Create needed functions for common attributes and their extensions

It seems that undefined content is only mentioned in RFC4287 because
link and category are elements and those usually need some content.

README.md

@@ -1,4 +1,3 @@
-# atom-feed
+# atom
 
 An extensible implementation of an Atom feed that aims to be very close to RFC4287.
-

category.go

@@ -1,22 +1,23 @@
 package atom
 
 import (
+	"encoding/xml"
 	"errors"
 	"fmt"
 	"html"
 )
 
 type Category struct {
+	XMLName xml.Name `xml:"category"`
 	*CommonAttributes
-	Content string `xml:",chardata"` // undefinedContent in RFC4287
 	Term   string `xml:"term,attr"`
 	Scheme IRI    `xml:"scheme,attr,omitempty"`
 	Label  string `xml:"label,attr,omitempty"`
 }
 
-// NewCategory creates a new Category. It returns a *Category and an error.
-func NewCategory(term, content string) (*Category, error) {
-	return &Category{Term: term, Content: content}, nil
+// NewCategory creates a new Category. It returns a *Category.
+func NewCategory(term string) *Category {
+	return &Category{Term: term}
 }
 
 // SetLabel sets the label of the Category.
@@ -41,9 +42,5 @@ func (c *Category) Check() error {
 		return fmt.Errorf("label attribute %v of category not correctly escaped", c.Label)
 	}
 
-	if c.Content == "" {
-		return errors.New("content element of category empty")
-	}
-
 	return nil
 }

commonAttributes.go

@@ -8,6 +8,22 @@ type CommonAttributes struct {
 	UndefinedAttributes []*ExtensionAttribute `xml:",any"`
 }
 
+// NewCommonAttributes creates a new set of CommonAttributes. It returns a
+// *CommonAttributes.
+func NewCommonAttributes() *CommonAttributes {
+	return new(CommonAttributes)
+}
+
+// AddExtensionAttribute adds the ExtensionAttribute to the CommonAttributes.
+func (c *CommonAttributes) AddExtensionAttribute(e *ExtensionAttribute) {
+	if c.UndefinedAttributes == nil {
+		c.UndefinedAttributes = make([]*ExtensionAttribute, 1)
+		c.UndefinedAttributes[0] = e
+	} else {
+		c.UndefinedAttributes = append(c.UndefinedAttributes, e)
+	}
+}
+
 // Check checks the CommonAttributes for incompatibilities with RFC4287. It
 // returns an error.
 func (c *CommonAttributes) Check() error {

entry.go

@@ -1,6 +1,7 @@
 package atom
 
 import (
+	"encoding/xml"
 	"errors"
 	"fmt"
 	"strings"
@@ -12,16 +13,17 @@ import (
 // a non-empty atom:summary element when the entry contains no atom:content
 // element.
 type Entry struct {
+	XMLName xml.Name `xml:"entry"`
 	*CommonAttributes
 	Authors      []*Person   `xml:"author,omitempty"`
-	Categories   []*Category         `xml:"category,omitempty"`
-	Content      Content             `xml:"content,omitempty"`
+	Categories   []*Category `xml:",omitempty"`
+	Content      Content     `xml:",omitempty"`
 	Contributors []*Person   `xml:"contributors,omitempty"`
-	ID           *ID                 `xml:"id"`
-	Links        []*Link             `xml:"link,omitempty"`
+	ID           *ID
+	Links        []*Link             `xml:",omitempty"`
 	Published    *Date               `xml:"published,omitempty"`
 	Rights       Text                `xml:"rights,omitempty"`
-	Source       *Source             `xml:"source,omitempty"`
+	Source       *Source             `xml:",omitempty"`
 	Summary      Text                `xml:"summary,omitempty"`
 	Title        Text                `xml:"title"`
 	Updated      *Date               `xml:"updated"`
@@ -62,8 +64,13 @@ func NewEntry(title string) (*Entry, error) {
 		return nil, fmt.Errorf("error creating new entry: %v", err)
 	}
 
