132 lines
3.4 KiB
Perl
Executable File
132 lines
3.4 KiB
Perl
Executable File
#!/usr/bin/env perl
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#
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# Copyright (C) 2001-2023 Graeme Walker <graeme_walker@users.sourceforge.net>
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#
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# Copying and distribution of this file, with or without modification,
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# are permitted in any medium without royalty provided the copyright
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# notice and this notice are preserved. This file is offered as-is,
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# without any warranty.
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# ===
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#
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# emailrelay-bcc-check.pl
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#
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# An example E-MailRelay "--filter" script that rejects e-mail messages that
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# have a non-empty "Bcc:" recipient list unless the "Bcc:" recipient list
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# contains a single addressee that matches the envelope recipient. This has
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# the effect of checking that a submitting user agent is behaving correctly
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# as per RFC-5322 3.6.3.
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#
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# Bcc handling is generally only a concern for e-mail user agent programs
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# and not relays and proxies. User agents should normally submit a message
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# separately for each Bcc recipient with either no "Bcc:" field or with the
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# "Bcc:" field containing that one recipient.
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#
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# Note that correct parsing of content files is beyond the scope of a simple
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# example script like this, and incorrect Bcc handling can have a serious
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# privacy implications.
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#
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use strict ;
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use FileHandle ;
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$SIG{__DIE__} = sub { (my $e = join(" ",@_)) =~ s/\n/ /g ; print "<<error: $e>>\n" ; exit 99 } ;
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my $content = $ARGV[0] or die "usage error\n" ;
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my $verbose = 1 ;
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# read the bcc list from the content file
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my %c = headers( $content ) ;
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my @bcc = split( /,/ , $c{Bcc} ) ; # todo -- allow for commas in quoted strings
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map { print "BCC=[$_]\n" } @bcc if $verbose ;
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# allow if there is no bcc list or it's empty
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exit 0 if scalar(@bcc) == 0 ;
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my $bcc = $bcc[0] =~ s/^\s*"?//r =~ s/"?\s*$//r ;
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exit 0 if( $bcc =~ m/^\s*$/ ) ;
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# read the recipient list from the envelope file
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my @rcp = read_fields( find_envelope($content) , qr/^X-MailRelay-To-Remote:\s*(.*)/ ) ;
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map { print "RECIPIENT=[$_]\n" } @rcp if $verbose ;
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# allow if there are no (remote) recipients at all
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exit 0 if scalar(@rcp) == 0 ;
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my $rcp = $rcp[0] ;
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# allow if one recipient matching one bcc
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exit 0 if( scalar(@rcp) == 1 && scalar(@bcc) == 1 && $bcc =~ m/\Q$rcp\E/ ) ;
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# deny otherwise
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print "<<bcc error>>\n" ;
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exit 1 ;
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sub headers
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{
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my ( $file ) = @_ ;
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my $fh = open_file( $file ) ;
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my %h = read_headers( $fh ) ;
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$fh->close() or die ;
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return %h ;
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}
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sub read_headers
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{
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my ( $fh ) = @_ ;
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my %h = () ;
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my $k ;
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while(<$fh>)
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{
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chomp( my $line = $_ ) ;
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$line =~ s/\r$// ;
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last if ( $line eq "" ) ;
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my ( $a , $b , $c , $d ) = ( $line =~ m/^(\S*):\s*(.*)|^(\s)(.*)/ ) ;
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if( $a ) { $h{$a} = $b ; $k = $a }
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if( $k && $d ) { $h{$k} .= "$c$d" } # folding
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}
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return %h ;
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}
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sub open_file
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{
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my ( $file ) = @_ ;
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my $fh = new FileHandle( $file , "r" ) or die "cannot open [$file]: $!\n" ;
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return $fh ;
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}
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sub envelope
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{
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my ( $content , $ext ) = @_ ;
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$ext = "" if !defined($ext) ;
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$content =~ m/\.content$/ or die "invalid content filename [$content]\n" ;
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( my $envelope = $content ) =~ s/\.content$/.envelope/ ;
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$envelope .= $ext ;
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return $envelope ;
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}
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sub find_envelope
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{
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my ( $content ) = @_ ;
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map { return $_ if -f $_ } map { envelope($content,$_) } ( "" , ".new" , ".busy" ) ;
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die "no envelope for [$content]\n" ;
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}
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sub read_fields
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{
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my ( $file , $re ) = @_ ;
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return map { s/$re/$1/ ; $_ } grep { m/$re/ } read_all( $file ) ;
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}
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sub read_all
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{
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my ( $file ) = @_ ;
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my $fh = open_file( $file ) ;
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my @lines = () ;
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while(<$fh>)
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{
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chomp( my $line = $_ ) ;
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$line =~ s/\r$// ;
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push @lines , $line ;
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}
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$fh->close() or die ;
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return @lines ;
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}
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