diff --git a/serve.py b/serve.py
index 087bc1a..97aa379 100755
--- a/serve.py
+++ b/serve.py
@@ -8,6 +8,7 @@ import uuid
 import logging.config
 import argparse
 from concurrent.futures import ThreadPoolExecutor
+import mimetypes
 
 # user installed libraries
 import tornado.ioloop
@@ -92,10 +93,12 @@ class LoginHandler(BaseHandler):
 class LogoutHandler(BaseHandler):
     @tornado.web.authenticated
     def get(self):
-        self.learn.logout(self.current_user)
         self.clear_cookie('user')
         self.redirect(self.get_argument('next', '/'))
 
+    def on_finish(self):
+        self.learn.logout(self.current_user)
+
 # ----------------------------------------------------------------------------
 class ChangePasswordHandler(BaseHandler):
     @tornado.web.authenticated
@@ -159,6 +162,7 @@ class FileHandler(BaseHandler):
         uid = self.current_user
         public_dir = self.learn.get_current_public_dir(uid)
         filepath = path.expanduser(path.join(public_dir, filename))
+
         try:
             f = open(filepath, 'rb')
         except FileNotFoundError:
@@ -166,6 +170,11 @@ class FileHandler(BaseHandler):
         except PermissionError:
             logging.error(f'No permission: {filepath}')
         else:
+            content_type = mimetypes.guess_type(filename)
+            self.set_header("Content-Type", content_type[0])
+
+            # divide the file into chunks and write one chunk at a time, so
+            # that the write does not block the ioloop for very long.
             with f:
                 chunk = f.read(self.chunk_size)
                 while chunk:
@@ -173,12 +182,11 @@ class FileHandler(BaseHandler):
                         self.write(chunk)   # write the cunk to response
                         await self.flush()  # flush the current chunk to socket
                     except iostream.StreamClosedError:
-                        # client closed the connection
-                        break
+                        break  # client closed the connection
                     finally:
                         del chunk
                         await gen.sleep(0.000000001) # 1 nanosecond (hack)
-                        # in tornnado 5.0 use `await asyncio.sleep(0)` instead
+                        # FIXME in the upcomming tornado 5.0 use `await asyncio.sleep(0)` instead
                     chunk = f.read(self.chunk_size)
 
 
--
libgit2 0.21.2