Fix nil dereference bug in entry checkAuthors

LICENSE

@@ -208,8 +208,8 @@ If you develop a new program, and you want it to be of the greatest possible use
 
 To do so, attach the following notices to the program. It is safest to attach them to the start of each source file to most effectively state the exclusion of warranty; and each file should have at least the “copyright” line and a pointer to where the full notice is found.
 
-     atom-feed
-     Copyright (C) 2024  jason
+     atom
+     Copyright (C) 2024  Jason Streifling
 
      This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.
 
@@ -221,7 +221,7 @@ Also add information on how to contact you by electronic and paper mail.
 
 If the program does terminal interaction, make it output a short notice like this when it starts in an interactive mode:
 
-     atom-feed  Copyright (C) 2024  jason
+     atom  Copyright (C) 2024  Jason Streifling
      This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
      This is free software, and you are welcome to redistribute it under certain conditions; type `show c' for details.
 

README.md

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

atom.go

@@ -1,4 +1,4 @@
-package atomfeed
+package atom
 
 import (
 	"mime"
@@ -12,33 +12,18 @@ type (
 	EmailAddress string
 	LanguageTag  string
 	MediaType    string
-	// URI          string
-	IRI string
+	IRI          string
 )
 
-// func isValidURL(uri URI) bool {
-// 	_, err := url.ParseRequestURI(string(uri))
-// 	return err == nil
-// }
-//
-// func isValidURN(uri URI) bool {
-// 	pattern := `\A(?i:urn:(?!urn:)(?<nid>[a-z0-9][a-z0-9-]{1,31}):(?<nss>(?:[-a-z0-9()+,.:=@;$_!*'&~\/]|%[0-9a-f]{2})+)(?:\?\+(?<rcomponent>.*?))?(?:\?=(?<qcomponent>.*?))?(?:#(?<fcomponent>.*?))?)\z`
-// 	return regexp.MustCompile(pattern).MatchString(string(uri))
-// }
-//
-// // isValidURI checks whether an URI is valid or not.
-// func isValidURI(uri URI) bool {
-// 	return isValidURL(uri) || isValidURN(uri)
-// }
-
-// isValidIRI checks whether an IRI is valid or not.
-// The used pattern stems from
+// isValidIRI checks whether an IRI is valid or not. It returns a bool.
 // https://www.w3.org/2011/04/XMLSchema/TypeLibrary-IRI-RFC3987.xsd
 func isValidIRI(iri IRI) bool {
 	pattern := `((([A-Za-z])[A-Za-z0-9+\-\.]*):((//(((([A-Za-z0-9\-\._~ -퟿豈-﷏ﷰ-￯𐀀-🿽𠀀-𯿽𰀀-𿿽񀀀-񏿽񐀀-񟿽񠀀-񯿽񰀀-񿿽򀀀-򏿽򐀀-򟿽򠀀-򯿽򰀀-򿿽󀀀-󏿽󐀀-󟿽󡀀-󯿽!$&'()*+,;=:]|(%[0-9A-Fa-f][0-9A-Fa-f]))*@))?((\[((((([0-9A-Fa-f]{0,4}:)){6}(([0-9A-Fa-f]{0,4}:[0-9A-Fa-f]{0,4})|(([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5])))))|(::(([0-9A-Fa-f]{0,4}:)){5}(([0-9A-Fa-f]{0,4}:[0-9A-Fa-f]{0,4})|(([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5])))))|(([0-9A-Fa-f]{0,4})?::(([0-9A-Fa-f]{0,4}:)){4}(([0-9A-Fa-f]{0,4}:[0-9A-Fa-f]{0,4})|(([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5])))))|((((([0-9A-Fa-f]{0,4}:))?