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resolver.go
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resolver.go
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// Copyright 2017 Google Inc. All Rights Reserved.
//
// 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.
package util
import (
"errors"
"fmt"
"strings"
"google.golang.org/grpc/naming"
)
// fixedBackends implements the naming.Watcher interface by returning
// a fixed set of servers.
type fixedBackends struct {
pendingServers []string
done chan struct{}
}
func newFixedBackends(servers []string) *fixedBackends {
return &fixedBackends{
pendingServers: servers,
done: make(chan struct{}),
}
}
// Next returns a set of updates describing changes to available servers;
// it will return the original set on first invocation, and block forever
// thereafter.
func (fb *fixedBackends) Next() ([]*naming.Update, error) {
if len(fb.pendingServers) == 0 {
// Block until there is an update. There will never be an update, so
// this blocks until Close() closes the channel.
<-fb.done
return nil, errors.New("watcher closed")
}
updates := make([]*naming.Update, len(fb.pendingServers))
for i, server := range fb.pendingServers {
updates[i] = &naming.Update{Op: naming.Add, Addr: server}
}
fb.pendingServers = nil
return updates, nil
}
// Close terminates the Watcher.
func (fb *fixedBackends) Close() {
close(fb.done)
}
// FixedBackendResolver implements the naming.Resolver interface by
// just returning a fixedBackends object for the comma-separated names
// in the target.
type FixedBackendResolver struct{}
// Resolve returns a fixedBackends object for the given target.
func (f FixedBackendResolver) Resolve(target string) (naming.Watcher, error) {
backends := strings.Split(target, ",")
if len(backends) == 0 || (len(backends) == 1 && backends[0] == "") {
return nil, fmt.Errorf("no backends found in %v", target)
}
return newFixedBackends(backends), nil
}