From 3c2beaf70ecd39b28e1d6ea64870ed2343bfb4ba Mon Sep 17 00:00:00 2001
From: Scott Kitterman <scott@kitterman.com>
Date: Mon, 29 Oct 2018 19:53:12 -0400
Subject: [PATCH]     - Python 3.7 compatibility fixup for
 dkim.canonicalization.       strip_trailing_lines due to changed RE.sub()
 processing (LP: #1800313)

---
 ChangeLog                | 2 ++
 dkim/canonicalization.py | 9 ++++++++-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/ChangeLog b/ChangeLog
index cfc36e1..6492417 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -3,6 +3,8 @@ UNRELEASED Version 0.9.0
       (Thomas Ward)
     - PEP8 Blank Lines Style Issues (LP: #1782596)
       (Thomas Ward)
+    - Python 3.7 compatibility fixup for dkim.canonicalization.
+      strip_trailing_lines due to changed RE.sub() processing (LP: #1800313)
 
 2018-06-16 Version 0.8.1
     - Correctly fold lines at or near the maximum line length (fix folding
diff --git a/dkim/canonicalization.py b/dkim/canonicalization.py
index c69cd23..bb04b1c 100644
--- a/dkim/canonicalization.py
+++ b/dkim/canonicalization.py
@@ -41,7 +41,14 @@ def compress_whitespace(content):
 
 
 def strip_trailing_lines(content):
-    return re.sub(b"(\r\n)*$", b"\r\n", content)
+    content =  re.sub(b"(\r\n)*$", b"\r\n", content)
+    # Yes, this is horrible, but regex processing changed in python3.7 and it
+    # is the least horrible solution I came up with for python2.7, python3.7,
+    # and python3 << 3.7 combined support.  Better solution welcome.
+    if len(content) >= 4:
+        if (content[len(content)-4:] == b'\r\n\r\n'):
+            content = content[:len(content)-2]
+    return content
 
 
 def unfold_header_value(content):