Golang Context.Err方法代码示例

// GetBlocks returns a channel where the caller may receive blocks that
// correspond to the provided |keys|. Returns an error if BitSwap is unable to
// begin this request within the deadline enforced by the context.
//
// NB: Your request remains open until the context expires. To conserve
// resources, provide a context with a reasonably short deadline (ie. not one
// that lasts throughout the lifetime of the server)
func (bs *Bitswap) GetBlocks(ctx context.Context, keys []key.Key) (<-chan *blocks.Block, error) {
	select {
	case <-bs.process.Closing():
		return nil, errors.New("bitswap is closed")
	default:
	}
	promise := bs.notifications.Subscribe(ctx, keys...)

	for _, k := range keys {
		log.Event(ctx, "Bitswap.GetBlockRequest.Start", &k)
	}

	bs.wm.WantBlocks(keys)

	req := &blockRequest{
		keys: keys,
		ctx:  ctx,
	}
	select {
	case bs.findKeys <- req:
		return promise, nil
	case <-ctx.Done():
		return nil, ctx.Err()
	}
}

func readMsgCtx(ctx context.Context, r msgio.Reader, p proto.Message) ([]byte, error) {
	var msg []byte

	// read in a goroutine so we can exit when our context is cancelled.
	done := make(chan error)
	go func() {
		var err error
		msg, err = r.ReadMsg()
		select {
		case done <- err:
		case <-ctx.Done():
		}
	}()

	select {
	case <-ctx.Done():
		return nil, ctx.Err()
	case e := <-done:
		if e != nil {
			return nil, e
		}
	}

	return msg, proto.Unmarshal(msg, p)
}

// gatedDialAttempt is an attempt to dial a node. It is gated by the swarm's
// dial synchronization systems: dialsync and dialbackoff.
func (s *Swarm) gatedDialAttempt(ctx context.Context, p peer.ID) (*Conn, error) {
	var logdial = lgbl.Dial("swarm", s.LocalPeer(), p, nil, nil)
	defer log.EventBegin(ctx, "swarmDialAttemptSync", logdial).Done()

	// check if we already have an open connection first
	conn := s.bestConnectionToPeer(p)
	if conn != nil {
		return conn, nil
	}

	// check if there's an ongoing dial to this peer
	if ok, wait := s.dsync.Lock(p); ok {
		// ok, we have been charged to dial! let's do it.
		// if it succeeds, dial will add the conn to the swarm itself.

		defer log.EventBegin(ctx, "swarmDialAttemptStart", logdial).Done()
		ctxT, cancel := context.WithTimeout(ctx, s.dialT)
		conn, err := s.dial(ctxT, p)
		cancel()
		s.dsync.Unlock(p)
		log.Debugf("dial end %s", conn)
		if err != nil {
			log.Event(ctx, "swarmDialBackoffAdd", logdial)
			s.backf.AddBackoff(p) // let others know to backoff

			// ok, we failed. try again. (if loop is done, our error is output)
			return nil, fmt.Errorf("dial attempt failed: %s", err)
		}
		log.Event(ctx, "swarmDialBackoffClear", logdial)
		s.backf.Clear(p) // okay, no longer need to backoff
		return conn, nil

	} else {
		// we did not dial. we must wait for someone else to dial.

		// check whether we should backoff first...
		if s.backf.Backoff(p) {
			log.Event(ctx, "swarmDialBackoff", logdial)
			return nil, ErrDialBackoff
		}

		defer log.EventBegin(ctx, "swarmDialWait", logdial).Done()
		select {
		case <-wait: // wait for that other dial to finish.

			// see if it worked, OR we got an incoming dial in the meantime...
			conn := s.bestConnectionToPeer(p)
			if conn != nil {
				return conn, nil
			}
			return nil, ErrDialFailed
		case <-ctx.Done(): // or we may have to bail...
			return nil, ctx.Err()
		}
	}
}

// Fsync flushes the content in the file to disk, but does not
// update the dag tree internally
func (fi *File) Fsync(ctx context.Context, req *fuse.FsyncRequest) error {
	errs := make(chan error, 1)
	go func() {
		errs <- fi.fi.Sync()
	}()
	select {
	case err := <-errs:
		return err
	case <-ctx.Done():
		return ctx.Err()
	}
}

