动手写RPC框架 - GeeRPC第一天 服务端与消息编码

err = client.Call("Arith.Multiply", args, &reply)

package codec

import "io"

type Header struct {
	ServiceMethod string // format "Service.Method"
	Seq           uint64 // sequence number chosen by client
	Error         string
}

type Codec interface {
	io.Closer
	ReadHeader(*Header) error
	ReadBody(interface{}) error
	Write(*Header, interface{}) error
}

type NewCodecFunc func(io.ReadWriteCloser) Codec

type Type string

const (
	GobType  Type = "application/gob"
	JsonType Type = "application/json" // not implemented
)

var NewCodecFuncMap map[Type]NewCodecFunc

func init() {
	NewCodecFuncMap = make(map[Type]NewCodecFunc)
	NewCodecFuncMap[GobType] = NewGobCodec
}

package codec

import (
	"bufio"
	"encoding/gob"
	"io"
	"log"
)

type GobCodec struct {
	conn io.ReadWriteCloser
	buf  *bufio.Writer
	dec  *gob.Decoder
	enc  *gob.Encoder
}

var _ Codec = (*GobCodec)(nil)

func NewGobCodec(conn io.ReadWriteCloser) Codec {
	buf := bufio.NewWriter(conn)
	return &GobCodec{
		conn: conn,
		buf:  buf,
		dec:  gob.NewDecoder(conn),
		enc:  gob.NewEncoder(buf),
	}
}

func (c *GobCodec) ReadHeader(h *Header) error {
	return c.dec.Decode(h)
}

func (c *GobCodec) ReadBody(body interface{}) error {
	return c.dec.Decode(body)
}

func (c *GobCodec) Write(h *Header, body interface{}) (err error) {
	defer func() {
		_ = c.buf.Flush()
		if err != nil {
			_ = c.Close()
		}
	}()
	if err := c.enc.Encode(h); err != nil {
		log.Println("rpc codec: gob error encoding header:", err)
		return err
	}
	if err := c.enc.Encode(body); err != nil {
		log.Println("rpc codec: gob error encoding body:", err)
		return err
	}
	return nil
}

func (c *GobCodec) Close() error {
	return c.conn.Close()
}

package geerpc

const MagicNumber = 0x3bef5c

type Option struct {
	MagicNumber int        // MagicNumber marks this's a geerpc request
	CodecType   codec.Type // client may choose different Codec to encode body
}

var DefaultOption = &Option{
	MagicNumber: MagicNumber,
	CodecType:   codec.GobType,
}

| Option | Header1 | Body1 | Header2 | Body2 | ...

// Server represents an RPC Server.
type Server struct{}

// NewServer returns a new Server.
func NewServer() *Server {
	return &Server{}
}

// DefaultServer is the default instance of *Server.
var DefaultServer = NewServer()

// Accept accepts connections on the listener and serves requests
// for each incoming connection.
func (server *Server) Accept(lis net.Listener) {
	for {
		conn, err := lis.Accept()
		if err != nil {
			log.Println("rpc server: accept error:", err)
			return
		}
		go server.ServeConn(conn)
	}
}

// Accept accepts connections on the listener and serves requests
// for each incoming connection.
func Accept(lis net.Listener) { DefaultServer.Accept(lis) }

lis, _ := net.Listen("tcp", ":9999")
geerpc.Accept(lis)

// ServeConn runs the server on a single connection.
// ServeConn blocks, serving the connection until the client hangs up.
func (server *Server) ServeConn(conn io.ReadWriteCloser) {
	defer func() { _ = conn.Close() }()
	var opt Option
	if err := json.NewDecoder(conn).Decode(&opt); err != nil {
		log.Println("rpc server: options error: ", err)
		return
	}
	if opt.MagicNumber != MagicNumber {
		log.Printf("rpc server: invalid magic number %x", opt.MagicNumber)
		return
	}
	f := codec.NewCodecFuncMap[opt.CodecType]
	if f == nil {
		log.Printf("rpc server: invalid codec type %s", opt.CodecType)
		return
	}
	server.serveCodec(f(conn))
}

