Merge pull request #749 from matan1008/patch/allowing-seek-to-same-po…

…sition-in-restreamed

Patch Optional() when restreamed issue

construct/lib/bitstream.py

@@ -54,7 +54,10 @@ def close(self):
             raise ValueError("closing stream but %d unwritten bytes remain, %d is encoded unit" % (len(self.wbuffer), self.encoderunit))
 
     def seek(self, at, whence=0):
-        raise IOError
+        if whence == 0 and at == self.sincereadwritten:
+            pass
+        else:
+            raise IOError
 
     def seekable(self):
         return False

tests/test_core.py

@@ -758,10 +758,29 @@ def test_optional():
     assert d.parse(b"\x01\x00\x00\x00") == 1
     assert d.build(1) == b"\x01\x00\x00\x00"
     assert d.parse(b"???") == None
+    assert d.parse(b"") == None
     assert d.build(None) == b""
     assert raises(d.sizeof) == SizeofError
 
-def test_select_buildfromnone():
+def test_optional_in_struct_issue_747():
+    d = Struct("field" / Optional(Int32ul))
+    assert d.parse(b"\x01\x00\x00\x00") == {"field": 1}
+    assert d.build({"field": 1}) == b"\x01\x00\x00\x00"
+    assert d.parse(b"???") == {"field": None}
+    assert d.build({"field": None}) == b""
+    assert d.parse(b"") == {"field": None}
+    assert raises(d.sizeof) == SizeofError
+
+def test_optional_in_bit_struct_issue_747():
+    d = BitStruct("field" / Optional(Octet))
+    assert d.parse(b"\x01") == {"field": 1}
+    assert d.build({"field": 1}) == b"\x01"
+    assert d.parse(b"???") == {"field": ord("?")}
+    assert d.build({"field": None}) == b""
+    assert d.parse(b"") == {"field": None}
+    assert raises(d.sizeof) == SizeofError
+
+def test_select_buildfromnone_issue_747():
     d = Struct("select" / Select(Int32ub, Default(Bytes(3), b"abc")))
     assert d.parse(b"def") == dict(select=b"def")
     assert d.parse(b"\x01\x02\x03\x04") == dict(select=0x01020304)