From c11f245d643ee5b5ee2d530009123b589f7ca7b5 Mon Sep 17 00:00:00 2001
From: Thomas Leonard <thomas.leonard@unikernel.com>
Date: Sun, 26 Jun 2016 12:04:47 +0100
Subject: [PATCH] Cope with writing a frame failing

If a client disconnects suddenly then we may get an error trying to map
its grant to send the frame.

Fixes #8.
---
 firewall.ml | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/firewall.ml b/firewall.ml
index 97ce185..4b98302 100644
--- a/firewall.ml
+++ b/firewall.ml
@@ -16,7 +16,14 @@ let transmit ~frame iface =
      cases. *)
   let frame = fixup_checksums frame |> Cstruct.concat in
   let packet = Cstruct.shift frame Wire_structs.sizeof_ethernet in
-  iface#writev [packet]
+  Lwt.catch
+    (fun () -> iface#writev [packet])
+    (fun ex ->
+       Log.warn (fun f -> f "Failed to write packet to %a: %s"
+                    Ipaddr.V4.pp_hum iface#other_ip
+                    (Printexc.to_string ex));
+       Lwt.return ()
+    )
 
 let forward_ipv4 t frame =
   let packet = Cstruct.shift frame Wire_structs.sizeof_ethernet in