[gnus] / lisp / nnimap.el

;;; nnimap.el --- imap backend for Gnus
;; Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005
;;        Free Software Foundation, Inc.

;; Author: Simon Josefsson <jas@pdc.kth.se>
;;         Jim Radford <radford@robby.caltech.edu>
;; Keywords: mail

;; This file is part of GNU Emacs.

;; GNU Emacs is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation; either version 2, or (at your option)
;; any later version.

;; GNU Emacs is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs; see the file COPYING.  If not, write to the
;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
;; Boston, MA 02111-1307, USA.

;;; Commentary:

;; Todo, major things:
;;
;;   o Fix Gnus to view correct number of unread/total articles in group buffer
;;   o Fix Gnus to handle leading '.' in group names (fixed?)
;;   o Finish disconnected mode (moving articles between mailboxes unplugged)
;;   o Sieve
;;   o MIME (partial article fetches)
;;   o Split to other backends, different split rules for different
;;     servers/inboxes
;;
;; Todo, minor things:
;;
;;   o Don't require half of Gnus -- backends should be standalone
;;   o Verify that we don't use IMAP4rev1 specific things (RFC2060 App B)
;;   o Dont uid fetch 1,* in nnimap-retrive-groups (slow)
;;   o Split up big fetches (1,* header especially) in smaller chunks
;;   o What do I do with gnus-newsgroup-*?
;;   o Tell Gnus about new groups (how can we tell?)
;;   o Respooling (fix Gnus?) (unnecessary?)
;;   o Add support for the following: (if applicable)
;;       request-list-newsgroups, request-regenerate
;;       list-active-group,
;;       request-associate-buffer, request-restore-buffer,
;;   o Do The Right Thing when UIDVALIDITY changes (what's the right thing?)
;;   o Support RFC2221 (Login referrals)
;;   o IMAP2BIS compatibility? (RFC2061)
;;   o ACAP stuff (perhaps a different project, would be nice to ACAPify
;;     .newsrc.eld)
;;   o What about Gnus's article editing, can we support it?  NO!
;;   o Use \Draft to support the draft group??
;;   o Duplicate suppression
;;   o Rewrite UID SEARCH UID X as UID FETCH X (UID) for those with slow servers

;;; Code:

(require 'imap)
(require 'nnoo)
(require 'nnmail)
(require 'nnheader)
(require 'mm-util)
(require 'gnus)
(require 'gnus-range)
(require 'gnus-start)
(require 'gnus-int)
(require 'parse-time)

(eval-when-compile (require 'cl))

(nnoo-declare nnimap)

(defconst nnimap-version "nnimap 1.0")

(defgroup nnimap nil
  "Reading IMAP mail with Gnus."
  :group 'gnus)

(defvoo nnimap-address nil
  "Address of physical IMAP server.  If nil, use the virtual server's name.")

(defvoo nnimap-server-port nil
  "Port number on physical IMAP server.
If nil, defaults to 993 for TLS/SSL connections and 143 otherwise.")

;; Splitting variables

(defcustom nnimap-split-crosspost t
  "If non-nil, do crossposting if several split methods match the mail.
If nil, the first match found will be used."
  :group 'nnimap
  :type 'boolean)

(defcustom nnimap-split-inbox nil
  "Name of mailbox to split mail from.

Mail is read from this mailbox and split according to rules in
`nnimap-split-rule'.

This can be a string or a list of strings."
  :group 'nnimap
  :type '(choice (string)
                 (repeat string)))

(define-widget 'nnimap-strict-function 'function
  "This widget only matches values that are functionp.

Warning: This means that a value that is the symbol of a not yet
loaded function will not match.  Use with care."
  :match 'nnimap-strict-function-match)

(defun nnimap-strict-function-match (widget value)
  "Ignoring WIDGET, match if VALUE is a function."
  (functionp value))

(defcustom nnimap-split-rule nil
  "Mail will be split according to these rules.

Mail is read from mailbox(es) specified in `nnimap-split-inbox'.

If you'd like, for instance, one mail group for mail from the
\"gnus-imap\" mailing list, one group for junk mail and leave
everything else in the incoming mailbox, you could do something like
this:

\(setq nnimap-split-rule '((\"INBOX.gnus-imap\"   \"From:.*gnus-imap\")
                          (\"INBOX.junk\"        \"Subject:.*buy\")))

As you can see, `nnimap-split-rule' is a list of lists, where the
first element in each \"rule\" is the name of the IMAP mailbox (or the
symbol `junk' if you want to remove the mail), and the second is a
regexp that nnimap will try to match on the header to find a fit.

