manager.py

"""A base class for contents managers."""
# Copyright (c) Jupyter Development Team.
# Distributed under the terms of the Modified BSD License.
import itertools
import json
import re
import warnings
from fnmatch import fnmatch

from nbformat import ValidationError, sign
from nbformat import validate as validate_nb
from nbformat.v4 import new_notebook
from tornado.web import HTTPError, RequestHandler
from traitlets import (
    Any,
    Bool,
    Dict,
    Instance,
    List,
    TraitError,
    Type,
    Unicode,
    default,
    validate,
)
from traitlets.config.configurable import LoggingConfigurable

from jupyter_server.transutils import _i18n
from jupyter_server.utils import ensure_async, import_item

from ...files.handlers import FilesHandler
from .checkpoints import AsyncCheckpoints, Checkpoints

copy_pat = re.compile(r"\-Copy\d*\.")


class ContentsManager(LoggingConfigurable):
    """Base class for serving files and directories.

    This serves any text or binary file,
    as well as directories,
    with special handling for JSON notebook documents.

    Most APIs take a path argument,
    which is always an API-style unicode path,
    and always refers to a directory.

    - unicode, not url-escaped
    - '/'-separated
    - leading and trailing '/' will be stripped
    - if unspecified, path defaults to '',
      indicating the root path.

    """

    root_dir = Unicode("/", config=True)

    allow_hidden = Bool(False, config=True, help="Allow access to hidden files")

    notary = Instance(sign.NotebookNotary)

    def _notary_default(self):
        return sign.NotebookNotary(parent=self)

    hide_globs = List(
        Unicode(),
        [
            "__pycache__",
            "*.pyc",
            "*.pyo",
            ".DS_Store",
            "*.so",
            "*.dylib",
            "*~",
        ],
        config=True,
        help="""
        Glob patterns to hide in file and directory listings.
    """,
    )

    untitled_notebook = Unicode(
        _i18n("Untitled"),
        config=True,
        help="The base name used when creating untitled notebooks.",
    )

    untitled_file = Unicode(
        "untitled", config=True, help="The base name used when creating untitled files."
    )

    untitled_directory = Unicode(
        "Untitled Folder",
        config=True,
        help="The base name used when creating untitled directories.",
    )

    pre_save_hook = Any(
        None,
        config=True,
        allow_none=True,
        help="""Python callable or importstring thereof

        To be called on a contents model prior to save.

        This can be used to process the structure,
        such as removing notebook outputs or other side effects that
        should not be saved.

        It will be called as (all arguments passed by keyword)::

            hook(path=path, model=model, contents_manager=self)

        - model: the model to be saved. Includes file contents.
          Modifying this dict will affect the file that is stored.
        - path: the API path of the save destination
        - contents_manager: this ContentsManager instance
        """,
    )

    @validate("pre_save_hook")
    def _validate_pre_save_hook(self, proposal):
        value = proposal["value"]
        if isinstance(value, str):
            value = import_item(self.pre_save_hook)
        if not callable(value):
            raise TraitError("pre_save_hook must be callable")
        if callable(self.pre_save_hook):
            warnings.warn(
                f"Overriding existing pre_save_hook ({self.pre_save_hook.__name__}) with a new one ({value.__name__}).",
                stacklevel=2,
            )
        return value

    post_save_hook = Any(
        None,
        config=True,
        allow_none=True,
        help="""Python callable or importstring thereof

        to be called on the path of a file just saved.

        This can be used to process the file on disk,
        such as converting the notebook to a script or HTML via nbconvert.

