b2: Fix link sharing #3314

backend/b2/b2.go

@@ -629,6 +629,10 @@ func (f *Fs) list(ctx context.Context, dir string, recurse bool, prefix string,
 		if err != nil {
 			return err
 		}
+		// Check that there are matching files
+		if len(response.Files) == 0 {
+			return fs.ErrorDirNotFound
+		}
 		for i := range response.Files {
 			file := &response.Files[i]
 			// Finish if file name no longer has prefix
@@ -1227,6 +1231,15 @@ func (f *Fs) PublicLink(ctx context.Context, remote string) (link string, err er
 	} else {
 		RootURL = f.opt.DownloadURL
 	}
+	_, err = f.NewObject(ctx, remote)
+	if err == fs.ErrorObjectNotFound || err == fs.ErrorNotAFile {
+		err = f.list(ctx, remote, false, "", 1, f.opt.Versions, func(remote string, object *api.File, isDirectory bool) error {
+			return errEndList
+		})
+	}
+	if err != nil {
+		return "", err
+	}
 	absPath := "/" + path.Join(f.root, remote)
 	link = RootURL + "/file/" + urlEncode(f.bucket) + absPath
 	bucketType, err := f.getbucketType()