Setup Graphql subscription with ActionCable Rails

README.md

Some useful links:

https://github.com/rmosolgo/graphql-ruby/commit/a329ff3cb84cc83da15b6283cf80dcdd68f49286#diff-d206d5f8891deaca408fcccd141e6193R63

https://gist.github.com/bbugh/742942596156830c597aaf0ea7a2d800

https://graphql-ruby.org/subscriptions/subscription_classes#terminating-the-subscription-with-unsubscribe

https://evilmartians.com/chronicles/graphql-on-rails-3-on-the-way-to-perfection

https://github.com/rmosolgo/graphql-ruby/tree/v1.8.0/guides/subscriptions

https://github.com/rmosolgo/graphql-ruby/blob/v1.8.0/lib/graphql/subscriptions/action_cable_subscriptions.rb

add_item_mutation.rb

# app/graphql/mutations/add_item_mutation.rb

module Mutations
  class AddItemMutation < Mutations::BaseMutation
    argument :attributes, Types::ItemAttributes, required: true

    field :item, Types::ItemType, null: true
    field :errors, [String], null: false

    def resolve(attributes:)
      check_authentication!

      item = Item.new(attributes.merge(user: context[:current_user]))

      if item.save
        MartianLibrarySchema.subscriptions.trigger("itemAdded", {}, item, scope: context[:current_user].id)
        { item: item }
      else
        { errors: item.errors.full_messages }
      end
    end
  end
end

cable.yml

# config/cable.yml

development:
  adapter: redis
  url: redis://localhost:6379/1

test:
  adapter: async

production:
  adapter: redis
  url: redis://localhost:6379/1
  channel_prefix: xyz_production

connection.rb

# app/channels/application_cable/connection.rb

module ApplicationCable
  class Connection < ActionCable::Connection::Base
    identified_by :current_user

    def connect
      self.current_user = find_verified_user
    end

    private
    
    def find_verified_user
      token = request.params[:token].to_s
      email = Base64.decode64(token)
      current_user = User.find_by(email: email)
      return current_user if current_user

      reject_unauthorized_connection
    end
  end
end

development.rb

# config/environments/development.rb
# config/environments/production.rb

Rails.application.configure do
  :
  :
  config.action_cable.allowed_request_origins = [ENV['UI_HOST_DOMAIN']] # <- ActionCable needs to know the domain or a pattern of domain to allow the connection
end

Graphql subscription with ActionCable

{ Ref: https://evilmartians.com/chronicles/graphql-on-rails-3-on-the-way-to-perfection }

(Rails - 5, Graphql-ruby - 1.8.x) 

# Gemfile

gem 'redis'

graphql_channel.rb

# app/channels/graphql_channel.rb

class GraphqlChannel < ApplicationCable::Channel
  def subscribed
    @subscription_ids = []
  end

  def execute(data)
    result = execute_query(data)

    payload = {
      result: result.subscription? ? { data: nil } : result.to_h,
      more: result.subscription?
    }

    # Track the subscription here so we can remove it
    # on unsubscribe.
    @subscription_ids << context[:subscription_id] if result.context[:subscription_id]

    transmit(payload)
  end

  def unsubscribed
    @subscription_ids.each { |sid|
      Schema.subscriptions.delete_subscription(sid)
    }
  end

  private

  def execute_query(data)
    Schema.execute(
      query: data['query'],
      context: context,
      variables: ensure_hash(data['variables']),
      operation_name: data['operationName']
    )
  end

  def context
    {
      current_user_id: current_user.id, # <- `current_user_id` will be used as scope to broadcast message only to this user. 
      current_user: current_user,
      channel: self
    }
  end

  def ensure_hash(ambiguous_param)
    case ambiguous_param
    when String
      if ambiguous_param.present?
        ensure_hash(JSON.parse(ambiguous_param))
      else
        {}
      end
    when Hash, ActionController::Parameters
      ambiguous_param
    when nil
      {}
    else
      raise ArgumentError, "Unexpected parameter: #{ambiguous_param}"
    end
  end
end

martian_library_schema.rb

# app/graphql/martian_library_schema.rb

class MartianLibrarySchema < GraphQL::Schema
  use GraphQL::Subscriptions::ActionCableSubscriptions, redis: Redis.new

  mutation(Types::MutationType)
  query(Types::QueryType)
  subscription(Types::SubscriptionType)
end

subscription_type.rb

# app/graphql/types/subscription_type.rb

# Ref: https://github.com/rmosolgo/graphql-ruby/commit/a329ff3cb84cc83da15b6283cf80dcdd68f49286#diff-d206d5f8891deaca408fcccd141e6193R63

Types::SubscriptionType = GraphQL::ObjectType.define do

  field :item_added, Types::ItemType, null: false, description: "An item was added" do
    subscription_scope :current_user_id
  end

  # The return value of the method is not used;
  # only the raised error affects the behavior of the subscription.
  # If the error is raised, it will be added to the response's `"errors"` key and
  # the subscription won't be created.
  # TODO: write a policy to authorize. something like
  # context[:current_account].can_subscribe_to?(account_id)
  def account_status
    raise GraphQL::ExecutionError, 'Can not subscribe to this topic' if context[:current_user].blank?
  end
end