[FIX] ir_mail_server: make attachment filename work properly on GMail

The default Python encoding for mail header parameters
is RFC2231, which produces headers of the form:
  Content-Disposition: attachment; filename*="utf-8abcd%C3%A9.pdf"
This works fine for e.g. Thunderbird but on GMail
such headers appear as `noname`.
We are therefore falling back to RFC2047 encoding
which will instead give something like:
  Content-Disposition: attachment; filename="=?utf-8?b?UmVxdWVzdCf?="

bzr revid: odo@openerp.com-20120316130803-zo4fwuk7h6bq6k54

openerp/addons/base/ir/ir_mail_server.py

@@ -22,6 +22,7 @@
 from email.MIMEText import MIMEText
 from email.MIMEBase import MIMEBase
 from email.MIMEMultipart import MIMEMultipart
+from email.Charset import Charset
 from email.Header import Header
 from email.Utils import formatdate, make_msgid, COMMASPACE
 from email import Encoders
@@ -97,6 +98,26 @@ def encode_header(header_text):
     return header_text_ascii if header_text_ascii\
          else Header(header_text_utf8, 'utf-8')
 
+def encode_header_param(param_text):
+    """Returns an appropriate RFC2047 encoded representation of the given
+       header parameter value, suitable for direct assignation as the
+       param value (e.g. via Message.set_param() or Message.add_header())
+       RFC2822 assumes that headers contain only 7-bit characters,
+       so we ensure it is the case, using RFC2047 encoding when needed.
+
+       :param param_text: unicode or utf-8 encoded string with header value
+       :rtype: string
+       :return: if ``param_text`` represents a plain ASCII string,
+                return the same 7-bit string, otherwise returns an
+                ASCII string containing the RFC2047 encoded text.
+    """
+    # For details see the encode_header() method that uses the same logic
+    if not param_text: return ""
+    param_text_utf8 = tools.ustr(param_text).encode('utf-8')
+    param_text_ascii = try_coerce_ascii(param_text_utf8)
+    return param_text_ascii if param_text_ascii\
+         else Charset('utf8').header_encode(param_text_utf8)
+
 name_with_email_pattern = re.compile(r'("[^<@>]+")\s*<([^ ,<@]+@[^> ,]+)>')
 address_pattern = re.compile(r'([^ ,<@]+@[^> ,]+)')
 
@@ -334,14 +355,16 @@ class ir_mail_server(osv.osv):
 
         if attachments:
             for (fname, fcontent) in attachments:
-                filename_utf8 = ustr(fname).encode('utf-8')
+                filename_rfc2047 = encode_header_param(fname)
                 part = MIMEBase('application', "octet-stream")
+
+                # The default RFC2231 encoding of Message.add_header() works in Thunderbird but not GMail
+                # so we fix it by using RFC2047 encoding for the filename instead.
+                part.set_param('name', filename_rfc2047)
+                part.add_header('Content-Disposition', 'attachment', filename=filename_rfc2047)
+
                 part.set_payload(fcontent)
                 Encoders.encode_base64(part)
-                # Force RFC2231 encoding for attachment filename
-                # See email.message.Message.add_header doc
-                part.add_header('Content-Disposition', 'attachment',
-                                filename=('utf-8',None,filename_utf8)) 
                 msg.attach(part)
         return msg