As I own my own mail server, my mail setup is very much engineered to fit my own needs. This means everything works as I think it should, but it also means I have to hack things myself if I need them. This time, I needed a program that can move IMAP mails to archive mailboxes.
(Side note: My IMAP mail server is dovecot, which supports keeping mail in different namespaces in separate storage system. For current mail, Maildir is handy: needs no locking, and it’s hard to corrupt a mailbox. For archiving, mbox is better, because one mailbox takes up only one file.)
The plan was this: For every mail in “mail.lisp.sbcl.arch”, I want it to move the mail to the mail box “archive.<year>.lisp.sbcl.arch”. This would have been a tedious mark&drag operation in any gui-based mailer, and hopelessly slow in the emacs-based mailers (which support this operation) like wanderlust. Mel-base to the rescue!
I’ll keep it short: This code was the result. It requires mel-base (obviously), and I only tested it on sbcl.
So, this is how you use it:
- Install mel-base.
- Create a file passwords.lisp in the same directory as message-archiver.lisp, with contents like these:
1 2 3
- load message-archiver.lisp.
(imap-archiver:archive-messages "lisp.phemlock"); and it will move all mails in the mailbox “mail.lisp.phemlock” to the mailbox “archive.<year>.lisp.phemlock”, with <year> being the year in the message’s Date: header field.
But wait! This is very slow on current versions of mel-base (0.7-2)! Why? The code that copies a message from one folder to another works the same for all folder types: it reads the entire message from the server and sends it back again. As a side effect, this removes all marks. Ow. But we’re lucky that Jochen Schmidt is a good hacker and designed mel such that this is easily fixed.
Like everything else in mel-base, operations on a folder have their own protocol, and copying messages from a folder to another has its own generic function, copy-message-using-folders:
(defgeneric COPY-MESSAGE-USING-FOLDERS (message message-folder sink-folder))
(defmethod copy-message-using-folders :around ((message message) (message-folder imap-folder) (sink-folder imap-folder))
"Copy a message between two imap folders. We can optimize this case if the folders are on the same server."
(if (and (equal (host message-folder) (host sink-folder))
(equal (username message-folder) (username sink-folder))
(equal (password message-folder) (password sink-folder))
(equal (imap-port message-folder) (imap-port sink-folder)))
(send-command message-folder "~A uid copy ~A ~A" "UID" (uid message) (mailbox sink-folder))
(process-response message-folder :on-uid (lambda (m) m)))
;; if we're not using the same server, play it safe
The lesson for today: Good libraries provide functionality that works well enough for the typical use case. Great libraries let you extend them to support your own use cases.