DEV: Separate FileCheckpointManager and GenericFileCheckpointManager.

- Adds a `GenericCheckpointMixin` as a helper for implementing the two
  boundary-traversing Checkpoint API methods, `create_checkpoint` and
  `restore_checkpoint`.

- `GenericFileCheckpointManager` is implemented as a subclass of
  `FileCheckpointManager` using `GenericCheckpointMixin`.  Note that
  this is the safe subtyping relationship because of method
  signature *contra*variance: `FileCheckpointManager` accepts
  `FileContentsManager` in its method signatures type, whereas
  `GenericFileCheckpointManager` accepts any `ContentsManager`.

- Moved Checkpoint-related classes to their own files.

IPython/html/services/contents/checkpoints.py

@@ -0,0 +1,112 b''
+"""
+Classes for managing Checkpoints.
+"""
+
+# Copyright (c) IPython Development Team.
+# Distributed under the terms of the Modified BSD License.
+
+from IPython.config.configurable import LoggingConfigurable
+
+
+class CheckpointManager(LoggingConfigurable):
+    """
+    Base class for managing checkpoints for a ContentsManager.
+
+    Subclasses are required to implement:
+
+    create_checkpoint(self, contents_mgr, path)
+    restore_checkpoint(self, contents_mgr, checkpoint_id, path)
+    rename_checkpoint(self, checkpoint_id, old_path, new_path)
+    delete_checkpoint(self, checkpoint_id, path)
+    list_checkpoints(self, path)
+    """
+    def create_checkpoint(self, contents_mgr, path):
+        """Create a checkpoint."""
+        raise NotImplementedError("must be implemented in a subclass")
+
+    def restore_checkpoint(self, contents_mgr, checkpoint_id, path):
+        """Restore a checkpoint"""
+        raise NotImplementedError("must be implemented in a subclass")
+
+    def rename_checkpoint(self, checkpoint_id, old_path, new_path):
+        """Rename a single checkpoint from old_path to new_path."""
+        raise NotImplementedError("must be implemented in a subclass")
+
+    def delete_checkpoint(self, checkpoint_id, path):
+        """delete a checkpoint for a file"""
+        raise NotImplementedError("must be implemented in a subclass")
+
+    def list_checkpoints(self, path):
+        """Return a list of checkpoints for a given file"""
+        raise NotImplementedError("must be implemented in a subclass")
+
+    def rename_all_checkpoints(self, old_path, new_path):
+        """Rename all checkpoints for old_path to new_path."""
+        for cp in self.list_checkpoints(old_path):
+            self.rename_checkpoint(cp['id'], old_path, new_path)
+
+    def delete_all_checkpoints(self, path):
+        """Delete all checkpoints for the given path."""
+        for checkpoint in self.list_checkpoints(path):
+            self.delete_checkpoint(checkpoint['id'], path)
+
+
+class GenericCheckpointMixin(object):
+    """
+    Helper for creating CheckpointManagers that can be used with any
+    ContentsManager.
+
+    Provides an implementation of `create_checkpoint` and `restore_checkpoint`
+    in terms of the following operations:
+
+    create_file_checkpoint(self, content, format, path)
+    create_notebook_checkpoint(self, nb, path)
+    get_checkpoint(self, checkpoint_id, path, type)
+
+    **Any** valid CheckpointManager implementation should also be valid when
+    this mixin is applied.
+    """
+
+    def create_checkpoint(self, contents_mgr, path):
+        model = contents_mgr.get(path, content=True)
+        type = model['type']
+        if type == 'notebook':
+            return self.create_notebook_checkpoint(
+                model['content'],
+                path,
+            )
+        elif type == 'file':
+            return self.create_file_checkpoint(
+                model['content'],
+                model['format'],
+                path,
+            )
+
+    def restore_checkpoint(self, contents_mgr, checkpoint_id, path):
+        """Restore a checkpoint."""
+        type = contents_mgr.get(path, content=False)['type']
+        model = self.get_checkpoint(checkpoint_id, path, type)
+        contents_mgr.save(model, path)
+
+    # Required Methods
+    def create_file_checkpoint(self, content, format, path):
+        """Create a checkpoint of the current state of a file
+
+        Returns a checkpoint model for the new checkpoint.
+        """
+        raise NotImplementedError("must be implemented in a subclass")
+
+    def create_notebook_checkpoint(self, nb, path):
+        """Create a checkpoint of the current state of a file
+
+        Returns a checkpoint model for the new checkpoint.
+        """
+        raise NotImplementedError("must be implemented in a subclass")
+
+    def get_checkpoint(self, checkpoint_id, path, type):
+        """Get the content of a checkpoint.
+
+        Returns an unvalidated model with the same structure as
+        the return value of ContentsManager.get
+        """
+        raise NotImplementedError("must be implemented in a subclass")

