Config

ebb.toml

@@ -0,0 +1,20 @@
+# ebb configuration.
+#
+# ebb looks for this file at $EBB_CONFIG, ./ebb.toml, then /etc/ebb/ebb.toml,
+# and refuses to start without it.
+#
+# Features are enabled by presence: a feature runs iff its section exists.
+# When a section is present, all of its keys are required.
+
+[dhcp]
+# If the ERTS user doesn't have privileges to bind to port 67, this will silently fail.
+listen_port = 67
+
+# IPv4 CIDR of the managed subnet. Leases are allocated from this range.
+range = "172.16.0.0/12"
+
+# How long granted leases last.
+lease_seconds = 3600
+
+# How long an unaccepted OFFER is held before its IP is reclaimed.
+offer_timeout_seconds = 300

include/dhcp.hrl

@@ -1,14 +1,8 @@
 -define(DHCP_MAGIC_COOKIE, 16#63825363).
-
--define(DEFAULT_LEASE_SECONDS, 3600).
 % TODO
 %-define(MAX_LEASE_SECONDS, 86400).
 %-define(MIN_LEASE_SECONDS, 300).
 
--define(DEFAULT_OFFER_TIMEOUT_SECONDS, 300).
-
--define(DEFAULT_CIDR_RANGE, "172.16.0.0/16").
-
 -record(dhcp_message, {
     % Header
     op :: op(),

priv/scripts/osx/pxe-boot.sh

@@ -0,0 +1,17 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# Subnet must match ebb's ?DEFAULT_CIDR_RANGE ("172.16.0.0/16").
+NET_START="172.16.0.1"
+NET_END="172.16.255.254"
+NET_MASK="255.255.0.0"
+
+exec sudo qemu-system-x86_64 \
+  -machine q35 \
+  -cpu qemu64 \
+  -m 512 \
+  -netdev vmnet-host,id=net0,start-address="${NET_START}",end-address="${NET_END}",subnet-mask="${NET_MASK}" \
+  -device e1000,netdev=net0,mac=52:54:00:12:34:56 \
+  -boot n \
+  -nographic \
+  -no-reboot

rebar.config

@@ -2,6 +2,7 @@
 {deps, [
     %{khepri, {git, "https://github.com/rabbitmq/khepri", {branch, main}}},
     {erl_cidr, "1.2.1"},
+    {tomerl, "0.5.0"},
     {eqwalizer_support,
         {git_subdir, "https://github.com/whatsapp/eqwalizer.git", {branch, "main"},
             "eqwalizer_support"}}

rebar.lock

@@ -1,13 +1,16 @@
 {"1.2.0",
 [{<<"eqwalizer_support">>,
   {git_subdir,"https://github.com/whatsapp/eqwalizer.git",
-              {ref,"6370858ff6f8a02e3c853cf034cdf3c5a85034dc"},
+              {ref,"01f151ca206bb019db0999a2c9c8c8aaae79bbab"},
               "eqwalizer_support"},
   0},
- {<<"erl_cidr">>,{pkg,<<"erl_cidr">>,<<"1.2.1">>},0}]}.
+ {<<"erl_cidr">>,{pkg,<<"erl_cidr">>,<<"1.2.1">>},0},
+ {<<"tomerl">>,{pkg,<<"tomerl">>,<<"0.5.0">>},0}]}.
 [
 {pkg_hash,[
- {<<"erl_cidr">>, <<"921BB463BCF10EAD937AE491E5BCAC2823E550B339A9893AC6574518553CC067">>}]},
+ {<<"erl_cidr">>, <<"921BB463BCF10EAD937AE491E5BCAC2823E550B339A9893AC6574518553CC067">>},
+ {<<"tomerl">>, <<"6E7CEAC151AC573B87B985F3D2112F29933B89BA0693FA741318D899A17AC318">>}]},
 {pkg_hash_ext,[
- {<<"erl_cidr">>, <<"FCF5D51B1CC1B26D1748AB39F9B614AB445AD17172A9396D48C6B5C15EA9EFCF">>}]}
+ {<<"erl_cidr">>, <<"FCF5D51B1CC1B26D1748AB39F9B614AB445AD17172A9396D48C6B5C15EA9EFCF">>},
+ {<<"tomerl">>, <<"2A7FB62F9EBF0E75561B39255638BC2B805B437C86FEC538657E7C3B576979FA">>}]}
 ].

src/ebb.app.src

@@ -5,7 +5,14 @@
     {mod, {ebb_app, []}},
     {applications, [
         kernel,
-        stdlib
+        stdlib,
+        tomerl
+        % NOTE: we also depend on the erl_cidr package, whose OTP app is
+        % confusingly named inet_cidr. Listing either name here breaks
+        % rebar3 dialyzer (app/package name mismatch). It is a pure
+        % library (no processes to start), so omitting it is safe in
+        % dev; a future release definition must include inet_cidr
+        % explicitly.
     ]},
     {env, []},
     {modules, []},

src/ebb_app.erl

@@ -10,7 +10,13 @@
 -export([start/2, stop/1]).
 