+	id, err := NewID(NewURN())
+	if err != nil {
+		return nil, fmt.Errorf("error creating new entry: %v", err)
+	}
+
 	return &Entry{
-		ID:      NewID(NewURN()),
+		ID:      id,
 		Title:   text,
 		Updated: NewDate(time.Now()),
 	}, nil

extensionAttribute.go

@@ -1,19 +1,24 @@
 package atom
 
 import (
-	"encoding/xml"
 	"errors"
+	"fmt"
 )
 
 type ExtensionAttribute struct {
-	Value   any `xml:",attr"`
-	XMLName xml.Name
+	Attr string `xml:",attr"`
+}
+
+// NewExtensionAttribute creates a new ExtensionAttribute. It returns a
+// *ExtensionAttribute.
+func NewExtensionAttribute(name, value string) *ExtensionAttribute {
+	return &ExtensionAttribute{Attr: fmt.Sprint(name, `="`, value, `"`)}
 }
 
 // Check checks the ExtensionAttribute for incompatibilities with RFC4287. It
 // returns an error.
 func (e *ExtensionAttribute) Check() error {
-	if e.Value == nil {
+	if e.Attr == "" {
 		return errors.New("value element of extension attribute empty")
 	}
 

feed.go

@@ -11,19 +11,19 @@ type Feed struct {
 	XMLName xml.Name `xml:"http://www.w3.org/2005/Atom feed"`
 	*CommonAttributes
 	Authors      []*Person   `xml:"author,omitempty"`
-	Categories   []*Category         `xml:"category,omitempty"`
+	Categories   []*Category `xml:",omitempty"`
 	Contributors []*Person   `xml:"contributor,omitempty"`
-	Generator    *Generator          `xml:"generator,omitempty"`
-	Icon         *Icon               `xml:"icon,omitempty"`
-	ID           *ID                 `xml:"id"`
-	Links        []*Link             `xml:"link,omitempty"`
-	Logo         *Logo               `xml:"logo,omitempty"`
+	Generator    *Generator  `xml:",omitempty"`
+	Icon         *Icon       `xml:",omitempty"`
+	ID           *ID
+	Links        []*Link             `xml:",omitempty"`
+	Logo         *Logo               `xml:",omitempty"`
 	Rights       Text                `xml:"rights,omitempty"`
 	Subtitle     Text                `xml:"subtitle,omitempty"`
 	Title        Text                `xml:"title"`
 	Updated      *Date               `xml:"updated"`
 	Extensions   []*ExtensionElement `xml:",any,omitempty"`
-	Entries      []*Entry            `xml:"entry,omitempty"`
+	Entries      []*Entry            `xml:",omitempty"`
 }
 
 // NewFeed creates a new Feed. It returns a *Feed and an error.
@@ -33,8 +33,13 @@ func NewFeed(title string) (*Feed, error) {
 		return nil, fmt.Errorf("error creating new feed: %v", err)
 	}
 
+	id, err := NewID(NewURN())
+	if err != nil {
+		return nil, fmt.Errorf("error creating new feed: %v", err)
+	}
+
 	return &Feed{
-		ID:      NewID(NewURN()),
+		ID:      id,
 		Title:   text,
 		Updated: NewDate(time.Now()),
 	}, nil

generator.go

@@ -1,16 +1,18 @@
 package atom
 
 import (
+	"encoding/xml"
 	"errors"
 	"fmt"
 	"html"
 )
 
 type Generator struct {
+	XMLName xml.Name `xml:"generator"`
 	*CommonAttributes
 	URI     IRI    `xml:"uri,attr,omitempty"`
 	Version string `xml:"version,attr,omitempty"`
-	Text    string `xml:"text"`
+	Text    string `xml:",chardata"`
 }
 
 // NewGenerator creates a new Generator. It returns a *Generator.

icon.go

@@ -1,18 +1,24 @@
 package atom
 
 import (
+	"encoding/xml"
 	"errors"
 	"fmt"
 )
 
 type Icon struct {
+	XMLName xml.Name `xml:"icon"`
 	*CommonAttributes
-	URI IRI `xml:"uri"`
+	URI IRI `xml:",chardata"`
 }
 