// Run runs the query at hand. pass in a list of peers to use first.
func (q *dhtQuery) Run(ctx context.Context, peers []peer.ID) (*dhtQueryResult, error) {
	select {
	case <-ctx.Done():
		return nil, ctx.Err()
	default:
	}

	ctx, cancel := context.WithCancel(ctx)
	defer cancel()

	runner := newQueryRunner(q)
	return runner.Run(ctx, peers)
}

func (np *nodePromise) Get(ctx context.Context) (*Node, error) {
	if np.cache != nil {
		return np.cache, nil
	}

	select {
	case blk := <-np.recv:
		np.cache = blk
	case <-np.ctx.Done():
		return nil, np.ctx.Err()
	case <-ctx.Done():
		return nil, ctx.Err()
	}
	return np.cache, 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
}

func (fi *File) Read(ctx context.Context, req *fuse.ReadRequest, resp *fuse.ReadResponse) error {
	_, err := fi.fi.Seek(req.Offset, os.SEEK_SET)
	if err != nil {
		return err
	}

	fisize, err := fi.fi.Size()
	if err != nil {
		return err
	}

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

	readsize := min(req.Size, int(fisize-req.Offset))
	n, err := fi.fi.CtxReadFull(ctx, resp.Data[:readsize])
	resp.Data = resp.Data[:n]
	return err
}

// GetBlock attempts to retrieve a particular block from peers within the
// deadline enforced by the context.
func (bs *Bitswap) GetBlock(parent context.Context, k key.Key) (*blocks.Block, error) {

	// Any async work initiated by this function must end when this function
	// returns. To ensure this, derive a new context. Note that it is okay to
	// listen on parent in this scope, but NOT okay to pass |parent| to
	// functions called by this one. Otherwise those functions won't return
	// when this context's cancel func is executed. This is difficult to
	// enforce. May this comment keep you safe.

	ctx, cancelFunc := context.WithCancel(parent)

	ctx = logging.ContextWithLoggable(ctx, logging.Uuid("GetBlockRequest"))
	log.Event(ctx, "Bitswap.GetBlockRequest.Start", &k)
	defer log.Event(ctx, "Bitswap.GetBlockRequest.End", &k)

	defer func() {
		cancelFunc()
	}()

	promise, err := bs.GetBlocks(ctx, []key.Key{k})
	if err != nil {
		return nil, err
	}

	select {
	case block, ok := <-promise:
		if !ok {
			select {
			case <-ctx.Done():
				return nil, ctx.Err()
			default:
				return nil, errors.New("promise channel was closed")
			}
		}
		return block, nil
	case <-parent.Done():
		return nil, parent.Err()
	}
}

func (c *Client) FindProvidersAsync(ctx context.Context, k key.Key, max int) <-chan peer.PeerInfo {
	ctx = logging.ContextWithLoggable(ctx, logging.Uuid("findProviders"))
	defer log.EventBegin(ctx, "findProviders", &k).Done()
	ch := make(chan peer.PeerInfo)
	go func() {
		defer close(ch)
		request := pb.NewMessage(pb.Message_GET_PROVIDERS, string(k), 0)
		response, err := c.proxy.SendRequest(ctx, request)
		if err != nil {
			log.Debug(err)
			return
		}
		for _, p := range pb.PBPeersToPeerInfos(response.GetProviderPeers()) {
			select {
			case <-ctx.Done():
				log.Debug(ctx.Err())
				return
			case ch <- p:
			}
		}
	}()
	return ch
}

// writeMsgCtx is used by the
func writeMsgCtx(ctx context.Context, w msgio.Writer, msg proto.Message) ([]byte, error) {
	enc, err := proto.Marshal(msg)
	if err != nil {
		return nil, err
	}

	// write in a goroutine so we can exit when our context is cancelled.
	done := make(chan error)
	go func(m []byte) {
		err := w.WriteMsg(m)
		select {
		case done <- err:
		case <-ctx.Done():
		}
	}(enc)

	select {
	case <-ctx.Done():
		return nil, ctx.Err()
	case e := <-done:
		return enc, e
	}
}

// nextEnvelope runs in the taskWorker goroutine. Returns an error if the
// context is cancelled before the next Envelope can be created.
func (e *Engine) nextEnvelope(ctx context.Context) (*Envelope, error) {
	for {
		nextTask := e.peerRequestQueue.Pop()
		for nextTask == nil {
			select {
			case <-ctx.Done():
				return nil, ctx.Err()
			case <-e.workSignal:
				nextTask = e.peerRequestQueue.Pop()
			}
		}

		// with a task in hand, we're ready to prepare the envelope...

		block, err := e.bs.Get(nextTask.Entry.Key)
		if err != nil {
			// If we don't have the block, don't hold that against the peer
			// make sure to update that the task has been 'completed'
			nextTask.Done()
			continue
		}

		return &Envelope{
			Peer:  nextTask.Target,
			Block: block,
			Sent: func() {
				nextTask.Done()
				select {
				case e.workSignal <- struct{}{}:
					// work completing may mean that our queue will provide new
					// work to be done.
				default:
				}
			},
		}, nil
	}
}