The second element can also be a function.  In that case, it will be
called narrowed to the headers with the first element of the rule as
the argument.  It should return a non-nil value if it thinks that the
mail belongs in that group.

This variable can also have a function as its value, the function will
be called with the headers narrowed and should return a group where it
thinks the article should be splitted to.  See `nnimap-split-fancy'.

To allow for different split rules on different virtual servers, and
even different split rules in different inboxes on the same server,
the syntax of this variable have been extended along the lines of:

\(setq nnimap-split-rule
      '((\"my1server\"    (\".*\"    ((\"ding\"    \"ding@gnus.org\")
                                  (\"junk\"    \"From:.*Simon\")))
        (\"my2server\"    (\"INBOX\" nnimap-split-fancy))
        (\"my[34]server\" (\".*\"    ((\"private\" \"To:.*Simon\")
                                  (\"junk\"    my-junk-func)))))

The virtual server name is in fact a regexp, so that the same rules
may apply to several servers.  In the example, the servers
\"my3server\" and \"my4server\" both use the same rules.  Similarly,
the inbox string is also a regexp.  The actual splitting rules are as
before, either a function, or a list with group/regexp or
group/function elements."
  :group 'nnimap
  :type '(choice :tag "Rule type"
                 (repeat :menu-tag "Single-server"
                         :tag "Single-server list"
                         (list (string :tag "Mailbox")
                               (choice :tag "Predicate"
                                       (regexp :tag "A regexp")
                                       (nnimap-strict-function :tag "A function"))))
                 (choice :menu-tag "A function"
                         :tag "A function"
                         (function-item nnimap-split-fancy)
                         (function-item nnmail-split-fancy)
                         (nnimap-strict-function :tag "User-defined function"))
                 (repeat :menu-tag "Multi-server (extended)"
                         :tag "Multi-server list"
                         (list (regexp :tag "Server regexp")
                               (list (regexp :tag "Incoming Mailbox regexp")
                                     (repeat :tag "Rules for matching server(s) and mailbox(es)"
                                             (list (string :tag "Destination mailbox")
                                                   (choice :tag "Predicate"
                                                           (regexp :tag "A Regexp")
                                                           (nnimap-strict-function :tag "A Function")))))))))

(defcustom nnimap-split-predicate "UNSEEN UNDELETED"
  "The predicate used to find articles to split.
If you use another IMAP client to peek on articles but always would
like nnimap to split them once it's started, you could change this to
\"UNDELETED\". Other available predicates are available in
RFC2060 section 6.4.4."
  :group 'nnimap
  :type 'string)

(defcustom nnimap-split-fancy nil
  "Like the variable `nnmail-split-fancy'."
  :group 'nnimap
  :type 'sexp)

(defvar nnimap-split-download-body-default nil
  "Internal variable with default value for `nnimap-split-download-body'.")

(defcustom nnimap-split-download-body 'default
  "Whether to download entire articles during splitting.
This is generally not required, and will slow things down considerably.
You may need it if you want to use an advanced splitting function that
analyses the body before splitting the article.
If this variable is nil, bodies will not be downloaded; if this
variable is the symbol `default' the default behaviour is
used (which currently is nil, unless you use a statistical
spam.el test); if this variable is another non-nil value bodies
will be downloaded."
  :version "22.1"
  :group 'nnimap
  :type '(choice (const :tag "Let system decide" deault)
                 boolean))

;; Performance / bug workaround variables

(defcustom nnimap-close-asynchronous t
  "Close mailboxes asynchronously in `nnimap-close-group'.
This means that errors caught by nnimap when closing the mailbox will
not prevent Gnus from updating the group status, which may be harmful.
However, it increases speed."
  :version "22.1"
  :type 'boolean
  :group 'nnimap)

(defcustom nnimap-dont-close t
  "Never close mailboxes.
This increases the speed of closing mailboxes (quiting group) but may
decrease the speed of selecting another mailbox later.  Re-selecting
the same mailbox will be faster though."
  :version "22.1"
  :type 'boolean
  :group 'nnimap)

(defcustom nnimap-retrieve-groups-asynchronous t
  "Send asynchronous STATUS commands for each mailbox before checking mail.
If you have mailboxes that rarely receives mail, this speeds up new
mail checking.  It works by first sending STATUS commands for each
mailbox, and then only checking groups which has a modified UIDNEXT
more carefully for new mail.

