[PATCH] Fallback to common charsets when charset is None or x-unknown

[Siddhesh Poyarekar]

Trying again after signing up to the mailing list (patch is slightly
modified from my first submission, which may either be in moderation
or may have gotten lost somehow):

On Wed, Jun 11, 2014 at 04:09:16PM +0530, Siddhesh Poyarekar wrote:
> Hi,
> 
> We recently encountered a case in our glibc patchwork instance on
> sourceware, where a patch was dropped because it had x-unknown
> charset.  I used the following patch to fix this in our instance.  The
> fix I used was to fall back on a set of encodings (instead of just
> utf-8) when the charset is not mentioned or if it is set as x-unknown.
> 
> I hope this is useful.  I'd love to know if you all think there is a
> better way to fix this so that I can implement that in our instance
> instead of my hack.
> 
> Cheers,
> Siddhesh

--- a/apps/patchwork/bin/parsemail.py	2014-06-11 15:53:12.685666812 +0530
+++ b/apps/patchwork/bin/parsemail.py	2014-06-11 15:53:03.991667186 +0530
@@ -147,6 +147,13 @@
         return match.group(1)
     return None
 
+def try_decode(payload, charset):
+    try:
+        payload = unicode(payload, charset)
+    except UnicodeDecodeError:
+        return None
+    return payload
+
 def find_content(project, mail):
     patchbuf = None
     commentbuf = ''
@@ -157,15 +164,27 @@
             continue
 
         payload = part.get_payload(decode=True)
-        charset = part.get_content_charset()
         subtype = part.get_content_subtype()
 
-        # if we don't have a charset, assume utf-8
-        if charset is None:
-            charset = 'utf-8'
-
         if not isinstance(payload, unicode):
-            payload = unicode(payload, charset)
+            charset = part.get_content_charset()
+
+            # If there is no charset or if it is unknown, then try some common
+            # charsets before we fail.
+            if charset is None or charset == 'x-unknown':
+                try_charsets = ['utf-8', 'windows-1252', 'ascii', 'iso-8859-1']
+            else:
+                try_charsets = [charset]
+
+            for cset in try_charsets:
+                decoded_payload = try_decode(payload, cset)
+                if decoded_payload is not None:
+                    break
+            payload = decoded_payload
+
+            # Could not find a valid decoded payload.  Fail.
+            if payload is None:
+                return (None, None)
 
         if subtype in ['x-patch', 'x-diff']:
             patchbuf = payload
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