If there is a non-ascii character in a header, parsing fails,
even on Py27.

This has huge Py2/Py3 complexities. The Py3 email package has tools
to handle this - we just need to use them. Py2, on the other hand,
needs a lot of hand-holding, as explained in the comments.

This is handy for mails with malformed headers containing weird
bytes.

Reported-by: Thomas Monjalon <thomas.monja...@6wind.com>
Suggested-by: Stephen Finucane <stephenfinuc...@hotmail.com>
Signed-off-by: Daniel Axtens <d...@axtens.net>

---

Many thanks to Thomas for his help debugging this, and to Stephen
for a much better patch.

This should probably go to a stable branch too. We'll need to start
some discussion about how to handle bug fixes for people not running
git mainline (like ozlabs.org and kernel.org).
---
 patchwork/parser.py | 65 ++++++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 60 insertions(+), 5 deletions(-)

diff --git a/patchwork/parser.py b/patchwork/parser.py
index 3389e96c4f3e..1b4cab1eb1a8 100644
--- a/patchwork/parser.py
+++ b/patchwork/parser.py
@@ -21,7 +21,7 @@
 
 import codecs
 import datetime
-from email.header import Header, decode_header
+from email.header import decode_header, make_header
 from email.utils import parsedate_tz, mktime_tz
 from fnmatch import fnmatch
 from functools import reduce
@@ -155,10 +155,65 @@ def find_date(mail):
 
 
 def find_headers(mail):
-    return reduce(operator.__concat__,
-                  ['%s: %s\n' % (k, Header(v, header_name=k,
-                                           continuation_ws='\t').encode())
-                   for (k, v) in list(mail.items())])
+    # We have some Py2/Py3 issues here.
+    #
+    # Firstly, the email parser (before we get here)
+    # Python 3: headers with weird chars are email.header.Header
+    #           class, others as str
+    # Python 2: every header is an str
+    #
+    # Secondly, the behaviour of decode_header:
+    # Python 3: weird headers are labelled as unknown-8bit
+    # Python 2: weird headers are not labelled differently, causing an
+    #           encoding issue when Py2 goes to then encode it in
+    #           make_header.
+    #
+    # Lastly, making matters worse, in Python2, unknown-8bit doesn't
+    # seem to be supported as an input to make_header, so not only do
+    # we have to detect dodgy headers, we have to fix them ourselves.
+    #
+    # We solve this by catching any Unicode errors, and then manually
+    # handling any interesting headers. This will only happen under
+    # Py2.
+
+    headers = {key: decode_header(value) for key, value in
+               mail.items()}
+
+    strings = []
+    for key, value in headers.items():
+        try:
+            header = make_header(value,
+                                 header_name=key,
+                                 continuation_ws='\t')
+        except UnicodeDecodeError:
+            # We should only get here under Python 2.
+            # At least one of the parts cannot be encoded as ascii.
+            # Find out which one and fix it somehow.
+            new_value=[]
+            for (part, coding) in value:
+                if (coding is not None or
+                    all([ord(x) in range(128) for x in part])):
+
+                    # we either have a coding hint or it's all ascii
+                    # let it through unchanged.
+                    # TODO: handle invalid data with a coding hint
+                    new_value += [(part, coding)]
+                else:
+                    # We have random bytes that aren't properly coded.
+                    # We should do the unknown-8bit coding ourselves.
+                    # For now, we're just going to replace any dubious
+                    # chars with ?. TODO: replace it with a proper QP
+                    # unknown-8bit codec.
+                    new_value += [(part.decode('ascii', errors='replace')
+                                   .encode('ascii', errors='replace'),
+                                   None)]
+            header = make_header(new_value,
+                                 header_name=key,
+                                 continuation_ws='\t')
+        finally:
+            strings += ['%s: %s' % (key, header.encode())]
+
+    return '\n'.join(strings)
 
 
 def find_references(mail):
-- 
2.7.4

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