Add a nil guard to prevent crashes when a link's media type cannot be parsed

pkg/content/iterator/html.go

@@ -37,7 +37,7 @@ func NewHTML(resource fetcher.Resource, locator manifest.Locator) *HTMLContentIt
 
 func HTMLFactory() ResourceContentIteratorFactory {
 	return func(resource fetcher.Resource, locator manifest.Locator) Iterator {
-		if resource.Link().MediaType.Matches(&mediatype.HTML, &mediatype.XHTML) {
+		if mt := resource.Link().MediaType; mt != nil && mt.Matches(&mediatype.HTML, &mediatype.XHTML) {
 			return NewHTML(resource, locator)
 		}
 		return nil

pkg/manifest/link.go

@@ -257,7 +257,7 @@ func (ll LinkList) FilterByRel(rel string) LinkList {
 // Finds the first link matching the given media type.
 func (ll LinkList) FirstWithMediaType(mt *mediatype.MediaType) *Link {
 	for _, link := range ll {
-		if link.MediaType.Matches(mt) {
+		if link.MediaType != nil && link.MediaType.Matches(mt) {
 			return &link
 		}
 	}
@@ -268,7 +268,7 @@ func (ll LinkList) FirstWithMediaType(mt *mediatype.MediaType) *Link {
 func (ll LinkList) FilterByMediaType(mt ...*mediatype.MediaType) LinkList {
 	flinks := make(LinkList, 0)
 	for _, link := range ll {
-		if link.MediaType.Matches(mt...) {
+		if link.MediaType != nil && link.MediaType.Matches(mt...) {
 			flinks = append(flinks, link)
 		}
 	}
@@ -278,7 +278,7 @@ func (ll LinkList) FilterByMediaType(mt ...*mediatype.MediaType) LinkList {
 // Returns whether all the resources in the collection are bitmaps.
 func (ll LinkList) AllAreBitmap() bool {
 	for _, link := range ll {
-		if !link.MediaType.IsBitmap() {
+		if link.MediaType == nil || !link.MediaType.IsBitmap() {
 			return false
 		}
 	}
@@ -288,7 +288,7 @@ func (ll LinkList) AllAreBitmap() bool {
 // Returns whether all the resources in the collection are audio clips.
 func (ll LinkList) AllAreAudio() bool {
 	for _, link := range ll {
-		if !link.MediaType.IsAudio() {
+		if link.MediaType == nil || !link.MediaType.IsAudio() {
 			return false
 		}
 	}
@@ -298,7 +298,7 @@ func (ll LinkList) AllAreAudio() bool {
 // Returns whether all the resources in the collection are video clips.
 func (ll LinkList) AllAreVideo() bool {
 	for _, link := range ll {
-		if !link.MediaType.IsVideo() {
+		if link.MediaType == nil || !link.MediaType.IsVideo() {
 			return false
 		}
 	}
@@ -308,7 +308,7 @@ func (ll LinkList) AllAreVideo() bool {
 // Returns whether all the resources in the collection are bitmaps or video clips.
 func (ll LinkList) AllAreVisual() bool {
 	for _, link := range ll {
-		if !link.MediaType.IsBitmap() && !link.MediaType.IsVideo() {
+		if link.MediaType == nil || (!link.MediaType.IsBitmap() && !link.MediaType.IsVideo()) {
 			return false
 		}
 	}
@@ -318,7 +318,7 @@ func (ll LinkList) AllAreVisual() bool {
 // Returns whether all the resources in the collection are HTML documents.
 func (ll LinkList) AllAreHTML() bool {
 	for _, link := range ll {
-		if !link.MediaType.IsHTML() {
+		if link.MediaType == nil || !link.MediaType.IsHTML() {
 			return false
 		}
 	}
@@ -328,7 +328,7 @@ func (ll LinkList) AllAreHTML() bool {
 // Returns whether all the resources in the collection are matching the given media type.
 func (ll LinkList) AllMatchMediaType(mt ...*mediatype.MediaType) bool {
 	for _, link := range ll {
-		if !link.MediaType.Matches(mt...) {
+		if link.MediaType == nil || !link.MediaType.Matches(mt...) {
 			return false
 		}
 	}

pkg/parser/audio/parser.go

@@ -214,7 +214,7 @@ func (p AudioParser) accepts(ctx context.Context, asset asset.PublicationAsset,
 		if extensions.IsHiddenOrThumbs(path) {
 			continue
 		}
-		if link.MediaType.IsBitmap() {
+		if link.MediaType != nil && link.MediaType.IsBitmap() {
 			continue
 		}
 		fext := filepath.Ext(strings.ToLower(path))

pkg/parser/image/parser.go

@@ -39,7 +39,7 @@ func (p ImageParser) Parse(ctx context.Context, asset asset.PublicationAsset, fe
 		path := link.URL(nil, nil).Path()
 
