Merge branch 'anders/diameter/capx_vs_dpr/OTP-14338'

* anders/diameter/capx_vs_dpr/OTP-14338:
  Let candidate peers be passed to diameter:call/4
  Comment on RFC ambiguity regarding application identifiers
  Remove trailing whitespace

4 files changed, 80 insertions, 25 deletions

diff --git a/lib/diameter/src/base/diameter.erl b/lib/diameter/src/base/diameter.erl
index 253f64133c..bd92e16fba 100644
--- a/lib/diameter/src/base/diameter.erl
+++ b/lib/diameter/src/base/diameter.erl
@@ -406,4 +406,5 @@ call(SvcName, App, Message) ->
    :: {extra, list()}
     | {filter, peer_filter()}
     | {timeout, 'Unsigned32'()}
+    | {peer, peer_ref()}
     | detach.
diff --git a/lib/diameter/src/base/diameter_capx.erl b/lib/diameter/src/base/diameter_capx.erl
index 837125339a..62b05644b2 100644
--- a/lib/diameter/src/base/diameter_capx.erl
+++ b/lib/diameter/src/base/diameter_capx.erl
@@ -416,7 +416,48 @@ bcaps(N, Caps) ->
 %% common_applications/3
 %%
 %% Identify the (local) applications to be supported on the connection
-%% in question.
+%% in question. The RFC says this:
+%%
+%% 2.4 Application Identifiers
+%%
+%%    Relay and redirect agents MUST advertise the Relay Application ID,
+%%    while all other Diameter nodes MUST advertise locally supported
+%%    applications.
+%%
+%% Taken literally, every Diameter node should then advertise support
+%% for the Diameter common messages application, with id 0, since no
+%% node can perform capabilities exchange without it. Expecting this,
+%% or regarding the support as implicit, renders the Result-Code 5010
+%% (DIAMETER_NO_COMMON_APPLICATION) meaningless however, since every
+%% node would regard the common application as being in common with
+%% the peer. In practice, nodes may or may not advertise support for
+%% Diameter common messages.
+%%
+%% That only explicitly advertised applications should be considered
+%% when computing the intersection with the peer is supported here:
+%%
+%% 5.3.  Capabilities Exchange
+%%
+%%    The receiver of the Capabilities-Exchange-Request (CER) MUST
+%%    determine common applications by computing the intersection of its
+%%    own set of supported Application Ids against all of the
+%%    Application-Id AVPs (Auth-Application-Id, Acct-Application-Id, and
+%%    Vendor-Specific-Application-Id) present in the CER.
+%%
+%% The same section also has the following about capabilities exchange
+%% messages.
+%%
+%%    The receiver only issues commands to its peers that have advertised
+%%    support for the Diameter application that defines the command.
+%%
+%% This statement is also difficult to interpret literally since it
+%% would disallow D[WP]R and more when Diameter common messages isn't
+%% advertised. In practice, diameter lets requests be sent as long as
+%% there's a dictionary configured to support it, peer selection by
+%% advertised application being possible to preempt by passing
+%% candidate peers directly to diameter:call/4. The peer can always
+%% answer 3001 (DIAMETER_COMMAND_UNSUPPORTED) or 3007
+%% (DIAMETER_APPLICATION_UNSUPPORTED) if this is objectionable.
 
 common_applications(LCaps, RCaps, #diameter_service{applications = Apps}) ->
     LA = app_union(LCaps),
diff --git a/lib/diameter/src/base/diameter_service.erl b/lib/diameter/src/base/diameter_service.erl
index 8e383818ea..a976a8b998 100644
--- a/lib/diameter/src/base/diameter_service.erl
+++ b/lib/diameter/src/base/diameter_service.erl
@@ -282,7 +282,8 @@ whois(SvcName) ->
                   | {alias, diameter:app_alias()},
       Opts :: {fun((Dict :: module()) -> [term()]),
                diameter:peer_filter(),
-               Xtra :: list()},
+               Xtra :: list(),
+               [diameter:peer_ref()]},
       TPid :: pid(),
       Caps :: #diameter_caps{},
       App  :: #diameter_app{},
@@ -310,10 +311,10 @@ pick(#state{options = SvcOpts}
      = S,
      #diameter_app{module = ModX, dictionary = Dict}
      = App0,
-     {DestF, Filter, Xtra}) ->
+     {DestF, Filter, Xtra, TPids}) ->
     App = App0#diameter_app{module = ModX ++ Xtra},
     [_,_] = RealmAndHost = diameter_lib:eval([DestF, Dict]),
-    case pick_peer(App, RealmAndHost, Filter, S) of
+    case pick_peer(App, RealmAndHost, [Filter | TPids], S) of
         {_TPid, _Caps} = TC ->
             {{TC, App}, SvcOpts};
         false = No ->
@@ -1522,8 +1523,14 @@ pick_peer(Local,
 
 %% peers/4
 
-peers(Alias, RH, Filter, T) ->
-    filter(Alias, RH, Filter, T, true).
+%% No peer options pointing at specific peers: search for them.
+peers(Alias, RH, [Filter], T) ->
+    filter(Alias, RH, Filter, T, true);
+
+%% Or just lookup.
+peers(_Alias, RH, [Filter | TPids], {PeerT, _AppT, _IdentT}) ->
+    {Ts, _} = filter(caps(PeerT, TPids), RH, Filter),
+    Ts.
 
