Minimal example (without GUI)

package main

import "C"
import "fmt"

func init(){
  // injection func
  fmt.Println("Injected")
}

func main(){}

To build the DLL you need to make function init()

Everything in this function will be executed after DLL injection.

Minimal example with GUI

I'm using library github.com/AllenDang/giu, basically easier imgui bindings for Go.

package main

import "C"
import "github.com/AllenDang/giu"

func init(){
	wnd := giu.NewMasterWindow("Hello world", 400, 200, giu.MasterWindowFlagsNotResizable)
	wnd.Run(func(){
		// some code
	})
}

func main(){}

You can also run this script without building DLL, for example if you want to test it, but build and inject dll is too long

Full example with GUI and button

Using syscall and windows libraries for requesting message box.

package main

import "C"
import (
    "golang.org/x/sys/windows"
    "github.com/AllenDang/giu"
    "syscall"
)

func init(){
	wnd := giu.NewMasterWindow("Hello world", 200, 50, giu.MasterWindowFlagsNotResizable)
	wnd.Run(func(){
		giu.SingleWindow().Layout(
			giu.Button("Example Button").OnClick(func(){
				requestMessage("Hello from DLL Gui", "Title")
			}),
		)
	})
}

func requestMessage(message, title string) {
	windows.MessageBox(
		windows.HWND(0),
		syscall.StringToUTF16Ptr(message),
		syscall.StringToUTF16Ptr(title),
		windows.MB_OK,
	)
}

func main(){}

More examples you can find here.

Building

You can build DLL only on Windows, which is obvious

Format: go build -o <filename> -buildmode=c-shared <filepath>

Example: go build -o dllmain.dll -buildmode=c-shared main.go