In summary, the default is O((1-p)*k+p*n) and changing it to nil makes
it O(n).  If p is small, then the default is probably faster."
  :version "22.1"
  :type 'boolean
  :group 'nnimap)

(defvoo nnimap-need-unselect-to-notice-new-mail nil
  "Unselect mailboxes before looking for new mail in them.
Some servers seem to need this under some circumstances.")

;; Authorization / Privacy variables

(defvoo nnimap-auth-method nil
  "Obsolete.")

(defvoo nnimap-stream nil
  "How nnimap will connect to the server.

The default, nil, will try to use the \"best\" method the server can
handle.

Change this if

1) you want to connect with TLS/SSL.  The TLS/SSL integration
   with IMAP is suboptimal so you'll have to tell it
   specifically.

2) your server is more capable than your environment -- i.e. your
   server accept Kerberos login's but you haven't installed the
   `imtest' program or your machine isn't configured for Kerberos.

Possible choices: gssapi, kerberos4, starttls, tls, ssl, network, shell.
See also `imap-streams' and `imap-stream-alist'.")

(defvoo nnimap-authenticator nil
  "How nnimap authenticate itself to the server.

The default, nil, will try to use the \"best\" method the server can
handle.

There is only one reason for fiddling with this variable, and that is
if your server is more capable than your environment -- i.e. you
connect to a server that accept Kerberos login's but you haven't
installed the `imtest' program or your machine isn't configured for
Kerberos.

Possible choices: gssapi, kerberos4, digest-md5, cram-md5, login, anonymous.
See also `imap-authenticators' and `imap-authenticator-alist'")

(defvoo nnimap-directory (nnheader-concat gnus-directory "overview/")
  "Directory to keep NOV cache files for nnimap groups.
See also `nnimap-nov-file-name'.")

(defvoo nnimap-nov-file-name "nnimap."
  "NOV cache base filename.
The group name and `nnimap-nov-file-name-suffix' will be appended.  A
typical complete file name would be
~/News/overview/nnimap.pdc.INBOX.ding.nov, or
~/News/overview/nnimap/pdc/INBOX/ding/nov if
`nnmail-use-long-file-names' is nil")

(defvoo nnimap-nov-file-name-suffix ".novcache"
  "Suffix for NOV cache base filename.")

(defvoo nnimap-nov-is-evil gnus-agent
  "If non-nil, never generate or use a local nov database for this backend.
Using nov databases should speed up header fetching considerably.
However, it will invoke a UID SEARCH UID command on the server, and
some servers implement this command inefficiently by opening each and
every message in the group, thus making it quite slow.
Unlike other backends, you do not need to take special care if you
flip this variable.")

(defvoo nnimap-expunge-on-close 'always ; 'ask, 'never
  "Whether to expunge a group when it is closed.
When a IMAP group with articles marked for deletion is closed, this
variable determine if nnimap should actually remove the articles or
not.

If always, nnimap always perform a expunge when closing the group.
If never, nnimap never expunges articles marked for deletion.
If ask, nnimap will ask you if you wish to expunge marked articles.

When setting this variable to `never', you can only expunge articles
by using `G x' (gnus-group-nnimap-expunge) from the Group buffer.")

(defvoo nnimap-list-pattern "*"
  "A string LIMIT or list of strings with mailbox wildcards used to limit available groups.
See below for available wildcards.

The LIMIT string can be a cons cell (REFERENCE . LIMIT), where
REFERENCE will be passed as the first parameter to LIST/LSUB.  The
semantics of this are server specific, on the University of Washington
server you can specify a directory.

Example:
 '(\"INBOX\" \"mail/*\" (\"~friend/mail/\" . \"list/*\"))

There are two wildcards * and %. * matches everything, % matches
everything in the current hierarchy.")

(defvoo nnimap-news-groups nil
  "IMAP support a news-like mode, also known as bulletin board mode,
where replies is sent via IMAP instead of SMTP.

This variable should contain a regexp matching groups where you wish
replies to be stored to the mailbox directly.

