[erlang-bugs] binary_to_term--are these bugs?

[Matthias Lang]

Most of your examples seem to say that appending extra data to the end
of something which was produced by term_to_binary() doesn't upset
binary_to_term().

That came up on the mailing list recently:

  http://www.erlang.org/pipermail/erlang-bugs/2007-November/000507.html

The last example is different, i.e.

 > <<131,67,0>>
 > '_'
 > [<<131,100,0,1,95>>]

67 is an ERL_CACHED_ATOM whereas 100 is an ERL_ATOM_EXT, which are two
different ways of representing the same thing, though the former has
some undesirable properties (tm), which is probably why
term_to_binary() won't generate it for you.

Matthias

======================================================================

John Hughes writes:
 > I've found some behaviour that I didn't expect in binary_to_term in R12B.
 > I'm testing the QuickCheck property
 > 
 >  
 > 
 > prop_binary_to_term() ->
 > 
 >     ?FORALL(Bin,binary(),
 > 
 >               case catch binary_to_term(Bin) of
 > 
 >                    {'EXIT',{badarg,_}} ->
 > 
 >                        true;
 > 
 >                    Term ->
 > 
 >                        Bins = term_to_binaries(Term),
 > 
 >                        ?WHENFAIL(io:format("~p~n~p~n",[Term,Bins]),
 > 
 >                                    lists:any(fun(Bin2)->Bin=:=Bin2
 > end,Bins))
 > 
 >               end).
 > 
 >  
 > 
 > term_to_binaries(T) ->
 > 
 >     lists:usort([term_to_binary(T,[{compressed,Level},{minor_version,Ver}])
 > 
 >                     || Level <- lists:seq(0,9),
 > 
 >                        Ver <- [0,1]]).
 > 
 >  
 > 
 > binary() ->
 > 
 >     ?LET(L,list(choose(0,255)),
 > 
 >            list_to_binary(L)).
 > 
 >  
 > 
 > The property says that any binary that binary_to_term successfully decodes,
 > must be an encoding of that term using some compression level and minor
 > version (the encoding options mentioned in the documentation). But it fails,
 > on, for example:
 > 
 >  
 > 
 > <<131,97,0,0>>
 > 
 > 0
 > 
 > [<<131,97,0>>]
 > 
 >  
 > 
 > Or
 > 
 >  
 > 
 > <<131,106,0>>
 > 
 > []
 > 
 > [<<131,106>>]
 > 
 >  
 > 
 > Or
 > 
 >  
 > 
 > <<131,106,191,1,69,44,184,180,64>>
 > 
 > []
 > 
 > [<<131,106>>]
 > 
 >  
 > 
 > Or
 > 
 >  
 > 
 > <<131,67,0>>
 > 
 > '_'
 > 
 > [<<131,100,0,1,95>>]
 > 
 >  
 > 
 > where the output in each case is the binary, the term it decodes to, and the
 > list of all possible encodings produced by term_to_binary.
 > 
 >  
 > 
 > Is this a bug?
 > 
 >  
 > 
 > John