go.chromium.org/luci@v0.0.0-20240309015107-7cdc2e660f33/cv/internal/gerrit/mirror.go (about)

     1  // Copyright 2021 The LUCI Authors.
     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 gerrit
    16  
    17  import (
    18  	"context"
    19  	"math/rand"
    20  
    21  	"google.golang.org/grpc"
    22  
    23  	"go.chromium.org/luci/common/api/gerrit"
    24  	"go.chromium.org/luci/common/data/rand/mathrand"
    25  	"go.chromium.org/luci/common/errors"
    26  )
    27  
    28  // MirrorIterator starts with the Gerrit host as is and then iterates over
    29  // mirrors.
    30  //
    31  // Fail-safe: if all mirrors have been used, uses the host as is. However,
    32  // users should use Empty() to detect this and if necessary should construct a
    33  // new MirrorIterator.
    34  //
    35  // Not goroutine-safe.
    36  type MirrorIterator []string
    37  
    38  func newMirrorIterator(ctx context.Context, mirrorHostPrefixes ...string) *MirrorIterator {
    39  	// First prefix "" means use host as is.
    40  	it := &MirrorIterator{""}
    41  	*it = append(*it, mirrorHostPrefixes...) // copy
    42  	// Shuffle the provided prefixes.
    43  	provided := (*it)[1:]
    44  	_ = mathrand.WithGoRand(ctx, func(r *rand.Rand) error {
    45  		rand.Shuffle(len(provided), func(i, j int) { provided[i], provided[j] = provided[j], provided[i] })
    46  		return nil
    47  	})
    48  	return it
    49  }
    50  
    51  // RetryIfStale retries the given function so long as it returns ErrStaleData
    52  // and there is not yet tried mirror.
    53  //
    54  // Executes the given function at least once. If there are no mirrors, defaults
    55  // to virtual gerrit host.
    56  //
    57  // Provides the given function with the grpc.CallOption which should be passed
    58  // to the respective Client RPC call.
    59  //
    60  // Returns whatever error the given function returned last.
    61  func (it *MirrorIterator) RetryIfStale(f func(opt grpc.CallOption) error) error {
    62  	for {
    63  		if err := f(it.Next()); errors.Unwrap(err) != ErrStaleData || it.Empty() {
    64  			return err
    65  		}
    66  	}
    67  }
    68  
    69  // Next returns a grpc.CallOption.
    70  func (it *MirrorIterator) Next() grpc.CallOption {
    71  	return gerrit.UseGerritMirror(it.next())
    72  }
    73  
    74  // next is an easily testable version of Next().
    75  func (it *MirrorIterator) next() func(host string) string {
    76  	prefix := "" // fail-safe to host as is when empty.
    77  	if len(*it) > 0 {
    78  		prefix = (*it)[0]
    79  		*it = (*it)[1:]
    80  	}
    81  	return func(host string) string { return prefix + host }
    82  }
    83  
    84  // Empty returns true if MirrorIterator has already iterated over all the mirrors.
    85  func (it *MirrorIterator) Empty() bool {
    86  	return len(*it) == 0
    87  }