grpc

Overview ¶

Package gRPC provides an exponential.ErrTransformer that can be used to detect non-retriable errors for gRPC calls. There is no direct support for gRPC streaming in this package.

Example using just defaults:

// This will retry any grpc error codes that are considered retriable.
grpcErrTransform, _ := grpc.New() // Uses defaults

backoff := exponential.WithErrTransformer(grpcErrTransform)

ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
req := &pb.HelloRequest{Name: "John"}
var resp *pb.HelloReply{}

err := backoff.Retry(
	ctx,
	func(ctx context.Context, r Record) error {
		var err error
		resp, err = client.SayHello(ctx, req)
		return err
	},
)
cancel()

Example setting an extra code for retries:

// The same as above, except we will retry on codes.DataLoss.
grpcErrTransform, err := grpc.New(WithExtraCodes(codes.DataLoss))
if err != nil {
	// Handle error
}
... // The rest is the same

Example with custom message inspection:

// We are going to provide a function that can inspect a proto.Message when
// the client did not send an error, but there was an error sent back from the server
// in the response.
respHasErr := func (msg proto.Message) error {
	r := msg.(*pb.HelloReply)

	if r.Error != "" {
		if r.PermanentErr {
			// This will stop retries.
			return fmt.Errorf("%s: %w", r.Error, errors.ErrPermanent)
		}
		// We can still retry.
		return fmt.Errorf("%s", r.Error)
	}
	return nil
}
grpcErrTransform, err := grpc.New(WithProtoToErr(respHasErr))
if err != nil {
	// Handle error
}

backoff := exponential.WithErrTransformer(grpcErrTransform)

ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
req := &pb.HelloRequest{Name: "John"}
var resp *pb.HelloReply{}

err := backoff.Retry(
	ctx,
	func(ctx context.Context, r Record) error {
		a, err := grpcErrTransform.RespToErr(client.SayHello(ctx, req)) // <- Notice the call wrapper
		if err != nil {
			return err
		}
		resp = a.(*pb.HelloReply)
		return nil
	},
)
cancel()