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[Server] Reject malformed MCP session ID headers #384

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[Server] Reject malformed MCP session ID headers #384

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14 changes: 12 additions & 2 deletions src/Server/Transport/StreamableHttpTransport.php
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Original file line number Diff line number Diff line change
Expand Up @@ -294,8 +294,18 @@ private static function normalizeMiddleware(iterable $middleware): array
private function handleRequest(ServerRequestInterface $request): ResponseInterface
{
$this->request = $request;
$sessionIdString = $request->getHeaderLine(self::SESSION_HEADER);
$this->sessionId = $sessionIdString ? Uuid::fromString($sessionIdString) : null;
$sessionIdHeaders = $request->getHeader(self::SESSION_HEADER);
if (\count($sessionIdHeaders) > 1) {
return $this->createErrorResponse(Error::forInvalidRequest(self::SESSION_HEADER.' header must not be repeated.'), 400);
}

$sessionIdString = $sessionIdHeaders[0] ?? '';

try {
$this->sessionId = $sessionIdString ? Uuid::fromString($sessionIdString) : null;
} catch (\InvalidArgumentException) {
return $this->createErrorResponse(Error::forInvalidRequest(self::SESSION_HEADER.' header must be a valid UUID.'), 400);
}

return match ($request->getMethod()) {
'OPTIONS' => $this->handleOptionsRequest(),
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33 changes: 33 additions & 0 deletions tests/Unit/Server/Transport/StreamableHttpTransportTest.php
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Original file line number Diff line number Diff line change
Expand Up @@ -85,6 +85,39 @@ public function testDefaultMiddlewareRejectsUnsupportedProtocolVersion(): void
$this->assertSame(400, $response->getStatusCode());
}

#[TestDox('malformed MCP session IDs are rejected as bad requests')]
public function testMalformedSessionIdHeaderReturnsBadRequest(): void
{
$request = $this->factory
->createServerRequest('POST', 'http://localhost/')
->withHeader('Host', 'localhost')
->withHeader(StreamableHttpTransport::SESSION_HEADER, '{"not":"a-token"}');

$transport = new StreamableHttpTransport($request, $this->factory, $this->factory);

$response = $transport->listen();

$this->assertSame(400, $response->getStatusCode());
$this->assertStringContainsString(StreamableHttpTransport::SESSION_HEADER, (string) $response->getBody());
}

#[TestDox('duplicate MCP session ID headers are rejected as bad requests')]
public function testDuplicateSessionIdHeadersReturnBadRequest(): void
{
$request = $this->factory
->createServerRequest('POST', 'http://localhost/')
->withHeader('Host', 'localhost')
->withHeader(StreamableHttpTransport::SESSION_HEADER, '2fb587fc-593f-47ce-9d9a-9c06f2b907a3')
->withAddedHeader(StreamableHttpTransport::SESSION_HEADER, '5e583da8-a677-4446-b723-4ddbe00fda62');

$transport = new StreamableHttpTransport($request, $this->factory, $this->factory);

$response = $transport->listen();

$this->assertSame(400, $response->getStatusCode());
$this->assertStringContainsString('must not be repeated', (string) $response->getBody());
}

#[TestDox('explicit empty middleware list disables defaults and emits a warning log')]
public function testEmptyMiddlewareListDisablesDefaultsAndWarns(): void
{
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