Added more error handling and necessary functions

commonAttributes.go

@@ -1,10 +1,13 @@
 package atom
 
-import "encoding/xml"
+import (
+	"encoding/xml"
+	"errors"
+)
 
 type CommonAttributes struct {
-	Base                IRI         `xml:"base,attr,omitempty"`
-	Lang                LanguageTag `xml:"lang,attr,omitempty"`
+	Base                string      `xml:"base,attr,omitempty"` // IRI
+	Lang                string      `xml:"lang,attr,omitempty"` // LanguageTag
 	UndefinedAttributes []*xml.Attr `xml:",attr,omitempty"`
 }
 
@@ -14,12 +17,21 @@ func NewCommonAttributes() *CommonAttributes {
 	return new(CommonAttributes)
 }
 
-// AddExtensionAttribute adds the ExtensionAttribute to the CommonAttributes.
-func (c *CommonAttributes) AddExtensionAttribute(name, value string) {
+// AddAttribute adds the Attribute to the CommonAttributes. It returns an error.
+func (c *CommonAttributes) AddAttribute(name, value string) error {
+	if name == "" {
+		return errors.New("error adding attribute: name string empty")
+	}
+	if value == "" {
+		return errors.New("error adding attribute: value string empty")
+	}
+
 	if c.UndefinedAttributes == nil {
 		c.UndefinedAttributes = make([]*xml.Attr, 1)
 		c.UndefinedAttributes[0] = &xml.Attr{Name: xml.Name{Local: name}, Value: value}
 	} else {
 		c.UndefinedAttributes = append(c.UndefinedAttributes, &xml.Attr{Name: xml.Name{Local: name}, Value: value})
 	}
+
+	return nil
 }