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// Copyright 2016 The etcd Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// Based on github.com/grpc-ecosystem/go-grpc-middleware/retry, but modified to support the more
// fine grained error checking required by write-at-most-once retry semantics of etcd.
package clientv3
import (
"context"
"io"
"sync"
"time"
"github.com/coreos/etcd/etcdserver/api/v3rpc/rpctypes"
"go.uber.org/zap"
"google.golang.org/grpc"
"google.golang.org/grpc/codes"
"google.golang.org/grpc/metadata"
"google.golang.org/grpc/status"
)
// unaryClientInterceptor returns a new retrying unary client interceptor.
//
// The default configuration of the interceptor is to not retry *at all*. This behaviour can be
// changed through options (e.g. WithMax) on creation of the interceptor or on call (through grpc.CallOptions).
func (c *Client) unaryClientInterceptor(logger *zap.Logger, optFuncs ...retryOption) grpc.UnaryClientInterceptor {
intOpts := reuseOrNewWithCallOptions(defaultOptions, optFuncs)
return func(ctx context.Context, method string, req, reply interface{}, cc *grpc.ClientConn, invoker grpc.UnaryInvoker, opts ...grpc.CallOption) error {
ctx = withVersion(ctx)
grpcOpts, retryOpts := filterCallOptions(opts)
callOpts := reuseOrNewWithCallOptions(intOpts, retryOpts)
// short circuit for simplicity, and avoiding allocations.
if callOpts.max == 0 {
return invoker(ctx, method, req, reply, cc, grpcOpts...)
}
var lastErr error
for attempt := uint(0); attempt < callOpts.max; attempt++ {
if err := waitRetryBackoff(ctx, attempt, callOpts); err != nil {
return err
}
logger.Debug(
"retrying of unary invoker",
zap.String("target", cc.Target()),
zap.Uint("attempt", attempt),
)
lastErr = invoker(ctx, method, req, reply, cc, grpcOpts...)
if lastErr == nil {
return nil
}
logger.Warn(
"retrying of unary invoker failed",
zap.String("target", cc.Target()),
zap.Uint("attempt", attempt),
zap.Error(lastErr),
)
if isContextError(lastErr) {
if ctx.Err() != nil {
// its the context deadline or cancellation.
return lastErr
}
// its the callCtx deadline or cancellation, in which case try again.
continue
}
if callOpts.retryAuth && rpctypes.Error(lastErr) == rpctypes.ErrInvalidAuthToken {
gterr := c.getToken(ctx)
if gterr != nil {
logger.Warn(
"retrying of unary invoker failed to fetch new auth token",
zap.String("target", cc.Target()),
zap.Error(gterr),
)
return gterr // lastErr must be invalid auth token
}
continue
}
if !isSafeRetry(c.lg, lastErr, callOpts) {
return lastErr
}
}
return lastErr
}
}
// streamClientInterceptor returns a new retrying stream client interceptor for server side streaming calls.
//
// The default configuration of the interceptor is to not retry *at all*. This behaviour can be
// changed through options (e.g. WithMax) on creation of the interceptor or on call (through grpc.CallOptions).
//
// Retry logic is available *only for ServerStreams*, i.e. 1:n streams, as the internal logic needs
// to buffer the messages sent by the client. If retry is enabled on any other streams (ClientStreams,
// BidiStreams), the retry interceptor will fail the call.
func (c *Client) streamClientInterceptor(logger *zap.Logger, optFuncs ...retryOption) grpc.StreamClientInterceptor {
intOpts := reuseOrNewWithCallOptions(defaultOptions, optFuncs)
return func(ctx context.Context, desc *grpc.StreamDesc, cc *grpc.ClientConn, method string, streamer grpc.Streamer, opts ...grpc.CallOption) (grpc.ClientStream, error) {
ctx = withVersion(ctx)
grpcOpts, retryOpts := filterCallOptions(opts)
callOpts := reuseOrNewWithCallOptions(intOpts, retryOpts)
// short circuit for simplicity, and avoiding allocations.
if callOpts.max == 0 {
return streamer(ctx, desc, cc, method, grpcOpts...)
}
if desc.ClientStreams {
return nil, status.Errorf(codes.Unimplemented, "clientv3/retry_interceptor: cannot retry on ClientStreams, set Disable()")
}
newStreamer, err := streamer(ctx, desc, cc, method, grpcOpts...)
if err != nil {
logger.Error("streamer failed to create ClientStream", zap.Error(err))
return nil, err // TODO(mwitkow): Maybe dial and transport errors should be retriable?
