initial commit;

.gitignore

@@ -0,0 +1,15 @@
+.eunit
+deps
+*.o
+*.beam
+*.plt
+*.swp
+erl_crash.dump
+ebin/*.beam
+doc/*.html
+doc/*.css
+doc/edoc-info
+doc/erlang.png
+rel/example_project
+.concrete/DEV_MODE
+.rebar

Emakefile

@@ -0,0 +1 @@
+{"src/*",  [debug_info, {i, "include/"}, {outdir, "ebin/"}]}.

LICENSE

@@ -0,0 +1,26 @@
+Copyright 2025 Peter Harpending <peterharpending@qpq.swiss>
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions
+are met:
+
+1. Redistributions of source code must retain the above copyright
+   notice, this list of conditions and the following disclaimer.
+
+2. Redistributions in binary form must reproduce the above copyright
+   notice, this list of conditions and the following disclaimer in
+   the documentation and/or other materials provided with the
+   distribution.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+POSSIBILITY OF SUCH DAMAGE.

ebin/fewd.app

@@ -0,0 +1,9 @@
+{application,fewd,
+             [{description,"Front End Web Dev in Erlang stuff"},
+              {registered,[]},
+              {included_applications,[]},
+              {applications,[stdlib,kernel]},
+              {vsn,"0.1.0"},
+              {modules,[fd_client,fd_client_man,fd_client_sup,fd_clients,
+                        fd_sup,fewd]},
+              {mod,{fewd,[]}}]}.

