1// Copyright 2016 Google Inc. All Rights Reserved.
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
15package internal
16
17import (
18	"errors"
19	"google.golang.org/grpc/naming"
20)
21
22// PoolResolver provides a fixed list of addresses to load balance between
23// and does not provide further updates.
24type PoolResolver struct {
25	poolSize int
26	dialOpt  *DialSettings
27	ch       chan []*naming.Update
28}
29
30// NewPoolResolver returns a PoolResolver
31// This is an EXPERIMENTAL API and may be changed or removed in the future.
32func NewPoolResolver(size int, o *DialSettings) *PoolResolver {
33	return &PoolResolver{poolSize: size, dialOpt: o}
34}
35
36// Resolve returns a Watcher for the endpoint defined by the DialSettings
37// provided to NewPoolResolver.
38func (r *PoolResolver) Resolve(target string) (naming.Watcher, error) {
39	if r.dialOpt.Endpoint == "" {
40		return nil, errors.New("No endpoint configured")
41	}
42	addrs := make([]*naming.Update, 0, r.poolSize)
43	for i := 0; i < r.poolSize; i++ {
44		addrs = append(addrs, &naming.Update{Op: naming.Add, Addr: r.dialOpt.Endpoint, Metadata: i})
45	}
46	r.ch = make(chan []*naming.Update, 1)
47	r.ch <- addrs
48	return r, nil
49}
50
51// Next returns a static list of updates on the first call,
52// and blocks indefinitely until Close is called on subsequent calls.
53func (r *PoolResolver) Next() ([]*naming.Update, error) {
54	return <-r.ch, nil
55}
56
57func (r *PoolResolver) Close() {
58	close(r.ch)
59}
60