unikernel/duniverse/arp/test/dune

@@ -0,0 +1,4 @@
+(test
+ (name tests)
+ (package arp)
+ (libraries arp macaddr cstruct alcotest))

unikernel/duniverse/arp/test/mirage/dune

@@ -0,0 +1,5 @@
+(test
+ (name tests)
+ (package arp)
+ (libraries alcotest lwt.unix logs logs.fmt fmt mirage-vnetif
+   duration ethernet arp arp.mirage cstruct bos))

unikernel/duniverse/arp/test/mirage/tests.ml

@@ -0,0 +1,530 @@
+open Lwt.Infix
+
+module B = Basic_backend.Make
+module V = Vnetif.Make(B)
+module E = Ethernet.Make(V)
+module A = Arp.Make(E)
+
+let src = Logs.Src.create "test_arp" ~doc:"Mirage ARP tester"
+module Log = (val Logs.src_log src : Logs.LOG)
+
+type arp_stack = {
+  backend : B.t;
+  netif: V.t;
+  ethif: E.t;
+  arp: A.t;
+}
+
+let first_ip = Ipaddr.V4.of_string_exn "192.168.3.1"
+let second_ip = Ipaddr.V4.of_string_exn "192.168.3.10"
+let sample_mac = Macaddr.of_string_exn "10:9a:dd:c0:ff:ee"
+
+let packet = (module Arp_packet : Alcotest.TESTABLE with type t = Arp_packet.t)
+
+let ip =
+  let module M = struct
+    type t = Ipaddr.V4.t
+    let pp = Ipaddr.V4.pp
+    let equal p q = (Ipaddr.V4.compare p q) = 0
+  end in
+  (module M : Alcotest.TESTABLE with type t = M.t)
+
+let macaddr =
+  let module M = struct
+    type t = Macaddr.t
+    let pp = Macaddr.pp
+    let equal p q = (Macaddr.compare p q) = 0
+  end in
+  (module M : Alcotest.TESTABLE with type t = M.t)
+
+let header_size = Ethernet.Packet.sizeof_ethernet
+let size = Arp_packet.size
+
+let check_header ~message expected actual =
+  Alcotest.(check packet) message expected actual
+
+let fail = Alcotest.fail
+let failf fmt = Fmt.kstr (fun s -> Alcotest.fail s) fmt
+
+let timeout ~time t =
+  let msg = Printf.sprintf "Timed out: didn't complete in %d milliseconds" time in
+  Lwt.pick [ t; Mirage_sleep.ns (Duration.of_ms time) >>= fun () -> fail msg; ]
+
+let check_response expected buf =
+  match Arp_packet.decode buf with
+  | Error s -> Alcotest.fail (Fmt.to_to_string Arp_packet.pp_error s)
+  | Ok actual ->
+    Alcotest.(check packet) "parsed packet comparison" expected actual
+
+let check_ethif_response expected buf =
+  let open Ethernet.Packet in
+  match of_cstruct buf with
+  | Error s -> Alcotest.fail s
+  | Ok ({ethertype; _}, arp) ->
+    match ethertype with
+    | `ARP -> check_response expected arp
+    | _ -> Alcotest.fail "Ethernet packet with non-ARP ethertype"
+
+let garp source_mac source_ip =
+  let open Arp_packet in
+  {
+    operation = Request;
+    source_mac;
+    target_mac = Macaddr.of_octets_exn "\000\000\000\000\000\000";
+    source_ip;
+    target_ip = source_ip;
+  }
+
+let fail_on_receipt netif buf =
+  Alcotest.fail (Format.asprintf "received traffic when none was expected on interface %a: %a"
+	  Macaddr.pp (V.mac netif) Cstruct.hexdump_pp buf)
+
+let single_check netif expected =
+  V.listen netif ~header_size (fun buf ->
+      match Ethernet.Packet.of_cstruct buf with
+      | Error _ -> failwith "sad face"
+      | Ok (_, payload) ->
+        check_response expected payload; V.disconnect netif) >|= fun _ -> ()
+
+(*  { Ethernet_packet.source = arp.source_mac;
+      destination = arp.target_mac;
+      ethertype = `ARP;
+    } *)
+
+let arp_reply ~from_netif ~to_netif ~from_ip ~to_ip arp =
+  let open Arp_packet in
+  let a =
+    { operation = Reply;
+      source_mac = V.mac from_netif;
+      target_mac = V.mac to_netif;
+      source_ip = from_ip;
+      target_ip = to_ip}
+  in
+  encode_into a arp ;
+  Arp_packet.size
+
+let arp_request ~from_netif ~to_mac ~from_ip ~to_ip arp =
+  let open Arp_packet in
+  let a =
+    { operation = Request;
+      source_mac = V.mac from_netif;
+      target_mac = to_mac;
+      source_ip = from_ip;
+      target_ip = to_ip}
+  in
+  encode_into a arp ;
+  Arp_packet.size
+
+let get_arp ?backend () =
+  let backend = match backend with
+    | None -> B.create ~use_async_readers:true ~yield:Lwt.pause ()
+    | Some b -> b
+  in
+  V.connect backend >>= fun netif ->
+  E.connect netif >>= fun ethif ->
+  A.connect ~probe_delay:(Duration.of_ms 2) ethif >>= fun arp ->
+  Lwt.return { backend; netif; ethif; arp }
+
+(* we almost always want two stacks on the same backend *)
+let two_arp () =
+  get_arp () >>= fun first ->
+  get_arp ~backend:first.backend () >>= fun second ->
+  Lwt.return (first, second)
+
+(* ...but sometimes we want three *)
+let three_arp () =
+  get_arp () >>= fun first ->
+  get_arp ~backend:first.backend () >>= fun second ->
+  get_arp ~backend:first.backend () >>= fun third ->
+  Lwt.return (first, second, third)
+
+let query_or_die arp ip expected_mac =
+  A.query arp ip >>= function
+  | Error `Timeout ->
+    Log.warn (fun f -> f "Timeout querying %a. Table contents: %a"
+                 Ipaddr.V4.pp ip A.pp arp);
+    fail "ARP query failed when success was mandatory";
+  | Ok mac ->
+    Alcotest.(check macaddr) "mismatch for expected query value" expected_mac mac;
+    Lwt.return_unit
+  | Error e -> failf "ARP query failed with %a" A.pp_error e
+
+let query_and_no_response arp ip =
+  A.query arp ip >>= function
+  | Error `Timeout ->
+    Log.warn (fun f -> f "Timeout querying %a. Table contents: %a" Ipaddr.V4.pp ip A.pp arp);
+    Lwt.return_unit
+  | Ok _ -> failf "expected nothing, found something in cache"
+  | Error e ->
+    Log.err (fun m -> m "another err");
+    failf "ARP query failed with %a" A.pp_error e
+
+let set_and_check ~listener ~claimant ip =
+  A.set_ips claimant.arp [ ip ] >>= fun () ->
+  Log.debug (fun f -> f "Set IP for %a to %a" Macaddr.pp (V.mac claimant.netif) Ipaddr.V4.pp ip);
+  Logs.debug (fun f -> f "Listener table contents after IP set on claimant: %a" A.pp listener);
+  query_or_die listener ip (V.mac claimant.netif)
+
+let start_arp_listener stack () =
+  let noop = (fun _ -> Lwt.return_unit) in
+  Log.debug (fun f -> f "starting arp listener for %a" Macaddr.pp (V.mac stack.netif));
+  let arpv4 frame =
+    Log.debug (fun f -> f "frame received for arpv4");
+    A.input stack.arp frame
+  in
+  E.input ~arpv4 ~ipv4:noop ~ipv6:noop stack.ethif
+
+let not_in_cache ~listen probe arp ip =
+  Lwt.pick [
+    single_check listen probe;
+    Mirage_sleep.ns (Duration.of_ms 100) >>= fun () ->
+    A.query arp ip >>= function
+    | Ok _ -> failf "entry in cache when it shouldn't be %a" Ipaddr.V4.pp ip
+    | Error `Timeout -> Lwt.return_unit
+    | Error e -> failf "error for %a while reading the cache: %a"
+                   Ipaddr.V4.pp ip A.pp_error e
+  ]
+
+let set_ip_sends_garp () =
+  two_arp () >>= fun (speak, listen) ->
+  let emit_garp =
+    Mirage_sleep.ns (Duration.of_ms 100) >>= fun () ->
+    A.set_ips speak.arp [ first_ip ] >>= fun () ->
+    Alcotest.(check (list ip)) "garp emitted when setting ip" [ first_ip ] (A.get_ips speak.arp);
+    Lwt.return_unit
+  in
+  let expected_garp = garp (V.mac speak.netif) first_ip in
+  timeout ~time:500 (
+  Lwt.join [
+    single_check listen.netif expected_garp;
+    emit_garp;
+  ]) >>= fun () ->
+  (* now make sure we have consistency when setting *)
+  A.set_ips speak.arp [] >>= fun () ->