 		// Filter out all irrelevant files
-		if extensions.IsHiddenOrThumbs(path) || !link.MediaType.IsBitmap() {
+		if extensions.IsHiddenOrThumbs(path) || link.MediaType == nil || !link.MediaType.IsBitmap() {
 			continue
 		}
 		readingOrder = append(readingOrder, link)
@@ -94,7 +94,7 @@ func (p ImageParser) accepts(ctx context.Context, asset asset.PublicationAsset,
 		if extensions.IsHiddenOrThumbs(path) {
 			continue
 		}
-		if link.MediaType.IsBitmap() {
+		if link.MediaType != nil && link.MediaType.IsBitmap() {
 			continue
 		}
 		fext := filepath.Ext(strings.ToLower(path))

pkg/streamer/a11y_infer.go

@@ -65,6 +65,9 @@ func inferA11yMetadataInPublicationManifest(ctx context.Context, pub *pub.Public
 
 		for _, link := range allResources {
 			mt := link.MediaType
+			if mt == nil {
+				continue
+			}
 			if mt.IsAudio() ||
 				mt.IsVideo() ||
 				mt.Matches(&mediatype.PDF) {
@@ -109,7 +112,7 @@ func inferA11yMetadataInPublicationManifest(ctx context.Context, pub *pub.Public
 		// audio or video resource (inspect "resources" and "readingOrder" in
 		// RWPM).
 		for _, link := range allResources {
-			if link.MediaType.IsAudio() || link.MediaType.IsVideo() {
+			if link.MediaType != nil && (link.MediaType.IsAudio() || link.MediaType.IsVideo()) {
 				inferredA11y.AccessModes = append(inferredA11y.AccessModes, manifest.A11yAccessModeAuditory)
 				break
 			}
@@ -119,7 +122,7 @@ func inferA11yMetadataInPublicationManifest(ctx context.Context, pub *pub.Public
 		// or a video resource (inspect "resources" and "readingOrder" in
 		// RWPM).
 		for _, link := range allResources {
-			if link.MediaType.IsBitmap() || link.MediaType.IsVideo() {
+			if link.MediaType != nil && (link.MediaType.IsBitmap() || link.MediaType.IsVideo()) {
 				inferredA11y.AccessModes = append(inferredA11y.AccessModes, manifest.A11yAccessModeVisual)
 				break
 			}
@@ -170,7 +173,7 @@ func inferA11yMetadataInPublicationManifest(ctx context.Context, pub *pub.Public
 		}
 
 		for _, link := range mf.Resources {
-			if link.MediaType.Matches(&mediatype.SMIL) {
+			if link.MediaType != nil && link.MediaType.Matches(&mediatype.SMIL) {
 				addFeature(manifest.A11yFeatureSynchronizedAudioText)
 				break
 			}

pkg/streamer/a11y_infer_test.go

@@ -46,6 +46,34 @@ func newLink(mt mediatype.MediaType, extension string) manifest.Link {
 	}
 }
 
+// A resource with an unparseable media type is treated as unclassified.
+func TestInferA11yMetadataTreatsNilMediaTypeAsUnclassified(t *testing.T) {
+	nilMediaTypeLink := manifest.Link{
+		Href: manifest.MustNewHREFFromString("file.ttf", false),
+	}
+	require.Nil(t, nilMediaTypeLink.MediaType)
+
+	m := manifest.Manifest{
+		Metadata: manifest.Metadata{
+			ConformsTo: manifest.Profiles{manifest.ProfileEPUB},
+			Layout:     manifest.LayoutReflowable,
+		},
+		ReadingOrder: []manifest.Link{
+			newLink(mediatype.HTML, "html"),
+		},
+		Resources: []manifest.Link{
+			nilMediaTypeLink,
+		},
+	}
+
+	require.NotPanics(t, func() {
+		res, err := inferA11yMetadataInPublicationManifest(context.TODO(), pub.New(m, nil, nil), nil)
+		require.NoError(t, err)
+		assert.NotNil(t, res)
+		assert.Contains(t, res.AccessModes, manifest.A11yAccessModeTextual)
+	})
+}
+
 // If the publication contains a reference to an audio or video resource
 // (inspect "resources" and "readingOrder" in RWPM).
 func TestInferAuditoryAccessMode(t *testing.T) {