[0-9A-Fa-f]{0,4}))?::(([0-9A-Fa-f]{0,4}:)){3}(([0-9A-Fa-f]{0,4}:[0-9A-Fa-f]{0,4})|(([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5])))))|((((([0-9A-Fa-f]{0,4}:)){0,2}[0-9A-Fa-f]{0,4}))?::(([0-9A-Fa-f]{0,4}:)){2}(([0-9A-Fa-f]{0,4}:[0-9A-Fa-f]{0,4})|(([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5])))))|((((([0-9A-Fa-f]{0,4}:)){0,3}[0-9A-Fa-f]{0,4}))?::[0-9A-Fa-f]{0,4}:(([0-9A-Fa-f]{0,4}:[0-9A-Fa-f]{0,4})|(([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5])))))|((((([0-9A-Fa-f]{0,4}:)){0,4}[0-9A-Fa-f]{0,4}))?::(([0-9A-Fa-f]{0,4}:[0-9A-Fa-f]{0,4})|(([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5])))))|((((([0-9A-Fa-f]{0,4}:)){0,5}[0-9A-Fa-f]{0,4}))?::[0-9A-Fa-f]{0,4})|((((([0-9A-Fa-f]{0,4}:)){0,6}[0-9A-Fa-f]{0,4}))?::))|(v[0-9A-Fa-f]+\.[A-Za-z0-9\-\._~!$&'()*+,;=:]+))\])|(([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5])))|(([A-Za-z0-9\-\._~ -퟿豈-﷏ﷰ-￯𐀀-🿽𠀀-𯿽𰀀-𿿽񀀀-񏿽񐀀-񟿽񠀀-񯿽񰀀-񿿽򀀀-򏿽򐀀-򟿽򠀀-򯿽򰀀-򿿽󀀀-󏿽󐀀-󟿽󡀀-󯿽]|(%[0-9A-Fa-f][0-9A-Fa-f])|[!$&'()*+,;=]))*)((:[0-9]*))?)((/(([A-Za-z0-9\-\._~ -퟿豈-﷏ﷰ-￯𐀀-🿽𠀀-𯿽𰀀-𿿽񀀀-񏿽񐀀-񟿽񠀀-񯿽񰀀-񿿽򀀀-򏿽򐀀-򟿽򠀀-򯿽򰀀-򿿽󀀀-󏿽󐀀-󟿽󡀀-󯿽]|(%[0-9A-Fa-f][0-9A-Fa-f])|[!$&'()*+,;=:@]))*))*)|(/(((([A-Za-z0-9\-\._~ -퟿豈-﷏ﷰ-￯𐀀-🿽𠀀-𯿽𰀀-𿿽񀀀-񏿽񐀀-񟿽񠀀-񯿽񰀀-񿿽򀀀-򏿽򐀀-򟿽򠀀-򯿽򰀀-򿿽󀀀-󏿽󐀀-󟿽󡀀-󯿽]|(%[0-9A-Fa-f][0-9A-Fa-f])|[!$&'()*+,;=:@]))+((/(([A-Za-z0-9\-\._~ -퟿豈-﷏ﷰ-￯𐀀-🿽𠀀-𯿽𰀀-𿿽񀀀-񏿽񐀀-񟿽񠀀-񯿽񰀀-񿿽򀀀-򏿽򐀀-򟿽򠀀-򯿽򰀀-򿿽󀀀-󏿽󐀀-󟿽󡀀-󯿽]|(%[0-9A-Fa-f][0-9A-Fa-f])|[!$&'()*+,;=:@]))*))*))?)|((([A-Za-z0-9\-\._~ -퟿豈-﷏ﷰ-￯𐀀-🿽𠀀-𯿽𰀀-𿿽񀀀-񏿽񐀀-񟿽񠀀-񯿽񰀀-񿿽򀀀-򏿽򐀀-򟿽򠀀-򯿽򰀀-򿿽󀀀-󏿽󐀀-󟿽󡀀-󯿽]|(%[0-9A-Fa-f][0-9A-Fa-f])|[!$&'()*+,;=:@]))+((/(([A-Za-z0-9\-\._~ -퟿豈-﷏ﷰ-￯𐀀-🿽𠀀-𯿽𰀀-𿿽񀀀-񏿽񐀀-񟿽񠀀-񯿽񰀀-񿿽򀀀-򏿽򐀀-򟿽򠀀-򯿽򰀀-򿿽󀀀-󏿽󐀀-󟿽󡀀-󯿽]|(%[0-9A-Fa-f][0-9A-Fa-f])|[!$&'()*+,;=:@]))*))*)|)((\?(([A-Za-z0-9\-\._~ -퟿豈-﷏ﷰ-￯𐀀-🿽𠀀-𯿽𰀀-𿿽񀀀-񏿽񐀀-񟿽񠀀-񯿽񰀀-񿿽򀀀-򏿽򐀀-򟿽򠀀-򯿽򰀀-򿿽󀀀-󏿽󐀀-󟿽󡀀-󯿽]|(%[0-9A-Fa-f][0-9A-Fa-f])|[!$&'()*+,;=:@])|[-󰀀-󿿽􀀀-􏿽/?])*))?((#((([A-Za-z0-9\-\._~ -퟿豈-﷏ﷰ-￯𐀀-🿽𠀀-𯿽𰀀-𿿽񀀀-񏿽񐀀-񟿽񠀀-񯿽񰀀-񿿽򀀀-򏿽򐀀-򟿽򠀀-򯿽򰀀-򿿽󀀀-󏿽󐀀-󟿽󡀀-󯿽]|(%[0-9A-Fa-f][0-9A-Fa-f])|[!$&'()*+,;=:@])|/|\?))*))?)`
 	return regexp.MustCompile(pattern).MatchString(string(iri))
 }
 
+// isCorrectlyEscaped checks whether a string is correctly escaped as per
+// RFC4287. It returns a bool.
 func isCorrectlyEscaped(text string) bool {
 	relevantEntities := []string{"&amp;", "&lt;", "&gt;", "&quot;", "&apos;"}
 
@@ -51,6 +36,8 @@ func isCorrectlyEscaped(text string) bool {
 	return true
 }
 
+// isCompositeMediaType checks whether a string is a composite media type. It
+// returns a bool.
 func isCompositeMediaType(mediaType string) bool {
 	mediaType, _, err := mime.ParseMediaType(mediaType)
 	if err != nil {
@@ -60,6 +47,8 @@ func isCompositeMediaType(mediaType string) bool {
 	return strings.HasPrefix(mediaType, "multipart/") || strings.HasPrefix(mediaType, "message/")
 }
 