IPython/html/services/contents/filecheckpoints.py

@@ -0,0 +1,198 b''
+"""
+File-based CheckpointManagers.
+"""
+import os
+import shutil
+
+from tornado.web import HTTPError
+
+from .checkpoints import (
+    CheckpointManager,
+    GenericCheckpointMixin,
+)
+from .fileio import FileManagerMixin
+
+from IPython.utils import tz
+from IPython.utils.path import ensure_dir_exists
+from IPython.utils.py3compat import getcwd
+from IPython.utils.traitlets import Unicode
+
+
+class FileCheckpointManager(FileManagerMixin, CheckpointManager):
+    """
+    A CheckpointManager that caches checkpoints for files in adjacent
+    directories.
+
+    Only works with FileContentsManager.  Use GenericFileCheckpointManager if
+    you want file-based checkpoints with another ContentsManager.
+    """
+
+    checkpoint_dir = Unicode(
+        '.ipynb_checkpoints',
+        config=True,
+        help="""The directory name in which to keep file checkpoints
+
+        This is a path relative to the file's own directory.
+
+        By default, it is .ipynb_checkpoints
+        """,
+    )
+
+    root_dir = Unicode(config=True)
+
+    def _root_dir_default(self):
+        try:
+            return self.parent.root_dir
+        except AttributeError:
+            return getcwd()
+
+    # ContentsManager-dependent checkpoint API
+    def create_checkpoint(self, contents_mgr, path):
+        """Create a checkpoint."""
+        checkpoint_id = u'checkpoint'
+        src_path = contents_mgr._get_os_path(path)
+        dest_path = self.checkpoint_path(checkpoint_id, path)
+        self._copy(src_path, dest_path)
+        return self.checkpoint_model(checkpoint_id, dest_path)
+
+    def restore_checkpoint(self, contents_mgr, checkpoint_id, path):
+        """Restore a checkpoint."""
+        src_path = self.checkpoint_path(checkpoint_id, path)
+        dest_path = contents_mgr._get_os_path(path)
+        self._copy(src_path, dest_path)
+
+    # ContentsManager-independent checkpoint API
+    def rename_checkpoint(self, checkpoint_id, old_path, new_path):
+        """Rename a checkpoint from old_path to new_path."""
+        old_cp_path = self.checkpoint_path(checkpoint_id, old_path)
+        new_cp_path = self.checkpoint_path(checkpoint_id, new_path)
+        if os.path.isfile(old_cp_path):
+            self.log.debug(
+                "Renaming checkpoint %s -> %s",
+                old_cp_path,
+                new_cp_path,
+            )
+            with self.perm_to_403():
+                shutil.move(old_cp_path, new_cp_path)
+
+    def delete_checkpoint(self, checkpoint_id, path):
+        """delete a file's checkpoint"""
+        path = path.strip('/')
+        cp_path = self.checkpoint_path(checkpoint_id, path)
+        if not os.path.isfile(cp_path):
+            self.no_such_checkpoint(path, checkpoint_id)
+
+        self.log.debug("unlinking %s", cp_path)
+        with self.perm_to_403():
+            os.unlink(cp_path)
+
+    def list_checkpoints(self, path):
+        """list the checkpoints for a given file
+
+        This contents manager currently only supports one checkpoint per file.
+        """
+        path = path.strip('/')
+        checkpoint_id = "checkpoint"
+        os_path = self.checkpoint_path(checkpoint_id, path)
+        if not os.path.isfile(os_path):
+            return []
+        else:
+            return [self.checkpoint_model(checkpoint_id, os_path)]
+
+    # Checkpoint-related utilities
+    def checkpoint_path(self, checkpoint_id, path):
+        """find the path to a checkpoint"""
+        path = path.strip('/')