src/fd_client.erl

@@ -0,0 +1,204 @@
+%%% @doc
+%%% front end web development lab Client
+%%%
+%%% An extremely naive (currently Telnet) client handler.
+%%% Unlike other modules that represent discrete processes, this one does not adhere
+%%% to any OTP behavior. It does, however, adhere to OTP.
+%%%
+%%% In some cases it is more comfortable to write socket handlers or a certain
+%%% category of state machines as "pure" Erlang processes. This approach is made
+%%% OTP-able by use of the proc_lib module, which is the underlying library used
+%%% to write the stdlib's behaviors like gen_server, gen_statem, gen_fsm, etc.
+%%%
+%%% http://erlang.org/doc/design_principles/spec_proc.html
+%%% @end
+
+-module(fd_client).
+-vsn("0.1.0").
+-author("Peter Harpending <peterharpending@qpq.swiss>").
+-copyright("Peter Harpending <peterharpending@qpq.swiss>").
+-license("BSD-2-Clause-FreeBSD").
+
+-export([start/1]).
+-export([start_link/1, init/2]).
+-export([system_continue/3, system_terminate/4,
+         system_get_state/1, system_replace_state/2]).
+
+
+%%% Type and Record Definitions
+
+
+-record(s, {socket = none :: none | gen_tcp:socket()}).
+
+
+%% An alias for the state record above. Aliasing state can smooth out annoyances
+%% that can arise from using the record directly as its own type all over the code.
+
+-type state() :: #s{}.
+
+
+%%% Service Interface
+
+
+-spec start(ListenSocket) -> Result
+    when ListenSocket :: gen_tcp:socket(),
+         Result       :: {ok, pid()}
+                       | {error, Reason},
+         Reason       :: {already_started, pid()}
+                       | {shutdown, term()}
+                       | term().
+%% @private
+%% How the fd_client_man or a prior fd_client kicks things off.
+%% This is called in the context of fd_client_man or the prior fd_client.
+
+start(ListenSocket) ->
+    fd_client_sup:start_acceptor(ListenSocket).
+
+
+-spec start_link(ListenSocket) -> Result
+    when ListenSocket :: gen_tcp:socket(),
+         Result       :: {ok, pid()}
+                       | {error, Reason},
+         Reason       :: {already_started, pid()}
+                       | {shutdown, term()}
+                       | term().
+%% @private
+%% This is called by the fd_client_sup. While start/1 is called to iniate a startup
+%% (essentially requesting a new worker be started by the supervisor), this is
+%% actually called in the context of the supervisor.
+
+start_link(ListenSocket) ->
+    proc_lib:start_link(?MODULE, init, [self(), ListenSocket]).
+
+
+-spec init(Parent, ListenSocket) -> no_return()
+    when Parent       :: pid(),
+         ListenSocket :: gen_tcp:socket().
+%% @private
+%% This is the first code executed in the context of the new worker itself.
+%% This function does not have any return value, as the startup return is
+%% passed back to the supervisor by calling proc_lib:init_ack/2.
+%% We see the initial form of the typical arity-3 service loop form here in the
+%% call to listen/3.
+
+init(Parent, ListenSocket) ->
+    ok = io:format("~p Listening.~n", [self()]),
+    Debug = sys:debug_options([]),
+    ok = proc_lib:init_ack(Parent, {ok, self()}),
+    listen(Parent, Debug, ListenSocket).
+
+
+-spec listen(Parent, Debug, ListenSocket) -> no_return()
+    when Parent       :: pid(),
+         Debug        :: [sys:dbg_opt()],
+         ListenSocket :: gen_tcp:socket().
+%% @private
+%% This function waits for a TCP connection. The owner of the socket is still
+%% the fd_client_man (so it can still close it on a call to fd_client_man:ignore/0),
+%% but the only one calling gen_tcp:accept/1 on it is this process. Closing the socket
+%% is one way a manager process can gracefully unblock child workers that are blocking
+%% on a network accept.
+%%
+%% Once it makes a TCP connection it will call start/1 to spawn its successor.
+
+listen(Parent, Debug, ListenSocket) ->
+    case gen_tcp:accept(ListenSocket) of
