Save without atomic writing and configuration (fix #739)

notebook/services/contents/fileio.py

@@ -22,6 +22,8 @@ import nbformat
 
 from ipython_genutils.py3compat import str_to_unicode
 
+from traitlets.config import Configurable
+from traitlets import Bool
 
 def copy2_safe(src, dst, log=None):
     """copy src to dst
@@ -39,24 +41,24 @@ def copy2_safe(src, dst, log=None):
 @contextmanager
 def atomic_writing(path, text=True, encoding='utf-8', log=None, **kwargs):
     """Context manager to write to a file only if the entire write is successful.
-    
+
     This works by copying the previous file contents to a temporary file in the
     same directory, and renaming that file back to the target if the context
     exits with an error. If the context is successful, the new data is synced to
     disk and the temporary file is removed.
-    
+
     Parameters
     ----------
     path : str
       The target file to write to.
-     
+
     text : bool, optional
       Whether to open the file in text mode (i.e. to write unicode). Default is
       True.
-    
+
     encoding : str, optional
       The encoding to use for files opened in text mode. Default is UTF-8.
-     
+
     **kwargs
       Passed to :func:`io.open`.
     """
@@ -100,7 +102,55 @@ def atomic_writing(path, text=True, encoding='utf-8', log=None, **kwargs):
         os.remove(tmp_path)
 
 
-class FileManagerMixin(object):
+
+@contextmanager
+def _simple_writing(path, text=True, encoding='utf-8', **kwargs):
+    """Context manager to write file without doing atomic writing
+    ( for weird filesystem eg: nfs).
+
+    Parameters
+    ----------
+    path : str
+      The target file to write to.
+
+    text : bool, optional
+      Whether to open the file in text mode (i.e. to write unicode). Default is
+      True.
+
+    encoding : str, optional
+      The encoding to use for files opened in text mode. Default is UTF-8.
+
+    **kwargs
+      Passed to :func:`io.open`.
+    """
+    # realpath doesn't work on Windows: http://bugs.python.org/issue9949
+    # Luckily, we only need to resolve the file itself being a symlink, not
+    # any of its directories, so this will suffice:
+    if os.path.islink(path):
+        path = os.path.join(os.path.dirname(path), os.readlink(path))
+
+    if text:
+        # Make sure that text files have Unix linefeeds by default
+        kwargs.setdefault('newline', '\n')
+        fileobj = io.open(path, 'w', encoding=encoding, **kwargs)
+    else:
+        fileobj = io.open(path, 'wb', **kwargs)
+
+    try:
+        yield fileobj
+    except:
+        fileobj.close()
+        raise
+
+    # Flush to disk
+    fileobj.flush()
+    os.fsync(fileobj.fileno())
+    fileobj.close()
+
+
+
+
+class FileManagerMixin(Configurable):
     """
     Mixin for ContentsAPI classes that interact with the filesystem.
 
@@ -119,6 +169,9 @@ class FileManagerMixin(object):
     log : logging.Logger
     """
 
+    use_atomic_writing = Bool(True, config=True, help="""flag to deactivate
+            atomic writing on slow (like networked) file system.""")
+
     @contextmanager
     def open(self, os_path, *args, **kwargs):
         """wrapper around io.open that turns permission errors into 403"""
@@ -130,8 +183,12 @@ class FileManagerMixin(object):
     def atomic_writing(self, os_path, *args, **kwargs):
         """wrapper around atomic_writing that turns permission errors to 403"""
         with self.perm_to_403(os_path):
-            with atomic_writing(os_path, *args, log=self.log, **kwargs) as f:
-                yield f
+            if self.use_atomic_writing:
+                with atomic_writing(os_path, *args, log=self.log, **kwargs) as f:
+                    yield f
+            else:
+                with simple_writing(os_path, *args, log=self.log, **kwargs) as f:
+                    yield f
 
     @contextmanager
     def perm_to_403(self, os_path=''):