arcp

Ruby SDK for ARCP v1. The wire protocol is specified in the ARCP spec. This gem implements the full v1 envelope, session handshake, job lifecycle, event stream, leases, and error model.

Install

gem 'arcp', '~> 1.0'

Requires Ruby 3.3+. Runs on the socketry/async reactor; pairs with falcon for hosting and async-websocket for the WebSocket transport.

Quickstart

require 'async'
require 'arcp'

Sync do
  runtime = Arcp::Runtime::Runtime.new(
    auth_verifier: Arcp::Auth::Bearer.from_token('demo', principal_id: 'alice'),
    heartbeat_interval_sec: nil
  )
  runtime.register_agent(
    name: 'echo', versions: ['1.0.0'], default: '1.0.0',
    handler: ->(ctx) {
      ctx.progress(current: 1, total: 1, units: 'message')
      ctx.finish(result: { 'echoed' => ctx.input })
    }
  )

  server_t, client_t = Arcp::Transport::MemoryTransport.pair
  server = Async { runtime.accept(server_t) }

  client = Arcp::Client.open(
    transport: client_t,
    auth: { 'scheme' => 'bearer', 'token' => 'demo' }
  )
  handle = client.submit_job(agent: 'echo', input: { 'msg' => 'hi' })
  handle.subscribe(client: client).each { |ev| puts ev.kind }
  puts handle.get_result(client: client).result.inspect

  client.close
  server.stop
end

What is ARCP

ARCP is a session-oriented protocol for invoking remote agents. A client opens a session, submits jobs, and receives a stream of structured events followed by a terminal result or error. The protocol covers capability negotiation, heartbeats, ordered acks, cursored job listing, cross-session observation, capability-bounded leases, and trace propagation.

Features

  • Capability negotiation (§6.2)
  • Heartbeat / ping-pong (§6.4)
  • Application-level ack (§6.5)
  • Cursored list_jobs (§6.6)
  • Cross-session job.subscribe with history replay (§7.6)
  • Agent versioning with name@version refs (§7.5)
  • result_chunk streaming with result_id terminator (§8.4)
  • progress events (§8.2)
  • lease_constraints.expires_at (§9)
  • cost.budget capability with BigDecimal arithmetic (§9.6)
  • Resume token + last_event_seq replay (§6.3)
  • Trace context propagation (§11)

Architecture

Arcp::Client            # session-oriented client
Arcp::Runtime::Runtime  # server-side runtime; accepts transports
Arcp::Runtime::JobContext # passed to agent handlers
Arcp::Session::*        # Hello, Welcome, CapabilitySet, Feature, AgentInventory, ...
Arcp::Job::*            # Submit, Accepted, Event, Result, JobError, Handle, Summary
Arcp::Job::EventKind    # 10 standard kinds
Arcp::Lease::*          # Lease, LeaseRequest, LeaseConstraints, CostBudget, Subsetting
Arcp::Transport::*      # MemoryTransport, WebSocketTransport, StdioTransport
Arcp::Auth::*           # AuthScheme, Bearer, Principal
Arcp::Errors::*         # 15 wire codes + 3 internal-only
Arcp::Trace             # Fiber-local Context, span helpers

Transports

  • Arcp::Transport::MemoryTransport.pair — in-process queue pair. Tests, embedded clients.
  • Arcp::Transport::WebSocketTransport — wraps an Async::WebSocket::Connection. Production transport.
  • Arcp::Transport::StdioTransport — newline-delimited JSON over a pair of IOs. Co-process agents.

Deployment

Run the runtime as a daemon under the socketry/async reactor. Host WebSocket endpoints with falcon. The runtime is fiber-based and multiplexes sessions on the reactor; do not deploy under request-per-thread servers like Puma.

Errors

15 wire codes, each mapped to an Arcp::Errors::* subclass with a retryable? default: Cancelled, InvalidRequest, Unauthenticated, PermissionDenied, JobNotFound, AgentNotAvailable, DuplicateKey, RateLimited, Internal, HeartbeatLost, Backpressure, ProtocolViolation, Timeout, ResumeWindowExpired, LeaseSubsetViolation, AgentVersionNotAvailable, LeaseExpired, BudgetExhausted. Three additional codes are library-internal and never appear on the wire (UNNEGOTIATED_FEATURE, plus the abstract Arcp::Error base and the generic Internal fallback).

Documentation

See docs/ for guides, concepts, and reference. Start with docs/getting-started.md.

Conformance

Spec-to-code matrix in CONFORMANCE.md.

Development

bundle install
bundle exec rake          # spec + rubocop + steep
bundle exec rake docs     # build doc tree

License

Apache-2.0. See LICENSE.