lua封装的etcd client

       最近一年一直从事webrtc的开发，webrtc的服务性能测试也达到了大多大厂宣扬的并发性能，甚至略超过声网。这两天在我们的工程上实现了比较简单的Webrtc的CDN调度算法和故障转移，其中涉及到了如何根据服务器的资源进行调度，比如上行下行带宽/CPU占有率/内存占有率等，于是采用了webrtc服务器主动上报节点信息和资源到etcd。
       api7项目的王院生实现了https://github.com/api7/lua-resty-etcd，不过它是基于openresty的ngx.socket和ngx.json和ngx.base64的，我们是不能再引入openresty的，于是去掉了这些依赖，不过工程中关于API的封装还是参考了他的实现。
       目前etcd-lua使用的是lua5.3，且仅在etcd API V3上测试过，没有测试过v2。
       工程放开源在https://github.com/zhiyong0804/etcd-lua
       写了个例子如下，本来想写个API接口介绍的，但是怎奈作为程序员最痛恨的就是“没有文档，没有注释，要写文档，要写注释”。如果有人需要使用的话，看这个例子和源码就能理解API接口怎么样了，本来也不复杂的。

json = require('cjson')
sr   = require('systeminfo')

etcd = require('etcd').new({
       hosts = {
           "http://ip1:port1",
           "http://ip2:port2",
           "http://ip3:port3"
       },
       prefix = "/v3alpha"
  })

local leaseInfo  = {}
local system     = {}
local net        = "eth0"
local bandwidth  = 100*1024*1024
local interface  = "eth0"
local usage      = {} -- 当前服务器资源占用配置
local started    = false
local cpu_core   = 0
local key        = "/test/127.0.0.1"

function report_system_info()
  local cpu_usage = sr.getCpuOccupy()
  local mem_usage = sr.calcMemUsage()
  local rx_usage, tx_usage = sr.getTxrxUsage(interface)

  if not started then
      system["cpu"] = 0
      system["mem"] = 0
      system["rx"]  = 0
      system["tx"]  = 0

      started = true
  else
      system["cpu"] = sr.calcCpuUsage(usage["cpu"], cpu_usage)
      system["mem"] = mem_usage
      system["rx"], system["tx"]  = sr.calcTxrxUsage(usage["rx"], usage["tx"], rx_usage, tx_usage, bandwidth)
  end

  -- 将当前获取的所有系统信息保存起来，以便计算资源占有率
  usage["cpu"] = cpu_usage
  usage["mem"] = mem_usage
  usage["rx"]  = rx_usage
  usage["tx"]  = tx_usage

  system["country_code"] = "CN"
  system["updated"]      = os.time()

  if etcd ~= nil then
      local res, status = etcd:set(key, system, {timeout = 1, lease=leaseInfo.ID})
      print("res : "..dumpTable(res).."  status : ")
      etcd:keepalive(leaseInfo.ID)
  end

  print("collect system info" .. dumpTable(system))

  local res, status = etcd:get(key, {timeout = 1, lease=leaseInfo.ID})

  print("get key response : "..dumpTable(res).."  status : "..status)
end

-- Methods
function init()
  print("Initializing...")

  if etcd == nil then
      print("Initializ failed since etcd is nil")
      return nil
  end
  print("Initialized")

  -- 申请key的租约, 一秒钟， 租约ID由服务器分配
  local res, status = etcd:grant(1)
  if res == nil then
      print("err is : " .. err)
  end
  print("grant etcd lease response : " .. dumpTable(res))
  if status ~= 200 or res.ID == nil then
      print("grant etcd key lease failed.")
      return nil;
  end

  leaseInfo = {
      ID  = res.ID,
      ttl = 1,
  }

  cpu_core = sr.getCpuCore()

  report_system_info()
end

-- Helper for logging tables
-- https://stackoverflow.com/a/27028488
function dumpTable(o)
  if type(o) == 'table' then
      local s = '{ '
      for k,v in pairs(o) do
          if type(k) ~= 'number' then k = '"'..k..'"' end
              s = s .. '['..k..'] = ' .. dumpTable(v) .. ','
          end
      return s .. '} '
  else
      return tostring(o)
  end
end

return init()