Content can also be empty

atom.go

@@ -1,10 +1,13 @@
 package atom
 
 import (
+	"encoding/xml"
+	"fmt"
 	"mime"
 	"regexp"
 	"strings"
 
+	"github.com/google/uuid"
 	"golang.org/x/text/language"
 )
 
@@ -61,8 +64,17 @@ func isXMLMediaType(mediaType string) bool {
 // isValidMediaType checks whether a string is a valid media type. It returns a
 // bool.
 func isValidMediaType(mediaType string) bool {
-	_, _, err := mime.ParseMediaType(mediaType)
+	mediaType, _, err := mime.ParseMediaType(mediaType)
-	return err == nil
+	if err != nil {
+		return false
+	}
+
+	typeParts := strings.Split(mediaType, "/")
+	if len(typeParts) != 2 || typeParts[0] == "" || typeParts[1] == "" {
+		return false
+	}
+
+	return true
 }
 
 // isValidLanguageTag checks whether a LanguageTag is valid. It returns a bool.
@@ -70,3 +82,14 @@ func isValidLanguageTag(tag LanguageTag) bool {
 	_, err := language.Parse(string(tag))
 	return err == nil
 }
+
+// NewURN generates an new valid IRI based on a UUID. It returns an IRI.
+func NewURN() IRI {
+	return IRI(fmt.Sprint("urn:uuid:", uuid.New()))
+}
+
+// isValidXML checks whether a string is valid XML. It returns a bool.
+func isValidXML(input string) bool {
+	var v interface{}
+	return xml.Unmarshal([]byte(input), &v) == nil
+}

category.go

@@ -8,17 +8,18 @@ import (
 
 type Category struct {
 	*CommonAttributes
-	Content Content `xml:"content"` // undefinedContent in RFC4287
+	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 string) (*Category, error) {
+func NewCategory(term, content string) (*Category, error) {
-	content, err := NewContent(InlineText, "", "")
+	if content != "" {
-	if err != nil {
+		if !isValidXML(content) {
-		return nil, fmt.Errorf("error creating content element: %v", err)
+			return nil, fmt.Errorf("%v not valid XML", content)
+		}
 	}
 
 	return &Category{Term: term, Content: content}, nil
@@ -46,11 +47,9 @@ func (c *Category) Check() error {
 		return fmt.Errorf("label attribute %v of category not correctly escaped", c.Label)
 	}
 
-	if c.Content == nil {
+	if c.Content != "" {
-		return errors.New("no content element of category")
+		if !isValidXML(c.Content) {
-	} else {
+			return fmt.Errorf("content element %v of category not valid XML", c.Content)
-		if err := c.Content.Check(); err != nil {
-			return fmt.Errorf("content element of category: %v", err)
 		}
 	}
 

date.go

@@ -7,7 +7,7 @@ import (
 
 type Date struct {
 	*CommonAttributes
-	DateTime string
+	DateTime string `xml:",chardata"`
 }
 
 // DateTime formats a time.Time to string formated as defined by RFC3339. It

entry.go

@@ -34,11 +34,16 @@ type Entry struct {
 // the atom:entry contains an atom:source element that contains an atom:author
 // element or, in an Atom Feed Document, the atom:feed element contains an
 // atom:author element itself.
-func (e *Entry) checkAuthors() error {
+func (e *Entry) checkAuthors(authorInFeed bool) error {
 	if e.Authors == nil {
+		if !authorInFeed {
+			if e.Source == nil {
+				return errors.New("no authors set in entry")
+			}
 			if e.Source.Authors == nil {
 				return errors.New("no authors set in entry")
 			}
+		}
 	} else {
 		for i, a := range e.Authors {
 			if err := a.Check(); err != nil {
@@ -58,7 +63,7 @@ func NewEntry(title string) (*Entry, error) {
 	}
 
 	return &Entry{
-		ID:      NewID(),
+		ID:      NewID(NewURN()),
 		Title:   text,
 		Updated: NewDate(time.Now()),
 	}, nil
@@ -135,7 +140,7 @@ func (e *Entry) Check() error {
 		}
 	}
 