+  Alcotest.(check (slist ip Ipaddr.V4.compare)) "list of bound IPs on initialization" [] (A.get_ips speak.arp);
+  A.set_ips speak.arp [ first_ip; second_ip ] >>= fun () ->
+  Alcotest.(check (slist ip Ipaddr.V4.compare)) "list of bound IPs after setting two IPs"
+    [ first_ip; second_ip ] (A.get_ips speak.arp);
+  Lwt.return_unit
+
+let add_get_remove_ips () =
+  get_arp () >>= fun stack ->
+  let check str expected =
+    Alcotest.(check (list ip)) str expected (A.get_ips stack.arp)
+  in
+  check "bound ips is an empty list on startup" [];
+  A.set_ips stack.arp [ first_ip; first_ip ] >>= fun () ->
+  check "set ips with duplicate elements result in deduplication" [first_ip];
+  A.remove_ip stack.arp first_ip >>= fun () ->
+  check "ip list is empty after removing only ip" [];
+  A.remove_ip stack.arp first_ip >>= fun () ->
+  check "ip list is empty after removing from empty list" [];
+  A.add_ip stack.arp first_ip >>= fun () ->
+  check "first ip is the only member of the set of bound ips" [first_ip];
+  A.add_ip stack.arp first_ip >>= fun () ->
+  check "adding ips is idempotent" [first_ip];
+  Lwt.return_unit
+
+let input_single_garp () =
+  two_arp () >>= fun (listen, speak) ->
+  (* set the IP on speak_arp, which should cause a GARP to be emitted which
+     listen_arp will hear and cache. *)
+  let one_and_done buf =
+    let arpbuf = Cstruct.shift buf 14 in
+    A.input listen.arp arpbuf >>= fun () ->
+    V.disconnect listen.netif
+  in
+  timeout ~time:500 (
+    Lwt.join [
+      (V.listen listen.netif ~header_size one_and_done >|= fun _ -> ());
+      Mirage_sleep.ns (Duration.of_ms 100) >>= fun () ->
+      Lwt.async (fun () -> A.query listen.arp first_ip >|= ignore) ;
+      A.set_ips speak.arp [ first_ip ];
+    ])
+    >>= fun () ->
+  (* try a lookup of the IP set by speak.arp, and fail if this causes listen_arp
+     to block or send an ARP query -- listen_arp should answer immediately from
+     the cache.  An attempt to resolve via query will result in a timeout, since
+     speak.arp has no listener running and therefore won't answer any arp
+     who-has requests. *)
+    timeout ~time:500 (query_or_die listen.arp first_ip (V.mac speak.netif)) (* >>= fun () ->
+                                                                                Time.sleep_ns (Duration.of_sec 5) *)
+
+let input_single_unicast () =
+  two_arp () >>= fun (listen, speak) ->
+  (* contrive to make a reply packet for the listener to hear *)
+  let for_listener =
+    arp_reply
+      ~from_netif:speak.netif ~to_netif:listen.netif
+      ~from_ip:first_ip ~to_ip:second_ip
+  in
+  let listener = start_arp_listener listen () in
+  timeout ~time:500 (
+  Lwt.choose [
+    (V.listen listen.netif ~header_size listener >|= fun _ -> ());
+    Mirage_sleep.ns (Duration.of_ms 2) >>= fun () ->
+    E.write speak.ethif (V.mac listen.netif) `ARP ~size for_listener >>= fun _ ->
+    query_and_no_response listen.arp first_ip
+  ])
+
+let input_resolves_wait () =
+  two_arp () >>= fun (listen, speak) ->
+  (* contrive to make a reply packet for the listener to hear *)
+  let for_listener = arp_reply ~from_netif:speak.netif ~to_netif:listen.netif
+                         ~from_ip:first_ip ~to_ip:second_ip in
+  (* initiate query when the cache is empty.  On resolution, fail for a timeout
+     and test the MAC if resolution was successful, then disconnect the
+     listening interface to ensure the test terminates.
+     Fail with a timeout message if the whole thing takes more than 5s. *)
+  let listener = start_arp_listener listen () in
+  let query_then_disconnect =
+    query_or_die listen.arp first_ip (V.mac speak.netif) >>= fun () ->
+    V.disconnect listen.netif
+  in
+  timeout ~time:5000 (
+    Lwt.join [
+      (V.listen listen.netif ~header_size listener >|= fun _ -> ());
+      query_then_disconnect;
+      Mirage_sleep.ns (Duration.of_ms 1) >>= fun () ->
+      E.write speak.ethif (V.mac listen.netif) `ARP ~size for_listener >|= function
+      | Ok x -> x
+      | Error _ -> failf "ethernet write failed"
+    ]
+  )
+
+let unreachable_times_out () =
+  get_arp () >>= fun speak ->
+  A.query speak.arp first_ip >>= function
+  | Ok _ -> failf "query claimed success when impossible for %a" Ipaddr.V4.pp first_ip
+  | Error `Timeout -> Lwt.return_unit
+  | Error e -> failf "error waiting for a timeout: %a" A.pp_error e
+
+let input_replaces_old () =
+  three_arp () >>= fun (listen, claimant_1, claimant_2) ->
+  (* query for IP to accept responses *)
+  Lwt.async (fun () -> A.query listen.arp first_ip >|= ignore) ;
+  Lwt.async (fun () ->
+      Log.debug (fun f -> f "arp listener started");
+      V.listen listen.netif ~header_size (start_arp_listener listen ()) >|= fun _ -> ());
+  timeout ~time:2000 (
+    set_and_check ~listener:listen.arp ~claimant:claimant_1 first_ip >>= fun () ->
+    set_and_check ~listener:listen.arp ~claimant:claimant_2 first_ip >>= fun () ->
+    V.disconnect listen.netif
+    )
+
+let os_linux_bsd () =
+  let cmd = Bos.Cmd.(v "uname" % "-s") in
+  match Bos.OS.Cmd.(run_out cmd |> out_string |> success) with
+  | Ok s when s = "FreeBSD" -> true
+  | Ok s when s = "Linux" -> true
+  | Ok _ -> false
+  | Error _ -> false
+
+let entries_expire () =
+  (* this test fails on windows and macOS for unknown reasons. please, if you
+     happen to have your hands on such a machine, investigate the issue. *)
+  if not (os_linux_bsd ()) then
+    Lwt.return_unit
+  else
+    two_arp () >>= fun (listen, speak) ->
+    A.set_ips listen.arp [ second_ip ] >>= fun () ->
+    (* here's what we expect listener to emit once its cache entry has expired *)
+    let expected_arp_query =
+      Arp_packet.({operation = Request;
+                   source_mac = V.mac listen.netif;
+                   target_mac = Macaddr.broadcast;
+                   source_ip = second_ip; target_ip = first_ip})
+    in
+    (* query for IP to accept responses *)
+    Lwt.async (fun () -> A.query listen.arp first_ip >|= ignore) ;
+    Lwt.async (fun () -> V.listen listen.netif ~header_size (start_arp_listener listen ()) >|= fun _ -> ());
+    let test =
+      Mirage_sleep.ns (Duration.of_ms 10) >>= fun () ->
+      set_and_check ~listener:listen.arp ~claimant:speak first_ip >>= fun () ->
+      (* sleep for 5s to make sure we hit `tick` often enough *)
+      Mirage_sleep.ns (Duration.of_sec 5) >>= fun () ->
+      (* asking now should generate a query *)
+      not_in_cache ~listen:speak.netif expected_arp_query listen.arp first_ip
+    in
+    timeout ~time:7000 test
+
+(* RFC isn't strict on how many times to try, so we'll just say any number
+   greater than 1 is fine *)
+let query_retries () =
+  two_arp () >>= fun (listen, speak) ->
+  let expected_query = Arp_packet.({source_mac = V.mac speak.netif;
+                                    target_mac = Macaddr.broadcast;
+                                    source_ip = Ipaddr.V4.any;
+                                    target_ip = first_ip;
+                                    operation = Request;})
+  in
+  let how_many = ref 0 in
+  let listener buf =
+    check_ethif_response expected_query buf;
