Fix jsonSerialize return typehint to silence PHP8.1 deprecation message

Add typehints to Error class

Author: lucasnetau

src/Error.php

@@ -26,10 +26,10 @@ class Error implements JsonSerializable
     ];
 
     /** @var int A Number that indicates the error type that occurred. */
-    protected $code;
+    protected int $code;
 
     /** @var string A String providing a short description of the error. */
-    protected $message;
+    protected string $message;
 
     /** @var mixed Additional information about the error */
     protected $data;
@@ -46,7 +46,7 @@ public function setCode(int $code)
         $this->code = $code;
     }
 
-    public function getCode()
+    public function getCode(): int
     {
         return $this->code;
     }
@@ -56,7 +56,7 @@ public function setMessage(string $message)
         $this->message = $message;
     }
 
-    public function getMessage()
+    public function getMessage(): string
     {
         return $this->message;
     }
@@ -71,10 +71,12 @@ public function getData()
         return $this->data;
     }
 
-    public function jsonSerialize()
+    public function jsonSerialize() : array
     {
-        $record = ['code' => $this->code,
-            'message' => $this->message];
+        $record = [
+            'code' => $this->code,
+            'message' => $this->message
+        ];
 
         if (null !== $this->data)
         {

src/Notification.php

@@ -85,12 +85,14 @@ public function getParam(string $name)
     }
 
     /**
-     * @return mixed
+     * @return array
      */
-    public function jsonSerialize()
+    public function jsonSerialize() : array
     {
-        $record = ['jsonrpc' => self::JSONRPC_VERSION,
-            'method' => $this->method];
+        $record = [
+            'jsonrpc' => RpcMessageInterface::JSONRPC_VERSION,
+            'method' => $this->method
+        ];
         if (!empty($this->params))
         {
             $record['params'] = $this->params;

src/Request.php

@@ -66,9 +66,9 @@ public function getId()
     }
 
     /**
-     * @return mixed
+     * @return array
      */
-    public function jsonSerialize()
+    public function jsonSerialize() : array
     {
         $record = parent::jsonSerialize();
         $record['id'] = $this->id;