1/*
 2 *
 3 * Copyright 2024 gRPC authors.
 4 *
 5 * Licensed under the Apache License, Version 2.0 (the "License");
 6 * you may not use this file except in compliance with the License.
 7 * You may obtain a copy of the License at
 8 *
 9 *     http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 *
17 */
18
19package gracefulswitch
20
21import (
22	"encoding/json"
23	"fmt"
24
25	"google.golang.org/grpc/balancer"
26	"google.golang.org/grpc/serviceconfig"
27)
28
29type lbConfig struct {
30	serviceconfig.LoadBalancingConfig
31
32	childBuilder balancer.Builder
33	childConfig  serviceconfig.LoadBalancingConfig
34}
35
36// ChildName returns the name of the child balancer of the gracefulswitch
37// Balancer.
38func ChildName(l serviceconfig.LoadBalancingConfig) string {
39	return l.(*lbConfig).childBuilder.Name()
40}
41
42// ParseConfig parses a child config list and returns a LB config for the
43// gracefulswitch Balancer.
44//
45// cfg is expected to be a json.RawMessage containing a JSON array of LB policy
46// names + configs as the format of the "loadBalancingConfig" field in
47// ServiceConfig.  It returns a type that should be passed to
48// UpdateClientConnState in the BalancerConfig field.
49func ParseConfig(cfg json.RawMessage) (serviceconfig.LoadBalancingConfig, error) {
50	var lbCfg []map[string]json.RawMessage
51	if err := json.Unmarshal(cfg, &lbCfg); err != nil {
52		return nil, err
53	}
54	for i, e := range lbCfg {
55		if len(e) != 1 {
56			return nil, fmt.Errorf("expected a JSON struct with one entry; received entry %v at index %d", e, i)
57		}
58
59		var name string
60		var jsonCfg json.RawMessage
61		for name, jsonCfg = range e {
62		}
63
64		builder := balancer.Get(name)
65		if builder == nil {
66			// Skip unregistered balancer names.
67			continue
68		}
69
70		parser, ok := builder.(balancer.ConfigParser)
71		if !ok {
72			// This is a valid child with no config.
73			return &lbConfig{childBuilder: builder}, nil
74		}
75
76		cfg, err := parser.ParseConfig(jsonCfg)
77		if err != nil {
78			return nil, fmt.Errorf("error parsing config for policy %q: %v", name, err)
79		}
80		return &lbConfig{childBuilder: builder, childConfig: cfg}, nil
81	}
82
83	return nil, fmt.Errorf("no supported policies found in config: %v", string(cfg))
84}