Example:
  '(\"^[^I][^N][^B][^O][^X].*$\")

This will match all groups not beginning with \"INBOX\".

Note that there is nothing technically different between mail-like and
news-like mailboxes.  If you wish to have a group with todo items or
similar which you wouldn't want to set up a mailing list for, you can
use this to make replies go directly to the group.")

(defvoo nnimap-expunge-search-string "UID %s NOT SINCE %s"
  "IMAP search command to use for articles that are to be expired.
The first %s is replaced by a UID set of articles to search on,
and the second %s is replaced by a date criterium.

One useful (and perhaps the only useful) value to change this to would
be `UID %s NOT SENTSINCE %s' to make nnimap use the Date: header
instead of the internal date of messages.  See section 6.4.4 of RFC
2060 for more information on valid strings.")

(defvoo nnimap-importantize-dormant t
  "If non-nil, mark \"dormant\" articles as \"ticked\" for other IMAP clients.
Note that within Gnus, dormant articles will still (only) be
marked as ticked.  This is to make \"dormant\" articles stand out,
just like \"ticked\" articles, in other IMAP clients.")

(defvoo nnimap-server-address nil
  "Obsolete.  Use `nnimap-address'.")

(defcustom nnimap-authinfo-file "~/.authinfo"
  "Authorization information for IMAP servers.  In .netrc format."
  :type
  '(choice file
           (repeat :tag "Entries"
                   :menu-tag "Inline"
                   (list :format "%v"
                         :value ("" ("login" . "") ("password" . ""))
                         (string :tag "Host")
                         (checklist :inline t
                                    (cons :format "%v"
                                          (const :format "" "login")
                                          (string :format "Login: %v"))
                                    (cons :format "%v"
                                          (const :format "" "password")
                                          (string :format "Password: %v"))))))
  :group 'nnimap)

(defcustom nnimap-prune-cache t
  "If non-nil, nnimap check whether articles still exist on server before using data stored in NOV cache."
  :type 'boolean
  :group 'nnimap)

(defvar nnimap-request-list-method 'imap-mailbox-list
  "Method to use to request a list of all folders from the server.
If this is 'imap-mailbox-lsub, then use a server-side subscription list to
restrict visible folders.")

(defcustom nnimap-id nil
  "Plist with client identity to send to server upon login.
Nil means no information is sent, symbol `no' to disable ID query
alltogheter, or plist with identifier-value pairs to send to
server.  RFC 2971 describes the list as follows:

   Any string may be sent as a field, but the following are defined to
   describe certain values that might be sent.  Implementations are free
   to send none, any, or all of these.  Strings are not case-sensitive.
   Field strings MUST NOT be longer than 30 octets.  Value strings MUST
   NOT be longer than 1024 octets.  Implementations MUST NOT send more
   than 30 field-value pairs.

     name            Name of the program
     version         Version number of the program
     os              Name of the operating system
     os-version      Version of the operating system
     vendor          Vendor of the client/server
     support-url     URL to contact for support
     address         Postal address of contact/vendor
     date            Date program was released, specified as a date-time
                       in IMAP4rev1
     command         Command used to start the program
     arguments       Arguments supplied on the command line, if any
                       if any
     environment     Description of environment, i.e., UNIX environment
                       variables or Windows registry settings

   Implementations MUST NOT send the same field name more than once.

An example plist would be '(\"name\" \"Gnus\" \"version\" gnus-version-number
\"os\" system-configuration \"vendor\" \"GNU\")."
  :group 'nnimap
  :type '(choice (const :tag "No information" nil)
                 (const :tag "Disable ID query" no)
                 (plist :key-type string :value-type string)))

(defcustom nnimap-debug nil
  "If non-nil, random debug spews are placed in *nnimap-debug* buffer.
Note that username, passwords and other privacy sensitive
information (such as e-mail) may be stored in the *nnimap-debug*
buffer.  It is not written to disk, however.  Do not enable this
variable unless you are comfortable with that."
  :group 'nnimap
  :type 'boolean)

;; Internal variables:

(defvar nnimap-debug-buffer "*nnimap-debug*")
(defvar nnimap-mailbox-info (gnus-make-hashtable 997))
(defvar nnimap-current-move-server nil)
(defvar nnimap-current-move-group nil)
(defvar nnimap-current-move-article nil)
(defvar nnimap-length)
(defvar nnimap-progress-chars '(?| ?/ ?- ?\\))
(defvar nnimap-progress-how-often 20)
(defvar nnimap-counter)
(defvar nnimap-server-buffer-alist nil) ;; Map server name to buffers.
(defvar nnimap-current-server nil) ;; Current server
(defvar nnimap-server-buffer nil) ;; Current servers' buffer

