client.go

package zrpc

import (
	"bufio"
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"log"
	"net"
	"net/http"
	"strings"
	"sync"
	"time"

	"github.com/ilaziness/zrpc/codec"
)

// Call 代表一次rpc调用的信息
type Call struct {
	Seq           uint64      // 请求ID
	ServiceMethod string      // 格式 "<service>.<method>"
	Args          interface{} // 参数
	Reply         interface{} // 回复
	Error         error       // 发送的错误
	Done          chan *Call  // 调用完成时写值
}

// done 调用结束通知调用方已完成
func (call *Call) done() {
	call.Done <- call
}

// Client rpc客户端，主要完成发送请求和接收返回结果
type Client struct {
	cc       codec.Codec // 编解码器，编码发送数据，解码接收数据
	opt      *Option
	sending  sync.Mutex // 保证请求有序发送
	header   codec.Header
	mu       sync.Mutex       // protect following
	seq      uint64           //请求编号ID
	pending  map[uint64]*Call //保存未处理完的请求，键是请求编号
	closing  bool             // 调用完毕已关闭
	shutdown bool             // 服务器已断开，一般是有错误发生导致
}

var _ io.Closer = (*Client)(nil)

var ErrShutdown = errors.New("connection is shut down")

// Close 关闭连接
func (client *Client) Close() error {
	client.mu.Lock()
	defer client.mu.Unlock()
	if client.closing {
		return ErrShutdown
	}
	client.closing = true
	return client.cc.Close()
}

// IsAvailable 客户端工作正常返回true
func (client *Client) IsAvailable() bool {
	client.mu.Lock()
	defer client.mu.Unlock()
	return !client.shutdown && !client.closing
}

// registerCall 把Call添加到pending，更新seq编号
func (client *Client) registerCall(call *Call) (uint64, error) {
	client.mu.Lock()
	defer client.mu.Unlock()
	if client.closing || client.shutdown {
		return 0, ErrShutdown
	}
	call.Seq = client.seq
	client.pending[call.Seq] = call
	client.seq++
	return call.Seq, nil
}

// removeCall 移除pending的call并返回
func (client *Client) removeCall(seq uint64) *Call {
	client.mu.Lock()
	defer client.mu.Unlock()
	call := client.pending[seq]
	delete(client.pending, seq)
	return call
}

// terminateCalls 客户端或者服务器发生错误时，结束所有待完成call，并通知错误信息
func (client *Client) terminateCalls(err error) {
	client.sending.Lock()
	defer client.sending.Unlock()
	client.mu.Lock()
	defer client.mu.Unlock()
	client.shutdown = true
	for _, call := range client.pending {
		call.Error = err
		call.done()
	}
}

// receive 接收响应
func (client *Client) receive() {
	var err error
	for err == nil {
		var h codec.Header
		if err = client.cc.ReadHeader(&h); err != nil {
			break
		}
		call := client.removeCall(h.Seq)
		switch {
		case call == nil:
			// 通常是写失败了或call已经被移除了
			err = client.cc.ReadBody(nil)
		case h.Error != "":
			// 服务端有错误发生
			call.Error = fmt.Errorf(h.Error)
			err = client.cc.ReadBody(nil)
			call.done()
		default:
			// 正常
			err = client.cc.ReadBody(call.Reply)
			if err != nil {
				call.Error = errors.New("reading body " + err.Error())
			}
			call.done()
		}
	}
	// 发生错误结束
	client.terminateCalls(err)
}

// NewClient 创建Clint实例
func NewClient(conn net.Conn, opt *Option) (*Client, error) {
	f := codec.NewCodecFuncMap[opt.CodecType]
	if f == nil {
		err := fmt.Errorf("invalid codec type %s", opt.CodecType)
		log.Println("rpc client: codec error:", err)
		return nil, err
	}
	// 先发送option到服务器，协商数据内容
	if err := json.NewEncoder(conn).Encode(opt); err != nil {
		log.Println("rpc client: options error: ", err)
		_ = conn.Close()
		return nil, err
	}
	return newClientCodec(f(conn), opt), nil
}

// NewHTTPClient new a Client instance via HTTP as transport protocol
func NewHTTPClient(conn net.Conn, opt *Option) (*Client, error) {
	_, _ = io.WriteString(conn, fmt.Sprintf("CONNECT %s HTTP/1.0\n\n", defaultRPCPath))

	// Require successful HTTP response
	// before switching to RPC protocol.
	resp, err := http.ReadResponse(bufio.NewReader(conn), &http.Request{Method: "CONNECT"})
	if err == nil && resp.Status == connected {
		return NewClient(conn, opt)
	}
	if err == nil {
		err = errors.New("unexpected HTTP response: " + resp.Status)
	}
	return nil, err
}

