Tendermint源码阅读（三）

关注点：BaseConfig相关配置

一、BaseConfig的所有配置项

源码文件
tendermint/config/config.go

// BaseConfig defines the base configuration for a Tendermint node
type BaseConfig struct {
    // chainID is unexposed and immutable but here for convenience
    chainID string

    // The root directory for all data.
    // This should be set in viper so it can unmarshal into this struct
    RootDir string `mapstructure:"home"`

    // TCP or UNIX socket address of the ABCI application,
    // or the name of an ABCI application compiled in with the Tendermint binary
    ProxyApp string `mapstructure:"proxy_app"`

    // A custom human readable name for this node
    Moniker string `mapstructure:"moniker"`

    // If this node is many blocks behind the tip of the chain, FastSync
    // allows them to catchup quickly by downloading blocks in parallel
    // and verifying their commits
    FastSync bool `mapstructure:"fast_sync"`

    // Database backend: leveldb | memdb
    DBBackend string `mapstructure:"db_backend"`

    // Database directory
    DBPath string `mapstructure:"db_dir"`

    // Output level for logging
    LogLevel string `mapstructure:"log_level"`

    // Path to the JSON file containing the initial validator set and other meta data
    Genesis string `mapstructure:"genesis_file"`

    // Path to the JSON file containing the private key to use as a validator in the consensus protocol
    PrivValidator string `mapstructure:"priv_validator_file"`

    // TCP or UNIX socket address for Tendermint to listen on for
    // connections from an external PrivValidator process
    PrivValidatorListenAddr string `mapstructure:"priv_validator_laddr"`

    // A JSON file containing the private key to use for p2p authenticated encryption
    NodeKey string `mapstructure:"node_key_file"`

    // Mechanism to connect to the ABCI application: socket | grpc
    ABCI string `mapstructure:"abci"`

    // TCP or UNIX socket address for the profiling server to listen on
    ProfListenAddress string `mapstructure:"prof_laddr"`

    // If true, query the ABCI app on connecting to a new peer
    // so the app can decide if we should keep the connection or not
    FilterPeers bool `mapstructure:"filter_peers"` // false
}

这是tendermint最基本的配置项，其中最为关键的配置项为RootDir，但是，我在代码中找了很久，都没有发现对这个配置项直接赋值的操作，那么，这个配置项是在哪初始化的呢？

rootCmd在执行的时候，预先执行了另外一个函数，我们来看看：

1 func PrepareBaseCmd(cmd *cobra.Command, envPrefix, defaultHome string) Executor {
2   cobra.OnInitialize(func() { initEnv(envPrefix) })
3   cmd.PersistentFlags().StringP(HomeFlag, "", defaultHome, "directory for config and data")
4   cmd.PersistentFlags().Bool(TraceFlag, false, "print out full stack trace on errors")
5   cmd.PersistentPreRunE = concatCobraCmdFuncs(bindFlagsLoadViper, cmd.PersistentPreRunE)
6   return Executor{cmd, os.Exit}
}

其中，在第3行代码中，注入了一个环境变量

home = ~./tendermint  # HomeFlag = "home", defaultHome=cfg.DefaultTendermintDir

再回头看看ParseConfig()这个函数

1 func ParseConfig() (*cfg.Config, error) {
2   conf := cfg.DefaultConfig()
3   err := viper.Unmarshal(conf)
4   if err != nil {
5       return nil, err
6   }
7   conf.SetRoot(conf.RootDir)
8   cfg.EnsureRoot(conf.RootDir)
9   return conf, err
}

在第二行中从代码中加载了默认配置，而第三行会从配置文件中加载配置，实际上，viper先从环境变量中加载对应的配置，下面是viper加载配置的方式：

Viper uses the following precedence order. Each item takes precedence over the item below it:

1. explicit call to Set
2. flag
3. env
4. config
5. key/value store
6. default

从上面可以看出，环境变量是可以覆盖配置文件中的设置的。这个原则可以类比12-Factor