Raising ReadError more consistently when reading off end of bitstring.

Should fix Bug #325.

bitstring/bits.py

@@ -173,7 +173,7 @@ def __getattr__(self, attribute: str) -> Any:
             raise AttributeError(f"'{self.__class__.__name__}' object has no attribute '{attribute}'.")
         if d.bitlength is not None and len(self) != d.bitlength:
             raise ValueError(f"bitstring length {len(self)} doesn't match length {d.bitlength} of property '{attribute}'.")
-        return d.read_fn(self, 0)
+        return d.get_fn(self)
 
     def __iter__(self) -> Iterable[bool]:
         return iter(self._bitstore)

bitstring/dtypes.py

@@ -296,6 +296,8 @@ def read_fn(bs, start):
                     return self.get_fn(bs[start:start + self.allowed_lengths.values[0]])
             else:
                 def read_fn(bs, start, length):
+                    if len(bs) < start + length:
+                        raise bitstring.ReadError(f"Needed a length of at least {length} bits, but only {len(bs) - start} bits were available.")
                     return self.get_fn(bs[start:start + length])
             self.read_fn = read_fn
         else:

tests/test_constbitstream.py

@@ -263,3 +263,12 @@ def test_windows_file_lock_bug():
         if platform.system() == 'Windows':
             # Expected failure. See bug #308
             pass
+
+def test_readerrors():
+    s = CBS('0b110')
+    s.read(3)
+    with pytest.raises(bitstring.ReadError):
+        _ = s.read(1)
+    s.pos = 1
+    with pytest.raises(bitstring.ReadError):
+        _ = s.read('u3')