modular

modular

Modular Go

Overview

Modular is a package that provides a structured way to create modular applications in Go. It allows you to build applications as collections of modules that can be easily added, removed, or replaced. Key features include:

• Module lifecycle management: Initialize, start, and gracefully stop modules
• Dependency management: Automatically resolve and order module dependencies
• Service registry: Register and retrieve application services
• Configuration management: Handle configuration for modules and services
• Configuration validation: Validate configurations with defaults, required fields, and custom logic
• Sample config generation: Generate sample configuration files in various formats
• Dependency injection: Inject required services into modules
• Multi-tenancy support: Build applications that serve multiple tenants with isolated configurations

Available Modules

Modular comes with a collection of reusable modules that you can incorporate into your applications:

For more information about the available modules, see the modules directory.

Installation

go get github.com/GoCodeAlone/modular

Usage

Basic Application

package main

import (
    "github.com/GoCodeAlone/modular"
    "log/slog"
    "os"
)

func main() {
    // Create a logger
    logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
    
    // Create config provider with application configuration
    config := &AppConfig{
        Name: "MyApp",
        Version: "1.0.0",
    }
    configProvider := modular.NewStdConfigProvider(config)
    
    // Create the application
    app := modular.NewStdApplication(configProvider, logger)
    
    // Register modules
    app.RegisterModule(NewDatabaseModule())
    app.RegisterModule(NewAPIModule())
    
    // Run the application (this will block until the application is terminated)
    if err := app.Run(); err != nil {
        logger.Error("Application error", "error", err)
        os.Exit(1)
    }
}

Creating a Module

type DatabaseModule struct {
    db     *sql.DB
    config *DatabaseConfig
}

func NewDatabaseModule() modular.Module {
    return &DatabaseModule{}
}

// RegisterConfig registers the module's configuration
func (m *DatabaseModule) RegisterConfig(app modular.Application) error {
    m.config = &DatabaseConfig{
        DSN: "postgres://user:password@localhost:5432/dbname",
    }
    app.RegisterConfigSection("database", modular.NewStdConfigProvider(m.config))
    return nil
}

// Name returns the module's unique name
func (m *DatabaseModule) Name() string {
    return "database"
}

// Dependencies returns other modules this module depends on
func (m *DatabaseModule) Dependencies() []string {
    return []string{} // No dependencies
}

// Init initializes the module
func (m *DatabaseModule) Init(app modular.Application) error {
    // Initialize database connection
    db, err := sql.Open("postgres", m.config.DSN)
    if (err != nil) {
        return err
    }
    m.db = db
    return nil
}

// ProvidesServices returns services provided by this module
func (m *DatabaseModule) ProvidesServices() []modular.ServiceProvider {
    return []modular.ServiceProvider{
        {
            Name:        "database",
            Description: "Database connection",
            Instance:    m.db,
        },
    }
}

// RequiresServices returns services required by this module
func (m *DatabaseModule) RequiresServices() []modular.ServiceDependency {
    return []modular.ServiceDependency{} // No required services
}

// Start starts the module
func (m *DatabaseModule) Start(ctx context.Context) error {
    return nil // Database is already connected
}

// Stop stops the module
func (m *DatabaseModule) Stop(ctx context.Context) error {
    return m.db.Close()
}

Service Dependencies

// A module that depends on another service
func (m *APIModule) RequiresServices() []modular.ServiceDependency {
    return []modular.ServiceDependency{
        {
            Name:     "database",
            Required: true,  // Application won't start if this service is missing
        },
        {
            Name:     "cache",
            Required: false, // Optional dependency
        },
    }
}

// Using constructor injection
func (m *APIModule) Constructor() modular.ModuleConstructor {
    return func(app modular.Application, services map[string]any) (modular.Module, error) {
        // Services that were requested in RequiresServices() are available here
        db := services["database"].(*sql.DB)
        
        // Create a new module instance with injected services
        return &APIModule{
            db: db,
        }, nil
    }
}

Interface-Based Service Matching

Modular supports finding and injecting services based on interface compatibility, regardless of the service name:

// Define an interface that services should implement
type LoggerService interface {
    Log(level string, message string)
}

// Require a service that implements a specific interface
func (m *MyModule) RequiresServices() []modular.ServiceDependency {
    return []modular.ServiceDependency{
        {
            Name:               "logger", // The name you'll use to access it in the Constructor
            Required:           true,
            MatchByInterface:   true, // Enable interface-based matching
            SatisfiesInterface: reflect.TypeOf((*LoggerService)(nil)).Elem(),
        },
    }
}

// Constructor will receive any service implementing LoggerService
func (m *MyModule) Constructor() modular.ModuleConstructor {
    return func(app modular.Application, services map[string]any) (modular.Module, error) {
        // This will work even if the actual registered service name is different
        logger := services["logger"].(LoggerService)
        return &MyModule{logger: logger}, nil
    }
}

See DOCUMENTATION.md for more advanced details about service dependencies and interface matching.

