Action Cable：客户端退订时如何获取客户端的订阅名？答案

【问题标题】：Action Cable: How to get the client's subscription name when the client unsubscribes?Action Cable：客户端退订时如何获取客户端的订阅名？
【发布时间】：2017-04-21 09:08:03
【问题描述】：

我正在使用 Devise 和 gem 'devise_token_auth' 在 Rails 5 API Action Cable 中实现聊天。

我有一个带有参数化订阅的ChatRequestChannel：

stream_from "chat_request_#{chat_request_chanel_token}_channel"

我需要以某种方式可靠地检索 unsubscribed 挂钩内的 chat_request_chanel_token 值 - 以向其他订阅者发送消息。这是我的代码：

class ChatRequestChannel < ApplicationCable::Channel
  def subscribed 

    answerer = params["answerer"]

    chat_request_chanel_token = answerer

    answerer_user = User.find_by email: answerer

    if answerer_user

      stream_from "chat_request_#{chat_request_chanel_token}_channel"

    else
# http://api.rubyonrails.org/classes/ActionCable/Channel/Base.html#class-ActionCable::Channel::Base-label-Rejecting+subscription+requests
      reject

    end

  end

  def unsubscribed
    # Any cleanup needed when channel is unsubscribed

      chat_request_chanel_token = "What to put here????"

      message = "Client disconnected"  

      ActionCable.server.broadcast "chat_request_#{chat_request_chanel_token}_channel",
                                   disconnected: message

  end
end

所有客户端订阅ChatRequestChannel 并使用这样的命令（answerer 参数因客户端而异）：

{"command":"subscribe","identifier":"{\"channel\":\"ChatRequestChannel\",\"answerer\":\"client1@example.com\"}"}

unsubscribed 钩子实际上是在客户端与 Action Cable 断开连接时调用的。所以我无法向unsubscribed 提供任何参数。

我建议每个客户应该只一个（每个参数）参数化订阅ChatRequestChannel。它是否存储在 Action Cable 中的某个位置并且可以检索？

【问题讨论】：

标签： ruby-on-rails actioncable

【解决方案1】：

我可能找到了。里面有一个数组streams

/var/lib/gems/2.3.0/gems/actioncable-5.0.1/lib/action_cable/channel/streams.rb

def stream_from(broadcasting, callback = nil, coder: nil, &block)
        broadcasting = String(broadcasting)

        # Don't send the confirmation until pubsub#subscribe is successful
        defer_subscription_confirmation!

        # Build a stream handler by wrapping the user-provided callback with
        # a decoder or defaulting to a JSON-decoding retransmitter.
        handler = worker_pool_stream_handler(broadcasting, callback || block, coder: coder)
        streams << [ broadcasting, handler ]

        connection.server.event_loop.post do
          pubsub.subscribe(broadcasting, handler, lambda do
            ensure_confirmation_sent
            logger.info "#{self.class.name} is streaming from #{broadcasting}"
          end)
        end
      end

见streams << [ broadcasting, handler ]这一行。

这是我基于它的代码：

module ApplicationCable
  class Channel < ActionCable::Channel::Base
    include ApplicationHelper

      def stream_name
        streams.try(:[],0).try(:[],0)
      end

      def token_from_stream_name

        stream_name ? stream_name.gsub(channel_name,"").slice(1..-"_channel".size-1) : ""

      end
  end
end

stream_name 方法现在可以在 unsubscribe 挂钩中使用。当客户端与服务器套接字断开连接时，会自动为每个客户端的订阅（对该频道的订阅）调用unsubscribed 挂钩。在unsubscribe 中调用stream_name 会返回当前正在停止的订阅的名称，以便您通知该频道的所有其他订阅者：

class ChatChannel < ApplicationCable::Channel
 .... 
  def unsubscribed
    # Any cleanup needed when channel is unsubscribed

    message = { user_id: current_user.id, online: :off }

    ActionCable.server.broadcast stream_name, chat_cancel: message      
  end
....
end

【讨论】：