}
retryingStreamer := &serverStreamingRetryingStream{
client: c,
ClientStream: newStreamer,
callOpts: callOpts,
ctx: ctx,
streamerCall: func(ctx context.Context) (grpc.ClientStream, error) {
return streamer(ctx, desc, cc, method, grpcOpts...)
},
}
return retryingStreamer, nil
}
}
// type serverStreamingRetryingStream is the implementation of grpc.ClientStream that acts as a
// proxy to the underlying call. If any of the RecvMsg() calls fail, it will try to reestablish
// a new ClientStream according to the retry policy.
type serverStreamingRetryingStream struct {
grpc.ClientStream
client *Client
bufferedSends []interface{} // single message that the client can sen
receivedGood bool // indicates whether any prior receives were successful
wasClosedSend bool // indicates that CloseSend was closed
ctx context.Context
callOpts *options
streamerCall func(ctx context.Context) (grpc.ClientStream, error)
mu sync.RWMutex
}
func (s *serverStreamingRetryingStream) setStream(clientStream grpc.ClientStream) {
s.mu.Lock()
s.ClientStream = clientStream
s.mu.Unlock()
}
func (s *serverStreamingRetryingStream) getStream() grpc.ClientStream {
s.mu.RLock()
defer s.mu.RUnlock()
return s.ClientStream
}
func (s *serverStreamingRetryingStream) SendMsg(m interface{}) error {
s.mu.Lock()
s.bufferedSends = append(s.bufferedSends, m)
s.mu.Unlock()
return s.getStream().SendMsg(m)
}
func (s *serverStreamingRetryingStream) CloseSend() error {
s.mu.Lock()
s.wasClosedSend = true
s.mu.Unlock()
return s.getStream().CloseSend()
}
func (s *serverStreamingRetryingStream) Header() (metadata.MD, error) {
return s.getStream().Header()
}
func (s *serverStreamingRetryingStream) Trailer() metadata.MD {
return s.getStream().Trailer()
}
func (s *serverStreamingRetryingStream) RecvMsg(m interface{}) error {
attemptRetry, lastErr := s.receiveMsgAndIndicateRetry(m)
if !attemptRetry {
return lastErr // success or hard failure
}
// We start off from attempt 1, because zeroth was already made on normal SendMsg().
for attempt := uint(1); attempt < s.callOpts.max; attempt++ {
if err := waitRetryBackoff(s.ctx, attempt, s.callOpts); err != nil {
return err
}
newStream, err := s.reestablishStreamAndResendBuffer(s.ctx)
if err != nil {
s.client.lg.Error("failed reestablishStreamAndResendBuffer", zap.Error(err))
return err // TODO(mwitkow): Maybe dial and transport errors should be retriable?
}
s.setStream(newStream)
s.client.lg.Warn("retrying RecvMsg", zap.Error(lastErr))
attemptRetry, lastErr = s.receiveMsgAndIndicateRetry(m)
if !attemptRetry {
return lastErr
}
}
return lastErr
}
func (s *serverStreamingRetryingStream) receiveMsgAndIndicateRetry(m interface{}) (bool, error) {
s.mu.RLock()
wasGood := s.receivedGood
s.mu.RUnlock()
err := s.getStream().RecvMsg(m)
if err == nil || err == io.EOF {
s.mu.Lock()
s.receivedGood = true
s.mu.Unlock()
return false, err
} else if wasGood {
// previous RecvMsg in the stream succeeded, no retry logic should interfere
return false, err
}
if isContextError(err) {
if s.ctx.Err() != nil {
return false, err
}
// its the callCtx deadline or cancellation, in which case try again.