-	if err := e.checkAuthors(); err != nil {
+	if err := e.checkAuthors(true); err != nil {
 		return fmt.Errorf("entry %v: %v", e.ID.URI, err)
 	}
 
@@ -208,7 +213,7 @@ func (e *Entry) Check() error {
 		// is not an XML media type [RFC3023], does not begin with "text/", and
 		// does not end with "/xml" or "+xml".
 		mediaType := e.Content.getType()
-		if !isXMLMediaType(mediaType) && !strings.HasPrefix(mediaType, "text/") {
+		if isValidMediaType(mediaType) && !isXMLMediaType(mediaType) && !strings.HasPrefix(mediaType, "text/") {
 			return fmt.Errorf("no summary element of entry %v but media type not xml", e.ID.URI)
 		}
 	}

feed.go

@@ -34,7 +34,7 @@ func NewFeed(title string) (*Feed, error) {
 	}
 
 	return &Feed{
-		ID:      NewID(),
+		ID:      NewID(NewURN()),
 		Title:   text,
 		Updated: NewDate(time.Now()),
 	}, nil
@@ -128,7 +128,7 @@ func (f *Feed) Check() error {
 	// least one atom:author element.
 	if f.Authors == nil {
 		for _, e := range f.Entries {
-			if err := e.checkAuthors(); err != nil {
+			if err := e.checkAuthors(false); err != nil {
 				return fmt.Errorf("no authors set in feed %v: %v", f.ID.URI, err)
 			}
 		}

id.go

@@ -3,18 +3,16 @@ package atom
 import (
 	"errors"
 	"fmt"
-
-	"github.com/google/uuid"
 )
 
 type ID struct {
 	*CommonAttributes
-	URI IRI `xml:"uri"`
+	URI IRI `xml:",chardata"`
 }
 
 // NewID creates a new ID. It returns a *ID.
-func NewID() *ID {
+func NewID(id IRI) *ID {
-	return &ID{URI: IRI(fmt.Sprint("urn:uuid:", uuid.New()))}
+	return &ID{URI: IRI(id)}
 }
 
 // Check checks the ID for incompatibilities with RFC4287. It returns an error.

inlineOtherContent.go

@@ -8,7 +8,7 @@ import (
 
 type InlineOtherContent struct {
 	*CommonAttributes
-	AnyElement any       `xml:"anyelement,omitempty"`
+	AnyElement any       `xml:",chardata"`
 	Type       MediaType `xml:"type,attr,omitempty"`
 }
 

inlineTextContent.go

@@ -3,13 +3,12 @@ package atom
 import (
 	"errors"
 	"fmt"
-	"reflect"
 )
 
 type InlineTextContent struct {
 	*CommonAttributes
 	Type string `xml:"type,attr,omitempty"` // Must be text or html
-	Texts []string `xml:"texts,omitempty"`
+	Text string `xml:",chardata"`
 }
 
 // newInlineTextContent creates a new InlineTextContent. It returns a
@@ -19,23 +18,12 @@ func newInlineTextContent(mediaType string, content any) (*InlineTextContent, er
 		return nil, fmt.Errorf("media type %v incompatible with inline text content", mediaType)
 	}
 
-	texts := make([]string, 0)
+	text, ok := content.(string)
-
+	if !ok {
-	t := reflect.TypeOf(content)
-	switch t.Kind() {
-	case reflect.Slice:
-		if t.Elem().Kind() == reflect.String {
-			for _, t := range content.([]string) {
-				texts = append(texts, t)
-			}
-		}
-	case reflect.String:
-		texts = append(texts, content.(string))
-	default:
 		return nil, fmt.Errorf("content type %T incompatible with inline text content", content)
 	}
 
-	return &InlineTextContent{Type: mediaType, Texts: texts}, nil
+	return &InlineTextContent{Type: mediaType, Text: text}, nil
 }
 
