Fixes #7 - added MemProtocol

src/aiofm/protocols.py

@@ -155,14 +155,20 @@ async def ls(self, path: Union[str, PurePath], pattern: str = None, *args, **kwa
 
     @asynccontextmanager
     async def open(self, path: Union[str, PurePath], *args, **kwargs):
-        mode = kwargs.get('mode', args[0] if len(args) else 'r')
+        mode = kwargs.pop('mode', args[0] if len(args) else 'r')
 
         try:
-            f = self._get_tree_item(self.tree, path)
-            io_class = ContextualBytesIO if 'b' in mode else ContextualStringIO
-            f = io_class(f, *args, **kwargs)
+            item = self._get_tree_item(self.tree, path)
+
+            if 'b' in mode:
+                f = ContextualBytesIO(item)
+            else:
+                f = ContextualStringIO(item.decode(kwargs.get('encoding', 'utf-8')))
 
             yield f
+
+            if 'w' in mode:
+                self._set_tree_item(self.tree, path, f.getvalue())
         except FileNotFoundError:
             if 'w' in mode or 'a' in mode:
                 f = ContextualStringIO(None, *args, **kwargs)

tests/aiofm/test_mem_protocol.py

@@ -371,6 +371,27 @@ async def test_open_existing_file_for_read():
     fs = MemProtocol()
     fs.tree = {'/': {'tmp': {'xxx': {}, 'a.txt': b'data data data'}}}
 
-    with pytest.raises(FileNotFoundError):
-        async with fs.open('/tmp/a.txt') as f:
-            assert f.readall() == 'data data data'
+    async with fs.open('/tmp/a.txt') as f:
+        assert f.read() == 'data data data'
+
+
+@pytest.mark.asyncio
+async def test_unclosed_file_does_not_change_fs():
+    fs = MemProtocol()
+    fs.tree = {'/': {'tmp': {'xxx': {}, 'a.txt': b'data data data'}}}
+
+    async with fs.open('/tmp/a.txt', mode='w') as f:
+        f.write('TEST TEST TEST')
+
+        assert fs.tree['/']['tmp']['a.txt'] == b'data data data'
+
+
+@pytest.mark.asyncio
+async def test_closed_file_changes_fs():
+    fs = MemProtocol()
+    fs.tree = {'/': {'tmp': {'xxx': {}, 'a.txt': b'data data data'}}}
+
+    async with fs.open('/tmp/a.txt', mode='w') as f:
+        f.write('TEST TEST TEST')
+
+    assert fs.tree['/']['tmp']['a.txt'] == b'TEST TEST TEST'