golang RPC 应用(1) :net/rpc的应用

RPC（Remote Procedure Call）—远程过程调用，它是一种通过网络从远程计算机程序上请求服务，而不需要了解底层网络技术的协议。RPC协议假定某些传输协议的存在，如TCP或UDP，为通信程序之间携带信息数据。在OSI网络通信模型中，RPC跨越了传输层和应用层。RPC使得开发包括网络分布式多程序在内的应用程序更加容易。---百度百科
实际后台开发中，rpc是服务器与服务器交互的方式之一，隐藏底层网络实现，代码程式化，开发效率高，BUG少。

通过一个简单的demo来说明go官方rpc包的应用。
项目结构:

rpc
    ----Makefile
    ----src
        ----client
            ----main.go
        ----protocol
            ----type.go
        ----server
            ----main.go

rpc/Makefile

GOPATH := $(shell pwd)
all:
    GOPATH=${GOPATH} go install client
    GOPATH=${GOPATH} go install server

rpc/protocol/type.go

package protocol

const(
    RPC_ADDITION = "Calculator.Addition"
    RPC_SUBTRACTION = "Calculator.Subtraction"
    RPC_MULTIPLICATION = "Calculator.Multiplication"
    RPC_DIVISION = "Calculator.Division"
)

type Param struct {
    A int32
    B int32
}

RPC客户端实现,包含同步(Call)和异步(Go)调用方式,通常为了效率会使用异步方式。
rpc/src/client/main.go

package main

import "net/rpc"
import (
    . "protocol"
    "fmt"
    "time"
)

var (    _CLIENT  *rpc.Client
    _RPC_MSG chan *rpc.Call
    _CAN_CANCEL chan bool
)

func main()  {
    DialRpcServer()
    //起个协程处理异步rpc调用结果
    go loop()

    //测试同步的方式调用rpc服务
    param := Param{A:int32(10),B:int32(30)}
    reply := int32(0)
    SyncCallRpcFunc(RPC_ADDITION, &param, &reply)
    fmt.Printf("Sync Call Addition Result %d \n", reply)
    SyncCallRpcFunc(RPC_SUBTRACTION, &param, &reply)
    fmt.Printf("Sync Call Subtraction Result %d \n", reply)
    ////测试异步的方式调用rpc服务
    ASyncCallRpcFunc(RPC_MULTIPLICATION, &param, &reply)
    ASyncCallRpcFunc(RPC_DIVISION, &param, &reply)
    //阻塞等待异步调用完成
    <- _CAN_CANCEL
}

func init(){
    _RPC_MSG = make(chan *rpc.Call, 1024)
    _CAN_CANCEL = make(chan bool)
}

func DialRpcServer(){
    c, e := rpc.DialHTTP("tcp", "127.0.0.1:2311")

    if e != nil {
        fmt.Errorf("Dial RPC Error %s", e.Error())
    }

    _CLIENT = c
}
//重连RPC服务器
func ReDialRpcServer() bool{
    c, e := rpc.DialHTTP("tcp", "127.0.0.1:2311")

    if e != nil {
        fmt.Printf("ReDial RPC Error %s \n", e.Error())

        return false
    }

    _CLIENT = c

    fmt.Println("ReDial Rpc Server Succ")

    return true
}
//同步rpc调用
func SyncCallRpcFunc(method string, args interface{}, reply interface{}){
    if nil == _CLIENT{
        for{//如果断线就等到重连上为止
            if ReDialRpcServer(){
                break
            }
            time.Sleep(5000 * time.Millisecond)
        }
    }

    _CLIENT.Call(method, args, reply)
}
//异步rpc调用
func ASyncCallRpcFunc(method string, args interface{}, reply interface{}){
    if nil == _CLIENT{
        for{//如果断线就等到重连上为止
            if ReDialRpcServer(){
                break
            }
            time.Sleep(5000 * time.Millisecond)
        }
    }
    // Go(serviceMethod string, args interface{}, reply interface{}, done chan *Call)的done如果填nil会构建个新的channel用于接受结果
    _CLIENT.Go(method, args, reply, _RPC_MSG)
}
//接收异步调用的返回
func loop(){
    for{
        select {
        case rpcMsg, ok := <- _RPC_MSG:
            if !ok{
                fmt.Errorf("Rpc Call Error")
            }
            rpcMsgHandler(rpcMsg)
        }
    }

    _CAN_CANCEL <- true
}
// 处理异步rpc的返回值
func rpcMsgHandler(msg * rpc.Call){
    switch msg.ServiceMethod {
    case RPC_ADDITION:
        reply := msg.Reply.(*int32)
        fmt.Printf("Addtoion Result [%d] \n", *reply)
    case RPC_SUBTRACTION:
        reply := msg.Reply.(*int32)
        fmt.Printf("Subtraction Result [%d] \n", *reply)
    case RPC_MULTIPLICATION:
        reply := msg.Reply.(*int32)
        fmt.Printf("Multiplication Result [%d] \n", *reply)
    case RPC_DIVISION:
        reply := msg.Reply.(*int32)
        fmt.Printf("Division Result [%d] \n", *reply)
    default:
        fmt.Errorf("Can Not Handler Reply [%s] \n", msg.ServiceMethod)

    }
}

RPC服务器的实现。
rpc/src/server/main.go

package main

import "net/rpc"
import (
    . "protocol"
    "errors"
    "net"
    "fmt"
    "net/http"
)

type Calculator struct {}

var (    _DATA *Calculator
    _CAN_CANCEL chan bool
)

func main()  {
    runRpcServer()
}

func init(){
    _DATA = new(Calculator)
    _CAN_CANCEL = make(chan bool)
}

func runRpcServer(){
    //rpc包里面定义了个DefaultServer，缺省的Register和HandleHTTP均是对DefaultServer作的操作，如果想定制新的Server，就自己写
    rpc.Register(_DATA)
    rpc.HandleHTTP()
    l,e := net.Listen("tcp","127.0.0.1:2311")
    if e != nil{
        fmt.Errorf("Create Listener Error %s", e.Error())
    }

    go http.Serve(l, nil)
    //阻塞主进程，等待客户端输入
    <-_CAN_CANCEL
}
//输出方法的格式要求：func (t *T) MethodName(argType T1, replyType *T2) error
func (*Calculator) Addition(param *Param, reply *int32) error{
    *reply = param.A + param.B

    return nil
}

func (*Calculator) Subtraction(param *Param, reply *int32) error{
    *reply = param.A - param.B
    return nil
}

func (*Calculator) Multiplication(param *Param, reply *int32) error{
    *reply = param.A * param.B

    return nil
}

func (*Calculator) Division(param *Param, reply *int32) error{
    if 0 == param.B{
        return errors.New("divide by zero")
    }
    *reply = param.A/param.B

    return nil
}

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