+    if !how_many = 0 then begin
+      how_many := !how_many + 1;
+      Lwt.return_unit
+    end else V.disconnect listen.netif
+  in
+  let ask () =
+    A.query speak.arp first_ip >>= function
+    | Error e -> failf "Received error before >1 query: %a" A.pp_error e
+    | Ok _ -> failf "got result from query for %a, erroneously" Ipaddr.V4.pp first_ip
+  in
+  Lwt.pick [
+    (V.listen listen.netif ~header_size listener >|= fun _ -> ());
+    Mirage_sleep.ns (Duration.of_ms 2) >>= ask;
+    Mirage_sleep.ns (Duration.of_sec 6) >>= fun () ->
+    fail "query didn't succeed or fail within 6s"
+  ]
+
+(* requests for us elicit a reply *)
+let requests_are_responded_to () =
+  let (answerer_ip, inquirer_ip) = (first_ip, second_ip) in
+  two_arp () >>= fun (inquirer, answerer) ->
+  (* neither has a listener set up when we set IPs, so no GARPs in the cache *)
+  A.add_ip answerer.arp answerer_ip >>= fun () ->
+  A.add_ip inquirer.arp inquirer_ip >>= fun () ->
+  let request = arp_request ~from_netif:inquirer.netif ~to_mac:Macaddr.broadcast
+      ~from_ip:inquirer_ip ~to_ip:answerer_ip
+  in
+  let expected_reply =
+    Arp_packet.({ operation = Reply;
+                  source_mac = V.mac answerer.netif;
+                  target_mac = V.mac inquirer.netif;
+                  source_ip = answerer_ip; target_ip = inquirer_ip})
+  in
+  let listener close_netif buf =
+    check_ethif_response expected_reply buf;
+    V.disconnect close_netif
+  in
+  let arp_listener =
+    V.listen answerer.netif ~header_size (start_arp_listener answerer ()) >|= fun _ -> ()
+  in
+  timeout ~time:1000 (
+    Lwt.join [
+      (* listen for responses and check them against an expected result *)
+      (V.listen inquirer.netif ~header_size (listener inquirer.netif) >|= fun _ -> ());
+      (* start the usual ARP listener, which should respond to requests *)
+      arp_listener;
+      (* send a request for the ARP listener to respond to *)
+      Mirage_sleep.ns (Duration.of_ms 100) >>= fun () ->
+      E.write inquirer.ethif Macaddr.broadcast `ARP ~size request >>= fun _ ->
+      Mirage_sleep.ns (Duration.of_ms 100) >>= fun () ->
+      V.disconnect answerer.netif
+    ];
+  )
+
+let requests_not_us () =
+  let (answerer_ip, inquirer_ip) = (first_ip, second_ip) in
+  two_arp () >>= fun (answerer, inquirer) ->
+  A.add_ip answerer.arp answerer_ip >>= fun () ->
+  A.add_ip inquirer.arp inquirer_ip >>= fun () ->
+  let ask ip buf =
+    let open Arp_packet in
+    encode_into
+      { operation = Request;
+        source_mac = V.mac inquirer.netif; target_mac = Macaddr.broadcast;
+        source_ip = inquirer_ip; target_ip = ip }
+      buf ;
+    size
+  in
+  let requests = List.map ask [ inquirer_ip; Ipaddr.V4.any;
+                                Ipaddr.V4.of_string_exn "255.255.255.255" ] in
+  let make_requests =
+    Lwt_list.iter_s (fun b -> E.write inquirer.ethif Macaddr.broadcast `ARP ~size b >|= fun _ -> ())
+      requests
+  in
+  let disconnect_listeners () =
+    Lwt_list.iter_s (V.disconnect) [answerer.netif; inquirer.netif]
+  in
+  Lwt.join [
+    (V.listen answerer.netif ~header_size (start_arp_listener answerer ()) >|= fun _ -> ());
+    (V.listen inquirer.netif ~header_size (fail_on_receipt inquirer.netif) >|= fun _ -> ());
+    make_requests >>= fun _ ->
+    Mirage_sleep.ns (Duration.of_ms 100) >>=
+    disconnect_listeners
+  ]
+
+let nonsense_requests () =
+  let (answerer_ip, inquirer_ip) = (first_ip, second_ip) in
+  three_arp () >>= fun (answerer, inquirer, checker) ->
+  A.set_ips answerer.arp [ answerer_ip ] >>= fun () ->
+  let request number arp =
+    let open Arp_packet in
+    encode_into
+      { operation = Request;
+	source_mac = V.mac inquirer.netif;
+	target_mac = Macaddr.broadcast;
+	source_ip = inquirer_ip;
+	target_ip = answerer_ip } arp ;
+    Cstruct.BE.set_uint16 arp 6 number;
+    Arp_packet.size
+  in
+  let requests = List.map request [0; 3; -1; 255; 256; 257; 65536] in
+  let make_requests =
+    Lwt_list.iter_s (fun l -> E.write inquirer.ethif Macaddr.broadcast `ARP ~size l >|= fun _ -> ()) requests in
+  let expected_probe = Arp_packet.{ operation = Request;
+                                    source_mac = V.mac answerer.netif;
+                                    source_ip = answerer_ip;
+                                    target_mac = Macaddr.broadcast;
+                                    target_ip = inquirer_ip; }
+  in
+  Lwt.async (fun () -> V.listen answerer.netif ~header_size (start_arp_listener answerer ()) >|= fun _ -> ());
+  timeout ~time:1000 (
+    Lwt.join [
+      (V.listen inquirer.netif ~header_size (fail_on_receipt inquirer.netif) >|= fun _ -> ());
+      make_requests >>= fun () ->
+      V.disconnect inquirer.netif >>= fun () ->
+      (* not sufficient to just check to see whether we've replied; it's equally
+         possible that we erroneously make a cache entry.  Make sure querying
+         inquirer_ip results in an outgoing request. *)
+      not_in_cache ~listen:checker.netif expected_probe answerer.arp inquirer_ip
+    ] )
+
+let packet () =
+  let first_mac  = Macaddr.of_string_exn "10:9a:dd:01:23:45" in
+  let second_mac = Macaddr.of_string_exn "00:16:3e:ab:cd:ef" in
+  let example_request =
+    Arp_packet.{ operation = Request;
+                 source_mac = first_mac;
+                 target_mac = second_mac;
+                 source_ip = first_ip;
+                 target_ip = second_ip;
+               }
+  in
+  let marshalled = Arp_packet.encode example_request in
+  match Arp_packet.decode marshalled with
+  | Error _ -> Alcotest.fail "couldn't unmarshal something we made ourselves"
+  | Ok unmarshalled ->
+    Alcotest.(check packet) "serialize/deserialize" example_request unmarshalled;
+    Lwt.return_unit
+
+let suite =
+  [
+    "conversions neither lose nor gain information", `Quick, packet;
+    "nonsense requests are ignored", `Quick, nonsense_requests;
+    "requests are responded to", `Quick, requests_are_responded_to;
+    "entries expire", `Quick, entries_expire;
+    "irrelevant requests are ignored", `Quick, requests_not_us;
+    "set_ip sets ip, sends GARP", `Quick, set_ip_sends_garp;
+    "add_ip, get_ip and remove_ip as advertised", `Quick, add_get_remove_ips;
+    "GARPs are heard and not cached", `Quick, input_single_garp;
+    "unsolicited unicast replies are heard and not cached", `Quick, input_single_unicast;
+    "solicited unicast replies resolve pending threads", `Quick, input_resolves_wait;
+    "entries are replaced with new information", `Quick, input_replaces_old;
+    "unreachable IPs time out", `Quick, unreachable_times_out;
+    "queries are tried repeatedly before timing out", `Quick, query_retries;
+  ]
+
+let run test () =
+  Lwt_main.run (test ())
+
+let () =
+  (* enable logging to stdout for all modules *)
+  Logs.set_reporter (Logs_fmt.reporter ());
+  Logs.set_level ~all:true (Some Logs.Debug);
+  let suite =
+    [ "arp", List.map (fun (d, s, f) -> d, s, run f) suite ]
+  in
+  Alcotest.run "arp" suite

unikernel/duniverse/arp/test/tests.ml

@@ -0,0 +1,878 @@
+let generate n =