+        {ok, Socket} ->
+            {ok, _} = start(ListenSocket),
+            {ok, Peer} = inet:peername(Socket),
+            ok = io:format("~p Connection accepted from: ~p~n", [self(), Peer]),
+            ok = fd_client_man:enroll(),
+            State = #s{socket = Socket},
+            loop(Parent, Debug, State);
+        {error, closed} ->
+            ok = io:format("~p Retiring: Listen socket closed.~n", [self()]),
+            exit(normal)
+     end.
+
+
+-spec loop(Parent, Debug, State) -> no_return()
+    when Parent :: pid(),
+         Debug  :: [sys:dbg_opt()],
+         State  :: state().
+%% @private
+%% The service loop itself. This is the service state. The process blocks on receive
+%% of Erlang messages, TCP segments being received themselves as Erlang messages.
+
+loop(Parent, Debug, State = #s{socket = Socket}) ->
+    ok = inet:setopts(Socket, [{active, once}]),
+    receive
+        {tcp, Socket, <<"bye\r\n">>} ->
+            ok = io:format("~p Client saying goodbye. Bye!~n", [self()]),
+            ok = gen_tcp:send(Socket, "Bye!\r\n"),
+            ok = gen_tcp:shutdown(Socket, read_write),
+            exit(normal);
+        {tcp, Socket, Message} ->
+            ok = io:format("~p received: ~tp~n", [self(), Message]),
+            ok = fd_client_man:echo(Message),
+            loop(Parent, Debug, State);
+        {relay, Sender, Message} when Sender == self() ->
+            ok = gen_tcp:send(Socket, ["Message from YOU: ", Message]),
+            loop(Parent, Debug, State);
+        {relay, Sender, Message} ->
+            From = io_lib:format("Message from ~tp: ", [Sender]),
+            ok = gen_tcp:send(Socket, [From, Message]),
+            loop(Parent, Debug, State);
+        {tcp_closed, Socket} ->
+            ok = io:format("~p Socket closed, retiring.~n", [self()]),
+            exit(normal);
+        {system, From, Request} ->
+            sys:handle_system_msg(Request, From, Parent, ?MODULE, Debug, State);
+        Unexpected ->
+            ok = io:format("~p Unexpected message: ~tp", [self(), Unexpected]),
+            loop(Parent, Debug, State)
+    end.
+
+
+-spec system_continue(Parent, Debug, State) -> no_return()
+    when Parent :: pid(),
+         Debug  :: [sys:dbg_opt()],
+         State  :: state().
+%% @private
+%% The function called by the OTP internal functions after a system message has been
+%% handled. If the worker process has several possible states this is one place
+%% resumption of a specific state can be specified and dispatched.
+
+system_continue(Parent, Debug, State) ->
+    loop(Parent, Debug, State).
+
+
+-spec system_terminate(Reason, Parent, Debug, State) -> no_return()
+    when Reason :: term(),
+         Parent :: pid(),
+         Debug  :: [sys:dbg_opt()],
+         State  :: state().
+%% @private
+%% Called by the OTP inner bits to allow the process to terminate gracefully.
+%% Exactly when and if this is callback gets called is specified in the docs:
+%% See: http://erlang.org/doc/design_principles/spec_proc.html#msg
+
+system_terminate(Reason, _Parent, _Debug, _State) ->
+    exit(Reason).
+
+
+
+-spec system_get_state(State) -> {ok, State}
+    when State :: state().
+%% @private
+%% This function allows the runtime (or anything else) to inspect the running state
+%% of the worker process at any arbitrary time.
+
+system_get_state(State) -> {ok, State}.
+
+
+-spec system_replace_state(StateFun, State) -> {ok, NewState, State}
+    when StateFun :: fun(),
+         State    :: state(),
+         NewState :: term().
+%% @private
+%% This function allows the system to update the process state in-place. This is most
+%% useful for state transitions between code types, like when performing a hot update
+%% (very cool, but sort of hard) or hot patching a running system (living on the edge!).
+
+system_replace_state(StateFun, State) ->
+    {ok, StateFun(State), State}.

