Golang context.Context類代碼示例

func Logf(ctx netcontext.Context, level int64, format string, args ...interface{}) {
	if f, ok := ctx.Value(&logOverrideKey).(logOverrideFunc); ok {
		f(level, format, args...)
		return
	}
	logf(fromContext(ctx), level, format, args...)
}

// NewClientStream creates a new Stream for the client side. This is called
// by generated code.
func NewClientStream(ctx context.Context, desc *StreamDesc, cc *ClientConn, method string, opts ...CallOption) (ClientStream, error) {
	var (
		t   transport.ClientTransport
		err error
	)
	t, err = cc.dopts.picker.Pick(ctx)
	if err != nil {
		return nil, toRPCErr(err)
	}
	// TODO(zhaoq): CallOption is omitted. Add support when it is needed.
	callHdr := &transport.CallHdr{
		Host:   cc.authority,
		Method: method,
		Flush:  desc.ServerStreams && desc.ClientStreams,
	}
	if cc.dopts.cp != nil {
		callHdr.SendCompress = cc.dopts.cp.Type()
	}
	cs := &clientStream{
		desc:    desc,
		codec:   cc.dopts.codec,
		cp:      cc.dopts.cp,
		dc:      cc.dopts.dc,
		tracing: EnableTracing,
	}
	if cc.dopts.cp != nil {
		callHdr.SendCompress = cc.dopts.cp.Type()
		cs.cbuf = new(bytes.Buffer)
	}
	if cs.tracing {
		cs.trInfo.tr = trace.New("grpc.Sent."+methodFamily(method), method)
		cs.trInfo.firstLine.client = true
		if deadline, ok := ctx.Deadline(); ok {
			cs.trInfo.firstLine.deadline = deadline.Sub(time.Now())
		}
		cs.trInfo.tr.LazyLog(&cs.trInfo.firstLine, false)
		ctx = trace.NewContext(ctx, cs.trInfo.tr)
	}
	s, err := t.NewStream(ctx, callHdr)
	if err != nil {
		cs.finish(err)
		return nil, toRPCErr(err)
	}
	cs.t = t
	cs.s = s
	cs.p = &parser{s: s}
	// Listen on ctx.Done() to detect cancellation when there is no pending
	// I/O operations on this stream.
	go func() {
		select {
		case <-t.Error():
			// Incur transport error, simply exit.
		case <-s.Context().Done():
			err := s.Context().Err()
			cs.finish(err)
			cs.closeTransportStream(transport.ContextErr(err))
		}
	}()
	return cs, nil
}

// WaitForStateChange blocks until the state changes to something other than the sourceState.
func (cc *Conn) WaitForStateChange(ctx context.Context, sourceState ConnectivityState) (ConnectivityState, error) {
	cc.mu.Lock()
	defer cc.mu.Unlock()
	if sourceState != cc.state {
		return cc.state, nil
	}
	done := make(chan struct{})
	var err error
	go func() {
		select {
		case <-ctx.Done():
			cc.mu.Lock()
			err = ctx.Err()
			cc.stateCV.Broadcast()
			cc.mu.Unlock()
		case <-done:
		}
	}()
	defer close(done)
	for sourceState == cc.state {
		cc.stateCV.Wait()
		if err != nil {
			return cc.state, err
		}
	}
	return cc.state, nil
}

