watch.go

Documentation: go.etcd.io/etcd/client/v3/namespace

     1  // Copyright 2017 The etcd 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 namespace
    16  
    17  import (
    18  	"context"
    19  	"sync"
    20  
    21  	"go.etcd.io/etcd/client/v3"
    22  )
    23  
    24  type watcherPrefix struct {
    25  	clientv3.Watcher
    26  	pfx string
    27  
    28  	wg       sync.WaitGroup
    29  	stopc    chan struct{}
    30  	stopOnce sync.Once
    31  }
    32  
    33  // NewWatcher wraps a Watcher instance so that all Watch requests
    34  // are prefixed with a given string and all Watch responses have
    35  // the prefix removed.
    36  func NewWatcher(w clientv3.Watcher, prefix string) clientv3.Watcher {
    37  	return &watcherPrefix{Watcher: w, pfx: prefix, stopc: make(chan struct{})}
    38  }
    39  
    40  func (w *watcherPrefix) Watch(ctx context.Context, key string, opts ...clientv3.OpOption) clientv3.WatchChan {
    41  	// since OpOption is opaque, determine range for prefixing through an OpGet
    42  	op := clientv3.OpGet(key, opts...)
    43  	end := op.RangeBytes()
    44  	pfxBegin, pfxEnd := prefixInterval(w.pfx, []byte(key), end)
    45  	if pfxEnd != nil {
    46  		opts = append(opts, clientv3.WithRange(string(pfxEnd)))
    47  	}
    48  
    49  	wch := w.Watcher.Watch(ctx, string(pfxBegin), opts...)
    50  
    51  	// translate watch events from prefixed to unprefixed
    52  	pfxWch := make(chan clientv3.WatchResponse)
    53  	w.wg.Add(1)
    54  	go func() {
    55  		defer func() {
    56  			close(pfxWch)
    57  			w.wg.Done()
    58  		}()
    59  		for wr := range wch {
    60  			for i := range wr.Events {
    61  				wr.Events[i].Kv.Key = wr.Events[i].Kv.Key[len(w.pfx):]
    62  				if wr.Events[i].PrevKv != nil {
    63  					wr.Events[i].PrevKv.Key = wr.Events[i].Kv.Key
    64  				}
    65  			}
    66  			select {
    67  			case pfxWch <- wr:
    68  			case <-ctx.Done():
    69  				return
    70  			case <-w.stopc:
    71  				return
    72  			}
    73  		}
    74  	}()
    75  	return pfxWch
    76  }
    77  
    78  func (w *watcherPrefix) Close() error {
    79  	err := w.Watcher.Close()
    80  	w.stopOnce.Do(func() { close(w.stopc) })
    81  	w.wg.Wait()
    82  	return err
    83  }
    84
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