storage.py

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#!/usr/bin/env python

#
# LSST Data Management System
# Copyright 2016 LSST Corporation.
#
# This product includes software developed by the
# LSST Project (http://www.lsst.org/).
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the LSST License Statement and
# the GNU General Public License along with this program.  If not,
# see <http://www.lsstcorp.org/LegalNotices/>.
#
from __future__ import absolute_import

from future import standard_library
import urllib.parse
from . import NoRepositroyAtRoot
standard_library.install_aliases()


class Storage:
    """Base class for storages"""

    storages = {}

    def __init__(self):
        self.repositoryCfgs = {}

    @staticmethod
    def registerStorageClass(scheme, cls):
        """Register derived classes for lookup by URI scheme.

        A scheme is a name that describes the form a resource at the beginning of a URI
        e.g. 'http' indicates HTML and related code, such as is found in http://www.lsst.org

        The only currently supported schemes are:
        * 'file' where the portion of the URI after the // indicates an absolute locaiton on disk.
          for example: file:/my_repository_folder/
        * '' (no scheme) where the entire string is a relative path on the local system
          for example "my_repository_folder" will indicate a folder in the current working directory with the
          same name.

        See documentation for the urlparse python library for more information.

        .. warning::

            Storage is 'wet paint' and very likely to change during factorization of Butler back end and
            storage formats (DM-6225). Use of it in production code other than via the 'old butler' API is
            strongly discouraged.

        Parameters
        ----------
        scheme : str
            Name of the `scheme` the class is being registered for, which appears at the beginning of a URI.
        cls : class object
            A class object that should be used for a given scheme.
        """
        if scheme in Storage.storages:
            raise RuntimeError("Scheme '%s' already registered:%s" % (scheme, Storage.storages[scheme]))
        Storage.storages[scheme] = cls

    def getRepositoryCfg(self, uri):
        """Get a RepositoryCfg from a location specified by uri.

        If a cfg is found then it is cached by the uri, so that multiple lookups
        are not performed on storages that might be remote.

        RepositoryCfgs are not supposed to change once they are created so this
        should not lead to stale data.
        """
        cfg = self.repositoryCfgs.get(uri, None)
        if cfg:
            return cfg
        parseRes = urllib.parse.urlparse(uri)
        if parseRes.scheme in Storage.storages:
            cfg = Storage.storages[parseRes.scheme].getRepositoryCfg(uri)
            if cfg:
                self.repositoryCfgs[uri] = cfg
        else:
            raise RuntimeError("No storage registered for scheme %s" % parseRes.scheme)
        return cfg

    @staticmethod
    def putRepositoryCfg(cfg, uri):
        """Write a RepositoryCfg object to a location described by uri"""
        ret = None
        parseRes = urllib.parse.urlparse(uri)
        if parseRes.scheme in Storage.storages:
            ret = Storage.storages[parseRes.scheme].putRepositoryCfg(cfg, uri)
        else:
            raise RuntimeError("No storage registered for scheme %s" % parseRes.scheme)
        return ret

    @staticmethod
    def getMapperClass(uri):
        """Get a mapper class cfg value from location described by uri.

        Note that in legacy repositories the mapper may be specified by a file called _mapper at the uri
        location, and in newer repositories the mapper would be specified by a RepositoryCfg stored at the uri
        location.

        .. warning::

            Storage is 'wet paint' and very likely to change during factorization of Butler back end and
            storage formats (DM-6225). Use of it in production code other than via the 'old butler' API is
            strongly discouraged.

        """
        ret = None
        parseRes = urllib.parse.urlparse(uri)
        if parseRes.scheme in Storage.storages:
            ret = Storage.storages[parseRes.scheme].getMapperClass(uri)
        else:
            raise RuntimeError("No storage registered for scheme %s" % parseRes.scheme)
        return ret

    @staticmethod
    def makeFromURI(uri, create=True):
        '''Instantiate a StorageInterface sublcass from a URI.

        .. warning::

            Storage is 'wet paint' and very likely to change during factorization of Butler back end and
            storage formats (DM-6225). Use of it in production code other than via the 'old butler' API is
            strongly discouraged.

        Parameters
        ----------
        uri : string
            The uri to the root location of a repository.
        create : bool, optional
            If True The StorageInterface subclass should create a new
            repository at the root location. If False then a new repository
            will not be created.