// newClientCodec 创建客户端编解码器
func newClientCodec(cc codec.Codec, opt *Option) *Client {
	client := &Client{
		seq:     1, // seq starts with 1, 0 means invalid call
		cc:      cc,
		opt:     opt,
		pending: make(map[uint64]*Call),
	}
	// 开启协程处理响应
	go client.receive()
	return client
}

// parseOptions 实现option为可选参数
func parseOptions(opts ...*Option) (*Option, error) {
	if len(opts) == 0 || opts[0] == nil {
		// 默认option
		return DefaultOption, nil
	}
	if len(opts) != 1 {
		return nil, errors.New("number of options is more than 1")
	}
	opt := opts[0]
	if opt.CodecType == "" {
		// 默认编解码器类型
		opt.CodecType = DefaultOption.CodecType
	}
	return opt, nil
}

type clientResult struct {
	client *Client
	err    error
}

// newClientFunc创建客户端方法
type newClientFunc func(conn net.Conn, opt *Option) (client *Client, err error)

func dialTimeout(f newClientFunc, network, address string, opts ...*Option) (client *Client, err error) {
	opt, err := parseOptions(opts...)
	if err != nil {
		return nil, err
	}
	// 用带超时控制的连接DialTimeout
	conn, err := net.DialTimeout(network, address, opt.ConnectTimeout)
	if err != nil {
		return nil, err
	}
	defer func() {
		if client == nil {
			_ = conn.Close()
		}
	}()

	// 连接服务器完成，创建rpc客户端对象
	ch := make(chan clientResult)
	go func() {
		client, err := f(conn, opt)
		ch <- clientResult{client: client, err: err}
	}()
	if opt.ConnectTimeout == 0 {
		result := <-ch
		return result.client, result.err
	}
	// 判断是否超时
	select {
	case <-time.After(opt.ConnectTimeout):
		return nil, fmt.Errorf("rpc client: connect timeout: expect within %s", opt.ConnectTimeout)
	case result := <-ch:
		return result.client, result.err
	}
}

// Dial 连接RPC服务器
func Dial(network, address string, opts ...*Option) (client *Client, err error) {
	return dialTimeout(NewClient, network, address, opts...)
}

// DialHTTP connects to an HTTP RPC server at the specified network address
// listening on the default HTTP RPC path.
func DialHTTP(network, address string, opts ...*Option) (*Client, error) {
	return dialTimeout(NewHTTPClient, network, address, opts...)
}

// XDial calls different functions to connect to a RPC server
// according the first parameter rpcAddr.
// rpcAddr is a general format (protocol@addr) to represent a rpc server
// eg, http@10.0.0.1:7001, tcp@10.0.0.1:9999, unix@/tmp/geerpc.sock
func XDial(rpcAddr string, opts ...*Option) (*Client, error) {
	parts := strings.Split(rpcAddr, "@")
	if len(parts) != 2 {
		return nil, fmt.Errorf("rpc client err: wrong format '%s', expect protocol@addr", rpcAddr)
	}
	protocol, addr := parts[0], parts[1]
	switch protocol {
	case "http":
		return DialHTTP("tcp", addr, opts...)
	default:
		// tcp, unix or other transport protocol
		return Dial(protocol, addr, opts...)
	}
}

// Go 异步调用接口，返回调用对象
func (client *Client) Go(serviceMethod string, args, reply interface{}, done chan *Call) *Call {
	if done == nil {
		done = make(chan *Call, 10)
	} else if cap(done) == 0 {
		log.Panic("rpc client: done channel is unbuffered")
	}
	call := &Call{
		ServiceMethod: serviceMethod,
		Args:          args,
		Reply:         reply,
		Done:          done,
	}
	client.send(call)
	return call
}

// Call 发起rpc调用，等待完成
func (client *Client) Call(ctx context.Context, serviceMethod string, args, reply interface{}) error {
	call := client.Go(serviceMethod, args, reply, make(chan *Call, 1))
	// 超时控制
	select {
	case <-ctx.Done():
		client.removeCall(call.Seq)
		return errors.New("rpc client: call failed: " + ctx.Err().Error())
	case <-call.Done:
		return call.Error
	}
}

// send 发送rpc请求
func (client *Client) send(call *Call) {
	// make sure that the client will send a complete request
	client.sending.Lock()
	defer client.sending.Unlock()

	// 注册call
	seq, err := client.registerCall(call)
	if err != nil {
		call.Error = err
		call.done()
		return
	}

	// 准备header
	client.header.ServiceMethod = call.ServiceMethod
	client.header.Seq = seq
	client.header.Error = ""

	// 编码发送请求
	if err := client.cc.Write(&client.header, call.Args); err != nil {
		call := client.removeCall(seq)
		// call may be nil, it usually means that Write partially failed,
		// client has received the response and handled
		if call != nil {
			call.Error = err
			call.done()
		}
	}
}