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.
-------------
%% creates a new state record with a unique id
new(SessionId, OldId) when OldId =:= undefined orelse is_integer(OldId) ->
Now = now(),
F = fun() ->
MaxId = mnesia:foldl(fun(Elem, Max) ->
case Elem#wstate.id of
M when M > Max -> M;
_ -> Max
end
end, 0, wstate),
WS = #wstate{id = MaxId + 1,
session_id = SessionId,
proceededby = OldId,
created = Now,
last_touched = Now,
values = undefined
},
mnesia:write(wstate, WS, write),
WS
end,
{atomic, Rec} = mnesia:transaction(F),
Rec.
%% Given the numeric id encodes for use in web pages.
encode(undefined) ->
undefined;
encode(Id) ->
IdBin = <<Id:128/integer-big>>,
IVec = crypto:rand_bytes(16),
IdCrypt = crypto:aes_cbc_128_encrypt(?KEY, IVec, IdBin),
MagicStr = <<IVec/binary, IdCrypt/binary>>,
B64 = http_base_64:encode(binary_to_list(MagicStr)),
sub_slash_and_plus(B64).
sub_slash_and_plus(Str) when is_list(Str) ->
lists:map(fun(Elem) ->
case Elem of
$+ -> $-;
$/ -> $_;
L -> L
end
end, Str).
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