+// isXMLMediaType checks whether a string is an xml media type. It returns a
+// bool.
 func isXMLMediaType(mediaType string) bool {
 	mediaType, _, err := mime.ParseMediaType(mediaType)
 	if err != nil {
@@ -69,11 +58,14 @@ func isXMLMediaType(mediaType string) bool {
 	return strings.HasSuffix(mediaType, "/xml") || strings.HasSuffix(mediaType, "+xml")
 }
 
+// isValidMediaType checks whether a string is a valid media type. It returns a
+// bool.
 func isValidMediaType(mediaType string) bool {
 	_, _, err := mime.ParseMediaType(mediaType)
 	return err == nil
 }
 
+// isValidLanguageTag checks whether a LanguageTag is valid. It returns a bool.
 func isValidLanguageTag(tag LanguageTag) bool {
 	_, err := language.Parse(string(tag))
 	return err == nil

category.go

@@ -1,4 +1,4 @@
-package atomfeed
+package atom
 
 import (
 	"errors"
@@ -14,6 +14,7 @@ type Category struct {
 	Label   string  `xml:"label,attr,omitempty"`
 }
 
+// NewCategory creates a new Category. It returns a *Category and an error.
 func NewCategory(term string) (*Category, error) {
 	content, err := NewContent(InlineText, "", "")
 	if err != nil {
@@ -23,10 +24,13 @@ func NewCategory(term string) (*Category, error) {
 	return &Category{Term: term, Content: content}, nil
 }
 
+// SetLabel sets the label of the Category.
 func (c *Category) SetLabel(label string) {
 	c.Label = html.UnescapeString(label)
 }
 
+// Check checks the Category for incompatibilities with RFC4287. It returns an
+// error.
 func (c *Category) Check() error {
 	if c.Term == "" {
 		return errors.New("term attribute of category empty")

commonAttributes.go

@@ -1,4 +1,4 @@
-package atomfeed
+package atom
 
 import "fmt"
 
@@ -8,6 +8,8 @@ type CommonAttributes struct {
 	UndefinedAttributes []*ExtensionAttribute `xml:",any"`
 }
 
+// Check checks the CommonAttributes for incompatibilities with RFC4287. It
+// returns an error.
 func (c *CommonAttributes) Check() error {
 	for i, e := range c.UndefinedAttributes {
 		if err := e.Check(); err != nil {

content.go

@@ -1,4 +1,4 @@
-package atomfeed
+package atom
 
 import (
 	"fmt"
@@ -18,6 +18,7 @@ type Content interface {
 	Check() error
 }
 
+// NewContent creates a new Content. It returns a Content and an error.
 func NewContent(contentType int, mediaType string, content any) (Content, error) {
 	switch contentType {
 	case 0:

date.go

@@ -1,4 +1,4 @@
-package atomfeed
+package atom
 
 import (
 	"errors"
@@ -10,14 +10,19 @@ type Date struct {
 	DateTime string
 }
 
+// DateTime formats a time.Time to string formated as defined by RFC3339. It
+// returns a string.
 func DateTime(t time.Time) string {
 	return string(t.Format(time.RFC3339))
 }
 
+// NewDate creates a new Date. It returns a *Date.
 func NewDate(t time.Time) *Date {
 	return &Date{DateTime: DateTime(t)}
 }
 
+// Check checks the Date for incompatibilities with RFC4287. It returns an
+// error.
 func (d *Date) Check() error {
 	if d.DateTime == "" {
 		return errors.New("date time element of date is empty")

entry.go

@@ -1,4 +1,4 @@
-package atomfeed
+package atom
 
 import (
 	"errors"
@@ -28,12 +28,17 @@ type Entry struct {
 	Extensions   []*ExtensionElement `xml:",any,omitempty"`
 }
 
+// checkAuthors checks the entry's authors for incompatibilities with RFC4287.
+// It returns an errors.
 // atom:entry elements MUST contain one or more atom:author elements, unless
 // 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 {
 	if e.Authors == nil {
+		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")
 		}
@@ -48,17 +53,69 @@ func (e *Entry) checkAuthors() error {
 	return nil
 }
 
-func alternateRelExists(l []*Link) bool {
-	for _, link := range l {
-		if link.Rel == "alternate" {
-			return true
-		}
+// NewEntry creates a new Entry. It returns a *Entry and an error.
+func NewEntry(title string) (*Entry, error) {
+	text, err := NewText("text", title)
+	if err != nil {
+		return nil, fmt.Errorf("error creating new entry: %v", err)
 	}
 
-	return false
+	return &Entry{
+		ID:      NewID(),
+		Title:   text,
+		Updated: NewDate(time.Now()),
+	}, nil
 }
 
