php-client-implementation

PHP MCP Client Implementation Guide

Client Class Structure

The Client class handles communication with MCP servers and manages the protocol lifecycle.

Basic Client Implementation

namespace MCP\Client;

use MCP\Shared\Protocol;
use MCP\Shared\Transport;
use MCP\Types\Implementation;
use MCP\Types\ClientCapabilities;
use MCP\Types\ServerCapabilities;
use React\Promise\Promise;
use React\Promise\PromiseInterface;

class Client extends Protocol {
    private ?ServerCapabilities $serverCapabilities = null;
    private ?Implementation $serverVersion = null;
    private ClientCapabilities $capabilities;
    private ?string $instructions = null;

    public function __construct(
        Implementation $clientInfo,
        ?ClientOptions $options = null
    ) {
        parent::__construct($clientInfo, $options);
        $this->capabilities = $options?->capabilities ?? new ClientCapabilities();
    }

    /**
     * Connect to server and perform initialization
     */
    public function connect(Transport $transport): PromiseInterface {
        return $this->protocol->connect($transport)
            ->then(function () {
                return $this->initialize();
            });
    }
}

Initialization Flow

private function initialize(): PromiseInterface {
    return $this->request([
        'method' => 'initialize',
        'params' => [
            'protocolVersion' => self::LATEST_PROTOCOL_VERSION,
            'capabilities' => $this->capabilities->toArray(),
            'clientInfo' => [
                'name' => $this->clientInfo->getName(),
                'version' => $this->clientInfo->getVersion()
            ]
        ]
    ])->then(function (array $result) {
        // Validate protocol version
        if (!in_array($result['protocolVersion'], self::SUPPORTED_PROTOCOL_VERSIONS)) {
            throw new McpError(
                ErrorCode::InvalidRequest,
                "Unsupported protocol version: {$result['protocolVersion']}"
            );
        }

        $this->serverCapabilities = ServerCapabilities::fromArray($result['capabilities']);
        $this->serverVersion = Implementation::fromArray($result['serverInfo']);
        $this->instructions = $result['instructions'] ?? null;

        // Send initialized notification
        return $this->notify([
            'method' => 'notifications/initialized'
        ]);
    });
}