Write data into socket with payload zero-copy

PR #134
Fixes #133

cheroot/_compat.py

@@ -65,3 +65,14 @@ def assert_native(n):
     """
     if not isinstance(n, str):
         raise TypeError('n must be a native str (got %s)' % type(n).__name__)
+
+
+if six.PY3:
+    """Python 3 has memoryview builtin."""
+    # Python 2.7 has it backported, but socket.write() does
+    # str(memoryview(b'0' * 100)) -> <memory at 0x7fb6913a5588>
+    # instead of accessing it correctly.
+    memoryview = memoryview
+else:
+    """Link memoryview to buffer under Python 2."""
+    memoryview = buffer  # noqa: F821

cheroot/makefile.py

@@ -15,6 +15,7 @@
 import six
 
 from . import errors
+from ._compat import memoryview
 
 
 class BufferedWriter(io.BufferedWriter):
@@ -64,10 +65,12 @@ def _drop(self):
 
     def write(self, data):
         """Sendall for non-blocking sockets."""
-        while data:
+        bytes_sent = 0
+        data_mv = memoryview(data)
+        payload_size = len(data_mv)
+        while bytes_sent < payload_size:
             try:
-                bytes_sent = self.send(data)
-                data = data[bytes_sent:]
+                bytes_sent += self.send(data_mv[bytes_sent:])
             except socket.error as e:
                 if e.args[0] not in errors.socket_errors_nonblocking:
                     raise