\f

(nnoo-define-basics nnimap)

;; Utility functions:

(defsubst nnimap-get-server-buffer (server)
  "Return buffer for SERVER, if nil use current server."
  (cadr (assoc (or server nnimap-current-server) nnimap-server-buffer-alist)))

(defun nnimap-remove-server-from-buffer-alist (server list)
  "Remove SERVER from LIST."
  (let (l)
    (dolist (e list)
      (unless (equal server (car-safe e))
        (push e l)))
    l))

(defun nnimap-possibly-change-server (server)
  "Return buffer for SERVER, changing the current server as a side-effect.
If SERVER is nil, uses the current server."
  (setq nnimap-current-server (or server nnimap-current-server)
        nnimap-server-buffer (nnimap-get-server-buffer nnimap-current-server)))

(defun nnimap-verify-uidvalidity (group server)
  "Verify stored uidvalidity match current one in GROUP on SERVER."
  (let* ((gnusgroup (gnus-group-prefixed-name
                     group (gnus-server-to-method
                            (format "nnimap:%s" server))))
         (new-uidvalidity (imap-mailbox-get 'uidvalidity))
         (old-uidvalidity (gnus-group-get-parameter gnusgroup 'uidvalidity))
         (dir (file-name-as-directory (expand-file-name nnimap-directory)))
         (nameuid (nnheader-translate-file-chars
                   (concat nnimap-nov-file-name
                           (if (equal server "")
                               "unnamed"
                             server) "." group "." old-uidvalidity
                           nnimap-nov-file-name-suffix) t))
         (file (if (or nnmail-use-long-file-names
                       (file-exists-p (expand-file-name nameuid dir)))
                   (expand-file-name nameuid dir)
                 (expand-file-name
                  (mm-encode-coding-string
                   (nnheader-replace-chars-in-string nameuid ?. ?/)
                   nnmail-pathname-coding-system)
                  dir))))
    (if old-uidvalidity
        (if (not (equal old-uidvalidity new-uidvalidity))
            ;; uidvalidity clash
            (gnus-delete-file file)
          (gnus-group-set-parameter gnusgroup 'uidvalidity new-uidvalidity)
          t)
      (gnus-group-add-parameter gnusgroup (cons 'uidvalidity new-uidvalidity))
      t)))

(defun nnimap-before-find-minmax-bugworkaround ()
  "Function called before iterating through mailboxes with
`nnimap-find-minmax-uid'."
  (when nnimap-need-unselect-to-notice-new-mail
    ;; XXX this is for UoW imapd problem, it doesn't notice new mail in
    ;; currently selected mailbox without a re-select/examine.
    (or (null (imap-current-mailbox nnimap-server-buffer))
        (imap-mailbox-unselect nnimap-server-buffer))))

(defun nnimap-find-minmax-uid (group &optional examine)
  "Find lowest and highest active article number in GROUP.
If EXAMINE is non-nil the group is selected read-only."
  (with-current-buffer nnimap-server-buffer
    (when (or (string= group (imap-current-mailbox))
              (imap-mailbox-select group examine))
      (let (minuid maxuid)
        (when (> (imap-mailbox-get 'exists) 0)
          (imap-fetch "1,*" "UID" nil 'nouidfetch)
          (imap-message-map (lambda (uid Uid)
                              (setq minuid (if minuid (min minuid uid) uid)
                                    maxuid (if maxuid (max maxuid uid) uid)))
                            'UID))
        (list (imap-mailbox-get 'exists) minuid maxuid)))))

(defun nnimap-possibly-change-group (group &optional server)
  "Make GROUP the current group, and SERVER the current server."
  (when (nnimap-possibly-change-server server)
    (with-current-buffer nnimap-server-buffer
      (if (or (null group) (imap-current-mailbox-p group))
          imap-current-mailbox
        (if (imap-mailbox-select group)
            (if (or (nnimap-verify-uidvalidity
                     group (or server nnimap-current-server))
                    (zerop (imap-mailbox-get 'exists group))
                    t ;; for OGnus to see if ignoring uidvalidity
                    ;; changes has any bad effects.
                    (yes-or-no-p
                     (format
                      "nnimap: Group %s is not uidvalid.  Continue? " group)))
                imap-current-mailbox
              (imap-mailbox-unselect)
              (error "nnimap: Group %s is not uid-valid" group))
          (nnheader-report 'nnimap (imap-error-text)))))))