// invalidRequest is a placeholder for response argv when error occurs
var invalidRequest = struct{}{}

func (server *Server) serveCodec(cc codec.Codec) {
	sending := new(sync.Mutex) // make sure to send a complete response
	wg := new(sync.WaitGroup)  // wait until all request are handled
	for {
		req, err := server.readRequest(cc)
		if err != nil {
			if req == nil {
				break // it's not possible to recover, so close the connection
			}
			req.h.Error = err.Error()
			server.sendResponse(cc, req.h, invalidRequest, sending)
			continue
		}
		wg.Add(1)
		go server.handleRequest(cc, req, sending, wg)
	}
	wg.Wait()
	_ = cc.Close()
}

// request stores all information of a call
type request struct {
	h            *codec.Header // header of request
	argv, replyv reflect.Value // argv and replyv of request
}

func (server *Server) readRequestHeader(cc codec.Codec) (*codec.Header, error) {
	var h codec.Header
	if err := cc.ReadHeader(&h); err != nil {
		if err != io.EOF && err != io.ErrUnexpectedEOF {
			log.Println("rpc server: read header error:", err)
		}
		return nil, err
	}
	return &h, nil
}

func (server *Server) readRequest(cc codec.Codec) (*request, error) {
	h, err := server.readRequestHeader(cc)
	if err != nil {
		return nil, err
	}
	req := &request{h: h}
	// TODO: now we don't know the type of request argv
	// day 1, just suppose it's string
	req.argv = reflect.New(reflect.TypeOf(""))
	if err = cc.ReadBody(req.argv.Interface()); err != nil {
		log.Println("rpc server: read argv err:", err)
	}
	return req, nil
}

func (server *Server) sendResponse(cc codec.Codec, h *codec.Header, body interface{}, sending *sync.Mutex) {
	sending.Lock()
	defer sending.Unlock()
	if err := cc.Write(h, body); err != nil {
		log.Println("rpc server: write response error:", err)
	}
}

func (server *Server) handleRequest(cc codec.Codec, req *request, sending *sync.Mutex, wg *sync.WaitGroup) {
	// TODO, should call registered rpc methods to get the right replyv
	// day 1, just print argv and send a hello message
	defer wg.Done()
	log.Println(req.h, req.argv.Elem())
	req.replyv = reflect.ValueOf(fmt.Sprintf("geerpc resp %d", req.h.Seq))
	server.sendResponse(cc, req.h, req.replyv.Interface(), sending)
}

package main

import (
	"encoding/json"
	"fmt"
	"geerpc"
	"geerpc/codec"
	"log"
	"net"
	"time"
)

func startServer(addr chan string) {
	// pick a free port
	l, err := net.Listen("tcp", ":0")
	if err != nil {
		log.Fatal("network error:", err)
	}
	log.Println("start rpc server on", l.Addr())
	addr <- l.Addr().String()
	geerpc.Accept(l)
}

func main() {
	addr := make(chan string)
	go startServer(addr)

	// in fact, following code is like a simple geerpc client
	conn, _ := net.Dial("tcp", <-addr)
	defer func() { _ = conn.Close() }()

	time.Sleep(time.Second)
	// send options
	_ = json.NewEncoder(conn).Encode(geerpc.DefaultOption)
	cc := codec.NewGobCodec(conn)
	// send request & receive response
	for i := 0; i < 5; i++ {
		h := &codec.Header{
			ServiceMethod: "Foo.Sum",
			Seq:           uint64(i),
		}
		_ = cc.Write(h, fmt.Sprintf("geerpc req %d", h.Seq))
		_ = cc.ReadHeader(h)
		var reply string
		_ = cc.ReadBody(&reply)
		log.Println("reply:", reply)
	}
}