50 lines
1.3 KiB
Python
50 lines
1.3 KiB
Python
"""
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This module provides a KEY_FUNCTION suitable for use with a memcache backend
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so that we can cache any keys, not just ones that memcache would ordinarily accept
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"""
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from django.utils.encoding import smart_str
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import hashlib
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import urllib
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def fasthash(string):
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"""
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Hashes `string` into a string representation of a 128-bit digest.
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"""
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md4 = hashlib.new("md4")
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md4.update(string)
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return md4.hexdigest()
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def cleaned_string(val):
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"""
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Converts `val` to unicode and URL-encodes special characters
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(including quotes and spaces)
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"""
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return urllib.quote_plus(smart_str(val))
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def safe_key(key, key_prefix, version):
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"""
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Given a `key`, `key_prefix`, and `version`,
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return a key that is safe to use with memcache.
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`key`, `key_prefix`, and `version` can be numbers, strings, or unicode.
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"""
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# Clean for whitespace and control characters, which
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# cause memcache to raise an exception
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key = cleaned_string(key)
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key_prefix = cleaned_string(key_prefix)
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version = cleaned_string(version)
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# Attempt to combine the prefix, version, and key
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combined = ":".join([key_prefix, version, key])
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# If the total length is too long for memcache, hash it
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if len(combined) > 250:
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combined = fasthash(combined)
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# Return the result
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return combined
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