arcp/arcp — ARCP PHP SDK

PHP 8.4 reference implementation of the Agent Runtime Control Protocol (ARCP) v1.0.

Status: v0.1 complete. The Phase 0 plan is in PLAN.md; the conformance matrix is in CONFORMANCE.md.

Quick start

composer install

# Tests
vendor/bin/phpunit --testdox

# Static analysis
vendor/bin/phpstan analyze
vendor/bin/psalm --no-cache

# Formatter
vendor/bin/php-cs-fixer fix --dry-run --diff

# Run a sample
php samples/02_tool_invoke_with_progress.php

# Run a runtime exposing a websocket port
bin/arcp serve --host 127.0.0.1 --port 8765

Requirements

• PHP 8.4 or newer.
• Composer 2.x.
• The pdo_sqlite, mbstring, and json extensions (bundled with most PHP distributions).

Architecture

+-----------------------------+
| Capability Layer            |
| (MCP Compatible)            |
+-----------------------------+
+-----------------------------+
| ARCP Runtime Layer          |
| - Identity & Sessions       |
| - Streams                   |
| - Jobs                      |
| - Subscriptions             |
| - Events                    |
| - Permissions & Leases      |
| - Artifacts                 |
| - Tracing & Metrics         |
+-----------------------------+
+-----------------------------+
| Transport Layer             |
| WebSocket / stdio (mandatory)|
+-----------------------------+

The runtime is Arcp\Runtime\ARCPRuntime; the client is Arcp\Client\ARCPClient. Both are async (Amp v3 + fibers) and both take a Arcp\Transport\Transport instance, which is one of MemoryTransport, WebSocketTransport, or StdioTransport.

Hello, ARCP

use Arcp\Auth\AuthRouter;
use Arcp\Auth\NoneAuth;
use Arcp\Client\ARCPClient;
use Arcp\Messages\Session\Auth;
use Arcp\Messages\Session\Capabilities;
use Arcp\Messages\Session\PeerInfo;
use Arcp\Runtime\ARCPRuntime;
use Arcp\Runtime\JobContext;
use Arcp\Runtime\ToolHandler;
use Arcp\Transport\MemoryTransport;

$runtime = new ARCPRuntime(authRouter: new AuthRouter([new NoneAuth()]));
$runtime->registerTool('echo', new class implements ToolHandler {
    public function invoke(array $args, JobContext $ctx, ?\Amp\Cancellation $c = null): mixed
    {
        return ['echoed' => $args];
    }
});

[$serverT, $clientT] = MemoryTransport::pair();
$serverFuture = $runtime->serveAsync($serverT);

$client = new ARCPClient($clientT);
$client->open(
    Auth::none(),
    new PeerInfo('demo', '0.1'),
    new Capabilities(anonymous: true),
);
$result = $client->invokeTool('echo', ['ping' => 'pong']);
print_r($result->value);

$client->close();
$serverFuture->await();

CLI

bin/arcp (registered in composer.json's bin):

Command	Purpose
arcp serve --host H --port P	Run a runtime accepting WebSocket connections.
arcp tail ws://host:port/	Subscribe and print every envelope.
arcp send ws://… <tool> -a '{"k":"v"}'	Invoke a tool and print the result.
arcp replay events.sqlite -a msg_xyz	Replay an event log file.

RFC mapping

RFC section	Implementation
§6.1 Envelope	src/Envelope/Envelope.php
§6.2 Message types	src/Messages/ + src/Envelope/MessageCatalog.php
§7 Capability negotiation	src/Runtime/ARCPRuntime.php
§8 Authentication	src/Auth/
§10 Jobs	src/Runtime/JobManager.php + JobContext
§11 Streaming	JobContext::openStream() (text/event/log/thought; binary base64 only)
§12 Human-in-the-loop	src/Client/Handlers/ + JobContext::requestHumanInput/Choice
§13 Subscriptions	src/Runtime/SubscriptionManager.php
§15 Permissions & leases	src/Runtime/LeaseManager.php
§16 Artifacts	src/Runtime/ArtifactStore.php
§17 Observability	src/Messages/Telemetry/
§18 Errors	src/Errors/
§19 Resume	src/Store/EventLog.php
§21 Extensions	src/Extensions/
§22 Transports	src/Transport/

Samples

Six runnable scripts under samples/, each backed by a single sentence of context at the top. They all use MemoryTransport to keep the example self-contained:

1. 01_minimal_session.php — handshake.
2. 02_tool_invoke_with_progress.php — tool + progress events.
3. 03_human_input_request.php — HITL input.
4. 04_permission_challenge.php — permission/lease.
5. 05_observer_subscription.php — passive observer.
6. 06_relay_human_in_the_loop.php — multi-channel HITL relay.

What's not implemented in v0.1

See PLAN.md §7 for the full list. Calls into out-of-scope surfaces throw UnimplementedException with the relevant RFC section.

License

Apache-2.0.