+  let data = Cstruct.create n in
+  for i = 0 to pred n do
+    Cstruct.set_uint8 data i (Random.int 256)
+  done;
+  data
+
+let rec gen_ip () =
+  let buf = generate 4 in
+  let ip = Ipaddr.V4.of_octets_exn (Cstruct.to_string buf) in
+  if ip = Ipaddr.V4.any || ip = Ipaddr.V4.broadcast then
+    gen_ip ()
+  else
+    buf, ip
+
+let rec gen_mac () =
+  let buf = generate 6 in
+  let mac = Macaddr.of_octets_exn (Cstruct.to_string buf) in
+  if mac = Macaddr.broadcast then
+    gen_mac ()
+  else
+    buf, mac
+
+let hdr = Cstruct.of_string "\000\001\008\000\006\004"
+
+let gen_int () =
+  let buf = generate 1 in
+  (buf, Cstruct.get_uint8 buf 0)
+
+let gen_op () =
+  let _, op = gen_int () in
+  let buf = Cstruct.create 2 in
+  let op = 1 + op mod 2 in
+  Cstruct.BE.set_uint16 buf 0 op ;
+  (if op = 1 then Arp_packet.Request else Arp_packet.Reply), buf
+
+let gen_arp () =
+  let sm, source_mac = gen_mac ()
+  and si, source_ip = gen_ip ()
+  and tm, target_mac = gen_mac ()
+  and ti, target_ip = gen_ip ()
+  and op, opb = gen_op ()
+  in
+  { Arp_packet.operation = op ; source_mac ; source_ip ; target_mac ; target_ip },
+  Cstruct.concat [ hdr ; opb ; sm ; si ; tm ; ti ]
+
+let p =
+  let module M = struct
+    type t = Arp_packet.t
+    let pp = Arp_packet.pp
+    let equal s t =
+        let open Arp_packet in
+        s.operation = t.operation &&
+        Macaddr.compare s.source_mac t.source_mac = 0 &&
+        Macaddr.compare s.target_mac t.target_mac = 0 &&
+        Ipaddr.V4.compare s.source_ip t.source_ip = 0 &&
+        Ipaddr.V4.compare s.target_ip t.target_ip = 0
+  end in
+  (module M : Alcotest.TESTABLE with type t = M.t)
+
+module Coding = struct
+  let gen_op_arp () =
+    let rec gen_op () =
+      let buf = generate 2 in
+      match Cstruct.BE.get_uint16 buf 0 with
+      | 1 | 2 -> gen_op ()
+      | x -> (x, buf)
+    in
+    let data = generate 20
+    and o, opb = gen_op ()
+    in
+    o, Cstruct.concat [ hdr ; opb ; data ]
+
+  let rec gen_unhandled_arp () =
+    (* some consistency -- hlen and plen *)
+    let htype = generate 2
+    and ptype = generate 2
+    in
+    (* if we don't have at least length m, we'll end up in Too_short *)
+    let rec i_min m () =
+      let buf, len = gen_int () in
+      if len < m then i_min m ()
+      else buf, len
+    in
+    let hl, hlen = i_min 6 ()
+    and pl, plen = i_min 4 ()
+    in
+    let my_hdr = Cstruct.concat [ htype ; ptype ; hl ; pl ] in
+    if Cstruct.equal my_hdr hdr then
+      gen_unhandled_arp ()
+    else
+      let rec gen_op () =
+        let buf = generate 2 in
+        match Cstruct.BE.get_uint16 buf 0 with
+        | 1 | 2 -> gen_op ()
+        | _ -> buf
+      in
+      let op = gen_op ()
+      and sha = generate hlen
+      and tha = generate hlen
+      and spa = generate plen
+      and tpa = generate plen
+      in
+      Cstruct.concat [ my_hdr ; op ; sha ; spa ; tha ; tpa ]
+
+  let gen_short_arp () =
+    let _, l = gen_int () in
+    generate (l mod 28)
+
+  let e =
+    let module M = struct
+      type t = Arp_packet.error
+      let pp = Arp_packet.pp_error
+      let equal a b =
+        let open Arp_packet in
+        match a, b with
+        | Too_short, Too_short -> true
+        | Unusable, Unusable -> true
+        | Unknown_operation x, Unknown_operation y -> x = y
+        | _ -> false
+    end in
+    (module M : Alcotest.TESTABLE with type t = M.t)
+
+  let repeat f n () =
+    for _i = 0 to n do
+      f ()
+    done
+
+  let check_r s res buf =
+    Alcotest.(check (result p e) s res (Arp_packet.decode buf))
+
+  let dec_valid_arp () =
+    let pkt, buf = gen_arp () in
+    check_r "decoding valid ARP frames" (Ok pkt) buf
+
+  let dec_unhandled_arp () =
+    let buf = gen_unhandled_arp () in
+    check_r "invalid header is error" (Error Arp_packet.Unusable) buf
+
+  let dec_short_arp () =
+    let buf = gen_short_arp () in
+    check_r "short is error" (Error Arp_packet.Too_short) buf
+
+  let dec_op_arp () =
+    let o, buf = gen_op_arp () in
+    check_r "invalid op is error" (Error (Arp_packet.Unknown_operation o)) buf
+
+  let dec_enc () =
+    let pkt, buf = gen_arp () in
+    let cbuf = Arp_packet.encode pkt in
+    Alcotest.(check bool "encoding produces same buffer" true (Cstruct.equal buf cbuf)) ;
+    match Arp_packet.decode buf with
+    | Error _ -> Alcotest.fail "decoding failed, should not happen"
+    | Ok pack ->
+      Alcotest.(check p "decoding worked" pkt pack) ;
+      let cbuf = Arp_packet.encode pack in
+      Alcotest.(check bool "encoding produces same buffer" true (Cstruct.equal buf cbuf))
+
+  let enc_into () =
+    let pkt, buf = gen_arp () in
+    let cbuf = Cstruct.create 28 in
+    Arp_packet.encode_into pkt cbuf ;
+    Alcotest.(check bool "encode_into works" true (Cstruct.equal cbuf buf))
+
+  let enc_fail () =
+    for i = 0 to 27 do
+      let buf = Cstruct.create i
+      and pkg, _ = gen_arp ()
+      in
+      Alcotest.check_raises "buffer is too small" (Invalid_argument "too small")
+        (fun () ->
+           try Arp_packet.encode_into pkg buf with Invalid_argument _ -> invalid_arg "too small")
+    done
+
+  let coder_tsts = [
+    "valid arp decoding", `Quick, (repeat dec_valid_arp 1000) ;
+    "unhandled arp decoding", `Quick, (repeat dec_unhandled_arp 1000) ;
+    "short arp decoding", `Quick, (repeat dec_short_arp 1000) ;
+    "invalid operation decoding", `Quick, (repeat dec_op_arp 1000) ;
+    "decoding is inverse of encoding", `Quick, (repeat dec_enc 1000) ;
+    "encode_into works", `Quick, (repeat enc_into 1000) ;
+    "encode_into fails with small bufs", `Quick, enc_fail ;
+  ]
+end
+
+module Handling = struct
+  let garp_of ip mac =
+    let mac0 = Macaddr.of_octets_exn (String.make 6 '\000') in
+    { Arp_packet.operation = Arp_packet.Request ;
+      source_ip = ip ; target_ip = ip ;
+      source_mac = mac ; target_mac = mac0 }
+
+  let gen_ip () = snd (gen_ip ())
+  and gen_mac () = snd (gen_mac ())
+
+  let m =
+    let module M = struct
+      type t = Macaddr.t
+      let pp = Macaddr.pp
+      let equal a b = Macaddr.compare a b = 0
+    end in
+    (module M : Alcotest.TESTABLE with type t = M.t)
+
+  let i =
+    let module M = struct
+      type t = Ipaddr.V4.t
+      let pp = Ipaddr.V4.pp
+      let equal a b = Ipaddr.V4.compare a b = 0
+    end in
+    (module M : Alcotest.TESTABLE with type t = M.t)
+
+  let create_raises () =
+    let mac = gen_mac () in
+    Alcotest.check_raises "timeout <= 0" (Invalid_argument "timeout must be strictly positive")
+      (fun () -> ignore(Arp_handler.create ~timeout:0 mac)) ;
+    Alcotest.check_raises "retries < 0" (Invalid_argument "retries must be positive")
+      (fun () -> ignore(Arp_handler.create ~retries:(-1) mac))
+
+  let basic_good () =
+    let mac = gen_mac ()
+    and ipaddr = gen_ip ()
+    in
+    let t, garp = Arp_handler.create ~ipaddr mac in
+    let garp = match garp with
+      | None -> Alcotest.fail "expected some garp"
+      | Some garp -> garp
+    in
+    Alcotest.(check bool "create has good GARP" true
+                (Cstruct.equal (Arp_packet.encode (garp_of ipaddr mac))
