Adding utilities to Base class.

Moving the quoted boundary fix to the Base class so that it can be used
by any subclass that needs to read an email.  Adding another utility to
extract message-id from a raw email.

offlineimap/folder/Maildir.py

@@ -226,45 +226,6 @@ class MaildirFolder(BaseFolder):
                         retval[uid] = date_excludees[uid]
         return retval
 
-    def _quote_boundary_fix(self, raw_msg_bytes):
-        """Modify a raw message to quote the boundary separator for multipart messages.
-
-        This function quotes only the first occurrence of the boundary field in
-        the email header, and quotes any boundary value.  Improperly quoted
-        boundary fields can give the internal python email library issues.
-
-        :returns: The raw byte stream containing the quoted boundary
-        """
-        # Use re.split to extract just the header, and search for the boundary in
-        # the context-type header and extract just the boundary and characters per
-        # RFC 2046 ( see https://tools.ietf.org/html/rfc2046#section-5.1.1 )
-        # We don't cap the length to 70 characters, because we are just trying to
-        # soft fix this message to resolve the python library looking for properly
-        # quoted boundaries.
-        try: boundary_field = \
-            re.search(b"content-type:.*(boundary=[\"]?[A-Za-z0-9'()+_,-./:=? ]+[\"]?)",
-              re.split(b'[\r]?\n[\r]?\n', raw_msg_bytes)[0],
-              (re.IGNORECASE|re.DOTALL)).group(1)
-        except AttributeError:
-            # No match
-            return raw_msg_bytes
-        # get the boundary field, and strip off any trailing ws (against RFC rules, leading ws is OK)
-        # if it was already quoted, well then there was nothing to fix
-        boundary, value = boundary_field.split(b'=', 1)
-        value = value.rstrip()
-        # ord(b'"') == 34
-        if value[0] == value[-1] == 34:
-            # Sanity Check - Do not requote if already quoted.
-            # A quoted boundary was the end goal so return the original
-            #
-            # No need to worry about if the original email did something like:
-            # boundary="ahahah  " as the email library will trim the ws for us
-            return raw_msg_bytes
-        else:
-            new_field = b''.join([boundary, b'="', value, b'"'])
-            return(raw_msg_bytes.replace(boundary_field, new_field, 1))
-
-
     # Interface from BaseFolder
     def quickchanged(self, statusfolder):
         """Returns True if the Maildir has changed