WP-LIT-MCP/src/Server/ServerRegistrar.php

<?php

declare(strict_types=1);

namespace LIT\MCP\Server;

use LIT\MCP\Abilities\ExposurePolicy;
use LIT\MCP\Guides\InstructionsBuilder;
use LIT\MCP\Integrations\IntegrationRegistry;
use LIT\MCP\Log;
use LIT\MCP\Plugin;
use WP\MCP\Core\McpAdapter;
use WP\MCP\Infrastructure\ErrorHandling\ErrorLogMcpErrorHandler;
use WPMedia\MCP\OAuth\Context as OAuthContext;
use WPMedia\MCP\OAuth\Transport\OAuthHttpTransport;
use WPMedia\MCP\OAuth\Transport\ServerRegistrar as OAuthServerRegistrar;

defined('ABSPATH') || exit;

/**
 * Registers the OAuth-protected MCP server with our own tool list.
 *
 * `register()` disables mcp-adapter's default server (`mcp_adapter_create_default_server`)
 * so no second, unprotected MCP endpoint is exposed alongside ours.
 *
 * wp-media/mcp-oauth hardcodes server id/route (token audience) and only three
 * meta-tools, and registers its own server unconditionally on the same
 * `mcp_adapter_init` action (priority 10). We register the same server id
 * first (priority 5) and, right before creating it, unhook mcp-oauth's own
 * `ServerRegistrar::register_server` callback so it never runs – see
 * `unhookOAuthDefaultServer()`. This avoids the duplicate-server-id WP_Error
 * (and the `_doing_it_wrong()` notice it used to trigger) entirely instead of
 * merely tolerating it – see spec §4.2.
 */
final class ServerRegistrar
{
    public const SERVER_ID = 'mcp-oauth-server';
    public const NAMESPACE = 'mcp';
    public const ROUTE = 'mcp-oauth-server';
    public const META_TOOLS = [
        'mcp-adapter/discover-abilities',
        'mcp-adapter/get-ability-info',
        'mcp-adapter/execute-ability',
    ];

    /** @var callable(): bool */
    private $oauthEnabled;

    /** @var callable(array<string, mixed>): mixed */
    private $createAdapterServer;

    /** @var callable(string): bool */
    private $classExists;

    private ExposurePolicy $policy;

    public function __construct(
        private IntegrationRegistry $registry,
        private InstructionsBuilder $instructions,
        ?callable $oauthEnabled = null,
        ?callable $createAdapterServer = null,
        ?callable $classExists = null,
        ?ExposurePolicy $policy = null
    ) {
        $this->policy = $policy ?? new ExposurePolicy();
        $this->oauthEnabled = $oauthEnabled
            ?? static fn (): bool => (new OAuthContext())->is_enabled();
        $this->classExists = $classExists
            ?? static fn (string $class): bool => class_exists($class);
        $this->createAdapterServer = $createAdapterServer
            ?? static function (array $args): mixed {
                return McpAdapter::instance()->create_server(
                    $args['id'],
                    $args['namespace'],
                    $args['route'],
                    $args['name'],
                    $args['description'],
                    $args['version'],
                    [OAuthHttpTransport::class],
                    ErrorLogMcpErrorHandler::class,
                    (new OAuthContext())->observability_handler(),
                    $args['tools']
                );
            };
    }

    public function register(): void
    {
        // mcp-adapter's default server is a second, unprotected (plain HttpTransport,
        // is_user_logged_in()) endpoint exposing execute-ability – and thus our own
        // abilities. We register our own OAuth-protected server instead; mcp-oauth's
        // ServerRegistrar registers the shared meta-abilities itself once this filter
        // disables the default server (see its ensure_shared_abilities_registered()).
        add_filter('mcp_adapter_create_default_server', '__return_false');

        add_action('mcp_adapter_init', [$this, 'createServer'], 5);
    }

    /** @return array<string, mixed>|null */
    public function serverArguments(): ?array
    {
        if (! ($this->oauthEnabled)()) {
            return null;
        }

        return [
            'id' => self::SERVER_ID,
            'namespace' => self::NAMESPACE,
            'route' => self::ROUTE,
            'name' => 'LIT MCP',
            'description' => $this->instructions->build(),
            'version' => Plugin::VERSION,
            'tools' => array_merge($this->policy->directNames($this->registry->abilities()), self::META_TOOLS),
        ];
    }

    public function createServer(): void
    {
        if (
            ! doing_action('mcp_adapter_init')
            || ! class_exists(McpAdapter::class)
            || ! class_exists(OAuthHttpTransport::class)
        ) {
            return;
        }

        $args = $this->serverArguments();
        if ($args === null) {
            return;
        }

        $this->unhookOAuthDefaultServer();

        $result = ($this->createAdapterServer)($args);

        if (is_wp_error($result)) {
            Log::failure('MCP server registration', $result->get_error_message());
        }
    }

    /**
     * Removes wp-media/mcp-oauth's own `mcp_adapter_init` callback so it never attempts to
     * register its (now redundant) copy of the `mcp-oauth-server` server.
     *
     * Reads the raw `WP_Hook` for `mcp_adapter_init` from `$GLOBALS['wp_filter']` – there is no
     * public API to look up a hooked callback by the class of its bound object, only by the exact
     * callable, which we don't have here. Removing a same-action, later-priority callback while an
     * earlier-priority one for the same action is running is explicitly supported by
     * `WP_Hook::remove_filter()` (it calls `resort_active_iterations()` for exactly this case).
     * No-op if the hook has not fired yet, has no callbacks, or the mcp-oauth package is absent.
     */
    public function unhookOAuthDefaultServer(): void
    {
        if (! ($this->classExists)(OAuthServerRegistrar::class)) {
            return;
        }

        $hook = $GLOBALS['wp_filter']['mcp_adapter_init'] ?? null;
        if (! is_object($hook) || ! isset($hook->callbacks) || ! is_array($hook->callbacks)) {
            return;
        }

        foreach ($hook->callbacks as $priority => $callbacks) {
            foreach ($callbacks as $callback) {
                $function = $callback['function'] ?? null;
                if (is_array($function) && ($function[0] ?? null) instanceof OAuthServerRegistrar) {
                    remove_action('mcp_adapter_init', $function, $priority);
                }
            }
        }
    }
}