upasfs – mail file server

upas/fs [ –DSbdfilnps ][ –c cachtarg ][ –f mailbox ][ –m mntpoint ]


Fs is a user level file system that caches mailboxes and presents them as a file system. A user normally starts fs in his/her profile after starting plumber(4) and before starting a window system, such as rio(1) or acme(1). The file system is used by nedmail(1), acme(1)'s mail reader, and imap4d and pop3 (both pop3(8)) to parse messages. Fs also generates plumbing messages used by biff and faces(1) to provide mail announcements.

The mailbox itself becomes a directory under /mail/fs. Each message in the mailbox becomes a numbered directory in the mailbox directory, and each attachment becomes a numbered directory in the message directory. Since an attachment may itself be a mail message, this structure can recurse ad nauseam.

Each message and attachment directory contains the files:
body            the message minus the RFC2822 style headers
cc              the address(es) from the CC: header
date            the date in the message, or if none, the time of delivery
digest          an SHA1 digest of the message contents
disposition     inline or file
a name to use to file an attachment
flags           persistant message flags as per IMAP
ffrom           the parsed name of the sender
from            the from address in the From: header, or if none, the address on the envelope.
header          the RFC822 headers
info            described below, essentially a summary of the header info
inreplyto       contents of the in–reply–to: header
lines           the number of lines in the message body
messageid       the parsed RFC2822 MessageID
mimeheader      the mime headers
raw             the undecoded MIME message
rawbody         the undecoded message body
rawheader       the undecoded message header
references      the parsed MessageIDs of each referenced message, one per line
replyto         the address to send any replies to.
subject         the contents of the subject line
to              the address(es) from the To: line.
type            the MIME content type
unixheader      the envelope header from the mailbox
unixdate        the date portion of the Unix From line.
unixdatesec     the mdir filename for mdir messages. The portion before the dot is always the date from the Unix From line in seconds since epoch.

The info file contains the following information, one item per line. Lists of addresses are single space separated.
sender address
recipient addresses
cc addresses
reply address
envelope date
MIME content type
MIME disposition
SHA1 digest
bcc addresses
in–reply–to: contents
RFC822 date
message senders
message id
number of lines in body
size of message
message flags
name from From: header

Deleting message directories causes the message to be removed from the mailbox.

The mailbox is scanned and the structure updated whenever the mailbox changes. Message directories are not renumbered. The results of the scan are recorded in mailbox.idx.

The file /mail/fs/ctl is used to direct fs to open, close, rename, create or remove new mailboxes, and also to delete or flag groups of messages atomically. The messages that can be written to this file are:
open path mboxname       opens a new mailbox. path is the file to open, and mboxname is the name that appears under /mail/fs.
close mboxname         close mboxname. The close takes affect only after all files open under /mail/fs/mboxname have been closed.
create mboxname        create a new mailbox, mboxname. The mailbox type must support creation.
rename [–t] old new      rename the mailbox old to new. The t flag truncates rather than removes the old mailbox. The renaming takes effect immedately. While mailboxes of any type may be renamed, it is not possible to use rename to convert folder types.
remove [–rt] mboxname   remove mboxname. The r flag removes any subfolders while the t flag truncates, rather than removes.
delete mboxname number ...
Delete the messages with the given numbers from mboxname.
flag mboxname flags number ...
flag the given messages.

The flags file records persistant message flags. These flags are a superset of the standard IMAP message flags. Flags are stored in order. Unset flags are represented by a `–' while set flags are represented by the following ordered characters
a   answered
D   deleted
d   draft
f   flagged
r   recent
s   seen
S   stored

Messages of the form [+–]flags may be written to the flags file. Fs maintains the r flag. Mail readers are expected to maintain other flags.

The options are:
D            Trace 9P protocol messages.
S            Log to console in addition to the standard places.
b            stands for biffing. Each time new mail is received, a message is printed to standard output containing the sender address, subject, and number of bytes. It is intended for people telnetting in who want mail announcements.
c cachetarg     attempt to keep the cache below cachetarg bytes.
d            loud debugging.
f file         use file as the mailbox instead of the default, /mail/box/username/mbox.
chatty index debugging.
l            logging. Turn on logging via syslog (and to the console with –S) to the file /sys/log/fs.
m mntpt       mount on mntpt rather than the default /mail/fs.
n            Don't open a mailbox initially. Overridden by –f.
p            turn off plumbing. Unless this is specified, fs sends a message to the plumb port, seemail, from source mailfs for each message received or deleted. The message contains the attributes sender=<contents of from file>, filetype=mail, mailtype=deleted or new, and length=<message length in
. The contents of the message is the full path name of the directory representing the message.
s            causes fs to put itself in /srv with a name of the form /srv/upasfs.user.

Fs will exit once all references to its directory have disappeared.

Fs interprets mailbox file names of the form /proto/host/user to mean access an account on host using the given protocol. Authentication is delegated to factotum(4). The final /user may be omitted, in which case the user name is gleaned from the key held by factotum. The following protocols are supported:

pop       cleartext POP with password authentication
apop      cleartext POP with challenge–response (APOP) authentication
poptls    TLS–encrypted POP with password authentication
apoptls   TLS–encrypted POP with challenge–response (APOP) authentication
imap      cleartext IMAP with CRAM–MD5 or password authentication
imaps     TLS–encrypted IMAP CRAM–MD5 or password authentication

The two IMAP protocols allow an optional fourth field specifying a mailbox name, for example /imap/server/user/stored.

Poptls and apoptls connect to port 110 in plaintext and start TLS using the POP STLS command. Imaps connects to port 993 and starts TLS before initiating the IMAP conversation. There should probably be pops, apops, and imaptls protocols as well. (Pops and apops would connect to port 995 and start TLS before initiating the POP conversation, and imaptls would connect to port 143 in plaintext and start TLS using the IMAP STARTTLS command. (That's the nice thing about standards--there's so many to choose from.))

/mail/box/*              mail directories
/mail/box/*/mbox          mailbox files
/mail/box/*/mbox.idx      mailbox indicies
/mail/box/*/L.mbox        mutual exclusion lock for altering mbox (mbox format only)


aliasmail(8), faces(1), filter(1), mail(1), marshal(1), mdir(6), mlmgr(1), nedmail(1), pop3(8), qer(8), rewrite(6), send(8), upasfs(4),
Erik Quanstrom ``Scaling Upas'', Proceedings of IWP9, October, 2008.