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Version: 0.47

Overview of app_v2.go

Synopsis

The Cosmos SDK allows much easier wiring of an app.go thanks to App Wiring and depinject. Learn more about the rationale of App Wiring in ADR-057.

note

Pre-requisite Readings​

This section is intended to provide an overview of the SimApp app_v2.go file with App Wiring.

app_config.go​

The app_config.go file is the single place to configure all modules parameters.

  1. Create the AppConfig variable:

    https://github.com/cosmos/cosmos-sdk/blob/v0.47.0-rc1/simapp/app_config.go#L91-L93

  2. Configure the runtime module:

    https://github.com/cosmos/cosmos-sdk/blob/v0.47.0-rc1/simapp/app_config.go#L94-L158

  3. Configure the modules defined in the BeginBlocker and EndBlocker and the tx module:

    https://github.com/cosmos/cosmos-sdk/blob/v0.47.0-rc1/simapp/app_config.go#L159-L177
    https://github.com/cosmos/cosmos-sdk/blob/v0.47.0-rc1/simapp/app_config.go#L192-L194

Complete app_config.go​

https://github.com/cosmos/cosmos-sdk/blob/v0.47.0-rc1/simapp/app_config.go#L52-L254

Alternative formats​

tip

The example above shows how to create an AppConfig using Go. However, it is also possible to create an AppConfig using YAML, or JSON.
The configuration can then be embed with go:embed and read with appconfig.LoadYAML, or appconfig.LoadJSON, in app_v2.go.

//go:embed app_config.yaml
var (
    appConfigYaml []byte
    appConfig = appconfig.LoadYAML(appConfigYaml)
)
modules:
  - name: runtime
    config:
      "@type": cosmos.app.runtime.v1alpha1.Module
      app_name: SimApp
      begin_blockers: [staking, auth, bank]
      end_blockers: [bank, auth, staking]
      init_genesis: [bank, auth, staking]
  - name: auth
    config:
      "@type": cosmos.auth.module.v1.Module
      bech32_prefix: cosmos
  - name: bank
    config:
      "@type": cosmos.bank.module.v1.Module
  - name: staking
    config:
      "@type": cosmos.staking.module.v1.Module
  - name: tx
    config:
      "@type": cosmos.tx.module.v1.Module

A more complete example of app.yaml can be found here.

app_v2.go​

app_v2.go is the place where SimApp is constructed. depinject.Inject facilitates that by automatically wiring the app modules and keepers, provided an application configuration AppConfig is provided. SimApp is constructed, when calling the injected *runtime.AppBuilder, with appBuilder.Build(...).
In short depinject and the runtime package abstract the wiring of the app, and the AppBuilder is the place where the app is constructed. runtime takes care of registering the codecs, KV store, subspaces and instantiating baseapp.

https://github.com/cosmos/cosmos-sdk/blob/v0.47.0-rc1/simapp/app_v2.go#L158-L291
danger

When using depinject.Inject, the injected types must be pointers.

Advanced Configuration​

In advanced cases, it is possible to inject extra (module) configuration in a way that is not (yet) supported by AppConfig.
In this case, use depinject.Configs for combining the extra configuration and AppConfig, and depinject.Supply to providing that extra configuration. More information on how work depinject.Configs and depinject.Supply can be found in the depinject documentation.

https://github.com/cosmos/cosmos-sdk/blob/v0.47.0-rc1/simapp/app_v2.go#L186-L216

Complete app_v2.go​

tip

Note that in the complete SimApp app_v2.go file, testing utilities are also defined, but they could as well be defined in a separate file.

https://github.com/cosmos/cosmos-sdk/blob/v0.47.0-rc1/simapp/app_v2.go#L75-L395