From c8746fb58808aa4378b4e2c376c6b031c2230f3b Mon Sep 17 00:00:00 2001
From: arcnmx <arcnmx@users.noreply.github.com>
Date: Fri, 2 Oct 2020 13:50:48 -0700
Subject: [PATCH] mpd: systemd socket activation

---
 modules/services/mpd.nix | 30 +++++++++++++++++++++++++++---
 1 file changed, 27 insertions(+), 3 deletions(-)

diff --git a/modules/services/mpd.nix b/modules/services/mpd.nix
index 3f05c22a3..a6ed0a483 100644
--- a/modules/services/mpd.nix
+++ b/modules/services/mpd.nix
@@ -50,7 +50,7 @@ in {
         '';
       };
 
-     musicDirectory = mkOption {
+      musicDirectory = mkOption {
         type = with types; either path str;
         default = "${config.home.homeDirectory}/music";
         defaultText = "$HOME/music";
@@ -96,7 +96,14 @@ in {
         '';
       };
 
-     network = {
+      network = {
+        startWhenNeeded = mkOption {
+          type = types.bool;
+          default = false;
+          description = ''
+           Enable systemd socket activation.
+          '';
+        };
 
         listenAddress = mkOption {
           type = types.str;
@@ -143,7 +150,7 @@ in {
         Description = "Music Player Daemon";
       };
 
-      Install = {
+      Install = mkIf (!cfg.network.startWhenNeeded) {
         WantedBy = [ "default.target" ];
       };
 
@@ -154,6 +161,23 @@ in {
         ExecStartPre = ''${pkgs.bash}/bin/bash -c "${pkgs.coreutils}/bin/mkdir -p '${cfg.dataDir}' '${cfg.playlistDirectory}'"'';
       };
     };
+    systemd.user.sockets.mpd = mkIf cfg.network.startWhenNeeded {
+      Socket = {
+        ListenStream = let
+          listen =
+            if cfg.network.listenAddress == "any"
+            then toString cfg.network.port
+            else "${cfg.network.listenAddress}:${toString cfg.network.port}";
+        in [ listen "%t/mpd/socket" ];
+
+        Backlog = 5;
+        KeepAlive = true;
+      };
+
+      Install = {
+        WantedBy = [ "sockets.target" ];
+      };
+    };
   };
 
 }