CedarBackup3.extend.capacity — Cedar Backup v3 documentation

# Source code for CedarBackup3.extend.capacity

    # -*- coding: iso-8859-1 -*-
    # vim: set ft=python ts=3 sw=3 expandtab:
    # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # #
    #
    #              C E D A R
    #          S O L U T I O N S       "Software done right."
    #           S O F T W A R E
    #
    # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # #
    #
    # Copyright (c) 2008,2010,2015 Kenneth J. Pronovici.
    # All rights reserved.
    #
    # This program is free software; you can redistribute it and/or
    # modify it under the terms of the GNU General Public License,
    # Version 2, as published by the Free Software Foundation.
    #
    # 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.
    #
    # Copies of the GNU General Public License are available from
    # the Free Software Foundation website, http://www.gnu.org/.
    #
    # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # #
    #
    # Author   : Kenneth J. Pronovici <pronovic@ieee.org>
    # Language : Python 3 (>= 3.4)
    # Project  : Cedar Backup, release 3
    # Purpose  : Provides an extension to check remaining media capacity.
    #
    # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # #

    ########################################################################
    # Module documentation
    ########################################################################

    """
    Provides an extension to check remaining media capacity.

    Some users have asked for advance warning that their media is beginning to fill
    up.  This is an extension that checks the current capacity of the media in the
    writer, and prints a warning if the media is more than X% full, or has fewer
    than X bytes of capacity remaining.

    :author: Kenneth J. Pronovici <pronovic@ieee.org>
    """

    ########################################################################
    # Imported modules
    ########################################################################

    # System modules
    import logging
    from functools import total_ordering

    # Cedar Backup modules
    from CedarBackup3.util import displayBytes
    from CedarBackup3.config import ByteQuantity, readByteQuantity, addByteQuantityNode
    from CedarBackup3.xmlutil import createInputDom, addContainerNode, addStringNode
    from CedarBackup3.xmlutil import readFirstChild, readString
    from CedarBackup3.actions.util import createWriter, checkMediaState

    ########################################################################
    # Module-wide constants and variables
    ########################################################################

    logger = logging.getLogger("CedarBackup3.log.extend.capacity")

    ########################################################################
    # Percentage class definition
    ########################################################################

    @total_ordering
    class PercentageQuantity(object):

       """
       Class representing a percentage quantity.

       The percentage is maintained internally as a string so that issues of
       precision can be avoided.  It really isn't possible to store a floating
       point number here while being able to losslessly translate back and forth
       between XML and object representations.  (Perhaps the Python 2.4 Decimal
       class would have been an option, but I originally wanted to stay compatible
       with Python 2.3.)

       Even though the quantity is maintained as a string, the string must be in a
       valid floating point positive number.  Technically, any floating point
       string format supported by Python is allowble.  However, it does not make
       sense to have a negative percentage in this context.

       """

       def __init__(self, quantity=None):
          """
          Constructor for the ``PercentageQuantity`` class.
          Args:
             quantity: Percentage quantity, as a string (i.e. "99.9" or "12")
          Raises:
             ValueError: If the quantity value is invaid
          """
          self._quantity = None
          self.quantity = quantity

       def __repr__(self):
          """
          Official string representation for class instance.
          """
          return "PercentageQuantity(%s)" % (self.quantity)

       def __str__(self):
          """
          Informal string representation for class instance.
          """
          return self.__repr__()

       def __eq__(self, other):
          """Equals operator, iplemented in terms of original Python 2 compare operator."""
          return self.__cmp__(other) == 0

       def __lt__(self, other):
          """Less-than operator, iplemented in terms of original Python 2 compare operator."""
          return self.__cmp__(other) < 0

       def __gt__(self, other):
          """Greater-than operator, iplemented in terms of original Python 2 compare operator."""
          return self.__cmp__(other) > 0

       def __cmp__(self, other):
          """
          Original Python 2 comparison operator.
          Lists within this class are "unordered" for equality comparisons.
          Args:
             other: Other object to compare to
          Returns:
              -1/0/1 depending on whether self is ``<``, ``=`` or ``>`` other
          """
          if other is None:
             return 1
          if self.quantity != other.quantity:
             if float(self.quantity or 0.0) < float(other.quantity or 0.0):
                return -1
             else:
                return 1
          return 0

