From 1f29b33d3f71b8a40f5ae76bf20b95618b518654 Mon Sep 17 00:00:00 2001
From: Eric Wong <e@80x24.org>
Date: Wed, 18 May 2016 01:23:05 +0000
Subject: unsubscribe: get off mah lawn^H^H^Hist

While public-inbox is intended primarily for archival,
SMTP list subscriptions are still in use in most places
and users are likely to want a good unsubscribe mechanism.

HTTP (or HTTPS) links in the List-Unsubscribe header are
often preferable since some users may use an incorrect
email address for mailto: links.

Thus, it is useful to provide an example which generates an
HTTPS link for users to click on.  The default .psgi requires
a POST confirmation (as destructive actions with GET are
considered bad practice).  However, the "confirm" parameter
may be disabled for a true "one-click" unsubscribe.

The generated URLs are hopefully short enough and both shell
and highlighting-friendly to reduce copy+paste errors.
---
 lib/PublicInbox/Unsubscribe.pm | 179 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 179 insertions(+)
 create mode 100644 lib/PublicInbox/Unsubscribe.pm

(limited to 'lib')

diff --git a/lib/PublicInbox/Unsubscribe.pm b/lib/PublicInbox/Unsubscribe.pm
new file mode 100644
index 00000000..1f5ce315
--- /dev/null
+++ b/lib/PublicInbox/Unsubscribe.pm
@@ -0,0 +1,179 @@
+# Copyright (C) 2016 all contributors <meta@public-inbox.org>
+# License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
+#
+# Standalone PSGI app to handle HTTP(s) unsubscribe links generated
+# by milters like examples/unsubscribe.milter to mailing lists.
+#
+# This does not depend on any other modules in the PublicInbox::*
+# and ought to be usable with any mailing list software.
+package PublicInbox::Unsubscribe;
+use strict;
+use warnings;
+use Crypt::CBC;
+use Plack::Util;
+use MIME::Base64 qw(decode_base64url);
+my $CODE_URL = 'git://80x24.org/public-inbox.git';
+my @CT_HTML = ('Content-Type', 'text/html; charset=UTF-8');
+
+sub new {
+	my ($class, %opt) = @_;
+	my $key_file = $opt{key_file};
+	defined $key_file or die "`key_file' needed";
+	open my $fh, '<', $key_file or die
+		"failed to open key_file=$key_file: $!\n";
+	my ($key, $iv);
+	if (read($fh, $key, 8) != 8 || read($fh, $iv, 8) != 8 ||
+				read($fh, my $end, 8) != 0) {
+		die "key_file must be 16 bytes\n";
+	}
+
+	# these parameters were chosen to generate shorter parameters
+	# to reduce the possibility of copy+paste errors
+	my $cipher = Crypt::CBC->new(-key => $key,
+			-iv => $iv,
+			-header => 'none',
+			-cipher => 'Blowfish');
+
+	my $e = $opt{owner_email} or die "`owner_email' not specified\n";
+	my $unsubscribe = $opt{unsubscribe} or
+		die "`unsubscribe' callback not given\n";
+
+	bless {
+		pi_config => $opt{pi_config}, # PublicInbox::Config
+		owner_email => $opt{owner_email},
+		cipher => $cipher,
+		unsubscribe => $unsubscribe,
+		contact => qq(<a\nhref="mailto:$e">$e</a>),
+		code_url => $opt{code_url} || $CODE_URL,
+		confirm => $opt{confirm},
+	}, $class;
+}
+
+# entry point for PSGI
+sub call {
+	my ($self, $env) = @_;
+	my $m = $env->{REQUEST_METHOD};
+	if ($m eq 'GET' || $m eq 'HEAD') {
+		$self->{confirm} ? confirm_prompt($self, $env)
+				 : finalize_unsub($self, $env);
+	} elsif ($m eq 'POST') {
+		finalize_unsub($self, $env);
+	} else {
+		r($self, 405,
+			Plack::Util::encode_html($m).' method not allowed');
+	}
+}
+
+sub _user_list_addr {
+	my ($self, $env) = @_;
+	my ($blank, $u, $list) = split('/', $env->{PATH_INFO});
