Fixed possible IOException if forwarding-secret-file path is a directory (#743)

* Fixed possible IOException if path is a directory

* Removed File usage

* Catch possible NumberFormatException on invalid config version

!Files.exists -> Files.notExists

proxy/src/main/java/com/velocitypowered/proxy/config/VelocityConfiguration.java

@@ -424,7 +424,7 @@ public class VelocityConfiguration implements ProxyConfig {
 
     // Create the forwarding-secret file on first-time startup if it doesn't exist
     Path defaultForwardingSecretPath = Path.of("forwarding.secret");
-    if (!path.toFile().exists() && !defaultForwardingSecretPath.toFile().exists()) {
+    if (Files.notExists(path) && Files.notExists(defaultForwardingSecretPath)) {
       Files.writeString(defaultForwardingSecretPath, generateRandomString(12));
     }
 
@@ -448,8 +448,16 @@ public class VelocityConfiguration implements ProxyConfig {
     CommentedFileConfig defaultConfig = CommentedFileConfig.of(tmpFile, TomlFormat.instance());
     defaultConfig.load();
 
-    // Whether or not this config is version 1.0 which uses the deprecated "forwarding-secret" parameter
-    boolean legacyConfig = config.getOrElse("config-version", "").equalsIgnoreCase("1.0");
+    // TODO: migrate this on Velocity Polymer
+    double configVersion;
+    try {
+      configVersion = Double.parseDouble(config.getOrElse("config-version", "1.0"));
+    } catch (NumberFormatException e) {
+      configVersion = 1.0;
+    }
+
+    // Whether or not this config version is older than 2.0 which uses the deprecated "forwarding-secret" parameter
+    boolean legacyConfig = configVersion < 2.0;
 
     String forwardingSecretString;
     byte[] forwardingSecret;
@@ -478,8 +486,19 @@ public class VelocityConfiguration implements ProxyConfig {
       // New handling
       forwardingSecretString = System.getenv().getOrDefault("VELOCITY_FORWARDING_SECRET", "");
       if (forwardingSecretString.isEmpty()) {
-        String forwardSecretFile = config.getOrElse("forwarding-secret-file", "");
-        forwardingSecretString = String.join("", Files.readAllLines(Path.of(forwardSecretFile)));
+        String forwardSecretFile = config.get("forwarding-secret-file");
+        Path secretPath = forwardSecretFile == null
+            ? defaultForwardingSecretPath
+            : Path.of(forwardSecretFile);
+        if (Files.exists(secretPath)) {
+          if (Files.isRegularFile(secretPath)) {
+            forwardingSecretString = String.join("", Files.readAllLines(secretPath));
+          } else {
+            throw new RuntimeException("The file " + forwardSecretFile + " is not a valid file or it is a directory.");
+          }
+        } else {
+          throw new RuntimeException("The forwarding-secret-file does not exists.");
+        }
       }
     }
     forwardingSecret = forwardingSecretString.getBytes(StandardCharsets.UTF_8);