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//go:build windows
package cwriter
import (
"bytes"
"io"
"unsafe"
"golang.org/x/sys/windows"
)
var kernel32 = windows.NewLazySystemDLL("kernel32.dll")
var (
procSetConsoleCursorPosition = kernel32.NewProc("SetConsoleCursorPosition")
procFillConsoleOutputCharacter = kernel32.NewProc("FillConsoleOutputCharacterW")
)
// Writer is a buffered terminal writer, which moves cursor N lines up
// on each flush except the first one, where N is a number of lines of
// a previous flush.
type Writer struct {
*bytes.Buffer
out io.Writer
ew escWriter
lines int
fd int
terminal bool
termSize func(int) (int, int, error)
}
// Flush flushes the underlying buffer.
// It's caller's responsibility to pass correct number of lines.
func (w *Writer) Flush(lines int) error {
if w.lines > 0 {
err := w.clearLines(w.lines)
if err != nil {
return err
}
}
w.lines = lines
_, err := w.WriteTo(w.out)
return err
}
func (w *Writer) clearLines(n int) error {
if !w.terminal {
// hope it's cygwin or similar
return w.ew.ansiCuuAndEd(w.out, n)
}
var info windows.ConsoleScreenBufferInfo
if err := windows.GetConsoleScreenBufferInfo(windows.Handle(w.fd), &info); err != nil {
return err
}
info.CursorPosition.Y -= int16(n)
if info.CursorPosition.Y < 0 {
info.CursorPosition.Y = 0
}
_, _, _ = procSetConsoleCursorPosition.Call(
uintptr(w.fd),
uintptr(uint32(uint16(info.CursorPosition.Y))<<16|uint32(uint16(info.CursorPosition.X))),
)
// clear the lines
cursor := &windows.Coord{
X: info.Window.Left,
Y: info.CursorPosition.Y,
}
count := uint32(info.Size.X) * uint32(n)
_, _, _ = procFillConsoleOutputCharacter.Call(
uintptr(w.fd),
uintptr(' '),
uintptr(count),
*(*uintptr)(unsafe.Pointer(cursor)),
uintptr(unsafe.Pointer(new(uint32))),
)
return nil
}
// GetSize returns the visible dimensions of the given terminal.
// These dimensions don't include any scrollback buffer height.
func GetSize(fd int) (width, height int, err error) {
var info windows.ConsoleScreenBufferInfo
if err := windows.GetConsoleScreenBufferInfo(windows.Handle(fd), &info); err != nil {
return 0, 0, err
}
// terminal.GetSize from crypto/ssh adds "+ 1" to both width and height:
// https://go.googlesource.com/crypto/+/refs/heads/release-branch.go1.14/ssh/terminal/util_windows.go#75
// but looks like this is a root cause of issue #66, so removing both "+ 1" have fixed it.
return int(info.Window.Right - info.Window.Left), int(info.Window.Bottom - info.Window.Top), nil
}
// IsTerminal returns whether the given file descriptor is a terminal.
func IsTerminal(fd int) bool {
var st uint32
err := windows.GetConsoleMode(windows.Handle(fd), &st)
return err == nil
}
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