dlna: cds: don't specify childCount at all when unknown

Basically, solving #3541 with a different approach - bringing in
the upstream upnpav module, and changing ChildCount from int to a
*int to avoid childCount="0" in the XML output when that value is
simply unknown.

Current approach is leading to some recursion issues and according
to the DLNA spec it shouldn't be necessary, anyway.

cmd/serve/dlna/cds.go

@@ -16,8 +16,8 @@ import (
 
 	"github.com/anacrolix/dms/dlna"
 	"github.com/anacrolix/dms/upnp"
-	"github.com/anacrolix/dms/upnpav"
 	"github.com/pkg/errors"
+	"github.com/rclone/rclone/cmd/serve/dlna/upnpav"
 	"github.com/rclone/rclone/fs"
 	"github.com/rclone/rclone/vfs"
 )
@@ -77,16 +77,10 @@ func (cds *contentDirectoryService) cdsObjectToUpnpavObject(cdsObject object, fi
 	}
 
 	if fileInfo.IsDir() {
-		children, err := cds.readContainer(cdsObject, host)
-		if err != nil {
-			return nil, err
-		}
-
 		obj.Class = "object.container.storageFolder"
 		obj.Title = fileInfo.Name()
 		return upnpav.Container{
-			Object:     obj,
-			ChildCount: len(children),
+			Object: obj,
 		}, nil
 	}
 

cmd/serve/dlna/dlna_test.go

@@ -122,8 +122,8 @@ func TestContentDirectoryBrowseMetadata(t *testing.T) {
 	// expect a <container> element
 	require.Contains(t, string(body), html.EscapeString("<container "))
 	require.NotContains(t, string(body), html.EscapeString("<item "))
-	// with a non-zero childCount
-	require.Regexp(t, " childCount=&#34;[1-9]", string(body))
+	// if there is a childCount, it better not be zero
+	require.NotContains(t, string(body), html.EscapeString(" childCount=\"0\""))
 }
 
 // Check that the X_MS_MediaReceiverRegistrar is faked out properly.

cmd/serve/dlna/upnpav/upnpav.go

@@ -0,0 +1,63 @@
+package upnpav
+
+import (
+	"encoding/xml"
+	"time"
+)
+
+const (
+	// NoSuchObjectErrorCode : The specified ObjectID is invalid.
+	NoSuchObjectErrorCode = 701
+)
+
+// Resource description
+type Resource struct {
+	XMLName      xml.Name `xml:"res"`
+	ProtocolInfo string   `xml:"protocolInfo,attr"`
+	URL          string   `xml:",chardata"`
+	Size         uint64   `xml:"size,attr,omitempty"`
+	Bitrate      uint     `xml:"bitrate,attr,omitempty"`
+	Duration     string   `xml:"duration,attr,omitempty"`
+	Resolution   string   `xml:"resolution,attr,omitempty"`
+}
+
+// Container description
+type Container struct {
+	Object
+	XMLName    xml.Name `xml:"container"`
+	ChildCount *int     `xml:"childCount,attr"`
+}
+
+// Item description
+type Item struct {
+	Object
+	XMLName  xml.Name `xml:"item"`
+	Res      []Resource
+	InnerXML string `xml:",innerxml"`
+}
+
+// Object description
+type Object struct {
+	ID          string    `xml:"id,attr"`
+	ParentID    string    `xml:"parentID,attr"`
+	Restricted  int       `xml:"restricted,attr"` // indicates whether the object is modifiable
+	Class       string    `xml:"upnp:class"`
+	Icon        string    `xml:"upnp:icon,omitempty"`
+	Title       string    `xml:"dc:title"`
+	Date        Timestamp `xml:"dc:date"`
+	Artist      string    `xml:"upnp:artist,omitempty"`
+	Album       string    `xml:"upnp:album,omitempty"`
+	Genre       string    `xml:"upnp:genre,omitempty"`
+	AlbumArtURI string    `xml:"upnp:albumArtURI,omitempty"`
+	Searchable  int       `xml:"searchable,attr"`
+}
+
+// Timestamp wraps time.Time for formatting purposes
+type Timestamp struct {
+	time.Time
+}
+
+// MarshalXML formats the Timestamp per DIDL-Lite spec
+func (t Timestamp) MarshalXML(e *xml.Encoder, start xml.StartElement) error {
+	return e.EncodeElement(t.Format("2006-01-02"), start)
+}