+        parent, name = ('/' + path).rsplit('/', 1)
+        parent = parent.strip('/')
+        basename, ext = os.path.splitext(name)
+        filename = u"{name}-{checkpoint_id}{ext}".format(
+            name=basename,
+            checkpoint_id=checkpoint_id,
+            ext=ext,
+        )
+        os_path = self._get_os_path(path=parent)
+        cp_dir = os.path.join(os_path, self.checkpoint_dir)
+        with self.perm_to_403():
+            ensure_dir_exists(cp_dir)
+        cp_path = os.path.join(cp_dir, filename)
+        return cp_path
+
+    def checkpoint_model(self, checkpoint_id, os_path):
+        """construct the info dict for a given checkpoint"""
+        stats = os.stat(os_path)
+        last_modified = tz.utcfromtimestamp(stats.st_mtime)
+        info = dict(
+            id=checkpoint_id,
+            last_modified=last_modified,
+        )
+        return info
+
+    # Error Handling
+    def no_such_checkpoint(self, path, checkpoint_id):
+        raise HTTPError(
+            404,
+            u'Checkpoint does not exist: %s@%s' % (path, checkpoint_id)
+        )
+
+
+class GenericFileCheckpointManager(GenericCheckpointMixin,
+                                   FileCheckpointManager):
+    """
+    Local filesystem CheckpointManager that works with any conforming
+    ContentsManager.
+    """
+    def create_file_checkpoint(self, content, format, path):
+        """Create a checkpoint from the current content of a notebook."""
+        path = path.strip('/')
+        # only the one checkpoint ID:
+        checkpoint_id = u"checkpoint"
+        os_checkpoint_path = self.checkpoint_path(checkpoint_id, path)
+        self.log.debug("creating checkpoint for %s", path)
+        with self.perm_to_403():
+            self._save_file(os_checkpoint_path, content, format=format)
+
+        # return the checkpoint info
+        return self.checkpoint_model(checkpoint_id, os_checkpoint_path)
+
+    def create_notebook_checkpoint(self, nb, path):
+        """Create a checkpoint from the current content of a notebook."""
+        path = path.strip('/')
+        # only the one checkpoint ID:
+        checkpoint_id = u"checkpoint"
+        os_checkpoint_path = self.checkpoint_path(checkpoint_id, path)
+        self.log.debug("creating checkpoint for %s", path)
+        with self.perm_to_403():
+            self._save_notebook(os_checkpoint_path, nb)
+
+        # return the checkpoint info
+        return self.checkpoint_model(checkpoint_id, os_checkpoint_path)
+
+    def get_checkpoint(self, checkpoint_id, path, type):
+        """Get the content of a checkpoint.
+
+        Returns a model suitable for passing to ContentsManager.save.
+        """
+        path = path.strip('/')
+        self.log.info("restoring %s from checkpoint %s", path, checkpoint_id)
+        os_checkpoint_path = self.checkpoint_path(checkpoint_id, path)
+        if not os.path.isfile(os_checkpoint_path):
+            self.no_such_checkpoint(path, checkpoint_id)
+
+        if type == 'notebook':
+            return {
+                'type': type,
+                'content': self._read_notebook(
+                    os_checkpoint_path,
+                    as_version=4,
+                ),
+            }
+        elif type == 'file':
+            content, format = self._read_file(os_checkpoint_path, format=None)
+            return {
+                'type': type,
+                'content': content,
+                'format': format,
+            }
+        else:
+            raise HTTPError(500, u'Unexpected type %s' % type)