(defun nnimap-replace-whitespace (string)
  "Return STRING with all whitespace replaced with space."
  (when string
    (while (string-match "[\r\n\t]+" string)
      (setq string (replace-match " " t t string)))
    string))

;; Required backend functions

(defun nnimap-retrieve-headers-progress ()
  "Hook to insert NOV line for current article into `nntp-server-buffer'."
  (and (numberp nnmail-large-newsgroup)
       (zerop (% (incf nnimap-counter) nnimap-progress-how-often))
       (> nnimap-length nnmail-large-newsgroup)
       (nnheader-message 6 "nnimap: Retrieving headers... %c"
                         (nth (/ (% nnimap-counter
                                    (* (length nnimap-progress-chars)
                                       nnimap-progress-how-often))
                                 nnimap-progress-how-often)
                              nnimap-progress-chars)))
  (with-current-buffer nntp-server-buffer
    (let (headers lines chars uid mbx)
      (with-current-buffer nnimap-server-buffer
        (setq uid imap-current-message
              mbx imap-current-mailbox
              headers (nnimap-demule
                       (if (imap-capability 'IMAP4rev1)
                           ;; xxx don't just use car? alist doesn't contain
                           ;; anything else now, but it might...
                           (nth 2 (car (imap-message-get uid 'BODYDETAIL)))
                         (imap-message-get uid 'RFC822.HEADER)))
              lines (imap-body-lines (imap-message-body imap-current-message))
              chars (imap-message-get imap-current-message 'RFC822.SIZE)))
      (nnheader-insert-nov
       (with-temp-buffer
         (buffer-disable-undo)
         (insert headers)
         (let ((head (nnheader-parse-naked-head uid)))
           (mail-header-set-number head uid)
           (mail-header-set-chars head chars)
           (mail-header-set-lines head lines)
           (mail-header-set-xref
            head (format "%s %s:%d" (system-name) mbx uid))
           head))))))

(defun nnimap-retrieve-which-headers (articles fetch-old)
  "Get a range of articles to fetch based on ARTICLES and FETCH-OLD."
  (with-current-buffer nnimap-server-buffer
    (if (numberp (car-safe articles))
        (imap-search
         (concat "UID "
                 (imap-range-to-message-set
                  (gnus-compress-sequence
                   (append (gnus-uncompress-sequence
                            (and fetch-old
                                 (cons (if (numberp fetch-old)
                                           (max 1 (- (car articles) fetch-old))
                                         1)
                                       (1- (car articles)))))
                           articles)))))
      (mapcar (lambda (msgid)
                (imap-search
                 (format "HEADER Message-Id \"%s\"" msgid)))
              articles))))

(defun nnimap-group-overview-filename (group server)
  "Make file name for GROUP on SERVER."
  (let* ((dir (file-name-as-directory (expand-file-name nnimap-directory)))
         (uidvalidity (gnus-group-get-parameter
                       (gnus-group-prefixed-name
                        group (gnus-server-to-method
                               (format "nnimap:%s" server)))
                       'uidvalidity))
         (name (nnheader-translate-file-chars
                (concat nnimap-nov-file-name
                        (if (equal server "")
                            "unnamed"
                          server) "." group nnimap-nov-file-name-suffix) t))
         (nameuid (nnheader-translate-file-chars
                   (concat nnimap-nov-file-name
                           (if (equal server "")
                               "unnamed"
                             server) "." group "." uidvalidity
                           nnimap-nov-file-name-suffix) t))
         (oldfile (if (or nnmail-use-long-file-names
                          (file-exists-p (expand-file-name name dir)))
                      (expand-file-name name dir)
                    (expand-file-name
                     (mm-encode-coding-string
                      (nnheader-replace-chars-in-string name ?. ?/)
                      nnmail-pathname-coding-system)
                     dir)))
         (newfile (if (or nnmail-use-long-file-names
                          (file-exists-p (expand-file-name nameuid dir)))
                      (expand-file-name nameuid dir)
                    (expand-file-name
                     (mm-encode-coding-string
                      (nnheader-replace-chars-in-string nameuid ?. ?/)
                      nnmail-pathname-coding-system)
                     dir))))
    (when (and (file-exists-p oldfile) (not (file-exists-p newfile)))
      (message "nnimap: Upgrading novcache filename...")
      (sit-for 1)
      (gnus-make-directory (file-name-directory newfile))
      (unless (ignore-errors (rename-file oldfile newfile) t)
        (if (ignore-errors (copy-file oldfile newfile) t)
            (delete-file oldfile)
          (error "Can't rename `%s' to `%s'" oldfile newfile))))
    newfile))