src/fd_client_man.erl

@@ -0,0 +1,298 @@
+%%% @doc
+%%% front end web development lab Client Manager
+%%%
+%%% This is the "manager" part of the service->worker pattern.
+%%% It keeps track of who is connected and can act as a router among the workers.
+%%% Having this process allows us to abstract and customize service-level concepts
+%%% (the high-level ideas we care about in terms of solving an external problem in the
+%%% real world) and keep them separate from the lower-level details of supervision that
+%%% OTP should take care of for us.
+%%% @end
+
+-module(fd_client_man).
+-vsn("0.1.0").
+-behavior(gen_server).
+-author("Peter Harpending <peterharpending@qpq.swiss>").
+-copyright("Peter Harpending <peterharpending@qpq.swiss>").
+-license("BSD-2-Clause-FreeBSD").
+
+-export([listen/1, ignore/0]).
+-export([enroll/0, echo/1]).
+-export([start_link/0]).
+-export([init/1, handle_call/3, handle_cast/2, handle_info/2,
+         code_change/3, terminate/2]).
+
+
+%%% Type and Record Definitions
+
+
+-record(s, {port_num = none :: none | inet:port_number(),
+            listener = none :: none | gen_tcp:socket(),
+            clients  = []   :: [pid()]}).
+
+
+-type state()   :: #s{}.
+
+
+
+%%% Service Interface
+
+
+-spec listen(PortNum) -> Result
+    when PortNum :: inet:port_number(),
+         Result  :: ok
+                  | {error, Reason},
+         Reason  :: {listening, inet:port_number()}.
+%% @doc
+%% Tell the service to start listening on a given port.
+%% Only one port can be listened on at a time in the current implementation, so
+%% an error is returned if the service is already listening.
+
+listen(PortNum) ->
+    gen_server:call(?MODULE, {listen, PortNum}).
+
+
+-spec ignore() -> ok.
+%% @doc
+%% Tell the service to stop listening.
+%% It is not an error to call this function when the service is not listening.
+
+ignore() ->
+    gen_server:cast(?MODULE, ignore).
+
+
+
+%%% Client Process Interface
+
+
+-spec enroll() -> ok.
+%% @doc
+%% Clients register here when they establish a connection.
+%% Other processes can enroll as well.
+
+enroll() ->
+    gen_server:cast(?MODULE, {enroll, self()}).
+
+
+-spec echo(Message) -> ok
+    when Message :: string().
+%% @doc
+%% The function that tells the manager to broadcast a message to all clients.
+%% This can broadcast arbitrary strings to clients from non-clients as well.
+
+echo(Message) ->
+    gen_server:cast(?MODULE, {echo, Message, self()}).
+
+
+
+%%% Startup Functions
+
+
+-spec start_link() -> Result
+    when Result :: {ok, pid()}
+                 | {error, Reason :: term()}.
+%% @private
+%% This should only ever be called by fd_clients (the service-level supervisor).
+
+start_link() ->
+    gen_server:start_link({local, ?MODULE}, ?MODULE, none, []).
+
+
+-spec init(none) -> {ok, state()}.
+%% @private
+%% Called by the supervisor process to give the process a chance to perform any
+%% preparatory work necessary for proper function.
+
+init(none) ->
+    ok = io:format("Starting.~n"),
+    State = #s{},
+    {ok, State}.
+
+
+
+%%% gen_server Message Handling Callbacks
+
+
+-spec handle_call(Message, From, State) -> Result
+    when Message  :: term(),
+         From     :: {pid(), reference()},
+         State    :: state(),
+         Result   :: {reply, Response, NewState}
+                   | {noreply, State},
+         Response :: ok
+                   | {error, {listening, inet:port_number()}},
+         NewState :: state().
+%% @private
+%% The gen_server:handle_call/3 callback.
+%% See: http://erlang.org/doc/man/gen_server.html#Module:handle_call-3
+
+handle_call({listen, PortNum}, _, State) ->
+    {Response, NewState} = do_listen(PortNum, State),
+    {reply, Response, NewState};
+handle_call(Unexpected, From, State) ->
+    ok = io:format("~p Unexpected call from ~tp: ~tp~n", [self(), From, Unexpected]),
+    {noreply, State}.
+
+
+-spec handle_cast(Message, State) -> {noreply, NewState}
+    when Message  :: term(),
+         State    :: state(),
+         NewState :: state().
+%% @private
+%% The gen_server:handle_cast/2 callback.
+%% See: http://erlang.org/doc/man/gen_server.html#Module:handle_cast-2
+
+handle_cast({enroll, Pid}, State) ->
+    NewState = do_enroll(Pid, State),
+    {noreply, NewState};
+handle_cast({echo, Message, Sender}, State) ->
+    ok = do_echo(Message, Sender, State),
+    {noreply, State};
+handle_cast(ignore, State) ->
+    NewState = do_ignore(State),
+    {noreply, NewState};
+handle_cast(Unexpected, State) ->
+    ok = io:format("~p Unexpected cast: ~tp~n", [self(), Unexpected]),