        It will be called as (all arguments passed by keyword)::

            hook(os_path=os_path, model=model, contents_manager=instance)

        - path: the filesystem path to the file just written
        - model: the model representing the file
        - contents_manager: this ContentsManager instance
        """,
    )

    @validate("post_save_hook")
    def _validate_post_save_hook(self, proposal):
        value = proposal["value"]
        if isinstance(value, str):
            value = import_item(value)
        if not callable(value):
            raise TraitError("post_save_hook must be callable")
        if callable(self.post_save_hook):
            warnings.warn(
                f"Overriding existing post_save_hook ({self.post_save_hook.__name__}) with a new one ({value.__name__}).",
                stacklevel=2,
            )
        return value

    def run_pre_save_hook(self, model, path, **kwargs):
        """Run the pre-save hook if defined, and log errors"""
        warnings.warn(
            "run_pre_save_hook is deprecated, use run_pre_save_hooks instead.",
            DeprecationWarning,
            stacklevel=2,
        )
        if self.pre_save_hook:
            try:
                self.log.debug("Running pre-save hook on %s", path)
                self.pre_save_hook(model=model, path=path, contents_manager=self, **kwargs)
            except HTTPError:
                # allow custom HTTPErrors to raise,
                # rejecting the save with a message.
                raise
            except Exception:
                # unhandled errors don't prevent saving,
                # which could cause frustrating data loss
                self.log.error("Pre-save hook failed on %s", path, exc_info=True)

    def run_post_save_hook(self, model, os_path):
        """Run the post-save hook if defined, and log errors"""
        warnings.warn(
            "run_post_save_hook is deprecated, use run_post_save_hooks instead.",
            DeprecationWarning,
            stacklevel=2,
        )
        if self.post_save_hook:
            try:
                self.log.debug("Running post-save hook on %s", os_path)
                self.post_save_hook(os_path=os_path, model=model, contents_manager=self)
            except Exception as e:
                self.log.error("Post-save hook failed o-n %s", os_path, exc_info=True)
                raise HTTPError(500, "Unexpected error while running post hook save: %s" % e) from e

    _pre_save_hooks = List()
    _post_save_hooks = List()

    def register_pre_save_hook(self, hook):
        if isinstance(hook, str):
            hook = import_item(hook)
        if not callable(hook):
            raise RuntimeError("hook must be callable")
        self._pre_save_hooks.append(hook)

    def register_post_save_hook(self, hook):
        if isinstance(hook, str):
            hook = import_item(hook)
        if not callable(hook):
            raise RuntimeError("hook must be callable")
        self._post_save_hooks.append(hook)

    def run_pre_save_hooks(self, model, path, **kwargs):
        """Run the pre-save hooks if any, and log errors"""
        pre_save_hooks = [self.pre_save_hook] if self.pre_save_hook is not None else []
        pre_save_hooks += self._pre_save_hooks
        for pre_save_hook in pre_save_hooks:
            try:
                self.log.debug("Running pre-save hook on %s", path)
                pre_save_hook(model=model, path=path, contents_manager=self, **kwargs)
            except HTTPError:
                # allow custom HTTPErrors to raise,
                # rejecting the save with a message.
                raise
            except Exception:
                # unhandled errors don't prevent saving,
                # which could cause frustrating data loss
                self.log.error(
                    "Pre-save hook %s failed on %s",
                    pre_save_hook.__name__,
                    path,
                    exc_info=True,
                )

    def run_post_save_hooks(self, model, os_path):
        """Run the post-save hooks if any, and log errors"""
        post_save_hooks = [self.post_save_hook] if self.post_save_hook is not None else []
        post_save_hooks += self._post_save_hooks
        for post_save_hook in post_save_hooks:
            try:
                self.log.debug("Running post-save hook on %s", os_path)
                post_save_hook(os_path=os_path, model=model, contents_manager=self)
            except Exception as e:
                self.log.error(
                    "Post-save %s hook failed on %s",
                    post_save_hook.__name__,
                    os_path,
                    exc_info=True,
                )
                raise HTTPError(500, "Unexpected error while running post hook save: %s" % e) from e

    checkpoints_class = Type(Checkpoints, config=True)
    checkpoints = Instance(Checkpoints, config=True)
    checkpoints_kwargs = Dict(config=True)

    @default("checkpoints")
    def _default_checkpoints(self):
        return self.checkpoints_class(**self.checkpoints_kwargs)

    @default("checkpoints_kwargs")
    def _default_checkpoints_kwargs(self):
        return dict(
            parent=self,
            log=self.log,
        )

    files_handler_class = Type(
        FilesHandler,
        klass=RequestHandler,
        allow_none=True,
        config=True,
        help="""handler class to use when serving raw file requests.

