Dynamic Plugin Loading in Go

Many applications benefit from the ability to extend their functionality at runtime without recompiling the core application. This is particularly useful for plugins, feature toggles, or configuration-driven behavior. This challenge focuses on implementing dynamic loading of code in Go using the plugin system.

Problem Description

Your task is to create a Go program that can load and execute functions from external shared libraries (plugins) dynamically. The main application should be able to discover and use functions provided by these plugins.

What needs to be achieved:

1. Create a main application that serves as the host for plugins.
2. Create one or more plugin libraries that expose specific functions.
3. The main application must load these plugins at runtime based on a configuration or command-line argument.
4. The main application should be able to call functions exported by the loaded plugins.

Key Requirements:

• Plugin Interface: Define a common interface or set of conventions that plugins must adhere to so the main application can interact with them consistently.
• Loading Mechanism: Implement a mechanism within the main application to load .so files (or .dylib on macOS, .dll on Windows) dynamically.
• Function Invocation: Safely access and invoke functions exported by the loaded plugins.
• Error Handling: Gracefully handle errors during plugin loading and function invocation.

Expected Behavior:

The main application should be able to:

1. Be started with a specification of which plugin(s) to load.
2. Load the specified plugin(s).
3. Call a specific, exported function from each loaded plugin.
4. Display the result of the called function.

Important Edge Cases:

• Loading a plugin that does not exist.
• Loading a plugin that exports no compatible functions.
• Calling a function that is not exported by the plugin.
• Plugin incompatibility (e.g., Go version mismatch).

Examples

Example 1: Simple Greeting Plugin

Let's assume you have a plugin named greeter.so that exports a function Greet.

• Plugin Code (greeter/greeter.go):

  package main
  
  import "fmt"
  
  // Greet exports a greeting message.
  func Greet() string {
      return "Hello from the greeter plugin!"
  }
  
  // The main function is required for plugins but is not executed by the host.
  func main() {}
  

  (This would be compiled into greeter.so)

• Main Application Input: Assume the greeter.so plugin is placed in a ./plugins/ directory. The main application is run with an argument specifying the plugin to load and the function to call. For simplicity, let's imagine a command like: go run main.go --plugin ./plugins/greeter.so --function Greet

• Main Application Output:

  Plugin loaded successfully.
  Function 'Greet' executed.
  Result: Hello from the greeter plugin!
  

• Explanation: The main application finds greeter.so, loads it, looks for the Greet symbol, calls it, and prints the returned string.

Example 2: Calculator Plugin

Let's assume you have a plugin named calculator.so that exports a function Add which takes two integers and returns their sum.

• Plugin Code (calculator/calculator.go):

  package main
  
  import "fmt"
  
  // Add takes two integers and returns their sum.
  func Add(a, b int) int {
      return a + b
  }
  
  // The main function is required for plugins but is not executed by the host.
  func main() {}
  

  (This would be compiled into calculator.so)

• Main Application Input: Assume calculator.so is in ./plugins/. The main application is run with: go run main.go --plugin ./plugins/calculator.so --function Add --args "5,10"

• Main Application Output:

  Plugin loaded successfully.
  Function 'Add' executed.
  Result: 15
  

• Explanation: The main application loads calculator.so, finds Add, parses the arguments "5" and "10" as integers, calls Add(5, 10), and prints the result.

Constraints

• Plugins must be compiled for the same operating system and architecture as the main application.
• Plugins must be built using go build -buildmode=plugin.
• Functions exposed by plugins must be exported (start with a capital letter).
• The primary mechanism for interaction will be through exported functions that return specific types or can be marshaled/unmarshaled (e.g., using interface{} and type assertions, or gob encoding). For this challenge, focus on simple types or interface{}.
• The main application should gracefully exit if a plugin cannot be loaded or a function cannot be found/called.

Notes

• The plugin package in Go is your primary tool here. Familiarize yourself with plugin.Open() and plugin.Lookup().
• Consider how you will handle passing arguments to and receiving results from plugin functions. Using interface{} and type assertions is a common approach for flexibility, but requires careful error handling.
• The plugin package relies on a shared symbol table. This means the Go version used to build the plugin must be compatible with the Go version used to build the host application.
• For simplicity in this challenge, you can assume the main application knows the expected signature of the functions it's trying to call. In a real-world scenario, you might need more sophisticated reflection or a plugin registry.