server.go

package minirpc

import (
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"log"
	"minirpc/codec"
	"net"
	"net/http"
	"reflect"
	"strings"
	"sync"
	"time"
)

const MagicNumber = 0x3bef5c

const (
	connected        = "200 Connected to Mini RPC"
	defaultRPCPath   = "/_minirpc_"
	defaultDebugPath = "/debug/minirpc"
)

type Option struct {
	MagicNumber    int           // MagicNumber marks this's a minirpc request
	CodecType      codec.Type    // client may choose different Codec to encode body
	ConnectTimeout time.Duration // 0 means no limit
	HandleTimeout  time.Duration
}

var DefaultOption = &Option{
	MagicNumber:    MagicNumber,
	CodecType:      codec.GobType,
	ConnectTimeout: time.Second * 10,
}

// Server represents an RPC Server
type Server struct {
	serviceMap sync.Map
}

func NewServer() *Server {
	return &Server{}
}

var DefaultServer = NewServer()

// 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), &opt)
}

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

func (server *Server) serveCodec(cc codec.Codec, opt *Option) {
	sending := new(sync.Mutex) // make sure to send a complete response
	wg := new(sync.WaitGroup)  // wait until all request are handled
	for {
		// 读取请求
		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()
			// 回复请求报文必须逐个发送，并发易导致客户端无法解析，使用锁 sending 保证
			server.sendResponse(cc, req.h, invalidRequest, sending)
			continue
		}
		wg.Add(1)
		// 并发处理请求
		go server.handleRequest(cc, req, sending, wg, opt.HandleTimeout)
	}
	wg.Wait()
	_ = cc.Close()
}

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

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}
	req.svc, req.mtype, err = server.findService(h.ServiceMethod)
	if err != nil {
		return req, err
	}
	// 创建两个入参实例
	req.argv = req.mtype.newArgv()
	req.replyv = req.mtype.newReplyv()

	// make sure that argvi is a pointer, ReadBody need a pointer as parameter
	argvi := req.argv.Interface()
	if req.argv.Type().Kind() != reflect.Ptr {
		argvi = req.argv.Addr().Interface()
	}
	// 将请求报文反序列化为第一个入参 argv
	if err = cc.ReadBody(argvi); err != nil {
		log.Println("rpc server: read body err: ", err)
		return req, 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 err: ", err)
	}
}

// 处理超时实现与客户端类似，使用 time.After 结合 select + chan
// 这里需要确保 sendResponse 仅调用一次，因此将整个过程拆分为 called 和 sent 两个阶段，在这段代码中只会发生如下两种情况：
// called 信道接收到消息，代表处理没有超时，继续执行 sendResponse
// time.After() 先于 called 接收到消息，说明处理已经超时，called 和 sent 都将被阻塞。在 case <-time.After(timeout) 处调用 sendResponse
func (server *Server) handleRequest(cc codec.Codec, req *request, sending *sync.Mutex, wg *sync.WaitGroup, timeout time.Duration) {
	defer wg.Done()
	called := make(chan struct{})
	sent := make(chan struct{})
	go func() {
		err := req.svc.call(req.mtype, req.argv, req.replyv)
		called <- struct{}{}
		if err != nil {
			req.h.Error = err.Error()
			server.sendResponse(cc, req.h, invalidRequest, sending)
			sent <- struct{}{}
			return
		}
		server.sendResponse(cc, req.h, req.replyv.Interface(), sending)
		sent <- struct{}{}
	}()

	if timeout == 0 {
		<-called
		<-sent
		return
	}
	select {
	case <-time.After(timeout):
		req.h.Error = fmt.Sprintf("rpc server: request handle timeout: expect within %s", timeout)
		server.sendResponse(cc, req.h, invalidRequest, sending)
	case <-called:
		<-sent
	}
}

// accepts connections on the listener and serves requests for each incomming connection.
func (server *Server) Accept(lis net.Listener) {
	// for 循环等待 socket 连接建立并开启子协程处理，处理过程交给 ServeConn
	for {
		conn, err := lis.Accept()
		if err != nil {
			log.Println("rpc server: accept error: ", err)
			return
		}
		go server.ServeConn(conn)
	}
}

func Accept(lis net.Listener) {
	DefaultServer.Accept(lis)
}

func (server *Server) Register(rcvr interface{}) error {
	s := newService(rcvr)
	if _, dup := server.serviceMap.LoadOrStore(s.name, s); dup {
		return errors.New("rpc: service already defined: " + s.name)
	}
	return nil
}

// Register publishes the receiver's methods in the DefaultServer
func Register(rcvr interface{}) error { return DefaultServer.Register(rcvr) }

func (server *Server) findService(serviceMethod string) (svc *service, mtype *methodType, err error) {
	// 对Service.Method 进行分割
	dot := strings.LastIndex(serviceMethod, ".")
	if dot < 0 {
		err = errors.New("rpc server: service/method request ill-formed: " + serviceMethod)
		return
	}
	serviceName, methodName := serviceMethod[:dot], serviceMethod[dot+1:]
	// 从 serviceMap 中找对应 service 实例
	svci, ok := server.serviceMap.Load(serviceName)
	if !ok {
		err = errors.New("rpc server: can't find service " + serviceName)
		return
	}
	svc = svci.(*service)
	// 再从实例 method 中找对应
	mtype = svc.method[methodName]
	if mtype == nil {
		err = errors.New("rpc server: can't find method " + methodName)
	}
	return
}

// ServeHTTP implements an http.Handler that answers RPC requests.
func (server *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	if r.Method != "CONNECT" {
		w.Header().Set("Content-Type", "text/plain; charset=utf-8")
		w.WriteHeader(http.StatusMethodNotAllowed)
		_, _ = io.WriteString(w, "405 must CONNECT\n")
		return
	}
	conn, _, err := w.(http.Hijacker).Hijack()
	if err != nil {
		log.Print("rpc hijacking ", r.RemoteAddr, ": ", err.Error())
		return
	}
	_, _ = io.WriteString(conn, "HTTP/1.0 "+connected+"\n\n")
	server.ServeConn(conn)
}

// HandleHTTP registers an HTTP handler for RPC messages on rpcPath
// It's still necessary to invoke http.Serve(), typically in a go statement
func (server *Server) HandleHTTP() {
	http.Handle(defaultRPCPath, server)
}

// HandleHTTP is a convenient approach for default server to register HTTP handlers
func HandleHTTP() {
	DefaultServer.HandleHTTP()
}