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Merge PR cosmos#6806: Docs & Cleanup
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,116 @@ | ||
| # Server | ||
|
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||
| The `server` package is responsible for providing the mechanisms necessary to | ||
| start an ABCI Tendermint application and providing the CLI framework necessary | ||
| to fully bootstrap an application. The package exposes two core commands, `StartCmd` | ||
| and `ExportCmd`. | ||
|
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||
| ## Preliminary | ||
|
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| The root command of an application typically is constructed with three core | ||
| sub-commands, query commands, tx commands, and auxiliary commands such as genesis | ||
| utilities, and starting an application binary. | ||
|
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| It is vital that the root command of an application set the appropriate `PersistentPreRun(E)` | ||
| function so all child commands have access to the server and client contexts. | ||
| These contexts are set as their default values initially and maybe modified, | ||
| scoped to the command, in their respective `PersistentPreRun(E)` functions. Note, | ||
| the `client.Context` is typically pre-populated with "default" values that may be | ||
| useful for all commands to inherit and override if necessary. | ||
|
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| Example: | ||
|
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| ```go | ||
| var ( | ||
| rootCmd = &cobra.Command{ | ||
| Use: "simd", | ||
| Short: "simulation app", | ||
| PersistentPreRunE: func(cmd *cobra.Command, _ []string) error { | ||
| if err := client.SetCmdClientContextHandler(initClientCtx, cmd); err != nil { | ||
| return err | ||
| } | ||
|
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| return server.InterceptConfigsPreRunHandler(cmd) | ||
| }, | ||
| } | ||
|
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| encodingConfig = simapp.MakeEncodingConfig() | ||
| initClientCtx = client.Context{}. | ||
| WithJSONMarshaler(encodingConfig.Marshaler). | ||
| WithTxConfig(encodingConfig.TxConfig). | ||
| WithCodec(encodingConfig.Amino). | ||
| WithInput(os.Stdin). | ||
| WithAccountRetriever(types.NewAccountRetriever(encodingConfig.Marshaler)). | ||
| WithBroadcastMode(flags.BroadcastBlock). | ||
| WithHomeDir(simapp.DefaultNodeHome) | ||
| ) | ||
| ``` | ||
|
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| The `SetCmdClientContextHandler` call reads persistent flags via `ReadPersistentCommandFlags` | ||
| which creates a `client.Context` and sets that on the root command's `Context`. | ||
|
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| The `InterceptConfigsPreRunHandler` call creates a viper literal, default `server.Context`, | ||
| and a logger and sets that on the root command's `Context`. The `server.Context` | ||
| will be modified and saved to disk via the internal `interceptConfigs` call, which | ||
| either reads or creates a Tendermint configuration based on the home path provided. | ||
| In addition, `interceptConfigs` also reads and loads the application configuration, | ||
| `app.toml`, and binds that to the `server.Context` viper literal. This is vital | ||
| so the application can get access to not only the CLI flags, but also to the | ||
| application configuration values provided by this file. | ||
|
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| ## `StartCmd` | ||
|
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| The `StartCmd` accepts an `AppCreator` function which returns an `Application`. | ||
| The `AppCreator` is responsible for constructing the application based on the | ||
| options provided to it via `AppOptions`. The `AppOptions` interface type defines | ||
| a single method, `Get() interface{}`, and is implemented as a [viper](https://github.com/spf13/viper) | ||
| literal that exists in the `server.Context`. All the possible options an application | ||
| may use and provide to the construction process are defined by the `StartCmd` | ||
| and by the application's config file, `app.toml`. | ||
|
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| The application can either be started in-process or as an external process. The | ||
| former creates a Tendermint service and the latter creates a Tendermint Node. | ||
|
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| Under the hood, `StartCmd` will call `GetServerContextFromCmd`, which provides | ||
| the command access to a `server.Context`. This context provides access to the | ||
| viper literal, the Tendermint config and logger. This allows flags to be bound | ||
| the viper literal and passed to the application construction. | ||
|
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| Example: | ||
|
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| ```go | ||
| func newApp(logger log.Logger, db dbm.DB, traceStore io.Writer, appOpts server.AppOptions) server.Application { | ||
| var cache sdk.MultiStorePersistentCache | ||
|
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| if cast.ToBool(appOpts.Get(server.FlagInterBlockCache)) { | ||
| cache = store.NewCommitKVStoreCacheManager() | ||
| } | ||
|
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| skipUpgradeHeights := make(map[int64]bool) | ||
| for _, h := range cast.ToIntSlice(appOpts.Get(server.FlagUnsafeSkipUpgrades)) { | ||
| skipUpgradeHeights[int64(h)] = true | ||
| } | ||
|
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| pruningOpts, err := server.GetPruningOptionsFromFlags(appOpts) | ||
| if err != nil { | ||
| panic(err) | ||
| } | ||
|
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| return simapp.NewSimApp( | ||
| logger, db, traceStore, true, skipUpgradeHeights, | ||
| cast.ToString(appOpts.Get(flags.FlagHome)), | ||
| cast.ToUint(appOpts.Get(server.FlagInvCheckPeriod)), | ||
| baseapp.SetPruning(pruningOpts), | ||
| baseapp.SetMinGasPrices(cast.ToString(appOpts.Get(server.FlagMinGasPrices))), | ||
| baseapp.SetHaltHeight(cast.ToUint64(appOpts.Get(server.FlagHaltHeight))), | ||
| baseapp.SetHaltTime(cast.ToUint64(appOpts.Get(server.FlagHaltTime))), | ||
| baseapp.SetInterBlockCache(cache), | ||
| baseapp.SetTrace(cast.ToBool(appOpts.Get(server.FlagTrace))), | ||
| ) | ||
| } | ||
| ``` | ||
|
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||
| Note, some of the options provided are exposed via CLI flags in the start command | ||
| and some are also allowed to be set in the application's `app.toml`. It is recommend | ||
| to use the `cast` package for type safety guarantees and due to the limitations of | ||
| CLI flag types. |
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