Dynamic Plugin Loading in Go

Modern applications often benefit from extensibility, allowing new features or functionalities to be added without recompiling the core application. This challenge focuses on implementing a robust plugin loading mechanism in Go, enabling your application to dynamically discover and utilize external code modules at runtime.

Problem Description

You need to design and implement a Go program that can load and execute code from external shared libraries (plugins) dynamically. These plugins will expose a predefined interface, allowing the main application to interact with them in a consistent manner.

Key Requirements:

1. Plugin Interface: Define a clear Go interface that all plugins must implement. This interface should include at least one method for the plugin to perform its core functionality and another for it to identify itself.
2. Plugin Discovery: The application should be able to discover available plugins. For this challenge, assume plugins are located in a specific directory.
3. Dynamic Loading: Implement the logic to load these discovered plugins as shared libraries (.so files on Linux/macOS, .dll on Windows) at runtime.
4. Instantiation and Interaction: Once loaded, the application must be able to instantiate the plugin's implementation of the defined interface and call its methods.
5. Error Handling: Gracefully handle potential errors during discovery, loading, instantiation, and execution of plugins. This includes cases where a plugin file is missing, corrupted, or doesn't implement the required interface.

Expected Behavior:

The application should:

• Scan a designated plugin directory.
• For each discovered shared library, attempt to load it.
• If loading is successful, try to find a symbol (function or variable) that represents the plugin's entry point (e.g., a function that returns an instance of the plugin interface).
• If an entry point is found, create an instance of the plugin.
• Call the plugin's methods to demonstrate its functionality.
• Report any errors encountered.

Edge Cases to Consider:

• No plugins found in the directory.
• Plugin files that are not valid Go shared libraries.
• Plugins that do not implement the required interface.
• Plugins that panic during initialization or execution.
• Concurrency: While not explicitly required for this basic version, consider how thread safety might be important in a real-world scenario.

Examples

Example 1: Basic Plugin Functionality

Let's define a simple Plugin interface:

package main

type Plugin interface {
	Name() string
	Execute(data string) (string, error)
}

And a plugin implementation:

package main

import "fmt"

type GreeterPlugin struct{}

func (p *GreeterPlugin) Name() string {
	return "Greeter"
}

func (p *GreeterPlugin) Execute(data string) (string, error) {
	if data == "" {
		return "", fmt.Errorf("input data cannot be empty")
	}
	return fmt.Sprintf("Hello, %s!", data), nil
}

// This function will be the entry point for the plugin loader
func NewPlugin() Plugin {
	return &GreeterPlugin{}
}

Input:

• A directory named plugins containing a shared library greeter.so (or greeter.dll) compiled from the GreeterPlugin code.
• The main application calls LoadPlugins("plugins") and then iterates through loaded plugins, calling Execute("World").

Output:

Loaded plugin: Greeter
Plugin output: Hello, World!

Explanation:

The application finds greeter.so, loads it, finds the NewPlugin symbol, instantiates GreeterPlugin, registers it, and then calls Execute("World") on it, producing the greeting.

Example 2: Plugin with an Error

Input:

• Same plugins directory and greeter.so as Example 1.
• The main application calls Execute("").

Output:

Loaded plugin: Greeter
Plugin error: input data cannot be empty

Explanation:

The application successfully loads and instantiates the plugin, but when Execute("") is called, the plugin returns an error, which the application correctly reports.

Example 3: Invalid Plugin File

Input:

• A plugins directory containing a file named invalid.txt with arbitrary content.

Output:

Error loading plugin invalid.txt: %w (e.g., "plugin: failed to load shared library: invalid.txt: invalid ELF header" or similar OS-level error)

Explanation:

The application attempts to load invalid.txt, but it's not a valid shared library, so the loading process fails with an appropriate error message.

Constraints

• Plugins will be compiled as Go shared libraries.
• The entry point for each plugin will be a function named NewPlugin that returns an instance of the defined Plugin interface.
• Plugins will be located in a single, specified directory (e.g., ./plugins).
• The application should support loading plugins on Linux, macOS, and Windows.
• The plugin loading mechanism should not cause the main application to crash.

Notes

• You will need to use the plugin package in Go's standard library for dynamic loading.
• Remember to compile your plugin code into a shared library. For example, using go build -buildmode=plugin -o greeter.so greeter.go.
• Consider how you will manage multiple plugins. A map or slice to store loaded plugins would be appropriate.
• The plugin package uses symbol lookup. Ensure your plugin's entry point function is exported (starts with an uppercase letter).