nixos/prometheus: add smokeping and corresponding NixOS test

nixos/modules/services/monitoring/prometheus/exporters.nix

@@ -47,6 +47,7 @@ let
     "rspamd"
     "rtl_433"
     "snmp"
+    "smokeping"
     "sql"
     "surfboard"
     "tor"

nixos/modules/services/monitoring/prometheus/exporters/smokeping.nix

@@ -0,0 +1,60 @@
+{ config, lib, pkgs, options }:
+
+with lib;
+
+let
+  cfg = config.services.prometheus.exporters.smokeping;
+  goDuration = types.mkOptionType {
+    name = "goDuration";
+    description = "Go duration (https://golang.org/pkg/time/#ParseDuration)";
+    check = x: types.str.check x && builtins.match "(-?[0-9]+(\.[0-9]+)?(ns|us|µs|ms|s|m|h))+" x != null;
+    inherit (types.str) merge;
+  };
+in
+{
+  port = 9374;
+  extraOpts = {
+    telemetryPath = mkOption {
+      type = types.str;
+      default = "/metrics";
+      description = ''
+        Path under which to expose metrics.
+      '';
+    };
+    pingInterval = mkOption {
+      type = goDuration;
+      default = "1s";
+      description = ''
+        Interval between pings.
+      '';
+    };
+    buckets = mkOption {
+      type = types.commas;
+      default = "5e-05,0.0001,0.0002,0.0004,0.0008,0.0016,0.0032,0.0064,0.0128,0.0256,0.0512,0.1024,0.2048,0.4096,0.8192,1.6384,3.2768,6.5536,13.1072,26.2144";
+      description = ''
+        List of buckets to use for the response duration histogram.
+      '';
+    };
+    hosts = mkOption {
+      type = with types; listOf str;
+      description = ''
+        List of endpoints to probe.
+      '';
+    };
+  };
+  serviceOpts = {
+    serviceConfig = {
+      AmbientCapabilities = [ "CAP_NET_RAW" ];
+      ExecStart = ''
+        ${pkgs.prometheus-smokeping-prober}/bin/smokeping_prober \
+          --web.listen-address ${cfg.listenAddress}:${toString cfg.port} \
+          --web.telemetry-path ${cfg.telemetryPath} \
+          --buckets ${cfg.buckets} \
+          --ping.interval ${cfg.pingInterval} \
+          --privileged \
+          ${concatStringsSep " \\\n  " cfg.extraFlags} \
+          ${concatStringsSep " " cfg.hosts}
+      '';
+    };
+  };
+}

nixos/tests/prometheus-exporters.nix

@@ -670,6 +670,27 @@ let
       '';
     };
 
+    smokeping = {
+      exporterConfig = {
+        enable = true;
+        hosts = ["127.0.0.1"];
+      };
+      exporterTest = ''
+        wait_for_unit("prometheus-smokeping-exporter.service")
+        wait_for_open_port(9374)
+        wait_until_succeeds(
+            "curl -sSf localhost:9374/metrics | grep '{}' | grep -qv ' 0$'".format(
+                'smokeping_requests_total{host="127.0.0.1",ip="127.0.0.1"} '
+            )
+        )
+        wait_until_succeeds(
+            "curl -sSf localhost:9374/metrics | grep -q '{}'".format(
+                'smokeping_response_ttl{host="127.0.0.1",ip="127.0.0.1"}'
+            )
+        )
+      '';
+    };
+
     snmp = {
       exporterConfig = {
         enable = true;