fmtPosixRepositoryCfg.py

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#
# LSST Data Management System
# Copyright 2017 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/>.
#
 
import copy
import errno
import yaml
import os
import urllib
from . import PosixStorage, RepositoryCfg, safeFileIo, ParentsMismatch
 
 
__all__ = []
 
try:
    # PyYAML >=5.1 prefers a different loader
    # We need to use Unsafe because obs packages do not register
    # constructors but rely on python object syntax.
    Loader = yaml.UnsafeLoader
except AttributeError:
    Loader = yaml.Loader
 
 
def _write(butlerLocation, cfg):
    """Serialize a RepositoryCfg to a location.
 
    When the location is the same as cfg.root, the RepositoryCfg is to be written at the root location of
    the repository. In that case, root is not written in the serialized cfg; it is implicit in the
    location of the cfg. This allows the cfg to move from machine to machine without modification.
 
    Parameters
    ----------
    butlerLocation : ButlerLocation
        The location to write the RepositoryCfg.
    cfg : RepositoryCfg instance
        The RepositoryCfg to be serialized.
    """
    def setRoot(cfg, loc):
        loc = os.path.split(loc)[0]  # remove the `repoistoryCfg.yaml` file name
        if loc is None or cfg.root == loc:
            cfg = copy.copy(cfg)
            cfg.root = None
        return cfg
 
    # This class supports schema 'file' and also treats no schema as 'file'.
    # Split the URI and take only the path; remove the schema from loc if it's there.
    loc = butlerLocation.storage.root
    parseRes = urllib.parse.urlparse(loc if loc is not None else cfg.root)
    loc = os.path.join(parseRes.path, butlerLocation.getLocations()[0])
    try:
        with safeFileIo.SafeLockedFileForRead(loc) as f:
            existingCfg = _doRead(f, parseRes.path)
            if existingCfg == cfg:
                cfg.dirty = False
                return
    except IOError as e:
        if e.errno != errno.ENOENT:  # ENOENT is 'No such file or directory'
            raise
    with safeFileIo.SafeLockedFileForWrite(loc) as f:
        existingCfg = _doRead(f, parseRes.path)
        if existingCfg is None:
            cfgToWrite = setRoot(cfg, loc)
        else:
            if existingCfg == cfg:
                cfg.dirty = False
                return
            try:
                existingCfg.extend(cfg)
                cfgToWrite = setRoot(existingCfg, loc)
            except ParentsMismatch as e:
                raise RuntimeError("Can not extend existing repository cfg because: {}".format(e))
        yaml.dump(cfgToWrite, f)
        cfg.dirty = False
 
 
def _doRead(fileObject, uri):
    """Get a persisted RepositoryCfg from an open file object.
 
    Parameters
    ----------
    fileObject : an open file object
        the file that contains the RepositoryCfg.
    uri : string
        path to the repositoryCfg
 
    Returns
    -------
    A RepositoryCfg instance or None
    """
    repositoryCfg = yaml.load(fileObject, Loader=Loader)
    if repositoryCfg is not None:
        if repositoryCfg.root is None:
            repositoryCfg.root = uri
    return repositoryCfg
 
 
def _read(butlerLocation):
    """Deserialize a RepositoryCfg from a location.
 
    Parameters
    ----------
    butlerLocation : ButlerLocation
        The lcoation from which to read the RepositoryCfg.
 
    Returns
    -------
    RepositoryCfg
        The deserialized RepoistoryCfg.
 
    Raises
    ------
    IOError
        Raised if no repositoryCfg exists at the location.
    """
    repositoryCfg = None
    loc = butlerLocation.storage.root
    fileLoc = os.path.join(loc, butlerLocation.getLocations()[0])
    try:
        with safeFileIo.SafeLockedFileForRead(fileLoc) as f:
            repositoryCfg = _doRead(f, loc)
    except IOError as e:
        if e.errno != errno.ENOENT:  # ENOENT is 'No such file or directory'
            raise
    return repositoryCfg
 
 
PosixStorage.registerFormatters(RepositoryCfg, _read, _write)