Golang Context.Err方法代碼示例

// GetBlock attempts to retrieve a particular block from peers within the
// deadline enforced by the context
//
// TODO ensure only one active request per key
func (bs *bitswap) Block(parent context.Context, k u.Key) (*blocks.Block, error) {
	log.Debugf("Get Block %v", k)
	now := time.Now()
	defer func() {
		log.Debugf("GetBlock took %f secs", time.Now().Sub(now).Seconds())
	}()

	ctx, cancelFunc := context.WithCancel(parent)
	defer cancelFunc()

	bs.wantlist.Add(k)
	promise := bs.notifications.Subscribe(ctx, k)

	const maxProviders = 20
	peersToQuery := bs.routing.FindProvidersAsync(ctx, k, maxProviders)

	go func() {
		message := bsmsg.New()
		for _, wanted := range bs.wantlist.Keys() {
			message.AddWanted(wanted)
		}
		for peerToQuery := range peersToQuery {
			log.Debugf("bitswap got peersToQuery: %s", peerToQuery)
			go func(p peer.Peer) {

				log.Debugf("bitswap dialing peer: %s", p)
				err := bs.sender.DialPeer(ctx, p)
				if err != nil {
					log.Errorf("Error sender.DialPeer(%s)", p)
					return
				}

				response, err := bs.sender.SendRequest(ctx, p, message)
				if err != nil {
					log.Errorf("Error sender.SendRequest(%s) = %s", p, err)
					return
				}
				// FIXME ensure accounting is handled correctly when
				// communication fails. May require slightly different API to
				// get better guarantees. May need shared sequence numbers.
				bs.strategy.MessageSent(p, message)

				if response == nil {
					return
				}
				bs.ReceiveMessage(ctx, p, response)
			}(peerToQuery)
		}
	}()

	select {
	case block := <-promise:
		bs.wantlist.Remove(k)
		return &block, nil
	case <-parent.Done():
		return nil, parent.Err()
	}
}

// Handshake3 exchanges local and remote service information
func Handshake3(ctx context.Context, c Conn) (*handshake.Handshake3Result, error) {
	rpeer := c.RemotePeer()
	lpeer := c.LocalPeer()

	// setup + send the message to remote
	var remoteH, localH *hspb.Handshake3
	localH = handshake.Handshake3Msg(lpeer, c.RemoteMultiaddr())
	localB, err := proto.Marshal(localH)
	if err != nil {
		return nil, err
	}

	c.Out() <- localB
	log.Debugf("Handshake1: sent to %s", rpeer)

	// wait + listen for response
	select {
	case <-ctx.Done():
		return nil, ctx.Err()

	case <-c.Closing():
		return nil, errors.New("Handshake3: error remote connection closed")

	case remoteB, ok := <-c.In():
		if !ok {
			return nil, fmt.Errorf("Handshake3 error receiving from conn: %v", rpeer)
		}

		remoteH = new(hspb.Handshake3)
		err = proto.Unmarshal(remoteB, remoteH)
		if err != nil {
			return nil, fmt.Errorf("Handshake3 could not decode remote msg: %q", err)
		}

		log.Debugf("Handshake3 received from %s", rpeer)
	}

	// actually update our state based on the new knowledge
	res, err := handshake.Handshake3Update(lpeer, rpeer, remoteH)
	if err != nil {
		log.Errorf("Handshake3 failed to update %s", rpeer)
	}
	res.RemoteObservedAddress = c.RemoteMultiaddr()
	return res, nil
}

func ContextDo(ctx context.Context, f func() error) error {

	ch := make(chan error)

	go func() {
		select {
		case <-ctx.Done():
		case ch <- f():
		}
	}()
	select {
	case <-ctx.Done():
		return ctx.Err()
	case val := <-ch:
		return val
	}
	return nil
}

// Handshake1 exchanges local and remote versions and compares them
// closes remote and returns an error in case of major difference
func Handshake1(ctx context.Context, c Conn) error {
	rpeer := c.RemotePeer()
	lpeer := c.LocalPeer()

	var remoteH, localH *hspb.Handshake1
	localH = handshake.Handshake1Msg()

	myVerBytes, err := proto.Marshal(localH)
	if err != nil {
		return err
	}

	c.Out() <- myVerBytes
	log.Debugf("Sent my version (%s) to %s", localH, rpeer)

	select {
	case <-ctx.Done():
		return ctx.Err()

	case <-c.Closing():
		return errors.New("remote closed connection during version exchange")

	case data, ok := <-c.In():
		if !ok {
			return fmt.Errorf("error retrieving from conn: %v", rpeer)
		}

		remoteH = new(hspb.Handshake1)
		err = proto.Unmarshal(data, remoteH)
		if err != nil {
			return fmt.Errorf("could not decode remote version: %q", err)
		}

		log.Debugf("Received remote version (%s) from %s", remoteH, rpeer)
	}

	if err := handshake.Handshake1Compatible(localH, remoteH); err != nil {
		log.Infof("%s (%s) incompatible version with %s (%s)", lpeer, localH, rpeer, remoteH)
		return err
	}

	log.Debugf("%s version handshake compatible %s", lpeer, rpeer)
	return nil
}

// sendMessage sends a message out (actual leg work. SendMessage is to export w/o rid)
func (s *service) sendMessage(ctx context.Context, m msg.NetMessage, rid RequestID) error {

	// serialize ServiceMessage wrapper
	data, err := wrapData(m.Data(), rid)
	if err != nil {
		return err
	}

	// log.Debug("Service send message [to = %s]", m.Peer())

	// send message
	m2 := msg.New(m.Peer(), data)
	select {
	case s.Outgoing <- m2:
	case <-ctx.Done():
		return ctx.Err()
	}

	return nil
}

func (f *fauxSender) SendRequest(ctx context.Context, m msg.NetMessage) (msg.NetMessage, error) {
	f.Lock()
	handlers := make([]mesHandleFunc, len(f.handlers))
	copy(handlers, f.handlers)
	f.Unlock()

	for _, h := range handlers {
		reply := h(m)
		if reply != nil {
			return reply, nil
		}
	}

	// no reply? ok force a timeout
	select {
	case <-ctx.Done():
	}

	return nil, ctx.Err()
}

// SendRequest sends a request message out and awaits a response.
func (s *service) SendRequest(ctx context.Context, m msg.NetMessage) (msg.NetMessage, error) {

	// check if we should bail given our contexts
	select {
	default:
	case <-s.Closing():
		return nil, fmt.Errorf("service closed: %s", s.Context().Err())
	case <-ctx.Done():
		return nil, ctx.Err()
	}

	// create a request
	r, err := NewRequest(m.Peer().ID())
	if err != nil {
		return nil, err
	}

	// register Request
	s.RequestsLock.Lock()
	s.Requests[r.Key()] = r
	s.RequestsLock.Unlock()

	// defer deleting this request
	defer func() {
		s.RequestsLock.Lock()
		delete(s.Requests, r.Key())
		s.RequestsLock.Unlock()
	}()

	// check if we should bail after waiting for mutex
	select {
	default:
	case <-s.Closing():
		return nil, fmt.Errorf("service closed: %s", s.Context().Err())
	case <-ctx.Done():
		return nil, ctx.Err()
	}

	// Send message
	s.sendMessage(ctx, m, r.ID)

	// wait for response
	m = nil
	err = nil
	select {
	case m = <-r.Response:
	case <-s.Closed():
		err = fmt.Errorf("service closed: %s", s.Context().Err())
	case <-ctx.Done():
		err = ctx.Err()
	}

	if m == nil {
		return nil, ErrNoResponse
	}

	return m, err
}