       def _setQuantity(self, value):
          """
          Property target used to set the quantity
          The value must be a non-empty string if it is not ``None``.
          Raises:
             ValueError: If the value is an empty string
             ValueError: If the value is not a valid floating point number
             ValueError: If the value is less than zero
          """
          if value is not None:
             if len(value) < 1:
                raise ValueError("Percentage must be a non-empty string.")
             floatValue = float(value)
             if floatValue < 0.0 or floatValue > 100.0:
                raise ValueError("Percentage must be a positive value from 0.0 to 100.0")
          self._quantity = value # keep around string

       def _getQuantity(self):
          """
          Property target used to get the quantity.
          """
          return self._quantity

       def _getPercentage(self):
          """
          Property target used to get the quantity as a floating point number.
          If there is no quantity set, then a value of 0.0 is returned.
          """
          if self.quantity is not None:
             return float(self.quantity)
          return 0.0

       quantity = property(_getQuantity, _setQuantity, None, doc="Percentage value, as a string")
       percentage = property(_getPercentage, None, None, "Percentage value, as a floating point number.")

    ########################################################################
    # CapacityConfig class definition
    ########################################################################

    @total_ordering
    class CapacityConfig(object):

       """
       Class representing capacity configuration.

       The following restrictions exist on data in this class:

          - The maximum percentage utilized must be a PercentageQuantity
          - The minimum bytes remaining must be a ByteQuantity

       """

       def __init__(self, maxPercentage=None, minBytes=None):
          """
          Constructor for the ``CapacityConfig`` class.

          Args:
             maxPercentage: Maximum percentage of the media that may be utilized
             minBytes: Minimum number of free bytes that must be available
          """
          self._maxPercentage = None
          self._minBytes = None
          self.maxPercentage = maxPercentage
          self.minBytes = minBytes

       def __repr__(self):
          """
          Official string representation for class instance.
          """
          return "CapacityConfig(%s, %s)" % (self.maxPercentage, self.minBytes)

       def __str__(self):
          """
          Informal string representation for class instance.
          """
          return self.__repr__()

       def __eq__(self, other):
          """Equals operator, iplemented in terms of original Python 2 compare operator."""
          return self.__cmp__(other) == 0

       def __lt__(self, other):
          """Less-than operator, iplemented in terms of original Python 2 compare operator."""
          return self.__cmp__(other) < 0

       def __gt__(self, other):
          """Greater-than operator, iplemented in terms of original Python 2 compare operator."""
          return self.__cmp__(other) > 0

       def __cmp__(self, other):
          """
          Original Python 2 comparison operator.
          Args:
             other: Other object to compare to
          Returns:
              -1/0/1 depending on whether self is ``<``, ``=`` or ``>`` other
          """
          if other is None:
             return 1
          if self.maxPercentage != other.maxPercentage:
             if (self.maxPercentage or PercentageQuantity()) < (other.maxPercentage or PercentageQuantity()):
                return -1
             else:
                return 1
          if self.minBytes != other.minBytes:
             if (self.minBytes or ByteQuantity()) < (other.minBytes or ByteQuantity()):
                return -1
             else:
                return 1
          return 0

       def _setMaxPercentage(self, value):
          """
          Property target used to set the maxPercentage value.
          If not ``None``, the value must be a ``PercentageQuantity`` object.
          Raises:
             ValueError: If the value is not a ``PercentageQuantity``
          """
          if value is None:
             self._maxPercentage = None
          else:
             if not isinstance(value, PercentageQuantity):
                raise ValueError("Value must be a ``PercentageQuantity`` object.")
             self._maxPercentage = value

       def _getMaxPercentage(self):
          """
          Property target used to get the maxPercentage value
          """
          return self._maxPercentage

       def _setMinBytes(self, value):
          """
          Property target used to set the bytes utilized value.
          If not ``None``, the value must be a ``ByteQuantity`` object.
          Raises:
             ValueError: If the value is not a ``ByteQuantity``
          """
          if value is None:
             self._minBytes = None
          else:
             if not isinstance(value, ByteQuantity):
                raise ValueError("Value must be a ``ByteQuantity`` object.")
             self._minBytes = value

       def _getMinBytes(self):
          """
          Property target used to get the bytes remaining value.
          """
          return self._minBytes

       maxPercentage = property(_getMaxPercentage, _setMaxPercentage, None, "Maximum percentage of the media that may be utilized.")
       minBytes = property(_getMinBytes, _setMinBytes, None, "Minimum number of free bytes that must be available.")

    ########################################################################
    # LocalConfig class definition
    ########################################################################

    @total_ordering
    class LocalConfig(object):

       """
       Class representing this extension's configuration document.

