os: Support reading Ctrl + Space from os.Stdin on Windows.

[lonnywong]

I'm writing an SSH client in Go, and want to pass Ctrl + Space to the server.

We can read Ctrl + Space from os.Stdin on MacOS and Linux, but not on Windows.

package main

import (
	"fmt"
	"os"

	"golang.org/x/term"
)

func main() {
	fd := int(os.Stdin.Fd())
	state, err := term.MakeRaw(fd)
	if err != nil {
		fmt.Println(err)
		return
	}
	defer term.Restore(fd, state)

	fmt.Printf("Please press some keys ...\r\n")
	buf := make([]byte, 100)
	for {
		n, err := os.Stdin.Read(buf)
		fmt.Printf("n = %d, err = %v, buf = %#v\r\n", n, err, buf[:n])
		if n > 0 && buf[0] == '\x03' { // `ctrl + c` to exit
			break
		}
	}
}

Related to:

1. Bug Report: Control+Space not sent to terminal emulator. microsoft/terminal#2865
2. modify key event logic to fix ctrl+space not being sent PowerShell/openssh-portable#569

[seankhliao]

This doesn't look like a go issue. os.Stdin has no concept of key combinations, it is just a stream of bytes. It is the terminal emulator's responsibility to turn key combinations into a byte sequence that's passed to programs

[lonnywong]

@seankhliao When the Ctrl+Space is pressed, Go could generate a byte \x00 to os.Stdin. Now there's no byte generates on Windows.
It works on MacOS and Linux, just not work on Windows.

[lonnywong]

I think it's Go's job to generate bytes to os.Stdin.
On MacOS and Linux, Go generates \x00 to os.Stdin when Ctrl+Space is pressing.
On Windows, Go generates nothing to os.Stdin when Ctrl+Space is pressing.
I do think it's a Go issue.

[seankhliao]

As mentioned in your linked issues, eg microsoft/terminal#2865 (comment) , it is the terminal's responsibility to convert any key presses into byte sequences for Go to consume (in your case, a null byte). Go does not observe the key presses, nor will Go generate any events into os.Stdin. os.Stdin is a file descriptor for a stream of bytes whose input is controlled by the parent process.

Closing as not a Go bug.