Check if the type of contents is a composite media type

atom.go

@@ -1,8 +1,31 @@
 package atomfeed
 
+import (
+	"mime"
+	"strings"
+)
+
 type (
 	EmailAddress string
 	LanguageTag  string
 	MediaType    string
 	URI          string
 )
+
+func isCompositeMediaType(mediaType string) bool {
+	mediaType, _, err := mime.ParseMediaType(mediaType)
+	if err != nil {
+		return false
+	}
+
+	return strings.HasPrefix(mediaType, "multipart/") || strings.HasPrefix(mediaType, "message/")
+}
+
+func isXMLMediaType(mediaType string) bool {
+	mediaType, _, err := mime.ParseMediaType(mediaType)
+	if err != nil {
+		return false
+	}
+
+	return strings.HasSuffix(mediaType, "/xml") || strings.HasSuffix(mediaType, "+xml")
+}

entry.go

@@ -4,7 +4,6 @@ import (
 	"encoding/xml"
 	"errors"
 	"fmt"
-	"mime"
 	"strings"
 )
 
@@ -59,10 +58,6 @@ func alternateRelExists(l []*Link) bool {
 	return false
 }
 
-func isXMLMediaType(mediaType string) bool {
-	return strings.HasSuffix(mediaType, "/xml") || strings.HasSuffix(mediaType, "+xml")
-}
-
 func (e *Entry) AddExtension(name string, value any) {
 	e.Extensions = append(e.Extensions, &ExtensionElement{XMLName: xml.Name{Local: name}, Value: value})
 }
@@ -148,10 +143,7 @@ func (e *Entry) Check() error {
 		// "type" attribute of atom:content is a MIME media type [MIMEREG], but
 		// is not an XML media type [RFC3023], does not begin with "text/", and
 		// does not end with "/xml" or "+xml".
-		mediaType, _, err := mime.ParseMediaType(e.Content.getType())
-		if err != nil {
-			return fmt.Errorf("type attribute of content element of entry %v: %v", e.ID.URI, err)
-		}
+		mediaType := e.Content.getType()
 		if !isXMLMediaType(mediaType) && !strings.HasPrefix(mediaType, "text/") {
 			return fmt.Errorf("no summary element of entry %v but media type not xml", e.ID.URI)
 		}

inlineOtherContent.go

@@ -1,5 +1,7 @@
 package atomfeed
 
+import "errors"
+
 type InlineOtherContent struct {
 	*CommonAttributes
 	Type       MediaType `xml:"type,attr,omitempty"`
@@ -12,4 +14,10 @@ func (i *InlineOtherContent) hasSRC() bool { return false }
 
 func (i *InlineOtherContent) getType() string { return string(i.Type) }
 
-func (i *InlineOtherContent) Check() error { return nil }
+func (i *InlineOtherContent) Check() error {
+	if isCompositeMediaType(i.getType()) {
+		return errors.New("type attribute of inline other content must not be a composite type")
+	}
+
+	return nil
+}

outOfLineContent.go

@@ -15,6 +15,10 @@ func (o *OutOfLineContent) hasSRC() bool { return true }
 func (o *OutOfLineContent) getType() string { return string(o.Type) }
 
 func (o *OutOfLineContent) Check() error {
+	if isCompositeMediaType(o.getType()) {
+		return errors.New("type attribute of out of line content must not be a composite type")
+	}
+
 	if o.SRC == "" {
 		return errors.New("src attribute of out of line content empty")
 	}