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Cap MCP stdio session timeouts #81

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Merged
lezama merged 1 commit into from
Jun 3, 2026
Merged

Cap MCP stdio session timeouts #81

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56 changes: 43 additions & 13 deletions includes/class-openclawp-mcp-client-transport.php
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Original file line number Diff line number Diff line change
Expand Up @@ -30,8 +30,9 @@

final class OpenclaWP_Mcp_Client_Transport {

private const PROTOCOL_VERSION = '2025-06-18';
private const READ_TIMEOUT_SECONDS = 15;
private const PROTOCOL_VERSION = '2025-06-18';
private const READ_TIMEOUT_SECONDS = 15;
private const EXECUTION_LIMIT_BUFFER_SECONDS = 5;

/**
* Probe a configured server: initialize + tools/list. Returns the tool
Expand Down Expand Up @@ -159,7 +160,7 @@ private static function call_stdio( array $config, string $tool_name, array $arg

/**
* @param array<string,mixed> $config
* @return array{process:resource, pipes:array<int,resource>, id:int}|\WP_Error
* @return array{process:resource, pipes:array<int,resource>, id:int, deadline:?float}|\WP_Error
*/
private static function open_stdio_session( array $config ) {
$command = (string) ( $config['command'] ?? '' );
Expand Down Expand Up @@ -194,14 +195,15 @@ private static function open_stdio_session( array $config ) {
stream_set_blocking( $pipes[2], false );

return array(
'process' => $process,
'pipes' => $pipes,
'id' => 0,
'process' => $process,
'pipes' => $pipes,
'id' => 0,
'deadline' => self::request_execution_deadline(),
);
}

/**
* @param array{process:resource, pipes:array<int,resource>, id:int} $session
* @param array{process:resource, pipes:array<int,resource>, id:int, deadline:?float} $session
*/
private static function close_stdio_session( array $session ): void {
foreach ( $session['pipes'] as $pipe ) {
Expand All @@ -218,7 +220,7 @@ private static function close_stdio_session( array $session ): void {
/**
* Send a JSON-RPC request frame and block for the matching response.
*
* @param array{process:resource, pipes:array<int,resource>, id:int} $session
* @param array{process:resource, pipes:array<int,resource>, id:int, deadline:?float} $session
*
* @return mixed|\WP_Error
*/
Expand All @@ -237,8 +239,12 @@ private static function send_stdio( array &$session, string $method, $params ) {
return new \WP_Error( 'mcp_client_write_failed', sprintf( 'write to stdin failed for %s', $method ) );
}

$deadline = microtime( true ) + self::READ_TIMEOUT_SECONDS;
$buffer = '';
$started_at = microtime( true );
$deadline = $started_at + self::READ_TIMEOUT_SECONDS;
if ( isset( $session['deadline'] ) && is_float( $session['deadline'] ) ) {
$deadline = min( $deadline, $session['deadline'] );
}
$buffer = '';

while ( microtime( true ) < $deadline ) {
$chunk = @fgets( $session['pipes'][1] ); // phpcs:ignore WordPress.PHP.NoSilencedErrors.Discouraged
Expand All @@ -252,7 +258,8 @@ private static function send_stdio( array &$session, string $method, $params ) {
sprintf( 'process exited (code %d) before %s response: %s', (int) $status['exitcode'], $method, is_string( $stderr ) ? trim( $stderr ) : '' )
);
}
usleep( 50000 ); // 50ms
$remaining_usec = (int) max( 1000, min( 50000, ( $deadline - microtime( true ) ) * 1000000 ) );
usleep( $remaining_usec );
continue;
}

Expand Down Expand Up @@ -284,16 +291,17 @@ private static function send_stdio( array &$session, string $method, $params ) {
return $decoded['result'] ?? array();
}

$elapsed = max( 0.0, microtime( true ) - $started_at );
return new \WP_Error(
'mcp_client_timeout',
sprintf( 'timed out waiting for %s response after %ds', $method, self::READ_TIMEOUT_SECONDS )
sprintf( 'timed out waiting for %s response after %.1fs', $method, $elapsed )
);
}