IPython/html/services/contents/fileio.py

@@ -0,0 +1,166 b''
+"""
+Utilities for file-based Contents/Checkpoints managers.
+"""
+
+# Copyright (c) IPython Development Team.
+# Distributed under the terms of the Modified BSD License.
+
+import base64
+from contextlib import contextmanager
+import errno
+import io
+import os
+import shutil
+
+from tornado.web import HTTPError
+
+from IPython.html.utils import (
+    to_api_path,
+    to_os_path,
+)
+from IPython import nbformat
+from IPython.utils.io import atomic_writing
+from IPython.utils.py3compat import str_to_unicode
+
+
+class FileManagerMixin(object):
+    """
+    Mixin for ContentsAPI classes that interact with the filesystem.
+
+    Provides facilities for reading, writing, and copying both notebooks and
+    generic files.
+
+    Shared by FileContentsManager and FileCheckpointManager.
+
+    Note
+    ----
+    Classes using this mixin must provide the following attributes:
+
+    root_dir : unicode
+        A directory against against which API-style paths are to be resolved.
+
+    log : logging.Logger
+    """
+
+    @contextmanager
+    def open(self, os_path, *args, **kwargs):
+        """wrapper around io.open that turns permission errors into 403"""
+        with self.perm_to_403(os_path):
+            with io.open(os_path, *args, **kwargs) as f:
+                yield f
+
+    @contextmanager
+    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, **kwargs) as f:
+                yield f
+
+    @contextmanager
+    def perm_to_403(self, os_path=''):
+        """context manager for turning permission errors into 403."""
+        try:
+            yield
+        except OSError as e:
+            if e.errno in {errno.EPERM, errno.EACCES}:
+                # make 403 error message without root prefix
+                # this may not work perfectly on unicode paths on Python 2,
+                # but nobody should be doing that anyway.
+                if not os_path:
+                    os_path = str_to_unicode(e.filename or 'unknown file')
+                path = to_api_path(os_path, root=self.root_dir)
+                raise HTTPError(403, u'Permission denied: %s' % path)
+            else:
+                raise
+
+    def _copy(self, src, dest):
+        """copy src to dest
+
+        like shutil.copy2, but log errors in copystat
+        """
+        shutil.copyfile(src, dest)
+        try:
+            shutil.copystat(src, dest)
+        except OSError:
+            self.log.debug("copystat on %s failed", dest, exc_info=True)
+
+    def _get_os_path(self, path):
+        """Given an API path, return its file system path.
+
+        Parameters
+        ----------
+        path : string
+            The relative API path to the named file.
+
+        Returns
+        -------
+        path : string
+            Native, absolute OS path to for a file.
+        """
+        return to_os_path(path, self.root_dir)
+
+    def _read_notebook(self, os_path, as_version=4):
+        """Read a notebook from an os path."""
+        with self.open(os_path, 'r', encoding='utf-8') as f:
+            try:
+                return nbformat.read(f, as_version=as_version)
+            except Exception as e:
+                raise HTTPError(
+                    400,
+                    u"Unreadable Notebook: %s %r" % (os_path, e),
+                )
+
+    def _save_notebook(self, os_path, nb):
+        """Save a notebook to an os_path."""
+        with self.atomic_writing(os_path, encoding='utf-8') as f:
+            nbformat.write(nb, f, version=nbformat.NO_CONVERT)
+
+    def _read_file(self, os_path, format):
+        """Read a non-notebook file.
+
+        os_path: The path to be read.
+        format:
+          If 'text', the contents will be decoded as UTF-8.
+          If 'base64', the raw bytes contents will be encoded as base64.
+          If not specified, try to decode as UTF-8, and fall back to base64
+        """
+        if not os.path.isfile(os_path):
+            raise HTTPError(400, "Cannot read non-file %s" % os_path)
+
+        with self.open(os_path, 'rb') as f:
+            bcontent = f.read()
+
+        if format is None or format == 'text':
+            # Try to interpret as unicode if format is unknown or if unicode
+            # was explicitly requested.
+            try:
+                return bcontent.decode('utf8'), 'text'
+            except UnicodeError:
+                if format == 'text':
+                    raise HTTPError(
+                        400,
+                        "%s is not UTF-8 encoded" % os_path,
+                        reason='bad format',
+                    )
+        return base64.encodestring(bcontent).decode('ascii'), 'base64'
+
+    def _save_file(self, os_path, content, format):
+        """Save content of a generic file."""
+        if format not in {'text', 'base64'}:
+            raise HTTPError(
+                400,
+                "Must specify format of file contents as 'text' or 'base64'",
+            )
+        try:
+            if format == 'text':
+                bcontent = content.encode('utf8')
+            else:
+                b64_bytes = content.encode('ascii')
+                bcontent = base64.decodestring(b64_bytes)
+        except Exception as e:
+            raise HTTPError(
+                400, u'Encoding error saving %s: %s' % (os_path, e)
+            )
+
+        with self.atomic_writing(os_path, text=False) as f:
+            f.write(bcontent)

IPython/html/services/contents/filemanager.py

@@ -3,9 +3,7 b''
 # Copyright (c) IPython Development Team.
 # Distributed under the terms of the Modified BSD License.
 
-import base64
-from contextlib import contextmanager
-import errno
+
 import io
 import os
 import shutil
@@ -13,25 +11,23 b' import mimetypes'
 
 from tornado import web
 
-from .manager import (
-    CheckpointManager,
-    ContentsManager,
-)
+from .filecheckpoints import FileCheckpointManager
+from .fileio import FileManagerMixin
+from .manager import ContentsManager
+
 from IPython import nbformat
-from IPython.utils.io import atomic_writing
 from IPython.utils.importstring import import_item
-from IPython.utils.path import ensure_dir_exists
 from IPython.utils.traitlets import Any, Unicode, Bool, TraitError
-from IPython.utils.py3compat import getcwd, string_types, str_to_unicode
+from IPython.utils.py3compat import getcwd, string_types
 from IPython.utils import tz
 from IPython.html.utils import (
     is_hidden,
     to_api_path,
-    to_os_path,
 )
 
