Ruby EventMachine - 如何将值从 EM::Deferrable 返回到主 EM 循环？

Question

我现在正在使用 EventMachine 玩了几天，恕我直言，它的学习曲线很陡；-) 我尝试通过触发回调中需要的 HttpHeaderCrawler.query() 来返回哈希。但是在这种情况下我得到的不是散列 {'http_status' => xxx, 'http_version' => xxx} 而是一个 EventMachine::HttpClient 对象本身。

我想保持 EM.run block 干净，并想在自己的类/模块中执行所有逻辑，那么如何将这样的值返回到主循环中以通过回调访问它？非常感谢 ;-)

#!/usr/bin/env ruby

require 'eventmachine'
require 'em-http-request'

class HttpHeaderCrawler
  include EM::Deferrable

  def query(uri)
    http = EM::HttpRequest.new(uri).get
    http.callback do
      http_header = {
        "http_status" => http.response_header.http_status,
        "http_version" => http.response_header.http_version
      }
      puts "Returns to EM main loop: #{http_header}"
      succeed(http_header)
    end
  end
end

EM.run do
  domains = ['http://www.google.com', 'http://www.facebook.com', 'http://www.twitter.com']
  domains.each do |domain|
    hdr = HttpHeaderCrawler.new.query(domain)
    hdr.callback do |header|
      puts "Received from HttpHeaderCrawler: #{header}"
    end
  end
end

此代码段产生以下输出:

Returns to EM main loop: {"http_status"=>302, "http_version"=>"1.1"}
Received from HttpHeaderCrawler: #<EventMachine::HttpClient:0x00000100d57388>
Returns to EM main loop: {"http_status"=>301, "http_version"=>"1.1"}
Received from HttpHeaderCrawler: #<EventMachine::HttpClient:0x00000100d551a0>
Returns to EM main loop: {"http_status"=>200, "http_version"=>"1.1"}
Received from HttpHeaderCrawler: #<EventMachine::HttpClient:0x00000100d56280>

Answer 1

我认为问题是 #query 返回 http.callback，它返回 http 对象本身，而它应该返回 self，即HttpHeaderCrawler。看看这是否有效。

def query(uri)
  http = EM::HttpRequest.new(uri).get
  http.callback do
    http_header = {
      "http_status" => http.response_header.http_status,
      "http_version" => http.response_header.http_version
    }
    puts "Returns to EM main loop: #{http_header}"
    succeed(http_header)
  end
  self
end