What is the recommended way of encoding/decoding XDR types in erlang?

Question

In another SO discussion, we were talking about interfacing an erlang application to another non-erlang app that is using XDR encoded packets for network communications.

Unfortunately, I couldn't really find any real pointers on dealing with XDR data using erlang.

So what is the recommended way of dealing with XDR encoded data in erlang?

Thanks

PS: So far, I could find the following resources:

• Getting Erlang to talk to the outside world (2002, PDF, only mentions XDR shortly)

• Sendmail Meets Erlang: Experiences Using Erlang for Email Applications (2000, also nothing relevant in here, but still an interesting read)

• And then there's this posting, which is relevant and provides some XDR routines, but is from 08/2000, and so even predates erlang's support for the bits syntax.

Answer 1

It has been 4 days since this question was asked and still there are no answers. I did some searching and determined that XDR is meant to be a encode/decode strategy for cross platform communication. The original docs were written in 1995 and is replaced with a version in 2006.

With all like protocols there is a cost to encode/decode. The cost will never be zero because there is a wrapper around the structure.

Nonetheless, in modern applications I tend to use XML or JSON. This makes debugging easier and that I do not have to put a decode step in my logger code.

I know that this is ANSWER not directed at XDR, however, JSON and XML are cross platform, have a reasonable performance model, plenty of tools and libraries... and are basically a reasonable alternative to XDR.

[update] - based on your comment... you'll have to build your own. Sorry.

Answer 2

Building your own XDR encode and decode library isn't difficult.

Encoding Erlang terms to XDR is trivial:

%% @spec push_bool(bool()) -> binary()

push_bool(Value) ->
    case Value of
        true ->
           <<0, 0, 0, 1>>;
        false ->
            <<0, 0, 0, 0>>
    end.

Going the other way is a bit more verbose, depending on how you would like error reporting to be done. I've chosen exceptions:

%% @spec pull_bool(binary()) -> {bool(), binary()}

pull_bool(Bin) ->
    {Value, Tail} = 
        try
            <<0, 0, 0, V, T/binary>> = Bin,
            {V, T}
        catch 
            error:{badmatch, _} -> 
                throw({xdr_error, "Invalid boolean value"})
        end,
    Result = case Value of
                 0 -> false;
                 1 -> true;
                 _ -> throw({xdr_error, "Invalid boolean value"})
             end, 
    {Result, Tail}.

There really aren't that many XDR data types in total so it would maybe be a couple of hundred lines of code in total.

Answer 3

There is a project called 'rpc' in the jungerl erlang source collection. It has a code-generator that produces erlang code to manage xdr-based protocols.