        Default is a fallback that talks to the ContentsManager API,
        which may be inefficient, especially for large files.

        Local files-based ContentsManagers can use a StaticFileHandler subclass,
        which will be much more efficient.

        Access to these files should be Authenticated.
        """,
    )

    files_handler_params = Dict(
        config=True,
        help="""Extra parameters to pass to files_handler_class.

        For example, StaticFileHandlers generally expect a `path` argument
        specifying the root directory from which to serve files.
        """,
    )

    def get_extra_handlers(self):
        """Return additional handlers

        Default: self.files_handler_class on /files/.*
        """
        handlers = []
        if self.files_handler_class:
            handlers.append((r"/files/(.*)", self.files_handler_class, self.files_handler_params))
        return handlers

    # ContentsManager API part 1: methods that must be
    # implemented in subclasses.

    def dir_exists(self, path):
        """Does a directory exist at the given path?

        Like os.path.isdir

        Override this method in subclasses.

        Parameters
        ----------
        path : string
            The path to check

        Returns
        -------
        exists : bool
            Whether the path does indeed exist.
        """
        raise NotImplementedError

    def is_hidden(self, path):
        """Is path a hidden directory or file?

        Parameters
        ----------
        path : string
            The path to check. This is an API path (`/` separated,
            relative to root dir).

        Returns
        -------
        hidden : bool
            Whether the path is hidden.

        """
        raise NotImplementedError

    def file_exists(self, path=""):
        """Does a file exist at the given path?

        Like os.path.isfile

        Override this method in subclasses.

        Parameters
        ----------
        path : string
            The API path of a file to check for.

        Returns
        -------
        exists : bool
            Whether the file exists.
        """
        raise NotImplementedError("must be implemented in a subclass")

    def exists(self, path):
        """Does a file or directory exist at the given path?

        Like os.path.exists

        Parameters
        ----------
        path : string
            The API path of a file or directory to check for.

        Returns
        -------
        exists : bool
            Whether the target exists.
        """
        return self.file_exists(path) or self.dir_exists(path)

    def get(self, path, content=True, type=None, format=None):
        """Get a file or directory model."""
        raise NotImplementedError("must be implemented in a subclass")

    def save(self, model, path):
        """
        Save a file or directory model to path.

        Should return the saved model with no content.  Save implementations
        should call self.run_pre_save_hook(model=model, path=path) prior to
        writing any data.
        """
        raise NotImplementedError("must be implemented in a subclass")

    def delete_file(self, path):
        """Delete the file or directory at path."""
        raise NotImplementedError("must be implemented in a subclass")

    def rename_file(self, old_path, new_path):
        """Rename a file or directory."""
        raise NotImplementedError("must be implemented in a subclass")

    # ContentsManager API part 2: methods that have useable default
    # implementations, but can be overridden in subclasses.

    def delete(self, path):
        """Delete a file/directory and any associated checkpoints."""
        path = path.strip("/")
        if not path:
            raise HTTPError(400, "Can't delete root")
        self.delete_file(path)
        self.checkpoints.delete_all_checkpoints(path)

    def rename(self, old_path, new_path):
        """Rename a file and any checkpoints associated with that file."""
        self.rename_file(old_path, new_path)
        self.checkpoints.rename_all_checkpoints(old_path, new_path)

    def update(self, model, path):
        """Update the file's path

        For use in PATCH requests, to enable renaming a file without
        re-uploading its contents. Only used for renaming at the moment.
        """
        path = path.strip("/")
        new_path = model.get("path", path).strip("/")
        if path != new_path:
            self.rename(path, new_path)
        model = self.get(new_path, content=False)
        return model

    def info_string(self):
        return "Serving contents"

    def get_kernel_path(self, path, model=None):
        """Return the API path for the kernel

        KernelManagers can turn this value into a filesystem path,
        or ignore it altogether.