-// NewIcon creates a new Icon. It returns a *Icon.
-func NewIcon(uri string) *Icon {
-	return &Icon{URI: IRI(uri)}
+// NewIcon creates a new Icon. It returns a *Icon and an error.
+func NewIcon(uri IRI) (*Icon, error) {
+	if !isValidIRI(uri) {
+		return nil, fmt.Errorf("uri %v not correctly formatted", uri)
+	}
+
+	return &Icon{URI: uri}, nil
 }
 
 // Check checks the Icon for incompatibilities with RFC4287. It returns an

id.go

@@ -1,18 +1,24 @@
 package atom
 
 import (
+	"encoding/xml"
 	"errors"
 	"fmt"
 )
 
 type ID struct {
+	XMLName xml.Name `xml:"id"`
 	*CommonAttributes
 	URI IRI `xml:",chardata"`
 }
 
-// NewID creates a new ID. It returns a *ID.
-func NewID(id IRI) *ID {
-	return &ID{URI: IRI(id)}
+// NewID creates a new ID. It returns a *ID and an error.
+func NewID(uri IRI) (*ID, error) {
+	if !isValidIRI(uri) {
+		return nil, fmt.Errorf("uri %v not correctly formatted", uri)
+	}
+
+	return &ID{URI: IRI(uri)}, nil
 }
 
 // Check checks the ID for incompatibilities with RFC4287. It returns an error.

inlineOtherContent.go

@@ -1,12 +1,14 @@
 package atom
 
 import (
+	"encoding/xml"
 	"errors"
 	"fmt"
 	"mime"
 )
 
 type InlineOtherContent struct {
+	XMLName xml.Name `xml:"content"`
 	*CommonAttributes
 	AnyElement any       `xml:",chardata"`
 	Type       MediaType `xml:"type,attr,omitempty"`

inlineTextContent.go

@@ -1,11 +1,13 @@
 package atom
 
 import (
+	"encoding/xml"
 	"errors"
 	"fmt"
 )
 
 type InlineTextContent struct {
+	XMLName xml.Name `xml:"content"`
 	*CommonAttributes
 	Type string `xml:"type,attr,omitempty"` // Must be text or html
 	Text string `xml:",chardata"`

inlineXHTMLContent.go

@@ -1,14 +1,16 @@
 package atom
 
 import (
+	"encoding/xml"
 	"errors"
 	"fmt"
 )
 
 type InlineXHTMLContent struct {
+	XMLName xml.Name `xml:"content"`
 	*CommonAttributes
+	XHTMLDiv *XHTMLDiv
 	Type     string `xml:"type,attr"`
-	XHTMLDiv XHTMLDiv
 }
 
 // newInlineXHTMLContent creates a new InlineXHTMLContent. It returns a
@@ -18,7 +20,7 @@ func newInlineXHTMLContent(mediaType string, content any) (*InlineXHTMLContent,
 		return nil, fmt.Errorf("media type %v incompatible with inline xhtml content", mediaType)
 	}
 
-	xhtmlDiv, ok := content.(XHTMLDiv)
+	xhtmlDiv, ok := content.(*XHTMLDiv)
 	if !ok {
 		return nil, fmt.Errorf("content type %T incompatible with inline xhtml content", content)
 	}

link.go

@@ -1,15 +1,16 @@
 package atom
 
 import (
+	"encoding/xml"
 	"errors"
 	"fmt"
 	"strings"
 )
 
 type Link struct {
+	XMLName xml.Name `xml:"link"`
 	*CommonAttributes
 	Title    string      `xml:"title,attr,omitempty"`
-	Content  string      `xml:",chardata"` // undefinedContent in RFC4287
 	Href     IRI         `xml:"href,attr"`
 	Rel      string      `xml:"rel,attr,omitempty"`
 	Type     MediaType   `xml:"type,attr,omitempty"`
@@ -17,9 +18,9 @@ type Link struct {
 	Length   uint        `xml:"length,attr,omitempty"`
 }
 