Configuration Management

// Define your configuration struct
type AppConfig struct {
    Name    string `json:"name" yaml:"name" default:"DefaultApp" desc:"Application name"`
    Version string `json:"version" yaml:"version" required:"true" desc:"Application version"`
    Debug   bool   `json:"debug" yaml:"debug" default:"false" desc:"Enable debug mode"`
}

// Implement ConfigValidator interface for custom validation
func (c *AppConfig) Validate() error {
    // Custom validation logic
    if c.Version == "0.0.0" {
        return fmt.Errorf("invalid version: %s", c.Version)
    }
    return nil
}

Configuration Validation and Default Values

Modular now includes powerful configuration validation features:

Default Values with Struct Tags

// Define struct with default values
type ServerConfig struct {
    Host        string `yaml:"host" default:"localhost" desc:"Server host"`
    Port        int    `yaml:"port" default:"8080" desc:"Server port"`
    ReadTimeout int    `yaml:"readTimeout" default:"30" desc:"Read timeout in seconds"`
    Debug       bool   `yaml:"debug" default:"false" desc:"Enable debug mode"`
}

Default values are automatically applied to fields that have zero/empty values when configurations are loaded.

Required Field Validation

type DatabaseConfig struct {
    Host     string `yaml:"host" default:"localhost" desc:"Database host"`
    Port     int    `yaml:"port" default:"5432" desc:"Database port"`
    Name     string `yaml:"name" required:"true" desc:"Database name"` // Must be provided
    User     string `yaml:"user" default:"postgres" desc:"Database user"`
    Password string `yaml:"password" required:"true" desc:"Database password"` // Must be provided
}

Required fields are validated during configuration loading, and appropriate errors are returned if they're missing.

Custom Validation Logic

// Implement the ConfigValidator interface
func (c *AppConfig) Validate() error {
    // Validate environment is one of the expected values
    validEnvs := map[string]bool{"dev": true, "test": true, "prod": true}
    if !validEnvs[c.Environment] {
        return fmt.Errorf("%w: environment must be one of [dev, test, prod]", modular.ErrConfigValidationFailed)
    }
    
    // Additional custom validation
    if c.Server.Port < 1024 || c.Server.Port > 65535 {
        return fmt.Errorf("%w: server port must be between 1024 and 65535", modular.ErrConfigValidationFailed)
    }
    
    return nil
}

Generating Sample Configuration Files

// Generate a sample configuration file
cfg := &AppConfig{}
err := modular.SaveSampleConfig(cfg, "yaml", "config-sample.yaml")
if err != nil {
    log.Fatalf("Error generating sample config: %v", err)
}

Sample configurations can be generated in YAML, JSON, or TOML formats, with all default values pre-populated.

Command-Line Integration

func main() {
    // Generate sample config file if requested
    if len(os.Args) > 1 && os.Args[1] == "--generate-config" {
        format := "yaml"
        if len(os.Args) > 2 {
            format = os.Args[2]
        }
        outputFile := "config-sample." + format
        if len(os.Args) > 3 {
            outputFile = os.Args[3]
        }
        
        cfg := &AppConfig{}
        if err := modular.SaveSampleConfig(cfg, format, outputFile); err != nil {
            fmt.Printf("Error generating sample config: %v\n", err)
            os.Exit(1)  // Error condition should exit with non-zero code
        }
        fmt.Printf("Sample config generated at %s\n", outputFile)
        os.Exit(0)
    }
    
    // Continue with normal application startup...
}

Multi-Tenant Support

Modular provides built-in support for multi-tenant applications through:

Tenant Contexts

// Creating a tenant context
tenantID := modular.TenantID("tenant1")
ctx := modular.NewTenantContext(context.Background(), tenantID)

// Using tenant context with the application
tenantCtx, err := app.WithTenant(tenantID)
if err != nil {
    log.Fatal("Failed to create tenant context:", err)
}

// Extract tenant ID from a context
if id, ok := modular.GetTenantIDFromContext(ctx); ok {
    fmt.Println("Current tenant:", id)
}