        The default value here will start kernels in the directory of the
        notebook server. FileContentsManager overrides this to use the
        directory containing the notebook.
        """
        return ""

    def increment_filename(self, filename, path="", insert=""):
        """Increment a filename until it is unique.

        Parameters
        ----------
        filename : unicode
            The name of a file, including extension
        path : unicode
            The API path of the target's directory
        insert : unicode
            The characters to insert after the base filename

        Returns
        -------
        name : unicode
            A filename that is unique, based on the input filename.
        """
        # Extract the full suffix from the filename (e.g. .tar.gz)
        path = path.strip("/")
        basename, dot, ext = filename.rpartition(".")
        if ext != "ipynb":
            basename, dot, ext = filename.partition(".")

        suffix = dot + ext

        for i in itertools.count():
            if i:
                insert_i = "{}{}".format(insert, i)
            else:
                insert_i = ""
            name = "{basename}{insert}{suffix}".format(
                basename=basename, insert=insert_i, suffix=suffix
            )
            if not self.exists("{}/{}".format(path, name)):
                break
        return name

    def validate_notebook_model(self, model, validation_error=None):
        """Add failed-validation message to model"""
        try:
            # If we're given a validation_error dictionary, extract the exception
            # from it and raise the exception, else call nbformat's validate method
            # to determine if the notebook is valid.  This 'else' condition may
            # pertain to server extension not using the server's notebook read/write
            # functions.
            if validation_error is not None:
                e = validation_error.get("ValidationError")
                if isinstance(e, ValidationError):
                    raise e
            else:
                validate_nb(model["content"])
        except ValidationError as e:
            model["message"] = "Notebook validation failed: {}:\n{}".format(
                str(e),
                json.dumps(e.instance, indent=1, default=lambda obj: "<UNKNOWN>"),
            )
        return model

    def new_untitled(self, path="", type="", ext=""):
        """Create a new untitled file or directory in path

        path must be a directory

        File extension can be specified.

        Use `new` to create files with a fully specified path (including filename).
        """
        path = path.strip("/")
        if not self.dir_exists(path):
            raise HTTPError(404, "No such directory: %s" % path)

        model = {}
        if type:
            model["type"] = type

        if ext == ".ipynb":
            model.setdefault("type", "notebook")
        else:
            model.setdefault("type", "file")

        insert = ""
        if model["type"] == "directory":
            untitled = self.untitled_directory
            insert = " "
        elif model["type"] == "notebook":
            untitled = self.untitled_notebook
            ext = ".ipynb"
        elif model["type"] == "file":
            untitled = self.untitled_file
        else:
            raise HTTPError(400, "Unexpected model type: %r" % model["type"])

        name = self.increment_filename(untitled + ext, path, insert=insert)
        path = "{0}/{1}".format(path, name)
        return self.new(model, path)

    def new(self, model=None, path=""):
        """Create a new file or directory and return its model with no content.

        To create a new untitled entity in a directory, use `new_untitled`.
        """
        path = path.strip("/")
        if model is None:
            model = {}

        if path.endswith(".ipynb"):
            model.setdefault("type", "notebook")
        else:
            model.setdefault("type", "file")

        # no content, not a directory, so fill out new-file model
        if "content" not in model and model["type"] != "directory":
            if model["type"] == "notebook":
                model["content"] = new_notebook()
                model["format"] = "json"
            else:
                model["content"] = ""
                model["type"] = "file"
                model["format"] = "text"

        model = self.save(model, path)
        return model

    def copy(self, from_path, to_path=None):
        """Copy an existing file and return its new model.