-// AddExtension adds the extension to the entry
+// AddAuthor adds the Person as an author to the Entry.
+func (e *Entry) AddAuthor(p *Person) {
+	if e.Authors == nil {
+		e.Authors = make([]*Person, 1)
+		e.Authors[0] = p
+	} else {
+		e.Authors = append(e.Authors, p)
+	}
+
+	e.Updated.DateTime = DateTime(time.Now())
+}
+
+// AddCategory adds the Category to the Entry.
+func (e *Entry) AddCategory(c *Category) {
+	if e.Categories == nil {
+		e.Categories = make([]*Category, 1)
+		e.Categories[0] = c
+	} else {
+		e.Categories = append(e.Categories, c)
+	}
+
+	e.Updated.DateTime = DateTime(time.Now())
+}
+
+// AddContributor adds the Person as a contributor to the Entry.
+func (e *Entry) AddContributor(c *Person) {
+	if e.Contributors == nil {
+		e.Contributors = make([]*Person, 1)
+		e.Contributors[0] = c
+	} else {
+		e.Contributors = append(e.Contributors, c)
+	}
+
+	e.Updated.DateTime = DateTime(time.Now())
+}
+
+// AddLink adds the Link to the Entry.
+func (e *Entry) AddLink(l *Link) {
+	if e.Links == nil {
+		e.Links = make([]*Link, 1)
+		e.Links[0] = l
+	} else {
+		e.Links = append(e.Links, l)
+	}
+
+	e.Updated.DateTime = DateTime(time.Now())
+}
+
+// AddExtension adds the ExtensionElement to the Entry.
 func (e *Entry) AddExtension(x *ExtensionElement) {
 	if e.Extensions == nil {
 		e.Extensions = make([]*ExtensionElement, 1)
@@ -70,6 +127,8 @@ func (e *Entry) AddExtension(x *ExtensionElement) {
 	e.Updated.DateTime = DateTime(time.Now())
 }
 
+// Check checks the Entry for incompatibilities with RFC4287. It returns an
+// error.
 func (e *Entry) Check() error {
 	if e.ID == nil {
 		return errors.New("no id element of entry")

extensionAttribute.go

@@ -1,4 +1,4 @@
-package atomfeed
+package atom
 
 import (
 	"encoding/xml"
@@ -10,6 +10,8 @@ type ExtensionAttribute struct {
 	XMLName xml.Name
 }
 
+// Check checks the ExtensionAttribute for incompatibilities with RFC4287. It
+// returns an error.
 func (e *ExtensionAttribute) Check() error {
 	if e.Value == nil {
 		return errors.New("value element of extension attribute empty")

extensionElement.go

@@ -1,4 +1,4 @@
-package atomfeed
+package atom
 
 import (
 	"encoding/xml"
@@ -10,10 +10,14 @@ type ExtensionElement struct {
 	XMLName xml.Name
 }
 
+// NewExtensionElement creates a new ExtensionElement. It returns a
+// *ExtensionElement.
 func NewExtensionElement(name string, value any) *ExtensionElement {
 	return &ExtensionElement{XMLName: xml.Name{Local: name}, Value: value}
 }
 
+// Check checks the ExtensionElement for incompatibilities with RFC4287. It
+// returns an error.
 func (e *ExtensionElement) Check() error {
 	if e.Value == nil {
 		return errors.New("value element of extension element empty")

feed.go

@@ -1,4 +1,4 @@
-package atomfeed
+package atom
 
 import (
 	"encoding/xml"
@@ -26,7 +26,7 @@ type Feed struct {
 	Entries      []*Entry            `xml:"entry,omitempty"`
 }
 
-// NewFeed creates a new feed.
+// NewFeed creates a new Feed. It returns a *Feed and an error.
 func NewFeed(title string) (*Feed, error) {
 	text, err := NewText("text", title)
 	if err != nil {
@@ -40,7 +40,7 @@ func NewFeed(title string) (*Feed, error) {
 	}, nil
 }
 
-// AddAuthor adds the person as an author to the feed.
+// AddAuthor adds the Person as an author to the Feed.
 func (f *Feed) AddAuthor(p *Person) {
 	if f.Authors == nil {
 		f.Authors = make([]*Person, 1)
@@ -52,7 +52,7 @@ func (f *Feed) AddAuthor(p *Person) {
 	f.Updated.DateTime = DateTime(time.Now())
 }
 
-// AddCategory adds the category to the feed.
+// AddCategory adds the Category to the Feed.
 func (f *Feed) AddCategory(c *Category) {
 	if f.Categories == nil {
 		f.Categories = make([]*Category, 1)
@@ -64,7 +64,7 @@ func (f *Feed) AddCategory(c *Category) {
 	f.Updated.DateTime = DateTime(time.Now())
 }
 
-// AddContributor adds the contributor to the feed.
+// AddContributor adds the Person as a contributor to the Feed.
 func (f *Feed) AddContributor(c *Person) {
 	if f.Contributors == nil {
 		f.Contributors = make([]*Person, 1)
@@ -76,8 +76,7 @@ func (f *Feed) AddContributor(c *Person) {
 	f.Updated.DateTime = DateTime(time.Now())
 }
 
-// AddLink adds the link to the feed.
-// There should be one link with rel "self".
+// AddLink adds the Link to the Feed. There should be one Link with Rel "self".
 func (f *Feed) AddLink(l *Link) {
 	if f.Links == nil {
 		f.Links = make([]*Link, 1)
@@ -89,7 +88,7 @@ func (f *Feed) AddLink(l *Link) {
 	f.Updated.DateTime = DateTime(time.Now())
 }
 