Tenant-Aware Configuration

// Register a tenant service in your module
func (m *MultiTenantModule) ProvidesServices() []modular.ServiceProvider {
    return []modular.ServiceProvider{
        {
            Name:        "tenantService",
            Description: "Tenant management service",
            Instance:    modular.NewStandardTenantService(m.logger),
        },
        {
            Name:        "tenantConfigLoader",
            Description: "Tenant configuration loader",
            Instance:    modular.DefaultTenantConfigLoader("./configs/tenants"),
        },
    }
}

// Create tenant-aware configuration
func (m *MultiTenantModule) RegisterConfig(app *modular.Application) {
    // Default config
    defaultConfig := &MyConfig{
        Setting: "default",
    }
    
    // Get tenant service (must be provided by another module)
    var tenantService modular.TenantService
    app.GetService("tenantService", &tenantService)
    
    // Create tenant-aware config provider
    tenantAwareConfig := modular.NewTenantAwareConfig(
        modular.NewStdConfigProvider(defaultConfig),
        tenantService,
        "mymodule",
    )
    
    app.RegisterConfigSection("mymodule", tenantAwareConfig)
}

// Using tenant-aware configs in your code
func (m *MultiTenantModule) ProcessRequestWithTenant(ctx context.Context) {
    // Get config specific to the tenant in the context
    config, ok := m.config.(*modular.TenantAwareConfig)
    if !ok {
        // Handle non-tenant-aware config
        return
    }
    
    // Get tenant-specific configuration
    myConfig := config.GetConfigWithContext(ctx).(*MyConfig)
    
    // Use tenant-specific settings
    fmt.Println("Tenant setting:", myConfig.Setting)
}

Tenant-Aware Modules

// Implement the TenantAwareModule interface
type MultiTenantModule struct {
    modular.Module
    tenantData map[modular.TenantID]*TenantData
}

func (m *MultiTenantModule) OnTenantRegistered(tenantID modular.TenantID) {
    // Initialize resources for this tenant
    m.tenantData[tenantID] = &TenantData{
        initialized: true,
    }
}

func (m *MultiTenantModule) OnTenantRemoved(tenantID modular.TenantID) {
    // Clean up tenant resources
    delete(m.tenantData, tenantID)
}

Loading Tenant Configurations

// Set up a file-based tenant config loader
configLoader := modular.NewFileBasedTenantConfigLoader(modular.TenantConfigParams{
    ConfigNameRegex: regexp.MustCompile("^tenant-[\\w-]+\\.(json|yaml)$"),
    ConfigDir:       "./configs/tenants",
    ConfigFeeders:   []modular.Feeder{},
})

// Register the loader as a service
app.RegisterService("tenantConfigLoader", configLoader)

Key Interfaces

Module

The core interface that all modules must implement:

type Module interface {
    RegisterConfig(app *Application)
    Init(app *Application) error
    Start(ctx context.Context) error
    Stop(ctx context.Context) error
    Name() string
    Dependencies() []string
    ProvidesServices() []ServiceProvider
    RequiresServices() []ServiceDependency
}

TenantAwareModule

Interface for modules that need to respond to tenant lifecycle events:

type TenantAwareModule interface {
    Module
    OnTenantRegistered(tenantID TenantID)
    OnTenantRemoved(tenantID TenantID)
}

TenantService

Interface for managing tenants:

type TenantService interface {
    GetTenantConfig(tenantID TenantID, section string) (ConfigProvider, error)
    GetTenants() []TenantID
    RegisterTenant(tenantID TenantID, configs map[string]ConfigProvider) error
}

ConfigProvider

Interface for configuration providers:

type ConfigProvider interface {
    GetConfig() any
}

ConfigValidator

Interface for implementing custom configuration validation logic:

type ConfigValidator interface {
    Validate() error
}

CLI Tool

Modular comes with a command-line tool (modcli) to help you create new modules and configurations.

Installation

You can install the CLI tool using one of the following methods:

Using go install (recommended)

go install github.com/GoCodeAlone/modular/cmd/modcli@latest

This will download, build, and install the latest version of the CLI tool directly to your GOPATH's bin directory, which should be in your PATH.

Download pre-built binaries

Download the latest release from the GitHub Releases page and add it to your PATH.

Build from source

# Clone the repository
git clone https://github.com/GoCodeAlone/modular.git
cd modular/cmd/modcli

# Build the CLI tool
go build -o modcli

# Move to a directory in your PATH
mv modcli /usr/local/bin/  # Linux/macOS
# or add the current directory to your PATH

Usage

Generate a new module:

modcli generate module --name MyFeature

Generate a configuration:

modcli generate config --name Server

For more details on available commands:

modcli --help

Each command includes interactive prompts to guide you through the process of creating modules or configurations with the features you need.

License

MIT License