        If to_path not specified, it will be the parent directory of from_path.
        If to_path is a directory, filename will increment `from_path-Copy#.ext`.
        Considering multi-part extensions, the Copy# part will be placed before the first dot for all the extensions except `ipynb`.
        For easier manual searching in case of notebooks, the Copy# part will be placed before the last dot.

        from_path must be a full path to a file.
        """
        path = from_path.strip("/")

        if to_path is not None:
            to_path = to_path.strip("/")

        if "/" in path:
            from_dir, from_name = path.rsplit("/", 1)
        else:
            from_dir = ""
            from_name = path

        model = self.get(path)
        model.pop("path", None)
        model.pop("name", None)
        if model["type"] == "directory":
            raise HTTPError(400, "Can't copy directories")

        is_destination_specified = to_path is not None
        if not is_destination_specified:
            to_path = from_dir
        if self.dir_exists(to_path):
            name = copy_pat.sub(".", from_name)
            to_name = self.increment_filename(name, to_path, insert="-Copy")
            to_path = "{0}/{1}".format(to_path, to_name)
        elif is_destination_specified:
            if "/" in to_path:
                to_dir, to_name = to_path.rsplit("/", 1)
                if not self.dir_exists(to_dir):
                    raise HTTPError(404, "No such parent directory: %s to copy file in" % to_dir)
        else:
            raise HTTPError(404, "No such directory: %s" % to_path)

        model = self.save(model, to_path)
        return model

    def log_info(self):
        self.log.info(self.info_string())

    def trust_notebook(self, path):
        """Explicitly trust a notebook

        Parameters
        ----------
        path : string
            The path of a notebook
        """
        model = self.get(path)
        nb = model["content"]
        self.log.warning("Trusting notebook %s", path)
        self.notary.mark_cells(nb, True)
        self.check_and_sign(nb, path)

    def check_and_sign(self, nb, path=""):
        """Check for trusted cells, and sign the notebook.

        Called as a part of saving notebooks.

        Parameters
        ----------
        nb : dict
            The notebook dict
        path : string
            The notebook's path (for logging)
        """
        if self.notary.check_cells(nb):
            self.notary.sign(nb)
        else:
            self.log.warning("Notebook %s is not trusted", path)

    def mark_trusted_cells(self, nb, path=""):
        """Mark cells as trusted if the notebook signature matches.

        Called as a part of loading notebooks.

        Parameters
        ----------
        nb : dict
            The notebook object (in current nbformat)
        path : string
            The notebook's path (for logging)
        """
        trusted = self.notary.check_signature(nb)
        if not trusted:
            self.log.warning("Notebook %s is not trusted", path)
        self.notary.mark_cells(nb, trusted)

    def should_list(self, name):
        """Should this file/directory name be displayed in a listing?"""
        return not any(fnmatch(name, glob) for glob in self.hide_globs)

    # Part 3: Checkpoints API
    def create_checkpoint(self, path):
        """Create a checkpoint."""
        return self.checkpoints.create_checkpoint(self, path)

    def restore_checkpoint(self, checkpoint_id, path):
        """
        Restore a checkpoint.
        """
        self.checkpoints.restore_checkpoint(self, checkpoint_id, path)

    def list_checkpoints(self, path):
        return self.checkpoints.list_checkpoints(path)

    def delete_checkpoint(self, checkpoint_id, path):
        return self.checkpoints.delete_checkpoint(checkpoint_id, path)


class AsyncContentsManager(ContentsManager):
    """Base class for serving files and directories asynchronously."""

    checkpoints_class = Type(AsyncCheckpoints, config=True)
    checkpoints = Instance(AsyncCheckpoints, config=True)
    checkpoints_kwargs = Dict(config=True)

    @default("checkpoints")
    def _default_checkpoints(self):
        return self.checkpoints_class(**self.checkpoints_kwargs)

    @default("checkpoints_kwargs")
    def _default_checkpoints_kwargs(self):
        return dict(
            parent=self,
            log=self.log,
        )

    # ContentsManager API part 1: methods that must be
    # implemented in subclasses.

    async def dir_exists(self, path):
        """Does a directory exist at the given path?

        Like os.path.isdir

        Override this method in subclasses.

