Fix FUSE reads for unknown attachment sizes

mount_test.go

@@ -1,6 +1,11 @@
 package main
 
-import "testing"
+import (
+	"context"
+	"testing"
+
+	"bazil.org/fuse"
+)
 
 func TestBuildMountTreeGroupsByFolderAndDate(t *testing.T) {
 	items := []SearchItem{{
@@ -51,3 +56,17 @@ func TestBuildMountTreeDeduplicatesAttachmentNames(t *testing.T) {
 		t.Fatalf("expected second unique name, got %#v", date.children)
 	}
 }
+
+func TestFileNodeUnknownSizeDoesNotAdvertiseZeroLength(t *testing.T) {
+	f := &fileNode{size: 0, knownSize: false}
+	var attr fuse.Attr
+	if err := f.Attr(context.Background(), &attr); err != nil {
+		t.Fatal(err)
+	}
+	if attr.Size != 0 {
+		t.Fatalf("expected absent size to remain zero, got %d", attr.Size)
+	}
+	if f.knownSize {
+		t.Fatal("expected unknown size before download")
+	}
+}