rtu_framer: fix processing of incomplete frames (#466)

* rtu_framer: fix processing of incomplete frames

* rtu_framer: fix test case

pymodbus/framer/rtu_framer.py

@@ -137,7 +137,13 @@ def isFrameReady(self):
 
         :returns: True if ready, False otherwise
         """
-        return len(self._buffer) > self._hsize
+        if len(self._buffer) > self._hsize:
+            if not self._header:
+                self.populateHeader()
+
+            return self._header and len(self._buffer) >= self._header['len']
+        else:
+            return False
 
     def populateHeader(self, data=None):
         """

test/test_framers.py

@@ -88,7 +88,13 @@ def test_reset_framer(rtu_framer, data):
     assert rtu_framer._buffer == b''
 
 
-@pytest.mark.parametrize("data", [(b'', False), (b'abcd', True)])
+@pytest.mark.parametrize("data", [
+    (b'', False),
+    (b'\x11\x03\x06', False),
+    (b'\x11\x03\x06\xAE\x41\x56\x52\x43\x40\x49', False),
+    (b'\x11\x03\x06\xAE\x41\x56\x52\x43\x40\x49\xAD', True),
+    (b'\x11\x03\x06\xAE\x41\x56\x52\x43\x40\x49\xAD\xAB\xCD', True)
+])
 def test_is_frame_ready(rtu_framer, data):
     data, expected = data
     rtu_framer._buffer = data
@@ -185,4 +191,4 @@ def test_decode_ascii_data(ascii_framer, data):
         assert data.get("unit") == 1
         assert data.get("fcode") == 1
     else:
-        assert not data
+        assert not data