        Parameters
        ----------
        path : string
            The path to check

        Returns
        -------
        exists : bool
            Whether the path does indeed exist.
        """
        raise NotImplementedError

    async def is_hidden(self, path):
        """Is path a hidden directory or file?

        Parameters
        ----------
        path : string
            The path to check. This is an API path (`/` separated,
            relative to root dir).

        Returns
        -------
        hidden : bool
            Whether the path is hidden.

        """
        raise NotImplementedError

    async def file_exists(self, path=""):
        """Does a file exist at the given path?

        Like os.path.isfile

        Override this method in subclasses.

        Parameters
        ----------
        path : string
            The API path of a file to check for.

        Returns
        -------
        exists : bool
            Whether the file exists.
        """
        raise NotImplementedError("must be implemented in a subclass")

    async def exists(self, path):
        """Does a file or directory exist at the given path?

        Like os.path.exists

        Parameters
        ----------
        path : string
            The API path of a file or directory to check for.

        Returns
        -------
        exists : bool
            Whether the target exists.
        """
        return await ensure_async(self.file_exists(path)) or await ensure_async(
            self.dir_exists(path)
        )

    async def get(self, path, content=True, type=None, format=None):
        """Get a file or directory model."""
        raise NotImplementedError("must be implemented in a subclass")

    async def save(self, model, path):
        """
        Save a file or directory model to path.

        Should return the saved model with no content.  Save implementations
        should call self.run_pre_save_hook(model=model, path=path) prior to
        writing any data.
        """
        raise NotImplementedError("must be implemented in a subclass")

    async def delete_file(self, path):
        """Delete the file or directory at path."""
        raise NotImplementedError("must be implemented in a subclass")

    async def rename_file(self, old_path, new_path):
        """Rename a file or directory."""
        raise NotImplementedError("must be implemented in a subclass")

    # ContentsManager API part 2: methods that have useable default
    # implementations, but can be overridden in subclasses.

    async def delete(self, path):
        """Delete a file/directory and any associated checkpoints."""
        path = path.strip("/")
        if not path:
            raise HTTPError(400, "Can't delete root")

        await self.delete_file(path)
        await self.checkpoints.delete_all_checkpoints(path)

    async def rename(self, old_path, new_path):
        """Rename a file and any checkpoints associated with that file."""
        await self.rename_file(old_path, new_path)
        await self.checkpoints.rename_all_checkpoints(old_path, new_path)

    async def update(self, model, path):
        """Update the file's path

        For use in PATCH requests, to enable renaming a file without
        re-uploading its contents. Only used for renaming at the moment.
        """
        path = path.strip("/")
        new_path = model.get("path", path).strip("/")
        if path != new_path:
            await self.rename(path, new_path)
        model = await self.get(new_path, content=False)
        return model

    async def increment_filename(self, filename, path="", insert=""):
        """Increment a filename until it is unique.

        Parameters
        ----------
        filename : unicode
            The name of a file, including extension
        path : unicode
            The API path of the target's directory
        insert : unicode
            The characters to insert after the base filename

        Returns
        -------
        name : unicode
            A filename that is unique, based on the input filename.
        """
        # Extract the full suffix from the filename (e.g. .tar.gz)
        path = path.strip("/")
        basename, dot, ext = filename.rpartition(".")
        if ext != "ipynb":
            basename, dot, ext = filename.partition(".")

        suffix = dot + ext

        for i in itertools.count():
            if i:
                insert_i = "{}{}".format(insert, i)
            else:
                insert_i = ""
            name = "{basename}{insert}{suffix}".format(
                basename=basename, insert=insert_i, suffix=suffix
            )
            file_exists = await ensure_async(self.exists("{}/{}".format(path, name)))
            if not file_exists:
                break
        return name

    async def new_untitled(self, path="", type="", ext=""):
        """Create a new untitled file or directory in path

        path must be a directory

        File extension can be specified.