 start(_StartType, _StartArgs) ->
-    ebb_sup:start_link().
+    case ebb_config:load() of
+        ok ->
+            ebb_sup:start_link();
+        {error, Reason} ->
+            logger:critical("Refusing to start: ~s", [Reason]),
+            {error, {config_error, lists:flatten(Reason)}}
+    end.
 
 stop(_State) ->
     ok.

src/ebb_config.erl

@@ -0,0 +1,160 @@
+-module(ebb_config).
+-moduledoc """
+Configuration for ebb, loaded from a TOML file into persistent terms. A
+configuration file is required to boot ebb. The file is resolved in this order:
+
+1. The path in the `EBB_CONFIG` environment variable
+2. `./ebb.toml`
+3. `/etc/ebb/ebb.toml`
+""".
+
+-export([load/0, get/1, enabled/1]).
+%% Exported for tests
+-export([load_file/1]).
+
+-define(PT_KEY, ?MODULE).
+-define(LOCAL_PATH, "ebb.toml").
+-define(SYSTEM_PATH, "/etc/ebb/ebb.toml").
+
+%%--------------------------------------------------------------------
+%% API
+%%--------------------------------------------------------------------
+
+-doc """
+Returns an error if no file can be found, the file is unreadable or
+unparseable, or any required key is missing.
+""".
+-spec load() -> ok | {error, io_lib:chars()}.
+load() ->
+    case resolve_path() of
+        {path, Path} ->
+            load_file(Path);
+        {error, Reason} ->
+            {error, Reason}
+    end.
+
+-doc """
+Load configuration from an explicit path. See also `load/0`.
+""".
+-spec load_file(file:name_all()) -> ok | {error, io_lib:chars()}.
+load_file(Path) ->
+    case tomerl:read_file(Path) of
+        {ok, Raw} ->
+            try
+                store(Path, atomize(Raw))
+            catch
+                throw:{unknown_key, Key} ->
+                    {error,
+                        io_lib:format("unknown configuration key \"~s\" in ~s", [
+                            Key, Path
+                        ])}
+            end;
+        {error, Reason} ->
+            {error, io_lib:format("cannot read ~s: ~p", [Path, Reason])}
+    end.
+
+store(Path, Config) ->
+    case missing_keys(Config) of
+        [] ->
+            persistent_term:put(?PT_KEY, Config),
+            logger:notice("Loaded configuration from ~s, enabled features: ~p", [
+                Path, [F || F <- maps:keys(features()), is_map_key(F, Config)]
+            ]),
+            ok;
+        Missing ->
+            {error,
+                io_lib:format("~s is missing required keys: ~s", [
+                    Path, string:join(Missing, ", ")
+                ])}
+    end.
+
+-doc """
+Fetch a configuration value by path, e.g. `get([dhcp, listen_port])`.
+Crashes on unknown paths; see `features/0`.
+""".
+-spec get([atom()]) -> term().
+get(Path) when is_list(Path) ->
+    lists:foldl(fun maps:get/2, persistent_term:get(?PT_KEY), Path).
+
+-doc """
+Features are gated by presence: a feature is enabled iff its section
+exists in the configuration file.
+""".
+-spec enabled(atom()) -> boolean().
+enabled(Feature) ->
+    is_map_key(Feature, persistent_term:get(?PT_KEY)).
+
+%%--------------------------------------------------------------------
+%% Internal
+%%--------------------------------------------------------------------
+
+%% Known feature sections and the keys each requires when present.
+%% An absent section simply disables the feature.
+features() ->
+    #{
+        dhcp => [listen_port, range, lease_seconds, offer_timeout_seconds]
+    }.
+
+missing_keys(Config) ->
+    maps:fold(
+        fun(Feature, RequiredKeys, Acc) ->
+            case Config of
+                #{Feature := Section} ->
+                    Acc ++
+                        [
+                            atom_to_list(Feature) ++ "." ++ atom_to_list(Key)
+                         || Key <- RequiredKeys, not is_map_key(Key, Section)
+                        ];
+                #{} ->
+                    Acc
+            end
+        end,
+        [],
+        features()
+    ).
+
+resolve_path() ->
+    case os:getenv("EBB_CONFIG") of
+        false -> search_default_paths();
+        "" -> search_default_paths();
+        Path -> explicit_path(Path)
+    end.
+
+search_default_paths() ->
+    case lists:search(fun filelib:is_regular/1, [?LOCAL_PATH, ?SYSTEM_PATH]) of
+        {value, Path} ->
+            {path, Path};
+        false ->
+            {error,
+                io_lib:format(
+                    "no configuration file found; provide ~s, ~s,"
+                    " or set EBB_CONFIG",
+                    [?LOCAL_PATH, ?SYSTEM_PATH]
+                )}
+    end.
+
+explicit_path(Path) ->
+    case filelib:is_regular(Path) of
+        true ->
+            {path, Path};
+        false ->
+            {error,
+                io_lib:format(
+                    "EBB_CONFIG points at ~s, which does not exist"
+                    " or is not a regular file",
+                    [Path]
+                )}
+    end.
+
+%% tomerl produces binary keys; convert them (and table arrays) to the
+%% atom-keyed shape used internally.
+atomize(Map) when is_map(Map) ->
+    maps:fold(
+        fun(K, V, Acc) -> Acc#{binary_to_existing_atom(K) => atomize(V)} end,
+        #{},
+        Map
+    );
+atomize(List) when is_list(List) ->
+    [atomize(V) || V <- List];
+atomize(Value) ->
+    Value.