// dialPeer opens a connection to peer, and makes sure to identify
// the connection once it has been opened.
func (h *BasicHost) dialPeer(ctx context.Context, p peer.ID) error {
	log.Debugf("host %s dialing %s", h.ID, p)
	c, err := h.Network().DialPeer(ctx, p)
	if err != nil {
		return err
	}

	// identify the connection before returning.
	done := make(chan struct{})
	go func() {
		h.ids.IdentifyConn(c)
		close(done)
	}()

	// respect don contexteone
	select {
	case <-done:
	case <-ctx.Done():
		return ctx.Err()
	}

	log.Debugf("host %s finished dialing %s", h.ID, p)
	return nil
}

// Dial connects to a peer over a particular address
// Ensures raddr is part of peer.Addresses()
// Example: d.DialAddr(ctx, peer.Addresses()[0], peer)
func (d *Dialer) Dial(ctx context.Context, raddr ma.Multiaddr, remote peer.ID) (Conn, error) {
	logdial := lgbl.Dial("conn", d.LocalPeer, remote, nil, raddr)
	logdial["encrypted"] = (d.PrivateKey != nil) // log wether this will be an encrypted dial or not.
	defer log.EventBegin(ctx, "connDial", logdial).Done()

	var connOut Conn
	var errOut error
	done := make(chan struct{})

	// do it async to ensure we respect don contexteone
	go func() {
		defer func() {
			select {
			case done <- struct{}{}:
			case <-ctx.Done():
			}
		}()

		maconn, err := d.rawConnDial(ctx, raddr, remote)
		if err != nil {
			errOut = err
			return
		}

		if d.Wrapper != nil {
			maconn = d.Wrapper(maconn)
		}

		c, err := newSingleConn(ctx, d.LocalPeer, remote, maconn)
		if err != nil {
			maconn.Close()
			errOut = err
			return
		}

		if d.PrivateKey == nil || EncryptConnections == false {
			log.Warning("dialer %s dialing INSECURELY %s at %s!", d, remote, raddr)
			connOut = c
			return
		}

		c2, err := newSecureConn(ctx, d.PrivateKey, c)
		if err != nil {
			errOut = err
			c.Close()
			return
		}

		connOut = c2
	}()

	select {
	case <-ctx.Done():
		logdial["error"] = ctx.Err()
		logdial["dial"] = "failure"
		return nil, ctx.Err()
	case <-done:
		// whew, finished.
	}

	if errOut != nil {
		logdial["error"] = errOut
		logdial["dial"] = "failure"
		return nil, errOut
	}

	logdial["dial"] = "success"
	return connOut, nil
}

// FindPeersConnectedToPeer searches for peers directly connected to a given peer.
func (dht *IpfsDHT) FindPeersConnectedToPeer(ctx context.Context, id peer.ID) (<-chan peer.PeerInfo, error) {

	peerchan := make(chan peer.PeerInfo, asyncQueryBuffer)
	peersSeen := peer.Set{}

	peers := dht.routingTable.NearestPeers(kb.ConvertPeerID(id), AlphaValue)
	if len(peers) == 0 {
		return nil, kb.ErrLookupFailure
	}

	// setup the Query
	query := dht.newQuery(key.Key(id), func(ctx context.Context, p peer.ID) (*dhtQueryResult, error) {

		pmes, err := dht.findPeerSingle(ctx, p, id)
		if err != nil {
			return nil, err
		}

		var clpeers []peer.PeerInfo
		closer := pmes.GetCloserPeers()
		for _, pbp := range closer {
			pi := pb.PBPeerToPeerInfo(pbp)

			// skip peers already seen
			if _, found := peersSeen[pi.ID]; found {
				continue
			}
			peersSeen[pi.ID] = struct{}{}

			// if peer is connected, send it to our client.
			if pb.Connectedness(*pbp.Connection) == inet.Connected {
				select {
				case <-ctx.Done():
					return nil, ctx.Err()
				case peerchan <- pi:
				}
			}

			// if peer is the peer we're looking for, don't bother querying it.
			// TODO maybe query it?
			if pb.Connectedness(*pbp.Connection) != inet.Connected {
				clpeers = append(clpeers, pi)
			}
		}

		return &dhtQueryResult{closerPeers: clpeers}, nil
	})

	// run it! run it asynchronously to gen peers as results are found.
	// this does no error checking
	go func() {
		if _, err := query.Run(ctx, peers); err != nil {
			log.Debug(err)
		}

		// close the peerchan channel when done.
		close(peerchan)
	}()

	return peerchan, nil
}