;;; nnimap.el --- IMAP interface for Gnus  -*- lexical-binding: t; -*-

;; Copyright (C) 2010-2021 Free Software Foundation, Inc.

;; Author: Lars Magne Ingebrigtsen <larsi@gnus.org>
;;         Simon Josefsson <simon@josefsson.org>

;; 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 3 of the License, 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.  If not, see <https://www.gnu.org/licenses/>.

;;; Commentary:

;; nnimap interfaces Gnus with IMAP servers.

;;; Code:

(eval-when-compile
  (require 'cl-lib)
  (require 'subr-x))

(require 'nnheader)
(require 'gnus-util)
(require 'gnus)
(require 'nnoo)
(require 'netrc)
(require 'utf7)
(require 'nnmail)

(autoload 'auth-source-forget+ "auth-source")
(autoload 'auth-source-search "auth-source")

(nnoo-declare nnimap)

(defvoo nnimap-address nil
  "The address of the IMAP server.")

(defvoo nnimap-user nil
  "Username to use for authentication to the IMAP server.")

(defvoo nnimap-server-port nil
  "The IMAP port used.
If nnimap-stream is `ssl', this will default to `imaps'.  If not,
it will default to `imap'.")

(defvoo nnimap-use-namespaces nil
  "Whether to use IMAP namespaces.
If in Gnus your folder names in all start with (e.g.) `INBOX',
you probably want to set this to t.  The effects of this are
purely cosmetic, but changing this variable will affect the
names of your nnimap groups. ")

(defvoo nnimap-stream 'undecided
  "How nnimap talks to the IMAP server.
The value should be either `undecided', `ssl' or `tls',
`network', `starttls', `plain', or `shell'.

If the value is `undecided', nnimap tries `ssl' first, then falls
back on `network'.")

(defvoo nnimap-shell-program (if (boundp 'imap-shell-program)
				 (if (listp imap-shell-program)
				     (car imap-shell-program)
				   imap-shell-program)
			       "ssh %s imapd")
  "What command to execute to connect to an IMAP server.
This will only be used if the connection type is `shell'.  See
the `open-network-stream' documentation for an explanation of
the format.")

(defvoo nnimap-inbox nil
  "The mail box where incoming mail arrives and should be split out of.
This can be a string or a list of strings
For example, \"INBOX\" or (\"INBOX\" \"SENT\").")

(defvoo nnimap-split-methods nil
  "How mail is split.
Uses the same syntax as `nnmail-split-methods'.")

(defvoo nnimap-split-fancy nil
  "Uses the same syntax as `nnmail-split-fancy'.")

(defvoo nnimap-unsplittable-articles '(%Deleted %Seen)
  "Articles with the flags in the list will not be considered when splitting.")

(make-obsolete-variable 'nnimap-split-rule "see `nnimap-split-methods'."
                        "24.1")

(defvoo nnimap-authenticator nil
  "How nnimap authenticate itself to the server.
Possible choices are nil (use default methods), `anonymous',
`login', `plain' and `cram-md5'.")

(defvoo nnimap-expunge 'on-exit
  "When to expunge deleted messages.
If `never', deleted articles are marked with the IMAP \\Delete
flag but not automatically expunged. If `immediately', deleted
articles are immediately expunged (this requires the server to
support the UID EXPUNGE command). If `on-exit', deleted articles
are flagged, and all flagged articles are expunged when the group
is closed.

For backwards compatibility, this variable may also be set to t
or nil. If the server supports UID EXPUNGE, both t and nil are
equivalent to `immediately'. If the server does not support UID
EXPUNGE nil is equivalent to `never', while t will immediately
expunge ALL articles that are currently flagged as deleted
(i.e., potentially not only the article that was just deleted).")

(defvoo nnimap-streaming t
  "If non-nil, try to use streaming commands with IMAP servers.
Switching this off will make nnimap slower, but it helps with
some servers.")

(defvoo nnimap-connection-alist nil)

(defvoo nnimap-current-infos nil)

(defvoo nnimap-namespace nil)

(defvoo nnimap-fetch-partial-articles nil
  "If non-nil, Gnus will fetch partial articles.
If t, Gnus will fetch only the first part.  If a string, it
will fetch all parts that have types that match that string.  A
likely value would be \"text/\" to automatically fetch all
textual parts.")

(defvoo nnimap-keepalive-intervals (cons (* 60 15)
                                         (* 60 5))
  "Configuration for the nnimap keepalive timer.
The value is a cons of two integers (each representing a number
of seconds): the first is how often to run the keepalive
function, the second is the seconds of inactivity required to
send the actual keepalive command.

Set to nil to disable keepalive commands altogether.")

(defgroup nnimap nil
  "IMAP for Gnus."
  :group 'gnus)

(defcustom nnimap-request-articles-find-limit nil
  "Limit the number of articles to look for after moving an article."
  :type '(choice (const nil) integer)
  :version "24.4")

(define-obsolete-variable-alias
  'nnimap-split-download-body-default 'nnimap-split-download-body
  "28.1")

(defcustom nnimap-split-download-body nil
  "If non-nil, make message bodies available for consideration during splitting.
This requires downloading the full message from the IMAP server
during splitting, which may be slow."
  :version "28.1"
  :type 'boolean)

(defvar nnimap--split-download-body nil
  "Like `nnimap-split-download-body', but for internal use.")

(defvar nnimap-process nil)

(defvar nnimap-status-string "")

(defvar nnimap-keepalive-timer nil)
(defvar nnimap-process-buffers nil)

(cl-defstruct nnimap
  group process commands capabilities select-result newlinep server
  last-command-time greeting examined stream-type initial-resync)

(defvar nnimap-object nil)

(defvar nnimap-mark-alist
  '((read "\\Seen" %Seen)
    (tick "\\Flagged" %Flagged)
    (reply "\\Answered" %Answered)
    (expire "gnus-expire")
    (dormant "gnus-dormant")
    (score "gnus-score")
    (save "gnus-save")
    (download "gnus-download")
    (forward "gnus-forward")))

(defvar nnimap-quirks
  '(("QRESYNC" "Zimbra" "QRESYNC ")
    ("MOVE" "Dovecot" nil)))

(defvar nnimap-inhibit-logging nil)

(defun nnimap-group-to-imap (group)
  "Convert Gnus group name to IMAP mailbox name."
  (let* ((inbox (if nnimap-namespace
                    (substring nnimap-namespace 0 -1) nil)))
    (utf7-encode
     (cond ((or (not inbox)
                (string-equal group inbox))
            group)
           ((string-prefix-p "#" group)
            (substring group 1))
           (t
            (concat nnimap-namespace group))) t)))

(defun nnimap-buffer ()
  (nnimap-find-process-buffer nntp-server-buffer))

(defun nnimap-header-parameters ()
  (let (params)
    (push "UID" params)
    (push "RFC822.SIZE" params)
    (when (nnimap-capability "X-GM-EXT-1")
      (push "X-GM-LABELS" params))
    (push "BODYSTRUCTURE" params)
    (push (format
	   (if (nnimap-ver4-p)
	       "BODY.PEEK[HEADER.FIELDS %s]"
	     "RFC822.HEADER.LINES %s")
	   (append '(Subject From Date Message-Id
			     References In-Reply-To Xref)
		   nnmail-extra-headers))
	  params)
    (format "%s" (nreverse params))))

(deffoo nnimap-retrieve-headers (articles &optional group server _fetch-old)
  (with-current-buffer nntp-server-buffer
    (erase-buffer)
    (when (nnimap-change-group group server)
      (with-current-buffer (nnimap-buffer)
	(erase-buffer)
	(nnimap-wait-for-response
	 (nnimap-send-command
	  "UID FETCH %s %s"
	  (nnimap-article-ranges (gnus-compress-sequence articles))
	  (nnimap-header-parameters))
	 t)
	(unless (process-live-p (get-buffer-process (current-buffer)))
	  (error "Server closed connection"))
	(nnimap-transform-headers)
	(nnheader-remove-cr-followed-by-lf))
      (insert-buffer-substring
       (nnimap-find-process-buffer (current-buffer))))
    'headers))

(defun nnimap-transform-headers ()
  "Transform server's FETCH response into parsable headers."
  (goto-char (point-min))
  (let (seen-articles article lines size string labels)
    (cl-block nil
      (while (not (eobp))
	(while (not (looking-at "\\* [0-9]+ FETCH"))
	  (delete-region (point) (progn (forward-line 1) (point)))
	  (when (eobp)
	    (cl-return)))
	(goto-char (match-end 0))
	;; Unfold quoted {number} strings.
	(while (or (looking-at "[ (]{\\([0-9]+\\)}\r?\n")
		   (re-search-forward
		    "[^]][ (]{\\([0-9]+\\)}\r?\n"
		    (save-excursion
		      ;; Start of the header section.
		      (or (re-search-forward "] {[0-9]+}\r?\n" nil t)
			  ;; Start of the next FETCH.
			  (re-search-forward "\\* [0-9]+ FETCH" nil t)
			  (point-max)))
		    t))
	  (setq size (string-to-number (match-string 1)))
	  (delete-region (+ (match-beginning 0) 2) (point))
	  (setq string (buffer-substring (point) (+ (point) size)))
	  (delete-region (point) (+ (point) size))
	  (insert (format "%S" (subst-char-in-string ?\n ?\s string))))
	(beginning-of-line)
	(setq article
	      (and (re-search-forward "UID \\([0-9]+\\)" (line-end-position)
				      t)
		   (match-string 1)))
	;; If we've already got headers for this article, or this
	;; FETCH line doesn't provide headers for the article, skip
	;; it.  See bug#35433.
	(if (or (member article seen-articles)
		(save-excursion
		  (forward-line)
		  (null (looking-at-p
			 ;; We're expecting a mail-ish header.
			 "^[!-9;-~]+:[[:space:]]?"))))
	    (delete-region (line-beginning-position)
			   (1+ (line-end-position)))
	  (setq lines nil)
	  (beginning-of-line)
	  (setq size
		(and (re-search-forward "RFC822.SIZE \\([0-9]+\\)"
					(line-end-position)
					t)
		     (match-string 1)))
	  (beginning-of-line)
	  (when (search-forward "X-GM-LABELS" (line-end-position) t)
	    (setq labels (ignore-errors (read (current-buffer)))))
	  (beginning-of-line)
	  (when (search-forward "BODYSTRUCTURE" (line-end-position) t)
	    (let ((structure (ignore-errors
			       (read (current-buffer)))))
	      (while (and (consp structure)
			  (not (atom (car structure))))
		(setq structure (car structure)))
	      (setq lines (if (and
			       (stringp (car structure))
			       (equal (upcase (nth 0 structure)) "MESSAGE")
			       (equal (upcase (nth 1 structure)) "RFC822"))
			      (nth 9 structure)
			    (nth 7 structure)))))
	  (delete-region (line-beginning-position) (line-end-position))
	  (insert (format "211 %s Article retrieved." article))
	  (forward-line 1)
	  (when size
	    (insert (format "Chars: %s\n" size)))
	  (when lines
	    (insert (format "Lines: %s\n" lines)))
	  (when labels
	    (insert (format "X-GM-LABELS: %s\n" labels)))
	  ;; Most servers have a blank line after the headers, but
	  ;; Davmail doesn't.
	  (unless (re-search-forward "^\r$\\|^)\r?$" nil t)
	    (goto-char (point-max)))
	  (delete-region (line-beginning-position) (line-end-position))
	  (insert ".")
	  (forward-line 1)
	  (push article seen-articles))))))

(defun nnimap-unfold-quoted-lines ()
  ;; Unfold quoted {number} strings.
  (let (size string)
    (while (re-search-forward " {\\([0-9]+\\)}\r?\n" nil t)
      (setq size (string-to-number (match-string 1)))
      (delete-region (1+ (match-beginning 0)) (point))
      (setq string (buffer-substring (point) (+ (point) size)))
      (delete-region (point) (+ (point) size))
      (insert (format "%S" string)))))

(defun nnimap-get-length ()
  (and (re-search-forward "{\\([0-9]+\\)}" (line-end-position) t)
       (string-to-number (match-string 1))))

(defun nnimap-article-ranges (ranges)
  (let (result)
    (cond
     ((numberp ranges)
      (number-to-string ranges))
     ((numberp (cdr ranges))
      (format "%d:%d" (car ranges) (cdr ranges)))
     (t
      (dolist (elem ranges)
	(push
	 (if (consp elem)
	     (format "%d:%d" (car elem) (cdr elem))
	   (number-to-string elem))
	 result))
      (mapconcat #'identity (nreverse result) ",")))))

(deffoo nnimap-open-server (server &optional defs no-reconnect)
  (if (nnimap-server-opened server)
      t
    (unless (assq 'nnimap-address defs)
      (setq defs (append defs (list (list 'nnimap-address server)))))
    (nnoo-change-server 'nnimap server defs)
    (if no-reconnect
	(nnimap-find-connection nntp-server-buffer)
      (or (nnimap-find-connection nntp-server-buffer)
	  (nnimap-open-connection nntp-server-buffer)))))

(defun nnimap-make-process-buffer (buffer)
  (with-current-buffer
      (generate-new-buffer (format " *nnimap %s %s %s*"
				   nnimap-address nnimap-server-port
                                   buffer))
    (mm-disable-multibyte)
    (buffer-disable-undo)
    (gnus-add-buffer)
    (setq-local after-change-functions nil) ;FIXME: Why?
    (setq-local nnimap-object
                (make-nnimap :server (nnoo-current-server 'nnimap)
                             :initial-resync 0))
    (push (list buffer (current-buffer)) nnimap-connection-alist)
    (push (current-buffer) nnimap-process-buffers)
    (current-buffer)))

(defvar auth-source-creation-prompts)

(defun nnimap-credentials (address ports user)
  (let* ((auth-source-creation-prompts
          '((user  . "IMAP user at %h: ")
            (secret . "IMAP password for %u@%h: ")))
         (found (nth 0 (auth-source-search :max 1
                                           :host address
                                           :port ports
                                           :user user
                                           :require '(:user :secret)
                                           :create t))))
    (if found
        (list (plist-get found :user)
	      (let ((secret (plist-get found :secret)))
		(if (functionp secret)
		    (funcall secret)
		  secret))
	      (plist-get found :save-function))
      nil)))

(defun nnimap-keepalive ()
  (let ((now (current-time))
        ;; Set this so we don't wait for a response.
        (nnimap-streaming t))
    (dolist (buffer nnimap-process-buffers)
      (when (buffer-live-p buffer)
	(with-current-buffer buffer
	  (when (and nnimap-object
		     (nnimap-last-command-time nnimap-object)
		     (time-less-p
		      (cdr nnimap-keepalive-intervals)
		      (time-subtract
		       now
		       (nnimap-last-command-time nnimap-object))))
            (with-local-quit
              (ignore-errors          ;E.g. "buffer foo has no process".
                (nnimap-send-command "NOOP")))))))))

(defun nnimap-open-connection (buffer)
  ;; Be backwards-compatible -- the earlier value of nnimap-stream was
  ;; `ssl' when nnimap-server-port was nil.  Sort of.
  (when (and nnimap-server-port
	     (eq nnimap-stream 'undecided))
    (setq nnimap-stream 'ssl))
  (let ((stream
	 (if (eq nnimap-stream 'undecided)
	     (cl-loop for type in '(ssl network)
		   for stream = (let ((nnimap-stream type))
				  (nnimap-open-connection-1 buffer))
		   while (eq stream 'no-connect)
		   finally (return stream))
	   (nnimap-open-connection-1 buffer))))
    (if (eq stream 'no-connect)
	nil
      stream)))

;; This is only needed for Windows XP or earlier
(defun nnimap-map-port (port)
  (declare-function x-server-version "xfns.c" (&optional terminal))
  (if (and (eq system-type 'windows-nt)
           (<= (car (x-server-version)) 5)
           (equal port "imaps"))
      "993"
    port))

(defun nnimap-open-connection-1 (buffer)
  (unless (or nnimap-keepalive-timer
              (null nnimap-keepalive-intervals))
    (setq nnimap-keepalive-timer (run-at-time
                                  (car nnimap-keepalive-intervals)
                                  (car nnimap-keepalive-intervals)
				  #'nnimap-keepalive)))
  (with-current-buffer (nnimap-make-process-buffer buffer)
    (let* ((coding-system-for-read 'binary)
	   (coding-system-for-write 'binary)
	   (ports
	    (cond
	     ((memq nnimap-stream '(network plain starttls))
	      (nnheader-message 7 "Opening connection to %s..."
				nnimap-address)
	      '("imap" "143"))
	     ((eq nnimap-stream 'shell)
	      (nnheader-message 7 "Opening connection to %s via shell..."
				nnimap-address)
	      '("imap"))
	     ((memq nnimap-stream '(ssl tls))
	      (nnheader-message 7 "Opening connection to %s via tls..."
				nnimap-address)
	      '("imaps" "imap" "993" "143"))
	     (t
	      (error "Unknown stream type: %s" nnimap-stream))))
           login-result credentials)
      (when nnimap-server-port
	(push nnimap-server-port ports))
      (let* ((stream-list
	      (open-network-stream
	       "*nnimap*" (current-buffer) nnimap-address
	       (nnimap-map-port (car ports))
	       :type nnimap-stream
	       :warn-unless-encrypted t
	       :return-list t
	       :shell-command nnimap-shell-program
	       :capability-command "1 CAPABILITY\r\n"
               :always-query-capabilities t
	       :end-of-command "\r\n"
	       :success " OK "
	       :starttls-function
	       (lambda (capabilities)
		 (when (string-match-p "STARTTLS" capabilities)
		   "1 STARTTLS\r\n"))))
	     (stream (car stream-list))
	     (props (cdr stream-list))
	     (greeting (plist-get props :greeting))
	     (capabilities (plist-get props :capabilities))
	     (stream-type (plist-get props :type))
             (server (nnoo-current-server 'nnimap)))
	(when (and stream (not (memq (process-status stream) '(open run))))
	  (setq stream nil))

        (when (eq (process-type stream) 'network)
          ;; Use TCP-keepalive so that connections that pass through a NAT
          ;; router don't hang when left idle.
          (set-network-process-option stream :keepalive t))

	(setf (nnimap-process nnimap-object) stream)
	(setf (nnimap-stream-type nnimap-object) stream-type)
	(if (not stream)
	    (progn
	      (nnheader-report 'nnimap "Unable to contact %s:%s via %s"
			       nnimap-address (car ports) nnimap-stream)
	      'no-connect)
	  (set-process-query-on-exit-flag stream nil)
	  (if (not (string-match-p "[*.] \\(OK\\|PREAUTH\\)" greeting))
	      (nnheader-report 'nnimap "%s" greeting)
	    ;; Store the greeting (for debugging purposes).
	    (setf (nnimap-greeting nnimap-object) greeting)
	    (setf (nnimap-capabilities nnimap-object)
		  (mapcar #'upcase
			  (split-string capabilities)))
	    (unless (string-match-p "[*.] PREAUTH" greeting)
	      (if (not (setq credentials
			     (if (eq nnimap-authenticator 'anonymous)
				 (list "anonymous"
				       (message-make-address))
                               ;; Look for the credentials based on
                               ;; the virtual server name and the address
                               (nnimap-credentials
				(gnus-delete-duplicates
				 (list server nnimap-address))
                                ports
                                nnimap-user))))
		  (setq nnimap-object nil)
		(let ((nnimap-inhibit-logging t))
		  (setq login-result
			(nnimap-login (car credentials) (cadr credentials))))
		(if (car login-result)
		    (progn
		      ;; Save the credentials if a save function exists
		      ;; (such a function will only be passed if a new
		      ;; token was created).
		      (when (functionp (nth 2 credentials))
			(funcall (nth 2 credentials)))
		      ;; See if CAPABILITY is set as part of login
		      ;; response.
		      (dolist (response (cddr (nnimap-command "CAPABILITY")))
			(when (string= "CAPABILITY" (upcase (car response)))
			  (setf (nnimap-capabilities nnimap-object)
				(mapcar #'upcase (cdr response)))))
                      (when (and nnimap-use-namespaces
                                 (nnimap-capability "NAMESPACE"))
                        (erase-buffer)
                        (nnimap-wait-for-response (nnimap-send-command "NAMESPACE"))
                        (let ((response (nnimap-last-response-string)))
                          (when (string-match
                                 "^\\*\\W+NAMESPACE\\W+((\"\\([^\"\n]+\\)\"\\W+\"\\(.\\)\"))\\W+"
                                 response)
                            (setq nnimap-namespace (match-string 1 response))))))
                  ;; If the login failed, then forget the credentials
		  ;; that are now possibly cached.
		  (dolist (host (list (nnoo-current-server 'nnimap)
				      nnimap-address))
		    (dolist (port ports)
                      (auth-source-forget+ :host host :port port)))
		  (delete-process (nnimap-process nnimap-object))
		  (setq nnimap-object nil))))
	    (when nnimap-object
	      (when (nnimap-capability "QRESYNC")
		(nnimap-command "ENABLE QRESYNC"))
              (nnheader-message 7 "Opening connection to %s...done"
				nnimap-address)
	      (nnimap-process nnimap-object))))))))

(autoload 'rfc2104-hash "rfc2104")

(defun nnimap-login (user password)
  (cond
   ;; Prefer plain LOGIN if it's enabled (since it requires fewer
   ;; round trips than CRAM-MD5, and it's less likely to be buggy),
   ;; and we're using an encrypted connection.
   ((and (not (nnimap-capability "LOGINDISABLED"))
	 (eq (nnimap-stream-type nnimap-object) 'tls)
	 (or (null nnimap-authenticator)
             (eq nnimap-authenticator 'anonymous)
	     (eq nnimap-authenticator 'login)))
    (nnimap-command "LOGIN %S %S" user password))
   ((and (nnimap-capability "AUTH=CRAM-MD5")
	 (or (null nnimap-authenticator)
	     (eq nnimap-authenticator 'cram-md5)))
    (erase-buffer)
    (let ((sequence (nnimap-send-command "AUTHENTICATE CRAM-MD5"))
	  (challenge (nnimap-wait-for-line "^\\+\\(.*\\)\n")))
      (process-send-string
       (get-buffer-process (current-buffer))
       (concat
	(base64-encode-string
	 (concat user " "
		 (rfc2104-hash 'md5 64 16 password
			       (base64-decode-string challenge)))
	 t)
	"\r\n"))
      (nnimap-wait-for-response sequence)))
   ((and (not (nnimap-capability "LOGINDISABLED"))
	 (or (null nnimap-authenticator)
             (eq nnimap-authenticator 'anonymous)
	     (eq nnimap-authenticator 'login)))
    (nnimap-command "LOGIN %S %S" user password))
   ((and (nnimap-capability "AUTH=PLAIN")
	 (or (null nnimap-authenticator)
	     (eq nnimap-authenticator 'plain)))
    (nnimap-command
     "AUTHENTICATE PLAIN %s"
     (base64-encode-string
      (format "\000%s\000%s"
	      (nnimap-quote-specials user)
	      (nnimap-quote-specials password))
      t)))))

(defun nnimap-quote-specials (string)
  (with-temp-buffer
    (insert string)
    (goto-char (point-min))
    (while (re-search-forward "[\\\"]" nil t)
      (forward-char -1)
      (insert "\\")
      (forward-char 1))
    (buffer-string)))

(defun nnimap-find-parameter (parameter elems)
  (let (result)
    (dolist (elem elems)
      (cond
       ((equal (car elem) parameter)
	(setq result (cdr elem)))
       ((and (equal (car elem) "OK")
	     (consp (cadr elem))
	     (equal (caadr elem) parameter))
	(setq result (cdr (cadr elem))))))
    result))

(deffoo nnimap-close-server (&optional server defs)
  (when (nnoo-change-server 'nnimap server defs)
    (ignore-errors
      (delete-process (get-buffer-process (nnimap-buffer))))
    (nnoo-close-server 'nnimap server)
    t))

(deffoo nnimap-request-close ()
  t)

(deffoo nnimap-server-opened (&optional server)
  (and (nnoo-current-server-p 'nnimap server)
       nntp-server-buffer
       (gnus-buffer-live-p nntp-server-buffer)
       (nnimap-find-connection nntp-server-buffer)))

(deffoo nnimap-status-message (&optional _server)
  nnimap-status-string)

(deffoo nnimap-request-article (article &optional group server to-buffer)
  (with-current-buffer nntp-server-buffer
    (let ((result (nnimap-change-group group server))
	  parts structure)
      (when (stringp article)
	(setq article (nnimap-find-article-by-message-id group server article)))
      (when (and result
		 article)
	(erase-buffer)
	(with-current-buffer (nnimap-buffer)
	  (erase-buffer)
	  (when nnimap-fetch-partial-articles
	    (nnimap-command "UID FETCH %d (BODYSTRUCTURE)" article)
	    (goto-char (point-min))
	    (when (re-search-forward "FETCH.*BODYSTRUCTURE" nil t)
	      (setq structure (ignore-errors
				(let ((start (point)))
				  (forward-sexp 1)
				  (downcase-region start (point))
				  (goto-char start)
				  (read (current-buffer))))
		    parts (nnimap-find-wanted-parts structure))))
	  (when (if parts
		    (nnimap-get-partial-article article parts structure)
		  (nnimap-get-whole-article article))
	    (let ((buffer (current-buffer)))
	      (with-current-buffer (or to-buffer nntp-server-buffer)
		(nnheader-insert-buffer-substring buffer)
		(nnheader-ms-strip-cr)))
	    (cons group article)))))))

(deffoo nnimap-request-head (article &optional group server to-buffer)
  (when (nnimap-change-group group server)
    (with-current-buffer (nnimap-buffer)
      (when (stringp article)
	(setq article (nnimap-find-article-by-message-id group server article)))
      (if (null article)
	  nil
	(nnimap-get-whole-article
	 article (format "UID FETCH %%d %s"
			 (nnimap-header-parameters)))
	(let ((buffer (current-buffer)))
	  (with-current-buffer (or to-buffer nntp-server-buffer)
	    (erase-buffer)
	    (insert-buffer-substring buffer)
	    (nnheader-ms-strip-cr)
	    (cons group article)))))))

(deffoo nnimap-request-articles (articles &optional group server)
  (with-current-buffer nntp-server-buffer
    (let ((result (nnimap-change-group group server)))
      (when result
	(erase-buffer)
	(with-current-buffer (nnimap-buffer)
	  (erase-buffer)
	  (when (nnimap-command
		 (if (nnimap-ver4-p)
		     "UID FETCH %s BODY.PEEK[]"
		   "UID FETCH %s RFC822.PEEK")
		 (nnimap-article-ranges (gnus-compress-sequence articles)))
	    (let ((buffer (current-buffer)))
	      (with-current-buffer nntp-server-buffer
		(nnheader-insert-buffer-substring buffer)
		(nnheader-ms-strip-cr)))
	    t))))))

(defun nnimap-get-whole-article (article &optional command)
  (let ((result
	 (nnimap-command
	  (or command
	      (if (nnimap-ver4-p)
		  "UID FETCH %d BODY.PEEK[]"
		"UID FETCH %d RFC822.PEEK"))
	  article)))
    ;; Check that we really got an article.
    (goto-char (point-min))
    (unless (re-search-forward "\\* [0-9]+ FETCH" nil t)
      (setq result nil))
    (when result
      ;; Remove any data that may have arrived before the FETCH data.
      (beginning-of-line)
      (unless (bobp)
	(delete-region (point-min) (point)))
      (let ((bytes (nnimap-get-length)))
	(delete-region (line-beginning-position)
		       (progn (forward-line 1) (point)))
	(goto-char (+ (point) bytes))
	(delete-region (point) (point-max)))
      t)))

(defun nnimap-capability (capability)
  (member capability (nnimap-capabilities nnimap-object)))

(defun nnimap-ver4-p ()
  (nnimap-capability "IMAP4REV1"))

(defun nnimap-get-partial-article (article parts structure)
  (let ((result
	 (nnimap-command
	  "UID FETCH %d (%s %s)"
	  article
	  (if (nnimap-ver4-p)
	      "BODY.PEEK[HEADER]"
	    "RFC822.HEADER")
	  (if (nnimap-ver4-p)
	      (mapconcat (lambda (part)
			   (format "BODY.PEEK[%s]" part))
			 parts " ")
	    (mapconcat (lambda (part)
			 (format "RFC822.PEEK[%s]" part))
		       parts " ")))))
    (when result
      (nnimap-convert-partial-article structure))))

(defun nnimap-convert-partial-article (structure)
  ;; First just skip past the headers.
  (goto-char (point-min))
  (let ((bytes (nnimap-get-length))
	id parts)
    ;; Delete "FETCH" line.
    (delete-region (line-beginning-position)
		   (progn (forward-line 1) (point)))
    (goto-char (+ (point) bytes))
    ;; Collect all the body parts.
    (while (looking-at ".*BODY\\[\\([.0-9]+\\)\\]")
      (setq id (match-string 1)
	    bytes (or (nnimap-get-length) 0))
      (beginning-of-line)
      (delete-region (point) (progn (forward-line 1) (point)))
      (push (list id (buffer-substring (point) (+ (point) bytes)))
	    parts)
      (delete-region (point) (+ (point) bytes)))
    ;; Delete trailing junk.
    (delete-region (point) (point-max))
    ;; Now insert all the parts again where they fit in the structure.
    (nnimap-insert-partial-structure structure parts)
    t))

(defun nnimap-insert-partial-structure (structure parts &optional subp)
  (let (type boundary)
    (let ((bstruc structure))
      (while (consp (car bstruc))
	(pop bstruc))
      (setq type (car bstruc))
      (setq bstruc (car (cdr bstruc)))
      (let ((has-boundary (member "boundary" bstruc)))
        (when has-boundary
          (setq boundary (cadr has-boundary)))))
    (when subp
      (insert (format "Content-type: multipart/%s; boundary=%S\n\n"
		      (downcase type) boundary)))
    (while (not (stringp (car structure)))
      (insert "\n--" boundary "\n")
      (if (consp (caar structure))
	  (nnimap-insert-partial-structure (pop structure) parts t)
	(let ((bit (pop structure)))
	  (insert (format "Content-type: %s/%s"
			  (downcase (nth 0 bit))
			  (downcase (nth 1 bit))))
	  (if (member-ignore-case "CHARSET" (nth 2 bit))
	      (insert (format
		       "; charset=%S\n"
		       (cadr (member-ignore-case "CHARSET" (nth 2 bit)))))
	    (insert "\n"))
	  (insert (format "Content-transfer-encoding: %s\n"
			  (nth 5 bit)))
	  (insert "\n")
	  (when (assoc (nth 9 bit) parts)
	    (insert (cadr (assoc (nth 9 bit) parts)))))))
    (insert "\n--" boundary "--\n")))

(defun nnimap-find-wanted-parts (structure)
  (flatten-tree (nnimap-find-wanted-parts-1 structure "")))

(defun nnimap-find-wanted-parts-1 (structure prefix)
  (let ((num 1)
	parts)
    (while (consp (car structure))
      (let ((sub (pop structure)))
	(if (consp (car sub))
	    (push (nnimap-find-wanted-parts-1
		   sub (if (string= prefix "")
			   (number-to-string num)
			 (format "%s.%s" prefix num)))
		  parts)
	  (let ((type (format "%s/%s" (nth 0 sub) (nth 1 sub)))
		(id (if (string= prefix "")
			(number-to-string num)
		      (format "%s.%s" prefix num))))
	    (setcar (nthcdr 9 sub) id)
	    (when (if (eq nnimap-fetch-partial-articles t)
		      (equal id "1")
		    (string-match nnimap-fetch-partial-articles type))
	      (push id parts))))
	(cl-incf num)))
    (nreverse parts)))

(deffoo nnimap-request-group (group &optional server dont-check info)
  (let ((result (nnimap-change-group
		 ;; Don't SELECT the group if we're going to select it
		 ;; later, anyway.
		 (if (and (not dont-check)
			  (assoc group nnimap-current-infos))
		     nil
		   group)
		 server))
	(info (when info (list info)))
	active)
    (with-current-buffer nntp-server-buffer
      (when result
	(when (or (not dont-check)
		  (not (setq active
			     (nth 2 (assoc group nnimap-current-infos)))))
	  (let ((sequences (nnimap-retrieve-group-data-early
			    server info)))
	    (nnimap-finish-retrieve-group-infos server info sequences
						t)
	    (setq active (nth 2 (assoc group nnimap-current-infos)))))
	(setq active (or active '(0 . 1)))
	(erase-buffer)
	(insert (format "211 %d %d %d %S\n"
			(- (cdr active) (car active))
			(car active)
			(cdr active)
			group))
	t))))

(deffoo nnimap-request-group-scan (group &optional server info)
  (when (nnimap-change-group nil server)
    (let (marks high low)
      (with-current-buffer (nnimap-buffer)
	(erase-buffer)
	(let ((group-sequence
	       (nnimap-send-command "SELECT %S" (nnimap-group-to-imap group)))
	      (flag-sequence
	       (nnimap-send-command "UID FETCH 1:* FLAGS")))
	  (setf (nnimap-group nnimap-object) group)
	  (nnimap-wait-for-response flag-sequence)
	  (setq marks
		(nnimap-flags-to-marks
		 (nnimap-parse-flags
		  (list (list group-sequence flag-sequence
			      1 group "SELECT")))))
	  (when (and info
		     marks)
	    (nnimap-update-infos marks (list info))
	    (nnimap-store-info info (gnus-active (gnus-info-group info))))
	  (goto-char (point-max))
	  (let ((uidnext (nth 5 (car marks))))
	    (setq high (or (if uidnext
			       (1- uidnext)
			     (nth 3 (car marks)))
			   0)
		  low (or (nth 4 (car marks)) uidnext 1)))))
      (with-current-buffer nntp-server-buffer
	(erase-buffer)
	(insert
	 (format
	  "211 %d %d %d %S\n" (1+ (- high low)) low high
	  group))
	t))))

(deffoo nnimap-request-create-group (group &optional server _args)
  (when (nnimap-change-group nil server)
    (with-current-buffer (nnimap-buffer)
      (car (nnimap-command "CREATE %S" (nnimap-group-to-imap group))))))

(deffoo nnimap-request-delete-group (group &optional _force server)
  (when (nnimap-change-group nil server)
    (with-current-buffer (nnimap-buffer)
      (car (nnimap-command "DELETE %S" (nnimap-group-to-imap group))))))

(deffoo nnimap-request-rename-group (group new-name &optional server)
  (when (nnimap-change-group nil server)
    (with-current-buffer (nnimap-buffer)
      (nnimap-unselect-group)
      (car (nnimap-command "RENAME %S %S"
			   (nnimap-group-to-imap group) (nnimap-group-to-imap new-name))))))

(defun nnimap-unselect-group ()
  ;; Make sure we don't have this group open read/write by asking
  ;; to examine a mailbox that doesn't exist.  This seems to be
  ;; the only way that allows us to reliably go back to unselected
  ;; state on Courier.
  (nnimap-command "EXAMINE DOES.NOT.EXIST"))

(deffoo nnimap-request-expunge-group (group &optional server)
  (when (nnimap-change-group group server)
    (with-current-buffer (nnimap-buffer)
      (car (nnimap-command "EXPUNGE")))))

(defun nnimap-get-flags (spec)
  (let ((articles nil)
	elems end)
    (with-current-buffer (nnimap-buffer)
      (erase-buffer)
      (nnimap-wait-for-response (nnimap-send-command
				 "UID FETCH %s FLAGS" spec))
      (setq end (point))
      (subst-char-in-region (point-min) (point-max)
			    ?\\ ?% t)
      (goto-char (point-min))
      (while (search-forward " FETCH " end t)
	(setq elems (read (current-buffer)))
	(push (cons (cadr (memq 'UID elems))
		    (cadr (memq 'FLAGS elems)))
	      articles)))
    (nreverse articles)))

(deffoo nnimap-close-group (_group &optional server)
  (when (eq nnimap-expunge 'on-exit)
    (nnoo-change-server 'nnimap server nil)
    (with-current-buffer (nnimap-buffer)
      (nnimap-command "EXPUNGE"))))

(deffoo nnimap-request-move-article (article group server accept-form
					     &optional _last
					     internal-move-group)
  (with-temp-buffer
    (mm-disable-multibyte)
    (when (funcall (if internal-move-group
		       'nnimap-request-head
		     'nnimap-request-article)
		   article group server (current-buffer))
      ;; If the move is internal (on the same server), just do it the
      ;; easy way.
      (let ((message-id (message-field-value "message-id")))
	(if internal-move-group
            (with-current-buffer (nnimap-buffer)
              (let* ((can-move (and (nnimap-capability "MOVE")
				    (equal (nnimap-quirk "MOVE") "MOVE")))
		     (command (if can-move
				  "UID MOVE %d %S"
				"UID COPY %d %S"))
		     (result (nnimap-command
			      command article
                              (nnimap-group-to-imap internal-move-group))))
                (when (and (car result) (not can-move))
                  (nnimap-delete-article article))
                (cons internal-move-group
                      (or (nnimap-find-uid-response
			   "COPYUID"
			   ;; Server gives different responses for MOVE and COPY.
			   (if can-move (caddr result) (cadr result)))
                          (nnimap-find-article-by-message-id
                           internal-move-group server message-id
                           nnimap-request-articles-find-limit)))))
	  ;; Move the article to a different method.
	  (when-let* ((result (eval accept-form t)))
	    (nnimap-change-group group server)
	    (nnimap-delete-article article)
	    result))))))

(deffoo nnimap-request-expire-articles (articles group &optional server force)
  (cond
   ((null articles)
    nil)
   ((not (nnimap-change-group group server))
    articles)
   ((and force
	 (eq nnmail-expiry-target 'delete))
    (nnimap-delete-article (gnus-compress-sequence articles))
    nil)
   (t
    (let ((deletable-articles
	   (if (or force
		   (eq nnmail-expiry-wait 'immediate))
	       articles
	     (gnus-sorted-intersection
	      articles
	      (nnimap-find-expired-articles group)))))
      (if (null deletable-articles)
	  articles
	(if (eq nnmail-expiry-target 'delete)
	    (nnimap-delete-article (gnus-compress-sequence deletable-articles))
	  (setq deletable-articles
		(nnimap-process-expiry-targets
		 deletable-articles group server)))
	;; Return the articles we didn't delete.
	(gnus-sorted-complement articles deletable-articles))))))

(defun nnimap-process-expiry-targets (articles group server)
  (let ((deleted-articles nil)
        (articles-to-delete nil))
    (cond
     ;; shortcut further processing if we're going to delete the articles
     ((eq nnmail-expiry-target 'delete)
      (setq articles-to-delete articles)
      t)
     ;; or just move them to another folder on the same IMAP server
     ((and (not (functionp nnmail-expiry-target))
	   (gnus-server-equal (gnus-group-method nnmail-expiry-target)
			      (gnus-server-to-method
			       (format "nnimap:%s" server))))
      (and (nnimap-change-group group server)
	   (with-current-buffer (nnimap-buffer)
	     (nnheader-message 7 "Expiring articles from %s: %s" group articles)
             (let ((can-move (and (nnimap-capability "MOVE")
				  (equal (nnimap-quirk "MOVE") "MOVE"))))
               (nnimap-command
                (if can-move
                    "UID MOVE %s %S"
                  "UID COPY %s %S")
                (nnimap-article-ranges (gnus-compress-sequence articles))
                (nnimap-group-to-imap (gnus-group-real-name nnmail-expiry-target)))
               (if can-move
                   (setq deleted-articles articles)
                 (setq articles-to-delete articles)))))
      t)
     (t
      (dolist (article articles)
	(let ((target nnmail-expiry-target))
	  (with-temp-buffer
	    (mm-disable-multibyte)
	    (when (nnimap-request-article article group server (current-buffer))
	      (when (functionp target)
		(setq target (funcall target group)))
	      (if (and target
		       (not (eq target 'delete)))
		  (if (or (gnus-request-group target t)
			  (gnus-request-create-group target))
		      (progn
			(nnmail-expiry-target-group target group)
			(nnheader-message 7 "Expiring article %s:%d to %s"
					  group article target))
		    (setq target nil))
		(nnheader-message 7 "Expiring article %s:%d" group article))
	      (when target
		(push article articles-to-delete))))))
      (setq articles-to-delete (nreverse articles-to-delete))))
    ;; Change back to the current group again.
    (nnimap-change-group group server)
    (when articles-to-delete
      (nnimap-delete-article (gnus-compress-sequence articles-to-delete))
      (setq deleted-articles articles-to-delete))
    deleted-articles))

(defun nnimap-find-expired-articles (group)
  (let ((cutoff (nnmail-expired-article-p group nil nil)))
    (when cutoff
      (with-current-buffer (nnimap-buffer)
	(let ((result
	       (nnimap-command
		"UID SEARCH SENTBEFORE %s"
		(let ((system-time-locale "C"))
		  (upcase (format-time-string "%d-%b-%Y" cutoff))))))
	  (and (car result)
	       (delete 0 (mapcar #'string-to-number
				 (cdr (assoc "SEARCH" (cdr result)))))))))))

(defun nnimap-find-article-by-message-id (group server message-id
						&optional limit)
  "Search for message with MESSAGE-ID in GROUP from SERVER.
If LIMIT, first try to limit the search to the N last articles."
  (with-current-buffer (nnimap-buffer)
    (erase-buffer)
    (let* ((change-group-result (nnimap-change-group group server nil t))
           (number-of-article
            (and (listp change-group-result)
                 (catch 'found
                   (dolist (result (cdr change-group-result))
                     (when (equal "EXISTS" (cadr result))
                       (throw 'found (car result)))))))
           (sequence
            (nnimap-send-command
	     "UID SEARCH%s HEADER Message-Id %S"
	     (if (and limit number-of-article)
		 ;; The -1 is because IMAP message
		 ;; numbers are one-based rather than
		 ;; zero-based.
		 (format " %s:*" (- (string-to-number number-of-article)
				    limit -1))
	       "")
	     message-id)))
      (when (nnimap-wait-for-response sequence)
        (let ((article (car (last (cdr (assoc "SEARCH"
					      (nnimap-parse-response)))))))
          (if article
              (string-to-number article)
            (when (and limit number-of-article)
              (nnimap-find-article-by-message-id group server message-id))))))))

(defun nnimap-delete-article (articles)
  "Delete ARTICLES."
  (with-current-buffer (nnimap-buffer)
    (nnimap-command "UID STORE %s +FLAGS.SILENT (\\Deleted)"
		    (nnimap-article-ranges articles))
    (cond
     ((eq nnimap-expunge 'immediately)
      (if (nnimap-capability "UIDPLUS")
	  (nnimap-command "UID EXPUNGE %s"
			  (nnimap-article-ranges articles))
	(nnheader-message
	 3 (concat "nnimap-expunge set to `immediately', but "
		   "server doesn't support UIDPLUS"))
	nil))

     ((memq nnimap-expunge '(on-exit never)) nil)

     ((nnimap-capability "UIDPLUS")
      (nnimap-command "UID EXPUNGE %s"
		      (nnimap-article-ranges articles)))

     (nnimap-expunge
      (nnimap-command "EXPUNGE"))

     (t
      (nnheader-message
       7 "Article marked for deletion, but not expunged.")
      nil))))

(deffoo nnimap-request-scan (&optional _group server)
  (when (and (nnimap-change-group nil server)
	     nnimap-inbox
	     nnimap-split-methods)
    (nnheader-message 7 "nnimap %s splitting mail..." server)
    (if (listp nnimap-inbox)
       (dolist (nnimap-inbox nnimap-inbox)
         (nnimap-split-incoming-mail))
      (nnimap-split-incoming-mail))
    (nnheader-message 7 "nnimap %s splitting mail...done" server)))

(defun nnimap-marks-to-flags (marks)
  (let (flags flag)
    (dolist (mark marks)
      (when (setq flag (cadr (assq mark nnimap-mark-alist)))
	(push flag flags)))
    flags))

(deffoo nnimap-request-update-group-status (group status &optional server)
  (when (nnimap-change-group nil server)
    (let ((command (assoc
		    status
		    '((subscribe "SUBSCRIBE")
		      (unsubscribe "UNSUBSCRIBE")))))
      (when command
	(with-current-buffer (nnimap-buffer)
	  (nnimap-command "%s %S" (cadr command) (nnimap-group-to-imap group)))))))

(deffoo nnimap-request-set-mark (group actions &optional server)
  (when (nnimap-change-group group server)
    (let (sequence)
      (with-current-buffer (nnimap-buffer)
	(erase-buffer)
	;; Just send all the STORE commands without waiting for
	;; response.  If they're successful, they're successful.
	(dolist (action actions)
	  (cl-destructuring-bind (range action marks) action
	    ;; If we add a tick mark, then also mark the message as
	    ;; read.  Other IMAP clients can have marked messages
	    ;; without having them read, but Gnus can't.
	    (when (and (memq 'tick marks)
		       (eq action 'add))
	      (push 'read marks))
	    (let ((flags (nnimap-marks-to-flags marks)))
	      (when flags
		(setq sequence (nnimap-send-command
				"UID STORE %s %sFLAGS.SILENT (%s)"
				(nnimap-article-ranges range)
				(cond
				 ((eq action 'del) "-")
				 ((eq action 'add) "+")
				 ((eq action 'set) ""))
				(mapconcat #'identity flags " ")))))))
	;; Wait for the last command to complete to avoid later
	;; synchronization problems with the stream.
	(when sequence
	  (nnimap-wait-for-response sequence))))))

(deffoo nnimap-request-accept-article (group &optional server _last)
  (unless group
    ;; We're respooling.  Find out where mail splitting would place
    ;; this article.
    (setq group
	  (caar
	   (nnmail-article-group
	    ;; We don't really care about the article number, because
	    ;; that's determined by the IMAP server later.  So just
	    ;; return the group name.
	    (lambda (group)
	       (list (list group)))))))
  (when (nnimap-change-group nil server)
    (nnmail-check-syntax)
    (let ((message-id (message-field-value "message-id"))
	  sequence message)
      (nnimap-add-cr)
      (setq message (buffer-substring-no-properties (point-min) (point-max)))
      (with-current-buffer (nnimap-buffer)
	(when (setq message (or (nnimap-process-quirk "OK Gimap " 'append message)
				message))
	  ;; If we have this group open read-only, then unselect it
	  ;; before appending to it.
	  (when (equal (nnimap-examined nnimap-object) group)
	    (nnimap-unselect-group))
	  (erase-buffer)
	  (setq sequence (nnimap-send-command
			  "APPEND %S {%d}" (nnimap-group-to-imap group)
			  (length message)))
	  (unless nnimap-streaming
	    (nnimap-wait-for-connection "^[+]"))
	  (process-send-string (get-buffer-process (current-buffer)) message)
	  (process-send-string (get-buffer-process (current-buffer))
			       (if (nnimap-newlinep nnimap-object)
				   "\n"
				 "\r\n"))
	  (let ((result (nnimap-get-response sequence)))
	    (if (not (nnimap-ok-p result))
		(progn
		  (nnheader-report 'nnimap "%s" result)
		  nil)
	      (cons group
		    (or (nnimap-find-uid-response "APPENDUID" (car result))
			(nnimap-find-article-by-message-id
			 group server message-id
                         nnimap-request-articles-find-limit))))))))))

(defun nnimap-process-quirk (greeting-match type data)
  (when (and (nnimap-greeting nnimap-object)
	     (string-match greeting-match (nnimap-greeting nnimap-object))
	     (eq type 'append)
	     (string-match "\000" data))
    (let ((choice (gnus-multiple-choice
		   "Message contains NUL characters.  Delete, continue, abort? "
		   '((?d "Delete NUL characters")
		     (?c "Try to APPEND the message as is")
		     (?a "Abort")))))
      (cond
       ((eq choice ?a)
	(nnheader-report 'nnimap "Aborted APPEND due to NUL characters"))
       ((eq choice ?c)
	data)
       (t
	(with-temp-buffer
	  (insert data)
	  (goto-char (point-min))
	  (while (search-forward "\000" nil t)
	    (replace-match "" t t))
	  (buffer-string)))))))

(defun nnimap-ok-p (value)
  (and (consp value)
       (consp (car value))
       (equal (caar value) "OK")))

(defun nnimap-find-uid-response (name list)
  (let ((result (car (last (nnimap-find-response-element name list)))))
    (and result
	 (string-to-number result))))

(defun nnimap-find-response-element (name list)
  (let (result)
    (dolist (elem list)
      (when (and (consp elem)
		 (equal name (car elem)))
	(setq result elem)))
    result))

(deffoo nnimap-request-replace-article (article group buffer)
  (let (group-art)
    (when (and (nnimap-change-group group)
	       ;; Put the article into the group.
	       (with-current-buffer buffer
		 (setq group-art
		       (nnimap-request-accept-article group nil t))))
      (nnimap-delete-article (list article))
      ;; Return the new article number.
      (cdr group-art))))

(defun nnimap-add-cr ()
  (goto-char (point-min))
  (while (re-search-forward "\r?\n" nil t)
    (replace-match "\r\n" t t)))

(defun nnimap-get-groups ()
  (erase-buffer)
  (let* ((sequence (nnimap-send-command "LIST \"\" \"*\""))
         (prefix nnimap-namespace)
         (prefix-len (if prefix (length prefix) nil))
         (inbox (if prefix
                    (substring prefix 0 -1) nil))
         groups)
    (nnimap-wait-for-response sequence)
    (subst-char-in-region (point-min) (point-max)
			  ?\\ ?% t)
    (goto-char (point-min))
    (nnimap-unfold-quoted-lines)
    (goto-char (point-min))
    (while (search-forward "* LIST " nil t)
      (let ((flags (read (current-buffer)))
	    (_separator (read (current-buffer)))
	    (group (buffer-substring-no-properties
		    (progn (skip-chars-forward " \"")
			   (point))
		    (progn (end-of-line)
			   (skip-chars-backward " \r\"")
			   (point)))))
	(unless (member '%Noselect flags)
          (let* ((group (utf7-decode (if (stringp group) group
                                       (format "%s" group)) t))
                 (group (cond ((or (not prefix)
                                   (equal inbox group))
                               group)
                              ((string-prefix-p prefix group)
                               (substring group prefix-len))
                              (t
                               (concat "#" group)))))
            (push group groups)))))
    (nreverse groups)))

(defun nnimap-get-responses (sequences)
  (let (responses)
    (dolist (sequence sequences)
      (goto-char (point-min))
      (when (re-search-forward (format "^%d " sequence) nil t)
        (push (list sequence (nnimap-parse-response))
              responses)))
    responses))

(deffoo nnimap-request-list (&optional server)
  (when (nnimap-change-group nil server)
    (with-current-buffer nntp-server-buffer
      (erase-buffer)
      (let ((groups
	     (with-current-buffer (nnimap-buffer)
	       (nnimap-get-groups)))
	    sequences responses)
	(when groups
	  (with-current-buffer (nnimap-buffer)
	    (setf (nnimap-group nnimap-object) nil)
	    (dolist (group groups)
	      (setf (nnimap-examined nnimap-object) group)
	      (push (list (nnimap-send-command "EXAMINE %S"
					       (nnimap-group-to-imap group))
			  group)
		    sequences))
	    (nnimap-wait-for-response (caar sequences))
	    (setq responses
		  (nnimap-get-responses (mapcar #'car sequences))))
	  (dolist (response responses)
	    (let* ((sequence (car response))
		   (response (cadr response))
		   (group (cadr (assoc sequence sequences))))
	      (when (and group
			 (equal (caar response) "OK"))
		(let ((uidnext (nnimap-find-parameter "UIDNEXT" response))
		      highest exists)
		  (dolist (elem response)
		    (when (equal (cadr elem) "EXISTS")
		      (setq exists (string-to-number (car elem)))))
		  (when uidnext
		    (setq highest (1- (string-to-number (car uidnext)))))
		  (cond
		   ((null highest)
		    (insert (format "%S 0 1 y\n" group)))
		   ((zerop exists)
		    ;; Empty group.
		    (insert (format "%S %d %d y\n" group
				    highest (1+ highest))))
		   (t
		    ;; Return the widest possible range.
		    (insert (format "%S %d 1 y\n" group
				    (or highest exists)))))))))
	  t)))))

(deffoo nnimap-request-newgroups (_date &optional server)
  (when (nnimap-change-group nil server)
    (with-current-buffer nntp-server-buffer
      (erase-buffer)
      (dolist (group (with-current-buffer (nnimap-buffer)
		       (nnimap-get-groups)))
	(unless (assoc group nnimap-current-infos)
	  ;; Insert dummy numbers here -- they don't matter.
	  (insert (format "%S 0 1 y\n" group))))
      t)))

(deffoo nnimap-retrieve-group-data-early (server infos)
  (when (and (nnimap-change-group nil server)
	     infos)
    (with-current-buffer (nnimap-buffer)
      (erase-buffer)
      (setf (nnimap-group nnimap-object) nil)
      (setf (nnimap-initial-resync nnimap-object) 0)
      (let ((qresyncp (nnimap-capability "QRESYNC"))
	    params sequences active uidvalidity modseq group
	    unexist)
	;; Go through the infos and gather the data needed to know
	;; what and how to request the data.
	(dolist (info infos)
	  (setq params (gnus-info-params info)
		group (gnus-group-real-name (gnus-info-group info))
		active (cdr (assq 'active params))
		unexist (assq 'unexist (gnus-info-marks info))
		uidvalidity (cdr (assq 'uidvalidity params))
		modseq (cdr (assq 'modseq params)))
	  (setf (nnimap-examined nnimap-object) group)
	  (if (and qresyncp
		   uidvalidity
		   active
		   modseq
		   unexist)
	      (push
	       (list (nnimap-send-command "EXAMINE %S (%s (%s %s))"
					  (nnimap-group-to-imap group)
					  (nnimap-quirk "QRESYNC")
					  uidvalidity modseq)
		     'qresync
		     nil group 'qresync)
	       sequences)
	    (let ((command
		   (if uidvalidity
		       "EXAMINE"
		     ;; If we don't have a UIDVALIDITY, then this is
		     ;; the first time we've seen the group, so we
		     ;; have to do a SELECT (which is slower than an
		     ;; examine), but will tell us whether the group
		     ;; is read-only or not.
		     "SELECT"))
		  start)
	      (if (and active uidvalidity unexist)
		  ;; Fetch the last 100 flags.
		  (setq start (max 1 (- (cdr active) 100)))
		(cl-incf (nnimap-initial-resync nnimap-object))
		(setq start 1))
	      (push (list (nnimap-send-command "%s %S" command
					       (nnimap-group-to-imap group))
			  (nnimap-send-command "UID FETCH %d:* FLAGS" start)
			  start group command)
		    sequences))))
	sequences))))

(defun nnimap-quirk (command)
  (let ((quirk (assoc command nnimap-quirks)))
    ;; If this server is of a type that matches a quirk, then return
    ;; the "quirked" command instead of the proper one.
    (if (or (null quirk)
	    (not (string-match (nth 1 quirk) (nnimap-greeting nnimap-object))))
	command
      (nth 2 quirk))))

(deffoo nnimap-finish-retrieve-group-infos (server infos sequences
						   &optional dont-insert)
  (when (and sequences
	     (nnimap-change-group nil server t)
	     ;; Check that the process is still alive.
	     (get-buffer-process (nnimap-buffer))
	     (memq (process-status (get-buffer-process (nnimap-buffer)))
		   '(open run)))
    (with-current-buffer (nnimap-buffer)
      ;; Wait for the final data to trickle in.
      (when (nnimap-wait-for-response (if (eq (cadar sequences) 'qresync)
					  (caar sequences)
					(cadar sequences))
				      t)
	;; Now we should have most of the data we need, no matter
	;; whether we're QRESYNCING, fetching all the flags from
	;; scratch, or just fetching the last 100 flags per group.
	(nnimap-update-infos (nnimap-flags-to-marks
			      (nnimap-parse-flags
			       (nreverse sequences)))
			     infos)
	(unless dont-insert
	  ;; Finally, just return something resembling an active file in
	  ;; the nntp buffer, so that the agent can save the info, too.
	  (with-current-buffer nntp-server-buffer
	    (erase-buffer)
	    (dolist (info infos)
	      (let* ((group (gnus-info-group info))
		     (active (gnus-active group)))
		(when active
		  (insert (format "%S %d %d y\n"
				  (gnus-group-real-name group)
				  (cdr active)
				  (car active))))))))))))

(defun nnimap-update-infos (flags infos)
  (dolist (info infos)
    (let* ((group (gnus-group-real-name (gnus-info-group info)))
	   (marks (cdr (assoc group flags))))
      (when marks
	(nnimap-update-info info marks)))))

(defun nnimap-update-info (info marks)
  (cl-destructuring-bind (existing flags high low uidnext start-article
				   permanent-flags uidvalidity
				   vanished highestmodseq)
      marks
    (cond
     ;; Ignore groups with no UIDNEXT/marks.  This happens for
     ;; completely empty groups.
     ((and (not existing)
	   (not uidnext))
      (let ((active (cdr (assq 'active (gnus-info-params info)))))
	(when active
	  (gnus-set-active (gnus-info-group info) active))))
     ;; We have a mismatch between the old and new UIDVALIDITY
     ;; identifiers, so we have to re-request the group info (the next
     ;; time).  This virtually never happens.
     ((let ((old-uidvalidity
	     (cdr (assq 'uidvalidity (gnus-info-params info)))))
	(and old-uidvalidity
	     (not (equal old-uidvalidity uidvalidity))
             (or (not start-article)
                 (> start-article 1))))
      (gnus-group-remove-parameter info 'uidvalidity)
      (gnus-group-remove-parameter info 'modseq))
     ;; We have the data needed to update.
     (t
      (let* ((group (gnus-info-group info))
	     (completep (and start-article
			     (= start-article 1)))
	     (active (or (gnus-active group)
			 (cdr (assq 'active (gnus-info-params info))))))
	(when uidnext
	  (setq high (1- uidnext)))
	;; First set the active ranges based on high/low.
	(if (or completep
		(not (gnus-active group)))
	    (gnus-set-active group
			     (cond
			      (active
			       (cons (min (or low (car active))
					  (car active))
				     (max (or high (cdr active))
					  (cdr active))))
			      ((and low high)
			       (cons low high))
			      (uidnext
			       ;; No articles in this group.
			       (cons uidnext (1- uidnext)))
			      (start-article
			       (cons start-article (1- start-article)))
			      (t
			       ;; No articles and no uidnext.
			       nil)))
	  (gnus-set-active group
			   (cons (car active)
				 (or high (1- uidnext)))))
	;; See whether this is a read-only group.
	(unless (eq permanent-flags 'not-scanned)
	  (gnus-group-set-parameter
	   info 'permanent-flags
	   (and (or (memq '%* permanent-flags)
		    (memq '%Seen permanent-flags))
		permanent-flags)))
	;; Update marks and read articles if this isn't a
	;; read-only IMAP group.
	(when (setq permanent-flags
		    (cdr (assq 'permanent-flags (gnus-info-params info))))
	  (if (and highestmodseq
		   (not start-article))
	      ;; We've gotten the data by QRESYNCing.
	      (nnimap-update-qresync-info
	       info existing (nnimap-imap-ranges-to-gnus-ranges vanished) flags)
	    ;; Do normal non-QRESYNC flag updates.
	    ;; Update the list of read articles.
	    (unless start-article
	      (setq start-article 1))
	    (let* ((unread
		    (gnus-compress-sequence
                     (seq-difference
                      (seq-difference
		       existing
		       (gnus-sorted-union
			(cdr (assoc '%Seen flags))
                        (cdr (assoc '%Deleted flags)))
                       #'eq)
                      (cdr (assoc '%Flagged flags))
                      #'eq)))
		   (read (gnus-range-difference
			  (cons start-article high) unread)))
	      (when (> start-article 1)
		(setq read
		      (gnus-range-nconcat
		       (if (> start-article 1)
			   (gnus-sorted-range-intersection
			    (cons 1 (1- start-article))
			    (gnus-info-read info))
			 (gnus-info-read info))
		       read)))
	      (when (or (not (listp permanent-flags))
			(memq '%Seen permanent-flags))
		(setf (gnus-info-read info) read))
	      ;; Update the marks.
	      (setq marks (gnus-info-marks info))
	      (dolist (type (cdr nnimap-mark-alist))
		(when (or (not (listp permanent-flags))
			  (memq (car (assoc (caddr type) flags))
				permanent-flags)
			  (memq '%* permanent-flags))
		  (let ((old-marks (assoc (car type) marks))
			(new-marks
			 (gnus-compress-sequence
			  (cdr (or (assoc (caddr type) flags) ; %Flagged
				   (assoc (intern (cadr type) obarray) flags)
				   (assoc (cadr type) flags)))))) ; "\Flagged"
		    (setq marks (delq old-marks marks))
		    (pop old-marks)
		    (when (and old-marks
			       (> start-article 1))
		      (setq old-marks (gnus-range-difference
				       old-marks
				       (cons start-article high)))
		      (setq new-marks (gnus-range-nconcat old-marks new-marks)))
		    (when new-marks
		      (push (cons (car type) new-marks) marks)))))
	      ;; Keep track of non-existing articles.
	      (let* ((old-unexists (assq 'unexist marks))
		     (active (gnus-active group))
		     (unexists
		      (if completep
			  (gnus-range-difference
			   active
			   (gnus-compress-sequence existing))
			(gnus-add-to-range
			 (cdr old-unexists)
			 (gnus-list-range-difference
			  existing (gnus-active group))))))
		(when (> (car active) 1)
		  (setq unexists (gnus-range-add
				  (cons 1 (1- (car active)))
				  unexists)))
		(if old-unexists
		    (setcdr old-unexists unexists)
		  (push (cons 'unexist unexists) marks)))
	      (gnus-info-set-marks info marks t))))
	;; Tell Gnus whether there are any \Recent messages in any of
	;; the groups.
	(let ((recent (cdr (assoc '%Recent flags))))
	  (when (and active
		     recent
		     (> (car (last recent)) (cdr active)))
	    (push (list (cons group 0)) nnmail-split-history)))
	;; Note the active level for the next run-through.
	(gnus-group-set-parameter info 'active (gnus-active group))
	(gnus-group-set-parameter info 'uidvalidity uidvalidity)
	(gnus-group-set-parameter info 'modseq highestmodseq)
	(nnimap-store-info info (gnus-active group)))))))

(defun nnimap-update-qresync-info (info existing vanished flags)
  ;; Add all the vanished articles to the list of read articles.
  (setf (gnus-info-read info)
        (gnus-add-to-range
         (gnus-add-to-range
          (gnus-range-add (gnus-info-read info)
			  vanished)
	  (cdr (assq '%Flagged flags)))
	 (cdr (assq '%Seen flags))))
  (let ((marks (gnus-info-marks info)))
    (dolist (type (cdr nnimap-mark-alist))
      (let ((ticks (assoc (car type) marks))
	    (new-marks
	     (cdr (or (assoc (caddr type) flags) ; %Flagged
		      (assoc (intern (cadr type) obarray) flags)
		      (assoc (cadr type) flags))))) ; "\Flagged"
	(when new-marks
	  (setq marks (delq ticks marks))
	  (pop ticks)
	  ;; Add the new marks we got.
	  (setq ticks (gnus-add-to-range ticks new-marks))
	  ;; Remove the marks from messages that don't have them.
	  (setq ticks (gnus-remove-from-range
		       ticks
		       (gnus-compress-sequence
			(gnus-sorted-complement existing new-marks))))
	  (when ticks
	    (push (cons (car type) ticks) marks))
	  (gnus-info-set-marks info marks t))))
    ;; Add vanished to the list of unexisting articles.
    (when vanished
      (let* ((old-unexists (assq 'unexist marks))
	     (unexists (gnus-range-add (cdr old-unexists) vanished)))
	(if old-unexists
	    (setcdr old-unexists unexists)
	  (push (cons 'unexist unexists) marks)))
      (gnus-info-set-marks info marks t))))

(defun nnimap-imap-ranges-to-gnus-ranges (irange)
  (if (zerop (length irange))
      nil
    (let ((result nil))
      (dolist (elem (split-string irange ","))
	(push
	 (if (string-match ":" elem)
	     (let ((numbers (split-string elem ":")))
	       (cons (string-to-number (car numbers))
		     (string-to-number (cadr numbers))))
	   (string-to-number elem))
	 result))
      (nreverse result))))

(defun nnimap-store-info (info active)
  (let* ((group (gnus-group-real-name (gnus-info-group info)))
	 (entry (assoc group nnimap-current-infos)))
    (if entry
	(setcdr entry (list info active))
      (push (list group info active) nnimap-current-infos))))

(defun nnimap-flags-to-marks (groups)
  (let (data group uidnext articles start-article mark permanent-flags
	     uidvalidity vanished highestmodseq)
    (dolist (elem groups)
      (setq group (car elem)
	    uidnext (nth 1 elem)
	    start-article (nth 2 elem)
	    permanent-flags (nth 3 elem)
	    uidvalidity (nth 4 elem)
	    vanished (nth 5 elem)
	    highestmodseq (nth 6 elem)
	    articles (nthcdr 7 elem))
      (let ((high (caar articles))
	    marks low existing)
	(dolist (article articles)
	  (setq low (car article))
	  (push (car article) existing)
	  (dolist (flag (cdr article))
	    (setq mark (assoc flag marks))
	    (if (not mark)
		(push (list flag (car article)) marks)
	      (setcdr mark (cons (car article) (cdr mark))))))
	(push (list group existing marks high low uidnext start-article
		    permanent-flags uidvalidity vanished highestmodseq)
	      data)))
    data))

(defun nnimap-parse-flags (sequences)
  (goto-char (point-min))
  ;; Change \Delete etc to %Delete, so that the Emacs Lisp reader can
  ;; read it.
  (subst-char-in-region (point-min) (point-max)
			?\\ ?% t)
  (let (start end articles groups uidnext elems permanent-flags
	      uidvalidity vanished highestmodseq)
    (dolist (elem sequences)
      (cl-destructuring-bind (group-sequence flag-sequence totalp group command)
	  elem
	(setq start (point))
	(when (and
	       ;; The EXAMINE was successful.
	       (search-forward (format "\n%d OK " group-sequence) nil t)
	       (progn
		 (forward-line 1)
		 (setq end (point))
		 (goto-char start)
		 (setq permanent-flags
		       (if (equal command "SELECT")
			   (and (search-forward "PERMANENTFLAGS " end t)
				(read (current-buffer)))
			 'not-scanned))
		 (goto-char start)
		 (setq uidnext
		       (and (search-forward "UIDNEXT " end t)
			    (read (current-buffer))))
		 (goto-char start)
		 (setq uidvalidity
		       (and (re-search-forward "UIDVALIDITY \\([0-9]+\\)"
					       end t)
			    ;; Store UIDVALIDITY as a string; before bignums,
			    ;; it was usually too big for 32-bit Emacsen,
			    ;; and we don't want to change the format now.
			    (match-string 1)))
		 (goto-char start)
		 (setq vanished
		       (and (eq flag-sequence 'qresync)
			    (re-search-forward "^\\* VANISHED .*? \\([0-9:,]+\\)"
					       end t)
			    (match-string 1)))
		 (goto-char start)
		 (setq highestmodseq
		       (and (re-search-forward "HIGHESTMODSEQ \\([0-9]+\\)"
					       end t)
			    (match-string 1)))
		 (goto-char end)
		 (forward-line -1))
	       ;; The UID FETCH FLAGS was successful.
	       (or (eq flag-sequence 'qresync)
		   (search-forward (format "\n%d OK " flag-sequence) nil t)))
	  (if (eq flag-sequence 'qresync)
	      (progn
		(goto-char start)
		(setq start end))
	    (setq start (point))
	    (goto-char end))
	  (while (re-search-forward "^\\* [0-9]+ FETCH " start t)
	    (progn
	      (setq elems (read (current-buffer)))
	      (push (cons (cadr (memq 'UID elems))
			  (cadr (memq 'FLAGS elems)))
		    articles)))
	  (push (nconc (list group uidnext totalp permanent-flags uidvalidity
			     vanished highestmodseq)
		       articles)
		groups)
	  (if (eq flag-sequence 'qresync)
	      (goto-char end)
	    (setq end (point)))
	  (setq articles nil))))
    groups))

(defun nnimap-find-process-buffer (buffer)
  (cadr (assoc buffer nnimap-connection-alist)))

(deffoo nnimap-request-post (&optional _server)
  (setq nnimap-status-string "Read-only server")
  nil)

(defvar gnus-refer-thread-use-search) ;; gnus-sum.el
(declare-function gnus-fetch-headers "gnus-sum"
		  (articles &optional limit force-new dependencies))

(autoload 'nnselect-search-thread "nnselect")

(deffoo nnimap-request-thread (header &optional group server)
  (if gnus-refer-thread-use-search
      (nnselect-search-thread header)
    (when (nnimap-change-group group server)
      (let* ((cmd (nnimap-make-thread-query header))
             (result (with-current-buffer (nnimap-buffer)
                       (nnimap-command  "UID SEARCH %s" cmd))))
        (when result
          (gnus-fetch-headers
           (and (car result)
		(delete 0 (mapcar #'string-to-number
				  (cdr (assoc "SEARCH" (cdr result))))))
           nil t))))))

(defun nnimap-change-group (group &optional server no-reconnect read-only)
  "Change group to GROUP if non-nil.
If SERVER is set, check that server is connected, otherwise retry
to reconnect, unless NO-RECONNECT is set to t.  Return nil if
unsuccessful in connecting.
If GROUP is nil, return t.
If READ-ONLY is set, send EXAMINE rather than SELECT to the server.
Return the server's response to the SELECT or EXAMINE command."
  (let ((open-result t))
    (when (and server
	       (not (nnimap-server-opened server)))
      (setq open-result (nnimap-open-server server nil no-reconnect)))
    (cond
     ((not open-result)
      nil)
     ((not group)
      t)
     (t
      (with-current-buffer (nnimap-buffer)
        (let ((result (nnimap-command "%s %S"
                                      (if read-only
                                          "EXAMINE"
                                        "SELECT")
                                      (nnimap-group-to-imap group))))
          (when (car result)
            (setf (nnimap-group nnimap-object) group
                  (nnimap-select-result nnimap-object) result)
            result)))))))

(defun nnimap-find-connection (buffer)
  "Find the connection delivering to BUFFER."
  (let ((entry (assoc buffer nnimap-connection-alist)))
    (when entry
      (if (and (buffer-live-p (cadr entry))
	       (get-buffer-process (cadr entry))
	       (memq (process-status (get-buffer-process (cadr entry)))
		     '(open run)))
	  (get-buffer-process (cadr entry))
	(setq nnimap-connection-alist (delq entry nnimap-connection-alist))
	nil))))

;; Leave room for `open-network-stream' to issue a couple of IMAP
;; commands before nnimap starts.
(defvar nnimap-sequence 5)

(defun nnimap-send-command (&rest args)
  (setf (nnimap-last-command-time nnimap-object) (current-time))
  (process-send-string
   (get-buffer-process (current-buffer))
   (nnimap-log-command
    (format "%d %s%s\n"
	    (cl-incf nnimap-sequence)
	    (apply #'format args)
	    (if (nnimap-newlinep nnimap-object)
		""
	      "\r"))))
  ;; Some servers apparently can't have many outstanding
  ;; commands, so throttle them.
  (unless nnimap-streaming
    (nnimap-wait-for-response nnimap-sequence))
  nnimap-sequence)

(defvar nnimap-record-commands nil
  "If non-nil, log commands to the \"*imap log*\" buffer.")

