1.先要获取openid（略，因为发红包的时候是需要用户的openid）
2.执行发红包的action

def confirm
    opetions = {
                 mch_billno: _record.no_num,
                 total_amount: 1 * 100, # money * 100
                 client_ip: request.remote_ip
               }
end

因为在微信接口中的金额都是用分计算的，而红包最低是一元发送。所以测试的时候都搞一元好了。
3.发红包的方法

def self.send_reward(openid, opetions={})
    options = {
                mch_id: ,#商户编号
                nonce_str: ,#随机字符串
                mch_billno: , # 商户订单号
                wxappid: , # 公众账号appid
                nick_name: , # 提供方名称
                send_name: , # 发送方名称
                re_openid: openid, # 用户openid
                total_amount: opetions[:total_amount], # 付款金额
                min_value: opetions[:total_amount], # 最小红包金额
                max_value: opetions[:total_amount], # 最大红包金额
                total_num: 1, # 红包发放总人数
                wishing: , # 红包祝福语
                client_ip: opetions[:client_ip], # Ip地址
                act_name: , # 活动名称
                remark: , # 备注
              }

    _sign = Weixin.md5_with_partner_key(options)#签名

    xml = "<xml>
           <mch_id>#{ options[:mch_id] }</mch_id>
           <nonce_str>#{ options[:nonce_str] }</nonce_str>
           <mch_billno>#{ options[:mch_billno] }</mch_billno>
           <wxappid>#{ options[:wxappid] }</wxappid>
           <nick_name>#{ options[:nick_name] }</nick_name>
           <send_name>#{ options[:send_name] }</send_name>
           <re_openid>#{ options[:re_openid] }</re_openid>
           <total_amount>#{ options[:total_amount] }</total_amount>
           <min_value>#{ options[:min_value] }</min_value>
           <max_value>#{ options[:max_value] }</max_value>
           <total_num>#{ options[:total_num] }</total_num>
           <wishing>#{ options[:wishing] }</wishing>
           <client_ip>#{ options[:client_ip] }</client_ip>
           <act_name>#{ options[:act_name] }</act_name>
           <remark>#{ options[:remark] }</remark>
           <sign>#{ _sign }</sign>
          </xml>"

    xml = Nokogiri::XML xml

    uri = URI.parse('https://api.mch.weixin.qq.com/mmpaymkttransfers/sendredpack')

    cert = File.read("#{ Rails.root }/lib/jingyou_cert/apiclient_cert.pem")

    key = File.read("#{ Rails.root }/lib/jingyou_cert/apiclient_key.pem")

    http = Net::HTTP.new(uri.host, uri.port)

    http.use_ssl = true if uri.scheme == 'https'

    http.cert = OpenSSL::X509::Certificate.new(cert)

    http.key = OpenSSL::PKey::RSA.new(key, '商户编号')

    http.ca_file = File.join("#{ Rails.root }/lib/jingyou_cert/rootca.pem")

    http.verify_mode = OpenSSL::SSL::VERIFY_PEER

    http.start { http.request_post(uri.path, xml.to_xml) { |res| res.body } }
end

def self.md5_with_partner_key(params)
    str = params.sort.map { |item| item.join('=') }.join('&')
    str << "&key=#{ app_secret }"
    Digest::MD5.hexdigest(str).upcase
end