Use RPC to make a kv storage server

Go example: kv.go on schedule page
A toy key/value storage server – Put(key,value), Get(key)->value
Uses Go’s RPC library
Common:
Declare Args and Reply struct for each server handler.
Client:
connect()'s Dial() creates a TCP connection to the server
get() and put() are client “stubs”
Call() asks the RPC library to perform the call
you specify server function name, arguments, place to put reply
library marshalls args, sends request, waits, unmarshalls reply
return value from Call() indicates whether it got a reply
usually you’ll also have a reply.Err indicating service-level failure
Server:
Go requires server to declare an object with methods as RPC handlers
Server then registers that object with the RPC library
Server accepts TCP connections, gives them to RPC library
The RPC library
reads each request
creates a new goroutine for this request
unmarshalls request
looks up the named object (in table create by Register())
calls the object’s named method (dispatch)
marshalls reply
writes reply on TCP connection
The server’s Get() and Put() handlers
Must lock, since RPC library creates a new goroutine for each request
read args; modify reply

server

//
// Server
//package mainimport ("log""net""net/rpc""sync"
)const (OK       = "OK"ErrNoKey = "ErrNoKey"
)type Err stringtype PutArgs struct {Key   stringValue string}type PutReply struct {Err Err        
}type GetArgs struct {Key string
}type GetReply struct {Err   ErrValue string     
}type KV struct {mu   sync.Mutexdata map[string]string
}func server() {kv := new(KV)kv.data = map[string]string{}rpcs := rpc.NewServer()rpcs.Register(kv)l, e := net.Listen("tcp", ":3306")if e != nil {log.Fatal("listen error:", e)}go func() {for {conn, err := l.Accept()if err == nil {go rpcs.ServeConn(conn)} else {break}}l.Close()}()
}func (kv *KV) Get(args *GetArgs, reply *GetReply) error {kv.mu.Lock()defer kv.mu.Unlock()val, ok := kv.data[args.Key]if ok {reply.Err = OKreply.Value = val} else {reply.Err = ErrNoKeyreply.Value = ""}return nil
}func (kv *KV) Put(args *PutArgs, reply *PutReply) error {kv.mu.Lock()defer kv.mu.Unlock()kv.data[args.Key] = args.Valuereply.Err = OKreturn nil
}//
// main
//func main() {server()time.Sleep(time.Second * 10)
}

client

package mainimport ("fmt""log""net/rpc"
)//
// Common RPC request/reply definitions
//const (OK       = "OK"ErrNoKey = "ErrNoKey"
)type Err stringtype PutArgs struct {Key   stringValue string
}type PutReply struct {Err Err
}type GetArgs struct {Key string
}type GetReply struct {Err   ErrValue string
}//
// Client
//func connect() *rpc.Client {client, err := rpc.Dial("tcp", ":3306")if err != nil {log.Fatal("dialing:", err)}return client
}func get(key string) string {client := connect()args := GetArgs{"subject"}reply := GetReply{}err := client.Call("KV.Get", &args, &reply)if err != nil {log.Fatal("error:", err)}client.Close()return reply.Value
}func put(key string, val string) {client := connect()args := PutArgs{"subject", "6.824"}reply := PutReply{}err := client.Call("KV.Put", &args, &reply)if err != nil {log.Fatal("error:", err)}client.Close()
}func main() {put("subject", "6.824")fmt.Printf("Put(subject, 6.824) done\n")fmt.Printf("get(subject) -> %s\n", get("subject"))
}

Result

Put(subject, 6.824) done
get(subject) -> 6.824