(defun nnimap-retrieve-headers-from-file (group server)
  (with-current-buffer nntp-server-buffer
    (let ((nov (nnimap-group-overview-filename group server)))
      (when (file-exists-p nov)
        (mm-insert-file-contents nov)
        (set-buffer-modified-p nil)
        (let ((min (ignore-errors (goto-char (point-min))
                                  (read (current-buffer))))
              (max (ignore-errors (goto-char (point-max))
                                  (forward-line -1)
                                  (read (current-buffer)))))
          (if (and (numberp min) (numberp max))
              (cons min max)
            ;; junk, remove it, it's saved later
            (erase-buffer)
            nil))))))

(defun nnimap-retrieve-headers-from-server (articles group server)
  (with-current-buffer nnimap-server-buffer
    (let ((imap-fetch-data-hook '(nnimap-retrieve-headers-progress))
          (nnimap-length (gnus-range-length articles))
          (nnimap-counter 0))
      (imap-fetch (imap-range-to-message-set articles)
                  (concat "(UID RFC822.SIZE BODY "
                          (let ((headers
                                 (append '(Subject From Date Message-Id
                                                   References In-Reply-To Xref)
                                         (copy-sequence
                                          nnmail-extra-headers))))
                            (if (imap-capability 'IMAP4rev1)
                                (format "BODY.PEEK[HEADER.FIELDS %s])" headers)
                              (format "RFC822.HEADER.LINES %s)" headers)))))
      (with-current-buffer nntp-server-buffer
        (sort-numeric-fields 1 (point-min) (point-max)))
      (and (numberp nnmail-large-newsgroup)
           (> nnimap-length nnmail-large-newsgroup)
           (nnheader-message 6 "nnimap: Retrieving headers...done")))))

(defun nnimap-dont-use-nov-p (group server)
  (or gnus-nov-is-evil nnimap-nov-is-evil
      (unless (and (gnus-make-directory
                    (file-name-directory
                     (nnimap-group-overview-filename group server)))
                   (file-writable-p
                    (nnimap-group-overview-filename group server)))
        (message "nnimap: Nov cache not writable, %s"
                 (nnimap-group-overview-filename group server)))))

(deffoo nnimap-retrieve-headers (articles &optional group server fetch-old)
  (when (nnimap-possibly-change-group group server)
    (with-current-buffer nntp-server-buffer
      (erase-buffer)
      (if (nnimap-dont-use-nov-p group server)
          (nnimap-retrieve-headers-from-server
           (gnus-compress-sequence articles) group server)
        (let (uids cached low high)
          (when (setq uids (nnimap-retrieve-which-headers articles fetch-old)
                      low (car uids)
                      high (car (last uids)))
            (if (setq cached (nnimap-retrieve-headers-from-file group server))
                (progn
                  ;; fetch articles with uids before cache block
                  (when (< low (car cached))
                    (goto-char (point-min))
                    (nnimap-retrieve-headers-from-server
                     (cons low (1- (car cached))) group server))
                  ;; fetch articles with uids after cache block
                  (when (> high (cdr cached))
                    (goto-char (point-max))
                    (nnimap-retrieve-headers-from-server
                     (cons (1+ (cdr cached)) high) group server))
                  (when nnimap-prune-cache
                    ;; remove nov's for articles which has expired on server
                    (goto-char (point-min))
                    (dolist (uid (gnus-set-difference articles uids))
                      (when (re-search-forward (format "^%d\t" uid) nil t)
                        (gnus-delete-line)))))
              ;; nothing cached, fetch whole range from server
              (nnimap-retrieve-headers-from-server
               (cons low high) group server))
            (when (buffer-modified-p)
              (nnmail-write-region
               (point-min) (point-max)
               (nnimap-group-overview-filename group server) nil 'nomesg))
            (nnheader-nov-delete-outside-range low high))))
      'nov)))

