Building a plugin

Learn to build a plugin with go build -buildmode=plugin.

Building a plugin

A plugin is a package with package main that doesn't need a main function. Every exported (upper-case) function and variable becomes a symbol of the plugin.

// selam/selam.go
package main

func Selam(ad string) string { return "Merhaba " + ad }

Build: go build -buildmode=plugin -o selam.so ./selam

Version matching

The safest way to build the main program and the plugin with the same module versions is to keep them in the same repository or share the same go.mod. Loading a plugin built differently gives the error "plugin was built with a different version of package".

Exercise Write a plugin function

Add the function func Ikiye(n int) int to the code that will be built as a plugin (it returns twice n). In main, print fmt.Println(Ikiye(21)) as a test.

Show example solution

package main

import "fmt"

func Ikiye(n int) int { return n * 2 }

func main() {
    fmt.Println(Ikiye(21))
}

Test yourself

Which flag is needed to build a plugin?
- -o plugin
- -buildmode=plugin
- -plugin
- -shared=true
Show answer

-buildmode=plugin — go build -buildmode=plugin produces a shared object (.so); -o sets the file name.

Build command

go build ____ -o selam.so ./selam

Show answer

go build -buildmode=plugin -o selam.so ./selam

Plugin source

package main

Plugin package name
func Selam

Exported symbol
func yardimci

Hidden (lower case)
-o selam.so

Output file

Next lesson: Loading a plugin

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