vt-enable

As Windows 10 and 11 terminals support ANSI escape sequences natively, correct processing requires the so-called Virtual Terminal Processing Mode to be enabled. Unfortunately, it's not guaranteed that the VT mode is on by default.

This is a minimalistic package with a single function – enable the VT mode on Windows.

Installation

$ go get github.com/flexits/vt-enable@latest

Usage

Just call Enable() before outputting any escape sequences:

package main

import (
	// ...
  "github.com/flexits/vt-enable"
)

func main() {
	// Enable VT mode for Windows; a no-op on other OSes.
	vt.Enable()
	
	// ...
}

Alternatively, put the call into the init() function.

Internals

The operation is based on the WinAPI SetConsoleMode call. The pure implementation is provided below,however, the golang.org/x/sys/windows package provides convenient wrappers, and the resulting code is much shorter.

const (
	ENABLE_VIRTUAL_TERMINAL_PROCESSING = 0x0004
	STD_OUTPUT_HANDLE                  = 0xFFFF_FFFF - 10
)

func EnableAnsi() error {
	modKernel32 := windows.NewLazyDLL("kernel32.dll")
	procGetStdHandle := modKernel32.NewProc("GetStdHandle")
	procGetConsoleMode := modKernel32.NewProc("GetConsoleMode")
	procSetConsoleMode := modKernel32.NewProc("SetConsoleMode")
	// sets all bits to 1, resuting in the maximum posiible value
	maxUintptr := ^uintptr(0)

	h, _, err := procGetStdHandle.Call(uintptr(STD_OUTPUT_HANDLE))
	if h == maxUintptr {
		return err
		// TODO use windows.GetLastError() to get the actual code
	}
	if h == 0 {
		return errors.New("no associated standard handles")
	}

	var mode uint32
	r, _, err := procGetConsoleMode.Call(h, uintptr(unsafe.Pointer(&mode)))
	if r == 0 {
		return err
		// TODO use windows.GetLastError() to get the actual code
	}

	newMode := mode | ENABLE_VIRTUAL_TERMINAL_PROCESSING
	r, _, err = procSetConsoleMode.Call(h, uintptr(newMode))
	if r == 0 {
		return err
		// TODO use windows.GetLastError() to get the actual code
	}

	return nil
}