Golang context.Background函數代碼示例

func main() {
	flag.Parse()

	flagsOk := true
	if flag.Lookup("project").Value.String() == "" {
		fmt.Fprintf(os.Stderr, "Flag --project is required\n")
		flagsOk = false
	}

	var sourceFlagCount int
	if flag.Lookup("dataset").Value.String() != "" {
		sourceFlagCount++
	}
	if flag.Lookup("jobid").Value.String() != "" {
		sourceFlagCount++
	}
	if sourceFlagCount != 1 {
		fmt.Fprintf(os.Stderr, "Exactly one of --dataset or --jobid must be set\n")
		flagsOk = false
	}

	if !flagsOk {
		os.Exit(1)
	}

	tableRE, err := regexp.Compile(*table)
	if err != nil {
		fmt.Fprintf(os.Stderr, "--table is not a valid regular expression: %q\n", *table)
		os.Exit(1)
	}

	httpClient, err := google.DefaultClient(context.Background(), bigquery.Scope)
	if err != nil {
		log.Fatalf("Creating http client: %v", err)
	}

	client, err := bigquery.NewClient(httpClient, *project)
	if err != nil {
		log.Fatalf("Creating bigquery client: %v", err)
	}

	if *jobID != "" {
		printQueryResults(client, *jobID)
		return
	}
	ds := client.Dataset(*dataset)
	var tables []*bigquery.Table
	tables, err = ds.ListTables(context.Background())
	if err != nil {
		log.Fatalf("Listing tables: %v", err)
	}
	for _, t := range tables {
		if tableRE.MatchString(t.TableID) {
			printTable(client, t)
		}
	}
}

func printQueryResults(client *bigquery.Client, queryJobID string) {
	job, err := client.JobFromID(context.Background(), queryJobID)
	if err != nil {
		log.Fatalf("Loading job: %v", err)
	}

	it, err := client.Read(context.Background(), job)
	if err != nil {
		log.Fatalf("Reading: %v", err)
	}

	// TODO: print schema.
	printValues(it)
}

// rebuildTable deletes the table if it exists, then creates the table, with the index column family.
func rebuildTable() error {
	ctx, _ := context.WithTimeout(context.Background(), 5*time.Minute)
	adminClient.DeleteTable(ctx, *tableName)
	if err := adminClient.CreateTable(ctx, *tableName); err != nil {
		return fmt.Errorf("CreateTable: %v", err)
	}
	time.Sleep(20 * time.Second)
	if err := adminClient.CreateColumnFamily(ctx, *tableName, indexColumnFamily); err != nil {
		return fmt.Errorf("CreateColumnFamily: %v", err)
	}
	if err := adminClient.CreateColumnFamily(ctx, *tableName, contentColumnFamily); err != nil {
		return fmt.Errorf("CreateColumnFamily: %v", err)
	}

	// Open the prototype table.  It contains a number of documents to get started with.
	prototypeTable := client.Open(prototypeTableName)

	var (
		writeErr error          // Set if any write fails.
		mu       sync.Mutex     // Protects writeErr
		wg       sync.WaitGroup // Used to wait for all writes to finish.
	)
	copyRowToTable := func(row bigtable.Row) bool {
		mu.Lock()
		failed := writeErr != nil
		mu.Unlock()
		if failed {
			return false
		}
		mut := bigtable.NewMutation()
		for family, items := range row {
			for _, item := range items {
				// Get the column name, excluding the column family name and ':' character.
				columnWithoutFamily := item.Column[len(family)+1:]
				mut.Set(family, columnWithoutFamily, bigtable.Now(), item.Value)
			}
		}
		wg.Add(1)
		go func() {
			// TODO: should use a semaphore to limit the number of concurrent writes.
			if err := table.Apply(ctx, row.Key(), mut); err != nil {
				mu.Lock()
				writeErr = err
				mu.Unlock()
			}
			wg.Done()
		}()
		return true
	}

	// Create a filter that only accepts the column families we're interested in.
	filter := bigtable.FamilyFilter(indexColumnFamily + "|" + contentColumnFamily)
	// Read every row from prototypeTable, and call copyRowToTable to copy it to our table.
	err := prototypeTable.ReadRows(ctx, bigtable.InfiniteRange(""), copyRowToTable, bigtable.RowFilter(filter))
	wg.Wait()
	if err != nil {
		return err
	}
	return writeErr
}

