A folder must be opened before accessing its messages. Only
one folder can be opened at a time. Opening a second folder
automatically closes the first folder. When opening a folder,
the SMAP server's response indicates how many messages there
are in the folder. The messages are numbered consecutively,
from 1 to the message count returned by the OPEN command.
New messages can be added to the folder while it is open. Other application can also remove or modify existing messages, while the folder is opened. There are two mechanisms by which the SMAP client is notified about these changes.
The SMAP client explicitly requests to be notified about any
other changes by issuing either the NOOP or the EXPUNGE command. The server's response to the
client includes notification of any messages that were added,
modified, or removed from the server.
The NOOP and EXPUNGE commands work like all other commands:
the server does the requested action, and replies accordingly.
The second mechanism uses the IDLE
command, which works a little differently. The server's initial
reply includes any changes to the folder's contents, as with
NOOP and EXPUNGE, but the story doesn't end there. The
client's next command, after IDLE,
must be the RESUME command. Until
the server receives the RESUME,
the server may immediately notify the client any time the
folder's contents change. SMAP servers that are not capable of
immediate notification of this type should periodically poll
the folder for changes, until they get a RESUME.
When the client is waiting for user input it should issue
the IDLE command, so that it knows
about any changes to the folder made by other applications, and
react immediately. The client issues a RESUME when it finally has something to do.
This can be a result of user input, or caused by a change to
the folder's contents (when new mail arrives, for example, the
client may want to automatically download its headers).
Messages in the folder are always consecutively numbered, starting with message #1. The messages are renumbered after removing a message; and new messages are added at the end. For example: a folder has five messages, numbered 1 through 5. The third message is removed, and messages #4 and #5 become messages #3 and #4, respectively. When two more messages are added to the folder, they become messages #5 and message #6.
The client may send the “RESUME” command at the same time the server is sending a message to the client concerning some changes to the folder that just occured. The SMAP client should always wait and process any remaining folder content notification changes, until it receives that status reply for “RESUME”.
C: OPEN "Saved Mail" 2002
S: * EXISTS 17
S: +OK Folder opened
The OPEN command opens a
folder. If another folder is already opened, the other folder
is closed. The other folder is closed automatically, whether
or not the OPEN command
ultimately succeeds.
The whitespace-delimited words after “OPEN” specify the folder to
open. If it's a valid folder, the server response includes a
"* EXISTS" single line
reply.
SMAP servers are encouraged to offer concurrent access to
the same folder to multiple application. SMAP servers that
are unable to do so should reject the OPEN command if the folder is already opened
by someone else.
C: SOPEN "28378jhaskdjk9@localhost" "Saved Mail" 2002
S: * SNAPSHOTEXISTS "28378jhaskdjk9@localhost"
S: * EXPUNGE 10-13
S: * EXISTS 25
S: +OK Folder opened
The SOPEN command enables
folder snapshots, and opens a previously folder snapshot. A
folder snapshot is a saved, or cached, copy of the folder's
contents. Both the SMAP client and the SMAP server maintain
synchronizes cached copies, or snapshots, of the folder's
contents. This includes the list of messages in the folder,
and the message state flags. Normally, after opening a folder
the SMAP client needs to download the entire list of
messages, and their states, from the server. Restoring a
previously snapshot eliminates that step.
The first whitespace-delimited word after SOPEN is a snapshot identifier, as returned
by a “*
SNAPSHOT” message (see NOOP). The remaining
words specify the name of the folder, as in OPEN.
The server responds with a “* SNAPSHOTEXISTS”
message, with a copy of the snapshot identifier, followed by
zero or more “*
EXPUNGE”, “* FETCH msgnum FLAGS”,
and “*
EXISTS” message that reflect any changes to the
folder's contents that occured since the snapshot was made.
When the final +OK is received,
the folder's contents are brough up to date, and the SMAP
client should issue a NOOP
command to make an updated snapshot.
If the server is unable to find the requested snapshot, it
should respond just like to the OPEN command, with a single “* EXISTS” message.
If the client does not receive a “* SNAPSHOTEXISTS”
message, the client will conclude that the requested snapshot
is not available. This is not an error condition. The
requested snapshot might be too old, and the server decided
that it should be removed by now.
A client that wants to use snapshots, but does not have a
saved snapshot, should use the SOPEN command with an empty string for a
snapshot identifier. This is because the server would not
normally make snapshots if the client used the OPEN command to open a folder. The server
responds to an SOPEN with an
empty identifier in the same way as to an OPEN command, but enable and make
snapshots.
C: CLOSE
S: +OK Folder closed
The CLOSE command closes the
currently-opened folder. This command should always succeed,
and should ideally do nothing if no folder is currently
open.
SMAP servers that do not support concurrent access to the same folder, by multiple applications, should release the folder so that other applications can open it.