+                   (Arp_packet.encode (fst garp)))) ;
+    Alcotest.(check (list i) "ip is sensible" [ipaddr] (Arp_handler.ips t)) ;
+    Alcotest.(check (option m) "own entry is in cache"
+                (Some mac) (Arp_handler.in_cache t ipaddr)) ;
+    Alcotest.(check (option m) "any is not in cache" None
+                (Arp_handler.in_cache t Ipaddr.V4.any)) ;
+    Alcotest.(check (option m) "broadcast is not in cache" None
+                (Arp_handler.in_cache t Ipaddr.V4.broadcast))
+
+  let remove_good () =
+    let mac = gen_mac ()
+    and ipaddr = gen_ip ()
+    in
+    let t, _garp = Arp_handler.create ~ipaddr mac in
+    Alcotest.(check (list i) "ip is sensible" [ipaddr] (Arp_handler.ips t)) ;
+    Alcotest.(check (option m) "own entry is in cache"
+                (Some mac) (Arp_handler.in_cache t ipaddr)) ;
+    let t = Arp_handler.remove t ipaddr in
+    Alcotest.(check (option m) "own entry is no longer in cache" None
+                (Arp_handler.in_cache t ipaddr))
+
+  let remove_no () =
+    let mac = gen_mac ()
+    and ipaddr = gen_ip ()
+    in
+    let t, _garp = Arp_handler.create ~ipaddr mac in
+    Alcotest.(check (list i) "ip is sensible" [ipaddr] (Arp_handler.ips t)) ;
+    Alcotest.(check (option m) "own entry is in cache"
+                (Some mac) (Arp_handler.in_cache t ipaddr)) ;
+    let t = Arp_handler.remove t Ipaddr.V4.any in
+    Alcotest.(check (option m) "own entry is still in cache" (Some mac)
+                (Arp_handler.in_cache t ipaddr))
+
+  let alias_good () =
+    let mac = gen_mac ()
+    and ipaddr = gen_ip ()
+    in
+    let t, _garp = Arp_handler.create ~ipaddr mac in
+    Alcotest.(check (list i) "ip is sensible" [ipaddr] (Arp_handler.ips t)) ;
+    Alcotest.(check (option m) "own entry is in cache"
+                (Some mac) (Arp_handler.in_cache t ipaddr)) ;
+    let t, _, _ = Arp_handler.alias t ipaddr in
+    Alcotest.(check (option m) "own entry is still in cache" (Some mac)
+                (Arp_handler.in_cache t ipaddr)) ;
+    let ip' = gen_ip () in
+    let t, _, _ = Arp_handler.alias t ip' in
+    Alcotest.(check (option m) "own entry is still in cache" (Some mac)
+                (Arp_handler.in_cache t ipaddr)) ;
+    Alcotest.(check (option m) "aliased entry is in cache" (Some mac)
+                (Arp_handler.in_cache t ip'))
+
+  let alias_remove_inverse () =
+    let mac = gen_mac ()
+    and ipaddr = gen_ip ()
+    in
+    let t, _garp = Arp_handler.create ~ipaddr mac in
+    let ip' = gen_ip () in
+    let t, _, _ = Arp_handler.alias t ip' in
+    Alcotest.(check (option m) "own entry is in cache" (Some mac)
+                (Arp_handler.in_cache t ipaddr)) ;
+    Alcotest.(check (option m) "aliased entry is in cache" (Some mac)
+                (Arp_handler.in_cache t ip')) ;
+    let t = Arp_handler.remove t ip' in
+    Alcotest.(check (option m) "aliased entry is no longer in cache" None
+                (Arp_handler.in_cache t ip'))
+
+  let static_good () =
+    let mac = gen_mac ()
+    and ipaddr = gen_ip ()
+    in
+    let t, _garp = Arp_handler.create ~ipaddr mac in
+    let ip' = gen_ip () in
+    let mac' = gen_mac () in
+    let t, _ = Arp_handler.static t ip' mac' in
+    Alcotest.(check (option m) "own entry is in cache" (Some mac)
+                (Arp_handler.in_cache t ipaddr)) ;
+    Alcotest.(check (option m) "static entry is in cache" (Some mac')
+                (Arp_handler.in_cache t ip')) ;
+    let t = Arp_handler.remove t ip' in
+    Alcotest.(check (option m) "static entry is no longer in cache" None
+                (Arp_handler.in_cache t ip'))
+
+  let static_alias_good () =
+    let mac = gen_mac ()
+    and ipaddr = gen_ip ()
+    in
+    let t, _garp = Arp_handler.create ~ipaddr mac in
+    let ip' = gen_ip () in
+    let mac' = gen_mac () in
+    let t, _ = Arp_handler.static t ip' mac' in
+    Alcotest.(check (option m) "own entry is in cache" (Some mac)
+                (Arp_handler.in_cache t ipaddr)) ;
+    Alcotest.(check (option m) "static entry is in cache" (Some mac')
+                (Arp_handler.in_cache t ip')) ;
+    let t, _, _ = Arp_handler.alias t ip' in
+    Alcotest.(check (option m) "alias entry overwrote static one" (Some mac)
+                (Arp_handler.in_cache t ip')) ;
+    let t, _ = Arp_handler.static t ip' mac' in
+    Alcotest.(check (option m) "static entry overwrite aliased one" (Some mac')
+                (Arp_handler.in_cache t ip')) ;
+    let t = Arp_handler.remove t ip' in
+    Alcotest.(check (option m) "static entry is no longer in cache" None
+                (Arp_handler.in_cache t ip'))
+
+  let more_good () =
+    let mac = gen_mac ()
+    and ipaddr = gen_ip ()
+    in
+    let t, _garp = Arp_handler.create ~ipaddr mac in
+    let rec more_entries acc t = function
+      | 0 -> acc, t
+      | n ->
+        let ip' = gen_ip () in
+        if List.mem ip' (List.map fst acc) then
+          more_entries acc t n
+        else
+          let t, e =
+            if n mod 2 = 0 then
+              let mac' = gen_mac () in
+              let t, _ = Arp_handler.static t ip' mac' in
+              (t, (ip', mac'))
+            else
+              let t, _, _ = Arp_handler.alias t ip' in
+              (t, (ip', mac))
+          in
+          more_entries (e::acc) t (pred n)
+    in
+    let acc, t = more_entries [(ipaddr,mac)] t 100 in
+    List.iter (fun (ip, mac) ->
+        Alcotest.(check (option m) "entry is in cache" (Some mac)
+                    (Arp_handler.in_cache t ip)))
+      acc ;
+    List.iter (fun (ip, _) ->
+        let t = Arp_handler.remove t ip in
+        Alcotest.(check (option m) "entry is no longer in cache" None
+                    (Arp_handler.in_cache t ip)))
+      acc ;
+    let t = List.fold_left (fun t (ip, _) -> Arp_handler.remove t ip) t acc in
+    Alcotest.(check (option m) "own entry is no longer in cache" None
+                (Arp_handler.in_cache t ipaddr))
+
+  let packet =
+    let module M = struct
+      type t = Arp_packet.t
+      let pp = Arp_packet.pp
+      let equal = Arp_packet.equal
+    end in
+    (module M : Alcotest.TESTABLE with type t = M.t)
+
+  let out =
+    let module M = struct
+      type t = Arp_packet.t * Macaddr.t
+      let pp ppf (cs, mac) =
+        Format.fprintf ppf "out: %a to %a" Arp_packet.pp cs Macaddr.pp mac
+      let equal (acs, amac) (bcs, bmac) =
+        Arp_packet.equal acs bcs && Macaddr.compare amac bmac = 0
+    end in
+    (module M : Alcotest.TESTABLE with type t = M.t)
+
+  let qres =
+    let module M = struct
+      type t = int list Arp_handler.qres
+      let pp ppf = function
+        | Arp_handler.Mac mac -> Format.fprintf ppf "ok %a" Macaddr.pp mac
+        | Arp_handler.RequestWait ((cs, mac), xs) ->
+          Format.fprintf ppf "requestwait %a to %a, wait %s"
+            Arp_packet.pp cs Macaddr.pp mac
+            (String.concat ", " (List.map string_of_int xs))
+        | Arp_handler.Wait xs ->
+          Format.fprintf ppf "wait %s"
+            (String.concat ", " (List.map string_of_int xs))