+    {noreply, State}.
+
+
+-spec handle_info(Message, State) -> {noreply, NewState}
+    when Message  :: term(),
+         State    :: state(),
+         NewState :: state().
+%% @private
+%% The gen_server:handle_info/2 callback.
+%% See: http://erlang.org/doc/man/gen_server.html#Module:handle_info-2
+
+handle_info({'DOWN', Mon, process, Pid, Reason}, State) ->
+    NewState = handle_down(Mon, Pid, Reason, State),
+    {noreply, NewState};
+handle_info(Unexpected, State) ->
+    ok = io:format("~p Unexpected info: ~tp~n", [self(), Unexpected]),
+    {noreply, State}.
+
+
+
+%%% OTP Service Functions
+
+-spec code_change(OldVersion, State, Extra) -> Result
+    when OldVersion :: {down, Version} | Version,
+         Version    :: term(),
+         State      :: state(),
+         Extra      :: term(),
+         Result     :: {ok, NewState}
+                     | {error, Reason :: term()},
+         NewState   :: state().
+%% @private
+%% The gen_server:code_change/3 callback.
+%% See: http://erlang.org/doc/man/gen_server.html#Module:code_change-3
+
+code_change(_, State, _) ->
+    {ok, State}.
+
+
+-spec terminate(Reason, State) -> no_return()
+    when Reason :: normal
+                 | shutdown
+                 | {shutdown, term()}
+                 | term(),
+         State  :: state().
+%% @private
+%% The gen_server:terminate/2 callback.
+%% See: http://erlang.org/doc/man/gen_server.html#Module:terminate-2
+
+terminate(_, _) ->
+    ok.
+
+
+
+%%% Doer Functions
+
+-spec do_listen(PortNum, State) -> {Result, NewState}
+    when PortNum  :: inet:port_number(),
+         State    :: state(),
+         Result   :: ok
+                   | {error, Reason :: {listening, inet:port_number()}},
+         NewState :: state().
+%% @private
+%% The "doer" procedure called when a "listen" message is received.
+
+do_listen(PortNum, State = #s{port_num = none}) ->
+    SocketOptions =
+        [inet6,
+         {packet,    line},
+         {active,    once},
+         {mode,      binary},
+         {keepalive, true},
+         {reuseaddr, true}],
+    {ok, Listener} = gen_tcp:listen(PortNum, SocketOptions),
+    {ok, _} = fd_client:start(Listener),
+    {ok, State#s{port_num = PortNum, listener = Listener}};
+do_listen(_, State = #s{port_num = PortNum}) ->
+    ok = io:format("~p Already listening on ~p~n", [self(), PortNum]),
+    {{error, {listening, PortNum}}, State}.
+
+
+-spec do_ignore(State) -> NewState
+    when State    :: state(),
+         NewState :: state().
+%% @private
+%% The "doer" procedure called when an "ignore" message is received.
+
+do_ignore(State = #s{listener = none}) ->
+    State;
+do_ignore(State = #s{listener = Listener}) ->
+    ok = gen_tcp:close(Listener),
+    State#s{port_num = none, listener = none}.
+
+
+-spec do_enroll(Pid, State) -> NewState
+    when Pid      :: pid(),
+         State    :: state(),
+         NewState :: state().
+
+do_enroll(Pid, State = #s{clients = Clients}) ->
+    case lists:member(Pid, Clients) of
+        false ->
+            Mon = monitor(process, Pid),
+            ok = io:format("Monitoring ~tp @ ~tp~n", [Pid, Mon]),
+            State#s{clients = [Pid | Clients]};
+        true ->
+            State
+    end.
+
+
+-spec do_echo(Message, Sender, State) -> ok
+    when Message :: string(),
+         Sender  :: pid(),
+         State   :: state().
+%% @private
+%% The "doer" procedure called when an "echo" message is received.
+
+do_echo(Message, Sender, #s{clients = Clients}) ->
+    Send = fun(Client) -> Client ! {relay, Sender, Message} end,
+    lists:foreach(Send, Clients).
+
+
+-spec handle_down(Mon, Pid, Reason, State) -> NewState
+    when Mon      :: reference(),
+         Pid      :: pid(),
+         Reason   :: term(),
+         State    :: state(),
+         NewState :: state().
+%% @private
+%% Deal with monitors. When a new process enrolls as a client a monitor is set and
+%% the process is added to the client list. When the process terminates we receive
+%% a 'DOWN' message from the monitor. More sophisticated work managers typically have
+%% an "unenroll" function, but this echo service doesn't need one.
+
+handle_down(Mon, Pid, Reason, State = #s{clients = Clients}) ->
+    case lists:member(Pid, Clients) of
+        true ->
+            NewClients = lists:delete(Pid, Clients),
+            State#s{clients = NewClients};
+        false ->
+            Unexpected = {'DOWN', Mon, process, Pid, Reason},
+            ok = io:format("~p Unexpected info: ~tp~n", [self(), Unexpected]),
+            State
+    end.

