action_cable.cr

A 1:1 Crystal port of actioncable 8.1.4 (Rails' Action Cable) under the same ActionCable namespace. WebSocket layer is fiber-per-connection on top of the Crystal stdlib HTTP::WebSocket (no nio4r + thread pool), speaking the exact Rails JSON protocol (welcome / subscription_confirmation / ping / disconnect, commands subscribe/message/unsubscribe) — the official @rails/actioncable JS client works unchanged. Pubsub adapters: Async (in-process, default), PostgreSQL LISTEN/NOTIFY, Redis pubsub. The hot path carries a Bun/uWS-style fast broadcast (encode-once envelopes, per-connection cork buffers, 1 write per batch, 1 MiB backpressure cap): 2.72M msg/s fan-out vs 2.52M for bun-publish. Suite: 51/51, including 33 oracle cases recorded with the real actioncable 8.1.4.

⚠️ EXPERIMENTAL FRAMEWORK, DO NOT USE IN PRODUCTION YET.

Installation

dependencies:
  action_cable_cr:
    github: OrelSokolov/action_cable.cr

shards install

Depends on active_support.cr, active_record.cr, action_pack.cr and the pg / redis shards.

Usage

require "action_cable_cr"

class ActionCable::Connection
  identified_by :current_user

  def connect
    reject_unauthorized_connection! unless session["warden.user.user.key"]?
    self.current_user = session["user_gid"]
  end
end

class ChatChannel < ActionCable::Channel::Base
  def subscribed
    stream_from "chat_#{params["room"]}"
  end

  def speak(data)                       # public method = client RPC action
    ActionCable.server.broadcast("chat_#{params["room"]}", data)
  end

  periodically :transmit_presence, every: 30
end

server = ActionCable::Server.new                # Async adapter by default
HTTP::Server.new([server.ws_handler]).listen(3000)  # ws://localhost:3000/cable

Cross-process setups swap the adapter (SubscriptionAdapter::Redis.new(url) or SubscriptionAdapter::PostgreSQL.new(url)); remote disconnect:

ActionCable.server.remote_connections.where(current_user: "1").disconnect(reconnect: true)

Feature comparison vs actioncable 8.1.4

Connection & protocol

Channel DSL

Server, pubsub & performance

Deviations & Crystal-specific notes

• transmit is public (private in Ruby; Crystal has no send); streams became public stream_names for testing.
• unsubscribe(channel, callback) → unsubscribe(channel): Crystal Procs have no identity, so it drops in-process callbacks but not the underlying Redis subscription.
• Identifier values are Strings only (gid strings); params is Hash(String, String) instead of HashWithIndifferentAccess; INTERNAL is named constants instead of a heterogeneous hash.
• periodically is a macro DSL (a Proc is unspellable in a class body); every: accepts Time::Span or seconds, ArgumentError on ≤ 0.
• The gid app name comes from ActionCable.gid_app (ENV CRAILS_APP_NAME, default "app"), not GlobalID.app.
• broadcast returns nil, not a PUBLISH recipient count; PG NOTIFY payloads are capped at ~8000 bytes.

Full list with rationale: PLAN.md (Russian).

Testing

crystal spec          # stream_for/pubsub suites need a local PostgreSQL
                      # (db crails_ac_test) and a local Redis, else they fail

Oracle: 33 cases (20 channel/protocol + 5 pubsub + 8 stream_for) recorded with the real actioncable 8.1.4 (oracle/cases.rb, oracle/pubsub_cases.rb, oracle/stream_for_cases.rb → expected*.yml); the Crystal specs replay them 1:1 without edits. The pubsub cases mirror the Redis adapter's behavior against both the Redis and PostgreSQL adapters. Full suite: 51/51.