;; Copyright (C) 2003 Dale Mellor
;;
;; This file is part of GNU mcron.
;;
;; GNU mcron is free software: you can redistribute it and/or modify it under
;; the terms of the GNU General Public License as published by the Free
;; Software Foundation, either version 3 of the License, or (at your option)
;; any later version.
;;
;; GNU mcron is distributed in the hope that it will be useful, but WITHOUT
;; ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
;; FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
;; more details.
;;
;; You should have received a copy of the GNU General Public License along
;; with GNU mcron. If not, see <http://www.gnu.org/licenses/>.
;; This module provides the (with-mail-out action . user) procedure. This
;; procedure runs the action in a child process, allowing the user control over
;; the input and output (including standard error). The input is governed (only
;; in the case of a string action) by the placing of percentage signs in the
;; string; the first delimits the true action from the standard input, and
;; subsequent ones denote newlines to be placed into the input. The output (if
;; there actually is any) is controlled by the MAILTO environment variable. If
;; this is not defined, output is e-mailed to the user passed as argument, if
;; any, or else the owner of the action; if defined but empty then any output is
;; sunk to /dev/null; otherwise output is e-mailed to the address held in the
;; MAILTO variable.
(define-module (mcron redirect)
#:export (with-mail-out)
#:use-module ((mcron config) :select (config-sendmail))
#:use-module (mcron vixie-time))
;; An action string consists of a sequence of characters forming a command
;; executable by the shell, possibly followed by an non-escaped percentage
;; sign. The text after the percentage sign is to be fed to the command's
;; standard input, with further unescaped percents being substituted with
;; newlines. The escape character can itself be escaped.
;;
;; This regexp separates the two halves of the string, and indeed determines if
;; the second part is present.
(define action-string-regexp (make-regexp "((\\\\%|[^%])*)%(.*)$"))
;; This regexp identifies an escaped percentage sign.
(define e-percent (make-regexp "\\\\%"))
;; Function to execute some action (this may be a shell command, lamdba function
;; or list of scheme procedures) in a forked process, with the input coming from
;; the string, and output (including the error output) being sent to a pipe
;; opened on a mail transport.
(use-modules (ice-9 popen))
(define (with-mail-out action . user)
;; Determine the name of the user who is to recieve the mail, looking for a
;; name in the optional user argument, then in the MAILTO environment
;; variable, and finally in the LOGNAME environment variable. (The case
;; MAILTO="" is dealt with specially below.)
(let* ((mailto (getenv "MAILTO"))
(user (cond (mailto mailto)
((not (null? user)) (car user))
(else (getenv "LOGNAME"))))
(parent->child (pipe))
(child->parent (pipe))
(child-pid (primitive-fork)))
;; The child process. Close redundant ends of pipes, remap the standard
;; streams, and run the action, taking care to chop off the input part of an
;; action string.
(if (eqv? child-pid 0)
(begin
(close (cdr parent->child))
(close (car child->parent))
(dup2 (port->fdes (car parent->child)) 0)
(close (car parent->child))
(dup2 (port->fdes (cdr child->parent)) 1)
(close (cdr child->parent))
(dup2 1 2)
(cond ((string? action)
(let ((match (regexp-exec action-string-regexp action)))
(system (if match
(let ((action (match:substring match 1)))
(do ((match (regexp-exec e-percent action)
(regexp-exec e-percent action)))
((not match))
(set! action (string-append
(match:prefix match)
"%"
(match:suffix match))))
action)
action))))
((procedure? action) (action))
((list? action) (primitive-eval action)))
(primitive-exit 0)))
;; The parent process. Get rid of redundant pipe ends.
(close (car parent->child))
(close (cdr child->parent))
;; Put stuff to child from after '%' in command line, replacing
;; other %'s with newlines. Ugly or what?
(if (string? action)
(let ((port (cdr parent->child))
(match (regexp-exec action-string-regexp action)))
(if (and match
(match:substring match 3))
(with-input-from-string (match:substring match 3)
(lambda ()
(let loop ()
(let ((next-char (read-char)))
(if (not (eof-object? next-char))
(cond
((char=? next-char #\%)
(newline port)
(loop))
((char=? next-char #\\)
(let ((escape (read-char)))
(if (eof-object? escape)
(display #\\ port)
(if (char=? escape #\%)
(begin
(display #\% port)
(loop))
(begin
(display #\\ port)
(display escape port)
(loop))))))
(else
(display next-char port)
(loop)))))))))))
;; So the child process doesn't hang on to its input expecting more stuff.
(close (cdr parent->child))
;; That's got streaming into the child's input out of the way, now we stream
;; the child's output to a mail sink, but only if there is something there
;; in the first place.
(if (eof-object? (peek-char (car child->parent)))
(read-char (car child->parent))
(begin
(set-current-output-port (if (and (string? mailto)
(string=? mailto ""))
(open-output-file "/dev/null")
(open-output-pipe
(string-append config-sendmail
" "
user))))
(set-current-input-port (car child->parent))
(display "To: ") (display user) (newline)
(display "From: mcron") (newline)
(display (string-append "Subject: " user "@" (gethostname)))
(newline)
(newline)
(do ((next-char (read-char) (read-char)))
((eof-object? next-char))
(display next-char))))
(close (car child->parent))
(waitpid child-pid)))
