How to Implement a Cross-Platform Global Hotkey in Go?

Implementing a Global Hotkey in Go

Challenge: Implementing a cross-platform (Mac, Linux, Windows) global hotkey in Go that responds to user input anywhere in the operating system.

Solution:

Utilizing the syscall package, one can access native operating system functions to register and listen for global hotkeys.

For Windows specifically:

1. Load User32 DLL: Load the user32.dll library, which contains the necessary functions for hotkey management.
2. Register Hotkeys: Use the RegisterHotKey function to register hotkeys with specific key combinations.
3. Handle Key Events: Employ the PeekMessage function to continuously check for and respond to message events. When a hotkey is pressed, its registered ID is stored in the WPARAM field, allowing the application to identify the pressed hotkey.

Example Application:

A simple Go application that demonstrates hotkey registration and handling on Windows:

package main

import (
    "fmt"
    "os"
    "time"

    "github.com/gonuts/syscall/՚user32"
)

type Hotkey struct {
    Id        int // Unique id
    Modifiers int // Mask of modifiers
    KeyCode   int // Key code, e.g. 'A'
}

func (h *Hotkey) String() string {
    mod := &bytes.Buffer{}
    if h.Modifiers&ModAlt != 0 {
        mod.WriteString("Alt+")
    }
    if h.Modifiers&ModCtrl != 0 {
        mod.WriteString("Ctrl+")
    }
    if h.Modifiers&ModShift != 0 {
        mod.WriteString("Shift+")
    }
    if h.Modifiers&ModWin != 0 {
        mod.WriteString("Win+")
    }
    return fmt.Sprintf("Hotkey[Id: %d, %s%c]", h.Id, mod, h.KeyCode)
}

const (
    ModAlt = 1 << iota
    ModCtrl
    ModShift
    ModWin
)

func main() {
    user32 := syscall.MustLoadDll("user32")
    defer user32.Release()

    reghotkey := user32.MustFindProc("RegisterHotKey")
    peekmsg := user32.MustFindProc("PeekMessageW")

    keys := map[int16]*Hotkey{
        1: &Hotkey{1, ModAlt + ModCtrl, 'O'},  // ALT+CTRL+O
        2: &Hotkey{2, ModAlt + ModShift, 'M'}, // ALT+SHIFT+M
        3: &Hotkey{3, ModAlt + ModCtrl, 'X'},  // ALT+CTRL+X
    }

    for _, v := range keys {
        r1, _, err := reghotkey.Call(
            0, uintptr(v.Id), uintptr(v.Modifiers), uintptr(v.KeyCode))
        if r1 == 1 {
            fmt.Println("Registered", v)
        } else {
            fmt.Println("Failed to register", v, ", error:", err)
        }
    }

    for {
        var msg = &MSG{}
        peekmsg.Call(uintptr(unsafe.Pointer(msg)), 0, 0, 0, 1)

        // Registered id is in the WPARAM field:
        if id := msg.WPARAM; id != 0 {
            fmt.Println("Hotkey pressed:", keys[id])
            if id == 3 { // CTRL+ALT+X = Exit
                fmt.Println("CTRL+ALT+X pressed, goodbye...")
                os.Exit(0)
            }
        }

        time.Sleep(time.Millisecond * 50)
    }
}

This example provides a complete implementation of hotkey registration and handling on Windows, which can be adapted for other operating systems using similar principles.

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