Mail Storage
============

'src/lib-storage/mail-storage.h' and 'mail-storage-private.h' describes mail
storage. Mail storage is mainly about being a common container for its
mailboxes. For example with <multi-dbox> [MailboxFormat.dbox.txt] each storage
has one directory where all the message bodies are written to, while the
per-mailbox directories only contain index files. With other mailbox formats
mail storage doesn't do much else than allow allocating <mailboxes>
[Design.Storage.Mailbox.txt].

The only public functions for mail storage are:

 * 'mail_storage_purge()' frees disk space used by expunged messages. Currently
   the only mailbox format that uses this is multi-dbox.
 * 'mail_storage_get_settings()' returns mail storage settings.
 * 'mail_storage_set_callbacks()' can be used to specify "OK" and "NO"
   callbacks, which are called when a long running operation wants to send a
   status update. For example "OK Stale mailbox lock file detected, will
   override in n seconds" or "NO Mailbox is locked, will abort in n seconds".

Methods that mail storage backends need to implement are:

 * 'get_setting_parser_info()': Returns storage-specific settings parser
   information.
 * 'alloc()': Allocate memory for a storage and set its virtual functions.
 * 'create(ns)': Initialize the storage based on given namespace settings. The
   same storage can be used by other namespaces, but they don't call 'create()'
   again. This function typically shouldn't fail, except when storage can't
   handle the wanted namespace settings.
 * 'destroy()': Destroys the storage.
 * 'add_list(list)': Called every time the storage is attached to a new
   namespace / mailbox list.
 * 'get_list_settings(ns, set)': Used to get storage's default settings.
 * 'autodetect(ns, set)': Returns TRUE if based on the given settings it looks
   like this storage should be handling the namespace. This is done when
   mail_location doesn't explicitly specify the mailbox format.
 * 'mailbox_alloc()': Allocate memory for <mailbox>
   [Design.Storage.Mailbox.txt].

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