 _script_exporter = None
 
+
 def _post_save_script(model, os_path, contents_manager, **kwargs):
     """convert notebooks to Python script after save with nbconvert
 
@@ -56,346 +52,6 b' def _post_save_script(model, os_path, contents_manager, **kwargs):'
         f.write(script)
 
 
-class FileManagerMixin(object):
-    """
-    Mixin for ContentsAPI classes that interact with the filesystem.
-
-    Provides facilities for reading, writing, and copying both notebooks and
-    generic files.
-
-    Shared by FileContentsManager and FileCheckpointManager.
-
-    Note
-    ----
-    Classes using this mixin must provide the following attributes:
-
-    root_dir : unicode
-        A directory against against which API-style paths are to be resolved.
-
-    log : logging.Logger
-    """
-
-    @contextmanager
-    def open(self, os_path, *args, **kwargs):
-        """wrapper around io.open that turns permission errors into 403"""
-        with self.perm_to_403(os_path):
-            with io.open(os_path, *args, **kwargs) as f:
-                yield f
-
-    @contextmanager
-    def atomic_writing(self, os_path, *args, **kwargs):
-        """wrapper around atomic_writing that turns permission errors into 403"""
-        with self.perm_to_403(os_path):
-            with atomic_writing(os_path, *args, **kwargs) as f:
-                yield f
-
-    @contextmanager
-    def perm_to_403(self, os_path=''):
-        """context manager for turning permission errors into 403."""
-        try:
-            yield
-        except OSError as e:
-            if e.errno in {errno.EPERM, errno.EACCES}:
-                # make 403 error message without root prefix
-                # this may not work perfectly on unicode paths on Python 2,
-                # but nobody should be doing that anyway.
-                if not os_path:
-                    os_path = str_to_unicode(e.filename or 'unknown file')
-                path = to_api_path(os_path, root=self.root_dir)
-                raise web.HTTPError(403, u'Permission denied: %s' % path)
-            else:
-                raise
-
-    def _copy(self, src, dest):
-        """copy src to dest
-
-        like shutil.copy2, but log errors in copystat
-        """
-        shutil.copyfile(src, dest)
-        try:
-            shutil.copystat(src, dest)
-        except OSError:
-            self.log.debug("copystat on %s failed", dest, exc_info=True)
-
-    def _get_os_path(self, path):
-        """Given an API path, return its file system path.
-
-        Parameters
-        ----------
-        path : string
-            The relative API path to the named file.
-
-        Returns
-        -------
-        path : string
-            Native, absolute OS path to for a file.
-        """
-        return to_os_path(path, self.root_dir)
-
-    def _read_notebook(self, os_path, as_version=4):
-        """Read a notebook from an os path."""
-        with self.open(os_path, 'r', encoding='utf-8') as f:
-            try:
-                return nbformat.read(f, as_version=as_version)
-            except Exception as e:
-                raise web.HTTPError(
-                    400,
-                    u"Unreadable Notebook: %s %r" % (os_path, e),
-                )
-
-    def _save_notebook(self, os_path, nb):
-        """Save a notebook to an os_path."""
-        with self.atomic_writing(os_path, encoding='utf-8') as f:
-            nbformat.write(nb, f, version=nbformat.NO_CONVERT)
-
-    def _read_file(self, os_path, format):
-        """Read a non-notebook file.
-
-        os_path: The path to be read.
-        format:
-          If 'text', the contents will be decoded as UTF-8.
-          If 'base64', the raw bytes contents will be encoded as base64.
-          If not specified, try to decode as UTF-8, and fall back to base64
-        """
-        if not os.path.isfile(os_path):
-            raise web.HTTPError(400, "Cannot read non-file %s" % os_path)
-
-        with self.open(os_path, 'rb') as f:
-            bcontent = f.read()
-
-        if format is None or format == 'text':
-            # Try to interpret as unicode if format is unknown or if unicode
-            # was explicitly requested.
-            try:
-                return bcontent.decode('utf8'), 'text'
-            except UnicodeError as e:
