On Jun 18 2007, [EMAIL PROTECTED] wrote:
Hi folks.
Here's our situation: Migrating from UW-IMAP. Have lots (as in, tens of
thousands) of clients set up using '~/mail' as the IMAP root, and using
subscriptions.
The rest of my original message is at the end for context. :) Brief:
Subscriptions in general are given to inconsistent behavior if there is any
difference in client settings from one session to the next. Dovecot writes
subscriptions without the namespace prefix and then prepends the current ns
prefix to every item in the subscription list for LSUB response.
So if the namespace prefix changes session-to-session; or if there are
legacy entries with more "full" paths in the subs file, LSUB returns
duplicates and paths that do not exist. This leads to very confused users
and in some cases data loss when they (reasonably) try to delete a
"duplicate" and find they've deleted the only copy of a folder.
In order to avoid this, I made a (very) simple two-part mod. The first bit
simply writes subscriptions with the ns prefix included:
diff cmd-subscribe.c cmd-subscribe.c.orig :
35c35 < if (mail_storage_set_subscribed(storage, verify_name, subscribe) <
0)
---
if (mail_storage_set_subscribed(storage, mailbox, subscribe) < 0)
The second changes LSUB so that it only returns entries from the
subscription list which match the ns prefix, and avoids prepending the ns
prefix to LSUB responses:
diff cmd-list.c cmd-list.c.orig :
138,141c138 < } else if (ctx->lsub && < strncmp(ctx->ns->prefix,
list->name, strlen(ctx->ns->prefix))) { < continue; < } else if
(!ctx->lsub) {
---
} else {
Now we err on the side of not showing some previously subscribed folders if
the client config changes, or if there is random junk in the subscriptions
file--rather than trying to show everything and returning duplicate and
non-existent mailbox paths in LSUB.
Hopefully Timo (or anyone else), you could offer some thoughts on whether
this is an acceptable strategy, or if I've overlooked something. Thanks
very much,
-Brian Hayden
Internet Services
University of Minnesota
Dovecot mail_location is using '~' for mbox storage. We've disabled full
filesystem access in Dovecot in order to use ACLs for shared folders.
Hence we have a hidden namespace for backwards compatibility with those
clients using '~/mail' (dovecot -n output is at the end of this message
so you can see exact settings). Here's the problem. If the client is not
taking advantage of this hidden namespace--say it's configured to use
plain old 'mail' as the root directory--LSUB and SUBSCRIBE work as I'd
expect. Subscribing to a folder called 'foo' puts this in the user's
subscriptions file:
mail/foo
And this (from Thunderbird's log) is the LSUB exchange:
48203776[ed8ebe0]: 2e03600:server.umn.edu:A:SendData: 6 lsub "" "mail/*"
48203776[ed8ebe0]: ReadNextLine [stream=ed8ef88 nb=26 needmore=0]
48203776[ed8ebe0]: 2e03600:serverl.umn.edu:A:CreateNewLineFromSocket: *
LSUB () "/" "mail/foo"
48203776[ed8ebe0]: ReadNextLine [stream=ed8ef88 nb=38 needmore=0]
(trimmed...)
48203776[ed8ebe0]:
2e03600:bhayden.email.umn.edu:A:CreateNewLineFromSocket:
6 OK Lsub completed.
All is well. However, when the client is configured with '~/mail' as the
root and hence triggers the hidden namespace for such, SUBSCRIBE only
writes a path relative to that namespace prefix. So as opposed the
'mail/foo' in the first example, we get:
foo
written to the subs folder.
This leads to three problems:
1. Folders subscribed to when using this namespace will either disappear
or break in a client using a different IMAP root setting that actually
refers to the same place. For example, if this user moves to a client
(such as both of the webmail offerings on campus) that use 'mail/' as the
prefix, these folders will not be visible.
This is a fairly sizeable population of our users, whom we aren't
necessarily in the position to say "too bad" to. :)
2. Users moved over from UW-IMAP, who were using '~/mail' for the IMAP
root, have a subscriptions file full of:
~/mail/bar
Dovecot, with the same client configuration (since it's expecting a bare
folder name to which it will prepend the namespace prefix), interprets
this as so:
49036288[fa7e740]: 2eabc00:server.umn.edu:A:CreateNewLineFromSocket: *
LSUB () "/" "~/mail/~/mail/foobar"
Leading to having the folder displayed in the client's list, but giving an
error on SELECT. Now, this one we could theoretically "solve" by scrubbing
the prefixes out of subs files as we convert; however, that leaves us with
#1 above, where the bare folder name in the subs file depends on (to the
average user) an obscure client config setting, which in practice in a
large heterogeneous environment is unreliable.
3. Users who have been using an IMAP root of 'mail' in some client and
subscribed to folders, who then use a client with the root set to
'~/mail' see what appears to be "duplicates" of the same folder at the
top level and then within a bogus 'mail/' subdirectory. They (quite
reasonably, from their perspective), delete one of these, only to find
they've deleted the only copy of said folder. Not good.
Also, users can't solve some of these problems by unsubbing and re-subbing
on their own, as trying to unsubscribe from a folder that doesn't exist
(such as ~/mail/~/mail/foobar in the example above) fails.
So, I'm wondering if there's any way to address this. I looked through
the list archives and code pretty thoroughly. Only thing I noticed was a
CVS log mentioning a "subscriptions=yes" setting for namespaces, which
sounded like it might address this problem. However, putting that setting
into dovecot.conf causes it to fail to start with a "Unrecognized config
option" error, and using an imap_executable wrapper that sets the env
variable as specified in the code (NAMESPACE_<number>_SUBSCRIPTIONS) sets
it, as I can see from the dovecot log output:
Namespace: type=private, prefix=~/mail/, sep=/, inbox=no, hidden=yes,
subscriptions=yes
But doesn't seem to have any effect. These two things combined lead me to
believe this option was deprecated at some point?
Any thoughts or suggestions? While we're moving away from UW for a reason
;), it does seem to handle this one thing more coherently as it
recognizes, for example, that if the server equivalent of mail_location's
storage is '~', then subscription file entries: '~/mail/foo' and
'mail/foo' are the same thing, while 'foo' is '~/foo'--regardless of
client settings or namespaces. Whereas in the same situation Dovecot
handles a client IMAP root of '~/mail' vs 'mail' differently, even though
they are in fact the same thing.
This is also internally inconsistent, because (as noted above) when a
namespace is not in effect Dovecot SUBSCRIBEs using a path relative to
the mail_location storage--including the client's IMAP root portion of
the path--whereas when a namespace is in effect it SUBSCRIBEs with only
the bare mailbox name without the current client's IMAP root to give it
context and meaning. Wouldn't it seem better to have these be consistent
in this respect?
We need to figure this out somehow before going any further with our
migration. We'll modify the source if necessary, but are hoping for a
solution that doesn't require maintaining local mods to the source code
unless we absolutely have to. :) And this seems like a basic enough issue
that it'd be good to handle it in the real codebase. Thanks for any help
or insight,
-Brian Hayden
Internet Services
University of Minnesota
