> length(lists:seq($a, $z) ++ lists:seq($A, $Z) ++ lists:seq($0, $9)).
62
> math:pow(62,10).
8.39299e+17
Mmm, very little chance of collision in the original algorithm.
gen_key() ->
F = fun() ->
choose_key(5)
end,
mensia:transaction(F)
choose_key(0) ->
%% time to panic
undefined;
choose_key(Count) when is_integer(Count) ->
Chars = lists:seq($a, $z) ++ lists:seq($A, $Z) ++ lists:seq($0, $9),
Key = [lists:nth(crypto:rand_uniform(1, length(Chars)), Chars) ||
N <- lists:seq(1, 10)],
case mnesia:read(cont, Key, read) of
[] ->
%% choose again
choose_key(Count - 1);
[_ContRec] ->
Key
end.
Just thinking about edge cases and what would be the correct course of
action when a key collision occurs.
Jeff.
jm wrote:
> Yariv Sadan wrote:
>
>> Yeah, it looks similar in the way it uses processes for user sessions.
>> Unfortunately, the documentation doesn't say much about how to use it
>> to build full apps.
>
> I know your code is really only a proof of concept, but I noticed that
> your gen_key() function doesn't test for key collisions. The code I've
> been testing is a little more complicated. It walks the mnesia table to
> find the max id and adds one then encodes to/from a modified base64. The
> modification to base64 is to replace $+ with $- and $/ with $_.
> Encryption/decryption of the integer id is added to avoid making the ids
> guessable, but this is frankly all a little heavy handed.
>
> I wont post all the code as there's about three or four versions/ways of
> doing things in the same file and not all of it works at the moment as I
> keep changing my mind on how to approach problems. Anyway, use anything
> that's proves useful.
>
> Really it comes down to how likely a key/id collision is and how to
> guarrantee that a unique key can be generated in near O(1) time for a
> large number of sessions.
>
>
> Jeff.
> -------------
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