-// NewLink creates a new Link. It returns a *Link and an error.
-func NewLink(href, content string) (*Link, error) {
-	return &Link{Href: IRI(href), Content: content}, nil
+// NewLink creates a new Link. It returns a *Link.
+func NewLink(href string) *Link {
+	return &Link{Href: IRI(href)}
 }
 
 // Check checks the Link for incompatibilities with RFC4287. It returns an
@@ -51,10 +52,6 @@ func (l *Link) Check() error {
 		}
 	}
 
-	if l.Content == "" {
-		return errors.New("content element of link empty")
-	}
-
 	return nil
 }
 

logo.go

@@ -1,20 +1,24 @@
 package atom
 
 import (
+	"encoding/xml"
 	"errors"
 	"fmt"
-
-	"github.com/google/uuid"
 )
 
 type Logo struct {
+	XMLName xml.Name `xml:"logo"`
 	*CommonAttributes
-	URI IRI `xml:"uri"`
+	URI IRI `xml:",chardata"`
 }
 
 // NewLogo creates a new Logo. It returns a *Logo.
-func NewLogo() *Logo {
-	return &Logo{URI: IRI(fmt.Sprint("urn:uuid:", uuid.New()))}
+func NewLogo(uri IRI) (*Logo, error) {
+	if !isValidIRI(uri) {
+		return nil, fmt.Errorf("uri %v not correctly formatted", uri)
+	}
+
+	return &Logo{URI: uri}, nil
 }
 
 // Check checks the Logo for incompatibilities with RFC4287. It returns an

outOfLineContent.go

@@ -1,12 +1,14 @@
 package atom
 
 import (
+	"encoding/xml"
 	"errors"
 	"fmt"
 	"mime"
 )
 
 type OutOfLineContent struct {
+	XMLName xml.Name `xml:"content"`
 	*CommonAttributes
 	Type MediaType `xml:"type,attr,omitempty"`
 	SRC  IRI       `xml:"src,attr"`

source.go

@@ -1,17 +1,21 @@
 package atom
 
-import "fmt"
+import (
+	"encoding/xml"
+	"fmt"
+)
 
 type Source struct {
+	XMLName xml.Name `xml:"source"`
 	*CommonAttributes
 	Authors      []*Person           `xml:"author,omitempty"`
-	Categories   []*Category         `xml:"category,omitempty"`
+	Categories   []*Category         `xml:",omitempty"`
 	Contributors []*Person           `xml:"contributor,omitempty"`
-	Generator    *Generator          `xml:"generator,omitempty"`
-	Icon         *Icon               `xml:"icon,omitempty"`
-	ID           *ID                 `xml:"id,omitempty"`
-	Links        []*Link             `xml:"link,omitempty"`
-	Logo         *Logo               `xml:"logo,omitempty"`
+	Generator    *Generator          `xml:",omitempty"`
+	Icon         *Icon               `xml:",omitempty"`
+	ID           *ID                 `xml:",omitempty"`
+	Links        []*Link             `xml:",omitempty"`
+	Logo         *Logo               `xml:",omitempty"`
 	Rights       Text                `xml:"rights,omitempty"`
 	Subtitle     Text                `xml:"subtitle,omitempty"`
 	Title        Text                `xml:"title,omitempty"`

text.go

@@ -20,7 +20,7 @@ func NewText(textType, content string) (Text, error) {
 	case "xhtml":
 		return &XHTMLText{
 			Type: textType,
-			XHTMLDiv: XHTMLDiv{
+			XHTMLDiv: &XHTMLDiv{
 				XMLNS:   "http://www.w3.org/1999/xhtml",
 				Content: content,
 			},

xhtmlText.go

@@ -7,8 +7,8 @@ import (
 
 type XHTMLText struct {
 	*CommonAttributes
+	XHTMLDiv *XHTMLDiv
 	Type     string `xml:"type,attr"` // Must be xhtml
-	XHTMLDiv XHTMLDiv
 }
 
 // isText checks whether the XHTMLText is a Text. It returns a bool.