(defun nnimap-open-connection (server)
  (if (not (imap-open nnimap-address nnimap-server-port nnimap-stream
                      nnimap-authenticator nnimap-server-buffer))
      (nnheader-report 'nnimap "Can't open connection to server %s" server)
    (unless (or (imap-capability 'IMAP4 nnimap-server-buffer)
                (imap-capability 'IMAP4rev1 nnimap-server-buffer))
      (imap-close nnimap-server-buffer)
      (nnheader-report 'nnimap "Server %s is not IMAP4 compliant" server))
    (let* ((list (progn (gnus-message 7 "Parsing authinfo file `%s'."
                                      nnimap-authinfo-file)
                        (netrc-parse nnimap-authinfo-file)))
           (port (if nnimap-server-port
                     (int-to-string nnimap-server-port)
                   "imap"))
           (user (netrc-machine-user-or-password 
                  "login"
                  list
                  (list server
                        (or nnimap-server-address
                            nnimap-address))
                  (list port)
                  (list "imap" "imaps")))
           (passwd (netrc-machine-user-or-password 
                    "password"
                    list
                    (list server
                          (or nnimap-server-address
                              nnimap-address))
                    (list port)
                    (list "imap" "imaps"))))
      (if (imap-authenticate user passwd nnimap-server-buffer)
          (prog2
              (setq nnimap-server-buffer-alist
                    (nnimap-remove-server-from-buffer-alist 
                     server
                     nnimap-server-buffer-alist))
              (push (list server nnimap-server-buffer)
                    nnimap-server-buffer-alist)
            (imap-id nnimap-id nnimap-server-buffer)
            (nnimap-possibly-change-server server))
        (imap-close nnimap-server-buffer)
        (kill-buffer nnimap-server-buffer)
        (nnheader-report 'nnimap "Could not authenticate to %s" server)))))

(deffoo nnimap-open-server (server &optional defs)
  (nnheader-init-server-buffer)
  (if (nnimap-server-opened server)
      t
    (unless (assq 'nnimap-server-buffer defs)
      (push (list 'nnimap-server-buffer (concat " *nnimap* " server)) defs))
    ;; translate `nnimap-server-address' to `nnimap-address' in defs
    ;; for people that configured nnimap with a very old version
    (unless (assq 'nnimap-address defs)
      (if (assq 'nnimap-server-address defs)
          (push (list 'nnimap-address
                      (cadr (assq 'nnimap-server-address defs))) defs)
        (push (list 'nnimap-address server) defs)))
    (nnoo-change-server 'nnimap server defs)
    (or nnimap-server-buffer
        (setq nnimap-server-buffer (cadr (assq 'nnimap-server-buffer defs))))
    (with-current-buffer (get-buffer-create nnimap-server-buffer)
      (nnoo-change-server 'nnimap server defs))
    (or (and nnimap-server-buffer
             (imap-opened nnimap-server-buffer)
             (if (with-current-buffer nnimap-server-buffer
                   (memq imap-state '(auth selected examine)))
                 t
               (imap-close nnimap-server-buffer)
               (nnimap-open-connection server)))
        (nnimap-open-connection server))))

(deffoo nnimap-server-opened (&optional server)
  "Whether SERVER is opened.
If SERVER is the current virtual server, and the connection to the
physical server is alive, this function return a non-nil value.  If
SERVER is nil, it is treated as the current server."
  ;; clean up autologouts??
  (and (or server nnimap-current-server)
       (nnoo-server-opened 'nnimap (or server nnimap-current-server))
       (imap-opened (nnimap-get-server-buffer server))))

(deffoo nnimap-close-server (&optional server)
  "Close connection to server and free all resources connected to it.
Return nil if the server couldn't be closed for some reason."
  (let ((server (or server nnimap-current-server)))
    (when (or (nnimap-server-opened server)
              (imap-opened (nnimap-get-server-buffer server)))
      (imap-close (nnimap-get-server-buffer server))
      (kill-buffer (nnimap-get-server-buffer server))
      (setq nnimap-server-buffer nil
            nnimap-current-server nil
            nnimap-server-buffer-alist
            (nnimap-remove-server-from-buffer-alist 
             server
             nnimap-server-buffer-alist)))