Golang plugins
Plugins are one of the few nearly forgotten features in Go, and frankly, I advise against using them. Unlike other features of the language, plugins only work on Linux, BSD, and macOS. Because they are built on dlopen, you cannot unload or replace a plugin once it has been loaded. On top of that, you need CGO, which brings complications of its own.
Despite the problems, plugins are an interesting feature and can be useful in some cases, such as loading a module dynamically.
Before compiling the plugin, you need to enable CGO.
export CGO_ENABLED=1
A plugin is written just like any other code we are used to. See the example below.
package main
import "fmt"
func Hello() error {
fmt.Println("hello, plugins!")
return nil
}
Create a project as usual, but do not name it plugin — that causes a compilation error.
To compile a plugin, use the -buildmode=plugin flag.
go build -buildmode=plugin
This produces a hello.so file containing the functions a main program can load.
If you want the plugin to have a name other than hello.so, use the -o flag, as in the example:
go build -buildmode=plugin -o novonome.so
To use a plugin, first load the file.
var p *plugin.Plugin
var err error
p, err = plugin.Open("./hello/hello.so")
if err != nil {
fmt.Println(err)
return
}
Then look up the function inside the plugin file.
var s plugin.Symbol
s, err = p.Lookup("Hello")
if err != nil {
fmt.Println(err)
return
}
The variable s is an interface. Convert it to the same signature as the Hello function that came from the plugin. Create a variable with the same name as the function so you can call it directly.
Hello := s.(func() error)
Now you can call Hello normally, like any other function in your code.
err = Hello()
if err != nil {
fmt.Println(err)
return
}
Plugins can be useful for building less monolithic systems. That said, this does not seem as relevant today as it once was. The lack of support for other platforms, the CGO requirement, and the impossibility of unloading plugins all make the feature less appealing.
Video explaining the code: