Merge changes made in Gnus master

2012-10-05  Katsumi Yamaoka  <yamaoka@jpl.org>
 * gnus.texi (Mail Source Specifiers):
 Document :leave keyword used for pop mail source.
2012-10-25  Tassilo Horn  <tsdh@gnu.org>
 * gnus-dired.el (gnus-dired-attach): Attach to last used message buffer
 by default.  Patch provided by Stephen Eglen.
2012-10-05  Katsumi Yamaoka  <yamaoka@jpl.org>
 New UIDL implementation.
 * mail-source.el (mail-sources, mail-source-keyword-map):
 Add :leave as a pop3 keyword.
 (mail-source-fetch-pop): Bind pop3-leave-mail-on-server.
 * pop3.el (pop3-leave-mail-on-server): Allow number.
 (pop3-uidl-file, pop3-uidl-file-backup): New user options.
 (pop3-movemail): Add UIDL support.
 (pop3-send-streaming-command): Take a list of mail numbers instead of
 the number of mails.
 (pop3-write-to-file): Add X-UIDL header.
 (pop3-uidl-stat, pop3-uidl-dele, pop3-uidl-load, pop3-uidl-save)
 (pop3-uidl-add-xheader): New functions.
 * message.el (message-ignored-resent-headers):
 Add X-Content-Length and X-UIDL headers.

7 files changed, 368 insertions, 46 deletions

diff --git a/doc/misc/ChangeLog b/doc/misc/ChangeLog
index d719a02e32e..768a846bd1a 100644
--- a/doc/misc/ChangeLog
+++ b/doc/misc/ChangeLog
@@ -1,3 +1,8 @@
+2012-11-02  Katsumi Yamaoka  <yamaoka@jpl.org>
+
+        * gnus.texi (Mail Source Specifiers):
+        Document :leave keyword used for pop mail source.
+
 2012-11-01  Glenn Morris  <rgm@gnu.org>
 
         * cl.texi: General copyedits for style, line-breaks, etc.
diff --git a/doc/misc/gnus.texi b/doc/misc/gnus.texi
index a9cd0d3567c..47ff355d946 100644
--- a/doc/misc/gnus.texi
+++ b/doc/misc/gnus.texi
@@ -14759,20 +14759,37 @@ This can be either the symbol @code{password} or the symbol @code{apop}
 and says what authentication scheme to use.  The default is
 @code{password}.
 
+@item :leave
+Non-@code{nil} if the mail is to be left on the @acronym{POP} server
+after fetching.  Mails once fetched will never be fetched again by the
+@acronym{UIDL} control.  Only the built-in @code{pop3-movemail} program
+(the default) supports this keyword.
+
+If this is neither @code{nil} nor a number, all mails will be left on
+the server.  If this is a number, leave mails on the server for this
+many days since you first checked new mails.  If this is @code{nil}
+(the default), mails will be deleted on the server right after fetching.
+
+@vindex pop3-uidl-file
+The @code{pop3-uidl-file} variable specifies the file to which the
+@acronym{UIDL} data are locally stored.  The default value is
+@file{~/.pop3-uidl}.
+
+Note that @acronym{POP} servers maintain no state information between
+sessions, so what the client believes is there and what is actually
+there may not match up.  If they do not, then you may get duplicate
+mails or the whole thing can fall apart and leave you with a corrupt
+mailbox.
+
 @end table
 
-@vindex pop3-movemail
+@findex pop3-movemail
 @vindex pop3-leave-mail-on-server
 If the @code{:program} and @code{:function} keywords aren't specified,
-@code{pop3-movemail} will be used.  If @code{pop3-leave-mail-on-server}
-is non-@code{nil} the mail is to be left on the @acronym{POP} server
-after fetching when using @code{pop3-movemail}.  Note that POP servers
-maintain no state information between sessions, so what the client
-believes is there and what is actually there may not match up.  If they
-do not, then you may get duplicate mails or the whole thing can fall
-apart and leave you with a corrupt mailbox.
+@code{pop3-movemail} will be used.
 
 Here are some examples for getting mail from a @acronym{POP} server.
+
 Fetch from the default @acronym{POP} server, using the default user
 name, and default fetcher:
 
@@ -14787,6 +14804,14 @@ Fetch from a named server with a named user and password:
      :user "user-name" :password "secret")
 @end lisp
 
+Leave mails on the server for 14 days:
+
+@lisp
+(pop :server "my.pop.server"
+     :user "user-name" :password "secret"
+     :leave 14)
+@end lisp
+
 Use @samp{movemail} to move the mail:
 
 @lisp
diff --git a/lisp/gnus/ChangeLog b/lisp/gnus/ChangeLog
index 8cb53de85fa..a2bb0a88baa 100644
--- a/lisp/gnus/ChangeLog
+++ b/lisp/gnus/ChangeLog
@@ -1,3 +1,28 @@
+2012-11-02  Tassilo Horn  <tsdh@gnu.org>
+
+        * gnus-dired.el (gnus-dired-attach): Attach to last used message buffer
+        by default.  Patch provided by Stephen Eglen.
+
+2012-11-02  Katsumi Yamaoka  <yamaoka@jpl.org>
+
+        New UIDL implementation.
+
+        * mail-source.el (mail-sources, mail-source-keyword-map):
+        Add :leave as a pop3 keyword.
+        (mail-source-fetch-pop): Bind pop3-leave-mail-on-server.
+
+        * pop3.el (pop3-leave-mail-on-server): Allow number.
+        (pop3-uidl-file, pop3-uidl-file-backup): New user options.
+        (pop3-movemail): Add UIDL support.
+        (pop3-send-streaming-command): Take a list of mail numbers instead of
+        the number of mails.
+        (pop3-write-to-file): Add X-UIDL header.
+        (pop3-uidl-stat, pop3-uidl-dele, pop3-uidl-load, pop3-uidl-save)
+        (pop3-uidl-add-xheader): New functions.
+
+        * message.el (message-ignored-resent-headers):
+        Add X-Content-Length and X-UIDL headers.
+
 2012-10-23  Stefan Monnier  <monnier@iro.umontreal.ca>
 
         * nndiary.el (nndiary-request-create-group-functions)
diff --git a/lisp/gnus/gnus-dired.el b/lisp/gnus/gnus-dired.el
index d341cea34bb..e15a6c732b5 100644
--- a/lisp/gnus/gnus-dired.el
+++ b/lisp/gnus/gnus-dired.el
@@ -155,8 +155,8 @@ filenames."
           (setq destination
                 (if (= (length bufs) 1)
                     (get-buffer (car bufs))
-                  (gnus-completing-read "Attach to which mail composition buffer"
-                                         bufs t)))
+                  (gnus-completing-read "Attach to buffer"
+                                         bufs t nil nil (car bufs))))
         ;; setup a new mail composition buffer
         (let ((mail-user-agent gnus-dired-mail-mode)
               ;; A workaround to prevent Gnus from displaying the Gnus
diff --git a/lisp/gnus/mail-source.el b/lisp/gnus/mail-source.el
index ad66fecc427..fc66414a9f0 100644
--- a/lisp/gnus/mail-source.el
+++ b/lisp/gnus/mail-source.el
@@ -63,7 +63,7 @@
 This variable is a list of mail source specifiers.
 See Info node `(gnus)Mail Source Specifiers'."
   :group 'mail-source
-  :version "23.1" ;; No Gnus
+  :version "24.4"
   :link '(custom-manual "(gnus)Mail Source Specifiers")
   :type `(choice
           (const :tag "None" nil)
@@ -159,7 +159,18 @@ See Info node `(gnus)Mail Source Specifiers'."
                                                    :value nil
                                                    (const :tag "Clear" nil)
                                                    (const starttls)
-                                                   (const :tag "SSL/TLS" ssl)))))
+                                                   (const :tag "SSL/TLS" ssl)))
+                                    (group :inline t
+                                           (const :format "" :value :leave)
+                                           (choice :format "\
+%{Leave mail on server%}:\n\t\t%[Value Menu%] %v"
+                                                   :value nil
+                                                   (const :tag "\
+Don't leave mails" nil)
+                                                   (const :tag "\
+Leave all mails" t)
+                                                   (number :tag "\
+Leave mails for this many days" :value 14)))))
                    (cons :tag "Maildir (qmail, postfix...)"
                          (const :format "" maildir)
                          (checklist :tag "Options" :greedy t
@@ -340,7 +351,8 @@ Common keywords should be listed here.")
        (:function)
        (:password)
        (:authentication password)
-       (:stream nil))
+       (:stream nil)
+       (:leave))
       (maildir
        (:path (or (getenv "MAILDIR") "~/Maildir/"))
        (:subdirs ("cur" "new"))
@@ -825,7 +837,8 @@ Deleting old (> %s day(s)) incoming mail file `%s'." diff bfile)
                     (pop3-port port)
                     (pop3-authentication-scheme
                      (if (eq authentication 'apop) 'apop 'pass))
-                    (pop3-stream-type stream))
+                    (pop3-stream-type stream)
+                    (pop3-leave-mail-on-server leave))
                 (if (or debug-on-quit debug-on-error)
                     (save-excursion (pop3-movemail mail-source-crash-box))
                   (condition-case err
diff --git a/lisp/gnus/message.el b/lisp/gnus/message.el
index 5360f008432..8905acb9d1f 100644
--- a/lisp/gnus/message.el
+++ b/lisp/gnus/message.el
@@ -592,8 +592,10 @@ Done before generating the new subject of a forward."
   ;; comes back to you (e.g. a mailing-list to which you subscribe, in which
   ;; case you may be removed from the list on the grounds that mail to you
   ;; bounced with a "mailing loop" error).
-  "^Return-receipt\\|^X-Gnus\\|^Gnus-Warning:\\|^>?From \\|^Delivered-To:"
+  "^Return-receipt\\|^X-Gnus\\|^Gnus-Warning:\\|^>?From \\|^Delivered-To:\
+\\|^X-Content-Length:\\|^X-UIDL:"
   "*All headers that match this regexp will be deleted when resending a message."
+  :version "24.4"
   :group 'message-interface
   :link '(custom-manual "(message)Resending")
   :type '(repeat :value-to-internal (lambda (widget value)
diff --git a/lisp/gnus/pop3.el b/lisp/gnus/pop3.el
index 25330989e00..f95bf26ad1d 100644
--- a/lisp/gnus/pop3.el
+++ b/lisp/gnus/pop3.el
@@ -98,20 +98,53 @@ set this to 1."
   :group 'pop3)
 
 (defcustom pop3-leave-mail-on-server nil
-  "*Non-nil if the mail is to be left on the POP server after fetching.
-
-If `pop3-leave-mail-on-server' is non-nil the mail is to be left
-on the POP server after fetching.  Note that POP servers maintain
-no state information between sessions, so what the client
-believes is there and what is actually there may not match up.
-If they do not, then you may get duplicate mails or the whole
-thing can fall apart and leave you with a corrupt mailbox."
-  ;; We can't use the UILD support from XEmacs mail-lib or cvs.m17n.org:
-  ;; http://thread.gmane.org/v9lld8fml4.fsf@marauder.physik.uni-ulm.de
-  ;; http://thread.gmane.org/b9yy8hzy9ej.fsf@jpl.org
-  ;; Any volunteer to re-implement this?
-  :version "22.1" ;; Oort Gnus
-  :type 'boolean
+  "Non-nil if the mail is to be left on the POP server after fetching.
+Mails once fetched will never be fetched again by the UIDL control.
+
+If this is neither nil nor a number, all mails will be left on the
+server.  If this is a number, leave mails on the server for this many
+days since you first checked new mails.  If this is nil, mails will be
+deleted on the server right after fetching.
+
+Gnus users should use the `:leave' keyword in a mail source to direct
+the behaviour per server, rather than directly modifying this value.
+
+Note that POP servers maintain no state information between sessions,
+so what the client believes is there and what is actually there may
+not match up.  If they do not, then you may get duplicate mails or
+the whole thing can fall apart and leave you with a corrupt mailbox."
+  :version "24.4"
+  :type '(choice (const :tag "Don't leave mails" nil)
+                 (const :tag "Leave all mails" t)
+                 (number :tag "Leave mails for this many days" :value 14))
+  :group 'pop3)
+
+(defcustom pop3-uidl-file "~/.pop3-uidl"
+  "File used to save UIDL."
+  :version "24.4"
+  :type 'file
+  :group 'pop3)
+
+(defcustom pop3-uidl-file-backup '(0 9)
+  "How to backup the UIDL file `pop3-uidl-file' when updating.
+If it is a list of numbers, the first one binds `kept-old-versions' and
+the other binds `kept-new-versions' to keep number of oldest and newest
+versions.  Otherwise, the value binds `version-control' (which see).
+
+Note: Backup will take place whenever you check new mails on a server.
+So, you may lose the backup files having been saved before a trouble
+if you set it so as to make too few backups whereas you have access to
+many servers."
+  :version "24.4"
+  :type '(choice (group :tag "Keep versions" :format "\n%v" :indent 3
+                        (number :tag "oldest")
+                        (number :tag "newest"))
+                 (sexp :format "%v"
+                       :match (lambda (widget value)
+                                (condition-case nil
+                                    (not (and (numberp (car value))
+                                              (numberp (car (cdr value)))))
+                                  (error t)))))
   :group 'pop3)
 
 (defvar pop3-timestamp nil
@@ -144,34 +177,66 @@ Shorter values mean quicker response, but are more CPU intensive.")
                        (truncate pop3-read-timeout))
                     1000))))))
 
+(defvar pop3-uidl)
+;; List of UIDLs of existing messages at pesent in the server:
+;; ("UIDL1" "UIDL2" "UIDL3"...)
+
+(defvar pop3-uidl-saved)
+;; Locally saved UIDL data; an alist of the server, the user, and the UIDL
+;; and timestamp pairs:
+;; (("SERVER_A" ("USER_A1" "UIDL1" TIMESTAMP1 "UIDL2" TIMESTAMP2...)
+;;              ("USER_A2" "UIDL1" TIMESTAMP1 "UIDL2" TIMESTAMP2...)
+;;              ...)
+;;  ("SERVER_B" ("USER_B1" "UIDL1" TIMESTAMP1 "UIDL2" TIMESTAMP2...)
+;;              ("USER_B2" "UIDL1" TIMESTAMP1 "UIDL2" TIMESTAMP2...)
+;;              ...))
+;; Where TIMESTAMP is the most significant two digits of an Emacs time,
+;; i.e. the return value of `current-time'.
+
 ;;;###autoload
 (defun pop3-movemail (file)
   "Transfer contents of a maildrop to the specified FILE.
 Use streaming commands."
-  (let* ((process (pop3-open-server pop3-mailhost pop3-port))
-         message-count message-total-size)
+  (let ((process (pop3-open-server pop3-mailhost pop3-port))
+        messages total-size
+        pop3-uidl
+        pop3-uidl-saved)
     (pop3-logon process)
-    (with-current-buffer (process-buffer process)
+    (if pop3-leave-mail-on-server
+        (setq messages (pop3-uidl-stat process)
+              total-size (cadr messages)
+              messages (car messages))
       (let ((size (pop3-stat process)))
-        (setq message-count (car size)
-              message-total-size (cadr size)))
-      (when (> message-count 0)
-        (pop3-send-streaming-command
-         process "RETR" message-count message-total-size)
-        (pop3-write-to-file file)
+        (dotimes (i (car size)) (push (1+ i) messages))
+        (setq messages (nreverse messages)
+              total-size (cadr size))))
+    (when messages
+      (with-current-buffer (process-buffer process)
+        (pop3-send-streaming-command process "RETR" messages total-size)
+        (pop3-write-to-file file messages)
         (unless pop3-leave-mail-on-server
-          (pop3-send-streaming-command
-           process "DELE" message-count nil))))
-    (pop3-quit process)
+          (pop3-send-streaming-command process "DELE" messages nil))))
+    (if pop3-leave-mail-on-server
+        (when (prog1 (pop3-uidl-dele process) (pop3-quit process))
+          (pop3-uidl-save))
+      (pop3-quit process)
+      ;; Remove UIDL data for the account that got not to leave mails.
+      (setq pop3-uidl-saved (pop3-uidl-load))
+      (let ((elt (assoc pop3-maildrop
+                        (cdr (assoc pop3-mailhost pop3-uidl-saved)))))
+        (when elt
+          (setcdr elt nil)
+          (pop3-uidl-save))))
     t))
 
-(defun pop3-send-streaming-command (process command count total-size)
+(defun pop3-send-streaming-command (process command messages total-size)
   (erase-buffer)
-  (let ((i 1)
+  (let ((count (length messages))
+        (i 1)
         (start-point (point-min))
         (waited-for 0))
-    (while (>= count i)
-      (process-send-string process (format "%s %d\r\n" command i))
+    (while messages
+      (process-send-string process (format "%s %d\r\n" command (pop messages)))
       ;; Only do 100 messages at a time to avoid pipe stalls.
       (when (zerop (% i pop3-stream-length))
         (setq start-point
@@ -207,7 +272,7 @@ Use streaming commands."
     (pop3-accept-process-output process))
   start-point)
 
-(defun pop3-write-to-file (file)
+(defun pop3-write-to-file (file messages)
   (let ((pop-buffer (current-buffer))
         (start (point-min))
         beg end
@@ -230,6 +295,8 @@ Use streaming commands."
               (pop3-clean-region hstart (point))
               (goto-char (point-max))
               (pop3-munge-message-separator hstart (point))
+              (when pop3-leave-mail-on-server
+                (pop3-uidl-add-xheader hstart (pop messages)))
               (goto-char (point-max))))))
       (let ((coding-system-for-write 'binary))
         (goto-char (point-min))
@@ -275,6 +342,184 @@ Use streaming commands."
     (pop3-quit process)
     message-count))
 
+(defun pop3-uidl-stat (process)
+  "Return a list of unread message numbers and total size."
+  (pop3-send-command process "UIDL")
+  (let (err messages size)
+    (if (condition-case code
+            (progn
+              (pop3-read-response process)
+              t)
+          (error (setq err (error-message-string code))
+                 nil))
+        (let ((start pop3-read-point)
+              saved list)
+          (with-current-buffer (process-buffer process)
+            (while (not (re-search-forward "^\\.\r\n" nil t))
+              (unless (memq (process-status process) '(open run))
+                (error "pop3 server closed the connection"))
+              (pop3-accept-process-output process)
+              (goto-char start))
+            (setq pop3-read-point (point-marker)
+                  pop3-uidl nil)
+            (while (progn (forward-line -1) (>= (point) start))
+              (when (looking-at "[0-9]+ \\([^\n\r ]+\\)")
+                (push (match-string 1) pop3-uidl)))
+            (when pop3-uidl
+              (setq pop3-uidl-saved (pop3-uidl-load)
+                    saved (cdr (assoc pop3-maildrop
+                                      (cdr (assoc pop3-mailhost
+                                                  pop3-uidl-saved)))))
+              (let ((i (length pop3-uidl)))
+                (while (> i 0)
+                  (unless (member (nth (1- i) pop3-uidl) saved)
+                    (push i messages))
+                  (decf i)))
+              (when messages
+                (setq list (pop3-list process)
+                      size 0)
+                (dolist (msg messages)
+                  (setq size (+ size (cdr (assq msg list)))))
+                (list messages size)))))
+      (message "%s doesn't support UIDL (%s), so we try a regressive way..."
+               pop3-mailhost err)
+      (sit-for 1)
+      (setq size (pop3-stat process))
+      (dotimes (i (car size)) (push (1+ i) messages))
+      (setcar size (nreverse messages))
+      size)))
+
+(defun pop3-uidl-dele (process)
+  "Delete messages according to `pop3-leave-mail-on-server'.
+Return non-nil if it is necessary to update the local UIDL file."
+  (let* ((ctime (current-time))
+         (srvr (assoc pop3-mailhost pop3-uidl-saved))
+         (saved (assoc pop3-maildrop (cdr srvr)))
+         i uidl mod new tstamp dele)
+    (setcdr (cdr ctime) nil)
+    ;; Add new messages to the data to be saved.
+    (cond ((and pop3-uidl saved)
+           (setq i (1- (length pop3-uidl)))
+           (while (>= i 0)
+             (unless (member (setq uidl (nth i pop3-uidl)) (cdr saved))
+               (push ctime new)
+               (push uidl new))
+             (decf i)))
+          (pop3-uidl
+           (setq new (apply 'nconc (mapcar (lambda (elt) (list elt ctime))
+                                           pop3-uidl)))))
+    (when new (setq mod t))
+    ;; List expirable messages and delete them from the data to be saved.
+    (setq ctime (when (numberp pop3-leave-mail-on-server)
+                  (/ (+ (* (car ctime) 65536.0) (cadr ctime)) 86400))
+          i (1- (length saved)))
+    (while (> i 0)
+      (if (member (setq uidl (nth (1- i) saved)) pop3-uidl)
+          (progn
+            (setq tstamp (nth i saved))
+            (if (and ctime
+                     (> (- ctime (/ (+ (* (car tstamp) 65536.0) (cadr tstamp))
