131 lines
4.4 KiB
Python
131 lines
4.4 KiB
Python
#
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# Copyright (C) 2016 The Android Open Source Project
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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 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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#
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"""Parses the contents of a Unix archive file generated using the 'ar' command.
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The constructor returns an Archive object, which contains dictionary from
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file name to file content.
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Typical usage example:
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archive = Archive(content)
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archive.Parse()
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"""
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import io
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class Archive(object):
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"""Archive object parses and stores Unix archive contents.
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Stores the file names and contents as it parses the archive.
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Attributes:
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files: a dictionary from file name (string) to file content (binary)
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"""
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GLOBAL_SIG = '!<arch>\n' # Unix global signature
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STRING_TABLE_ID = '//'
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STRING_TABLE_TERMINATOR = '/\n'
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SYM_TABLE_ID = '__.SYMDEF'
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FILE_ID_LENGTH = 16 # Number of bytes to store file identifier
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FILE_ID_TERMINATOR = '/'
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FILE_TIMESTAMP_LENGTH = 12 # Number of bytes to store file mod timestamp
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OWNER_ID_LENGTH = 6 # Number of bytes to store file owner ID
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GROUP_ID_LENGTH = 6 # Number of bytes to store file group ID
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FILE_MODE_LENGTH = 8 # Number of bytes to store file mode
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CONTENT_SIZE_LENGTH = 10 # Number of bytes to store content size
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END_TAG = '`\n' # Header end tag
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def __init__(self, file_content):
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"""Initialize and parse the archive contents.
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Args:
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file_content: Binary contents of the archive file.
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"""
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self.files = {}
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self._content = file_content
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self._cursor = 0
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self._string_table = dict()
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def ReadBytes(self, n):
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"""Reads n bytes from the content stream.
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Args:
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n: The integer number of bytes to read.
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Returns:
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The n-bit string (binary) of data from the content stream.
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Raises:
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ValueError: invalid file format.
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"""
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if self._cursor + n > len(self._content):
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raise ValueError('Invalid file. EOF reached unexpectedly.')
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content = self._content[self._cursor : self._cursor + n]
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self._cursor += n
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return content
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def Parse(self):
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"""Verifies the archive header and arses the contents of the archive.
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Raises:
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ValueError: invalid file format.
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"""
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# Check global header
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sig = self.ReadBytes(len(self.GLOBAL_SIG))
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if sig != self.GLOBAL_SIG:
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raise ValueError('File is not a valid Unix archive.')
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# Read files in archive
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while self._cursor < len(self._content):
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self.ReadFile()
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def ReadFile(self):
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"""Reads a file from the archive content stream.
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Raises:
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ValueError: invalid file format.
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"""
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name = self.ReadBytes(self.FILE_ID_LENGTH).strip()
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self.ReadBytes(self.FILE_TIMESTAMP_LENGTH)
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self.ReadBytes(self.OWNER_ID_LENGTH)
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self.ReadBytes(self.GROUP_ID_LENGTH)
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self.ReadBytes(self.FILE_MODE_LENGTH)
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size = self.ReadBytes(self.CONTENT_SIZE_LENGTH)
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content_size = int(size)
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if self.ReadBytes(len(self.END_TAG)) != self.END_TAG:
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raise ValueError('File is not a valid Unix archive. Missing end tag.')
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content = self.ReadBytes(content_size)
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if name == self.STRING_TABLE_ID:
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acc = 0
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names = content.split(self.STRING_TABLE_TERMINATOR)
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for string in names:
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self._string_table[acc] = string
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acc += len(string) + len(self.STRING_TABLE_TERMINATOR)
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elif name != self.SYM_TABLE_ID:
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if name.endswith(self.FILE_ID_TERMINATOR):
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name = name[:-len(self.FILE_ID_TERMINATOR)]
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elif name.startswith(self.FILE_ID_TERMINATOR):
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offset = int(name[len(self.FILE_ID_TERMINATOR):])
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if offset not in self._string_table:
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raise ValueError('Offset %s not in string table.', offset)
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name = self._string_table[offset]
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self.files[name] = content
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