[socket-nif] Add (partial) support for socket (level sctp) option associnfo

Added support for the SCTP option ASSOCINFO.

This option is a bit tricky. As the underlying structure (sctp_assocparams)
contains the assoc_id, it begs the question what happens if this option
is fetched for:

   * The own assoc (which means that we might have the assoc id in the
     descriptor and can initiate that part of the struct accordningly).
   * Another assoc: From assoc A asks for info with assoc_id set to
     that of assoc B.
   * The "owning" endpoint.
   * Another endpoint (an endpoint to which the assoc does not belong).

So, if the user calls socket:[getopt|setopt] for an association socket,
shall we require that the assoc_id field is set to -1? Or not set at all
and therefor filled in automatically by the nif-code?

And, if the user calls socket:[getopt|setopt] for an endpoint socket,
shall we require that the assoc_id field is set to a valid id? Or shall
it not be allowed?

Questions, questions...

OTP-14831

2 files changed, 27 insertions, 4 deletions

diff --git a/erts/preloaded/ebin/socket.beam b/erts/preloaded/ebin/socket.beam
index 63887692f9..0c496443bf 100644
--- a/erts/preloaded/ebin/socket.beam
+++ b/erts/preloaded/ebin/socket.beam
diff --git a/erts/preloaded/src/socket.erl b/erts/preloaded/src/socket.erl
index e3fb417a35..feb2e25312 100644
--- a/erts/preloaded/src/socket.erl
+++ b/erts/preloaded/src/socket.erl
@@ -95,6 +95,7 @@
               ipv6_mreq/0,
               ipv6_pmtudisc/0,
               sctp_event_subscribe/0,
+              sctp_assocparams/0,
 
 
               msg_hdr/0
@@ -187,6 +188,13 @@
                                   authentication   := boolean(),
                                   sender_dry       := boolean()}.
 
+-type sctp_assocparams() :: #{assoc_id       := integer(),
+                              max_rxt        := non_neg_integer(),
+                              num_peer_dests := non_neg_integer(),
+                              peer_rwnd      := non_neg_integer(),
+                              local_rwnd     := non_neg_integer(),
+                              cookie_life    := non_neg_integer()}.
+
 -type sockaddr_un()  :: #{family := local,
                           path   := binary() | string()}.
 -type sockaddr_in4() :: #{family := inet,
@@ -637,7 +645,7 @@
 -define(SOCKET_OPT_UDP_CORK,            1).
 
 %% -define(SOCKET_OPT_SCTP_ADAPTION_LAYER,          1).
-%% -define(SOCKET_OPT_SCTP_ASSOCINFO,               2).
+-define(SOCKET_OPT_SCTP_ASSOCINFO,               2).
 %% -define(SOCKET_OPT_SCTP_AUTH_ACTIVE_KEY,         3).
 %% -define(SOCKET_OPT_SCTP_AUTH_ASCONF,             4).
 %% -define(SOCKET_OPT_SCTP_AUTH_CHUNK,              5).
@@ -2172,8 +2180,23 @@ enc_setopt_value(udp, cork, V, _D, T, P)
 enc_setopt_value(udp = L, Opt, _V, _D, _T, _P) ->
     not_supported({L, Opt});
 
+enc_setopt_value(sctp, associnfo, #{assoc_id       := AssocId,
+                                    asocmaxrxt     := MaxRxt,
+                                    num_peer_dests := NumPeerDests,
+                                    peer_rwnd      := PeerRWND,
+                                    local_rwnd     := LocalRWND,
+                                    cookie_life    := CLife} = V,
+                 _D, _T, P)
+  when is_integer(AssocId) andalso
+       is_integer(MaxRxt)       andalso (MaxRxt >= 0)       andalso
+       is_integer(NumPeerDests) andalso (NumPeerDests >= 0) andalso
+       is_integer(PeerRWND)     andalso (PeerRWND >= 0)     andalso
+       is_integer(LocalRWND)    andalso (LocalRWND >= 0)    andalso
+       is_integer(CLife)        andalso (CLife >= 0)        andalso
+       (P =:= sctp) ->
+    V;
 enc_setopt_value(sctp, autoclose, V, _D, _T, P)
-  when is_integer(V) andalso (P =:= sctp) ->
+  when is_integer(V) andalso (V >= 0) andalso (P =:= sctp) ->
     V;
 enc_setopt_value(sctp, disable_fragments, V, _D, _T, P)
   when is_boolean(V) andalso (P =:= sctp) ->
@@ -2595,8 +2618,8 @@ enc_sockopt_key(udp = L, UnknownOpt, _Dir, _D, _T, _P) ->
 %% SCTP socket options
 enc_sockopt_key(sctp = L, adaption_layer = Opt, _Dir, _D, _T, _P) ->
     not_supported({L, Opt});
-enc_sockopt_key(sctp = L, associnfo = Opt, _Dir, _D, _T, _P) ->
-    not_supported({L, Opt});
+enc_sockopt_key(sctp = _L, associnfo = _Opt, _Dir, _D, _T, _P) ->
+    ?SOCKET_OPT_SCTP_ASSOCINFO;
 enc_sockopt_key(sctp = L, auth_active_key = Opt, _Dir, _D, _T, _P) ->
     not_supported({L, Opt});
 enc_sockopt_key(sctp = L, auth_asconf = Opt, _Dir, _D, _T, _P) ->