+
+	if (!defined $u || $u eq '') {
+		return r($self, 400, 'Bad request',
+			'Missing encrypted email address in path component');
+	}
+	if (!defined $list && $list eq '') {
+		return r($self, 400, 'Bad request',
+			'Missing mailing list name in path component');
+	}
+	my $user = eval { $self->{cipher}->decrypt(decode_base64url($u)) };
+	if (!defined $user) {
+		my $err = quotemeta($@);
+		my $errors = $env->{'psgi.errors'};
+		$errors->print("error decrypting: $u\n");
+		$errors->print("$_\n") for split("\n", $err);
+		return r($self, 400, 'Bad request', "Failed to decrypt: $u");
+	}
+
+	# The URLs are too damn long if we have the encrypted domain
+	# name in the query string
+	if (index($list, '@') < 0) {
+		my $host = (split(':', $env->{HTTP_HOST}))[0];
+		$list .= '@'.$host;
+	}
+	($user, $list);
+}
+
+sub confirm_prompt { # on GET
+	my ($self, $env) = @_;
+	my ($user_addr, $list_addr) = _user_list_addr($self, $env);
+	return $user_addr if ref $user_addr;
+
+	my $xl = Plack::Util::encode_html($list_addr);
+	my $xu = Plack::Util::encode_html($user_addr);
+	my @body = (
+		"Confirmation required to remove", '',
+		"\t$xu", '',
+		"from the mailing list at", '',
+		"\t$xl", '',
+		'You will get one last email once you hit "Confirm" below:',
+		qq(</pre><form\nmethod=post\naction="">) .
+		qq(<input\ntype=submit\nvalue="Confirm" />) .
+		'</form><pre>');
+
+	push @body, archive_info($self, $env, $list_addr);
+
+	r($self, 200, "Confirm unsubscribe for $xl", @body);
+}
+
+sub finalize_unsub { # on POST
+	my ($self, $env) = @_;
+	my ($user_addr, $list_addr) = _user_list_addr($self, $env);
+	return $user_addr if ref $user_addr;
+
+	my @archive = archive_info($self, $env, $list_addr);
+	if (my $err = $self->{unsubscribe}->($user_addr, $list_addr)) {
+		return r($self, 500, Plack::Util::encode_html($err), @archive);
+	}
+
+	my $xl = Plack::Util::encode_html($list_addr);
+	r($self, 200, "Unsubscribed from $xl",
+		'You may get one final goodbye message', @archive);
+}
+
+sub r {
+	my ($self, $code, $title, @body) = @_;
+	[ $code, [ @CT_HTML ], [
+		"<html><head><title>$title</title></head><body><pre>".
+		join("\n", "<b>$title</b>\n", @body) . '</pre><hr />'.
+		"<pre>This page is available under AGPL-3.0+\n" .
+		"git clone $self->{code_url}\n" .
+		qq(Email $self->{contact} if you have any questions).
+		'</pre></body></html>'
+	] ];
+}
+
+sub archive_info {
+	my ($self, $env, $list_addr) = @_;
+	my $archive_url = $self->{archive_urls}->{$list_addr};
+
+	unless ($archive_url) {
+		if (my $config = $self->{pi_config}) {
+			# PublicInbox::Config::lookup
+			my $inbox = $config->lookup($list_addr);
+			# PublicInbox::Inbox::base_url
+			$archive_url = $inbox->base_url if $inbox;
+		}
+	}
+
+	# protocol-relative URL:  "//example.com/" => "https://example.com/"
+	if ($archive_url =~ m!\A//!) {
+		$archive_url = "$env->{'psgi.url_scheme'}:$archive_url";
+	}
+
+	# maybe there are other places where we could map
+	# list_addr => archive_url without ~/.public-inbox/config
+	if ($archive_url) {
+		$archive_url = Plack::Util::encode_html($archive_url);
+		('',
+		'HTML and git clone-able archives are available at:',
+		qq(<a\nhref="$archive_url">$archive_url</a>))
+	} else {
+		('',
+		'There ought to be archives for this list,',
+		'but unfortunately the admin did not configure '.
+		__PACKAGE__. ' to show you the URL');
+	}
+}
+
+1;
-- 
cgit v1.2.3-24-ge0c7