1.使用ruby eventmachine和em-http-server gem，完成一个简单的提供文件下载功能的HttpServer

2.使用了EM的FileStreamer来异步发送文件，发送文件时先组装了header，然后调用FileStreamer

require 'rubygems'
require 'eventmachine'
require 'em-http-server'

class HTTPHandler < EM::HttpServer::Server
 attr_accessor :filename, :filesize, :path

 def process_http_request
 #send file async
 if @http_request_method.to_s =~ /GET/ && @http_request_uri.to_s.end_with?(filename)
  send_data "HTTP/1.1 200 OKn"
  send_data "Server: XiaoMin"
  send_data "Connection: Keep-Aliven"
  send_data "Keep-Alive: timeout=15n"
  send_data "Content-Type: application/octet-streamn"
  send_data "Content-Disposition: filename='#{filename}'n"
  send_data "Content-Length: #{filesize}n"
  send_data "n"

  streamer = EventMachine::FileStreamer.new(self, path)
  streamer.callback {
  # file was sent successfully
  close_connection_after_writing
  }
 else
  response = EM::DelegatedHttpResponse.new(self)
  response.status = 200
  response.content_type 'text/html'
  response.content = "Package HttpServer<br>usage: wget http://host:port/#{filename}"
  response.send_response
 end
 end

end

EM::run do
 path = '/tmp/aaa.tar.gz'
 EM::start_server("0.0.0.0", 8080, HTTPHandler) do |conn|
 conn.filename = File.basename(path)
 conn.filesize = File.size(path)
 conn.path = path
 end
end

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