From 04590235145c862e6805bd5f7764ed82ffd6e35e Mon Sep 17 00:00:00 2001
From: Ryan Lue <hello@ryanlue.com>
Date: Wed, 6 Nov 2019 16:15:22 +0800
Subject: [PATCH] Fixes issue #2754: Unparseable IMAP responses block email
 import from inbox

Some users experienced an error while fetching emails over IMAP (see
GitHub issue below for complete traceback). This error was caused by
certain unparseable character sequences in the responses Zammad received
from users' configured IMAP servers. The Zammad dev team was not able to
reproduce this issue when fetching identical emails from its own
servers.

Details remain unclear, but we have tracebacks from two distinct
occurrences of this issue, and the problematic strings followed the same
format:

  * "\"Jetzt"
  * "\"RE:"

This commit rescues the error in question, records details to the
application log, and allows IMAP fetch to proceed to the next message.
---
 app/models/channel/driver/imap.rb | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/app/models/channel/driver/imap.rb b/app/models/channel/driver/imap.rb
index b310d76dd..af67bf76b 100644
--- a/app/models/channel/driver/imap.rb
+++ b/app/models/channel/driver/imap.rb
@@ -208,6 +208,7 @@ example
     count_max             = 5000
     too_large_messages    = []
     active_check_interval = 20
+    result                = 'ok'
     notice                = ''
     message_ids.each do |message_id|
       count += 1
@@ -222,6 +223,18 @@ example
       message_meta = nil
       timeout(FETCH_METADATA_TIMEOUT) do
         message_meta = @imap.fetch(message_id, ['RFC822.SIZE', 'ENVELOPE', 'FLAGS', 'INTERNALDATE', 'RFC822.HEADER'])[0]
+      rescue Net::IMAP::ResponseParseError => e
+        raise if !e.message.match?(/unknown token/)
+
+        result = 'error'
+        notice += <<~NOTICE
+          One of your incoming emails could not be imported (#{e.message}).
+          Please remove it from your inbox directly
+          to prevent Zammad from trying to import it again.
+        NOTICE
+        Rails.logger.error "Net::IMAP failed to parse message #{message_id}: #{e.message} (#{e.class})"
+        Rails.logger.error '(See https://github.com/zammad/zammad/issues/2754 for more details)'
+        next
       end
 
       # ignore verify messages
@@ -300,7 +313,7 @@ example
 
     Rails.logger.info 'done'
     {
-      result:  'ok',
+      result:  result,
       fetched: count_fetched,
       notice:  notice,
     }