Handle read() returning None on a non-blocking socket

cheroot/makefile.py

@@ -46,7 +46,11 @@ def __init__(self, sock, mode='r', bufsize=io.DEFAULT_BUFFER_SIZE):
     def read(self, *args, **kwargs):
         """Capture bytes read."""
         val = super().read(*args, **kwargs)
-        self.bytes_read += len(val)
+        # A non-blocking socket with nothing available yet can make the
+        # underlying BufferedReader return None instead of b''. That's
+        # documented io.RawIOBase behavior, so don't choke on it here.
+        if val is not None:
+            self.bytes_read += len(val)
         return val
 
     def has_data(self):

cheroot/test/test_makefile.py

@@ -1,5 +1,7 @@
 """Tests for :py:mod:`cheroot.makefile`."""
 
+import errno
+
 from cheroot import makefile
 
 
@@ -9,9 +11,12 @@ class MockSocket:
     def __init__(self):
         """Initialize :py:class:`MockSocket`."""
         self.messages = []
+        self.would_block = False
 
     def recv_into(self, buf):
         """Simulate ``recv_into`` for Python 3."""
+        if self.would_block:
+            raise BlockingIOError(errno.EWOULDBLOCK, 'would block')
         if not self.messages:
             return 0
         msg = self.messages.pop(0)
@@ -44,6 +49,20 @@ def test_bytes_read():
     assert rfile.bytes_read == 3
 
 
+def test_read_on_nonblocking_socket_with_no_data():
+    """Reader should return ``None``, not crash, if nothing is available yet.
+
+    A non-blocking socket's ``read()`` can return ``None`` per the
+    documented ``io.RawIOBase`` contract when no data is available; this
+    used to blow up on ``len(None)``. Ref: cherrypy/cheroot#278
+    """
+    sock = MockSocket()
+    sock.would_block = True
+    rfile = makefile.MakeFile(sock, 'r')
+    assert rfile.read(256) is None
+    assert rfile.bytes_read == 0
+
+
 def test_bytes_written():
     """Writer should capture bytes written."""
     sock = MockSocket()