105 lines
2.7 KiB
Python
105 lines
2.7 KiB
Python
"""Guess which db package to use to open a db file."""
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import os
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import struct
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try:
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import dbm
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_dbmerror = dbm.error
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except ImportError:
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dbm = None
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# just some sort of valid exception which might be raised in the
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# dbm test
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_dbmerror = IOError
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def whichdb(filename):
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"""Guess which db package to use to open a db file.
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Return values:
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- None if the database file can't be read;
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- empty string if the file can be read but can't be recognized
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- the module name (e.g. "dbm" or "gdbm") if recognized.
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Importing the given module may still fail, and opening the
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database using that module may still fail.
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"""
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# Check for dbm first -- this has a .pag and a .dir file
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try:
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f = open(filename + os.extsep + "pag", "rb")
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f.close()
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f = open(filename + os.extsep + "dir", "rb")
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f.close()
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return "dbm"
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except IOError:
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# some dbm emulations based on Berkeley DB generate a .db file
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# some do not, but they should be caught by the dbhash checks
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try:
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f = open(filename + os.extsep + "db", "rb")
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f.close()
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# guarantee we can actually open the file using dbm
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# kind of overkill, but since we are dealing with emulations
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# it seems like a prudent step
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if dbm is not None:
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d = dbm.open(filename)
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d.close()
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return "dbm"
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except (IOError, _dbmerror):
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pass
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# Check for dumbdbm next -- this has a .dir and and a .dat file
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try:
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f = open(filename + os.extsep + "dat", "rb")
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f.close()
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f = open(filename + os.extsep + "dir", "rb")
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try:
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if f.read(1) in ["'", '"']:
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return "dumbdbm"
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finally:
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f.close()
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except IOError:
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pass
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# See if the file exists, return None if not
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try:
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f = open(filename, "rb")
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except IOError:
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return None
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# Read the start of the file -- the magic number
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s16 = f.read(16)
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f.close()
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s = s16[0:4]
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# Return "" if not at least 4 bytes
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if len(s) != 4:
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return ""
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# Convert to 4-byte int in native byte order -- return "" if impossible
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try:
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(magic,) = struct.unpack("=l", s)
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except struct.error:
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return ""
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# Check for GNU dbm
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if magic == 0x13579ace:
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return "gdbm"
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# Check for BSD hash
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if magic in (0x00061561, 0x61150600):
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return "dbhash"
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# BSD hash v2 has a 12-byte NULL pad in front of the file type
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try:
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(magic,) = struct.unpack("=l", s16[-4:])
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except struct.error:
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return ""
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# Check for BSD hash
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if magic in (0x00061561, 0x61150600):
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return "dbhash"
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# Unknown
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return ""
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