iclouddrive: fix uploads into an app container failing with 412 - fixes #9729

Writing any file into a third-party app container - the Obsidian, Pages or
Shortcuts folders that iCloud Drive shows alongside your own - failed with

    HTTP error 412 (412 Precondition Failed) returned body:
    "{ ... \"error_code\" : \"VALIDATING_REFERENCE_ERROR\", \"reason\" :
    \"Request has out of order children to be chained but the parents were
    missing\" }"

Reading from those paths worked, and so did creating directories in them, so
the failure looked like a missing parent when the parent was plainly there.

Items in an app container live in a different zone from ordinary iCloud Drive
folders: a folder under Documents has a drive ID like
FOLDER::com.apple.CloudDocs::<uuid>, while the Obsidian container has
FOLDER::iCloud.md.obsidian::documents#o2v. DownloadFile already accounts for
this - it deconstructs the item's own ID and addresses the zone it finds - but
CreateUpload and UpdateFile hardcoded defaultZone, and UpdateFile built the
resulting Drivewsid with a hardcoded com.apple.CloudDocs as well.

So rclone asked Apple to chain the new document to a parent in
com.apple.CloudDocs while the parent lived in iCloud.md.obsidian. The parent
really was missing from the zone being addressed, which is what the error said.

Take the zone from the parent's drive ID instead, the same way the download
path does, and build the new item's ID with ConstructDriveID. Uploads outside
an app container are unaffected: their parents are in com.apple.CloudDocs, so
the derived zone is the value that was previously hardcoded.

Verified against a real remote: files now upload into an Obsidian vault inside
the container and read back correctly with an unpatched binary afterwards.

backend/iclouddrive/api/drive.go

@@ -498,7 +498,7 @@ func (d *DriveService) CopyDocByItemID(ctx context.Context, itemID string) (*Dri
 }
 
 // CreateUpload creates an url for an upload.
-func (d *DriveService) CreateUpload(ctx context.Context, size int64, name string) (*UploadResponse, *http.Response, error) {
+func (d *DriveService) CreateUpload(ctx context.Context, size int64, name, zone string) (*UploadResponse, *http.Response, error) {
 	// first we need to request an upload url
 	values := map[string]any{
 		"filename":     name,
@@ -513,7 +513,7 @@ func (d *DriveService) CreateUpload(ctx context.Context, size int64, name string
 
 	opts := rest.Opts{
 		Method:       "POST",
-		Path:         "/ws/" + defaultZone + "/upload/web",
+		Path:         "/ws/" + zone + "/upload/web",
 		ExtraHeaders: d.icloud.Session.GetHeaders(map[string]string{}),
 		RootURL:      d.docsEndpoint,
 		Body:         body,
@@ -552,14 +552,14 @@ func (d *DriveService) Upload(ctx context.Context, in io.Reader, size int64, nam
 // ctx: the context.Context object for the request.
 // r: a pointer to the UpdateFileInfo struct containing the information for the file update.
 // Returns a pointer to the DriveItem struct representing the updated file, the http.Response object, and an error if any.
-func (d *DriveService) UpdateFile(ctx context.Context, r *UpdateFileInfo) (*DriveItem, *http.Response, error) {
+func (d *DriveService) UpdateFile(ctx context.Context, r *UpdateFileInfo, zone string) (*DriveItem, *http.Response, error) {
 	body, err := IntoReader(r)
 	if err != nil {
 		return nil, nil, err
 	}
 	opts := rest.Opts{
 		Method:       "POST",
-		Path:         "/ws/" + defaultZone + "/update/documents",
+		Path:         "/ws/" + zone + "/update/documents",
 		ExtraHeaders: d.icloud.Session.GetHeaders(map[string]string{}),
 		RootURL:      d.docsEndpoint,
 		Body:         body,
@@ -572,7 +572,7 @@ func (d *DriveService) UpdateFile(ctx context.Context, r *UpdateFileInfo) (*Driv
 
 	doc := responseInfo.Results[0].Document
 	item := DriveItem{
-		Drivewsid:    "FILE::com.apple.CloudDocs::" + doc.DocumentID,
+		Drivewsid:    ConstructDriveID(doc.DocumentID, zone, "FILE"),
 		Docwsid:      doc.DocumentID,
 		Itemid:       doc.ItemID,
 		Etag:         doc.Etag,
@@ -892,6 +892,18 @@ func DeconstructDriveID(id string) (docType, zone, docid string) {
 	return split[0], split[1], split[2]
 }
 
+// ZoneFromDriveID returns the zone a drive ID belongs to, or the default zone
+// for an ID that carries none. Items in an app container -- Obsidian, Pages,
+// Shortcuts -- live in that app's zone rather than com.apple.CloudDocs, and a
+// write addressed to the wrong zone cannot resolve its parent.
+func ZoneFromDriveID(id string) string {
+	_, zone, _ := DeconstructDriveID(id)
+	if zone == "" {
+		return defaultZone
+	}
+	return zone
+}
+
 // ConstructDriveID constructs a drive ID from the given components.
 func ConstructDriveID(id string, zone string, t string) string {
 	return strings.Join([]string{t, zone, id}, "::")

backend/iclouddrive/api/drive_test.go

@@ -0,0 +1,32 @@
+package api
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestZoneFromDriveID(t *testing.T) {
+	for _, test := range []struct {
+		name string
+		id   string
+		want string
+	}{
+		{"app container", "FOLDER::iCloud.md.obsidian::documents#o2v", "iCloud.md.obsidian"},
+		{"another app container", "FOLDER::com.apple.Pages::documents#7qt", "com.apple.Pages"},
+		{"ordinary folder", "FOLDER::com.apple.CloudDocs::B847FE2D", "com.apple.CloudDocs"},
+		{"file in a container", "FILE::iCloud.md.obsidian::abc123", "iCloud.md.obsidian"},
+		{"no zone", "root", defaultZone},
+		{"empty", "", defaultZone},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			assert.Equal(t, test.want, ZoneFromDriveID(test.id))
+		})
+	}
+}
+
+func TestZoneFromDriveIDRoundTrip(t *testing.T) {
+	id := ConstructDriveID("abc123", "iCloud.md.obsidian", "FILE")
+	assert.Equal(t, "FILE::iCloud.md.obsidian::abc123", id)
+	assert.Equal(t, "iCloud.md.obsidian", ZoneFromDriveID(id))
+}