-// AddExtension adds the extension to the feed.
+// AddExtension adds the Extension to the Feed.
 func (f *Feed) AddExtension(e *ExtensionElement) {
 	if f.Extensions == nil {
 		f.Extensions = make([]*ExtensionElement, 1)
@@ -101,7 +100,7 @@ func (f *Feed) AddExtension(e *ExtensionElement) {
 	f.Updated.DateTime = DateTime(time.Now())
 }
 
-// AddEntry adds the entry to the feed.
+// AddEntry adds the Entry to the Feed.
 func (f *Feed) AddEntry(e *Entry) {
 	if f.Entries == nil {
 		f.Entries = make([]*Entry, 1)
@@ -113,7 +112,8 @@ func (f *Feed) AddEntry(e *Entry) {
 	f.Updated.DateTime = DateTime(time.Now())
 }
 
-// Check checks the feed for incompatibilities with RFC4287.
+// Check checks the Feed for incompatibilities with RFC4287. It returns an
+// error.
 func (f *Feed) Check() error {
 	if f.ID == nil {
 		return errors.New("no id element of feed")
@@ -222,26 +222,7 @@ func (f *Feed) Check() error {
 	return nil
 }
 
-// TODO: Create complete link or delete
-func (f *Feed) Standardize() {
-	if f.Links == nil {
-		f.Links = make([]*Link, 1)
-		f.Links[0] = &Link{Rel: "self"}
-	} else {
-		selfExists := false
-		for _, l := range f.Links {
-			if l.Rel == "self" {
-				selfExists = true
-				break
-			}
-		}
-		if !selfExists {
-			f.Links = append(f.Links, &Link{Rel: "self"})
-		}
-	}
-}
-
-// ToXML converts the feed to XML.
+// ToXML converts the Feed to XML. It returns a string and an error.
 func (f *Feed) ToXML(encoding string) (string, error) {
 	xml, err := xml.MarshalIndent(f, "", "  ")
 	if err != nil {

generator.go

@@ -1,4 +1,4 @@
-package atomfeed
+package atom
 
 import (
 	"errors"
@@ -13,10 +13,13 @@ type Generator struct {
 	Text    string `xml:"text"`
 }
 
+// NewGenerator creates a new Generator. It returns a *Generator.
 func NewGenerator(text string) *Generator {
 	return &Generator{Text: html.UnescapeString(text)}
 }
 
+// Check checks the Generator for incompatibilities with RFC4287. It returns an
+// error.
 func (g *Generator) Check() error {
 	if g.URI != "" {
 		if !isValidIRI(g.URI) {

go.mod

@@ -1,4 +1,4 @@
-module streifling.com/jason/atom-feed
+module git.streifling.com/jason/atom
 
 go 1.23.2
 

icon.go

@@ -1,4 +1,4 @@
-package atomfeed
+package atom
 
 import (
 	"errors"
@@ -10,10 +10,13 @@ type Icon struct {
 	URI IRI `xml:"uri"`
 }
 
+// NewIcon creates a new Icon. It returns a *Icon.
 func NewIcon(uri string) *Icon {
 	return &Icon{URI: IRI(uri)}
 }
 
+// Check checks the Icon for incompatibilities with RFC4287. It returns an
+// error.
 func (i *Icon) Check() error {
 	if i.URI == "" {
 		return errors.New("uri element of icon empty")

id.go

@@ -1,4 +1,4 @@
-package atomfeed
+package atom
 
 import (
 	"errors"
@@ -12,10 +12,12 @@ type ID struct {
 	URI IRI `xml:"uri"`
 }
 
+// NewID creates a new ID. It returns a *ID.
 func NewID() *ID {
 	return &ID{URI: IRI(fmt.Sprint("urn:uuid:", uuid.New()))}
 }
 
+// Check checks the ID for incompatibilities with RFC4287. It returns an error.
 func (i *ID) Check() error {
 	if i.URI == "" {
 		return errors.New("uri element of id empty")

inlineOtherContent.go

@@ -1,4 +1,4 @@
-package atomfeed
+package atom
 
 import (
 	"errors"
@@ -12,6 +12,8 @@ type InlineOtherContent struct {
 	Type       MediaType `xml:"type,attr,omitempty"`
 }
 
+// newInlineOtherContent creates a new InlineOtherContent. It returns a
+// *InlineOtherContent and an error.
 func newInlineOtherContent(mediaType string, content any) (*InlineOtherContent, error) {
 	if mediaType, _, err := mime.ParseMediaType(mediaType); err != nil {
 		return nil, fmt.Errorf("media type %v incompatible with inline other content", mediaType)
@@ -20,12 +22,19 @@ func newInlineOtherContent(mediaType string, content any) (*InlineOtherContent,
 	return &InlineOtherContent{Type: MediaType(mediaType), AnyElement: content}, nil
 }
 
+// isContent checks whether the InlineOtherContent is a Content. It returns a
+// bool.
 func (i *InlineOtherContent) isContent() bool { return true }
 
+// hasSRC checks whether the InlineOtherContent has a SRC attribute. It returns
+// a bool.
 func (i *InlineOtherContent) hasSRC() bool { return false }
 