C: NOOP
S: * EXPUNGE 10-13 17
S: * FETCH 12 FLAGS=SEEN
S: * EXISTS 32
S: +OK Ok.
C: NOOP
S: * SNAPSHOT "89238yu90doi923@localhost"
C: +OK Ok.
NOOP polls the server for any
changes made to the folder's contents by other applications.
The server's response includes 0 or more single line replies before NOOP's status reply.
The single line replies may be sent in any order, and the SMAP client should process each single line reply individually, based on its current understanding of the folder's contents, which is taken into account when processing the next single line reply.
The “* EXPUNGE” single line reply
lists messages that have been removed from the folder. The
remaining words enumerate the removed message numbers.
“a-b” indicates
messages #a through #b, inclusive, and the entire list must
be sorted in strict numerically increasing order, with no
overlaps. This message indicates that the specified messages
have been removed, and the remaining messages were renumbered
by shifting over to fill in the gaps.
Some time may elapse before a server receives a
NOOP, after a message is
removed by some other application. Since the client will
not be aware of the removed message, the server must handle
client commands as if the message was not yet removed. For
example, after message #13 is removed, message #14 now
becomes message #13. Until the server receives a
NOOP, it should be aware that
client's FETCH and
STORE commands that reference
message #14 really reference message #13. The server must
process these commands accordingly, until the server
receives a NOOP, and notifies
the client.
Excessively long lists of expunged messages may result
in multiple * EXPUNGE
messages, instead of a single, huge *
EXPUNGE.
The * EXISTS message
indicates that new messages were added to the folder, and
specifies the new number of messages now in the folder.
The * FETCH message indicates
that an existing message attribute was changed. The next word
specifies the number of the changed message, and the
remaining word provide the new message attributes. See the
description of the
FETCH command for more
information.
The server creates snapshots of the folder's index when
the folder was opened with the SOPEN command. If the NOOP command did not report any changes to
the folder's contents, the server sends a “* SNAPSHOT”,
followed by a single word that specifies the saved snapshot's
identifier. The format of the snapshot's identifier is
defined by the server, and the client should treat it as an
opaque text string.
A client issues the NOOP
command when it wants the server to save the folder's
snapshot. If the server comes back with other messages that
report changes to the folder, the client should issue another
NOOP, and try again.
When the server finds no changes to the folder, and no
changes at all since the previous NOOP that returned a snapshot, the server
does not need to make a second, identical snapshot. A client
may not receive any response to a NOOP; neither a list of folder's changes,
nor a “*
SNAPSHOT” message. This indicates that the
folder's contents have not changed since the last snapshot.
The client should already know this; but if not, that's how
the server will remind it.
The server is not required to keep saved snapshots indefinitely. A server does not need to save more than two snapshots per session. After making snapshots A and B, after processing a request to make a third snapshot, C, the server may delete snapshot A.
The server cannot delete snapshot B, because the client
may crash or be disconnected before it receives the
server's acknowledgement of creating snapshot C, and the
next time the client reopens the same folder it will
specify snapshot B to the SOPEN command. If a client opens a folder
using SOPEN, but does not name
either A or B, (or C), the server may conclude that another
client is opening the same folder, and should not remove
any of the saved snapshots, unless they are very old.
C: EXPUNGE 7
S: * EXPUNGE 7 9 11
S: +OK Ok.
The EXPUNGE command is
similar NOOP, except that
EXPUNGE also removes messages
from the folder, and the server's response to EXPUNGE includes the removed messages. The
response also includes any additional messages removed by
other applications, and any other changes to the folder's
contents.
Message numbers to remove should follow the EXPUNGE command, as whitespace-delimited
words. An EXPUNGE without an
explicit message list is the same as an EXPUNGE that lists all messages that have
the DELETED flag set.
C: IDLE
S: +OK Idling...
[ ... some time passes ... ]
S: * FETCH 15 FLAGS=SEEN,DELETED
S: * EXPUNGE 4
C: RESUME
S: +OK Resumed...
The SMAP client sends the IDLE command to inform the server that
client wants to know about any changes to the folder's
contents immediately, without waiting for a NOOP or EXPUNGE. If the folder already had some
changed made by another process, the server will notify the
client immediately after the status reply.
The next command sent by the client (at some later time)
must be the RESUME command.
RESUME indicates that the client
is no longer interested in receiving folder updates, and the
server should wait until another NOOP, EXPUNGE,
or IDLE before notifying the
client about any changes to the folder's contents.
The client must be aware that the folder's contents might
be changed after it sends a RESUME and before the server receives it. In
this case the client might receive additional single line
replies before the server responds to the RESUME. The client must still properly
process single line replies, until it receives the server's
status reply to the RESUME.