// FakeSingleContext returns a context whose Call invocations will be serviced
// by f, which should be a function that has two arguments of the input and output
// protocol buffer type, and one error return.
func FakeSingleContext(t *testing.T, service, method string, f interface{}) context.Context {
	fv := reflect.ValueOf(f)
	if fv.Kind() != reflect.Func {
		t.Fatal("not a function")
	}
	ft := fv.Type()
	if ft.NumIn() != 2 || ft.NumOut() != 1 {
		t.Fatalf("f has %d in and %d out, want 2 in and 1 out", ft.NumIn(), ft.NumOut())
	}
	for i := 0; i < 2; i++ {
		at := ft.In(i)
		if !at.Implements(protoMessageType) {
			t.Fatalf("arg %d does not implement proto.Message", i)
		}
	}
	if ft.Out(0) != errorType {
		t.Fatalf("f's return is %v, want error", ft.Out(0))
	}
	s := &single{
		t:       t,
		service: service,
		method:  method,
		f:       fv,
	}
	return internal.WithCallOverride(context.Background(), s.call)
}

// DoCancelAfterFirstResponse cancels the RPC after receiving the first message from the server.
func DoCancelAfterFirstResponse(tc testpb.TestServiceClient) {
	ctx, cancel := context.WithCancel(context.Background())
	stream, err := tc.FullDuplexCall(ctx)
	if err != nil {
		grpclog.Fatalf("%v.FullDuplexCall(_) = _, %v", tc, err)
	}
	respParam := []*testpb.ResponseParameters{
		{
			Size: proto.Int32(31415),
		},
	}
	pl := clientNewPayload(testpb.PayloadType_COMPRESSABLE, 27182)
	req := &testpb.StreamingOutputCallRequest{
		ResponseType:       testpb.PayloadType_COMPRESSABLE.Enum(),
		ResponseParameters: respParam,
		Payload:            pl,
	}
	if err := stream.Send(req); err != nil {
		grpclog.Fatalf("%v.Send(%v) = %v", stream, req, err)
	}
	if _, err := stream.Recv(); err != nil {
		grpclog.Fatalf("%v.Recv() = %v", stream, err)
	}
	cancel()
	if _, err := stream.Recv(); grpc.Code(err) != codes.Canceled {
		grpclog.Fatalf("%v compleled with error code %d, want %d", stream, grpc.Code(err), codes.Canceled)
	}
	grpclog.Println("CancelAfterFirstResponse done")
}

// NewRemoteContext returns a context that gives access to the production
// APIs for the application at the given host. All communication will be
// performed over SSL unless the host is localhost.
func NewRemoteContext(host string, client *http.Client) (context.Context, error) {
	// Add an appcfg header to outgoing requests.
	t := client.Transport
	if t == nil {
		t = http.DefaultTransport
	}
	client.Transport = &headerAddingRoundTripper{t}

	url := url.URL{
		Scheme: "https",
		Host:   host,
		Path:   "/_ah/remote_api",
	}
	if host == "localhost" || strings.HasPrefix(host, "localhost:") {
		url.Scheme = "http"
	}
	u := url.String()
	appID, err := getAppID(client, u)
	if err != nil {
		return nil, fmt.Errorf("unable to contact server: %v", err)
	}
	rc := &remoteContext{
		client: client,
		url:    u,
	}
	ctx := internal.WithCallOverride(context.Background(), rc.call)
	ctx = internal.WithLogOverride(ctx, rc.logf)
	ctx = internal.WithAppIDOverride(ctx, appID)
	return ctx, nil
}

// DoPerRPCCreds performs a unary RPC with per RPC OAUTH2 token.
func DoPerRPCCreds(tc testpb.TestServiceClient, serviceAccountKeyFile, oauthScope string) {
	jsonKey := getServiceAccountJSONKey(serviceAccountKeyFile)
	pl := clientNewPayload(testpb.PayloadType_COMPRESSABLE, largeReqSize)
	req := &testpb.SimpleRequest{
		ResponseType:   testpb.PayloadType_COMPRESSABLE.Enum(),
		ResponseSize:   proto.Int32(int32(largeRespSize)),
		Payload:        pl,
		FillUsername:   proto.Bool(true),
		FillOauthScope: proto.Bool(true),
	}
	token := GetToken(serviceAccountKeyFile, oauthScope)
	kv := map[string]string{"authorization": token.TokenType + " " + token.AccessToken}
	ctx := metadata.NewContext(context.Background(), metadata.MD{"authorization": []string{kv["authorization"]}})
	reply, err := tc.UnaryCall(ctx, req)
	if err != nil {
		grpclog.Fatal("/TestService/UnaryCall RPC failed: ", err)
	}
	user := reply.GetUsername()
	scope := reply.GetOauthScope()
	if !strings.Contains(string(jsonKey), user) {
		grpclog.Fatalf("Got user name %q which is NOT a substring of %q.", user, jsonKey)
	}
	if !strings.Contains(oauthScope, scope) {
		grpclog.Fatalf("Got OAuth scope %q which is NOT a substring of %q.", scope, oauthScope)
	}
	grpclog.Println("PerRPCCreds done")
}

