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57 lines
1.2 KiB
Python
57 lines
1.2 KiB
Python
"""Guess which db package to use to open a db file."""
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import struct
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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 + ".pag", "rb")
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f.close()
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f = open(filename + ".dir", "rb")
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f.close()
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return "dbm"
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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 first 4 bytes of the file -- the magic number
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s = f.read(4)
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f.close()
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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 == 0x061561:
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return "dbhash"
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# Unknown
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return ""
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