json.md

JSON

This section adds nothing new to the earlier concepts. It just uses a different "wire" format for the data, JSON instead of gob. As such, clients or servers could be written in other languasge that understand sockets and JSON.

JSON RPC client

A client that calls both functions of the arithmetic server is

/* JSONArithCLient
 */

package main

import (
	"net/rpc/jsonrpc"
	"fmt"
	"log"
	"os"
)

type Args struct {
	A, B int
}

type Quotient struct {
	Quo, Rem int
}

func main() {
	if len(os.Args) != 2 {
		fmt.Println("Usage: ", os.Args[0], "server:port")
		log.Fatal(1)
	}
	service := os.Args[1]

	client, err := jsonrpc.Dial("tcp", service)
	if err != nil {
		log.Fatal("dialing:", err)
	}
	// Synchronous call
	args := Args{17, 8}
	var reply int
	err = client.Call("Arith.Multiply", args, &reply)
	if err != nil {
		log.Fatal("arith error:", err)
	}
	fmt.Printf("Arith: %d*%d=%d\n", args.A, args.B, reply)

	var quot Quotient
	err = client.Call("Arith.Divide", args, &quot)
	if err != nil {
		log.Fatal("arith error:", err)
	}
	fmt.Printf("Arith: %d/%d=%d remainder %d\n", args.A, args.B, quot.Quo, quot.Rem)

}

JSON RPC server

A version of the server that uses JSON encoding is

/* JSONArithServer
 */

package main

import (
	"fmt"
	"net/rpc"
	"net/rpc/jsonrpc"
	"os"
	"net"
	"errors"
)
//import ("fmt"; "rpc"; "os"; "net"; "log"; "http")

type Args struct {
	A, B int
}

type Quotient struct {
	Quo, Rem int
}

type Arith int

func (t *Arith) Multiply(args *Args, reply *int) error {
	*reply = args.A * args.B
	return nil
}

func (t *Arith) Divide(args *Args, quo *Quotient) error {
	if args.B == 0 {
		return errors.New("divide by zero")
	}
	quo.Quo = args.A / args.B
	quo.Rem = args.A % args.B
	return nil
}

func main() {

	arith := new(Arith)
	rpc.Register(arith)

	tcpAddr, err := net.ResolveTCPAddr("tcp", ":1234")
	checkError(err)

	listener, err := net.ListenTCP("tcp", tcpAddr)
	checkError(err)

	/* This works:
	rpc.Accept(listener)
	*/
	/* and so does this:
	 */
	for {
		conn, err := listener.Accept()
		if err != nil {
			continue
		}
		jsonrpc.ServeConn(conn)
	}

}

func checkError(err error) {
	if err != nil {
		fmt.Println("Fatal error ", err.Error())
		os.Exit(1)
	}
}

Conclusion

RPC is a popular means of distributing applications. Several ways of doing it have been presented here. What is missing from Go is support for the currently fashionable (but extremely badly enginereed) SOAP RPC mechanism.