Fix FUSE reads for unknown attachment sizes

mount.go

@@ -12,6 +12,7 @@ import (
 
 	"bazil.org/fuse"
 	"bazil.org/fuse/fs"
+	"bazil.org/fuse/fuseutil"
 )
 
 type docspellFS struct {
@@ -27,6 +28,7 @@ type fileNode struct {
 	name         string
 	attachmentID string
 	size         uint64
+	knownSize    bool
 	modTime      time.Time
 	client       *DocspellClient
 	data         []byte
@@ -100,7 +102,7 @@ func buildMountTree(client *DocspellClient, items []SearchItem) *dirNode {
 				name = fmt.Sprintf("%s - %02d - %s", base, i+1, name)
 			}
 			name = uniqueName(dir.children, name)
-			dir.children[name] = &fileNode{name: name, attachmentID: att.ID, size: uint64(att.Size), modTime: modTime, client: client}
+			dir.children[name] = &fileNode{name: name, attachmentID: att.ID, size: uint64(att.Size), knownSize: att.Size > 0, modTime: modTime, client: client}
 		}
 	}
 	return root
@@ -179,13 +181,28 @@ func (d *dirNode) ReadDirAll(ctx context.Context) ([]fuse.Dirent, error) {
 
 func (f *fileNode) Attr(ctx context.Context, a *fuse.Attr) error {
 	a.Mode = 0444
-	a.Size = f.size
+	if f.knownSize {
+		a.Size = f.size
+	}
 	a.Mtime = f.modTime
 	a.Ctime = f.modTime
 	return nil
 }
 
+func (f *fileNode) Read(ctx context.Context, req *fuse.ReadRequest, resp *fuse.ReadResponse) error {
+	data, err := f.load(ctx)
+	if err != nil {
+		return err
+	}
+	fuseutil.HandleRead(req, resp, data)
+	return nil
+}
+
 func (f *fileNode) ReadAll(ctx context.Context) ([]byte, error) {
+	return f.load(ctx)
+}
+
+func (f *fileNode) load(ctx context.Context) ([]byte, error) {
 	if f.data != nil {
 		return f.data, nil
 	}
@@ -195,5 +212,6 @@ func (f *fileNode) ReadAll(ctx context.Context) ([]byte, error) {
 	}
 	f.data = data
 	f.size = uint64(len(data))
+	f.knownSize = true
 	return data, nil
 }

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")
+	}
+}