Lua JSONRPC学习笔记

JSON RPC

　　JSON RPC 为利用json数据格式来执行远程调用方式，

作用同xmlrpc，不过与xmlrpc相比， jsonrpc更加轻量，json更加节省数据量，更加可读性高。

官网网站：

http://www.json-rpc.org/

JSONRPC协议规范：

http://www.json-rpc.org/wiki/specification

lua实现的jsonrpc项目：

https://github.com/craigmj/json4lua

http://json.luaforge.net/

JSON

JSON为一种字符串方式数据组织的格式，以便于传输， 其语法同JAVASCRIPT对象写法（JS Object Notation）。

官网：

http://www.json.org/ 

lua实现的json项目：

https://github.com/craigmj/json4lua

LUA JSON 编解码

下载 json lua实现代码包， 解压后，将json文件夹放到lua path下，即lua安装目录下。

下载网址：

https://github.com/craigmj/json4lua

其中example文件夹下有演示代码 example.lua, 演示了如何将 一个 lua table编码为JSON字符串， 又如何将此字符串，恢复为LUA table。

--[[
JSON4Lua example script.
Demonstrates the simple functionality of the json module.
]]--
json = require('json')


-- Object to JSON encode
test = {
  one='first',two='second',three={2,3,5}
}

jsonTest = json.encode(test)

print('JSON encoded test is: ' .. jsonTest)

-- Now JSON decode the json string
result = json.decode(jsonTest)

print ("The decoded table result:")
table.foreach(result,print)
print ("The decoded table result.three")
table.foreach(result.three, print)

LUA JSON RPC

lua json的下载安装包，已经包括 json rpc的实现， 只需要从example中测试 jsonrpc的 客户端和 服务器端例子即可。

 客户端依赖 luasocket 来发起http请求。

 服务器端代码经过改造， 宿主与xavante， 有连接到来时， 触发执行。

客户端：

require ("json.rpc")

result, error = json.rpc.call("http://localhost:12345","echo","Test echo!")
print("echo call="..result)

print("

")

result, error = json.rpc.call("http://localhost:12345","average", 1, 3)
print("average="..result.average)

服务器端代码：

xavante = require("xavante")

wsapi = require("wsapi")
wsapi.xavante = require("wsapi.xavante")
wsapi.request = require("wsapi.request")

require ('json')

-- The Lua class that is to serve JSON RPC requests
local myServer = {
  echo = function (msg) return msg end,
  average = function(...)
    local total=0
    local count=0
    for i=1, table.getn(arg) do
      total = total + arg[i]
      count = count + 1
    end
    return { average= total/count, sum = total, n=count }
  end
}

-- JSON RPC 服务器端处理主体程序
local function serve(luaClass, packReturn, req)
  local postData =  req.POST.post_data    -- SAPI.Request.getpostdata()  --[[{ "id":1, "method":"echo","params":["Hi there"]}]]  --

  -- @TODO Catch an error condition on decoding the data
  local jsonRequest = json.decode(postData)
  local jsonResponse = {}
  jsonResponse.id = jsonRequest.id
  local method = luaClass[ jsonRequest.method ]

  if not method then
    jsonResponse.error = 'Method ' .. jsonRequest.method .. ' does not exist at this server.'
  else
    local callResult = { pcall( method, unpack( jsonRequest.params ) ) }
    if callResult[1] then    -- Function call successfull
      table.remove(callResult,1)
      if packReturn and table.getn(callResult)>1 then
        jsonResponse.result = callResult
      else
        jsonResponse.result = unpack(callResult)    -- NB: Does not support multiple argument returns
      end
    else
      jsonResponse.error = callResult[2]
    end
  end 
  
  -- Output the result
  -- TODO: How to be sure that the result and error tags are there even when they are nil in Lua?
  -- Can force them by hand... ?
  return json.encode( jsonResponse ) 
end

---  WSAPI handler
-- @param wsapi_env WSAPI environment
function wsapi_handler(wsapi_env)
   local headers = { ["Content-type"] = "text/plain" }
   local req = wsapi.request.new(wsapi_env)

   local r = serve(myServer, nil, req)
   print("r="..r)
   headers["Content-length"] = tostring(#r)

   local function xmlrpc_reply(wsapienv)
      coroutine.yield(r)
   end

   return 200, headers, coroutine.wrap(xmlrpc_reply)
end

local rules = {{ match = ".", with = wsapi.xavante.makeHandler(wsapi_handler) }}
local config = { server = {host = "*", port = 12345}, defaultHost = { rules = rules} }

xavante.HTTP(config)
xavante.start()

代码实现了， 客户端和服务通过JSONRPC调用，实现 echo 和 做平均计算的例子。