return true, err
}
if s.callOpts.retryAuth && rpctypes.Error(err) == rpctypes.ErrInvalidAuthToken {
gterr := s.client.getToken(s.ctx)
if gterr != nil {
s.client.lg.Warn("retry failed to fetch new auth token", zap.Error(gterr))
return false, err // return the original error for simplicity
}
return true, err
}
return isSafeRetry(s.client.lg, err, s.callOpts), err
}
func (s *serverStreamingRetryingStream) reestablishStreamAndResendBuffer(callCtx context.Context) (grpc.ClientStream, error) {
s.mu.RLock()
bufferedSends := s.bufferedSends
s.mu.RUnlock()
newStream, err := s.streamerCall(callCtx)
if err != nil {
return nil, err
}
for _, msg := range bufferedSends {
if err := newStream.SendMsg(msg); err != nil {
return nil, err
}
}
if err := newStream.CloseSend(); err != nil {
return nil, err
}
return newStream, nil
}
func waitRetryBackoff(ctx context.Context, attempt uint, callOpts *options) error {
waitTime := time.Duration(0)
if attempt > 0 {
waitTime = callOpts.backoffFunc(attempt)
}
if waitTime > 0 {
timer := time.NewTimer(waitTime)
select {
case <-ctx.Done():
timer.Stop()
return contextErrToGrpcErr(ctx.Err())
case <-timer.C:
}
}
return nil
}
// isSafeRetry returns "true", if request is safe for retry with the given error.
func isSafeRetry(lg *zap.Logger, err error, callOpts *options) bool {
if isContextError(err) {
return false
}
switch callOpts.retryPolicy {
case repeatable:
return isSafeRetryImmutableRPC(err)
case nonRepeatable:
return isSafeRetryMutableRPC(err)
default:
lg.Warn("unrecognized retry policy", zap.String("retryPolicy", callOpts.retryPolicy.String()))
return false
}
}
func isContextError(err error) bool {
return grpc.Code(err) == codes.DeadlineExceeded || grpc.Code(err) == codes.Canceled
}
func contextErrToGrpcErr(err error) error {
switch err {
case context.DeadlineExceeded:
return status.Errorf(codes.DeadlineExceeded, err.Error())
case context.Canceled:
return status.Errorf(codes.Canceled, err.Error())
default:
return status.Errorf(codes.Unknown, err.Error())
}
}
var (
defaultOptions = &options{
retryPolicy: nonRepeatable,
max: 0, // disable
backoffFunc: backoffLinearWithJitter(50*time.Millisecond /*jitter*/, 0.10),
retryAuth: true,
}
)
// backoffFunc denotes a family of functions that control the backoff duration between call retries.
//
// They are called with an identifier of the attempt, and should return a time the system client should
// hold off for. If the time returned is longer than the `context.Context.Deadline` of the request
// the deadline of the request takes precedence and the wait will be interrupted before proceeding
// with the next iteration.
type backoffFunc func(attempt uint) time.Duration
// withRetryPolicy sets the retry policy of this call.
func withRetryPolicy(rp retryPolicy) retryOption {
return retryOption{applyFunc: func(o *options) {
o.retryPolicy = rp
}}
}
// withMax sets the maximum number of retries on this call, or this interceptor.
func withMax(maxRetries uint) retryOption {
return retryOption{applyFunc: func(o *options) {
o.max = maxRetries
}}
}
// WithBackoff sets the `BackoffFunc `used to control time between retries.
func withBackoff(bf backoffFunc) retryOption {
return retryOption{applyFunc: func(o *options) {
o.backoffFunc = bf
}}
}
type options struct {
retryPolicy retryPolicy
max uint
backoffFunc backoffFunc
retryAuth bool
}
// retryOption is a grpc.CallOption that is local to clientv3's retry interceptor.
type retryOption struct {
grpc.EmptyCallOption // make sure we implement private after() and before() fields so we don't panic.
applyFunc func(opt *options)
}
func reuseOrNewWithCallOptions(opt *options, retryOptions []retryOption) *options {
if len(retryOptions) == 0 {
return opt
}
optCopy := &options{}
*optCopy = *opt
for _, f := range retryOptions {
f.applyFunc(optCopy)
}
return optCopy
}
func filterCallOptions(callOptions []grpc.CallOption) (grpcOptions []grpc.CallOption, retryOptions []retryOption) {
for _, opt := range callOptions {
if co, ok := opt.(retryOption); ok {
retryOptions = append(retryOptions, co)
} else {
grpcOptions = append(grpcOptions, opt)
}
}
return grpcOptions, retryOptions
}
// BackoffLinearWithJitter waits a set period of time, allowing for jitter (fractional adjustment).
//
// For example waitBetween=1s and jitter=0.10 can generate waits between 900ms and 1100ms.
func backoffLinearWithJitter(waitBetween time.Duration, jitterFraction float64) backoffFunc {
return func(attempt uint) time.Duration {
return jitterUp(waitBetween, jitterFraction)
}
}