Re: [bug-mailutils] Problem with timeout interaction

[Sergey Poznyakoff]

Hello,

Alain Magloire <address@hidden> wrote:

> In any case, I do agree for POP3D if you quit before reaching
> the update state any messages mark deleted should be unmark
> and left untouch (except the UID, it is preserve across sessions).

Agreed.
 
> But my question is:
> In a POP3 session should the deleted messages in the update state(after the 
> QUIT)
> be __only the messages marked deleted in *that current pop3 session*__ not
> messages marked(via Status: d) in an unrelated action on the mailbox ?

No, I guess not. After a good thought I must admit that my proposition
about not using attribute_set_deleted() was completely wrong. We *have to*
use Status flag for keeping the deletion mark. I'll elaborate on this
below.
 
> I think, sergey, you bring a good point, that we probably should
> not use attribute_set_deleted() to mark message, but rather maintain
> our own list to not to interfere whith any previous state of the mailbox.

On the other hand, this seems to bring more questions than answers. Here
are few of them off the top of my head (there may be more of them...):

1) What is the semantics of the deletion mark, then? If we do not use it
to mark messages for deletion, what purpose does it serve?

2) Interoperation issue I (internal): once we modify pop3d to have its
internal list of deleted messages, we'll have to do the same for the
rest of utilities, which means moving this "internal list support" to
the core libmailbox.

3) Interoperation issue II (external): most existing MUAs use Status:
field to keep the deletion information. If we switch to the "internal
list" method, the compatibility between Mailutils and other MUAs will
be lost.

4) The expunge mechanism discerns messages to be deleted by the presence
of "D" mark in Status: field. If we switch to another method, this will
have to be rewritten.

5) A message may be marked as deleted *and* still remain in the mailbox.
It is normal. Whatever method we will be using for marking deleted
messages, we must provide for storing this information along with the
message itself for eventual future use (e.g. either unmarking or expunging).
The only place where such information may be stored is in the header. Thus,
we'll end up creating new Status field.

6) After all, keeping deletion mark in Status is logical and
complies to RFCs: that's what this header had been created for.

In short, my opinion is that Status: is the right place for the
deletion mark.


Returning to the the pop3d issue. The way Jeff proposed seems
to be a good solution. The only implication it brings is
the following: if the mailbox being opened already had some
messages marked for deletion, they will be unmarked before
exiting on timeout. I don't know if it is wrong. Possibly
we should even provide an option that will force pop3d to
clear any deletion marks from the messages in a mailbox right
after opening it. This will ensure a proper interoperation with
the clients like Eudora.

However, to fix this issue as well I propose the following
scenario:

1) In pop3d.h:

#define POP3_ATTRIBUTE_DELE 0x0001

2) In dele.c:

int
pop3d_dele (const char *arg)
{
  size_t num;
  message_t msg;
  attribute_t attr = NULL;

  /* ... */
  /* Everything remains untouched except this line: */
  attribute_set_userflag (attr, POP3_ATTRIBUTE_DELE);
  pop3d_outf ("+OK Message %d marked\r\n", num);
  return OK;
}

3) In extra.c (pop3d_abquit): No changes needed.

4) In quit.c

int
pop3d_quit (const char *arg)
{
  int err = OK;
  if (strlen (arg) != 0)
    return ERR_BAD_ARGS;

  if (state == TRANSACTION)
    {
      pop3d_fix_mark (); /* Note this. That's the only change */
      pop3d_unlock ();
      if (mailbox_flush (mbox, 1) != 0)
        err = ERR_FILE;
    ...

void
pop3d_fix_mark ()
{
  size_t i;
  size_t total = 0;

  mailbox_messages_count (mbox, &total);

  for (i = 1; i <= total; i++)
    {
       message_t msg = NULL;
       attribute_t attr = NULL;
       mailbox_get_message (mbox, i, &msg);
       message_get_attribute (msg, &attr);
       if (attribute_is_userflag (attr, POP3_ATTRIBUTE_DELE))
          attribute_set_deleted (attr);
    }
}                              

Advantages:

 1) No pop3d-inserted deletion marks are preserved when exiting on
 timeout.
 2) The deletion marks set via other MUAs are preserved.
 3) Minimal modifications to the code.

Now, if we provide an option telling pop3d to clear all deletion marks
at startup, then the administrator of the server is quite free to decide
whether he needs the marks cleaned up or preserved.
     
Regards,
Sergey