Add a feature switch to reachability

config.php.example

@@ -5,3 +5,5 @@ $state_file = "state.json"; // The location for the state file. If it does not e
 $error_reporting = false; // Whether PHP errors should be shown. Not recommended for production.
 
 $lobby_timeout_seconds = 30; // How long it should take for unresponsive lobbies to get auto-delisted.
+
+$check_reachability = true; // Whether to reach out to the lobby listing host to confirm the lobby is reachable.

index.php

@@ -28,16 +28,38 @@ if ($error_reporting) {
   ini_set('display_errors', 1);
 }
 
-if (!file_exists($state_file)) {
+$reachable = false;
-  $dirname = dirname($state_file);
+if (isset($_GET["new"])) {
-  if (!is_dir($dirname)) {
+  if ($check_reachability) {
-    mkdir($dirname, 0777, true);
+    require "enet_probe.php";
+    $host = $_SERVER['REMOTE_ADDR'];
+    if (!empty($_GET["host"])) {
+      $host = $_GET["host"];
+    }
+    $port = 50403;
+    if (!empty($_GET["port"]) && is_numeric($_GET["port"])) {
+      $port = intval($_GET["port"]);
+    }
+    $reachable = enet_probe($host, $port);
+  }
+  else {
+    $reachable = true;
   }
-
-  file_put_contents($state_file, json_encode([ "lobbies" => []]));
 }
 
-$state = json_decode(file_get_contents($state_file), true);
+$dirname = dirname($state_file);
+if (!is_dir($dirname)) {
+  mkdir($dirname, 0777, true);
+}
+
+$state_fp = fopen($state_file, "c+");
+flock($state_fp, LOCK_EX);
+
+$contents = stream_get_contents($state_fp);
+$state = json_decode($contents, true);
+if (empty($state)) {
+  $state = ["lobbies" => []];
+}
 
 $cutoff_timestamp = time() - $lobby_timeout_seconds;
 foreach (array_keys($state["lobbies"]) as $id) {
@@ -63,16 +85,6 @@ if (isset($_GET["list"])) {
   echo json_encode(["lobbies" => $list]);
 }
 elseif (isset($_GET["new"])) {
-  require "enet_probe.php";
-  $host = $_SERVER['REMOTE_ADDR'];
-  if (!empty($_GET["host"])) {
-    $host = $_GET["host"];
-  }
-  $port = 50403;
-  if (!empty($_GET["port"]) && is_numeric($_GET["port"])) {
-    $port = intval($_GET["port"]);
-  }
-  $reachable = enet_probe($host, $port);
   header("Content-Type: application/json");
   if ($reachable) {
     $id = generate_uuid_v4();
@@ -148,4 +160,9 @@ else {
   echo json_encode(["status" => "OK"]);
 }
 
-file_put_contents($state_file, json_encode($state, JSON_PRETTY_PRINT));
+ftruncate($state_fp, 0);
+rewind($state_fp);
+fwrite($state_fp, json_encode($state, JSON_PRETTY_PRINT));
+fflush($state_fp);
+flock($state_fp, LOCK_UN);
+fclose($state_fp);