From 45db3976d3f4790337e3e8bfb149f053e88174f9 Mon Sep 17 00:00:00 2001
From: Ivan Zakharyaschev <imz@altlinux.org>
Date: Mon, 9 Oct 2017 18:15:35 +0300
Subject: [PATCH] _{encodeTo,decodeOf}ModifiedUTF7(): 64th digit of the base is
 "," (RFC3501)

According to https://tools.ietf.org/html/rfc3501#section-5.1.3 ,
in comparison to Base64 encoding, "," should be used instead of "/"
as the greatest digit of the base.

Of course, this meant that the encodings used by an IMAP server (e.g.,
dovecot) and SOGo did not match when they were communicating with each
other.

For example, when SOGo attempts to create a folder whose encoding
includes the base64 "/" digit, it is not accepted as valid mUTF7 by
the IMAP server:

C[0x5649de0d5d30]: 5 LIST "" ""
S[0x5649de0f3640]: * LIST (\Noselect) "/" ""
S[0x5649de0f3640]: 5 OK List completed (0.001 + 0.040 + 0.039 secs).
C[0x5649de0d5d30]: 6 create "INBOX/&BD8EMAQ/BDA-"
S[0x5649de0f3640]: 6 NO Mailbox name is not valid mUTF-7 (0.001 + 0.000 secs).

In the other direction, when such a folder is listed by the IMAP
server, it appears with a ",", for example: "&BD8EMAQ/BDA-". And this
is not correctly decoded by SOGo due to the fact that "," is not known
to SOGo as a digit in this base and is mapped to -1 by the internal
table, which results in a wrong Unicode code.

An example of a Unicode string which would trigger this bug is a
string with U+043F CYRILLIC SMALL LETTER PE as the third letter:

$ printf '\x04\x3f\x04\x30\x04\x3f' | recode ucs-2..
$ printf '\x04\x3f\x04\x30\x04\x3f' | base64
BD8EMAQ/

Three two-byte Unicode (Cyrillic) characters correspond to eight 6-bit
base64 digits, the last one being "/":

U+043F                U+0430                 U+043F
0000 01|00 0011 1111  00|00 0100 0011 00|00  0000 0100 00|11 1111
      B|      D|       8|      E|      M|       A|      Q|      /|

This bug has been reported in:

https://sogo.nu/bugs/view.php?id=4308
https://bugzilla.altlinux.org/show_bug.cgi?id=32426
https://bugzilla.altlinux.org/show_bug.cgi?id=33722

and a part of the problem described in
https://sogo.nu/bugs/view.php?id=2318 must be caused by incorrect
mUTF7 encoding, too (and hence must have not been fixed completely
before):

And I see next messages when I try to open Cyrillic folder:
C[0x7fb2e23a77a0]: 5 select "&BBQEPgRBBEIEQwT/BEs-"
S[0x7fb2e21fb690]: 5 NO Invalid mailbox name: &BBQEPgRBBEIEQwT/BEs-

As can you see sogo sends wrong folder name:
received "&BBQEPgRBBEIEQwQ,BEs-"
sent "&BBQEPgRBBEIEQwT/BEs-"
---
 sope-mime/NGImap4/NSString+Imap4.m | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/sope-mime/NGImap4/NSString+Imap4.m b/sope-mime/NGImap4/NSString+Imap4.m
index 76f5486..b0788cc 100644
--- a/sope-mime/NGImap4/NSString+Imap4.m
+++ b/sope-mime/NGImap4/NSString+Imap4.m
@@ -279,7 +279,7 @@ static void _encodeToModifiedUTF7(unsigned char *_buf, int encLen,
 /* check metamail output for correctness */
 
 static unsigned char basis_64[] =
-   "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
+   "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+,";
 
 static void writeChunk(int c1, int c2, int c3, int pads, unsigned char **result_,
                        unsigned int *cntRes_) {
@@ -318,7 +318,7 @@ static void writeChunk(int c1, int c2, int c3, int pads, unsigned char **result_
 static char index_64[128] = {
     -1,-1,-1,-1, -1,-1,-1,-1, -1,-1,-1,-1, -1,-1,-1,-1,
     -1,-1,-1,-1, -1,-1,-1,-1, -1,-1,-1,-1, -1,-1,-1,-1,
-    -1,-1,-1,-1, -1,-1,-1,-1, -1,-1,-1,62, -1,-1,-1,63,
+    -1,-1,-1,-1, -1,-1,-1,-1, -1,-1,-1,62, 63,-1,-1,-1,
     52,53,54,55, 56,57,58,59, 60,61,-1,-1, -1,-1,-1,-1,
     -1, 0, 1, 2,  3, 4, 5, 6,  7, 8, 9,10, 11,12,13,14,
     15,16,17,18, 19,20,21,22, 23,24,25,-1, -1,-1,-1,-1,
-- 
2.7.4