Disterl: dist_listen_min/max

Similar to erlang inet_dist_listen_min.
https://www.erlang.org/doc/apps/kernel/kernel_app.html#inet_dist_listen

Needed for certain gateways/port forwarding scenarios.

Namely running local Wokwi simulator and connecting to that.

Signed-off-by: Peter M <petermm@gmail.com>

Author: petermm

libs/estdlib/src/net_kernel.erl

@@ -73,6 +73,8 @@
 %% @param Options options for distribution. Supported options are:
 %% - `name_domain' : whether name should be short or long
 %% - `proto_dist' : the module used for distribution (e.g. `socket_dist')
+%% - `dist_listen_min' : defines the min port range for the listener socket.
+%% - `dist_listen_max' : defines the max port range for the listener socket.
 %%-----------------------------------------------------------------------------
 -spec start(atom(), map()) -> {ok, pid()}.
 start(Name, Options0) when is_atom(Name) andalso is_map(Options0) ->
@@ -81,11 +83,31 @@ start(Name, Options0) when is_atom(Name) andalso is_map(Options0) ->
             case Key of
                 name_domain when Val =:= shortnames orelse Val =:= longnames -> ok;
                 proto_dist when is_atom(Val) -> ok;
+                dist_listen_min when is_integer(Val) -> ok;
+                dist_listen_max when is_integer(Val) -> ok;
                 _ -> error({invalid_option, Key, Val}, [Name, Options0])
             end
         end,
         Options0
     ),
+    % Check that if one of dist_listen_min and dist_listen_max are configured, both are configured.
+    % And verify dist_listen_max is larger or equal to dist_listen_min.
+    ok =
+        case {maps:is_key(dist_listen_min, Options0), maps:is_key(dist_listen_max, Options0)} of
+            {true, false} ->
+                error(missing_dist_listen_max, [Name, Options0]);
+            {false, true} ->
+                error(missing_dist_listen_min, [Name, Options0]);
+            {true, true} ->
+                Min = maps:get(dist_listen_min, Options0),
+                Max = maps:get(dist_listen_max, Options0),
+                if
+                    Min > Max -> error(invalid_port_range, [Name, Options0]);
+                    true -> ok
+                end;
+            _ ->
+                ok
+        end,
     Options1 = Options0#{name => Name},
     Options2 = split_name(Options1),
     net_kernel_sup:start(Options2);
@@ -189,13 +211,16 @@ init(Options) ->
     process_flag(trap_exit, true),
     LongNames = maps:get(name_domain, Options, longnames) =:= longnames,
     ProtoDist = maps:get(proto_dist, Options, socket_dist),
+    DistPortMin = maps:get(dist_listen_min, Options, 0),
+    DistPortMax = maps:get(dist_listen_max, Options, 0),
     Name = maps:get(name, Options),
     Node = maps:get(node, Options),
     Cookie = crypto:strong_rand_bytes(16),
     TickInterval = (?NET_TICK_TIME * 1000) div ?NET_TICK_INTENSITY,
     Self = self(),
     Ticker = spawn_link(fun() -> ticker(Self, TickInterval) end),
-    case ProtoDist:listen(Name) of
+    % Try ports in range until one succeeds
+    case try_listen_ports(ProtoDist, Name, DistPortMin, DistPortMax) of
         {ok, {Listen, _Address, Creation}} ->
             true = erlang:setnode(Node, Creation),
             AcceptPid = ProtoDist:accept(Listen),
@@ -214,6 +239,18 @@ init(Options) ->
             {stop, Reason}
     end.
 
+%% @hidden
+try_listen_ports(ProtoDist, Name, DistPortMin, DistPortMax) ->
+    try_listen_ports(ProtoDist, Name, DistPortMin, DistPortMax, DistPortMin).
+
+try_listen_ports(_ProtoDist, _Name, _DistPortMin, DistPortMax, Port) when Port > DistPortMax ->
+    {error, no_port_available};
+try_listen_ports(ProtoDist, Name, DistPortMin, DistPortMax, Port) ->
+    case ProtoDist:listen(Name, Port) of
+        {ok, _} = Success -> Success;
+        {error, _} -> try_listen_ports(ProtoDist, Name, DistPortMin, DistPortMax, Port + 1)
+    end.
+
 %% @hidden
 handle_call(get_state, _From, #state{longnames = Longnames} = State) ->
     NameDomain =

libs/estdlib/src/socket_dist.erl

@@ -22,6 +22,7 @@
 % dist interface
 -export([
     listen/1,
+    listen/2,
     accept/1,
     accept_connection/5,
     setup/5,
@@ -37,24 +38,37 @@
 
 -spec listen(string()) -> {ok, {any(), #net_address{}, pos_integer()}} | {error, any()}.
 listen(Name) ->
+    listen(Name, 0).
+
+-spec listen(string(), non_neg_integer()) ->
+    {ok, {any(), #net_address{}, pos_integer()}} | {error, any()}.
+listen(Name, SocketPort) ->
     {ok, LSock} = socket:open(inet, stream, tcp),
-    ok = socket:bind(LSock, #{
-        family => inet,
-        port => 0,
-        addr => {0, 0, 0, 0}
-    }),
-    ok = socket:listen(LSock),
-    {ok, #{addr := Addr, port := Port}} = socket:sockname(LSock),
-    ErlEpmd = net_kernel:epmd_module(),
-    Address = #net_address{
-        host = Addr,
-        protocol = tcp,
-        family = inet
-    },
-    case ErlEpmd:register_node(Name, Port) of
-        {ok, Creation} ->
-            {ok, {LSock, Address, Creation}};
-        Error ->
+    case
+        socket:bind(LSock, #{
+            family => inet,
+            port => SocketPort,
+            addr => {0, 0, 0, 0}
+        })
+    of
+        ok ->
+            ok = socket:listen(LSock),
+            {ok, #{addr := Addr, port := Port}} = socket:sockname(LSock),
+            ErlEpmd = net_kernel:epmd_module(),
+            Address = #net_address{
+                host = Addr,
+                protocol = tcp,
+                family = inet
+            },
+            case ErlEpmd:register_node(Name, Port) of
+                {ok, Creation} ->
+                    {ok, {LSock, Address, Creation}};
+                Error ->
+                    socket:close(LSock),
+                    Error
+            end;
+        {error, _} = Error ->
+            socket:close(LSock),
             Error
     end.