Check calculated value from binary.

binmap/__init__.py

@@ -178,6 +178,12 @@ def enumfield(
     return dataclasses.field(default=default, metadata={"enum": enumclass})
 
 
+    """
+    Field generator function for calculated fields
+
+    :param Callable function: function that calculates the field.
+    :return: dataclass field
+    """
 def calculatedfield(function: Callable) -> dataclasses.Field:
     return dataclasses.field(default=0, metadata={"function": function})
 
@@ -285,5 +291,8 @@ def frombytes(self, value: bytes):
             elif "autolength" in self.__datafieldsmap[name].metadata:
                 if arg != getattr(self, name):
                     raise ValueError("Length doesn't match")
+            elif "function" in self.__datafieldsmap[name].metadata:
+                if arg != self.__datafieldsmap[name].metadata["function"](self):
+                    raise ValueError("Wrong calculated value")
             else:
                 setattr(self, name, arg)

tests/test_binmap.py

@@ -596,7 +596,7 @@ class CalculatedField(binmap.BinmapDataclass):
     temp: types.signedchar = 0
     hum: types.unsignedchar = 0
 
-    def chk(self):
+    def chk(self) -> types.unsignedchar:
         return (self.temp + self.hum) & 0xFF
 
     checksum: types.unsignedchar = binmap.calculatedfield(chk)
@@ -610,3 +610,13 @@ def test_calculated_field(self):
 
         assert cf.checksum == 239
         assert bytes(cf) == b"\xe5\x0a\xef"
+
+    def test_calculated_field_binary(self):
+        cf = CalculatedField(b"\xe2\x12\xf4")
+        assert cf.temp == -30
+        assert cf.hum == 18
+        assert cf.checksum == 244
+
+        with pytest.raises(ValueError) as excinfo:
+            CalculatedField(b"\xe4\x18\x00")
+        assert "Wrong calculated value" in str(excinfo)