Poll for the internet more frequently on connection change

This significantly improves the time to detect Internet availability by
polling more frequently at the start. It then backs off exponentially to
the maximum interval time.

lib/vintage_net/interface/connectivity_checker.ex

@@ -5,8 +5,9 @@ defmodule VintageNet.Interface.ConnectivityChecker do
 
   require Record
 
-  @delay_to_first_check 100
-  @interval 30_000
+  @min_interval 500
+  @max_interval 30_000
+
   @ping_port 80
   @ping_timeout 5_000
 
@@ -23,7 +24,7 @@ defmodule VintageNet.Interface.ConnectivityChecker do
 
   @impl true
   def init(ifname) do
-    state = %{ifname: ifname, interval: @interval}
+    state = %{ifname: ifname, interval: @min_interval}
     {:ok, state, {:continue, :continue}}
   end
 
@@ -35,7 +36,7 @@ defmodule VintageNet.Interface.ConnectivityChecker do
 
     case VintageNet.get(lower_up_property(ifname)) do
       true ->
-        {:noreply, state, @delay_to_first_check}
+        {:noreply, state, @min_interval}
 
       _not_true ->
         # If the physical layer isn't up, don't start polling until
@@ -63,7 +64,7 @@ defmodule VintageNet.Interface.ConnectivityChecker do
 
     set_connectivity(ifname, connectivity)
 
-    {:noreply, state, interval}
+    {:noreply, state, next_interval(connectivity, interval)}
   end
 
   def handle_info(
@@ -83,7 +84,9 @@ defmodule VintageNet.Interface.ConnectivityChecker do
     # Physical layer is up. Optimistically assume that the LAN is accessible and
     # start polling again after a short delay
     set_connectivity(ifname, :lan)
-    {:noreply, state, @delay_to_first_check}
+
+    new_state = %{state | interval: @min_interval}
+    {:noreply, new_state, @min_interval}
   end
 
   defp ping(ifname) do
@@ -138,4 +141,11 @@ defmodule VintageNet.Interface.ConnectivityChecker do
   defp lower_up_property(ifname) do
     ["interface", ifname, "lower_up"]
   end
+
+  # Back off of checks if they're not working
+  defp next_interval(:internet, _interval), do: @max_interval
+
+  defp next_interval(_not_internet, interval) do
+    min(interval * 2, @max_interval)
+  end
 end