Two fixes

Don't send Content-Length header if not needed. (see #480)
Always use build_header... (see #473)

modoboa/extensions/webmail/views.py

@@ -1,6 +1,6 @@
 # coding: utf-8
 import os
-from rfc6266 import build_header
+from rfc6266 import build_header, parse_headers
 from django.conf import settings
 from django.http import HttpResponse
 from django.template import Template, Context
@@ -29,6 +29,14 @@ from templatetags import webextras
 def getattachment(request):
     """Fetch a message attachment
 
+    The tricky part here consists in properly format the
+    *Content-Disposition* header. We use the rfc6266 package to encode
+    headers according to RFC5987 and RFC6266.
+
+    Even if the header received from Dovecot is already encoded, we
+    decode and re-encode it to make sure it uses UTF-8. IE doesn't
+    support the ISO-8859-1 encoding even if it is allowed by RFCs.
+
     FIXME: par manque de caching, le bodystructure du message est
     redemandé pour accéder aux headers de cette pièce jointe.
 
@@ -52,15 +60,20 @@ def getattachment(request):
         if type(disp[1][0]) != dict:
             atype, fieldname, filename = disp[0], disp[1][0], disp[1][1]
         else:
-            atype, fieldname, filename = disp[0], disp[1][0]['struct'][0], disp[1][0]['struct'][1]
+            atype, fieldname, filename = \
+                disp[0], disp[1][0]['struct'][0], disp[1][0]['struct'][1]
         if fieldname.endswith('*'):
             cd = '%s; %s=%s' % (atype, fieldname, filename)
         else:
             cd = '%s; %s="%s"' % (atype, fieldname, filename)
+        fname = parse_headers(cd).filename_unsafe
     else:
-        cd = build_header(request.GET["fname"])
-    resp["Content-Disposition"] = cd
-    resp["Content-Length"] = partdef["size"]
+        fname = request.GET.get("fname", None)
+        if fname is None:
+            raise WebmailError(_("Invalid request"))
+    resp["Content-Disposition"] = build_header(fname)
+    if int(partdef["size"]) < 200:
+        resp["Content-Length"] = partdef["size"]
     return resp