Soft limit CIDR range for IPv6 network to 288230376151711744 devices (#1344)

That should be enough for most of users (c).

Closes #1340

apps/fz_http/lib/fz_http/devices/device.ex

@@ -145,7 +145,7 @@ defmodule FzHttp.Devices.Device do
   end
 
   defp put_default_ip(changeset, field) do
-    cidr_string = FzHttp.Config.fetch_env!(:fz_http, :"wireguard_#{field}_network")
+    cidr_string = wireguard_network(field)
     {:ok, cidr_inet} = EctoNetwork.INET.cast(cidr_string)
     cidr = CIDR.parse(cidr_string)
     offset = Enum.random(2..(cidr.hosts - 2))
@@ -162,6 +162,16 @@ defmodule FzHttp.Devices.Device do
     end
   end
 
+  defp wireguard_network(field) do
+    cidr_string = FzHttp.Config.fetch_env!(:fz_http, :"wireguard_#{field}_network")
+    [inet, network] = String.split(cidr_string, "/")
+    network = String.to_integer(network)
+    "#{inet}/#{limit_cidr_range(field, network)}"
+  end
+
+  defp limit_cidr_range(:ipv4, network), do: network
+  defp limit_cidr_range(:ipv6, network), do: max(network, 70)
+
   defp ipv4_address do
     FzHttp.Config.fetch_env!(:fz_http, :wireguard_ipv4_address)
     |> EctoNetwork.INET.cast()

apps/fz_http/test/fz_http/devices/device/query_test.exs

@@ -112,6 +112,38 @@ defmodule FzHttp.Devices.Device.QueryTest do
       assert Repo.one(queryable) == %Postgrex.INET{address: {64_768, 0, 0, 0, 0, 3, 3, 4}}
     end
 
+    test "selects available IPv6 at end of CIDR range" do
+      cidr = string_to_inet("fd00::/106")
+      gateway_ip = string_to_inet("fd00::3:3:3")
+      offset = 4_194_304
+
+      queryable = next_available_address(cidr, offset, [gateway_ip])
+
+      assert Repo.one(queryable) == %Postgrex.INET{address: {64_768, 0, 0, 0, 0, 0, 63, 65_535}}
+    end
+
+    test "works when offset is out of IPv6 CIDR range" do
+      cidr = string_to_inet("fd00::/106")
+      gateway_ip = string_to_inet("fd00::3:3:3")
+      offset = 4_194_305
+
+      queryable = next_available_address(cidr, offset, [gateway_ip])
+
+      assert Repo.one(queryable) == %Postgrex.INET{address: {64_768, 0, 0, 0, 0, 0, 64, 0}}
+    end
+
+    test "works when netmask allows a large number of devices" do
+      cidr = string_to_inet("fd00::/70")
+      gateway_ip = string_to_inet("fd00::3:3:3")
+      offset = 9_223_372_036_854_775_807
+
+      queryable = next_available_address(cidr, offset, [gateway_ip])
+
+      assert Repo.one(queryable) == %Postgrex.INET{
+               address: {64_768, 0, 0, 0, 32_767, 65_535, 65_535, 65_534}
+             }
+    end
+
     test "selects nothing when IPv6 CIDR range is exhausted" do
       cidr = string_to_inet("fd00::3:2:0/126")
       gateway_ip = string_to_inet("fd00::3:2:1")

apps/fz_http/test/fz_http/devices_test.exs

@@ -82,6 +82,12 @@ defmodule FzHttp.DevicesTest do
       refute is_nil(device.ipv6)
     end
 
+    test "soft limit max network range for IPv6", %{device: device} do
+      FzHttp.Config.put_env(:wireguard_ipv6_network, "fd00::/20")
+      attrs = %{@device_attrs | ipv4: nil, ipv6: nil, user_id: device.user_id}
+      assert {:ok, _device} = Devices.create_device(attrs)
+    end
+
     test "returns error when device IP can't be assigned due to CIDR pool exhaustion", %{
       device: device
     } do