Separate folder name from remote folder ID

[philipwhiuk]

I've been looking into various folder related issues recently and I've come to the conclusion we need to introduce the concept of remote folder ID.

This will help in the following circumstances:

1. For Show subfolders as real subfolders in folder list #630 we will be able to use the folder name as the actual name (i.e. Computing.K9 will become K9.
2. For Support for IMAP shared (not under INBOX) folders #1342 we will be able to uniquely identify folders as to which namespace they are under
3. For Support newer Exchange servers #606 we will then be able to support EWS which mostly uses a 'unique ID' to reference folders rather than name.

This will impact the following areas of code:

Database Structure

The folders table will have a new column, remoteID

Existing folders will have their current folderName copied to the remoteID column during migration.

Stores

All access to folders will be via the ID, not the name. Hence the folder cache will map from ID to Folder<?>

When the folder list is refreshed (getPersonalNamespaces() [which is by the way a terribly IMAP specific name]) we can update the name of existing folders.

[philipwhiuk]

Just to record what I wrote on IRC:

We currently have 3 versions of identifying the folder:

• Database ID
• Folder Name
• Folder Display Name

We store the Database ID and the FolderName
The Folder Display Name is computer in the FolderInfoHolder class from FolderName and list of special folders.

For example, in IMAP for a given folder we have the following:

IMAP Namespace: "."
DB ID: 3
Folder Name: Spam
Folder Display Name: Spam (Spam)
DB Entry: 3 | Spam

The change I propose changes this to:

IMAP Namespace: "."
DB ID: 3
Folder ID: Spam
Folder Name: Spam
Folder Display Name: Spam (Spam)
DB Entry: 3 | Spam | Spam

3 | Spam | Spam

When we implement multiple namespaces it will change to:

DB ID: 3
Folder ID: /Spam
Folder Name: Spam
Folder Display Name: Spam (Spam)
DB Entry: 3 | /Spam | Spam

and we can support other folders in different namespaces for example:

DB ID: 4
Folder ID: Global/Spam
Folder Name: Spam
Folder Display Name: Spam (Spam)
DB Entry: 4 | Global/Spam | Spam

When then we implement sub folders properly it allow:

DB ID: 4
Folder ID:/Computing.K9
Folder Name: K9
Folder Display Name: K9
DB Entry: 4 | /Computing.K9 | K9

For EWS (which uses unique IDs instead of obvious names) it will allow:

DB ID: 5
Folder ID: abcd134
Folder Name: Inbox
Folder Display Name: Inbox
DB Entry: 5 | abcd134 | Inbox

[philipwhiuk]

Progress on this is going fairly well. I have a build on my phone that mostly works but I need to tidy it up a lot and make sure everything works as expected:

I've run into a few walls which I'm knocking down as I go:

• The Pop3Store is ancient and needs modernisation. Modernise Pop3Store #2731
• The Migration code is dependent on stuff that uses post-migration queries Migrations should not depend on the Account/LocalStore/Folder/Message classes #2730

My remoteFolderId branch is pushed but I'm still tidying it up, so it'll probably see a decent amount of rebasing before I get to PR territory.

[cketti]

This work has been completed.

For folder hierarchy support see #630.