+// getType returns the Type of the InlineOtherContent as a string.
 func (i *InlineOtherContent) getType() string { return string(i.Type) }
 
+// Check checks the InlineOtherContent for incompatibilities with RFC4287. It
+// returns an error.
 func (i *InlineOtherContent) Check() error {
 	mediaType := i.getType()
 

inlineTextContent.go

@@ -1,4 +1,4 @@
-package atomfeed
+package atom
 
 import (
 	"errors"
@@ -12,6 +12,8 @@ type InlineTextContent struct {
 	Texts []string `xml:"texts,omitempty"`
 }
 
+// newInlineTextContent creates a new InlineTextContent. It returns a
+// *InlineTextContent and an error.
 func newInlineTextContent(mediaType string, content any) (*InlineTextContent, error) {
 	if mediaType != "text" && mediaType != "html" && mediaType != "" {
 		return nil, fmt.Errorf("media type %v incompatible with inline text content", mediaType)
@@ -36,12 +38,19 @@ func newInlineTextContent(mediaType string, content any) (*InlineTextContent, er
 	return &InlineTextContent{Type: mediaType, Texts: texts}, nil
 }
 
+// isContent checks whether the InlineTextContent is a Content. It returns a
+// bool.
 func (i *InlineTextContent) isContent() bool { return true }
 
+// hasSRC checks whether the InlineTextContent has a SRC attribute. It returns
+// a bool.
 func (i *InlineTextContent) hasSRC() bool { return false }
 
+// getType returns the Type of the InlineTextContent as a string.
 func (i *InlineTextContent) getType() string { return i.Type }
 
+// Check checks the InlineTextContent for incompatibilities with RFC4287. It
+// returns an error.
 func (i *InlineTextContent) Check() error {
 	if i.Type != "" && i.Type != "text" && i.Type != "html" {
 		return errors.New("type attribute of inline text content must be text or html if not omitted")

inlineXHTMLContent.go

@@ -1,4 +1,4 @@
-package atomfeed
+package atom
 
 import (
 	"errors"
@@ -12,6 +12,8 @@ type InlineXHTMLContent struct {
 	XHTMLDiv string `xml:"xhtmldiv"`
 }
 
+// newInlineXHTMLContent creates a new InlineXHTMLContent. It returns a
+// *InlineXHTMLContent and an error.
 func newInlineXHTMLContent(mediaType string, content any) (*InlineXHTMLContent, error) {
 	if mediaType != "xhtml" {
 		return nil, fmt.Errorf("media type %v incompatible with inline xhtml content", mediaType)
@@ -24,12 +26,19 @@ func newInlineXHTMLContent(mediaType string, content any) (*InlineXHTMLContent,
 	return &InlineXHTMLContent{Type: mediaType, XHTMLDiv: content.(string)}, nil
 }
 
+// isContent checks whether the InlineXHTMLContent is a Content. It returns a
+// bool.
 func (i *InlineXHTMLContent) isContent() bool { return true }
 
+// hasSRC checks whether the InlineXHTMLContent has a SRC attribute. It returns
+// a bool.
 func (i *InlineXHTMLContent) hasSRC() bool { return false }
 
+// getType returns the Type of the InlineXHTMLContent as a string.
 func (i *InlineXHTMLContent) getType() string { return i.Type }
 
+// Check checks the InlineXHTMLContent for incompatibilities with RFC4287. It
+// returns an error.
 func (i *InlineXHTMLContent) Check() error {
 	if i.Type != "xhtml" {
 		return errors.New("type attribute of inline xhtml content must be xhtml")

link.go

@@ -1,4 +1,4 @@
-package atomfeed
+package atom
 
 import (
 	"errors"
@@ -17,6 +17,7 @@ type Link struct {
 	Length   uint        `xml:"length,attr,omitempty"`
 }
 
+// NewLink creates a new Link. It returns a *Link and an error.
 func NewLink(href string) (*Link, error) {
 	content, err := NewContent(InlineText, "", "")
 	if err != nil {
@@ -26,6 +27,8 @@ func NewLink(href string) (*Link, error) {
 	return &Link{Href: IRI(href), Content: content}, nil
 }
 
+// Check checks the Link for incompatibilities with RFC4287. It returns an
+// error.
 func (l *Link) Check() error {
 	if l.Href == "" {
 		return errors.New("href attribute of link empty")
@@ -58,6 +61,8 @@ func (l *Link) Check() error {
 	return nil
 }
 