+      let equal a b = match a, b with
+        | Arp_handler.Mac a, Arp_handler.Mac b -> Macaddr.compare a b = 0
+        | Arp_handler.RequestWait ((csa, maca), xsa),
+          Arp_handler.RequestWait ((csb, macb), xsb) ->
+          Arp_packet.equal csa csb && Macaddr.compare maca macb = 0 &&
+          List.length xsa = List.length xsb &&
+          List.for_all (fun x -> List.mem x xsb) xsa
+        | Arp_handler.Wait xsa, Arp_handler.Wait xsb ->
+          List.length xsa = List.length xsb &&
+          List.for_all (fun x -> List.mem x xsb) xsa
+        |  _ -> false
+    end in
+    (module M : Alcotest.TESTABLE with type t = M.t)
+
+  let merge v = function
+    | None -> [v]
+    | Some xs -> v::xs
+
+  let handle_good () =
+    let mac = gen_mac ()
+    and ipaddr = gen_ip ()
+    in
+    let t, _garp = Arp_handler.create ~ipaddr mac in
+    let _t, res = Arp_handler.query t ipaddr (merge 1) in
+    Alcotest.check qres "own IP can be queried" (Arp_handler.Mac mac) res
+
+  let query source_mac source_ip target_ip =
+    { Arp_packet.operation = Arp_packet.Request ;
+      source_mac ; source_ip ;
+      target_mac = Macaddr.broadcast ; target_ip },
+    Macaddr.broadcast
+
+  let handle_gen_request () =
+    let mac = gen_mac ()
+    and ipaddr = gen_ip ()
+    in
+    let t, _garp = Arp_handler.create ~retries:1 ~ipaddr mac in
+    let other = gen_ip () in
+    let _, res = Arp_handler.query t other (merge 1) in
+    let out = query mac ipaddr other in
+    Alcotest.check qres "res is requestwait" (Arp_handler.RequestWait (out, [1])) res
+
+  let handle_gen_request_twice () =
+    let mac = gen_mac ()
+    and ipaddr = gen_ip ()
+    in
+    let t, _garp = Arp_handler.create ~ipaddr ~retries:1 mac in
+    let other = gen_ip () in
+    let t, res = Arp_handler.query t other (merge 1) in
+    let out = query mac ipaddr other in
+    Alcotest.check qres "res is requestwait" (Arp_handler.RequestWait (out, [1])) res ;
+    let _, res = Arp_handler.query t other (merge 2) in
+    Alcotest.check qres "res is wait" (Arp_handler.Wait [2;1]) res
+
+  let alias_wakes () =
+    let mac = gen_mac ()
+    and ipaddr = gen_ip ()
+    in
+    let t, _garp = Arp_handler.create ~ipaddr mac in
+    let other = gen_ip () in
+    let t, res = Arp_handler.query t other (merge 1) in
+    let out = query mac ipaddr other in
+    Alcotest.check qres "res is requestwait!" (Arp_handler.RequestWait (out, [1])) res ;
+    Alcotest.(check (option m) "query is not cache" None (Arp_handler.in_cache t other)) ;
+    let _, _, a = Arp_handler.alias t other in
+    Alcotest.(check (option (list int)) "alias wakes up" (Some [1]) a)
+
+  let static_wakes () =
+    let mac = gen_mac ()
+    and ipaddr = gen_ip ()
+    in
+    let t, _garp = Arp_handler.create ~ipaddr mac in
+    let other = gen_ip () in
+    let t, res = Arp_handler.query t other (merge 1) in
+    let out = query mac ipaddr other in
+    Alcotest.check qres "res is requestwait" (Arp_handler.RequestWait (out, [1])) res ;
+    let _, a = Arp_handler.static t other mac in
+    Alcotest.(check (option (list int)) "alias wakes up" (Some [1]) a)
+
+  let handle_timeout () =
+    let mac = gen_mac ()
+    and ipaddr = gen_ip ()
+    in
+    let t, _garp = Arp_handler.create ~retries:1 ~ipaddr mac in
+    let other = gen_ip () in
+    let t, _ = Arp_handler.query t other (merge 1) in
+    let t, _, a = Arp_handler.tick t in
+    Alcotest.(check (list (list int)) "tick didn't timeout" [] a) ;
+    let _, _, a = Arp_handler.tick t in
+    Alcotest.(check (list (list int)) "tick timed out" [[1]] a)
+
+  let req_before_timeout () =
+    let mac = gen_mac ()
+    and ipaddr = gen_ip ()
+    in
+    let t, _garp = Arp_handler.create ~timeout:1 ~ipaddr mac in
+    let other = gen_ip () in
+    let t, _ = Arp_handler.query t other (merge 1) in
+    let omac = gen_mac () in
+    let pkt =
+      Arp_packet.encode { Arp_packet.operation = Arp_packet.Reply ;
+                          source_ip = other ; source_mac = omac ;
+                          target_ip = ipaddr ; target_mac = mac }
+    in
+    let t, outp, wake = Arp_handler.input t pkt in
+    Alcotest.(check (option out) "out is none" None outp) ;
+    Alcotest.(check (option (pair m (list int))) "wake is correct"
+                (Some (omac, [1])) wake) ;
+    let _, outp, rs = Arp_handler.tick t in
+    Alcotest.(check bool "timeouts are empty" true (rs = [])) ;
+    Alcotest.(check (list out) "arp request is sent" [query mac ipaddr other] outp)
+
+  let multiple_reqs () =
+    let mac = gen_mac ()
+    and ipaddr = gen_ip ()
+    in
+    let t, _garp = Arp_handler.create ~retries:1 ~ipaddr mac in
+    let other = gen_ip () in
+    let t, res = Arp_handler.query t other (merge 1) in
+    let q = query mac ipaddr other in
+    Alcotest.check qres "query generates ARP request" (Arp_handler.RequestWait (q, [1])) res ;
+    let t, outs, touts = Arp_handler.tick t in
+    Alcotest.(check (list out) "tick generates second ARP request" [q] outs) ;
+    Alcotest.(check (list (list int)) "tick generated no timeout yet" [] touts) ;
+    let _, outs, touts = Arp_handler.tick t in
+    Alcotest.(check (list out) "tick generated no other request" [] outs) ;
+    Alcotest.(check (list (list int)) "tick generated a timeout" [[1]] touts)
+
+  let multiple_reqs_2 () =
+    let mac = gen_mac ()
+    and ipaddr = gen_ip ()
+    in
+    let t, _garp = Arp_handler.create ~retries:4 ~ipaddr mac in
+    let other = gen_ip () in
+    let t, res = Arp_handler.query t other (merge 1) in
+    let q = query mac ipaddr other in
+    Alcotest.check qres "query generates ARP request" (Arp_handler.RequestWait (q, [1])) res ;
+    let t, outs, touts = Arp_handler.tick t in
+    Alcotest.(check (list out) "tick generates second ARP request" [q] outs) ;
+    Alcotest.(check (list (list int)) "tick generated no timeout yet" [] touts) ;
+    let t, outs, touts = Arp_handler.tick t in
+    Alcotest.(check (list out) "tick generates third ARP request" [q] outs) ;
+    Alcotest.(check (list (list int)) "tick generated no timeout yet" [] touts) ;
+    let t, outs, touts = Arp_handler.tick t in
+    Alcotest.(check (list out) "tick generates fourth ARP request" [q] outs) ;
+    Alcotest.(check (list (list int)) "tick generated no timeout yet" [] touts) ;
+    let t, outs, touts = Arp_handler.tick t in
+    Alcotest.(check (list out) "tick generates fifth ARP request" [q] outs) ;
+    Alcotest.(check (list (list int)) "tick generated no timeout yet" [] touts) ;
+    let _, outs, touts = Arp_handler.tick t in
+    Alcotest.(check (list out) "tick generated no other request" [] outs) ;
+    Alcotest.(check (list (list int)) "tick generated a timeout" [[1]] touts)
+
+  let handle_reply () =
+    let mac = gen_mac ()
+    and ipaddr = gen_ip ()
+    in
+    let t, _garp = Arp_handler.create ~timeout:1 ~ipaddr mac in
+    let other = gen_ip () in
+    let omac = gen_mac () in
+    let pkt =
+      Arp_packet.encode { Arp_packet.operation = Arp_packet.Reply ;
+                          source_ip = other ; source_mac = omac ;
+                          target_ip = ipaddr ; target_mac = mac }