 // isContent checks whether the InlineTextContent is a Content. It returns a

inlineXHTMLContent.go

@@ -3,13 +3,12 @@ package atom
 import (
 	"errors"
 	"fmt"
-	"reflect"
 )
 
 type InlineXHTMLContent struct {
 	*CommonAttributes
 	Type     string `xml:"type,attr"`
-	XHTMLDiv string `xml:"xhtmldiv"`
+	XHTMLDiv XHTMLDiv
 }
 
 // newInlineXHTMLContent creates a new InlineXHTMLContent. It returns a
@@ -19,11 +18,12 @@ func newInlineXHTMLContent(mediaType string, content any) (*InlineXHTMLContent,
 		return nil, fmt.Errorf("media type %v incompatible with inline xhtml content", mediaType)
 	}
 
-	if reflect.TypeOf(content).Kind() != reflect.String {
+	xhtmlDiv, ok := content.(XHTMLDiv)
+	if !ok {
 		return nil, fmt.Errorf("content type %T incompatible with inline xhtml content", content)
 	}
 
-	return &InlineXHTMLContent{Type: mediaType, XHTMLDiv: content.(string)}, nil
+	return &InlineXHTMLContent{Type: mediaType, XHTMLDiv: xhtmlDiv}, nil
 }
 
 // isContent checks whether the InlineXHTMLContent is a Content. It returns a
@@ -44,8 +44,8 @@ func (i *InlineXHTMLContent) Check() error {
 		return errors.New("type attribute of inline xhtml content must be xhtml")
 	}
 
-	if i.XHTMLDiv == "" {
+	if err := i.XHTMLDiv.Check(); err != nil {
-		return errors.New("xhtmlDiv element of inline xhtml content empty")
+		return fmt.Errorf("xhtml div element %v of inline xhtml content %v: %v", i.XHTMLDiv, i, err)
 	}
 
 	return nil

link.go

@@ -9,7 +9,7 @@ import (
 type Link struct {
 	*CommonAttributes
 	Title    string      `xml:"title,attr,omitempty"`
-	Content  Content     `xml:"content"` // undefinedContent in RFC4287
+	Content  string      `xml:",chardata"` // undefinedContent in RFC4287
 	Href     IRI         `xml:"href,attr"`
 	Rel      string      `xml:"rel,attr,omitempty"`
 	Type     MediaType   `xml:"type,attr,omitempty"`
@@ -18,10 +18,11 @@ type Link struct {
 }
 
 // NewLink creates a new Link. It returns a *Link and an error.
-func NewLink(href string) (*Link, error) {
+func NewLink(href, content string) (*Link, error) {
-	content, err := NewContent(InlineText, "", "")
+	if content != "" {
-	if err != nil {
+		if !isValidXML(content) {
-		return nil, fmt.Errorf("error creating content element: %v", err)
+			return nil, fmt.Errorf("%v not valid XML", content)
+		}
 	}
 
 	return &Link{Href: IRI(href), Content: content}, nil
@@ -38,23 +39,27 @@ func (l *Link) Check() error {
 		}
 	}
 
-	if strings.Contains(l.Rel, ":") || !isValidIRI(IRI(l.Rel)) {
+	if l.Rel != "" {
+		if strings.Contains(l.Rel, ":") && !isValidIRI(IRI(l.Rel)) {
 			return fmt.Errorf("rel attribute %v of link %v not correctly formatted", l.Rel, l.Href)
 		}
+	}
 
+	if l.Type != "" {
 		if !isValidMediaType(string(l.Type)) {
 			return fmt.Errorf("type attribute %v of link %v invalid media type", l.Type, l.Href)
 		}
+	}
 
+	if l.HrefLang != "" {
 		if !isValidLanguageTag(l.HrefLang) {
 			return fmt.Errorf("hreflang attribute %v of link %v invalid language tag", l.Type, l.HrefLang)
 		}
+	}
 