       This is not a general-purpose configuration object like the main Cedar
       Backup configuration object.  Instead, it just knows how to parse and emit
       specific configuration values to this extension.  Third parties who need to
       read and write configuration related to this extension should access it
       through the constructor, ``validate`` and ``addConfig`` methods.

       *Note:* Lists within this class are "unordered" for equality comparisons.

       """

       def __init__(self, xmlData=None, xmlPath=None, validate=True):
          """
          Initializes a configuration object.

          If you initialize the object without passing either ``xmlData`` or
          ``xmlPath`` then configuration will be empty and will be invalid until it
          is filled in properly.

          No reference to the original XML data or original path is saved off by
          this class.  Once the data has been parsed (successfully or not) this
          original information is discarded.

          Unless the ``validate`` argument is ``False``, the :any:`LocalConfig.validate`
          method will be called (with its default arguments) against configuration
          after successfully parsing any passed-in XML.  Keep in mind that even if
          ``validate`` is ``False``, it might not be possible to parse the passed-in
          XML document if lower-level validations fail.

          *Note:* It is strongly suggested that the ``validate`` option always be set
          to ``True`` (the default) unless there is a specific need to read in
          invalid configuration from disk.

          Args:
             xmlData (String data): XML data representing configuration
             xmlPath (Absolute path to a file on disk): Path to an XML file on disk
             validate (Boolean true/false): Validate the document after parsing it
          Raises:
             ValueError: If both ``xmlData`` and ``xmlPath`` are passed-in
             ValueError: If the XML data in ``xmlData`` or ``xmlPath`` cannot be parsed
             ValueError: If the parsed configuration document is not valid
          """
          self._capacity = None
          self.capacity = None
          if xmlData is not None and xmlPath is not None:
             raise ValueError("Use either xmlData or xmlPath, but not both.")
          if xmlData is not None:
             self._parseXmlData(xmlData)
             if validate:
                self.validate()
          elif xmlPath is not None:
             with open(xmlPath) as f:
                xmlData = f.read()
             self._parseXmlData(xmlData)
             if validate:
                self.validate()

       def __repr__(self):
          """
          Official string representation for class instance.
          """
          return "LocalConfig(%s)" % (self.capacity)

       def __str__(self):
          """
          Informal string representation for class instance.
          """
          return self.__repr__()

       def __eq__(self, other):
          """Equals operator, iplemented in terms of original Python 2 compare operator."""
          return self.__cmp__(other) == 0

       def __lt__(self, other):
          """Less-than operator, iplemented in terms of original Python 2 compare operator."""
          return self.__cmp__(other) < 0

       def __gt__(self, other):
          """Greater-than operator, iplemented in terms of original Python 2 compare operator."""
          return self.__cmp__(other) > 0

       def __cmp__(self, other):
          """
          Original Python 2 comparison operator.
          Lists within this class are "unordered" for equality comparisons.
          Args:
             other: Other object to compare to
          Returns:
              -1/0/1 depending on whether self is ``<``, ``=`` or ``>`` other
          """
          if other is None:
             return 1
          if self.capacity != other.capacity:
             if self.capacity < other.capacity:
                return -1
             else:
                return 1
          return 0

       def _setCapacity(self, value):
          """
          Property target used to set the capacity configuration value.
          If not ``None``, the value must be a ``CapacityConfig`` object.
          Raises:
             ValueError: If the value is not a ``CapacityConfig``
          """
          if value is None:
             self._capacity = None
          else:
             if not isinstance(value, CapacityConfig):
                raise ValueError("Value must be a ``CapacityConfig`` object.")
             self._capacity = value

       def _getCapacity(self):
          """
          Property target used to get the capacity configuration value.
          """
          return self._capacity

       capacity = property(_getCapacity, _setCapacity, None, "Capacity configuration in terms of a ``CapacityConfig`` object.")

       def validate(self):
          """
          Validates configuration represented by the object.
          THere must be either a percentage, or a byte capacity, but not both.
          Raises:
             ValueError: If one of the validations fails
          """
          if self.capacity is None:
             raise ValueError("Capacity section is required.")
          if self.capacity.maxPercentage is None and self.capacity.minBytes is None:
             raise ValueError("Must provide either max percentage or min bytes.")
          if self.capacity.maxPercentage is not None and self.capacity.minBytes is not None:
             raise ValueError("Must provide either max percentage or min bytes, but not both.")

       def addConfig(self, xmlDom, parentNode):
          """
          Adds a <capacity> configuration section as the next child of a parent.