// DoClientStreaming performs a client streaming RPC.
func DoClientStreaming(tc testpb.TestServiceClient) {
	stream, err := tc.StreamingInputCall(context.Background())
	if err != nil {
		grpclog.Fatalf("%v.StreamingInputCall(_) = _, %v", tc, err)
	}
	var sum int
	for _, s := range reqSizes {
		pl := clientNewPayload(testpb.PayloadType_COMPRESSABLE, s)
		req := &testpb.StreamingInputCallRequest{
			Payload: pl,
		}
		if err := stream.Send(req); err != nil {
			grpclog.Fatalf("%v.Send(%v) = %v", stream, req, err)
		}
		sum += s
		grpclog.Printf("Sent a request of size %d, aggregated size %d", s, sum)

	}
	reply, err := stream.CloseAndRecv()
	if err != nil {
		grpclog.Fatalf("%v.CloseAndRecv() got error %v, want %v", stream, err, nil)
	}
	if reply.GetAggregatedPayloadSize() != int32(sum) {
		grpclog.Fatalf("%v.CloseAndRecv().GetAggregatePayloadSize() = %v; want %v", stream, reply.GetAggregatedPayloadSize(), sum)
	}
	grpclog.Println("ClientStreaming done")
}

// handleContent fetches the content of a document from the Bigtable and returns it.
func handleContent(w http.ResponseWriter, r *http.Request) {
	ctx, _ := context.WithTimeout(context.Background(), 10*time.Second)
	name := r.FormValue("name")
	if len(name) == 0 {
		http.Error(w, "No document name supplied.", http.StatusBadRequest)
		return
	}

	row, err := table.ReadRow(ctx, name)
	if err != nil {
		http.Error(w, "Error reading content: "+err.Error(), http.StatusInternalServerError)
		return
	}
	content := row[contentColumnFamily]
	if len(content) == 0 {
		http.Error(w, "Document not found.", http.StatusNotFound)
		return
	}
	var buf bytes.Buffer
	if err := contentTemplate.ExecuteTemplate(&buf, "", struct{ Title, Content string }{name, string(content[0].Value)}); err != nil {
		http.Error(w, "Error executing HTML template: "+err.Error(), http.StatusInternalServerError)
		return
	}
	io.Copy(w, &buf)
}

// printFeature gets the feature for the given point.
func printFeature(client pb.RouteGuideClient, point *pb.Point) {
	grpclog.Printf("Getting feature for point (%d, %d)", point.Latitude, point.Longitude)
	feature, err := client.GetFeature(context.Background(), point)
	if err != nil {
		grpclog.Fatalf("%v.GetFeatures(_) = _, %v: ", client, err)
	}
	grpclog.Println(feature)
}

func deleteTopic(client *pubsub.Client, argv []string) {
	checkArgs(argv, 2)
	topic := argv[1]
	err := client.Topic(topic).Delete(context.Background())
	if err != nil {
		log.Fatalf("Deleting topic failed: %v", err)
	}
	fmt.Printf("Topic %s was deleted.\n", topic)
}

func checkTopicExists(client *pubsub.Client, argv []string) {
	checkArgs(argv, 1)
	topic := argv[1]
	exists, err := client.Topic(topic).Exists(context.Background())
	if err != nil {
		log.Fatalf("Checking topic exists failed: %v", err)
	}
	fmt.Println(exists)
}

func createTopic(client *pubsub.Client, argv []string) {
	checkArgs(argv, 2)
	topic := argv[1]
	_, err := client.NewTopic(context.Background(), topic)
	if err != nil {
		log.Fatalf("Creating topic failed: %v", err)
	}
	fmt.Printf("Topic %s was created.\n", topic)
}

func checkSubscriptionExists(client *pubsub.Client, argv []string) {
	checkArgs(argv, 1)
	sub := argv[1]
	exists, err := client.Subscription(sub).Exists(context.Background())
	if err != nil {
		log.Fatalf("Checking subscription exists failed: %v", err)
	}
	fmt.Println(exists)
}

func deleteSubscription(client *pubsub.Client, argv []string) {
	checkArgs(argv, 2)
	sub := argv[1]
	err := client.Subscription(sub).Delete(context.Background())
	if err != nil {
		log.Fatalf("Deleting Subscription failed: %v", err)
	}
	fmt.Printf("Subscription %s was deleted.\n", sub)
}