+                                    86400))
+                        pop3-leave-mail-on-server))
+                ;; Mails to delete.
+                (progn
+                  (setq mod t)
+                  (push uidl dele))
+              ;; Mails to keep.
+              (push tstamp new)
+              (push uidl new)))
+        ;; Mails having been deleted in the server.
+        (setq mod t))
+      (decf i 2))
+    (cond (saved
+           (setcdr saved new))
+          (srvr
+           (setcdr (last srvr) (list (cons pop3-maildrop new))))
+          (t
+           (add-to-list 'pop3-uidl-saved
+                        (list pop3-mailhost (cons pop3-maildrop new))
+                        t)))
+    ;; Actually delete the messages in the server.
+    (when dele
+      (setq uidl nil
+            i (length pop3-uidl))
+      (while (> i 0)
+        (when (member (nth (1- i) pop3-uidl) dele)
+          (push i uidl))
+        (decf i))
+      (when uidl
+        (pop3-send-streaming-command process "DELE" uidl nil)))
+    mod))
+
+(defun pop3-uidl-load ()
+  "Load saved UIDL."
+  (when (file-exists-p pop3-uidl-file)
+    (with-temp-buffer
+      (condition-case code
+          (progn
+            (insert-file-contents pop3-uidl-file)
+            (goto-char (point-min))
+            (read (current-buffer)))
+        (error
+         (message "Error while loading %s (%s)"
+                  pop3-uidl-file (error-message-string code))
+         (sit-for 1)
+         nil)))))
+
+(defun pop3-uidl-save ()
+  "Save UIDL."
+  (with-temp-buffer
+    (if pop3-uidl-saved
+        (progn
+          (insert "(")
+          (dolist (srvr pop3-uidl-saved)
+            (when (cdr srvr)
+              (insert "(\"" (pop srvr) "\"\n  ")
+              (dolist (elt srvr)
+                (when (cdr elt)
+                  (insert "(\"" (pop elt) "\"\n   ")
+                  (while elt
+                    (insert (format "\"%s\" %s\n   " (pop elt) (pop elt))))
+                  (delete-char -4)
+                  (insert ")\n  ")))
+              (delete-char -3)
+              (if (eq (char-before) ?\))
+                  (insert ")\n ")
+                (goto-char (1+ (point-at-bol)))
+                (delete-region (point) (point-max)))))
+          (when (eq (char-before) ? )
+            (delete-char -2))
+          (insert ")\n"))
+      (insert "()\n"))
+    (let ((buffer-file-name pop3-uidl-file)
+          (delete-old-versions t)
+          (kept-new-versions kept-new-versions)
+          (kept-old-versions kept-old-versions)
+          (version-control version-control))
+      (if (consp pop3-uidl-file-backup)
+          (setq kept-new-versions (cadr pop3-uidl-file-backup)
+                kept-old-versions (car pop3-uidl-file-backup)
+                version-control t)
+        (setq version-control pop3-uidl-file-backup))
+      (save-buffer))))
+
+(defun pop3-uidl-add-xheader (start msgno)
+  "Add X-UIDL header."
+  (let ((case-fold-search t))
+    (save-restriction
+      (narrow-to-region start (progn
+                                (goto-char start)
+                                (search-forward "\n\n" nil 'move)
+                                (1- (point))))
+      (goto-char start)
+      (while (re-search-forward "^x-uidl:" nil t)
+        (while (progn
+                 (forward-line 1)
+                 (memq (char-after) '(?\t ? ))))
+        (delete-region (match-beginning 0) (point)))
+      (goto-char (point-max))
+      (insert "X-UIDL: " (nth (1- msgno) pop3-uidl) "\n"))))
+
 (defcustom pop3-stream-type nil
   "*Transport security type for POP3 connections.
 This may be either nil (plain connection), `ssl' (use an
@@ -663,6 +908,13 @@ and close the connection."
 ;; Possible responses:
 ;;  +OK [all delete marks removed]
 
+;; UIDL [msg]
+;; Arguments: a message-id (optional)
+;; Restrictions: transaction state; msg must not be deleted
+;; Possible responses:
+;;  +OK [uidl listing follows]
+;;  -ERR [no such message]
+
 ;;; UPDATE STATE
 
 ;; QUIT