nixos/tailscale: interface should be up prior to service finish (#396399)

nixos/modules/services/networking/tailscale.nix

@@ -84,6 +84,8 @@ in
       description = ''
         A file containing the auth key.
         Tailscale will be automatically started if provided.
+
+        Services that bind to Tailscale IPs should order using {option}`systemd.services.<name>.after` `tailscaled-autoconnect.service`.
       '';
     };
 
@@ -116,7 +118,7 @@ in
 
     extraUpFlags = mkOption {
       description = ''
-        Extra flags to pass to {command}`tailscale up`. Only applied if `authKeyFile` is specified.";
+        Extra flags to pass to {command}`tailscale up`. Only applied if {option}`services.tailscale.authKeyFile` is specified.
       '';
       type = types.listOf types.str;
       default = [ ];
@@ -183,12 +185,15 @@ in
       wants = [ "tailscaled.service" ];
       wantedBy = [ "multi-user.target" ];
       serviceConfig = {
-        Type = "oneshot";
+        Type = "notify";
       };
-      # https://github.com/tailscale/tailscale/blob/v1.72.1/ipn/backend.go#L24-L32
+      path = [
+        cfg.package
+        pkgs.jq
+      ];
+      enableStrictShellChecks = true;
       script =
         let
-          statusCommand = "${lib.getExe cfg.package} status --json --peers=false | ${lib.getExe pkgs.jq} -r '.BackendState'";
           paramToString = v: if (builtins.isBool v) then (lib.boolToString v) else (toString v);
           params = lib.pipe cfg.authKeyParameters [
             (lib.filterAttrs (_: v: v != null))
@@ -197,14 +202,35 @@ in
             (params: if params != "" then "?${params}" else "")
           ];
         in
+        # bash
         ''
-          while [[ "$(${statusCommand})" == "NoState" ]]; do
-            sleep 0.5
+          getState() {
+            tailscale status --json --peers=false | jq -r '.BackendState'
+          }
+
+          lastState=""
+          while state="$(getState)"; do
+            if [[ "$state" != "$lastState" ]]; then
+              # https://github.com/tailscale/tailscale/blob/v1.72.1/ipn/backend.go#L24-L32
+              case "$state" in
+                NeedsLogin)
+                  echo "Server needs authentication, sending auth key"
+                  tailscale up --auth-key "$(cat ${cfg.authKeyFile})${params}" ${escapeShellArgs cfg.extraUpFlags}
+                  ;;
+                Running)
+                  echo "Tailscale is running"
+                  systemd-notify --ready
+                  exit 0
+                  ;;
+                *)
+                  echo "Waiting for Tailscale State = Running or systemd timeout"
+                  ;;
+              esac
+            fi
+            echo "State = $state"
+            lastState="$state"
+            sleep .5
           done
-          status=$(${statusCommand})
-          if [[ "$status" == "NeedsLogin" || "$status" == "NeedsMachineAuth" ]]; then
-            ${lib.getExe cfg.package} up --auth-key "$(cat ${cfg.authKeyFile})${params}" ${escapeShellArgs cfg.extraUpFlags}
-          fi
         '';
     };