// Wait blocks until i) the new transport is up or ii) ctx is done or iii) cc is closed.
func (cc *Conn) Wait(ctx context.Context) (transport.ClientTransport, error) {
	for {
		cc.mu.Lock()
		switch {
		case cc.state == Shutdown:
			cc.mu.Unlock()
			return nil, ErrClientConnClosing
		case cc.state == Ready:
			cc.mu.Unlock()
			return cc.transport, nil
		default:
			ready := cc.ready
			if ready == nil {
				ready = make(chan struct{})
				cc.ready = ready
			}
			cc.mu.Unlock()
			select {
			case <-ctx.Done():
				return nil, transport.ContextErr(ctx.Err())
			// Wait until the new transport is ready or failed.
			case <-ready:
			}
		}
	}
}

func contextDone(ctx context.Context) bool {
	select {
	case <-ctx.Done():
		return true
	default:
		return false
	}
}

func WithCallOverride(ctx netcontext.Context, f CallOverrideFunc) netcontext.Context {
	// We avoid appending to any existing call override
	// so we don't risk overwriting a popped stack below.
	var cofs []CallOverrideFunc
	if uf, ok := ctx.Value(&callOverrideKey).([]CallOverrideFunc); ok {
		cofs = append(cofs, uf...)
	}
	cofs = append(cofs, f)
	return netcontext.WithValue(ctx, &callOverrideKey, cofs)
}

// wait blocks until it can receive from ctx.Done, closing, or proceed.
// If it receives from ctx.Done, it returns 0, the StreamError for ctx.Err.
// If it receives from closing, it returns 0, ErrConnClosing.
// If it receives from proceed, it returns the received integer, nil.
func wait(ctx context.Context, closing <-chan struct{}, proceed <-chan int) (int, error) {
	select {
	case <-ctx.Done():
		return 0, ContextErr(ctx.Err())
	case <-closing:
		return 0, ErrConnClosing
	case i := <-proceed:
		return i, nil
	}
}

func callOverrideFromContext(ctx netcontext.Context) (CallOverrideFunc, netcontext.Context, bool) {
	cofs, _ := ctx.Value(&callOverrideKey).([]CallOverrideFunc)
	if len(cofs) == 0 {
		return nil, nil, false
	}
	// We found a list of overrides; grab the last, and reconstitute a
	// context that will hide it.
	f := cofs[len(cofs)-1]
	ctx = netcontext.WithValue(ctx, &callOverrideKey, cofs[:len(cofs)-1])
	return f, ctx, true
}

func (c *ProtoClient) Call(ctx context.Context, method string, req, resp proto.Message) error {
	payload, err := proto.Marshal(req)
	if err != nil {
		return err
	}

	httpReq, err := http.NewRequest("POST", c.endpoint+method, bytes.NewReader(payload))
	if err != nil {
		return err
	}
	httpReq.Header.Set("Content-Type", "application/x-protobuf")
	if ua := c.userAgent; ua != "" {
		httpReq.Header.Set("User-Agent", ua)
	}

	errc := make(chan error, 1)
	cancel := makeReqCancel(httpReq)

	go func() {
		r, err := c.client.Do(httpReq)
		if err != nil {
			errc <- err
			return
		}
		defer r.Body.Close()

		body, err := ioutil.ReadAll(r.Body)
		if r.StatusCode != http.StatusOK {
			err = &ErrHTTP{
				StatusCode: r.StatusCode,
				Body:       body,
				err:        err,
			}
		}
		if err != nil {
			errc <- err
			return
		}
		errc <- proto.Unmarshal(body, resp)
	}()

	select {
	case <-ctx.Done():
		cancel(c.client.Transport) // Cancel the HTTP request.
		return ctx.Err()
	case err := <-errc:
		return err
	}
}

func ContextClient(ctx context.Context) (*http.Client, error) {
	if ctx != nil {
		if hc, ok := ctx.Value(HTTPClient).(*http.Client); ok {
			return hc, nil
		}
	}
	for _, fn := range contextClientFuncs {
		c, err := fn(ctx)
		if err != nil {
			return nil, err
		}
		if c != nil {
			return c, nil
		}
	}
	return http.DefaultClient, nil
}

