%%
%% %CopyrightBegin%
%%
%% Copyright Ericsson AB 2010-2011. All Rights Reserved.
%%
%% Licensed under the Apache License, Version 2.0 (the "License");
%% you may not use this file except in compliance with the License.
%% You may obtain a copy of the License at
%%
%% http://www.apache.org/licenses/LICENSE-2.0
%%
%% Unless required by applicable law or agreed to in writing, software
%% distributed under the License is distributed on an "AS IS" BASIS,
%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
%% See the License for the specific language governing permissions and
%% limitations under the License.
%%
%% %CopyrightEnd%
%%
%%
%% A diameter callback module that can redirect selected callbacks,
%% providing reasonable default implementations otherwise.
%%
%% To order alternate callbacks, configure a #diameter_callback record
%% as the Diameter application callback in question. The record has
%% one field for each callback function as well as 'default' and
%% 'extra' fields. A function-specific field can be set to a
%% diameter:evaluable() in order to redirect the callback
%% corresponding to that field, or to 'false' to request the default
%% callback implemented in this module. If neither of these fields are
%% set then the 'default' field determines the form of the callback: a
%% module name results in the usual callback as if the module had been
%% configured directly as the callback module, a diameter_evaluable()
%% in a callback applied to the atom-valued callback name and argument
%% list. For all callbacks not to this module, the 'extra' field is a
%% list of additional arguments, following arguments supplied by
%% diameter but preceeding those of the diameter:evaluable() being
%% applied.
%%
%% For example, the following config to diameter:start_service/2, in
%% an 'application' tuple, would result in only a mymod:peer_down/3
%% callback, this module implementing the remaining callbacks.
%%
%% {module, #diameter_callback{peer_down = {mymod, down, []}}}
%%
%% Equivalently, this can also be specified with a [Mod | Args]
%% field/value list as follows.
%%
%% {module, [diameter_callback, {peer_down, {mymod, down, []}}]}
%%
%% The following would result in this module suppying peer_up and
%% peer_down callback, others taking place in module mymod.
%%
%% {module, #diameter_callback{peer_up = false,
%% peer_down = false,
%% default = mymod}}
%%
%% The following would result in all callbacks taking place as
%% calls to mymod:diameter/2.
%%
%% {module, #diameter_callback{default = {mymod, diameter, []}}}
%%
%% The following are equivalent and result in all callbacks being
%% provided by this module.
%%
%% {module, #diameter_callback{}}
%% {module, diameter_callback}
%%
-module(diameter_callback).
%% Default callbacks when no aleternate is specified.
-export([peer_up/3,
peer_down/3,
pick_peer/4,
prepare_request/3,
prepare_retransmit/3,
handle_request/3,
handle_answer/4,
handle_error/4]).
%% Callbacks taking a #diameter_callback record.
-export([peer_up/4,
peer_down/4,
pick_peer/5,
prepare_request/4,
prepare_retransmit/4,
handle_request/4,
handle_answer/5,
handle_error/5]).
-include_lib("diameter/include/diameter.hrl").
%%% ----------------------------------------------------------
%%% # peer_up/3
%%% ----------------------------------------------------------
peer_up(_Svc, _Peer, State) ->
State.
peer_up(Svc, Peer, State, D) ->
cb(peer_up,
[Svc, Peer, State],
D#diameter_callback.peer_up,
D).
%%% ----------------------------------------------------------
%%% # peer_down/3
%%% ----------------------------------------------------------
peer_down(_Svc, _Peer, State) ->
State.
peer_down(Svc, Peer, State, D) ->
cb(peer_down,
[Svc, Peer, State],
D#diameter_callback.peer_down,
D).
%%% ----------------------------------------------------------
%%% # pick_peer/4
%%% ----------------------------------------------------------
pick_peer([Peer|_], _, _Svc, _State) ->
{ok, Peer};
pick_peer([], _, _Svc, _State) ->
false.
pick_peer(PeersL, PeersR, Svc, State, D) ->
cb(pick_peer,
[PeersL, PeersR, Svc, State],
D#diameter_callback.pick_peer,
D).
%%% ----------------------------------------------------------
%%% # prepare_request/3
%%% ----------------------------------------------------------
prepare_request(Pkt, _Svc, _Peer) ->
{send, Pkt}.
prepare_request(Pkt, Svc, Peer, D) ->
cb(prepare_request,
[Pkt, Svc, Peer],
D#diameter_callback.prepare_request,
D).
%%% ----------------------------------------------------------
%%% # prepare_retransmit/3
%%% ----------------------------------------------------------
prepare_retransmit(Pkt, _Svc, _Peer) ->
{send, Pkt}.
prepare_retransmit(Pkt, Svc, Peer, D) ->
cb(prepare_retransmit,
[Pkt, Svc, Peer],
D#diameter_callback.prepare_retransmit,
D).
%%% ----------------------------------------------------------
%%% # handle_request/3
%%% ----------------------------------------------------------
handle_request(_Pkt, _Svc, _Peer) ->
{protocol_error, 3001}. %% DIAMETER_COMMAND_UNSUPPORTED
handle_request(Pkt, Svc, Peer, D) ->
cb(handle_request,
[Pkt, Svc, Peer],
D#diameter_callback.handle_request,
D).
%%% ----------------------------------------------------------
%%% # handle_answer/4
%%% ----------------------------------------------------------
handle_answer(#diameter_packet{msg = Ans, errors = []}, _Req, _Svc, _Peer) ->
Ans;
handle_answer(#diameter_packet{msg = Ans, errors = Es}, _Req, _Svc, _Peer) ->
[Ans | Es].
handle_answer(Pkt, Req, Svc, Peer, D) ->
cb(handle_answer,
[Pkt, Req, Svc, Peer],
D#diameter_callback.handle_answer,
D).
%%% ---------------------------------------------------------------------------
%%% # handle_error/4
%%% ---------------------------------------------------------------------------
handle_error(Reason, _Req, _Svc, _Peer) ->
{error, Reason}.
handle_error(Reason, Req, Svc, Peer, D) ->
cb(handle_error,
[Reason, Req, Svc, Peer],
D#diameter_callback.handle_error,
D).
%% ===========================================================================
%% cb/4
%% Unspecified callback: use default field to determine something
%% appropriate.
cb(CB, Args, undefined, D) ->
cb(CB, Args, D);
%% Explicitly requested default.
cb(CB, Args, false, _) ->
apply(?MODULE, CB, Args);
%% A specified callback.
cb(_, Args, F, #diameter_callback{extra = X}) ->
diameter_lib:eval([[F|X] | Args]).
%% cb/3
%% No user-supplied default: call ours.
cb(CB, Args, #diameter_callback{default = undefined}) ->
apply(?MODULE, CB, Args);
%% Default is a module name: make the usual callback.
cb(CB, Args, #diameter_callback{default = M,
extra = X})
when is_atom(M) ->
apply(M, CB, Args ++ X);
%% Default is something else: apply if to callback name and arguments.
cb(CB, Args, #diameter_callback{default = F,
extra = X}) ->
diameter_lib:eval([F, CB, Args | X]).