+    in
+    let t, outp, w = Arp_handler.input t pkt in
+    Alcotest.(check (option out) "nothing to be sent" None outp) ;
+    Alcotest.(check (option (pair m (list int))) "noone wakes up" None w) ;
+    Alcotest.(check (option m) "received entry is not in cache" None
+                (Arp_handler.in_cache t other))
+
+  let handle_garp () =
+    let mac = gen_mac ()
+    and ipaddr = gen_ip ()
+    in
+    let t, _garp = Arp_handler.create ~timeout:1 ~ipaddr mac in
+    let other = gen_ip () in
+    let omac = gen_mac () in
+    let pkt = Arp_packet.encode (garp_of other omac) in
+    let t, outp, w = Arp_handler.input t pkt in
+    Alcotest.(check (option out) "nothing out" None outp) ;
+    Alcotest.(check (option (pair m (list int))) "nothin woken up" None w) ;
+    Alcotest.(check (option m) "received garp entry is not in cache" None
+                (Arp_handler.in_cache t other))
+
+  let answer_req_broadcast () =
+    let mac = gen_mac ()
+    and ipaddr = gen_ip ()
+    in
+    let t, _garp = Arp_handler.create ~timeout:1 ~ipaddr mac in
+    let other = gen_ip () in
+    let omac = gen_mac () in
+    let pkt, _ = query omac other ipaddr in
+    let _, outp, w = Arp_handler.input t (Arp_packet.encode pkt) in
+    Alcotest.(check (option (pair m (list int))) "nothin woken up" None w) ;
+    Alcotest.(check (option out) "request to us provokes a reply"
+                (Some ({ Arp_packet.operation = Arp_packet.Reply ;
+                         source_mac = mac ; source_ip = ipaddr ;
+                         target_mac = omac ; target_ip = other },
+                       omac)) outp)
+
+  let answer_req_unicast () =
+    let mac = gen_mac ()
+    and ipaddr = gen_ip ()
+    in
+    let t, _garp = Arp_handler.create ~timeout:1 ~ipaddr mac in
+    let other = gen_ip () in
+    let omac = gen_mac () in
+    let pkt =
+      Arp_packet.encode { Arp_packet.operation = Arp_packet.Request ;
+                          source_ip = other ; source_mac = omac ;
+                          target_ip = ipaddr ; target_mac = mac }
+    in
+    let _, outp, w = Arp_handler.input t pkt in
+    Alcotest.(check (option (pair m (list int))) "nothin woken up" None w) ;
+    Alcotest.(check (option out) "request to us provokes a reply"
+                (Some ({ Arp_packet.operation = Arp_packet.Reply ;
+                         source_mac = mac ; source_ip = ipaddr ;
+                         target_mac = omac ; target_ip = other },
+                       omac)) outp)
+
+  let not_answer_req () =
+    let mac = gen_mac ()
+    and ipaddr = gen_ip ()
+    in
+    let t, _garp = Arp_handler.create ~timeout:1 ~ipaddr mac in
+    let other = gen_ip () in
+    let third = gen_ip () in
+    let omac = gen_mac () in
+    let pkt, _ = query omac other third in
+    let _, outp, w = Arp_handler.input t (Arp_packet.encode pkt) in
+    Alcotest.(check (option out) "nothing out" None outp) ;
+    Alcotest.(check (option (pair m (list int))) "nothin woken up" None w)
+
+  let ignoring_random () =
+    let mac = gen_mac ()
+    and ipaddr = gen_ip ()
+    in
+    let t, _garp = Arp_handler.create ~timeout:1 ~ipaddr mac in
+    let pkt = generate 24 in
+    let _, outp, w = Arp_handler.input t pkt in
+    Alcotest.(check (option out) "nothing out" None outp) ;
+    Alcotest.(check (option (pair m (list int))) "nothin woken up" None w)
+
+  let reply_does_not_override () =
+    let mac = gen_mac ()
+    and ipaddr = gen_ip ()
+    in
+    let t, _garp = Arp_handler.create ~timeout:1 ~ipaddr mac in
+    let omac = gen_mac () in
+    let pkt =
+      Arp_packet.encode { Arp_packet.operation = Arp_packet.Reply ;
+                          source_ip = ipaddr ; source_mac = omac ;
+                          target_ip = ipaddr ; target_mac = mac }
+    in
+    let t, outp, w = Arp_handler.input t pkt in
+    Alcotest.(check (option out) "nothing out" None outp) ;
+    Alcotest.(check (option (pair m (list int))) "nothin woken up" None w) ;
+    Alcotest.(check (option m) "our entry is still in cache" (Some mac)
+                (Arp_handler.in_cache t ipaddr))
+
+  let reply_query () =
+    let mac = gen_mac ()
+    and ipaddr = gen_ip ()
+    in
+    let t, _garp = Arp_handler.create ~timeout:1 ~ipaddr mac in
+    let other = gen_ip () in
+    let omac = gen_mac () in
+    let pkt =
+      Arp_packet.encode { Arp_packet.operation = Arp_packet.Reply ;
+                          source_ip = other ; source_mac = omac ;
+                          target_ip = ipaddr ; target_mac = mac }
+    in
+    let q = query mac ipaddr other in
+    let t, r = Arp_handler.query t other (merge 1) in
+    Alcotest.check qres "r is request wait" (Arp_handler.RequestWait (q, [1])) r ;
+    let t, outp, w = Arp_handler.input t pkt in
+    Alcotest.(check (option out) "nothing out" None outp) ;
+    Alcotest.(check (option (pair m (list int))) "something woken up" (Some (omac, [1])) w) ;
+    let _t, res = Arp_handler.query t other (merge 2) in
+    Alcotest.check qres "dynamic entry can be queried" (Arp_handler.Mac omac) res
+
+  let reply_in_cache () =
+    let mac = gen_mac ()
+    and ipaddr = gen_ip ()
+    in
+    let t, _garp = Arp_handler.create ~timeout:1 ~ipaddr mac in
+    let other = gen_ip () in
+    let omac = gen_mac () in
+    let pkt =
+      Arp_packet.encode { Arp_packet.operation = Arp_packet.Reply ;
+                          source_ip = other ; source_mac = omac ;
+                          target_ip = ipaddr ; target_mac = mac }
+    in
+    let q = query mac ipaddr other in
+    let t, r = Arp_handler.query t other (merge 1) in
+    Alcotest.check qres "r is request wait" (Arp_handler.RequestWait (q, [1])) r ;
+    let t, outp, w = Arp_handler.input t pkt in
+    Alcotest.(check (option out) "nothing out" None outp) ;
+    Alcotest.(check (option (pair m (list int))) "something woken up" (Some (omac, [1])) w) ;
+    Alcotest.(check (option m) "entry in cache" (Some omac) (Arp_handler.in_cache t other)) ;
+    Alcotest.(check (list i) "ips do not include dynamic entries" [ipaddr] (Arp_handler.ips t))
+
+
+  let reply_overriden () =
+    let mac = gen_mac ()
+    and ipaddr = gen_ip ()
+    in
+    let t, _garp = Arp_handler.create ~timeout:1 ~ipaddr mac in
+    let other = gen_ip () in
+    let omac = gen_mac () in
+    let pkt =
+      Arp_packet.encode { Arp_packet.operation = Arp_packet.Reply ;
+                          source_ip = other ; source_mac = omac ;
+                          target_ip = ipaddr ; target_mac = mac }
+    in
+    let q = query mac ipaddr other in
+    let t, r = Arp_handler.query t other (merge 1) in
+    Alcotest.check qres "r is request wait" (Arp_handler.RequestWait (q, [1])) r ;
+    let t, outp, w = Arp_handler.input t pkt in
+    Alcotest.(check (option out) "nothing out" None outp) ;
+    Alcotest.(check (option (pair m (list int))) "something woken up" (Some (omac, [1])) w) ;
+    Alcotest.(check (option m) "entry in cache" (Some omac) (Arp_handler.in_cache t other)) ;
+    let t, outp, w = Arp_handler.input t pkt in
+    Alcotest.(check (option out) "nothing out" None outp) ;
