cosmos-sdk/depinject/README.md

Cosmos SDK Dependency Injection depinject Module

Overview

depinject is a dependency injection framework for the Cosmos SDK. This module together with core/appconfig are meant to simplify the definition of a blockchain by replacing most of app.go's boilerplate code with a configuration file (YAML or JSON).

Usage

depinject example

package main

import (
	"fmt"

	"cosmossdk.io/depinject"
)

type AnotherInt int

func main() {
	var (
	  x int
	  y AnotherInt
	)

	fmt.Printf("Before (%v, %v)\n", x, y)
	depinject.Inject(
		depinject.Provide(
			func() int { return 1 },
			func() AnotherInt { return AnotherInt(2) },
		),
		&x,
		&y,
	)
	fmt.Printf("After (%v, %v)\n", x, y)
}

Full example in real app

//go:embed app.yaml
var appConfigYaml []byte

var appConfig = appconfig.LoadYAML(appConfigYaml)

func NewSimApp(
	logger log.Logger,
	db dbm.DB,
	traceStore io.Writer,
	loadLatest bool,
	skipUpgradeHeights map[int64]bool,
	homePath string,
	invCheckPeriod uint,
	encodingConfig simappparams.EncodingConfig,
	appOpts servertypes.AppOptions,
	baseAppOptions ...func(*baseapp.BaseApp),
) *SimApp {
	app := &SimApp{
		invCheckPeriod: invCheckPeriod,
	}

	var (
		appBuilder *runtime.AppBuilder
		msgServiceRouter *baseapp.MsgServiceRouter
	)

	err := depinject.Inject(AppConfig,
		&appBuilder,
		&app.ParamsKeeper,
		&app.CapabilityKeeper,
		&app.appCodec,
		&app.legacyAmino,
		&app.interfaceRegistry,
		&app.AccountKeeper,
		&app.BankKeeper,
		&app.FeeGrantKeeper,
		&app.StakingKeeper,
		&msgServiceRouter,
	)
	if err != nil {
		panic(err)
	}
...

Debugging

Issues with resolving dependencies in the container can be done with logs and Graphviz renderings of the container tree. By default, whenever there is an error, logs will be printed to stderr and a rendering of the dependency graph in Graphviz DOT format will be saved to debug_container.dot.

Here is an example Graphviz rendering of a successful build of a dependency graph:

Rectangles represent functions, ovals represent types, rounded rectangles represent modules and the single hexagon represents the function which called Build. Black-colored shapes mark functions and types that were called/resolved without an error. Gray-colored nodes mark functions and types that could have been called/resolved in the container but were left unused.

Here is an example Graphviz rendering of a dependency graph build which failed:

Graphviz DOT files can be converted into SVG's for viewing in a web browser using the dot command-line tool, ex:

> dot -Tsvg debug_container.dot > debug_container.svg

Many other tools including some IDEs support working with DOT files.