src/fd_client_sup.erl

@@ -0,0 +1,70 @@
+%%% @doc
+%%% front end web development lab Client Supervisor
+%%%
+%%% This process supervises the client socket handlers themselves. It is a peer of the
+%%% fd_client_man (the manager interface to this network service component),
+%%% and a child of the supervisor named fd_clients.
+%%%
+%%% Because we don't know (or care) how many client connections the server may end up
+%%% handling this is a simple_one_for_one supervisor which can spawn and manage as
+%%% many identically defined workers as required, but cannot supervise any other types
+%%% of processes (one of the tradeoffs of the "simple" in `simple_one_for_one').
+%%%
+%%% http://erlang.org/doc/design_principles/sup_princ.html#id79244
+%%% @end
+
+-module(fd_client_sup).
+-vsn("0.1.0").
+-behaviour(supervisor).
+-author("Peter Harpending <peterharpending@qpq.swiss>").
+-copyright("Peter Harpending <peterharpending@qpq.swiss>").
+-license("BSD-2-Clause-FreeBSD").
+
+
+-export([start_acceptor/1]).
+-export([start_link/0]).
+-export([init/1]).
+
+
+
+-spec start_acceptor(ListenSocket) -> Result
+    when ListenSocket :: gen_tcp:socket(),
+         Result       :: {ok, pid()}
+                       | {error, Reason},
+         Reason       :: {already_started, pid()}
+                       | {shutdown, term()}
+                       | term().
+%% @private
+%% Spawns the first listener at the request of the fd_client_man when
+%% fewd:listen/1 is called, or the next listener at the request of the
+%% currently listening fd_client when a connection is made.
+%%
+%% Error conditions, supervision strategies and other important issues are
+%% explained in the supervisor module docs:
+%% http://erlang.org/doc/man/supervisor.html
+
+start_acceptor(ListenSocket) ->
+    supervisor:start_child(?MODULE, [ListenSocket]).
+
+
+-spec start_link() -> {ok, pid()}.
+%% @private
+%% This supervisor's own start function.
+
+start_link() ->
+    supervisor:start_link({local, ?MODULE}, ?MODULE, none).
+
+
+-spec init(none) -> {ok, {supervisor:sup_flags(), [supervisor:child_spec()]}}.
+%% @private
+%% The OTP init/1 function.
+
+init(none) ->
+    RestartStrategy = {simple_one_for_one, 1, 60},
+    Client    = {fd_client,
+                 {fd_client, start_link, []},
+                 temporary,
+                 brutal_kill,
+                 worker,
+                 [fd_client]},
+    {ok, {RestartStrategy, [Client]}}.

src/fd_clients.erl

@@ -0,0 +1,48 @@
+%%% @doc
+%%% front end web development lab Client Service Supervisor
+%%%
+%%% This is the service-level supervisor of the system. It is the parent of both the
+%%% client connection handlers and the client manager (which manages the client
+%%% connection handlers). This is the child of fd_sup.
+%%%
+%%% See: http://erlang.org/doc/apps/kernel/application.html
+%%% @end
+
+-module(fd_clients).
+-vsn("0.1.0").
+-behavior(supervisor).
+-author("Peter Harpending <peterharpending@qpq.swiss>").
+-copyright("Peter Harpending <peterharpending@qpq.swiss>").
+-license("BSD-2-Clause-FreeBSD").
+
+-export([start_link/0]).
+-export([init/1]).
+
+
+-spec start_link() -> {ok, pid()}.
+%% @private
+%% This supervisor's own start function.
+
+start_link() ->
+  supervisor:start_link({local, ?MODULE}, ?MODULE, none).
+
+-spec init(none) -> {ok, {supervisor:sup_flags(), [supervisor:child_spec()]}}.
+%% @private
+%% The OTP init/1 function.
+
+init(none) ->
+    RestartStrategy = {rest_for_one, 1, 60},
+    ClientMan = {fd_client_man,
+                 {fd_client_man, start_link, []},
+                 permanent,
+                 5000,
+                 worker,
+                 [fd_client_man]},
+    ClientSup = {fd_client_sup,
+                 {fd_client_sup, start_link, []},
+                 permanent,
+                 5000,
+                 supervisor,
+                 [fd_client_sup]},
+    Children  = [ClientSup, ClientMan],
+    {ok, {RestartStrategy, Children}}.

