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How to develop a config type plugin

This guide will introduce how to develop a config type plugin that relies on configuration for loading.

The config package provides two sets of different configuration interfaces, config.DataProvider and config.KVConfig. This guide uses the development of the KVConfig type configuration as an example, and the development of the DataProvider type configuration is similar.

Developing this plugin requires implementing the following two sub-functions:

• Implement loading the plugin by relying on configuration. For details, please refer to plugin.
• Implement the config.KVConfig interface and register the implementation with the config package.

The following steps will introduce the relevant development steps using trpc-config-etcd as an example.

Implement loading the plugin by relying on configuration

1. Determine the plugin configuration

The following is an example of setting the "Endpoint" and "Dialtimeout" configurations in the "trpc_go.yaml" configuration file:

plugins:                 
  config:
    etcd:
      endpoints:
        - localhost:2379
      dialtimeout: 5s

The plugin is encapsulated based on etcd-client, so the complete configuration is in Config.

2. Implement the plugin.Factory interface

// etcdPlugin etcd Configuration center plugin.
type etcdPlugin struct{}

// Type implements plugin.Factory.
func (p *etcdPlugin) Type() string {
    return pluginType
}

// Setup implements plugin.Factory.
func (p *etcdPlugin) Setup(name string, decoder plugin.Decoder) error {
    cfg := clientv3.Config{}
    err := decoder.Decode(&cfg)
    if err != nil {
        return err
    }
    c, err := New(cfg)
    if err != nil {
        return err
    }
    config.SetGlobalKV(c)
    config.Register(c)
    return nil
}

3. Call plugin.Register to register the plugin with the plugin package

func init() {
	plugin.Register(pluginName, NewPlugin())
}

Implement the config.KVConfig interface and register the implementation with the config package.

1. Implement the config.KVConfig interface

The plugin currently only supports Watch and Get read operations and does not support Put and Del write operations.

// Client etcd client.
type Client struct {
    cli *clientv3.Client
}

// Name returns plugin name.
func (c *Client) Name() string {
    return pluginName
}

// Get Obtains the configuration content value according to the key, and implement the config.KV interface.
func (c *Client) Get(ctx context.Context, key string, _ ...config.Option) (config.Response, error) {
    result, err := c.cli.Get(ctx, key)
    if err != nil {
        return nil, err
    }
    rsp := &getResponse{
        md: make(map[string]string),
    }

    if result.Count > 1 {
    // TODO: support multi keyvalues
        return nil, ErrNotImplemented
    }

    for _, v := range result.Kvs {
        rsp.val = string(v.Value)
    }
    return rsp, nil
}

// Watch monitors configuration changes and implements the config.Watcher interface.
func (c *Client) Watch(ctx context.Context, key string, opts ...config.Option) (<-chan config.Response, error) {
    rspCh := make(chan config.Response, 1)
    go c.watch(ctx, key, rspCh)
    return rspCh, nil
}

// watch adds watcher for etcd changes.
func (c *Client) watch(ctx context.Context, key string, rspCh chan config.Response) {
    rch := c.cli.Watch(ctx, key)
    for r := range rch {
        for _, ev := range r.Events {
            rsp := &watchResponse{
                val:       string(ev.Kv.Value),
                md:        make(map[string]string),
                eventType: config.EventTypeNull,
            }
            switch ev.Type {
                case clientv3.EventTypePut:
                    rsp.eventType = config.EventTypePut
                case clientv3.EventTypeDelete:
                    rsp.eventType = config.EventTypeDel
                default:
            }
            rspCh <- rsp
        }
    }
}

// ErrNotImplemented not implemented error
var ErrNotImplemented = errors.New("not implemented")

// Put creates or updates the configuration content value to implement the config.KV interface.
func (c *Client) Put(ctx context.Context, key, val string, opts ...config.Option) error {
    return ErrNotImplemented
}

// Del deletes the configuration item key and implement the config.KV interface.
func (c *Client) Del(ctx context.Context, key string, opts ...config.Option) error {
    return ErrNotImplemented
}

2. Register the implementation of config.KVConfig with the config package

The *etcdPlugin.Setup function has already called config.Register and config.SetGlobalKV.

config.SetGlobalKV(c)
config.Register(c)