valheim: restart only when a new Steam build ships

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

services/valheim-autoupdate.nix

@@ -0,0 +1,124 @@
+# services/valheim-autoupdate.nix — restart the Valheim server only when Steam
+# actually ships a new build.
+#
+# The Pelican egg already has AUTO_UPDATE=1, so steamcmd runs on every boot and
+# a restart *is* the update. The missing half is knowing when to bother, which
+# a plain nightly restart doesn't answer (it reboots players for nothing 364
+# nights out of 365). So, hourly:
+#
+#   1. installed buildid  <- steamapps/appmanifest_896660.acf in the server volume
+#   2. latest buildid     <- the container's own steamcmd, public branch
+#   3. differ, nobody playing -> POST restart to the wings daemon API
+#
+# Why the wings API and not `docker restart`: the egg's stop command is ^C, so
+# wings sends SIGINT and Valheim saves the world before exiting. docker's
+# SIGTERM would not. Auth reuses the node token already in /etc/pelican/config.yml
+# — read at *runtime*, so eval stays pure (see CLAUDE.md); no new secret, and
+# nothing to rotate by hand.
+#
+# Valheim has no console, no RCON and no broadcast command, so players cannot be
+# warned in-game — the only honest options are "restart on an empty server" or
+# "kick people mid-raid". This does the former and pushes an ntfy note instead.
+{ config, lib, pkgs, ... }:
+let
+  # Pelican server "hawk" (panel server id 3). Both the volume path and the
+  # container name are this uuid — wings names containers after the server.
+  serverUuid = "185008d8-8a04-4077-be78-63853dc06c0e";
+  steamAppId = "896660"; # valheim_server; 892970 is the client
+  gamePort = "25569";
+
+  autoupdate = pkgs.writeShellScript "valheim-autoupdate" ''
+    set -uo pipefail
+
+    uuid=${serverUuid}
+    appid=${steamAppId}
+    manifest=/var/lib/pelican/volumes/$uuid/steamapps/appmanifest_$appid.acf
+    wings_cfg=/etc/pelican/config.yml
+    state=/var/lib/valheim-autoupdate/announced
+    secret=/var/secrets/ntfy-url
+
+    docker=${pkgs.docker}/bin/docker
+    awk=${pkgs.gawk}/bin/awk
+    curl=${pkgs.curl}/bin/curl
+
+    notify() { # body
+      [ -f "$secret" ] || return 0
+      url=$(${pkgs.coreutils}/bin/tr -d '\n' < "$secret")
+      $curl -fsS --max-time 10 \
+        -H "Title: Valheim server" -H "Tags: shield" \
+        -d "$1" "$url" >/dev/null 2>&1 || true
+    }
+
+    # Nothing to restart, and no steamcmd to ask — a stopped server updates
+    # itself whenever it next boots anyway.
+    [ "$($docker inspect -f '{{.State.Running}}' "$uuid" 2>/dev/null)" = "true" ] || exit 0
+
+    installed=$($awk -F'"' '/"buildid"/{print $4; exit}' "$manifest" 2>/dev/null)
+    latest=$($docker exec "$uuid" \
+      ./steamcmd/steamcmd.sh +login anonymous +app_info_update 1 \
+        +app_info_print "$appid" +quit 2>/dev/null \
+      | $awk '/"branches"/{b=1} b && /"public"/{p=1} p && /"buildid"/{gsub(/"/,"",$2); print $2; exit}')
+
+    # Steam unreachable, rate-limited, or output we don't recognise: do nothing
+    # rather than guess. Next hour will try again.
+    case "$latest" in ""|*[!0-9]*) exit 0 ;; esac
+    case "$installed" in ""|*[!0-9]*) exit 0 ;; esac
+    [ "$installed" = "$latest" ] && exit 0
+
+    # ponytail: UDP conntrack entries for the game port are the cheap stand-in
+    # for a player count — no A2S challenge handshake to parse. They linger
+    # ~2min past the last packet, so this reads as "played very recently",
+    # which errs toward leaving people alone. Upgrade path if that's ever too
+    # coarse: query A2S_INFO on the query port (game port + 1) and read the
+    # players byte.
+    if ${pkgs.gnugrep}/bin/grep -q "dport=${gamePort} " /proc/net/nf_conntrack 2>/dev/null; then
+      if [ "$(${pkgs.coreutils}/bin/cat "$state" 2>/dev/null || true)" != "$latest" ]; then
+        notify "Valheim build $installed -> $latest is out. Someone is online, so the update waits until the server is empty."
+        ${pkgs.coreutils}/bin/printf '%s' "$latest" > "$state"
+      fi
+      echo "valheim-autoupdate: $installed -> $latest available, players connected, deferring"
+      exit 0
+    fi
+
+    token=$($awk '/^token:/{print $2}' "$wings_cfg")
+    if [ -z "$token" ]; then
+      echo "valheim-autoupdate: no wings token in $wings_cfg, cannot restart" >&2
+      exit 1
+    fi
+
+    echo "valheim-autoupdate: $installed -> $latest, server empty, restarting"
+    if $curl -fsS --max-time 30 -X POST \
+        -H "Authorization: Bearer $token" -H 'Content-Type: application/json' \
+        -d '{"action":"restart"}' \
+        "http://127.0.0.1:8443/api/servers/$uuid/power" >/dev/null; then
+      notify "Restarted for Valheim build $installed -> $latest."
+      ${pkgs.coreutils}/bin/printf '%s' "$latest" > "$state"
+    else
+      echo "valheim-autoupdate: wings power request failed" >&2
+      exit 1
+    fi
+  '';
+in
+{
+  config = lib.mkIf (config.networking.hostName == "FredOS-Mediaserver") {
+    systemd.services.valheim-autoupdate = {
+      description = "Restart the Valheim server when a new Steam build ships";
+      after = [ "docker-pelican-wings.service" ];
+      serviceConfig = {
+        Type = "oneshot";
+        ExecStart = autoupdate;
+        StateDirectory = "valheim-autoupdate";
+        # steamcmd's app_info_update round-trip is the slow part (~1min worst case).
+        TimeoutStartSec = "5min";
+      };
+    };
+    systemd.timers.valheim-autoupdate = {
+      wantedBy = [ "timers.target" ];
+      timerConfig = {
+        OnBootSec = "10min"; # let wings bring the game container up first
+        OnUnitActiveSec = "1h";
+        RandomizedDelaySec = "5min"; # don't hit Steam on the exact hour
+      };
+    };
+  };
+}