src/fd_sup.erl

@@ -0,0 +1,46 @@
+%%% @doc
+%%% front end web development lab Top-level Supervisor
+%%%
+%%% The very top level supervisor in the system. It only has one service branch: the
+%%% client handling service. In a more complex system the client handling service would
+%%% only be one part of a larger system. Were this a game system, for example, the
+%%% item data management service would be a peer, as would a login credential provision
+%%% service, game world event handling, and so on.
+%%%
+%%% See: http://erlang.org/doc/design_principles/applications.html
+%%% See: http://zxq9.com/archives/1311
+%%% @end
+
+-module(fd_sup).
+-vsn("0.1.0").
+-behaviour(supervisor).
+-author("Peter Harpending <peterharpending@qpq.swiss>").
+-copyright("Peter Harpending <peterharpending@qpq.swiss>").
+-license("BSD-2-Clause-FreeBSD").
+
+-export([start_link/0]).
+-export([init/1]).
+
+
+-spec start_link() -> {ok, pid()}.
+%% @private
+%% This supervisor's own start function.
+
+start_link() ->
+  supervisor:start_link({local, ?MODULE}, ?MODULE, []).
+
+
+-spec init([]) -> {ok, {supervisor:sup_flags(), [supervisor:child_spec()]}}.
+%% @private
+%% The OTP init/1 function.
+
+init([]) ->
+    RestartStrategy = {one_for_one, 1, 60},
+    Clients   = {fd_clients,
+                 {fd_clients, start_link, []},
+                 permanent,
+                 5000,
+                 supervisor,
+                 [fd_clients]},
+    Children  = [Clients],
+    {ok, {RestartStrategy, Children}}.

src/fewd.erl

@@ -0,0 +1,76 @@
+%%% @doc
+%%% front end web development lab
+%%% @end
+
+-module(fewd).
+-vsn("0.1.0").
+-behavior(application).
+-author("Peter Harpending <peterharpending@qpq.swiss>").
+-copyright("Peter Harpending <peterharpending@qpq.swiss>").
+-license("BSD-2-Clause-FreeBSD").
+
+-export([listen/1, ignore/0]).
+-export([start/0, start/1]).
+-export([start/2, stop/1]).
+
+
+
+-spec listen(PortNum) -> Result
+    when PortNum :: inet:port_num(),
+         Result  :: ok
+                  | {error, {listening, inet:port_num()}}.
+%% @doc
+%% Make the server start listening on a port.
+%% Returns an {error, Reason} tuple if it is already listening.
+
+listen(PortNum) ->
+    fd_client_man:listen(PortNum).
+
+
+-spec ignore() -> ok.
+%% @doc
+%% Make the server stop listening if it is, or continue to do nothing if it isn't.
+
+ignore() ->
+    fd_client_man:ignore().
+
+
+-spec start() -> ok.
+%% @doc
+%% Start the server in an "ignore" state.
+
+start() ->
+    ok = application:ensure_started(sasl),
+    ok = application:start(fewd),
+    io:format("Starting...").
+
+
+-spec start(PortNum) -> ok
+    when PortNum :: inet:port_number().
+%% @doc
+%% Start the server and begin listening immediately. Slightly more convenient when
+%% playing around in the shell.
+
+start(PortNum) ->
+    ok = start(),
+    ok = fd_client_man:listen(PortNum),
+    io:format("Startup complete, listening on ~w~n", [PortNum]).
+
+
+-spec start(normal, term()) -> {ok, pid()}.
+%% @private
+%% Called by OTP to kick things off. This is for the use of the "application" part of
+%% OTP, not to be called by user code.
+%% See: http://erlang.org/doc/apps/kernel/application.html
+
+start(normal, _Args) ->
+    fd_sup:start_link().
+
+
+-spec stop(term()) -> ok.
+%% @private
+%% Similar to start/2 above, this is to be called by the "application" part of OTP,
+%% not client code. Causes a (hopefully graceful) shutdown of the application.
+
+stop(_State) ->
+    ok.

zomp.meta

@@ -0,0 +1,17 @@
+{name,"front end web development lab"}.
+{type,app}.
+{modules,[]}.
+{prefix,"fd"}.
+{author,"Peter Harpending"}.
+{desc,"Front End Web Dev in Erlang stuff"}.
+{package_id,{"otpr","fewd",{0,1,0}}}.
+{deps,[]}.
+{key_name,none}.
+{a_email,"peterharpending@qpq.swiss"}.
+{c_email,"peterharpending@qpq.swiss"}.
+{copyright,"Peter Harpending"}.
+{file_exts,[]}.
+{license,"BSD-2-Clause-FreeBSD"}.
+{repo_url,[]}.
+{tags,[]}.
+{ws_url,[]}.