-	if l.Content == nil {
+	if l.Content != "" {
-		return fmt.Errorf("no content element of link %v", l.Href)
+		if !isValidXML(l.Content) {
-	} else {
+			return fmt.Errorf("content element %v of link not valid XML", l.Content)
-		if err := l.Content.Check(); err != nil {
-			return fmt.Errorf("content element of link %v: %v", l.Href, err)
 		}
 	}
 

outOfLineContent.go

@@ -4,7 +4,6 @@ import (
 	"errors"
 	"fmt"
 	"mime"
-	"reflect"
 )
 
 type OutOfLineContent struct {
@@ -20,15 +19,16 @@ func newOutOfLineContent(mediaType string, content any) (*OutOfLineContent, erro
 		return nil, fmt.Errorf("media type %v incompatible with out of line content", mediaType)
 	}
 
-	if reflect.TypeOf(content).Kind() != reflect.String {
+	iri, ok := content.(IRI)
+	if !ok {
 		return nil, fmt.Errorf("content type %T incompatible with out of line content", content)
 	}
 
-	if !isValidIRI(content.(IRI)) {
+	if !isValidIRI(iri) {
 		return nil, errors.New("content not a valid uri")
 	}
 
-	return &OutOfLineContent{Type: MediaType(mediaType), SRC: content.(IRI)}, nil
+	return &OutOfLineContent{Type: MediaType(mediaType), SRC: iri}, nil
 }
 
 // isContent checks whether the OutOfLineContent is a Content. It returns a

plainText.go

@@ -5,7 +5,7 @@ import "errors"
 type PlainText struct {
 	*CommonAttributes
 	Type string `xml:"type,attr,omitempty"` // Must be text or html
-	Text string `xml:"text"`
+	Text string `xml:",chardata"`
 }
 
 // isText checks whether the PlainText is a Text. It returns a bool.

xhtmlDiv.go

@@ -0,0 +1,30 @@
+package atom
+
+import (
+	"encoding/xml"
+	"errors"
+)
+
+type XHTMLDiv struct {
+	XMLName xml.Name `xml:"div"`
+	XMLNS   string   `xml:"xmlns,attr"`
+	Content string   `xml:",innerxml"`
+}
+
+// NewXHTMLDiv creates a new XHTMLDiv. It returns a *XHTMLDiv.
+func NewXHTMLDiv(content string) *XHTMLDiv {
+	return &XHTMLDiv{
+		XMLNS:   "http://www.w3.org/1999/xhtml",
+		Content: content,
+	}
+}
+
+// Check checks the XHTMLDiv for incompatibilities with RFC4287. It returns an
+// error.
+func (x *XHTMLDiv) Check() error {
+	if x.XMLNS != "http://www.w3.org/1999/xhtml" {
+		return errors.New("xmlns attribute of xhtml text must be http://www.w3.org/1999/xhtml")
+	}
+
+	return nil
+}

xhtmlText.go

@@ -1,16 +1,10 @@
 package atom
 
 import (
-	"encoding/xml"
 	"errors"
+	"fmt"
 )
 
-type XHTMLDiv struct {
-	XMLName xml.Name `xml:"div"`
-	XMLNS   string   `xml:"xmlns,attr"`
-	Content string   `xml:",innerxml"`
-}
-
 type XHTMLText struct {
 	*CommonAttributes
 	Type     string `xml:"type,attr"` // Must be xhtml
@@ -27,8 +21,8 @@ func (x *XHTMLText) Check() error {
 		return errors.New("type attribute of xhtml text must be xhtml")
 	}
 
-	if x.XHTMLDiv.XMLNS != "http://www.w3.org/1999/xhtml" {
+	if err := x.XHTMLDiv.Check(); err != nil {
-		return errors.New("xmlns attribute of xhtml text must be http://www.w3.org/1999/xhtml")
+		return fmt.Errorf("xhtml div element %v of xhtml text %v: %v", x.XHTMLDiv, x, err)
 	}
 
 	return nil