1 ;; Super-basic bell-and-whistle-free SMTP server.
3 ;; Intended for a single-user system
14 (chicken process-context)
15 (chicken process-context posix)
17 srfi-1 srfi-13 matchable base64)
19 (define lambdamail-version "LambdaMail v0.0.1")
21 (define-record config host port spool-dir user group)
22 (define-record message to from text user password)
23 (define (make-empty-message) (make-message "" "" "" "" ""))
26 ;;; Server initialization
29 (define (drop-privs config)
30 (let ((uid (config-user config))
31 (gid (config-group config)))
32 (if (not (null? gid)) ; Group first, since only root can switch groups.
33 (set! (current-group-id) gid))
35 (set! (current-user-id) uid))))
37 (define (run-server config)
38 (set-buffering-mode! (current-output-port) #:line)
39 (let ((listener (tcp-listen (config-port config) 10 "::")))
40 (print lambdamail-version
41 " listening on port " (config-port config) " ...")
42 (print "(Host name: " (config-host config)
43 ", Spool dir: " (config-spool-dir config) ")")
45 (server-loop listener config '())))
51 (define (server-loop listener config undelivered-messages)
52 (let* ((messages (append (receive-messages listener config) undelivered-messages)))
53 (server-loop listener config (deliver-messages config messages))))
56 ;;; Receiving messages
59 (define (receive-messages listener config)
61 (let-values (((in-port out-port) (tcp-accept listener)))
62 (let-values (((local-ip remote-ip) (tcp-addresses in-port)))
63 (print "Accepted connection from " remote-ip " on " (seconds->string)))
65 (set! messages (process-smtp (make-smtp-session in-port out-port config) config))
67 (print-error-message o)))
68 (print "Terminating connection.")
69 (close-input-port in-port)
70 (close-output-port out-port))
73 (define (make-smtp-session in-port out-port config)
78 (('get-line) (read-line in-port))
79 (('send-line strings ...) (write-line (conc (apply conc strings) "\r") out-port))
80 (('set-user! u) (set! user u))
81 (('set-password! p) (set! password p))
83 (('password) password)))))
85 (define (smtp-command? cmd-string input-string)
86 (string-prefix? cmd-string (string-downcase input-string)))
88 (define (smtp-command-args cmd-string input-string)
89 (if (> (string-length input-string) (string-length cmd-string))
90 (string-trim (string-drop input-string (string-length cmd-string)))
93 (define (process-smtp smtp-session config)
94 (smtp-session 'send-line "220 " (config-host config) lambdamail-version)
95 (let loop ((msg (make-empty-message))
96 (received-messages '()))
97 (let ((line (smtp-session 'get-line)))
101 ((smtp-command? "helo" line)
102 (smtp-session 'send-line "250 ok")
103 (loop msg received-messages))
104 ((smtp-command? "ehlo" line)
105 (smtp-session 'send-line
106 "250-" (config-host config)
107 " Hello " (smtp-command-args "ehlo" line))
108 (smtp-session 'send-line "250 AUTH PLAIN")
109 ;; (smtp-session 'send-line "250 STARTTLS")
110 (loop msg received-messages))
111 ((smtp-command? "auth plain" line)
112 (let* ((auth-string (smtp-command-args "auth plain" line))
113 (auth-decoded (base64-decode auth-string))
114 (auth-list (string-split auth-decoded "\x00"))
115 (user (car auth-list))
116 (password (cadr auth-list)))
117 (smtp-session 'set-user! user)
118 (smtp-session 'set-password! password)
119 (print "Attempted login, user: " user ", password: " password)
120 (smtp-session 'send-line "235 authentication successful")
121 (loop msg received-messages)))
122 ((smtp-command? "mail from:" line)
123 (message-from-set! msg (smtp-command-args "mail from:" line))
124 (smtp-session 'send-line "250 ok")
125 (loop msg received-messages))
126 ((smtp-command? "rcpt to:" line)
127 (message-to-set! msg (smtp-command-args "rcpt to:" line))
128 (smtp-session 'send-line "250 ok")
129 (loop msg received-messages))
130 ((smtp-command? "data" line)
131 (smtp-session 'send-line "354 intermediate")
132 (let text-loop ((text ""))
133 (let ((text-line (smtp-session 'get-line)))
134 (if (string=? "." text-line)
135 (message-text-set! msg text)
136 (text-loop (conc text text-line "\n")))))
137 (message-user-set! msg (smtp-session 'user))
138 (message-password-set! msg (smtp-session 'password))
139 (smtp-session 'send-line "250 ok")
140 (loop (make-empty-message) (cons msg received-messages)))
141 ((smtp-command? "quit" line)
142 (smtp-session 'send-line "221 closing transmission channel")
144 ((string=? "" (string-trim line))
145 (loop msg received-messages))
147 (smtp-session 'send-line "502 command not implemented")
148 (loop msg received-messages)))))))
151 ;;; Delivering messages
154 (define (deliver-messages config messages)
155 (print "Attempting delivery of " (length messages) " mail items.")
