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7446f8cbbf
Usually log lines start with a line ending, which means the first hit is always an empty line with reading things backwards. This empty line has no relevance, but only indicates we're at the end of the file. This commits stores the file starting position in all cases and ignores the output when we trying to yield the end of the file.
73 lines
2.8 KiB
Python
73 lines
2.8 KiB
Python
"""
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Copyright (c) 2015-2022 Ad Schellevis <ad@opnsense.org>
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All rights reserved.
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Redistribution and use in source and binary forms, with or without
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modification, are permitted provided that the following conditions are met:
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1. Redistributions of source code must retain the above copyright notice,
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this list of conditions and the following disclaimer.
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2. Redistributions in binary form must reproduce the above copyright
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notice, this list of conditions and the following disclaimer in the
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documentation and/or other materials provided with the distribution.
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THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
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INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
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AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
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OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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POSSIBILITY OF SUCH DAMAGE.
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"""
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import os
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def reverse_log_reader(filename, block_size=81920, start_pos=None):
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""" read log file in reverse order
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:param filename: filename or stream to parse
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:param block_size: max block size to examine per loop
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:param start_pos: start at position in file (None is end of file)
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:return: generator
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"""
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if hasattr(filename, 'read') is False:
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input_stream = open(filename, 'r', errors='replace')
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else:
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input_stream = filename
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if start_pos is None:
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input_stream.seek(0, os.SEEK_END)
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start_pos = input_stream.tell()
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file_byte_start = start_pos
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data = ''
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while file_byte_start > 0:
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if file_byte_start - block_size < 0:
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block_size = file_byte_start
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file_byte_start = 0
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else:
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file_byte_start -= block_size
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input_stream.seek(file_byte_start)
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data = input_stream.read(block_size) + data
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# split stream using begin of line (bol) and end of line (eol)
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bol = data.rfind('\n')
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eol = len(data)
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while bol > -1:
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line_end = file_byte_start + eol
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line = data[bol:eol]
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eol = bol
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bol = data.rfind('\n', 0, eol)
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if line_end != start_pos:
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yield {'line': line.strip().strip('\u0000'), 'pos': line_end}
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data = data[:eol] if bol == -1 else ''
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if file_byte_start == 0 and bol == -1:
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yield {'line': data.strip().strip('\u0000'), 'pos': len(data)}
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