        Use `new` to create files with a fully specified path (including filename).
        """
        path = path.strip("/")
        dir_exists = await ensure_async(self.dir_exists(path))
        if not dir_exists:
            raise HTTPError(404, "No such directory: %s" % path)

        model = {}
        if type:
            model["type"] = type

        if ext == ".ipynb":
            model.setdefault("type", "notebook")
        else:
            model.setdefault("type", "file")

        insert = ""
        if model["type"] == "directory":
            untitled = self.untitled_directory
            insert = " "
        elif model["type"] == "notebook":
            untitled = self.untitled_notebook
            ext = ".ipynb"
        elif model["type"] == "file":
            untitled = self.untitled_file
        else:
            raise HTTPError(400, "Unexpected model type: %r" % model["type"])

        name = await self.increment_filename(untitled + ext, path, insert=insert)
        path = "{0}/{1}".format(path, name)
        return await self.new(model, path)

    async def new(self, model=None, path=""):
        """Create a new file or directory and return its model with no content.

        To create a new untitled entity in a directory, use `new_untitled`.
        """
        path = path.strip("/")
        if model is None:
            model = {}

        if path.endswith(".ipynb"):
            model.setdefault("type", "notebook")
        else:
            model.setdefault("type", "file")

        # no content, not a directory, so fill out new-file model
        if "content" not in model and model["type"] != "directory":
            if model["type"] == "notebook":
                model["content"] = new_notebook()
                model["format"] = "json"
            else:
                model["content"] = ""
                model["type"] = "file"
                model["format"] = "text"

        model = await self.save(model, path)
        return model

    async def copy(self, from_path, to_path=None):
        """Copy an existing file and return its new model.

        If to_path not specified, it will be the parent directory of from_path.
        If to_path is a directory, filename will increment `from_path-Copy#.ext`.
        Considering multi-part extensions, the Copy# part will be placed before the first dot for all the extensions except `ipynb`.
        For easier manual searching in case of notebooks, the Copy# part will be placed before the last dot.

        from_path must be a full path to a file.
        """
        path = from_path.strip("/")

        if to_path is not None:
            to_path = to_path.strip("/")

        if "/" in path:
            from_dir, from_name = path.rsplit("/", 1)
        else:
            from_dir = ""
            from_name = path

        model = await self.get(path)
        model.pop("path", None)
        model.pop("name", None)
        if model["type"] == "directory":
            raise HTTPError(400, "Can't copy directories")

        is_destination_specified = to_path is not None
        if not is_destination_specified:
            to_path = from_dir
        if await ensure_async(self.dir_exists(to_path)):
            name = copy_pat.sub(".", from_name)
            to_name = await self.increment_filename(name, to_path, insert="-Copy")
            to_path = "{0}/{1}".format(to_path, to_name)
        elif is_destination_specified:
            if "/" in to_path:
                to_dir, to_name = to_path.rsplit("/", 1)
                if not await ensure_async(self.dir_exists(to_dir)):
                    raise HTTPError(404, "No such parent directory: %s to copy file in" % to_dir)
        else:
            raise HTTPError(404, "No such directory: %s" % to_path)

        model = await self.save(model, to_path)
        return model

    async def trust_notebook(self, path):
        """Explicitly trust a notebook

        Parameters
        ----------
        path : string
            The path of a notebook
        """
        model = await self.get(path)
        nb = model["content"]
        self.log.warning("Trusting notebook %s", path)
        self.notary.mark_cells(nb, True)
        self.check_and_sign(nb, path)

    # Part 3: Checkpoints API
    async def create_checkpoint(self, path):
        """Create a checkpoint."""
        return await self.checkpoints.create_checkpoint(self, path)

    async def restore_checkpoint(self, checkpoint_id, path):
        """
        Restore a checkpoint.
        """
        await self.checkpoints.restore_checkpoint(self, checkpoint_id, path)

    async def list_checkpoints(self, path):
        return await self.checkpoints.list_checkpoints(path)

    async def delete_checkpoint(self, checkpoint_id, path):
        return await self.checkpoints.delete_checkpoint(checkpoint_id, path)