[Client] Fix client transport leak on reconnect

CHANGELOG.md

@@ -11,6 +11,10 @@ All notable changes to `mcp/sdk` will be documented in this file.
 * Fix tools with an array shape parameter whose keys are nullable or unions (e.g. `array{name: string, nickname: string|null}`) rejecting valid arguments with `-32602`: a `null` inside the shape no longer turns the parameter into `array|null`, and such keys get their own types instead of `object`, including lists and nested shapes (`string[]|null`, `array{x: int}|null`).
 * Fix `array<string|null>` and other generics with a union element getting `items` of type `object`. A `null` inside a generic no longer makes the parameter nullable, and neither does a DocBlock class whose name contains `null`.
 
+### Client
+
+* Fix `Client::connect()` leaving the previous transport open when called again: it closes the current transport first, so no stdio process or HTTP session is left behind.
+
 0.9.0
 -----
 

docs/client/connecting.md

@@ -248,6 +248,8 @@ try {
 }
 ```
 
+Calling `connect()` again on the same client closes its current transport before opening the new one.
+
 ## Server Information
 
 After successful connection, retrieve server metadata:

src/Client.php

@@ -92,6 +92,8 @@ public static function builder(): Builder
      */
     public function connect(TransportInterface $transport): void
     {
+        $this->disconnect();
+
         $this->transport = $transport;
         $this->protocol->connect($transport, $this->config);
 

tests/Unit/Client/ClientTest.php

@@ -21,6 +21,29 @@
 
 final class ClientTest extends TestCase
 {
+    public function testReconnectClosesPreviousTransport(): void
+    {
+        $client = Client::builder()->build();
+        $firstTransport = $this->createMock(TransportInterface::class);
+        $firstTransport->expects($this->once())->method('close');
+        $firstTransport->method('setState')->willReturnCallback(static function (ClientStateInterface $state): void {
+            $state->setInitialized(true);
+        });
+
+        $secondTransport = $this->createMock(TransportInterface::class);
+        $secondTransport->expects($this->once())->method('close');
+        $secondTransport->method('setState')->willReturnCallback(static function (ClientStateInterface $state): void {
+            $state->setInitialized(true);
+        });
+
+        $client->connect($firstTransport);
+        $client->connect($secondTransport);
+
+        $this->assertTrue($client->isConnected());
+
+        $client->disconnect();
+    }
+
     public function testSendRootsListChangedSendsNotificationWhenCapabilityDeclared(): void
     {
         $sent = [];