src/ebb_dhcp_pool_mem.erl

@@ -61,7 +61,7 @@ dump() ->
 init([]) ->
     {ok, #{
         pool => [],
-        range => ?DEFAULT_CIDR_RANGE
+        range => ebb_config:get([dhcp, range])
     }}.
 
 handle_call({get_offer, Msg}, _From, #{pool := Pool} = State) ->
@@ -85,7 +85,7 @@ handle_call({create_offer, Msg}, _From, State) ->
                 % otherwise give them the default
                 Value;
             _ ->
-                ?DEFAULT_LEASE_SECONDS
+                ebb_config:get([dhcp, lease_seconds])
         end,
     % See next_ip/2 deficiencies
     {ok, ClientIP} = next_ip(Pool, Range),
@@ -95,7 +95,9 @@ handle_call({create_offer, Msg}, _From, State) ->
         subnet_mask = to_mask(Range),
         state = offered,
         expiration = erlang:send_after(
-            ?DEFAULT_OFFER_TIMEOUT_SECONDS * 1000, self(), {expire, ClientID}
+            ebb_config:get([dhcp, offer_timeout_seconds]) * 1000,
+            self(),
+            {expire, ClientID}
         ),
         duration = LeaseDuration
     },

src/ebb_dhcpd.erl

@@ -30,7 +30,8 @@ start_link() ->
     gen_server:start_link({local, ?MODULE}, ?MODULE, [], []).
 
 init([]) ->
-    {ok, Socket} = gen_udp:open(67, [{active, once}, {broadcast, true}, binary]),
+    Port = ebb_config:get([dhcp, listen_port]),
+    {ok, Socket} = gen_udp:open(Port, [{active, once}, {broadcast, true}, binary]),
     {ok, #{
         socket => Socket
     }}.
@@ -254,7 +255,7 @@ server_ip(Socket) ->
     end.
 
 guess_server_ip() ->
-    Cidr = inet_cidr:parse(?DEFAULT_CIDR_RANGE),
+    Cidr = inet_cidr:parse(ebb_config:get([dhcp, range])),
     {Start, _End, _Prefix} = Cidr,
     {ok, Addrs} = inet:getifaddrs(),
     case
@@ -275,5 +276,5 @@ send_broadcast(Socket, Packet) ->
     gen_udp:send(Socket, Bcast, 68, Packet).
 
 subnet_broadcast() ->
-    {_Start, End, _Prefix} = inet_cidr:parse(?DEFAULT_CIDR_RANGE),
+    {_Start, End, _Prefix} = inet_cidr:parse(ebb_config:get([dhcp, range])),
     End.

src/ebb_provision_sup.erl

@@ -0,0 +1,34 @@
+-module(ebb_provision_sup).
+-moduledoc """
+Supervisor for the provisioning feature, including:
+  - the DHCP listener and its lease pool. 
+
+Started by `ebb_sup` only when the `[dhcp]` section is present in the
+configuration.
+""".
+
+-behaviour(supervisor).
+
+-export([start_link/0]).
+-export([init/1]).
+
+start_link() ->
+    supervisor:start_link({local, ?MODULE}, ?MODULE, []).
+
+init([]) ->
+    SupFlags = #{
+        strategy => one_for_all,
+        intensity => 3,
+        period => 5
+    },
+    ChildSpecs = [
+        #{
+            id => ebb_dhcp_pool_mem,
+            start => {ebb_dhcp_pool_mem, start_link, []}
+        },
+        #{
+            id => ebb_dhcpd,
+            start => {ebb_dhcpd, start_link, []}
+        }
+    ],
+    {ok, {SupFlags, ChildSpecs}}.