[erlang-questions] Binary Parsing
Pete Stapley
pstapley@REDACTED
Sat Mar 21 22:01:38 CET 2009
Nevermind I found the answer in the mailing list archives.
http://www.erlang.org/pipermail/erlang-questions/2007-November/031091.html
Pete Stapley wrote:
> I am attempting to parse some Radius attributes with Erlang and I have
> run into a bit of a problem. I pass some binary data to parseAttributes
> and I want to start peeling off the attributes one by one. I first peel
> off Type which is one byte, then Length which is also one byte. Next I
> want to peel off the Attribute. The Length variable is the length of the
> attribute plus the Type and Length byte, so I have to subtract 2 bytes
> from the Length variable before peeling off the attribute. I have tried
> the method below without any luck. Is there a way to do this?
>
> Thanks,
>
> -define(BYTE, 8/unsigned-big-integer).
>
> parseAttributes(Bin) ->
> parseAttributes(Bin, []).
>
> parseAttributes(<<>>, Atts) ->
> {ok, Atts};
> %%problem is here, Length - 2 does not seem to work
> parseAttributes( <<Type:?BYTE, Length:?BYTE, Att:Length - 2/binary,
> Rest/binary>>, Atts) ->
> io:format("Type: ~p Length: ~p Att:~p Length: ~p~n", [Type, Length,
> Att, size(Rest)]),
> parseAttributes(Rest, Atts).
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