-                if format == 'text':
-                    raise web.HTTPError(
-                        400,
-                        "%s is not UTF-8 encoded" % os_path,
-                        reason='bad format',
-                    )
-        return base64.encodestring(bcontent).decode('ascii'), 'base64'
-
-    def _save_file(self, os_path, content, format):
-        """Save content of a generic file."""
-        if format not in {'text', 'base64'}:
-            raise web.HTTPError(
-                400,
-                "Must specify format of file contents as 'text' or 'base64'",
-            )
-        try:
-            if format == 'text':
-                bcontent = content.encode('utf8')
-            else:
-                b64_bytes = content.encode('ascii')
-                bcontent = base64.decodestring(b64_bytes)
-        except Exception as e:
-            raise web.HTTPError(400, u'Encoding error saving %s: %s' % (os_path, e))
-
-        with self.atomic_writing(os_path, text=False) as f:
-            f.write(bcontent)
-
-
-class FileCheckpointManager(FileManagerMixin, CheckpointManager):
-    """
-    A CheckpointManager that caches checkpoints for files in adjacent
-    directories.
-    """
-
-    checkpoint_dir = Unicode(
-        '.ipynb_checkpoints',
-        config=True,
-        help="""The directory name in which to keep file checkpoints
-
-        This is a path relative to the file's own directory.
-
-        By default, it is .ipynb_checkpoints
-        """,
-    )
-
-    root_dir = Unicode(config=True)
-
-    def _root_dir_default(self):
-        try:
-            return self.parent.root_dir
-        except AttributeError:
-            return getcwd()
-
-    # ContentsManager-dependent checkpoint API
-    def create_checkpoint(self, contents_mgr, path):
-        """
-        Create a checkpoint.
-
-        If contents_mgr is backed by the local filesystem, just copy the
-        appropriate file to the checkpoint directory.  Otherwise, ask the
-        ContentsManager for a model and write it ourselves.
-        """
-        if contents_mgr.backend == 'local_file':
-            # We know that the file is in the local filesystem, so just copy
-            # from the base location to our location.
-            checkpoint_id = u'checkpoint'
-            src_path = contents_mgr._get_os_path(path)
-            dest_path = self.checkpoint_path(checkpoint_id, path)
-            self._copy(src_path, dest_path)
-            return self.checkpoint_model(checkpoint_id, dest_path)
-        else:
-            return super(FileCheckpointManager, self).create_checkpoint(
-                contents_mgr, path,
-            )
-
-    def restore_checkpoint(self, contents_mgr, checkpoint_id, path):
-        """
-        Restore a checkpoint.
-
-        If contents_mgr is backed by the local filesystem, just copy the
-        appropriate file from the checkpoint directory.  Otherwise, load the
-        model and pass it to ContentsManager.save.
-        """
-        if contents_mgr.backend == 'local_file':
-            # We know that the file is in the local filesystem, so just copy
-            # from our base location to the location expected by content
-            src_path = self.checkpoint_path(checkpoint_id, path)
-            dest_path = contents_mgr._get_os_path(path)
-            self._copy(src_path, dest_path)
-        else:
-            super(FileCheckpointManager, self).restore_checkpoint(
-                contents_mgr, checkpoint_id, path
-            )
-
-    # ContentsManager-independent checkpoint API
-    def rename_checkpoint(self, checkpoint_id, old_path, new_path):
-        """Rename a checkpoint from old_path to new_path."""
-        old_cp_path = self.checkpoint_path(checkpoint_id, old_path)
-        new_cp_path = self.checkpoint_path(checkpoint_id, new_path)
-        if os.path.isfile(old_cp_path):
-            self.log.debug(
-                "Renaming checkpoint %s -> %s",
-                old_cp_path,
-                new_cp_path,
-            )
-            with self.perm_to_403():
-                shutil.move(old_cp_path, new_cp_path)
-
-    def delete_checkpoint(self, checkpoint_id, path):
-        """delete a file's checkpoint"""
-        path = path.strip('/')
-        cp_path = self.checkpoint_path(checkpoint_id, path)
