retry.go

Documentation: cloud.google.com/go/compute/metadata

     1  // Copyright 2021 Google LLC
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //      http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package metadata
    16  
    17  import (
    18  	"context"
    19  	"io"
    20  	"math/rand"
    21  	"net/http"
    22  	"time"
    23  )
    24  
    25  const (
    26  	maxRetryAttempts = 5
    27  )
    28  
    29  var (
    30  	syscallRetryable = func(error) bool { return false }
    31  )
    32  
    33  // defaultBackoff is basically equivalent to gax.Backoff without the need for
    34  // the dependency.
    35  type defaultBackoff struct {
    36  	max time.Duration
    37  	mul float64
    38  	cur time.Duration
    39  }
    40  
    41  func (b *defaultBackoff) Pause() time.Duration {
    42  	d := time.Duration(1 + rand.Int63n(int64(b.cur)))
    43  	b.cur = time.Duration(float64(b.cur) * b.mul)
    44  	if b.cur > b.max {
    45  		b.cur = b.max
    46  	}
    47  	return d
    48  }
    49  
    50  // sleep is the equivalent of gax.Sleep without the need for the dependency.
    51  func sleep(ctx context.Context, d time.Duration) error {
    52  	t := time.NewTimer(d)
    53  	select {
    54  	case <-ctx.Done():
    55  		t.Stop()
    56  		return ctx.Err()
    57  	case <-t.C:
    58  		return nil
    59  	}
    60  }
    61  
    62  func newRetryer() *metadataRetryer {
    63  	return &metadataRetryer{bo: &defaultBackoff{
    64  		cur: 100 * time.Millisecond,
    65  		max: 30 * time.Second,
    66  		mul: 2,
    67  	}}
    68  }
    69  
    70  type backoff interface {
    71  	Pause() time.Duration
    72  }
    73  
    74  type metadataRetryer struct {
    75  	bo       backoff
    76  	attempts int
    77  }
    78  
    79  func (r *metadataRetryer) Retry(status int, err error) (time.Duration, bool) {
    80  	if status == http.StatusOK {
    81  		return 0, false
    82  	}
    83  	retryOk := shouldRetry(status, err)
    84  	if !retryOk {
    85  		return 0, false
    86  	}
    87  	if r.attempts == maxRetryAttempts {
    88  		return 0, false
    89  	}
    90  	r.attempts++
    91  	return r.bo.Pause(), true
    92  }
    93  
    94  func shouldRetry(status int, err error) bool {
    95  	if 500 <= status && status <= 599 {
    96  		return true
    97  	}
    98  	if err == io.ErrUnexpectedEOF {
    99  		return true
   100  	}
   101  	// Transient network errors should be retried.
   102  	if syscallRetryable(err) {
   103  		return true
   104  	}
   105  	if err, ok := err.(interface{ Temporary() bool }); ok {
   106  		if err.Temporary() {
   107  			return true
   108  		}
   109  	}
   110  	if err, ok := err.(interface{ Unwrap() error }); ok {
   111  		return shouldRetry(status, err.Unwrap())
   112  	}
   113  	return false
   114  }
   115
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