# !/usr/bin/env python

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"""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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import sys

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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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# dbm linked with gdbm on OS/2 doesn't have .dir file

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if not (dbm.library == "GNU gdbm" and sys.platform == "os2emx"):

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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 a .dat file

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try:

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# First check for presence of files

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os.stat(filename + os.extsep + "dat")

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size = os.stat(filename + os.extsep + "dir").st_size

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# dumbdbm files with no keys are empty

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if size == 0:

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return "dumbdbm"

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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 (OSError, 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 in (0x13579ace, 0x13579acd, 0x13579acf):

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return "gdbm"

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# Check for old Berkeley db hash file format v2

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if magic in (0x00061561, 0x61150600):

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return "bsddb185"

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# Later versions of Berkeley db hash file have a 12-byte pad in

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# 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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if __name__ == "__main__":

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for filename in sys.argv[1:]:

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print whichdb(filename) or "UNKNOWN", filename

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