Kessoku: Parallel DI for Go

Kessoku is a compile-time dependency injection library that speeds up Go application startup through parallel initialization. Unlike google/wire (sequential), kessoku runs independent providers concurrently.

Use this skill when you are building or debugging kessoku injectors/providers, wiring async dependencies, migrating from google/wire, or troubleshooting go tool kessoku generation problems.

Supporting files: [PATTERNS.md](references/PATTERNS.md) for examples, [MIGRATION.md](references/MIGRATION.md) for wire migration, [TROUBLESHOOTING.md](references/TROUBLESHOOTING.md) for common errors.

When to Use Kessoku

• Slow startup: Multiple DB connections, API clients, or cache initialization
• Cold start optimization: Serverless/Lambda functions timing out
• google/wire alternative: Want compile-time DI with parallel execution

Quick Start

//go:generate go tool kessoku $GOFILE

package main

import "github.com/mazrean/kessoku"

var _ = kessoku.Inject[*App](
    "InitializeApp",
    kessoku.Async(kessoku.Provide(NewDB)),     // Parallel
    kessoku.Async(kessoku.Provide(NewCache)),  // Parallel
    kessoku.Provide(NewApp),                   // Waits for deps
)

Run: go generate ./... → generates *_band.go

API Reference

Common Patterns

Basic Injector

var _ = kessoku.Inject[*App](
    "InitializeApp",
    kessoku.Provide(NewConfig),
    kessoku.Provide(NewDB),
    kessoku.Provide(NewApp),
)
// Generates: func InitializeApp() *App

Parallel Initialization (Async)

var _ = kessoku.Inject[*App](
    "InitializeApp",
    kessoku.Async(kessoku.Provide(NewDB)),      // }
    kessoku.Async(kessoku.Provide(NewCache)),   // } Run in parallel
    kessoku.Async(kessoku.Provide(NewClient)),  // }
    kessoku.Provide(NewApp),
)
// Generates: func InitializeApp(ctx context.Context) (*App, error)

Interface Binding

var _ = kessoku.Inject[*App](
    "InitializeApp",
    kessoku.Bind[Repository](kessoku.Provide(NewPostgresRepo)),
    kessoku.Provide(NewApp),  // Receives Repository interface
)

Provider Sets (Reusability)

var DatabaseSet = kessoku.Set(
    kessoku.Provide(NewConfig),
    kessoku.Async(kessoku.Provide(NewDB)),
)

var _ = kessoku.Inject[*App]("InitializeApp",
    DatabaseSet,
    kessoku.Provide(NewApp),
)

Struct Field Expansion

var _ = kessoku.Inject[*DB](
    "InitializeDB",
    kessoku.Provide(NewConfig),   // Returns *Config{Host, Port}
    kessoku.Struct[*Config](),    // Expands to Host, Port fields
    kessoku.Provide(NewDB),       // Receives Host, Port separately
)

Key Points

• No build tag needed: Unlike wire's //go:build wireinject
• Async requires context: Generated function gets context.Context parameter
• Error propagation: Providers returning error make injector return error
• No cleanup functions: Wire-style cleanup func() returns are not supported — an unused cleanup return is silently discarded by codegen, and kessoku migrate rejects wire code using them; use an explicit Close method on the returned type instead

Support Files

For detailed information, see:

• [PATTERNS.md](references/PATTERNS.md) - Detailed patterns, examples, best practices
• [MIGRATION.md](references/MIGRATION.md) - Wire migration guide
• [TROUBLESHOOTING.md](references/TROUBLESHOOTING.md) - Common errors and solutions

Resources

• Repository: https://github.com/mazrean/kessoku
• Documentation: https://pkg.go.dev/github.com/mazrean/kessoku