Go Academy · Lesson

Designing a Plugin Interface

Shared interface contracts between host and plugin

Designing a Plugin Interface is a free Go Academy lesson on CoddyKit — lesson 2 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Go Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Interface-based plugins

Define a stable Go interface that plugins must implement. The host loads the plugin, retrieves the implementation, and calls it through the interface — no type assertions on every method.

type Processor interface {
    Name() string
    Process(ctx context.Context, data []byte) ([]byte, error)
}

Plugin entry point

Each plugin exports a known symbol (e.g., Plugin) that returns the interface implementation:

// In the plugin:
var Plugin processor // exported symbol

type processor struct{}
func (p processor) Name() string { return "my-processor" }
func (p processor) Process(ctx context.Context, data []byte) ([]byte, error) {
    return bytes.ToUpper(data), nil
}

Loading via interface

In the host, load the symbol and assert it to the interface:

sym, _ := p.Lookup("Plugin")
proc, ok := sym.(Processor)
if !ok { log.Fatal("plugin does not implement Processor") }

Registry pattern

Maintain a registry of loaded plugins by name:

var registry = map[string]Processor{}

func register(p Processor) { registry[p.Name()] = p }
func get(name string) (Processor, bool) {
    p, ok := registry[name]
    return p, ok
}

Interface versioning

Add a Version() method to the interface so the host can verify compatibility before registering the plugin.

type Versioned interface {
    APIVersion() string
}
if v, ok := proc.(Versioned); ok && v.APIVersion() != "1.0" {
    log.Fatalf("incompatible plugin version: %s", v.APIVersion())
}

Context and cancellation

Thread context through plugin method calls so the host can cancel long-running plugin operations on shutdown or request timeout.

Error handling contract

Define whether plugins should panic or return errors on failure. Returning errors is safer — panics in plugins may not be catchable by the host's recover middleware.

Configuration

Pass configuration to plugins at load time via an Init(config map[string]string) error method. This separates plugin creation from configuration.

Lifecycle management

Add Close() error to the interface for plugins that hold resources (DB connections, goroutines) that need cleanup on shutdown.

Testing plugins independently

Test the plugin implementation directly (as a Go package) without loading the .so binary. The interface makes mock testing straightforward.

Documentation contract

Document the interface contract clearly: which methods are called when, threading guarantees, and what constitutes an error vs a fatal condition.

Quick Check

Why define a stable Go interface for plugins instead of looking up individual function symbols?

Recap: Plugin Interface Design

Key points:

Define a stable interface the plugin must implement
Export a known symbol (var Plugin InterfaceType) from the plugin
Single type assertion at load time; all calls type-safe via interface
Add Version(), Init(), and Close() for lifecycle management

Frequently asked questions

Is the “Designing a Plugin Interface” lesson free?

Yes — the full text of “Designing a Plugin Interface” is free to read here on the web, and the Go Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Go Academy course, upgrade to CoddyKit PRO.

What will I learn in “Designing a Plugin Interface”?

Shared interface contracts between host and plugin You practise Go Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Go Academy?

No prior experience is required. Go Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 2 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Designing a Plugin Interface” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Go Academy lesson?

Yes. Every Go Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

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