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Replaced --alternative-strip-html option with --inline-flatten. This option does more. See --help

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This commit is contained in:
Mike Cardwell 2011-11-15 12:27:56 +00:00
parent 112f66f912
commit 62c6b463a7
1 changed files with 126 additions and 29 deletions
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155
gpgit.pl
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@ -26,9 +26,9 @@ use Mail::GnuPG;
use MIME::Parser;
## Parse args
my $encrypt_mode = 'pgpmime';
my $alternative_strip_html = 0;
my @recipients = ();
my $encrypt_mode = 'pgpmime';
my $inline_flatten = 0;
my @recipients = ();
{
help() unless @ARGV;
my @args = @ARGV;
@ -41,8 +41,8 @@ use MIME::Parser;
unless( defined $encrypt_mode && grep( $encrypt_mode eq $_, 'prefer-inline', 'pgpmime', 'inline-or-plain' ) ){
die "Bad value for --encrypt-mode\n";
}
} elsif( $key eq '--alternative-strip-html' ){
$alternative_strip_html = 1;
} elsif( $key eq '--inline-flatten' ){
$inline_flatten = 1;
} elsif( $key =~ /^.+\@.+$/ ){
push @recipients, $key;
} else {
@ -50,6 +50,9 @@ use MIME::Parser;
}
}
die "Missing recipients\n" unless @recipients;
if( $inline_flatten && $encrypt_mode eq 'pgpmime' ){
die "inline-flatten option makes no sense with \"pgpmime\" encrypt-mode. See --help\n"
}
}
## Set the home environment variable from the user running the script
@ -89,35 +92,51 @@ use MIME::Parser;
print $plain; exit 0;
}
## When we're in prefer-inline or inline-or-plain mode, we can't encrypt the common multipart/alternative,
## "text/plain followed by text/html" emails. Well, if we strip the HTML part, we can.
## If the user has specified that they prefer/need inline encryption, instead of PGP/MIME, and the email is multipart, then
## we need to attempt to flatten the message down into a single text/plain part. There are a couple of safe'ish lossy ways of
## doing this:
##
## Removing text/html from multipart/alternative entities that also have a text/plain part
## In this scenario, the two text parts are *supposed* to contain the same content. So it should be ok to strip the html part.
## We only do this if the text/plain part contains at least 10 characters of data.
##
## Removing images from multipart/related entities when they are referred to from a HTML part
## We'll be stripping the HTML parts, so if those HTML parts use a CID URL to refer to a related image, we may as well strip
## those images too as they will no longer be used in the display of the email
if( $alternative_strip_html ){
if( $inline_flatten ){
if( $encrypt_mode eq 'prefer-inline' || $encrypt_mode eq 'inline-or-plain' ){
if( $mime->mime_type eq 'multipart/alternative' ){
my @parts = $mime->parts();
if( int(@parts) == 2 && $parts[0]->mime_type eq 'text/plain' && $parts[1]->mime_type eq 'text/html' ){
## Only do this when the body of the text/plain part is at least 10 characters long. Handling empty text/plain parts
my $body = $parts[0]->bodyhandle->as_string;
$body =~ s/^[\s\r\n]*(.*?)[\s\r\n]*$/$1/s;
$mime->parts([$parts[0]]) if length($body) >= 10;
}
if( $mime->mime_type =~ /^multipart\/(alternative|related)$/ ){
## We're going to try several things to flatten the email to a single text/plain part. We want to work on a duplicate
## version of the message so we can fall back to the original if we don't manage to flatten all the way
my $new_mime = $mime->dup;
## We may already be able to safely flatten, if we have a multipart/x message with only a single child part. Unlikely
$new_mime->make_singlepart;
## multipart/related
flatten_related( $new_mime ) if $new_mime->mime_type eq 'multipart/related';
flatten_alternative( $new_mime ) if $new_mime->mime_type eq 'multipart/alternative';
## Keep the new message if it was succesfully flattened
$mime = $new_mime if $new_mime->mime_type !~ /^multipart\//;
}
}
}
## Encrypt
{
$mime->make_singlepart;
my $code;
if( $encrypt_mode eq 'pgpmime' ){
$code = $gpg->mime_encrypt( $mime, @recipients );
} elsif( $encrypt_mode eq 'prefer-inline' ){
$mime->make_singlepart;
$code = $mime->mime_type =~ /^text\/plain/
