Add hash and direct pick strategies

src/grpcbox_channel.erl

@@ -5,6 +5,7 @@
 -export([start_link/3,
          is_ready/1,
          pick/2,
+         pick/3,
          stop/1,
          stop/2]).
 -export([init/1,
@@ -58,11 +59,19 @@ is_ready(Name) ->
     gen_statem:call(?CHANNEL(Name), is_ready).
 
 %% @doc Picks a subchannel from a pool using the configured strategy.
--spec pick(name(), unary | stream) -> {ok, {pid(), grpcbox_client:interceptor() | undefined}} |
-                                   {error, undefined_channel | no_endpoints}.
+-spec pick(name(), unary | stream) ->
+    {ok, {pid(), grpcbox_client:interceptor() | undefined}} |
+    {error, undefined_channel | no_endpoints}.
 pick(Name, CallType) ->
+    pick(Name, CallType, undefined).
+
+%% @doc Picks a subchannel from a pool using the configured strategy.
+-spec pick(name(), unary | stream, term() | undefined) ->
+    {ok, {pid(), grpcbox_client:interceptor() | undefined}} |
+    {error, undefined_channel | no_endpoints}.
+pick(Name, CallType, Key) ->
     try
-        case gproc_pool:pick_worker(Name) of
+        case pick_worker(Name, Key) of
             false -> {error, no_endpoints};
             Pid when is_pid(Pid) ->
                 {ok, {Pid, interceptor(Name, CallType)}}
@@ -72,6 +81,11 @@ pick(Name, CallType) ->
             {error, undefined_channel}
     end.
 
+pick_worker(Name, undefined) ->
+    gproc_pool:pick_worker(Name);
+pick_worker(Name, Key) ->
+    gproc_pool:pick_worker(Name, Key).
+
 -spec interceptor(name(), unary | stream) -> grpcbox_client:interceptor() | undefined.
 interceptor(Name, CallType) ->
     case ets:lookup(?CHANNELS_TAB, {Name, CallType}) of
@@ -177,4 +191,3 @@ start_workers(Pool, StatsHandler, Encoding, Endpoints) ->
              Encoding, StatsHandler),
          Pid
      end || Endpoint={Transport, Host, Port, EndpointOptions} <- Endpoints].
-

src/grpcbox_client.erl

@@ -47,7 +47,8 @@
 
 get_channel(Options, Type) ->
     Channel = maps:get(channel, Options, default_channel),
-    grpcbox_channel:pick(Channel, Type).
+    Key =  maps:get(key, Options, undefined),
+    grpcbox_channel:pick(Channel, Type, Key).
 
 unary(Ctx, Service, Method, Input, Def, Options) ->
     unary(Ctx, filename:join([<<>>, Service, Method]), Input, Def, Options).