[DO NOT MERGE] Add a Endpoint.destroy which closes active connections

Previously there was no way to locate the connections associated with
an endpoint to shut them down. This patch adds a map of TCP `id` to
`unit Lwt.u` and a function `Endpoint.destroy` which triggers the
disconnection of all the active connections.

Related to #260

Signed-off-by: David Scott <dave.scott@docker.com>

Author: djs55

src/hostnet/hostnet_dns.ml

@@ -356,7 +356,7 @@ struct
     | Ok buffer ->
       Udp.write ~src_port:53 ~dst:src ~dst_port:src_port udp buffer
 
-  let handle_tcp ~t =
+  let handle_tcp ~t ~close =
     (* FIXME: need to record the upstream request *)
     let listeners _ =
       Log.debug (fun f -> f "DNS TCP handshake complete");
@@ -384,7 +384,10 @@ struct
             Lwt.async queries;
             loop ()
         in
-        loop ()
+        Lwt.pick [
+          loop ();
+          close
+        ]
       in
       Some f
     in

src/hostnet/hostnet_dns.mli

@@ -40,7 +40,7 @@ sig
     t:t -> udp:Udp.t -> src:Ipaddr.V4.t -> dst:Ipaddr.V4.t -> src_port:int ->
     Cstruct.t -> (unit, Udp.error) result Lwt.t
 
-  val handle_tcp: t:t -> (int -> (Tcp.flow -> unit Lwt.t) option) Lwt.t
+  val handle_tcp: t:t -> close:(unit Lwt.t) -> (int -> (Tcp.flow -> unit Lwt.t) option) Lwt.t
 
   val destroy: t -> unit Lwt.t
 end

src/hostnet/slirp.ml

@@ -257,6 +257,8 @@ struct
       clock:                    Clock.t;
       mutable pending:          Tcp.Id.Set.t;
       mutable last_active_time: float;
+      (* Tasks that will be signalled if the endpoint is destroyed *)
+      mutable on_destroy:       unit Lwt.u Tcp.Id.Map.t;
     }
     (** A generic TCP/IP endpoint *)
 
@@ -279,12 +281,17 @@ struct
 
       let pending = Tcp.Id.Set.empty in
       let last_active_time = Unix.gettimeofday () in
+      let on_destroy = Tcp.Id.Map.empty in
       let tcp_stack =
         { recorder; netif; ethif; arp; ipv4; icmpv4; udp4; tcp4; pending;
-          last_active_time; clock }
+          last_active_time; clock; on_destroy }
       in
       Lwt.return tcp_stack
 
+    let destroy t =
+      Tcp.Id.Map.iter (fun _ u -> Lwt.wakeup_later u ()) t.on_destroy;
+      t.on_destroy <- Tcp.Id.Map.empty
+
     let intercept_tcp_syn t ~id ~syn on_syn_callback (buf: Cstruct.t) =
       if syn then begin
         if Tcp.Id.Set.mem id t.pending then begin
@@ -295,9 +302,14 @@ struct
           Lwt.return_unit
         end else begin
           t.pending <- Tcp.Id.Set.add id t.pending;
+          (* Add a task to the "on_destroy" list which will be signalled if
+             the Endpoint is disconnected from the switch and we should close
+             connections. *)
+          let close, close_request = Lwt.task () in
+          t.on_destroy <- Tcp.Id.Map.add id close_request t.on_destroy;
           Lwt.finalize
             (fun () ->
-               on_syn_callback ()
+               on_syn_callback close
                >>= fun listeners ->
                let src = Stack_tcp_wire.dst id in
                let dst = Stack_tcp_wire.src id in
@@ -319,7 +331,7 @@ struct
       Mirage_flow_lwt.Proxy(Clock)(Stack_tcp)(Host.Sockets.Stream.Tcp)
 
     let input_tcp t ~id ~syn (ip, port) (buf: Cstruct.t) =
-      intercept_tcp_syn t ~id ~syn (fun () ->
+      intercept_tcp_syn t ~id ~syn (fun close ->
           Host.Sockets.Stream.Tcp.connect (ip, port)
           >>= function
           | Error (`Msg m) ->
@@ -341,9 +353,21 @@ struct
                   Lwt.return_unit
                 | Some socket ->
                   Lwt.finalize (fun () ->
-                      Proxy.proxy t.clock flow socket
+                    Lwt.pick [
+                      Lwt.map
+                        (function Error e -> Error (`Proxy e) | Ok x -> Ok x)
+                        (Proxy.proxy t.clock flow socket);
+                      Lwt.map
+                        (fun () -> Error `Close)
+                        close
+                    ]
                       >>= function
-                      | Error e ->
+                      | Error (`Close) ->
+                        Log.info (fun f ->
+                          f "%s proxy closed due to switch port disconnection"
+                            (Tcp.Flow.to_string tcp));
+                        Lwt.return_unit
+                      | Error (`Proxy e) ->
                         Log.debug (fun f ->
                             f "%s proxy failed with %a"
                               (Tcp.Flow.to_string tcp) Proxy.pp_error e);
@@ -354,6 +378,7 @@ struct
                       Log.debug (fun f ->
                           f "closing flow %s" (string_of_id tcp.Tcp.Flow.id));
                       tcp.Tcp.Flow.socket <- None;
+                      t.on_destroy <- Tcp.Id.Map.remove id t.on_destroy;
                       Tcp.Flow.remove tcp.Tcp.Flow.id;
                       Host.Sockets.Stream.Tcp.close socket
                     )
@@ -479,9 +504,9 @@ struct
       let id =
         Stack_tcp_wire.v ~src_port:53 ~dst:src ~src:dst ~dst_port:src_port
       in
-      Endpoint.intercept_tcp_syn t.endpoint ~id ~syn (fun () ->
+      Endpoint.intercept_tcp_syn t.endpoint ~id ~syn (fun close ->
           !dns >>= fun t ->
-          Dns_forwarder.handle_tcp ~t
+          Dns_forwarder.handle_tcp ~t ~close
         ) raw
       >|= ok
 
@@ -801,10 +826,11 @@ struct
          let now = Unix.gettimeofday () in
          let old_ips = IPMap.fold (fun ip endpoint acc ->
              let age = now -. endpoint.Endpoint.last_active_time in
-             if age > 300.0 then ip :: acc else acc
+             if age > 300.0 then (ip, endpoint) :: acc else acc
            ) t.endpoints [] in
-         List.iter (fun ip ->
+         List.iter (fun (ip, endpoint) ->
              Switch.remove t.switch ip;
+             Endpoint.destroy endpoint;
              t.endpoints <- IPMap.remove ip t.endpoints
            ) old_ips;
          Lwt.return_unit