 %% filter/5
 %%
diff --git a/lib/diameter/src/base/diameter_traffic.erl b/lib/diameter/src/base/diameter_traffic.erl
index af7ac10f13..85378babea 100644
--- a/lib/diameter/src/base/diameter_traffic.erl
+++ b/lib/diameter/src/base/diameter_traffic.erl
@@ -64,7 +64,8 @@
 
 %% Record diameter:call/4 options are parsed into.
 -record(options,
-        {filter = none  :: diameter:peer_filter(),
+        {peers = []     :: [diameter:peer_ref()],
+         filter = none  :: diameter:peer_filter(),
          extra = []     :: list(),
          timeout = 5000 :: 0..16#FFFFFFFF,  %% for outgoing requests
          detach = false :: boolean()}).
@@ -1305,36 +1306,41 @@ send_R(SvcName, AppOrAlias, Msg, CallOpts, Caller) ->
 %% make_options/1
 
 make_options(Options) ->
-    make_opts(Options, false, [], none, 5000).
+    make_opts(Options, [], false, [], none, 5000).
 
 %% Do our own recursion since this is faster than a lists:foldl/3
 %% setting elements in an #options{} accumulator.
 
-make_opts([], Detach, Extra, Filter, Tmo) ->
-    #options{detach = Detach,
+make_opts([], Peers, Detach, Extra, Filter, Tmo) ->
+    #options{peers = lists:reverse(Peers),
+             detach = Detach,
              extra = Extra,
              filter = Filter,
              timeout = Tmo};
 
-make_opts([{timeout, Tmo} | Rest], Detach, Extra, Filter, _)
+make_opts([{timeout, Tmo} | Rest], Peers, Detach, Extra, Filter, _)
   when is_integer(Tmo), 0 =< Tmo ->
-    make_opts(Rest, Detach, Extra, Filter, Tmo);
+    make_opts(Rest, Peers, Detach, Extra, Filter, Tmo);
 
-make_opts([{filter, F} | Rest], Detach, Extra, none, Tmo) ->
-    make_opts(Rest, Detach, Extra, F, Tmo);
-make_opts([{filter, F} | Rest], Detach, Extra, {all, Fs}, Tmo) ->
-    make_opts(Rest, Detach, Extra, {all, [F|Fs]}, Tmo);
-make_opts([{filter, F} | Rest], Detach, Extra, F0, Tmo) ->
-    make_opts(Rest, Detach, Extra, {all, [F0, F]}, Tmo);
+make_opts([{filter, F} | Rest], Peers, Detach, Extra, none, Tmo) ->
+    make_opts(Rest, Peers, Detach, Extra, F, Tmo);
+make_opts([{filter, F} | Rest], Peers, Detach, Extra, {all, Fs}, Tmo) ->
+    make_opts(Rest, Peers, Detach, Extra, {all, [F|Fs]}, Tmo);
+make_opts([{filter, F} | Rest], Peers, Detach, Extra, F0, Tmo) ->
+    make_opts(Rest, Peers, Detach, Extra, {all, [F0, F]}, Tmo);
 
-make_opts([{extra, L} | Rest], Detach, Extra, Filter, Tmo)
+make_opts([{extra, L} | Rest], Peers, Detach, Extra, Filter, Tmo)
   when is_list(L) ->
-    make_opts(Rest, Detach, Extra ++ L, Filter, Tmo);
+    make_opts(Rest, Peers, Detach, Extra ++ L, Filter, Tmo);
 
-make_opts([detach | Rest], _, Extra, Filter, Tmo) ->
-    make_opts(Rest, true, Extra, Filter, Tmo);
+make_opts([detach | Rest], Peers, _, Extra, Filter, Tmo) ->
+    make_opts(Rest, Peers, true, Extra, Filter, Tmo);
 
-make_opts([T | _], _, _, _, _) ->
+make_opts([{peer, TPid} | Rest], Peers, Detach, Extra, Filter, Tmo)
+  when is_pid(TPid) ->
+    make_opts(Rest, [TPid | Peers], Detach, Extra, Filter, Tmo);
+
+make_opts([T | _], _, _, _, _, _) ->
     ?ERROR({invalid_option, T}).
 
 %% ---------------------------------------------------------------------------
@@ -1684,8 +1690,8 @@ pick_peer(_, _, undefined, _) ->
 pick_peer(SvcName,
           AppOrAlias,
           Msg,
-          #options{filter = Filter, extra = Xtra}) ->
-    X = {fun(D) -> get_destination(D, Msg) end, Filter, Xtra},
+          #options{peers = TPids, filter = Filter, extra = Xtra}) ->
+    X = {fun(D) -> get_destination(D, Msg) end, Filter, Xtra, TPids},
     case diameter_service:pick_peer(SvcName, AppOrAlias, X) of
         false ->
             {error, no_connection};