3,9 +3,9 @@ package atom
 import "fmt"
 
 type CommonAttributes struct {
-	Base                IRI         `xml:"base,attr,omitempty"`
-	Lang                LanguageTag `xml:"lang,attr,omitempty"`
-	UndefinedAttributes []string    `xml:",attr"`
+	Base                IRI                   `xml:"base,attr,omitempty"`
+	Lang                LanguageTag           `xml:"lang,attr,omitempty"`
+	UndefinedAttributes []*ExtensionAttribute `xml:",attr"`
 }
 
 // NewCommonAttributes creates a new set of CommonAttributes. It returns a
@@ -15,21 +15,21 @@ func NewCommonAttributes() *CommonAttributes {
 }
 
 // AddExtensionAttribute adds the ExtensionAttribute to the CommonAttributes.
-func (c *CommonAttributes) AddExtensionAttribute(name, value string) {
+func (c *CommonAttributes) AddExtensionAttribute(e *ExtensionAttribute) {
 	if c.UndefinedAttributes == nil {
-		c.UndefinedAttributes = make([]string, 1)
-		c.UndefinedAttributes[0] = fmt.Sprint(name, `="`, value, `"`)
+		c.UndefinedAttributes = make([]*ExtensionAttribute, 1)
+		c.UndefinedAttributes[0] = e
 	} else {
-		c.UndefinedAttributes = append(c.UndefinedAttributes, fmt.Sprint(name, `="`, value, `"`))
+		c.UndefinedAttributes = append(c.UndefinedAttributes, e)
 	}
 }
 
 // Check checks the CommonAttributes for incompatibilities with RFC4287. It
 // returns an error.
 func (c *CommonAttributes) Check() error {
-	for _, a := range c.UndefinedAttributes {
-		if !isValidAttribute(a) {
-			return fmt.Errorf("attribute %v of undefined attributes of common attributes not correctly formatted", a)
+	for i, a := range c.UndefinedAttributes {
+		if err := a.Check(); err != nil {
+			return fmt.Errorf("extension attribute %v of common attributes: %v", i, err)
 		}
 	}
 
diff --git a/extensionAttribute.go b/extensionAttribute.go
new file mode 100644
index 0000000..492fda8
--- /dev/null
+++ b/extensionAttribute.go
@@ -0,0 +1,27 @@
+package atom
+
+import (
+	"encoding/xml"
+	"errors"
+)
+
+type ExtensionAttribute struct {
+	XMLName xml.Name
+	Value   string
+}
+
+// NewExtensionAttribute creates a new ExtensionAttribute. It returns a
+// *ExtensionAttribute.
+func NewExtensionAttribute(name, value string) *ExtensionAttribute {
+	return &ExtensionAttribute{XMLName: xml.Name{Local: name}, Value: value}
+}
+
+// Check checks the ExtensionAttribute for incompatibilities with RFC4287. It
+// returns an error.
+func (e *ExtensionAttribute) Check() error {
+	if e.Value == "" {
+		return errors.New("value of extension attribute empty")
+	}
+
+	return nil
+}