-        if not os.path.isfile(cp_path):
-            self.no_such_checkpoint(path, checkpoint_id)
-
-        self.log.debug("unlinking %s", cp_path)
-        with self.perm_to_403():
-            os.unlink(cp_path)
-
-    def list_checkpoints(self, path):
-        """list the checkpoints for a given file
-
-        This contents manager currently only supports one checkpoint per file.
-        """
-        path = path.strip('/')
-        checkpoint_id = "checkpoint"
-        os_path = self.checkpoint_path(checkpoint_id, path)
-        if not os.path.isfile(os_path):
-            return []
-        else:
-            return [self.checkpoint_model(checkpoint_id, os_path)]
-
-    # Checkpoint-related utilities
-    def checkpoint_path(self, checkpoint_id, path):
-        """find the path to a checkpoint"""
-        path = path.strip('/')
-        parent, name = ('/' + path).rsplit('/', 1)
-        parent = parent.strip('/')
-        basename, ext = os.path.splitext(name)
-        filename = u"{name}-{checkpoint_id}{ext}".format(
-            name=basename,
-            checkpoint_id=checkpoint_id,
-            ext=ext,
-        )
-        os_path = self._get_os_path(path=parent)
-        cp_dir = os.path.join(os_path, self.checkpoint_dir)
-        with self.perm_to_403():
-            ensure_dir_exists(cp_dir)
-        cp_path = os.path.join(cp_dir, filename)
-        return cp_path
-
-    def checkpoint_model(self, checkpoint_id, os_path):
-        """construct the info dict for a given checkpoint"""
-        stats = os.stat(os_path)
-        last_modified = tz.utcfromtimestamp(stats.st_mtime)
-        info = dict(
-            id=checkpoint_id,
-            last_modified=last_modified,
-        )
-        return info
-
-    def create_file_checkpoint(self, content, format, path):
-        """Create a checkpoint from the current content of a notebook."""
-        path = path.strip('/')
-        # only the one checkpoint ID:
-        checkpoint_id = u"checkpoint"
-        os_checkpoint_path = self.checkpoint_path(checkpoint_id, path)
-        self.log.debug("creating checkpoint for %s", path)
-        with self.perm_to_403():
-            self._save_file(os_checkpoint_path, content, format=format)
-
-        # return the checkpoint info
-        return self.checkpoint_model(checkpoint_id, os_checkpoint_path)
-
-    def create_notebook_checkpoint(self, nb, path):
-        """Create a checkpoint from the current content of a notebook."""
-        path = path.strip('/')
-        # only the one checkpoint ID:
-        checkpoint_id = u"checkpoint"
-        os_checkpoint_path = self.checkpoint_path(checkpoint_id, path)
-        self.log.debug("creating checkpoint for %s", path)
-        with self.perm_to_403():
-            self._save_notebook(os_checkpoint_path, nb)
-
-        # return the checkpoint info
-        return self.checkpoint_model(checkpoint_id, os_checkpoint_path)
-
-    def get_checkpoint(self, checkpoint_id, path, type):
-        """Get the content of a checkpoint.
-
-        Returns a model suitable for passing to ContentsManager.save.
-        """
-        path = path.strip('/')
-        self.log.info("restoring %s from checkpoint %s", path, checkpoint_id)
-        os_checkpoint_path = self.checkpoint_path(checkpoint_id, path)
-        if not os.path.isfile(os_checkpoint_path):
-            self.no_such_checkpoint(path, checkpoint_id)
-
-        if type == 'notebook':
-            return {
-                'type': type,
-                'content': self._read_notebook(
-                    os_checkpoint_path,
-                    as_version=4,
-                ),
-            }
-        elif type == 'file':
-            content, format = self._read_file(os_checkpoint_path, format=None)
-            return {
-                'type': type,
-                'content': content,
-                'format': format,
-            }
-        else:
-            raise web.HTTPError(
-                500,
-                u'Unexpected type %s' % type
-            )
-
-    # Error Handling
-    def no_such_checkpoint(self, path, checkpoint_id):
-        raise web.HTTPError(
-            404,
-            u'Checkpoint does not exist: %s@%s' % (path, checkpoint_id)
-        )
-
-
 class FileContentsManager(FileManagerMixin, ContentsManager):
 