/**
* Fire-and-forget JSON-RPC notification (no id, no response expected).
*
* @param array{process:resource, pipes:array<int,resource>, id:int} $session
* @param array{process:resource, pipes:array<int,resource>, id:int, deadline:?float} $session
*/
private static function notify_stdio( array $session, string $method, $params ): void {
$payload = wp_json_encode(
Expand All @@ -306,6 +314,28 @@ private static function notify_stdio( array $session, string $method, $params ):
@fwrite( $session['pipes'][0], $payload ); // phpcs:ignore WordPress.PHP.NoSilencedErrors.Discouraged
}

/**
* Estimate a request-local deadline that leaves time for PHP to unwind.
*
* A stdio operation can make more than one JSON-RPC request in sequence
* (initialize, then tools/list or tools/call). Keeping only a per-read
* timeout risks colliding with the host's max_execution_time before the
* transport can return a WP_Error.
*
* @return float|null Unix timestamp with microseconds, or null when PHP has no execution limit.
*/
private static function request_execution_deadline(): ?float {
$limit = (int) ini_get( 'max_execution_time' );
if ( $limit <= 0 ) {
return null;
}

$started_at = isset( $_SERVER['REQUEST_TIME_FLOAT'] ) ? (float) $_SERVER['REQUEST_TIME_FLOAT'] : microtime( true ); // phpcs:ignore WordPress.Security.ValidatedSanitizedInput.InputNotValidated
$deadline = $started_at + max( 1, $limit - self::EXECUTION_LIMIT_BUFFER_SECONDS );

return max( microtime( true ) + 1, $deadline );
}

// -------------------------------------------------------------------
// http
// -------------------------------------------------------------------
Expand Down
66 changes: 66 additions & 0 deletions tests/unit/McpClientTransportTest.php
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Original file line number Diff line number Diff line change
@@ -0,0 +1,66 @@
<?php
/**
* Unit tests for OpenclaWP_Mcp_Client_Transport.
*
* @package OpenclaWP\Tests
*/

declare( strict_types=1 );

namespace OpenclaWP\Tests\Unit;

use OpenclaWP_Mcp_Client_Transport;
use PHPUnit\Framework\TestCase;
use ReflectionMethod;

/**
* @covers OpenclaWP_Mcp_Client_Transport
*/
final class McpClientTransportTest extends TestCase {

private string $previous_max_execution_time = '0';
private $previous_request_time_float = null;
private bool $had_request_time_float = false;

protected function setUp(): void {
parent::setUp();
$this->previous_max_execution_time = (string) ini_get( 'max_execution_time' );
$this->had_request_time_float = array_key_exists( 'REQUEST_TIME_FLOAT', $_SERVER );
$this->previous_request_time_float = $_SERVER['REQUEST_TIME_FLOAT'] ?? null;
}

protected function tearDown(): void {
ini_set( 'max_execution_time', $this->previous_max_execution_time );
if ( $this->had_request_time_float ) {
$_SERVER['REQUEST_TIME_FLOAT'] = $this->previous_request_time_float;
} else {
unset( $_SERVER['REQUEST_TIME_FLOAT'] );
}
parent::tearDown();
}

public function test_request_execution_deadline_is_null_without_php_execution_limit(): void {
ini_set( 'max_execution_time', '0' );

$this->assertNull( self::request_execution_deadline() );
}

public function test_request_execution_deadline_leaves_margin_before_php_limit(): void {
$now = microtime( true );
$_SERVER['REQUEST_TIME_FLOAT'] = $now - 10;
ini_set( 'max_execution_time', '30' );

$deadline = self::request_execution_deadline();

$this->assertIsFloat( $deadline );
$this->assertGreaterThan( $now + 14, $deadline );
$this->assertLessThan( $now + 16, $deadline );
}

private static function request_execution_deadline(): ?float {
$method = new ReflectionMethod( OpenclaWP_Mcp_Client_Transport::class, 'request_execution_deadline' );
$method->setAccessible( true );

return $method->invoke( null );
}
}
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