+    Alcotest.(check (option (pair m (list int))) "nothing woken up" None w) ;
+    Alcotest.(check (option m) "entry in cache" (Some omac) (Arp_handler.in_cache t other))
+
+  let reply_overriden_other () =
+    let mac = gen_mac ()
+    and ipaddr = gen_ip ()
+    in
+    let t, _garp = Arp_handler.create ~timeout:1 ~ipaddr mac in
+    let other = gen_ip () in
+    let omac = gen_mac () in
+    let pkt =
+      Arp_packet.encode { Arp_packet.operation = Arp_packet.Reply ;
+                          source_ip = other ; source_mac = omac ;
+                          target_ip = ipaddr ; target_mac = mac }
+    in
+    let q = query mac ipaddr other in
+    let t, r = Arp_handler.query t other (merge 1) in
+    Alcotest.check qres "r is request wait" (Arp_handler.RequestWait (q, [1])) r ;
+    let t, outp, w = Arp_handler.input t pkt in
+    Alcotest.(check (option out) "nothing out" None outp) ;
+    Alcotest.(check (option (pair m (list int))) "something woken up" (Some (omac, [1])) w) ;
+    Alcotest.(check (option m) "entry in cache" (Some omac) (Arp_handler.in_cache t other)) ;
+    let omac = gen_mac () in
+    let pkt =
+      Arp_packet.encode { Arp_packet.operation = Arp_packet.Reply ;
+                          source_ip = other ; source_mac = omac ;
+                          target_ip = ipaddr ; target_mac = mac }
+    in
+    let t, outp, w = Arp_handler.input t pkt in
+    Alcotest.(check (option out) "nothing out" None outp) ;
+    Alcotest.(check (option (pair m (list int))) "nothing woken up" None w) ;
+    Alcotest.(check (option m) "overriden entry in cache" (Some omac)
+                (Arp_handler.in_cache t other))
+
+  let reply_times_out () =
+    let mac = gen_mac ()
+    and ipaddr = gen_ip ()
+    in
+    let t, _garp = Arp_handler.create ~timeout:1 ~ipaddr mac in
+    let other = gen_ip () in
+    let omac = gen_mac () in
+    let pkt =
+      Arp_packet.encode { Arp_packet.operation = Arp_packet.Reply ;
+                          source_ip = other ; source_mac = omac ;
+                          target_ip = ipaddr ; target_mac = mac }
+    in
+    let q = query mac ipaddr other in
+    let t, r = Arp_handler.query t other (merge 1) in
+    Alcotest.check qres "r is request wait" (Arp_handler.RequestWait (q, [1])) r ;
+    let t, outp, w = Arp_handler.input t pkt in
+    Alcotest.(check (option out) "nothing out" None outp) ;
+    Alcotest.(check (option (pair m (list int))) "something woken up" (Some (omac, [1])) w) ;
+    Alcotest.(check (option m) "entry in cache" (Some omac) (Arp_handler.in_cache t other)) ;
+    let t, outp, timeout = Arp_handler.tick t in
+    Alcotest.(check (list out) "request sent" [q] outp) ;
+    Alcotest.(check (list (list int)) "nothing timed out" [] timeout) ;
+    let t, outp, timeout = Arp_handler.tick t in
+    Alcotest.(check (list out) "nada sent" [] outp) ;
+    Alcotest.(check (list (list int)) "nothing timed out" [] timeout) ;
+    Alcotest.(check (option m) "entry no longer in cache" None
+                (Arp_handler.in_cache t other))
+
+  let dyn_not_advertised () =
+    let mac = gen_mac ()
+    and ipaddr = gen_ip ()
+    in
+    let t, _garp = Arp_handler.create ~timeout:1 ~ipaddr mac in
+    let other = gen_ip () in
+    let omac = gen_mac () in
+    let pkt =
+      Arp_packet.encode { Arp_packet.operation = Arp_packet.Reply ;
+                          source_ip = other ; source_mac = omac ;
+                          target_ip = ipaddr ; target_mac = mac }
+    in
+    let q = query mac ipaddr other in
+    let t, r = Arp_handler.query t other (merge 1) in
+    Alcotest.check qres "r is request wait" (Arp_handler.RequestWait (q, [1])) r ;
+    let t, outp, w = Arp_handler.input t pkt in
+    Alcotest.(check (option out) "nothing out" None outp) ;
+    Alcotest.(check (option (pair m (list int))) "something woken up" (Some (omac, [1])) w) ;
+    let third = gen_ip ()
+    and third_mac = gen_mac ()
+    in
+    let q, _ = query third_mac third other in
+    let _, outp, w = Arp_handler.input t (Arp_packet.encode q) in
+    Alcotest.(check (option out) "request a dynamic entry is not answered" None outp) ;
+    Alcotest.(check (option (pair m (list int))) "nothing woken up" None w)
+
+  let handle_reply_wakesup () =
+    let mac = gen_mac ()
+    and ipaddr = gen_ip ()
+    in
+    let t, _garp = Arp_handler.create ~timeout:1 ~ipaddr mac in
+    let other = gen_ip () in
+    let omac = gen_mac () in
+    let pkt =
+      Arp_packet.encode { Arp_packet.operation = Arp_packet.Reply ;
+                          source_ip = other ; source_mac = omac ;
+                          target_ip = ipaddr ; target_mac = mac }
+    in
+    let q = query mac ipaddr other in
+    let t, r = Arp_handler.query t other (merge 1) in
+    Alcotest.check qres "r is request wait" (Arp_handler.RequestWait (q, [1])) r ;
+    let t, r = Arp_handler.query t other (merge 2) in
+    Alcotest.check qres "r is wait" (Arp_handler.Wait [2;1]) r ;
+    let _, outp, w = Arp_handler.input t pkt in
+    Alcotest.(check (option out) "nothing out" None outp) ;
+    Alcotest.(check (option (pair m (list int))) "something woken up" (Some (omac, [2;1])) w)
+
+  let handl_tsts = [
+    "create raises", `Quick, create_raises ;
+    "basic tests", `Quick, basic_good ;
+    "remove test", `Quick, remove_good ;
+    "remove no test", `Quick, remove_no ;
+    "alias test", `Quick, alias_good ;
+    "alias remove test", `Quick, alias_remove_inverse ;
+    "static test", `Quick, static_good ;
+    "static alias test", `Quick, static_alias_good ;
+    "more tests", `Quick, more_good ;
+    "handle good", `Quick, handle_good ;
+    "handle generates req", `Quick, handle_gen_request ;
+    "handle generates req, next doesn't", `Quick, handle_gen_request_twice ;
+    "alias wakes", `Quick, alias_wakes ;
+    "static wakes", `Quick, static_wakes ;
+    "handle timeout", `Quick, handle_timeout ;
+    "request send before timeout", `Quick, req_before_timeout ;
+    "multiple requests are send", `Quick, multiple_reqs ;
+    "multiple requests are send 2", `Quick, multiple_reqs_2 ;
+    "handle reply", `Quick, handle_reply ;
+    "handle garp", `Quick, handle_garp ;
+    "answers broadcast request", `Quick, answer_req_broadcast ;
+    "answers unicast request", `Quick, answer_req_unicast ;
+    "not answering random request", `Quick, not_answer_req ;
+    "ignoring random", `Quick, ignoring_random ;
+    "reply does not harm static entries", `Quick, reply_does_not_override ;
+    "reply is in cache", `Quick, reply_in_cache ;
+    "dynamic entry can be queried", `Quick, reply_query ;
+    "reply times out", `Quick, reply_times_out ;
+    "dynamic entry overriden by same", `Quick, reply_overriden ;
+    "dynamic entry overriden by other", `Quick, reply_overriden_other ;
+    "dynamic entry is not advertised", `Quick, dyn_not_advertised ;
+    "reply wakes tasks", `Quick, handle_reply_wakesup ;
+  ]
+end
+
+let tests = [
+  "Coder", Coding.coder_tsts ;
+  "Handler", Handling.handl_tsts ;
+]
+
+let () =
+  Random.self_init ();
+  Alcotest.run "ARP tests" tests