google.golang.org/grpc@v1.72.2/internal/balancer/gracefulswitch/config.go (about)

     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  
    19  package gracefulswitch
    20  
    21  import (
    22  	"encoding/json"
    23  	"fmt"
    24  
    25  	"google.golang.org/grpc/balancer"
    26  	"google.golang.org/grpc/serviceconfig"
    27  )
    28  
    29  type 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.
    38  func 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.
    49  func 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  }