How to create a command-line interface (CLI) tool that supports plugins in Golang?

To create a command-line interface (CLI) tool that supports plugins in Golang, you can follow these steps:

Create a basic CLI application: Start by creating a basic CLI application using popular packages like cobra or urfave/cli. These packages provide easy-to-use APIs for building CLI applications and handling commands and flags.
Define a plugin interface: Define an interface that outlines the methods required for a plugin to work with your application. For example, you may have methods like Init, Execute, or Cleanup in this interface.

type Plugin interface {
    Init()
    Execute(args []string)
    Cleanup()
}

Implement the plugin interface: Implement the plugin interface in separate packages. Each package should represent a specific plugin for your application. For example, you may have plugins like PluginA, PluginB, etc., each implementing the interface methods.

type PluginA struct{}

func (p *PluginA) Init() {
    // Plugin initialization logic
}

func (p *PluginA) Execute(args []string) {
    // Plugin execution logic
}

func (p *PluginA) Cleanup() {
    // Plugin cleanup logic
}

Load plugins dynamically: Use Go's reflection capabilities to load plugins dynamically at runtime. Create a function that scans a specific directory for plugin packages and loads them using the plugin package. Iterate over the loaded plugins and initialize them in your CLI application.

func loadPlugins() ([]Plugin, error) {
    var plugins []Plugin

    // Scan plugin directory
    pluginFiles, err := ioutil.ReadDir("plugins")
    if err != nil {
        return nil, err
    }

    for _, file := range pluginFiles {
        // Load plugin package dynamically
        pluginName := file.Name()
        plugin, err := plugin.Open("plugins/" + pluginName)
        if err != nil {
            return nil, err
        }

        // Lookup and instantiate the plugin
        symPlugin, err := plugin.Lookup("Plugin")
        if err != nil {
            return nil, err
        }

        pluginInstance, ok := symPlugin.(Plugin)
        if !ok {
            return nil, errors.New("Plugin interface not implemented")
        }
        
        // Initialize plugin
        pluginInstance.Init()
        plugins = append(plugins, pluginInstance)
    }

    return plugins, nil
}

Use plugins in CLI commands: Initialize the plugins in your CLI command methods and delegate their execution. When executing a specific command, iterate over the loaded plugins and call the respective method on each plugin instance.

func myCommand(cmd *cobra.Command, args []string) {
    plugins, err := loadPlugins()
    if err != nil {
        log.Fatal(err)
    }

    for _, plugin := range plugins {
        plugin.Execute(args)
    }
}

Build and run your application: Build your CLI application using Go's build tools. Ensure that the plugins are placed in the appropriate directory relative to your built binary. Run your application, and it will dynamically load and use the plugins during execution.

Your CLI application is now ready to support plugins. Third-party developers or even you can create plugins by implementing the plugin interface and placing them in the designated directory. Restarting the application will load and use the newly added plugins.