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From Jochen Gazda <gazdahims...@gmail.com>
Subject ACL Support - cont. from server-user
Date Fri, 06 Jan 2012 11:25:21 GMT
Gentlemen,

Please read and comment.

I have started to implement the ACL support. In the very first phase I
would like to
 - add support for IMAP GETACL command and
 - add support for storing ACL at least for one storage backend.

During this first phase I would like to learn how to do things in a
James-compiliant way so that I will be able to implement other ACL
commands later.

1. A new interface org.apache.james.mailbox.MailboxACL and default
implementation org.apache.james.mailbox.store.SimpleMailboxACL
Stores an ACL applicable to a mailbox. Inspired by RFC4314 IMAP4
Access Control List (ACL) Extension.
Note: An ACL class that could serve our purpose exists in
com.sun.mail.imap. We will not stick to a proprietary API, will we?

2. MailboxACL usage:
org.apache.james.mailbox.store.mail.model.Mailbox<Id> and
implementations will be extended to store the related ACL:
    MailboxACL getACL();
    void setACL(MailboxACL acl);
This is probably OK.

3. MailboxACL usage: org.apache.james.mailbox.MessageManager.MetaData
will be extended to offer a read access to the ACL of the related
mailbox. This was approved by Norman Maurer.
        MailboxACL getACL();

4. MailboxACL usage: Under org.apache.james.imap ACL-related requests,
decoders, responses, encoders and processors will use MailboxACL.
It is probably OK as there is a lot of org.apache.james.mailbox.*
usage under org.apache.james.imap.

5. MailboxACL instantiation: Clearly, there will be (at least) two
places where MailboxACL will be instantiated:
  i. In Mailbox implementations when reading ACLs from their backends
  ii. In org.apache.james.imap decoders when parsing the ACL related
IMAP requests.

At the moment I have hardcoded a constructor of my default
implementation on both places. I am asking myself if some kind of
factory pattern should be used instead.

6. How to access an ACL stored in a mailbox backend from a subclass of
org.apache.james.imap.processor.AbstractMailboxProcessor:
At the moment I have this code to prepare a response for GETACL IMAP command:
            MessageManager messageManager =
getMailboxManager().getMailbox(buildFullPath(session, mailboxName),
mailboxSession);
            MetaData metaData = messageManager.getMetaData(false,
mailboxSession, FetchGroup.NO_COUNT);

I have not tested it yet, but principally, it should work. I only
wonder at two things with that code:

  i.  org.apache.james.mailbox.MailboxManager.getMailbox(MailboxPath,
MailboxSession)
      It returns a MessageManager rather than a Mailbox. Should it not
rather be called getMessageManager?

  ii. org.apache.james.mailbox.MessageManager.getMetaData(boolean,
MailboxSession, FetchGroup)
      Javadoc says "Gets current meta data for the mailbox." Why is
this method in MessageManager and not in MailboxManager?

7. What and in which order should the GetACLProcessor say after
sending the ACL response?
  i.  Should it send also unsolicitedResponses?
  ii. unsolicitedResponses should be sent before or after okComplete?
  iii. on MailboxException, we send no() and I wonder what should its
HumanReadableText say?
  iv. is the no() sufficient for all exceptions? What if somebody is
asking for ACL of a folder which
      (a) does not exist or
      (b) cannot be looked up by the current user?
      Isn't taggedBad more suitable for (a) and/or (b)?

Here is what I have now:

    @Override
    protected void doProcess(GetACLRequest message, ImapSession
session, String tag, ImapCommand command, Responder responder) {
        final MailboxManager mailboxManager = getMailboxManager();
        final MailboxSession mailboxSession =
ImapSessionUtils.getMailboxSession(session);
        try {
            String mailboxName = message.getMailboxName();
            MessageManager messageManager =
mailboxManager.getMailbox(buildFullPath(session, mailboxName),
mailboxSession);
            MetaData metaData = messageManager.getMetaData(false,
mailboxSession, FetchGroup.NO_COUNT);
            ACLResponse aclResponse = new ACLResponse(mailboxName,
metaData.getACL());
            responder.respond(aclResponse);
            okComplete(command, tag, responder);
            //FIXME should we send unsolicited responses here?
            //unsolicitedResponses(session, responder, false);
        } catch (MailboxException e) {
            // FIXME: be more specific in the human readable text.
            no(command, tag, responder,
HumanReadableText.GENERIC_FAILURE_DURING_PROCESSING);
        }
    }


8. Interpretation of ACLs:
To have ACL stored on every mailbox is far from being able to tell if
the given user can perform the given operation for the given
mailbox(es when copying/moving).
A new service responsible for resolving of ACLs is necessary. I
propose to call it MailboxACLResolver.
In which package should it be placed? Also in org.apache.james.mailbox?
Probably every single operation between IMAP and mailbox stores should
pass through this service. Where in the code should such a permission
enforcement be placed?
How should MailboxACLResolver be instantiated?

9. A new event type: org.apache.james.mailbox.MailboxListener.MailboxACLUpdated
It is quite clear what it should look like. It is also quite clear to
me where and how it should be fired.
But I cannot figure out who should listen to it and what the listener should do.


Thanks,

Gazda

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