          Third parties should use this function to write configuration related to
          this extension.

          We add the following fields to the document::

             maxPercentage  //cb_config/capacity/max_percentage
             minBytes       //cb_config/capacity/min_bytes

          Args:
             xmlDom: DOM tree as from ``impl.createDocument()``
             parentNode: Parent that the section should be appended to
          """
          if self.capacity is not None:
             sectionNode = addContainerNode(xmlDom, parentNode, "capacity")
             LocalConfig._addPercentageQuantity(xmlDom, sectionNode, "max_percentage", self.capacity.maxPercentage)
             if self.capacity.minBytes is not None: # because utility function fills in empty section on None
                addByteQuantityNode(xmlDom, sectionNode, "min_bytes", self.capacity.minBytes)

       def _parseXmlData(self, xmlData):
          """
          Internal method to parse an XML string into the object.

          This method parses the XML document into a DOM tree (``xmlDom``) and then
          calls a static method to parse the capacity configuration section.

          Args:
             xmlData (String data): XML data to be parsed
          Raises:
             ValueError: If the XML cannot be successfully parsed
          """
          (xmlDom, parentNode) = createInputDom(xmlData)
          self._capacity = LocalConfig._parseCapacity(parentNode)

       @staticmethod
       def _parseCapacity(parentNode):
          """
          Parses a capacity configuration section.

          We read the following fields::

             maxPercentage  //cb_config/capacity/max_percentage
             minBytes       //cb_config/capacity/min_bytes

          Args:
             parentNode: Parent node to search beneath

          Returns:
              ``CapacityConfig`` object or ``None`` if the section does not exist
          Raises:
             ValueError: If some filled-in value is invalid
          """
          capacity = None
          section = readFirstChild(parentNode, "capacity")
          if section is not None:
             capacity = CapacityConfig()
             capacity.maxPercentage = LocalConfig._readPercentageQuantity(section, "max_percentage")
             capacity.minBytes = readByteQuantity(section, "min_bytes")
          return capacity

       @staticmethod
       def _readPercentageQuantity(parent, name):
          """
          Read a percentage quantity value from an XML document.
          Args:
             parent: Parent node to search beneath
             name: Name of node to search for
          Returns:
              Percentage quantity parsed from XML document
          """
          quantity = readString(parent, name)
          if quantity is None:
             return None
          return PercentageQuantity(quantity)

       @staticmethod
       def _addPercentageQuantity(xmlDom, parentNode, nodeName, percentageQuantity):
          """
          Adds a text node as the next child of a parent, to contain a percentage quantity.

          If the ``percentageQuantity`` is None, then no node will be created.

          Args:
             xmlDom: DOM tree as from ``impl.createDocument()``
             parentNode: Parent node to create child for
             nodeName: Name of the new container node
             percentageQuantity: PercentageQuantity object to put into the XML document

          Returns:
              Reference to the newly-created node
          """
          if percentageQuantity is not None:
             addStringNode(xmlDom, parentNode, nodeName, percentageQuantity.quantity)

    ########################################################################
    # Public functions
    ########################################################################

    ###########################
    # executeAction() function
    ###########################

    # pylint: disable=W0613
    def executeAction(configPath, options, config):
       """
       Executes the capacity action.

       Args:
          configPath (String representing a path on disk): Path to configuration file on disk
          options (Options object): Program command-line options
          config (Config object): Program configuration
       Raises:
          ValueError: Under many generic error conditions
          IOError: If there are I/O problems reading or writing files
       """
       logger.debug("Executing capacity extended action.")
       if config.options is None or config.store is None:
          raise ValueError("Cedar Backup configuration is not properly filled in.")
       local = LocalConfig(xmlPath=configPath)
       if config.store.checkMedia:
          checkMediaState(config.store)  # raises exception if media is not initialized
       capacity = createWriter(config).retrieveCapacity()
       logger.debug("Media capacity: %s", capacity)
       if local.capacity.maxPercentage is not None:
          if capacity.utilized > local.capacity.maxPercentage.percentage:
             logger.error("Media has reached capacity limit of %s%%: %.2f%% utilized",
                          local.capacity.maxPercentage.quantity, capacity.utilized)
       else:
          if capacity.bytesAvailable < local.capacity.minBytes:
             logger.error("Media has reached capacity limit of %s: only %s available",
                          local.capacity.minBytes, displayBytes(capacity.bytesAvailable))
       logger.info("Executed the capacity extended action successfully.")