        Returns
        -------
        A Storage subclass instance, or if create is False and a repository
        does not exist at the root location then returns None.

        Raises
        ------
        RuntimeError
            When a StorageInterface subclass does not exist for the scheme
            indicated by the uri.
        '''
        ret = None
        parseRes = urllib.parse.urlparse(uri)
        if parseRes.scheme in Storage.storages:
            theClass = Storage.storages[parseRes.scheme]
            try:
                ret = theClass(uri=uri, create=create)
            except NoRepositroyAtRoot:
                pass
        else:
            raise RuntimeError("No storage registered for scheme %s" % parseRes.scheme)
        return ret

    @staticmethod
    def isPosix(uri):
        """Test if a URI is for a local filesystem storage.

        This is mostly for backward compatibility; Butler V1 repositories were only ever on the local
        filesystem. They may exist but not have a RepositoryCfg class. This enables conditional checking for a
        V1 Repository.

        This function treats 'file' and '' (no scheme) as posix storages, see
        the class docstring for more details.

        Parameters
        ----------
        uri : string
            URI to the root of a Repository.

        Returns
        -------
        Bool
            True if the URI is associated with a posix storage, else false.
        """
        parseRes = urllib.parse.urlparse(uri)
        if parseRes.scheme in ('file', ''):
            return True
        return False

    @staticmethod
    def relativePath(fromUri, toUri):
        """Get a relative path from a location to a location, if a relative path for these 2 locations exists.

        Parameters
        ----------
        fromPath : string
            A URI that describes a location at which to start.
        toPath : string
            A URI that describes a target location.

        Returns
        -------
        string
            A relative path that describes the path from fromUri to toUri, provided one exists. If a relative
            path between the two URIs does not exist then the entire toUri path is returned.
        """
        fromUriParseRes = urllib.parse.urlparse(fromUri)
        toUriParseRes = urllib.parse.urlparse(toUri)
        if fromUriParseRes.scheme != toUriParseRes.scheme:
            return toUri
        storage = Storage.storages.get(fromUriParseRes.scheme, None)
        if not storage:
            return toUri
        return storage.relativePath(fromUri, toUri)

    @staticmethod
    def absolutePath(fromUri, toUri):
        """Get an absolute path for the path from fromUri to toUri

        Parameters
        ----------
        fromUri : the starting location
            Description
        toUri : the location relative to fromUri
            Description

        Returns
        -------
        string
            URI that is absolutepath fromUri + toUri, if one exists. If toUri is absolute or if fromUri is not
            related to toUri (e.g. are of different storage types) then toUri will be returned.
        """
        fromUriParseRes = urllib.parse.urlparse(fromUri)
        toUriParseRes = urllib.parse.urlparse(toUri)
        if fromUriParseRes.scheme != toUriParseRes.scheme:
            return toUri
        storage = Storage.storages.get(fromUriParseRes.scheme, None)
        if not storage:
            return toUri
        return storage.absolutePath(fromUri, toUri)

    @staticmethod
    def search(uri, path):
        """Look for the given path in a storage root at URI; return None if it can't be found.

        If the path contains an HDU indicator (a number in brackets before the
        dot, e.g. 'foo.fits[1]', this will be stripped when searching and so
        will match filenames without the HDU indicator, e.g. 'foo.fits'. The
        path returned WILL contain the indicator though, e.g. ['foo.fits[1]'].


        Parameters
        ----------
        root : string
            URI to the the root location to search
        path : string
            A filename (and optionally prefix path) to search for within root.

        Returns
        -------
        string or None
            The location that was found, or None if no location was found.
        """
        parseRes = urllib.parse.urlparse(uri)
        storage = Storage.storages.get(parseRes.scheme, None)
        if storage:
            return storage.search(uri, path)
        return None

    @staticmethod
    def storageExists(uri):
        """Ask if a storage at the location described by uri exists

        Parameters
        ----------
        root : string
            URI to the the root location of the storage

        Returns
        -------
        bool
            True if the storage exists, false if not
        """
        parseRes = urllib.parse.urlparse(uri)
        storage = Storage.storages.get(parseRes.scheme, None)
        if storage:
            return storage.storageExists(uri)
        return None