Cleanup charset handling

- avoid copying the whole dict in _part_response
- avoid decode-encode-decode dance in get_message_html

maildump/web.py

@@ -99,10 +99,11 @@ def _part_url(part):
 
 def _part_response(part, body=None, charset=None):
     charset = charset or part['charset'] or 'utf-8'
+    if body is None:
+        body = part['body']
     if charset != 'utf-8':
-        part = dict(part)
-        part['body'] = part['body'].decode(charset).encode('utf-8')
-    io = StringIO(part['body'] if body is None else body)
+        body = body.decode(charset).encode('utf-8')
+    io = StringIO(body)
     io.seek(0)
     response = send_file(io, part['type'], part['is_attachment'], part['filename'])
     response.charset = charset
@@ -159,10 +160,7 @@ def get_message_html(message_id):
     if not part:
         return 404, 'part does not exist'
     charset = part['charset'] or 'utf-8'
-    if charset != 'utf-8':
-        part = dict(part)
-        part['body'] = part['body'].decode(charset).encode('utf-8')
-    soup = bs4.BeautifulSoup(part['body'].decode('utf-8'), 'html5lib')
+    soup = bs4.BeautifulSoup(part['body'].decode(charset), 'html5lib')
     _fix_cid_links(soup, message_id)
     return _part_response(part, str(soup), 'utf-8')