Create initial version of server

Just a very simple TCP echo server to get started with.

server/.gitignore

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+_build/*
+*.beam

server/rebar.config

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+{erl_opts, [debug_info]}.
+{deps, []}.

server/rebar.lock

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+[].

server/src/proto_sup.erl

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+% Copyright (c) Camden Dixie O'Brien
+% SPDX-License-Identifier: AGPL-3.0-only
+
+-module(proto_sup).
+-behaviour(supervisor).
+
+-export([start_link/1]).
+-export([init/1]).
+
+start_link(Port) ->
+	supervisor:start_link({local, ?MODULE}, ?MODULE, [Port]).
+
+init([Port]) ->
+	SupFlags = #{stragegy => one_for_all,
+				 intensity => 1,
+				 period => 5},
+	ChildSpecs = [tcp_server:child_spec(Port)],
+	{ok, {SupFlags, ChildSpecs}}.

server/src/study_system_server.app.src

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+{application, study_system_server,
+ [{description, "Study System Server"},
+  {vsn, "0.1.0"},
+  {registered, []},
+  {mod, {study_system_server_app, []}},
+  {applications, [kernel, stdlib]},
+  {env, []},
+  {modules, []},
+  {licenses, ["AGPL-3.0-only"]},
+  {links, []}]}.

server/src/study_system_server_app.erl

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+% Copyright (c) Camden Dixie O'Brien
+% SPDX-License-Identifier: AGPL-3.0-only
+
+-module(study_system_server_app).
+-behaviour(application).
+
+-export([start/2, stop/1]).
+
+start(_StartType, _StartArgs) ->
+	Port = application:get_env(study_system_server, port, 12888),
+	proto_sup:start_link(Port).
+
+stop(_State) ->
+	ok.

server/src/tcp_server.erl

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+% Copyright (c) Camden Dixie O'Brien
+% SPDX-License-Identifier: AGPL-3.0-only
+
+-module(tcp_server).
+-behaviour(gen_server).
+
+-export([start_link/1, child_spec/1]).
+-export([init/1, handle_call/3, handle_cast/2, handle_info/2,
+		 terminate/2, code_change/3]).
+
+-record(state, {socket, acceptor}).
+
+start_link(Port) ->
+	gen_server:start_link({local, ?MODULE}, ?MODULE, [Port], []).
+
+child_spec(Port) ->
+	#{id => ?MODULE,
+	  start => {?MODULE, start_link, [Port]},
+	  restart => permanent,
+	  shutdown => 5000,
+	  type => worker,
+	  modules => [?MODULE]}.
+
+init([Port]) ->
+	{ok, Socket} = gen_tcp:listen(Port, [binary, {active, true}]),
+	Pid = spawn_link(fun() -> acceptor_loop(Socket) end),
+	{ok, #state{socket = Socket, acceptor = Pid}}.
+
+handle_call(_Request, _From, State) ->
+	{reply, ok, State}.
+
+handle_cast(_Msg, State) ->
+	{noreply, State}.
+
+handle_info({'EXIT', Pid, Reason}, State = #state{acceptor = Pid}) ->
+	{stop, {acceptor_died, Reason}, State};
+handle_info(_Info, State) ->
+	{noreply, State}.
+
+terminate(_Reason, #state{socket = Socket}) ->
+	gen_tcp:close(Socket),
+	ok.
+
+code_change(_OldVsn, State, _Extra) ->
+	{ok, State}.
+
+acceptor_loop(Socket) ->
+	case gen_tcp:accept(Socket) of
+		{ok, ClientSocket} ->
+			gen_tcp:controlling_process(
+			  ClientSocket,
+			  spawn(fun() -> handle_connection(ClientSocket) end)),
+			acceptor_loop(Socket);
+		{error, closed} ->
+			ok
+	end.
+
+handle_connection(Socket) ->
+	receive
+		{tcp, Socket, Data} ->
+			gen_tcp:send(Socket, Data),
+			handle_connection(Socket);
+		{tcp_closed, Socket} ->
+			ok
+	end.