? $gpg->ascii_encrypt( $mime, @recipients )
: $gpg->mime_encrypt( $mime, @recipients );
} elsif( $encrypt_mode eq 'inline-or-plain' ){
$mime->make_singlepart;
if( $mime->mime_type =~ /^text\/plain/ ){
$code = $gpg->ascii_encrypt( $mime, @recipients );
} else {
@ -137,6 +156,78 @@ use MIME::Parser;
## Print out the encrypted version
print $mime->stringify;
## Flatten multipart/alternative by removing html parts when safe
sub flatten_alternative {
my $entity = shift;
my @parts = $entity->parts;
if( int(@parts) == 2 && $parts[0]->mime_type eq 'text/plain' && $parts[1]->mime_type eq 'text/html' ){
my $body = $parts[0]->bodyhandle->as_string;
$body =~ s/^[\s\r\n]*(.*?)[\s\r\n]*$/$1/s;
if( length($body) >= 10 ){
$entity->parts([$parts[0]]);
$entity->make_singlepart;
}
}
}
## Flatten multipart/related by removing images when safe
sub flatten_related {
my $entity = shift;
## Scan the existing parts
my( @parts, %cids );
foreach my $part ( $entity->parts ){
if( $part->mime_type =~ /^image\// ){
my $content_id = $part->head->get('Content-Id')||'';
$content_id =~ s/^<(.+?)>$/$1/;
$content_id =~ s/[\r\n]+//g;
if( length($content_id) ){
push @parts, { content_id => $content_id, part => $part };
next;
}
} elsif( $part->mime_type eq 'text/html' ){
$cids{$_} = 1 foreach get_cids_from_html( $part );
} elsif( $part->mime_type eq 'multipart/alternative' ){
foreach my $part ( grep( $_->mime_type eq 'text/html', $part->parts ) ){
$cids{$_} = 1 foreach get_cids_from_html( $part );
}
}
push @parts, { part => $part };
}
## Remove images linked to from HTML
my @new_parts;
foreach my $part ( @parts ){
next if exists $part->{content_id} && $cids{$part->{content_id}};
push @new_parts, $part->{part};
}
## If we've managed to get rid of at least one child part, then update the mime entity
if( int(@new_parts) < int(@parts) ){
$entity->parts(\@new_parts);
$entity->make_singlepart();
}
}
## Takes a HTML part, and looks for CID urls
sub get_cids_from_html {
my $entity = shift;
## Get the decoded HTML
my $html = $entity->bodyhandle->as_string;
## Replace newlines with spaces
$html =~ s/\s*[\r\n]+\s*/ /gsm;
## Parse out cid urls
my @cids;
$html =~ s/=\s*["']cid:(.+?)["'\s\/>]/push @cids,$1/egoism;
return @cids;
}
sub help {
print << "END_HELP";
Usage: gpgit.pl recipient1 recipient2
@ -159,18 +250,24 @@ will use inline if possible, and PGP/MIME if not. "inline-or-plain" will use
inline encryption for single part emails, and no encryption for multi-part
emails.
--alternative-strip-html
--inline-flatten
multipart/alternative emails containing a text/plain part followed by a
text/html part are quite common. These emails can only be encrypted using
PGP/MIME. So in inline-or-plain mode, they wont be encrypted, and in
prefer-inline mode, they will be encrypted using PGP/MIME. If you enable
this option, we strip off the HTML part of these emails, and pack them down
into a single part email so that inline encryption can be used. This only
happens if the body of the text/plain part is at least 10 characters long
as we don't want to keep blank text/plain parts. The text/plain and
text/html parts *should* contain the same information, so this *should*
be safe. It is disabled by default though.
Only makes sense when using an "inline" encrypt-mode. When you enable this
option, we attempt to convert multipart emails to a single part text/plain
email, so inline encryption can be used. The methods we use are "lossy", but
I believe them to be safe(ish):
1.) When we find a multipart/alternative part which contains two parts: A
text/plain part with at least 10 characters in it, and a text/html part,
we remove the text/html part. The text/plain part *should* contain the
same content as the text/html part, but without the HTML markup.
2.) When we find a multipart/related part which contains image parts which
are referred to from a HTML part via CID URLs, we remove those images.
We can do this, because we will be removing the HTML parts that are
referring to them, and so they *should* be redundant. We don't just
remove image parts, we only remove "related" image parts that are
referred by using CID URLs pointing at their Content-Id headers.
END_HELP
exit 0;
}