177 lines
4.5 KiB
Python
177 lines
4.5 KiB
Python
# Copyright (c) 2014 Dark Secret Software Inc.
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
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# implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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import datetime
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"""Binary data archiving library.
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Data is written in the following format:
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[HEADER]
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[PAYLOAD]
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[FOOTER]
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where:
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[HEADER] =
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[START-OF-BLOCK]
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[BLOCK-TYPE]
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[SIZE]
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[FOOTER] =
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[CRC]
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[END-OF-BLOCK]
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There are ArchiveReaders and ArchiveWriters which are managed
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by RollManager. The RollManager opens and closes Archivers as
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needed. "As needed" is determined by which RollChecker that was
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passed into the RollManager. Archive files can roll over based
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on file size or elapsed time (for writing). For reading, archive
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files are only rolled over when the EOF is reached.
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Roll Managers also take care of filename creation, compression
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of completed archives and transfer of archive files to remote
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storage locations.
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TODO: How will the ReadingRollManager know which files to read
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from, and in which order, if the filename is templated?
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"""
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def now():
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"""Broken out for testing."""
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return datetime.datetime.utcnow()
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class RollChecker(object):
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def start(self, archive):
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pass
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def check(self, archive):
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pass
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class TimeRollChecker(RollChecker):
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def __init__(self, timedelta):
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self.timedelta = timedelta
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def start(self, archive):
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self.start_time = now()
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self.end_time = self.start_time + self.timedelta
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def check(self, archive):
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return now() >= self.end_time
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class SizeRollChecker(RollChecker):
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def __init__(self, size_in_gb):
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self.size_in_gb = size_in_gb
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def check(self, archive):
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size = archive._get_file_handle().tell()
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return size / 1073741824 >= self.size_in_gb
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class RollManager(object):
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def __init__(self, filename_template, roll_checker, directory="."):
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self.filename_template = filename_template
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self.roll_checker = roll_checker
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self.directory = directory
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self.active_archive = None
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def _make_filename(self):
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f = now().strftime(self.filename_template)
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return f.replace(" ", "_")
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def get_active_archive(self):
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if not self.active_archive:
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filename = self._make_filename()
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self.active_archive = self.archive_class(filename)
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self.roll_checker.start(self.active_archive)
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return self.active_archive
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def _should_roll_archive(self):
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return False
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def _roll_archive(self):
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pass
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class ReadingRollManager(RollManager):
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def __init__(self, filename_template, roll_checker, directory="."):
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super(ReadingRollManager, self).__init__(filename_template,
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roll_checker, directory)
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self.archive_class = ArchiveReader
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def read_block(self):
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pass
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def read_header(self):
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pass
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def read_payload(self):
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pass
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class WritingRollManager(RollManager):
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def __init__(self, filename_template, roll_checker, directory="."):
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super(WritingRollManager, self).__init__(filename_template,
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roll_checker, directory)
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self.archive_class = ArchiveWriter
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def write(self, payload):
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a = self.get_active_archive()
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a.write(payload)
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if self._should_roll_archive(a):
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self._roll_archive()
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class Archive(object):
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def __init__(self, filename):
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self._handle = None
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self.filename = filename
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def get_file_handle(self):
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return self._handle
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class ArchiveWriter(Archive):
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"""The active Archive for appending.
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"""
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def __init__(self, filename):
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super(ArchiveWriter, self).__init__(filename)
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self._handle = open(filename, "wb+")
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def write(self, payload):
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pass
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class ArchiveReader(Archive):
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"""The active Archive for consuming.
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"""
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def __init__(self, filename):
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super(ArchiveReader, self).__init__(filename)
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def read_block(self):
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pass
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def read_header(self):
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pass
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def read_payload(self):
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pass
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