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Filename : Design.Storage.MailNamespace.txt
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Mail Namespace
==============

'src/lib-storage/mail-namespace.h' describes mail namespaces. See
<Namespaces.txt> for more information about what they are actually about.

Hierarchy separators and namespace prefixes
-------------------------------------------

A namespace and <mailbox list> [Design.Storage.MailboxList.txt] has 1:1
relationship. A namespace is mainly about dealing with hierarchy separators and
namespace prefixes, which mailbox list doesn't know or care much about.

Mailbox lists have their native hierarchy separators. For example with FS
layout the separator is '/', because child mailboxes are physically in
subdirectories and '/' is the separator for directories. With Maildir++ layout
the separator is (currently) hardcoded to '.' in the maildir directory name, so
that's its native hierarchy separator.

Dovecot allows separators to be configurable, so namespaces have two
separators:

 * 'ns->sep' is the configured virtual separator, which defaults to same as
   native separator.
 * 'ns->real_sep' is the native separator.

Namespaces also have prefixes. The prefixes are visible for users/clients and
they appear to be part of the actual mailbox name. One commonly used namespace
prefix is "INBOX.", so all mailboxes (other than INBOX itself) appear to be
children of the INBOX.

So the same mailbox can be visible in three different forms:

 * Virtual name uses the virtual separator and namespace prefix. For example
   "INBOX/foo/bar".
 * Storage name uses the native separator and doesn't have a namespace prefix.
   For example "foo.bar".
 * Physical directory name on disk can be different again. For example with
   Maildir++ it could be ".../Maildir/.foo.bar" (not the leading dot before
   "foo").

Users and owners
----------------

When accessing other users' shared mailboxes, there's a difference between a
namespace's user and owner:

 * 'ns->user' points to the mail user actually accessing the mailbox (e.g. the
   IMAP connection's mail user).
 * 'ns->owner' points to the mail user who shared the mailbox.

The distinction can be important sometimes. For example if user adds or removes
messages from the shared mailbox, the owner's quota must be updated instead of
the user's.

Functions
---------

Functions about finding namespaces:

 * 'mail_namespace_find()' returns namespace for given virtual name and changes
   the virtual name -> storage name. It also has a few variations:
    * 'mail_namespace_find_visible()' skips hidden=yes namespaces.
    * 'mail_namespace_find_subscribable()' skips subscriptions=no namespaces.
    * 'mail_namespace_find_unsubscribable()' skips subscriptions=yes
      namespaces.
 * 'mail_namespace_find_inbox()' returns the namespace with inbox=yes. (There
   can be only one.)
 * 'mail_namespace_find_prefix()' returns namespace that has the given prefix.
    * 'mail_namespace_find_prefix_nosep()' does the same, but ignores the
      trailing separator in prefix (e.g. "foo" would find namespace with
      prefix=foo/).

Functions about translating between virtual and storage names when the
namespace is known:

 * 'mail_namespace_fix_sep()' changes virtual separators -> native separators.
 * 'mail_namespace_get_storage_name()' changes virtual name -> storage name.
 * 'mail_namespace_get_vname()' changes storage name -> virtual name.
 * 'mail_namespace_update_name()' returns FALSE if virtual name doesn't
   actually match the given namespace. Otherwise returns TRUE and changes
   virtual name -> storage name.

A single namespace can currently point to only a single storage, but there is
already some code that attempts to make the transition to multiple storages per
namespace easier. In general you shouldn't try to access 'ns->storage'
directly. When creating new mailboxes,'mail_namespace_get_default_storage()'
returns the storage that should be used. For other purposes you should find the
storage via <mailbox list> [Design.Storage.MailboxList.txt] functions.

(This file was created from the wiki on 2019-06-19 12:42)