(defun nnimap-log-buffer ()
  (let ((name "*imap log*"))
    (or (get-buffer name)
        (with-current-buffer (gnus-get-buffer-create name)
	  (setq-local window-point-insertion-type t)
          (current-buffer)))))

(defun nnimap-log-command (command)
  (when nnimap-record-commands
    (with-current-buffer (nnimap-log-buffer)
      (goto-char (point-max))
      (insert (format-time-string "%H:%M:%S")
              " [" nnimap-address "] "
              (if nnimap-inhibit-logging
                  "(inhibited)\n"
                command))))
  command)

(defun nnimap-command (&rest args)
  (erase-buffer)
  (let* ((sequence (apply #'nnimap-send-command args))
	 (response (nnimap-get-response sequence)))
    (if (equal (caar response) "OK")
	(cons t response)
      (nnheader-report 'nnimap "%s"
		       (mapconcat (lambda (a)
				    (format "%s" a))
				  (car response) " "))
      nil)))

(defun nnimap-get-response (sequence)
  (nnimap-wait-for-response sequence)
  (nnimap-parse-response))

(defun nnimap-wait-for-connection (&optional regexp)
  (nnimap-wait-for-line (or regexp "^[*.] .*\n") "[*.] \\([A-Z0-9]+\\)"))

(defun nnimap-wait-for-line (regexp &optional response-regexp)
  (let ((process (get-buffer-process (current-buffer))))
    (goto-char (point-min))
    (while (and (memq (process-status process)
		      '(open run))
		(not (re-search-forward regexp nil t)))
      (nnheader-accept-process-output process)
      (goto-char (point-min)))
    (forward-line -1)
    (and (looking-at (or response-regexp regexp))
	 (match-string 1))))

(defun nnimap-wait-for-response (sequence &optional messagep)
  (let ((process (get-buffer-process (current-buffer)))
	openp)
    (condition-case nil
        (progn
	  (goto-char (point-max))
	  (while (and (setq openp (memq (process-status process)
					'(open run)))
		      (progn
			;; Skip past any "*" lines that the server has
			;; output.
			(while (and (not (bobp))
				    (progn
				      (forward-line -1)
				      (looking-at "\\*\\|[0-9]+ OK NOOP"))))
			(not (looking-at (format "%d .*\n" sequence)))))
	    (when messagep
	      (nnheader-message-maybe
	       7 "nnimap read %dk from %s%s" (/ (buffer-size) 1000)
	       nnimap-address
	       (if (not (zerop (nnimap-initial-resync nnimap-object)))
		   (format " (initial sync of %d group%s; please wait)"
			   (nnimap-initial-resync nnimap-object)
			   (if (= (nnimap-initial-resync nnimap-object) 1)
			       ""
			     "s"))
		 "")))
	    (nnheader-accept-process-output process)
	    (goto-char (point-max)))
	  (setf (nnimap-initial-resync nnimap-object) 0)
          openp)
      (quit
       (when debug-on-quit
	 (debug "Quit"))
       ;; The user hit C-g while we were waiting: kill the process, in case
       ;; it's a gnutls-cli process that's stuck (tends to happen a lot behind
       ;; NAT routers).
       (delete-process process)
       nil))))

(defun nnimap-parse-response ()
  (let ((lines (split-string (nnimap-last-response-string) "\r\n" t))
	result)
    (dolist (line lines)
      (push (cdr (nnimap-parse-line line)) result))
    ;; Return the OK/error code first, and then all the "continuation
    ;; lines" afterwards.
    (cons (pop result)
	  (nreverse result))))

;; Parse an IMAP response line lightly.  They look like
;; "* OK [UIDVALIDITY 1164213559] UIDs valid", typically, so parse
;; the lines into a list of strings and lists of string.
(defun nnimap-parse-line (line)
  (let (char result)
    (with-temp-buffer
      (mm-disable-multibyte)
      (insert line)
      (goto-char (point-min))
      (while (not (eobp))
	(if (eql (setq char (following-char)) ? )
	    (forward-char 1)
	  (push
	   (cond
	    ((eql char ?\[)
	     (split-string
	      (buffer-substring
	       (1+ (point))
	       (if (search-forward "]" (line-end-position) 'move)
		   (1- (point))
		 (point)))))
	    ((eql char ?\()
	     (split-string
	      (buffer-substring
	       (1+ (point))
	       (if (search-forward ")" (line-end-position) 'move)
		   (1- (point))
		 (point)))))
	    ((eql char ?\")
	     (forward-char 1)
	     (buffer-substring
	      (point)
	      (1- (or (search-forward "\"" (line-end-position) 'move)
		      (point)))))
	    (t
	     (buffer-substring (point) (if (search-forward " " nil t)
					   (1- (point))
					 (goto-char (point-max))))))
	   result)))
      (nreverse result))))

(defun nnimap-last-response-string ()
  (save-excursion
    (forward-line 1)
    (let ((end (point)))
      (forward-line -1)
      (when (not (bobp))
	(forward-line -1)
	(while (and (not (bobp))
		    (eql (following-char) ?*))
	  (forward-line -1))
	(unless (eql (following-char) ?*)
	  (forward-line 1)))
      (buffer-substring (point) end))))

(defvar nnimap-incoming-split-list nil)

(defun nnimap-fetch-inbox (articles)
  (erase-buffer)
  (nnimap-wait-for-response
   (nnimap-send-command
    "UID FETCH %s %s"
    (nnimap-article-ranges articles)
    (format "(UID %s%s)"
	    (format
	     (if (nnimap-ver4-p)
		 "BODY.PEEK"
	       "RFC822.PEEK"))
	    (cond
             ((or nnimap-split-download-body
                  nnimap--split-download-body)
	      "[]")
	     ((nnimap-ver4-p)
	      "[HEADER]")
	     (t
	      "[1]"))))
   t))

(defun nnimap-split-incoming-mail ()
  (with-current-buffer (nnimap-buffer)
    (let ((nnimap-incoming-split-list nil)
	  (nnmail-split-methods
	   (cond
	    ((eq nnimap-split-methods 'default)
	     nnmail-split-methods)
	    (nnimap-split-methods
	     nnimap-split-methods)
	    (nnimap-split-fancy
	     'nnmail-split-fancy)))
	  (nnmail-split-fancy (or nnimap-split-fancy
				  nnmail-split-fancy))
	  (nnmail-inhibit-default-split-group t)
	  (groups (nnimap-get-groups))
          (can-move (and (nnimap-capability "MOVE")
			 (equal (nnimap-quirk "MOVE") "MOVE")))
	  new-articles)
      (erase-buffer)
      (nnimap-command "SELECT %S" nnimap-inbox)
      (setf (nnimap-group nnimap-object) nnimap-inbox)
      (setq new-articles (nnimap-new-articles (nnimap-get-flags "1:*")))
      (when new-articles
	(nnimap-fetch-inbox new-articles)
	(nnimap-transform-split-mail)
	(nnheader-ms-strip-cr)
	(nnmail-cache-open)
	(nnmail-split-incoming (current-buffer)
			       #'nnimap-save-mail-spec
			       nil nil
			       #'nnimap-dummy-active-number
			       #'nnimap-save-mail-spec)
	(when nnimap-incoming-split-list
	  (let ((specs (nnimap-make-split-specs nnimap-incoming-split-list))
		sequences junk-articles)
	    ;; Create any groups that doesn't already exist on the
	    ;; server first.
	    (dolist (spec specs)
	      (when (and (not (member (car spec) groups))
			 (not (eq (car spec) 'junk)))
		(nnimap-command "CREATE %S" (nnimap-group-to-imap (car spec)))))
	    ;; Then copy over all the messages.
	    (erase-buffer)
	    (dolist (spec specs)
	      (let ((group (car spec))
		    (ranges (cdr spec)))
		(if (eq group 'junk)
		    (setq junk-articles ranges)
		  ;; Don't copy if the message is already in its
		  ;; target group.
		  (unless (string= group nnimap-inbox)
		    (push (list (nnimap-send-command
				 (if can-move
				     "UID MOVE %s %S"
				   "UID COPY %s %S")
				 (nnimap-article-ranges ranges)
				(nnimap-group-to-imap group))
				ranges)
			  sequences)))))
	    ;; Wait for the last COPY response...
	    (when (and (not can-move) sequences)
	      (nnimap-wait-for-response (caar sequences))
	      ;; And then mark the successful copy actions as deleted,
	      ;; and possibly expunge them.  Almost any non-nil
	      ;; setting of nnimap-expunge should lead to expunging
	      ;; here.
	      (let ((nnimap-expunge (and nnimap-expunge
					 (not (equal nnimap-expunge 'never))
					 'immediate)))
		(nnimap-delete-article
		 (nnimap-parse-copied-articles sequences))))
	    (when junk-articles
              (nnimap-delete-article junk-articles))))))))

(defun nnimap-parse-copied-articles (sequences)
  (let (sequence copied range)
    (goto-char (point-min))
    (while (re-search-forward "^\\([0-9]+\\) OK\\b" nil t)
      (setq sequence (string-to-number (match-string 1)))
      (when (setq range (cadr (assq sequence sequences)))
	(push (gnus-uncompress-range range) copied)))
    (gnus-compress-sequence (sort (apply #'nconc copied) #'<))))

(defun nnimap-new-articles (flags)
  (let (new)
    (dolist (elem flags)
      (unless (gnus-list-memq-of-list nnimap-unsplittable-articles
				      (cdr elem))
	(push (car elem) new)))
    (gnus-compress-sequence (nreverse new))))

(defun nnimap-make-split-specs (list)
  (let ((specs nil)
	entry)
    (dolist (elem list)
      (cl-destructuring-bind (article spec) elem
	(dolist (group (delete nil (mapcar #'car spec)))
	  (unless (setq entry (assoc group specs))
	    (push (setq entry (list group)) specs))
	  (setcdr entry (cons article (cdr entry))))))
    (dolist (entry specs)
      (setcdr entry (gnus-compress-sequence (sort (cdr entry) #'<))))
    specs))

(defun nnimap-transform-split-mail ()
  (goto-char (point-min))
  (let (article bytes)
    (cl-block nil
      (while (not (eobp))
	(while (not (looking-at "\\* [0-9]+ FETCH.+UID \\([0-9]+\\)"))
	  (delete-region (point) (progn (forward-line 1) (point)))
	  (when (eobp)
	    (cl-return)))
	(setq article (match-string 1)
	      bytes (nnimap-get-length))
	(delete-region (line-beginning-position) (line-end-position))
	;; Insert MMDF separator, and a way to remember what this
	;; article UID is.
	(insert (format "\^A\^A\^A\^A\n\nX-nnimap-article: %s" article))
	(forward-char (1+ bytes))
	(setq bytes (nnimap-get-length))
	(delete-region (line-beginning-position) (line-end-position))
	;; There's a body; skip past that.
	(when bytes
	  (forward-char (1+ bytes))
	  (delete-region (line-beginning-position) (line-end-position)))))))

(defun nnimap-dummy-active-number (_group &optional _server)
  1)

(defun nnimap-save-mail-spec (group-art &optional _server _full-nov)
  (let (article)
    (goto-char (point-min))
    (if (not (re-search-forward "X-nnimap-article: \\([0-9]+\\)" nil t))
	(error "Invalid nnimap mail")
      (setq article (string-to-number (match-string 1))))
    (push (list article
		(if (eq group-art 'junk)
		    (list (cons 'junk 1))
		  group-art))
	  nnimap-incoming-split-list)))

(defun nnimap-make-thread-query (header)
  (let* ((id  (mail-header-id header))
	 (refs (split-string
		(or (mail-header-references header)
		    "")))
	 (value
	  (format
	   "(OR HEADER REFERENCES %S HEADER Message-Id %S)"
	   id id)))
    (dolist (refid refs value)
      (setq value (format
		   "(OR (OR HEADER Message-Id %S HEADER REFERENCES %S) %s)"
		   refid refid value)))))


(provide 'nnimap)

;;; nnimap.el ends here