+// hasAlternateDuplicateLinks checks whether multiple Links with Rel
+// "alternate" also have Type and HrefLang in common. It returns a bool.
 // atom:feed/entry elements MUST NOT contain more than one atom:link element
 // with a rel attribute value of "alternate" that has the same combination of
 // type and hreflang attribute values.
@@ -76,3 +81,15 @@ func hasAlternateDuplicateLinks(l []*Link) bool {
 
 	return false
 }
+
+// alternateRelExists checks whether multiple Links with Rel "alternate" exist.
+// It returns a bool.
+func alternateRelExists(l []*Link) bool {
+	for _, link := range l {
+		if link.Rel == "alternate" {
+			return true
+		}
+	}
+
+	return false
+}

logo.go

@@ -1,15 +1,31 @@
-package atomfeed
+package atom
 
-import "errors"
+import (
+	"errors"
+	"fmt"
+
+	"github.com/google/uuid"
+)
 
 type Logo struct {
 	*CommonAttributes
 	URI IRI `xml:"uri"`
 }
 
+// NewLogo creates a new Logo. It returns a *Logo.
+func NewLogo() *Logo {
+	return &Logo{URI: IRI(fmt.Sprint("urn:uuid:", uuid.New()))}
+}
+
+// Check checks the Logo for incompatibilities with RFC4287. It returns an
+// error.
 func (l *Logo) Check() error {
 	if l.URI == "" {
 		return errors.New("uri element of logo empty")
+	} else {
+		if !isValidIRI(l.URI) {
+			return fmt.Errorf("uri element %v of logo not correctly formatted", l.URI)
+		}
 	}
 
 	return nil

outOfLineContent.go

@@ -1,4 +1,4 @@
-package atomfeed
+package atom
 
 import (
 	"errors"
@@ -13,6 +13,8 @@ type OutOfLineContent struct {
 	SRC  IRI       `xml:"src,attr"`
 }
 
+// newOutOfLineContent creates a new OutOfLineContent. It returns a
+// *OutOfLineContent and an error.
 func newOutOfLineContent(mediaType string, content any) (*OutOfLineContent, error) {
 	if mediaType, _, err := mime.ParseMediaType(mediaType); err != nil {
 		return nil, fmt.Errorf("media type %v incompatible with out of line content", mediaType)
@@ -29,12 +31,19 @@ func newOutOfLineContent(mediaType string, content any) (*OutOfLineContent, erro
 	return &OutOfLineContent{Type: MediaType(mediaType), SRC: content.(IRI)}, nil
 }
 
+// isContent checks whether the OutOfLineContent is a Content. It returns a
+// bool.
 func (o *OutOfLineContent) isContent() bool { return true }
 
+// hasSRC checks whether the OutOfLineContent has a SRC attribute. It returns a
+// bool.
 func (o *OutOfLineContent) hasSRC() bool { return true }
 
+// getType returns the Type of the OutOfLineContent as a string.
 func (o *OutOfLineContent) getType() string { return string(o.Type) }
 
+// Check checks the OutOfLineContent for incompatibilities with RFC4287. It
+// returns an error.
 func (o *OutOfLineContent) Check() error {
 	mediaType := o.getType()
 

person.go

@@ -1,4 +1,4 @@
-package atomfeed
+package atom
 
 import (
 	"errors"
@@ -14,11 +14,12 @@ type Person struct {
 	Extensions []*ExtensionElement `xml:",any,omitempty"`
 }
 
+// NewPerson creates a new Person. It returns a *Person.
 func NewPerson(name string) *Person {
 	return &Person{Name: name}
 }
 
-// AddExtension adds the extension to the person
+// AddExtension adds the Extension to the Person.
 func (p *Person) AddExtension(e *ExtensionElement) {
 	if p.Extensions == nil {
 		p.Extensions = make([]*ExtensionElement, 1)
@@ -28,6 +29,8 @@ func (p *Person) AddExtension(e *ExtensionElement) {
 	}
 }
 
+// Check checks the Person for incompatibilities with RFC4287. It returns an
+// error.
 func (p *Person) Check() error {
 	if p.Name == "" {
 		return errors.New("name element of person element empty")

plainText.go

@@ -1,4 +1,4 @@
-package atomfeed
+package atom
 
 import "errors"
 
@@ -8,8 +8,11 @@ type PlainText struct {
 	Text string `xml:"text"`
 }
 
+// isText checks whether the PlainText is a Text. It returns a bool.
 func (p *PlainText) isText() bool { return true }
 
+// Check checks the PlainText for incompatibilities with RFC4287. It returns an
+// error.
 func (p *PlainText) Check() error {
 	if p.Type != "" && p.Type != "text" && p.Type != "html" {
 		return errors.New("type attribute of plain text must be text or html if not omitted")

source.go

@@ -1,4 +1,4 @@
-package atomfeed
+package atom
 
 import "fmt"
 
@@ -12,99 +12,91 @@ type Source struct {
 	ID           *ID                 `xml:"id,omitempty"`
 	Links        []*Link             `xml:"link,omitempty"`
 	Logo         *Logo               `xml:"logo,omitempty"`
-	Rights       *Text               `xml:"rights,omitempty"`
-	Subtitle     *Text               `xml:"subtitle,omitempty"`
-	Title        *Text               `xml:"title,omitempty"`
+	Rights       Text                `xml:"rights,omitempty"`
+	Subtitle     Text                `xml:"subtitle,omitempty"`
+	Title        Text                `xml:"title,omitempty"`
 	Updated      *Date               `xml:"updated,omitempty"`
 	Extensions   []*ExtensionElement `xml:",any,omitempty"`
 }
 