     root_dir = Unicode(config=True)
@@ -468,9 +124,6 b' class FileContentsManager(FileManagerMixin, ContentsManager):'
     def _checkpoint_manager_class_default(self):
         return FileCheckpointManager
 
-    def _backend_default(self):
-        return 'local_file'
-
     def is_hidden(self, path):
         """Does the API style path correspond to a hidden directory or file?
 

IPython/html/services/contents/manager.py

@@ -11,6 +11,7 b' import re'
 
 from tornado.web import HTTPError
 
+from .checkpoints import CheckpointManager
 from IPython.config.configurable import LoggingConfigurable
 from IPython.nbformat import sign, validate, ValidationError
 from IPython.nbformat.v4 import new_notebook
@@ -29,77 +30,6 b' from IPython.utils.py3compat import string_types'
 copy_pat = re.compile(r'\-Copy\d*\.')
 
 
-class CheckpointManager(LoggingConfigurable):
-    """
-    Base class for managing checkpoints for a ContentsManager.
-    """
-
-    def create_checkpoint(self, contents_mgr, path):
-        model = contents_mgr.get(path, content=True)
-        type = model['type']
-        if type == 'notebook':
-            return self.create_notebook_checkpoint(
-                model['content'],
-                path,
-            )
-        elif type == 'file':
-            return self.create_file_checkpoint(
-                model['content'],
-                model['format'],
-                path,
-            )
-
-    def restore_checkpoint(self, contents_mgr, checkpoint_id, path):
-        """Restore a checkpoint."""
-        type = contents_mgr.get(path, content=False)['type']
-        model = self.get_checkpoint(checkpoint_id, path, type)
-        contents_mgr.save(model, path)
-
-    def create_file_checkpoint(self, content, format, path):
-        """Create a checkpoint of the current state of a file
-
-        Returns a checkpoint model for the new checkpoint.
-        """
-        raise NotImplementedError("must be implemented in a subclass")
-
-    def create_notebook_checkpoint(self, nb, path):
-        """Create a checkpoint of the current state of a file
-
-        Returns a checkpoint model for the new checkpoint.
-        """
-        raise NotImplementedError("must be implemented in a subclass")
-
-    def get_checkpoint(self, checkpoint_id, path, type):
-        """Get the content of a checkpoint.
-
-        Returns an unvalidated model with the same structure as
-        the return value of ContentsManager.get
-        """
-        raise NotImplementedError("must be implemented in a subclass")
-
-    def rename_checkpoint(self, checkpoint_id, old_path, new_path):
-        """Rename a single checkpoint from old_path to new_path."""
-        raise NotImplementedError("must be implemented in a subclass")
-
-    def delete_checkpoint(self, checkpoint_id, path):
-        """delete a checkpoint for a file"""
-        raise NotImplementedError("must be implemented in a subclass")
-
-    def list_checkpoints(self, path):
-        """Return a list of checkpoints for a given file"""
-        raise NotImplementedError("must be implemented in a subclass")
-
-    def rename_all_checkpoints(self, old_path, new_path):
-        """Rename all checkpoints for old_path to new_path."""
-        for cp in self.list_checkpoints(old_path):
-            self.rename_checkpoint(cp['id'], old_path, new_path)
-
-    def delete_all_checkpoints(self, path):
-        """Delete all checkpoints for the given path."""
-        for checkpoint in self.list_checkpoints(path):
-            self.delete_checkpoint(checkpoint['id'], path)
-
-
 class ContentsManager(LoggingConfigurable):
     """Base class for serving files and directories.
 
@@ -180,7 +110,6 b' class ContentsManager(LoggingConfigurable):'
     checkpoint_manager_class = Type(CheckpointManager, config=True)
     checkpoint_manager = Instance(CheckpointManager, config=True)
     checkpoint_manager_kwargs = Dict(allow_none=False, config=True)
-    backend = Unicode(default_value="")
 
     def _checkpoint_manager_default(self):
         return self.checkpoint_manager_class(**self.checkpoint_manager_kwargs)

IPython/html/services/contents/tests/test_contents_api.py

@@ -13,6 +13,9 b' pjoin = os.path.join'
 
 import requests
 
+from ..filecheckpoints import GenericFileCheckpointManager
+
+from IPython.config import Config
 from IPython.html.utils import url_path_join, url_escape, to_os_path
 from IPython.html.tests.launchnotebook import NotebookTestBase, assert_http_error
 from IPython.nbformat import read, write, from_dict
@@ -615,24 +618,12 b' class APITest(NotebookTestBase):'
             with self.patch_cp_root(td):
                 self.test_file_checkpoints()
 
-    @contextmanager
-    def patch_cm_backend(self):
-        """
-        Temporarily patch our ContentsManager to present a different backend.
-        """
-        mgr = self.notebook.contents_manager
-        old_backend = mgr.backend
-        mgr.backend = ""
-        try:
-            yield
-        finally:
-            mgr.backend = old_backend
-
-    def test_checkpoints_empty_backend(self):
-        with self.patch_cm_backend():
-            self.test_checkpoints()
-
-        with self.patch_cm_backend():
-            self.test_file_checkpoints()
 
+class GenericFileCheckpointsAPITest(APITest):
+    """
+    Run the tests from APITest with GenericFileCheckpointManager.
+    """
 
+    config = Config()
+    config.FileContentsManager.checkpoint_manager_class = \
+        GenericFileCheckpointManager