354 lines
14 KiB
Scheme
354 lines
14 KiB
Scheme
;;; POP3.scm --- implement the POP3 maildrop protocol in the Scheme Shell
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;;; This file is part of the Scheme Untergrund Networking package.
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;;; Copyright (c) 1998 by Eric Marsden
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;;; For copyright information, see the file COPYING which comes with
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;;; the distribution.
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;;; Overview ==============================================================
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;;
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;; The POP3 protocol allows access to email on a maildrop server. It
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;; is often used in configurations where users connect from a client
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;; machine which doesn't have a permanent network connection or isn't
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;; always turned on, situations which make local SMTP delivery
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;; impossible. It is the most common form of email access provided by
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;; Internet Service Providers.
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;;
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;; Two types of authentication are commonly used. The first, most
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;; basic type involves sending a user's password in clear over the
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;; network, and should be avoided. Unfortunately many POP3 clients
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;; only implement this basic authentication. The digest authentication
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;; system involves the server sending the client a "challenge" token;
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;; the client encodes this token with the pass phrase and sends the
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;; coded information to the server. This method avoids sending
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;; sensitive information over the network.
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;;
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;; Once connected, a client may request information about the number
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;; and size of the messages waiting on the server, download selected
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;; messages (either their headers or the entire content), and delete
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;; selected messages.
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;;; Entry points =======================================================
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;;
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;; (pop3-connect [host logfile]) -> connection
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;; Connect to the maildrop server named HOST. Optionally log the
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;; conversation with the server to LOGFILE, which will be appended
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;; to if it exists, and created otherwise. The environment variable
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;; MAILHOST, if set, will override the value of HOST.
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;;
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;; (pop3-login connection [login password]) -> status
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;; Log in to the mailhost. If a login and password are not
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;; provided, they are first searched for in the user's ~/.netrc
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;; file. USER/PASS authentication will be tried first, and if this
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;; fails, APOP authentication will be tried.
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;;
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;; (pop3-login/APOP connection login password) -> status
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;; Log in to the mailhost using APOP authentication.
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;;
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;; (pop3-stat connection) -> integer x integer
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;; Return the number of messages and the number of bytes waiting in
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;; the maildrop.
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;;
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;; (pop3-get connection msgid) -> status
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;; Download message number MSGID from the mailhost. MSGID must be
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;; positive and less than the number of messages returned by the
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;; pop3-stat call. The message contents are sent to
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;; (current-output-port).
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;;
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;; (pop3-headers connection msgid) -> status
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;; Download the headers of message number MSGID. The data is sent
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;; to (current-output-port).
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;;
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;; (pop3-last connection) -> integer
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;; Return the highest accessed message-id number for the current
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;; session. This isn't in the RFC, but seems to be supported by
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;; several servers.
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;;
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;; (pop3-delete connection msgid) -> status
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;; Mark message number MSGID for deletion. The message will not be
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;; deleted until the client logs out.
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;;
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;; (pop3-reset connection) -> status
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;; Any messages which have been marked for deletion are unmarked.
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;;
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;; (pop3-quit connection) -> status
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;; Close the connection with the mailhost.
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;;; Related work =====================================================
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;;
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;; * Emacs is distributed with a C program called movemail which can
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;; be compiled with support for the POP protocol. There is also an
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;; Emacs Lisp library called pop3.el by Richard Pieri which includes
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;; APOP support.
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;;
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;; * Shriram Krishnamurth has written a POP3 library for MzScheme (as
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;; well as support for the NNTP protocol, for SMTP, ...).
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;;
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;; * Siod (a small-footprint Scheme implementation by George Carette)
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;; includes support for the POP3 protocol.
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;;
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;; * rfc1939 describes the POP3 protocol.
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Communication is initiated by the client. The server responds to
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;; each request with a status indicator and an explanatory message.
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;; The client starts off by opening a connection to a well known port
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;; on the server machine (typically TCP 110, or 109 on some broken
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;; systems). Messages sent to the server are of the form
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;;
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;; CMD [ <space> arg ] <CR> <LF>
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;;
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;; Replies from the server are of the form
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;;
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;; status [ <space> Informative message ] <CR> <LF>
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;;
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;; where status is either "+OK" or "-ERR". If the server is sending
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;; data (the contents of a message for example), it marks the end of
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;; the data by a line consisting only of a decimal point (thus the
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;; bytes to look out for are <CR><LF>.<CR><LF>. Any lines in the data
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;; starting with a . have an additional . added to the beginning, to
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;; avoid the client thinking that the line marks the end of the
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;; message. The client should therefore replace double decimal points
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;; at the beginning of a line by a single decimal point.
