Wire formatting functions for replication of new/old riak_object formats

gistfile1.erl

-define(MAGIC, 42). %% as opposed to 131 for Erlang term_to_binary or 51 for riak_object
-define(W1_VER, 1). %% first non-just-term-to-binary wire format
-type wire_version() :: w0 | w1.

%% @doc Create a new binary wire formatted replication blob, complete with
%%      bucket and key for reconstruction on the other end. BinObj should be
%%      in the new format as obtained from riak_object:to_binary(v1, RObj).
new_w1(B, K, BinObj) when is_binary(B), is_binary(K), is_binary(BinObj) ->
    KLen = byte_size(K),
    BLen = byte_size(B),
    <<?MAGIC:8/integer, ?W1_VER:8/integer,
      BLen:32/integer, B:BLen/binary,
      KLen:32/integer, K:KLen/binary, BinObj/binary>>.

%% @doc Return the wire format version of the given wire blob
wire_version(<<131, _Rest/binary>>) ->
    w0;
wire_version(<<?MAGIC:8/integer, ?W1_VER:8/integer, _Rest/binary>>) ->
    w1;
wire_version(<<?MAGIC:8/integer, N:8/integer, _Rest/binary>>) ->
    %% TODO: convert to an atom like atom_of('w' + N)
    N.

%% @doc Convert a plain or binary riak object to repl wire format.
%%      Bucket and Key will only be added if the new riak_object
%%      binary format is supplied (because it doesn't contain them).
to_wire(w0, _B, _K, <<131,_/binary>>=Bin) ->
    Bin;
to_wire(w0, B, K, RObj) ->
    term_to_binary(RObj);
to_wire(w1, B, K, <<131,_/binary>>=Bin) ->
    %% no need to wrap a full old object. just use w0 format
    to_wire(w0, B, K, Bin);
to_wire(w1, B, K, <<_/binary>>=Bin) ->
    new_w1(B, K, Bin);
to_wire(w1, B, K, RObj) ->
    new_w1(w1, B, K, riak_object:to_binary(v1, RObj)).

%% @doc Convert from wire format to non-binary riak_object form
from_wire(<<131, _Rest/binary>>=BinObjTerm) ->
    binary_to_term(BinObjTerm);
from_wire(<<?MAGIC:8/integer, ?W1_VER:8/integer,
            BLen:32/integer, B:BLen/binary,
            KLen:32/integer, K:KLen/binary, BinObj/binary>>) ->
    riak_object:from_binary(B, K, BinObj).
from_wire(_) ->
    {error, unknown_wire_format}.