// 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)
		testHookDoReturned()
		result <- responseAndError{resp, err}
	}()

	var resp *http.Response

	select {
	case <-ctx.Done():
		testHookContextDoneBeforeHeaders()
		cancel()
		// Clean up after the goroutine calling client.Do:
		go func() {
			if r := <-result; r.resp != nil {
				testHookDidBodyClose()
				r.resp.Body.Close()
			}
		}()
		return nil, ctx.Err()
	case r := <-result:
		var err error
		resp, err = r.resp, r.err
		if err != nil {
			return resp, err
		}
	}

	c := make(chan struct{})
	go func() {
		select {
		case <-ctx.Done():
			cancel()
		case <-c:
			// The response's Body is closed.
		}
	}()
	resp.Body = &notifyingReader{resp.Body, c}

	return resp, nil
}

func Call(ctx netcontext.Context, service, method string, in, out proto.Message) error {
	if f, ctx, ok := callOverrideFromContext(ctx); ok {
		return f(ctx, service, method, in, out)
	}

	// Handle already-done contexts quickly.
	select {
	case <-ctx.Done():
		return ctx.Err()
	default:
	}

	c := fromContext(ctx)
	if c == nil {
		// Give a good error message rather than a panic lower down.
		return errors.New("not an App Engine context")
	}

	// Apply transaction modifications if we're in a transaction.
	if t := transactionFromContext(ctx); t != nil {
		if t.finished {
			return errors.New("transaction context has expired")
		}
		applyTransaction(in, &t.transaction)
	}

	var opts *appengine_internal.CallOptions
	if d, ok := ctx.Deadline(); ok {
		opts = &appengine_internal.CallOptions{
			Timeout: d.Sub(time.Now()),
		}
	}

	err := c.Call(service, method, in, out, opts)
	switch v := err.(type) {
	case *appengine_internal.APIError:
		return &APIError{
			Service: v.Service,
			Detail:  v.Detail,
			Code:    v.Code,
		}
	case *appengine_internal.CallError:
		return &CallError{
			Detail:  v.Detail,
			Code:    v.Code,
			Timeout: v.Timeout,
		}
	}
	return err
}

// Upload starts the process of a resumable upload with a cancellable context.
// It retries using the provided back off strategy until cancelled or the
// strategy indicates to stop retrying.
// It is called from the auto-generated API code and is not visible to the user.
// rx is private to the auto-generated API code.
// Exactly one of resp or err will be nil.  If resp is non-nil, the caller must call resp.Body.Close.
func (rx *ResumableUpload) Upload(ctx context.Context) (resp *http.Response, err error) {
	var pause time.Duration
	backoff := rx.Backoff
	if backoff == nil {
		backoff = DefaultBackoffStrategy()
	}

	for {
		// Ensure that we return in the case of cancelled context, even if pause is 0.
		if contextDone(ctx) {
			return nil, ctx.Err()
		}
		select {
		case <-ctx.Done():
			return nil, ctx.Err()
		case <-time.After(pause):
		}

		resp, err = rx.transferChunk(ctx)
		// It's possible for err and resp to both be non-nil here, but we expose a simpler
		// contract to our callers: exactly one of resp and err will be non-nil.  This means
		// that any response body must be closed here before returning a non-nil error.
		if err != nil {
			if resp != nil && resp.Body != nil {
				resp.Body.Close()
			}
			return nil, err
		}
		if resp.StatusCode == http.StatusCreated || resp.StatusCode == http.StatusOK {
			return resp, nil
		}

		if resp.StatusCode == statusResumeIncomplete {
			pause = 0
			backoff.Reset()
		} else {
			var retry bool
			pause, retry = backoff.Pause()
			if !retry {
				// Return the last response with its failing HTTP code.
				return resp, nil
			}
		}
		resp.Body.Close()
	}
}

func transactionFromContext(ctx netcontext.Context) *transaction {
	t, _ := ctx.Value(&transactionKey).(*transaction)
	return t
}

func fromContext(ctx netcontext.Context) appengine.Context {
	c, _ := ctx.Value(&contextKey).(appengine.Context)
	return c
}