+// Check checks the Source for incompatibilities with RFC4287. It returns an
+// error.
 func (s *Source) Check() error {
-	if s.Authors != nil {
-		for i, a := range s.Authors {
-			if err := a.Check(); err != nil {
-				return fmt.Errorf("author element %v of source: %v", i, err)
-			}
+	for i, a := range s.Authors {
+		if err := a.Check(); err != nil {
+			return fmt.Errorf("author element %v of source %v: %v", i, s.ID.URI, err)
 		}
 	}
 
-	if s.Categories != nil {
-		for i, c := range s.Categories {
-			if err := c.Check(); err != nil {
-				return fmt.Errorf("category element %v of source: %v", i, err)
-			}
+	for i, c := range s.Categories {
+		if err := c.Check(); err != nil {
+			return fmt.Errorf("category element %v of source %v: %v", i, s.ID.URI, err)
 		}
 	}
 
-	if s.Contributors != nil {
-		for i, c := range s.Contributors {
-			if err := c.Check(); err != nil {
-				return fmt.Errorf("contributor element %v of source: %v", i, err)
-			}
+	for i, c := range s.Contributors {
+		if err := c.Check(); err != nil {
+			return fmt.Errorf("contributor element %v of source %v: %v", i, s.ID.URI, err)
 		}
 	}
 
 	if s.Generator != nil {
 		if err := s.Generator.Check(); err != nil {
-			return fmt.Errorf("generator element of source: %v", err)
+			return fmt.Errorf("generator element of source %v: %v", s.ID.URI, err)
 		}
 	}
 
 	if s.Icon != nil {
 		if err := s.Icon.Check(); err != nil {
-			return fmt.Errorf("icon element of source: %v", err)
+			return fmt.Errorf("icon element of source %v: %v", s.ID.URI, err)
 		}
 	}
 
 	if s.ID != nil {
 		if err := s.ID.Check(); err != nil {
-			return fmt.Errorf("id element of source: %v", err)
+			return fmt.Errorf("id element of source %v: %v", s.ID.URI, err)
 		}
 	}
 
-	if s.Links != nil {
-		for i, l := range s.Links {
-			if err := l.Check(); err != nil {
-				return fmt.Errorf("link element %v of source: %v", i, err)
-			}
+	for i, l := range s.Links {
+		if err := l.Check(); err != nil {
+			return fmt.Errorf("link element %v of source %v: %v", i, s.ID.URI, err)
 		}
 	}
 
 	if s.Logo != nil {
 		if err := s.Logo.Check(); err != nil {
-			return fmt.Errorf("logo element of source: %v", err)
+			return fmt.Errorf("logo element of source %v: %v", s.ID.URI, err)
 		}
 	}
 
 	if s.Rights != nil {
-		if err := (*s.Rights).Check(); err != nil {
-			return fmt.Errorf("rights element of source: %v", err)
+		if err := s.Rights.Check(); err != nil {
+			return fmt.Errorf("rights element of source %v: %v", s.ID.URI, err)
 		}
 	}
 
 	if s.Subtitle != nil {
-		if err := (*s.Subtitle).Check(); err != nil {
-			return fmt.Errorf("subtitle element of source: %v", err)
+		if err := s.Subtitle.Check(); err != nil {
+			return fmt.Errorf("subtitle element of source %v: %v", s.ID.URI, err)
 		}
 	}
 
 	if s.Title != nil {
-		if err := (*s.Title).Check(); err != nil {
-			return fmt.Errorf("title element of source: %v", err)
+		if err := s.Title.Check(); err != nil {
+			return fmt.Errorf("title element of source %v: %v", s.ID.URI, err)
 		}
 	}
 
 	if s.Updated != nil {
 		if err := s.Updated.Check(); err != nil {
-			return fmt.Errorf("updated element of source: %v", err)
+			return fmt.Errorf("updated element of source %v: %v", s.ID.URI, err)
 		}
 	}
 
-	if s.Extensions != nil {
-		for i, e := range s.Extensions {
-			if err := e.Check(); err != nil {
-				return fmt.Errorf("extension element %v of source: %v", i, err)
-			}
+	for i, e := range s.Extensions {
+		if err := e.Check(); err != nil {
+			return fmt.Errorf("extension element %v of source %v: %v", i, s.ID.URI, err)
 		}
 	}
 

text.go

@@ -1,4 +1,4 @@
-package atomfeed
+package atom
 
 import (
 	"fmt"
@@ -10,6 +10,7 @@ type Text interface {
 	Check() error
 }
 
+// NewText creates a new Text. It returns a Text and an error.
 func NewText(textType, content string) (Text, error) {
 	switch textType {
 	case "text", "":

xhtmlText.go

@@ -1,4 +1,4 @@
-package atomfeed
+package atom
 
 import (
 	"encoding/xml"
@@ -17,8 +17,11 @@ type XHTMLText struct {
 	XHTMLDiv XHTMLDiv
 }
 
+// isText checks whether the XHTMLText is a Text. It returns a bool.
 func (x *XHTMLText) isText() bool { return true }
 
+// Check checks the XHTMLText for incompatibilities with RFC4287. It returns an
+// error.
 func (x *XHTMLText) Check() error {
 	if x.Type != "xhtml" {
 		return errors.New("type attribute of xhtml text must be xhtml")