Converting string to binary

Question

I have the following issue. I have a file which used for storing array of some records (unknown structure). All that I know that all records separated with "." (dot). One of the "fields" of this record is a binary value.

So the structure is:

multiline_text <<binary_value>> multiline_text .

I can read file chunk-by-chunk (because it pretty large) and parse data to get actual data "<>" but it's not a binary value it's a string. I'm trying to convert it binary (to convert to term late) but i have no success.

I tried to use BIF list_to_binary (but it won't work because it is not a list) - it's already a binary. I tried to convert it to list of integers, fold them and convert and it's still is not working.

I suppose I'm missing something basic (I'm newbie in Erlang). Are there any advices?

Diego Sevilla · Accepted Answer · 2012-06-08 11:50:47Z

2

If you get the binary you're interested in into an String in this format, for example:

S = "<< 1,2,3 >>".

then you can do something like this:

> {ok, T, _} = erl_scan:string(S ++ ".").
> {ok, Term} = erl_parse:parse_term(T). 
{ok,<<1,2,3>>}

and then you can use Term, that actually has the binary you just read as a string.

answered Jun 8, 2012 at 11:50

Diego Sevilla

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3 Comments

ravnur Over a year ago

Works for me. Thanks a lot! Is it hack or not?

Inaimathi Over a year ago

First glance, this makes me nervous about potential injection attacks. Is that an unfounded suspicion in general when using parse_term, or are you making the assumption that the binary value is coming from a trusted source?

Diego Sevilla Over a year ago

I think converting a string to a binary is not that problematic. It would be equally insecure as reading a buffer from a file.

KrHubert · Accepted Answer · 2012-06-08 12:11:29Z

1

Here is version without erl_parse. Just to study:

str2bin(Bin)->
Bin1 = string:strip(Bin, left, $<),
Bin2 = string:strip(Bin1, right, $>),
list_to_binary(lists:map(fun(Str) -> {Int, _Rest} = string:to_integer(string:strip(Str)), Int end, string:tokens(Bin2, ","))).

answered Jun 8, 2012 at 12:11

KrHubert

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