Golang Context.Err方法代码示例

// Do sends an HTTP request with the provided http.Client and returns an HTTP response.
// If the client is nil, http.DefaultClient is used.
// If the context is canceled or times out, ctx.Err() will be returned.
func Do(ctx context.Context, client *http.Client, req *http.Request) (*http.Response, error) {
	if client == nil {
		client = http.DefaultClient
	}

	// Request cancelation changed in Go 1.5, see cancelreq.go and cancelreq_go14.go.
	cancel := canceler(client, req)

	type responseAndError struct {
		resp *http.Response
		err  error
	}
	result := make(chan responseAndError, 1)

	go func() {
		resp, err := client.Do(req)
		result <- responseAndError{resp, err}
	}()

	select {
	case <-ctx.Done():
		cancel()
		return nil, ctx.Err()
	case r := <-result:
		return r.resp, r.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)
}

// 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
	}
}

// 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
}

// 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 {
		defer s.dsync.Unlock(p)

		// if this peer has been backed off, lets get out of here
		if s.backf.Backoff(p) {
			log.Event(ctx, "swarmDialBackoff", logdial)
			return nil, ErrDialBackoff
		}

		// 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()
		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()
		}
	}
}

// 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
}