test: add test for "Mixed-Up Mime" message mangling

Some MTAs mangle e-mail messages in transit in ways that are
repairable.

Microsoft Exchange (in particular, the version running today on
Office365's mailservers) appears to mangle multipart/encrypted
messages in a way that makes them undecryptable by the recipient.

I've documented this in section 4.1 "Mixed-up encryption" of draft -00
of
https://tools.ietf.org/html/draft-dkg-openpgp-pgpmime-message-mangling

Fortunately, it's possible to repair such a message, and notmuch can
do that so that a user who receives an encrypted message from a user
of office365.com can still decrypt the message.

Enigmail already knows about this particular kind of mangling.  It
describes it as "broken PGP email format probably caused by an old
Exchange server", and it tries to repair by directly changing the
message held by the user.  if this kind of repair goes wrong, the
repair process can cause data loss
(https://sourceforge.net/p/enigmail/bugs/987/, yikes).

The tests introduced here are currently broken.  In subsequent
patches, i'll introduce a non-destructive form of repair for notmuch
so that notmuch users can read mail that has been mangled in this way,
and the tests will succeed.

Signed-off-by: Daniel Kahn Gillmor <dkg@fifthhorseman.net>

test/T351-pgpmime-mangling.sh

@@ -0,0 +1,36 @@
+#!/usr/bin/env bash
+
+test_description='PGP/MIME message mangling'
+. $(dirname "$0")/test-lib.sh || exit 1
+
+add_gnupg_home
+add_email_corpus mangling
+
+bodytext='["body"][0]["content"][1]["content"]="The password is \"abcd1234!\", please do not tell anyone.\n"'
+
+test_begin_subtest "show 'Mixed-Up' mangled PGP/MIME message correctly"
+test_subtest_known_broken
+output=$(notmuch show --format=json --decrypt=true id:mixed-up@mangling.notmuchmail.org)
+test_json_nodes <<<"$output" \
+                'body:[0][0][0]'"$bodytext"
+
+test_begin_subtest "reply to 'Mixed-Up' mangled PGP/MIME message correctly"
+test_subtest_known_broken
+output=$(notmuch reply --format=json --decrypt=true id:mixed-up@mangling.notmuchmail.org)
+test_json_nodes <<<"$output" \
+                'body:["original"]'"$bodytext"
+
+test_begin_subtest "repaired 'Mixed-up' messages can be found with index.repaired=mixedup"
+test_subtest_known_broken
+output=$(notmuch search --output=messages property:index.repaired=mixedup)
+test_expect_equal "$output" id:mixed-up@mangling.notmuchmail.org
+
+test_begin_subtest "index cleartext of 'Mixed-Up' mangled PGP/MIME message"
+test_expect_success 'notmuch reindex --decrypt=true id:mixed-up@mangling.notmuchmail.org'
+
+test_begin_subtest "search cleartext of 'Mixed-Up' mangled PGP/MIME message"
+test_subtest_known_broken
+output=$(notmuch search --output=messages body:password)
+test_expect_equal "$output" id:mixed-up@mangling.notmuchmail.org
+
+test_done

test/corpora/mangling/mixed-up.eml

@@ -0,0 +1,33 @@
+From: test_suite@notmuchmail.org
+To: test_suite@notmuchmail.org
+Subject: Here is the password
+Date: Sat, 01 Jan 2000 12:00:00 +0000
+Message-ID: <mixed-up@mangling.notmuchmail.org>
+MIME-Version: 1.0
+Content-Type: multipart/mixed; boundary="=-=-="
+
+--=-=-=
+Content-Type: text/plain; charset="us-ascii"
+Content-Transfer-Encoding: quoted-printable
+
+
+--=-=-=
+Content-Type: application/pgp-encrypted
+Content-Transfer-Encoding: base64
+
+VmVyc2lvbjogMQ0K
+
+--=-=-=
+Content-Type: application/octet-stream
+Content-Transfer-Encoding: base64
+
+LS0tLS1CRUdJTiBQR1AgTUVTU0FHRS0tLS0tDQoNCmhJd0R4RTAyM3ExVXF4WUJCQUNwNzBlN0tQ
+eTlPWWFoZUlya0x6bWhxMWxScW15NTFhTDFqQkwwSy9xTjdyZksNCkJaRUcxY1I4amVMalRGZFBL
+UExWS0pJODByN0ZnS0kweXd2V3ZsNlIxYUUxVHk1Qm5WWFQ5WHpDckVIN2ZxQ2wNClNLSzgyRXZv
+bFhUb2hBWkhVcmg2SzY2ZVFRVFRJQUMxbjdCMEE4aEVyemtnYU00K3NlTjNMbHZlelQ2VExOS00N
+CkFUcHFzRWJNMk1WckdndzBiM29Vc0dHQVBFdDJNbWpORVlzcmlLbnF3dDZkSkRaYy8vWHloamdN
+UWF5aUQ4ZGENCk4xZ1Qzb3FndS9nS0NwQlpEWXpIZjlPdFZpMlVubEZEV3k2cnJNWkxqV0RuSXY0
+dmU5UG4vcW9sd0hWanpkSjENClpmak5DNXQwejNYQURLR3JqTjl3dXRyNHFtN1NUVzFySEFYSFA2
+OFRRVHhJMHFnSktqUFhOS1dFdzZnPQ0KPXBKRzQNCi0tLS0tRU5EIFBHUCBNRVNTQUdFLS0tLS0N
+Cg==
+--=-=-=--