go-micro client 客户端

　　go-micro 支持很多通信协议：http、tcp、grpc等，支持的编码方式也很多有json、protobuf、bytes、jsonrpc等。也可以根据自己的需要实现通信协议和编码方式。go-micro 默认的通信协议是http，默认的编码方式是protobuf。

　　主要代码定义如下：

// Client is the interface used to make requests to services.
// It supports Request/Response via Transport and Publishing via the Broker.
// It also supports bidiectional streaming of requests.
type Client interface {
	Init(...Option) error
	Options() Options
	NewMessage(topic string, msg interface{}, opts ...MessageOption) Message
	NewRequest(service, method string, req interface{}, reqOpts ...RequestOption) Request
	Call(ctx context.Context, req Request, rsp interface{}, opts ...CallOption) error
	Stream(ctx context.Context, req Request, opts ...CallOption) (Stream, error)
	Publish(ctx context.Context, msg Message, opts ...PublishOption) error
	String() string
}

// Message is the interface for publishing asynchronously
type Message interface {
	Topic() string
	Payload() interface{}
	ContentType() string
}

// Request is the interface for a synchronous request used by Call or Stream
type Request interface {
	Service() string
	Method() string
	ContentType() string
	Request() interface{}
	// indicates whether the request will be a streaming one rather than unary
	Stream() bool
}

// Stream is the inteface for a bidirectional synchronous stream
type Stream interface {
	Context() context.Context
	Request() Request
	Send(interface{}) error
	Recv(interface{}) error
	Error() error
	Close() error
}

// Option used by the Client
type Option func(*Options)

// CallOption used by Call or Stream
type CallOption func(*CallOptions)

// PublishOption used by Publish
type PublishOption func(*PublishOptions)

// MessageOption used by NewMessage
type MessageOption func(*MessageOptions)

// RequestOption used by NewRequest
type RequestOption func(*RequestOptions)

　　

　　client的连接使用了pool，减少生成和销毁的开销，不够用的话就另外生成：

func newPool(size int, ttl time.Duration) *pool {
	return &pool{
		size:  size,
		ttl:   int64(ttl.Seconds()),
		conns: make(map[string][]*poolConn),
	}
}

// NoOp the Close since we manage it
func (p *poolConn) Close() error {
	return nil
}

func (p *pool) getConn(addr string, tr transport.Transport, opts ...transport.DialOption) (*poolConn, error) {
	p.Lock()
	conns := p.conns[addr]
	now := time.Now().Unix()

	// while we have conns check age and then return one
	// otherwise we'll create a new conn
	for len(conns) > 0 {
		conn := conns[len(conns)-1]
		conns = conns[:len(conns)-1]
		p.conns[addr] = conns

		// if conn is old kill it and move on
		if d := now - conn.created; d > p.ttl {
			conn.Client.Close()
			continue
		}

		// we got a good conn, lets unlock and return it
		p.Unlock()

		return conn, nil
	}

	p.Unlock()

	// create new conn
	c, err := tr.Dial(addr, opts...)
	if err != nil {
		return nil, err
	}
	return &poolConn{c, time.Now().Unix()}, nil
}

func (p *pool) release(addr string, conn *poolConn, err error) {
	// don't store the conn if it has errored
	if err != nil {
		conn.Client.Close()
		return
	}

	// otherwise put it back for reuse
	p.Lock()
	conns := p.conns[addr]
	if len(conns) >= p.size {
		p.Unlock()
		conn.Client.Close()
		return
	}
	p.conns[addr] = append(conns, conn)
	p.Unlock()
}

　　封装request：

type rpcRequest struct {
	service     string
	method      string
	contentType string
	request     interface{}
	opts        RequestOptions
}

func newRequest(service, method string, request interface{}, contentType string, reqOpts ...RequestOption) Request {
	var opts RequestOptions

	for _, o := range reqOpts {
		o(&opts)
	}

	// set the content-type specified
	if len(opts.ContentType) > 0 {
		contentType = opts.ContentType
	}

	return &rpcRequest{
		service:     service,
		method:      method,
		request:     request,
		contentType: contentType,
		opts:        opts,
	}
}

　　

　　调用接口：

func (r *rpcClient) Call(ctx context.Context, request Request, response interface{}, opts ...CallOption) error {
	// make a copy of call opts
	callOpts := r.opts.CallOptions
	for _, opt := range opts {
		opt(&callOpts)
	}

	next, err := r.next(request, callOpts)
	if err != nil {
		return err
	}

	// check if we already have a deadline
	d, ok := ctx.Deadline()
	if !ok {
		// no deadline so we create a new one
		ctx, _ = context.WithTimeout(ctx, callOpts.RequestTimeout)
	} else {
		// got a deadline so no need to setup context
		// but we need to set the timeout we pass along
		opt := WithRequestTimeout(d.Sub(time.Now()))
		opt(&callOpts)
	}

	// should we noop right here?
	select {
	case <-ctx.Done():
		return errors.New("go.micro.client", fmt.Sprintf("%v", ctx.Err()), 408)
	default:
	}

	// make copy of call method
	rcall := r.call

	// wrap the call in reverse
	for i := len(callOpts.CallWrappers); i > 0; i-- {
		rcall = callOpts.CallWrappers[i-1](rcall)
	}

	// return errors.New("go.micro.client", "request timeout", 408)
	call := func(i int) error {
		// call backoff first. Someone may want an initial start delay
		t, err := callOpts.Backoff(ctx, request, i)
		if err != nil {
			return errors.InternalServerError("go.micro.client", "backoff error: %v", err.Error())
		}

		// only sleep if greater than 0
		if t.Seconds() > 0 {
			time.Sleep(t)
		}

		// select next node
		node, err := next()
		if err != nil && err == selector.ErrNotFound {
			return errors.NotFound("go.micro.client", "service %s: %v", request.Service(), err.Error())
		} else if err != nil {
			return errors.InternalServerError("go.micro.client", "error getting next %s node: %v", request.Service(), err.Error())
		}

		// set the address
		address := node.Address
		if node.Port > 0 {
			address = fmt.Sprintf("%s:%d", address, node.Port)
		}

		// make the call
		err = rcall(ctx, address, request, response, callOpts)
		r.opts.Selector.Mark(request.Service(), node, err)
		return err
	}

	ch := make(chan error, callOpts.Retries)
	var gerr error

	for i := 0; i <= callOpts.Retries; i++ {
		go func(i int) {
			ch <- call(i)
		}(i)

		select {
		case <-ctx.Done():
			return errors.New("go.micro.client", fmt.Sprintf("call timeout: %v", ctx.Err()), 408)
		case err := <-ch:
			// if the call succeeded lets bail early
			if err == nil {
				return nil
			}

			retry, rerr := callOpts.Retry(ctx, request, i, err)
			if rerr != nil {
				return rerr
			}

			if !retry {
				return err
			}

			gerr = err
		}
	}

	return gerr
}