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;;: [host x logfile] -> connection
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(define (pop3-connect . args)
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(let-optionals
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args
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((host-arg #f)
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(logfile #f))
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(let* ((host (or (getenv "MAILHOST")
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host-arg))
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(LOG (and logfile
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(open-output-file logfile
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(if (file-exists? logfile)
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(bitwise-ior open/write open/append)
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(bitwise-ior open/write open/create))
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#o600)))
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(hst-info (host-info host))
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(hostname (host-info:name hst-info))
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(srvc-info (service-info "pop3" "tcp"))
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(sock (socket-connect protocol-family/internet
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socket-type/stream
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hostname
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(service-info:port srvc-info)))
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(connection (make-pop3-connection hostname
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sock
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LOG "" "" #f #f)))
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(pop3-log connection
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(format #f "~%-- ~a: opened POP3 connection to ~a"
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;; (date->string (date))
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"Dummy date" ; (format-time-zone) is broken in v0.5.1
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hostname))
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;; read the challenge the server sends in its welcome banner
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(let* ((banner (pop3-read-response connection))
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(match (regexp-search (rx (posix-string "\\+OK .* (<[^>]+>)")) banner))
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(challenge (and match (match:substring match 1))))
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(set-pop3-connection-challenge! connection challenge))
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connection)))
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;; first try standard USER/PASS authentication, and switch to APOP
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;; authentication if the server prefers.
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;;: [string x string] -> status
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(define (pop3-login connection . args)
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(let ((netrc (and (< (length args) 2) (netrc-parse))))
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(let-optionals
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args
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((login (or (netrc-lookup-login netrc (pop3-connection-host-name connection) #f)
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(call-error "must provide a login" pop3-login args)))
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(password (or (netrc-lookup-password netrc
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(pop3-connection-host-name connection) #f)
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(call-error "must provide a password" pop3-login args))))
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(with-handler
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(lambda (result punt)
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(if (-ERR? result)
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(if (pop3-connection-challenge connection)
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(pop3-login/APOP connection login password)
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(error "login failed"))))
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(lambda ()
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(pop3-send-command connection (format #f "USER ~a" login))
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(pop3-send-command connection (format #f "PASS ~a" password))
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(set-pop3-connection-login! connection login)
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(set-pop3-connection-password! connection password)
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(set-pop3-connection-state! connection 'connected))))))
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;; Login to the server using APOP authentication (no cleartext
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;; passwords are sent over the network). The server appends a token to
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;; its welcome message, which is built from the server's fully
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;; qualified domain name and a unique serial number. The client
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;; concatenates this token and the pass phrase and applies the MD5
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;; digest algorithm (a one-way hash) to produce a digest. The user
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;; name and the digest are sent to the server to authenticate the
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;; user. The following example comes from the RFC:
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;;
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;; S: +OK POP3 server ready <1896.697170952@dbc.mtview.ca.us>
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;; C: APOP mrose c4c9334bac560ecc979e58001b3e22fb
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;; S: +OK maildrop has 1 message (369 octets)
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;;
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;; In this example, the shared secret is the string `tan-
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;; staaf'. Hence, the MD5 algorithm is applied to the string
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;;
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;; <1896.697170952@dbc.mtview.ca.us>tanstaaf
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;;
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;; which produces a digest value of
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;;
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;; c4c9334bac560ecc979e58001b3e22fb
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;;
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;;: connection x string x string -> status
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(define (pop3-login/APOP connection login password)
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(let* ((key (string-append (pop3-connection-challenge connection)
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password))
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(digest (number->string
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(md5-digest->number (md5-digest-for-string key))
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16))
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(status (pop3-send-command connection
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(format #f "APOP ~a ~a" login digest))))
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(set-pop3-connection-login! connection login)
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(set-pop3-connection-password! connection password)
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(set-pop3-connection-state! connection 'connected)
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status))
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;; return number of messages and number of bytes waiting at the maildrop
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;;: connection -> integer x integer
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(define (pop3-stat connection)
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(pop3-check-transaction-state connection 'pop3-stat)
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(let* ((response (pop3-send-command connection "STAT"))
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(match (regexp-search (rx (posix-string "([0-9]+) ([0-9]+)")) response)))
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(values (string->number (match:substring match 1))
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(string->number (match:substring match 2)))))
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;; dump the message number MSGID to (current-output-port)
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;;: connection x integer -> status
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(define (pop3-get connection msgid)
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(pop3-check-transaction-state connection 'pop3-get)
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(let ((status (pop3-send-command connection (format #f "RETR ~a" msgid))))
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(pop3-dump (socket:inport (pop3-connection-command-socket connection)))
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status))
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;;: connection x integer -> status
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(define (pop3-headers connection msgid)
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(pop3-check-transaction-state connection 'pop3-headers)
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(let ((status (pop3-send-command connection (format #f "TOP ~a 0" msgid))))
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(pop3-dump (socket:inport (pop3-connection-command-socket connection)))
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status))
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;; Return highest accessed message-id number for the session. This
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;; ain't in the RFC, but seems to be supported by several servers.
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;;: connection -> integer
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(define (pop3-last connection)
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(pop3-check-transaction-state connection 'pop3-last)
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(let ((response (pop3-send-command connection "LAST")))
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(string->number (car ((infix-splitter) response)))))
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;; mark the message number MSGID for deletion. Note that the messages
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;; are not truly deleted until the QUIT command is sent, and messages
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;; can be undeleted using the RSET command.
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;;: connection x integer -> status
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(define (pop3-delete connection msgid)
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(pop3-check-transaction-state connection 'pop3-delete)
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(pop3-send-command connection (format #f "DELE ~a" msgid)))
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;; any messages which have been marked for deletion are unmarked
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;;: connection -> status
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(define (pop3-reset connection)
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(pop3-check-transaction-state connection 'pop3-reset)
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(pop3-send-command connection "RSET"))
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;;: connection -> status
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(define (pop3-quit connection)
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(pop3-check-transaction-state connection 'pop3-quit)
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(let ((status (pop3-send-command connection "QUIT")))
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(close-socket (pop3-connection-command-socket connection))
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status))
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;;; Nothing exported below.
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(define-record-type pop3-connection :pop3-connection
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(make-pop3-connection host-name command-socket logfd login password challenge state)
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pop3-connection
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(host-name pop3-connection-host-name)
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(command-socket pop3-connection-command-socket)
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(logfd pop3-connection-logfd)
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(login pop3-connection-login set-pop3-connection-login!)
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(password pop3-connection-password set-pop3-connection-password!)
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(challenge pop3-connection-challenge set-pop3-connection-challenge!)
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(state pop3-connection-state set-pop3-connection-state!))
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;; cf /usr/local/src/scheme48-0.49/scheme/rts/condition.scm
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(define-condition-type '-ERR '(error))
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(define -ERR? (condition-predicate '-ERR))
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(define (pop3-check-transaction-state connection caller)
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(if (not (eq? (pop3-connection-state connection) 'connected))
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(call-error "not in transaction state" caller)))
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(define (pop3-read-response connection)
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(let* ((sock (pop3-connection-command-socket connection))
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(IN (socket:inport sock))
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(line (read-line IN)))
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(pop3-log connection (format #f "-> ~a" line))
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line))
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;; this could perhaps be improved
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(define (pop3-handle-response response command)
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(let ((match (regexp-search (rx (posix-string "^\\+OK(.*)")) response)))
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(if match
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(match:substring match 1)
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(let ((match2 (regexp-search (rx (posix-string "^-ERR(.*)")) response)))
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(if match2
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(signal '-ERR (match:substring match2 1) command)
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(signal '-ERR response command))))))
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(define (pop3-log connection line)
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(let ((LOG (pop3-connection-logfd connection)))
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(and LOG
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(write-string line LOG)
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(write-string "\n" LOG)
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(force-output LOG))))
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(define (pop3-send-command connection command)
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(let* ((sock (pop3-connection-command-socket connection))
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(OUT (socket:outport sock)))
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(write-string command OUT)
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(write-crlf OUT)
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(pop3-log connection (format #f "<- ~a" command))
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(pop3-handle-response (pop3-read-response connection) command)))
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;; who will write this in Scheme?
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(define (md5-digest str)
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(car (run/strings (md5sum) (<< ,str))))
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; the name of the program differs among the distributions
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; e.g. in FreeBSD it is called md5
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(define (pop3-dump fd)
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(let loop ((line (read-line fd)))
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(cond ((and (not (eof-object? line))
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(not (equal? line ".\r")))
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(and (eq? 0 (string-index line #\.)) ; fix byte-stuffed lines
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(eq? 1 (string-index line #\. 1))
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(set! line (substring line 1 (string-length line))))
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(write-string line)
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(newline)
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(loop (read-line fd))))))
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;; EOF
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