From 1a8b4811f7fb52f5375c4fd328f27d258b988867 Mon Sep 17 00:00:00 2001
From: Astro <astro@spaceboyz.net>
Date: Mon, 12 Apr 2021 23:32:21 +0200
Subject: [PATCH] nix/nixos-module/collectd: add dhcpcount.rb

---
 .../{collectd.nix => collectd/default.nix}    | 16 ++++++++
 nix/nixos-module/collectd/dhcpcount.rb        | 39 +++++++++++++++++++
 nix/nixos-module/default.nix                  |  2 +-
 3 files changed, 56 insertions(+), 1 deletion(-)
 rename nix/nixos-module/{collectd.nix => collectd/default.nix} (70%)
 create mode 100644 nix/nixos-module/collectd/dhcpcount.rb

diff --git a/nix/nixos-module/collectd.nix b/nix/nixos-module/collectd/default.nix
similarity index 70%
rename from nix/nixos-module/collectd.nix
rename to nix/nixos-module/collectd/default.nix
index b31803c..9851699 100644
--- a/nix/nixos-module/collectd.nix
+++ b/nix/nixos-module/collectd/default.nix
@@ -50,6 +50,22 @@ in
       hddtemp = "";
       sensors = "";
       thermal = "";
+    }) (lib.optionalAttrs config.services.dhcpd4.enable {
+      exec =
+        let
+          maxTimeout = builtins.foldl' (maxTimeout: net:
+            let
+              dhcpConf = config.site.net.${net}.dhcp;
+            in
+              if dhcpConf != null &&
+                 dhcpConf.server == hostName &&
+                 dhcpConf.time > maxTimeout
+              then dhcpConf.time
+              else maxTimeout
+          ) 180 (builtins.attrNames config.site.net);
+        in ''
+          Exec "collectd" "${pkgs.ruby}/bin/ruby" "${./dhcpcount.rb}" "${toString maxTimeout}"
+        '';
     }) ];
   };
 }
diff --git a/nix/nixos-module/collectd/dhcpcount.rb b/nix/nixos-module/collectd/dhcpcount.rb
new file mode 100644
index 000000000..22062e8
--- /dev/null
+++ b/nix/nixos-module/collectd/dhcpcount.rb
@@ -0,0 +1,39 @@
+#!/usr/bin/env ruby
+
+require 'date'
+
+INTERVAL = 10
+TIMEOUT = ARGV[0].to_i
+hostname = `hostname`.strip
+STDOUT.sync = true
+
+loop do
+  seen = {}
+  count = 0
+
+  addr = nil
+  starts = nil
+
+  IO::readlines("/var/lib/dhcp/dhcpd.leases").each do |line|
+    if line =~ /^lease (.+) \{/
+      addr = $1
+
+      starts = nil
+    elsif line =~ /starts \d+ (.+?);/
+      starts = DateTime.parse($1).to_time
+    elsif line =~ /^\}/
+      now = Time.now
+      if starts and
+         now >= starts and now < starts + TIMEOUT
+
+        unless seen[addr]
+          count += 1
+          seen[addr] = true
+        end
+      end
+    end
+  end
+  puts "PUTVAL \"#{hostname}/exec-dhcpd/current_sessions-leases\" interval=#{INTERVAL} N:#{count}"
+
+  sleep INTERVAL
+end
diff --git a/nix/nixos-module/default.nix b/nix/nixos-module/default.nix
index dfd1910..4dbc6b5 100644
--- a/nix/nixos-module/default.nix
+++ b/nix/nixos-module/default.nix
@@ -13,7 +13,7 @@ in {
     ../lib/config/options.nix
     ./defaults.nix
     ./network.nix
-    ./collectd.nix
+    ./collectd
   ] ++
   optionals (hostConfig.role == "server") [
     ./server/lxc-containers.nix