Add the next_hop script.

This script determines the next hop for a packet leaving this machine destined for the given address.

nix/configuration/roles/network/default.nix

@@ -15,6 +15,14 @@
 # "2001:4860:4860::8844#dns.google"
 # "2001:4860:4860::8888#dns.google"
 
+let
+  patchScriptBin =
+    filename: contents:
+    ((pkgs.writeScriptBin filename contents).overrideAttrs (old: {
+      buildCommand = "${old.buildCommand}\n patchShebangs $out";
+    }));
+  next_hop = (patchScriptBin "next_hop" (builtins.readFile ./files/next_hop_linux.bash));
+in
 {
   imports = [ ];
 
@@ -88,6 +96,7 @@
       arp-scan # To find devices on the network
       wavemon
       dhcpcd # For Android USB tethering.
+      next_hop
     ];
 
     boot.extraModprobeConfig = ''

nix/configuration/roles/network/files/next_hop_linux.bash

@@ -0,0 +1,7 @@
+#!/usr/bin/env bash
+#
+set -euo pipefail
+IFS=$'\n\t'
+DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
+
+exec ip route get "${@}"