Example on how to access the Guild Wars 2 Mumble Link API on Windows using Go. Not supposed to be good Go code, but it works.

gw2-golang-poc.go

package main

import (
	"fmt"
	"log"
	"syscall"
	"time"
	"unsafe"
	"unicode/utf16"
	"unicode/utf8"
	"bytes"
)

type MumbleVector [3]float32
type WChar uint16

type MumbleIdentity [256]uint16
func (id MumbleIdentity) String() string {
	buf := make([]byte, 4)
	var ret bytes.Buffer
	runes := utf16.Decode(id[:])
	count := 0
	for _, rune := range runes {
		utf8.EncodeRune(buf, rune)
		ret.WriteString(string(rune))
		count++
	}
	return ret.String()
}

type MumblePosition struct {
	Position MumbleVector
	Front MumbleVector
	Top MumbleVector
}

type MumbleData struct {
	Version uint32
	Tick uint32
	Avatar MumblePosition
	Name [256]WChar
	Camera MumblePosition
	Identity MumbleIdentity
	ContextLength uint32
	Context [256]byte
	Description [2048]WChar
}

func main() {
	file, _ := syscall.UTF16PtrFromString("MumbleLink")
	size := 100000 // I’ve tried unsafe.Sizeof(MumbleData{}) but that didn’t work.
	handle, err := syscall.CreateFileMapping(0, nil, syscall.PAGE_READWRITE, 0, uint32(size), file)
	if err != nil {
		log.Fatal(err)
	}
	defer syscall.CloseHandle(handle)
	addr, err := syscall.MapViewOfFile(handle, syscall.FILE_MAP_READ, 0, 0, 0)
	if err != nil {
		log.Fatal(err)
	}
	for {
		data := (*MumbleData)(unsafe.Pointer(addr))
		time.Sleep(1 * time.Second)
		fmt.Printf("ava %v cam %v id %v\n", data.Avatar.Position, data.Camera, data.Identity)
	}
}

size := 100000 // I’ve tried unsafe.Sizeof(MumbleData{}) but that didn’t work.

I think the size needs to be atleast the size of a page (4096 bytes). it probably won't work for size of mumbleLink as it is only 1050 ish bytes.

quote from https://learn.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-createfilemappinga :

The maximum size of the file mapping object must be a multiple of the minimum size of a large page returned by the GetLargePageMinimum function.