156 (filter (lambda (msg) (not (deliver-message msg config)))
159 (define (get-to-addresses config)
160 (map (lambda (p) (cons
161 (conc "<" (car p) "@" (config-host config) ">")
163 (map (lambda (file) (cons (pathname-file file) file))
164 (glob (conc (config-spool-dir config) "/*")))))
166 (define (remove-angle-brackets addr)
167 (let ((left-idx (substring-index "<" addr))
168 (right-idx (substring-index ">" addr)))
169 (substring addr (+ left-idx 1) right-idx)))
171 (define (deliver-message-local msg dest-dir)
172 (print "Delivering to maildir " dest-dir)
173 (with-output-to-file (conc dest-dir "/" (current-seconds))
175 (print (message-text msg)))))
177 (define (deliver-message msg config)
178 (let ((dest (assoc (message-to msg) (get-to-addresses config))))
180 (let ((dest-file (cdr dest)))
181 (if (directory-exists? dest-file)
182 (deliver-message-local msg dest-file))
183 (print "Message DELIVERED:"))
184 (print "Message REJECTED:"))
185 (print " * From: " (message-from msg))
186 (print " * To: " (message-to msg)))
190 ;;; Command line argument parsing
193 (define (print-usage progname)
195 progname " -h/--help\n"
196 progname " [-u/--user UID] [-g/--group GID] hostname [[port [spooldir]]\n"
198 "The -u and -g options can be used to set the UID and GID of the process\n"
199 "following the creation of the TCP port listener (which often requires root)."))
202 (let ((progname (pathname-file (car (argv))))
203 (config (make-config "" 25 "/var/spool/mail" '() '())))
204 (if (null? (cdr (argv)))
205 (print-usage progname)
206 (let loop ((args (cdr (argv))))
207 (let ((this-arg (car args))
208 (rest-args (cdr args)))
209 (if (string-prefix? "-" this-arg)
211 ((or (equal? this-arg "-u")
212 (equal? this-arg "--user"))
213 (config-user-set! config (string->number (car rest-args)))
214 (loop (cdr rest-args)))
215 ((or (equal? this-arg "-g")
216 (equal? this-arg "--group"))
217 (config-group-set! config (string->number (car rest-args)))
218 (loop (cdr rest-args)))
219 ((or (equal? this-arg "-h")
220 (equal? this-arg "--help"))
221 (print-usage progname))
223 (print "Unknown option " this-arg "\n")
224 (print-usage progname)))
226 (config-host-set! config this-arg)
227 (unless (null? rest-args)
228 (config-port-set! config (string->number (car rest-args)))
229 (unless (null? (cdr rest-args))
230 (config-spool-dir-set! config (cadr rest-args))))
231 (run-server config))))))))
235 ;; (run-server (make-config "thelambdalab.xyz" 2525 "/var/spool/mail"))