problem with using backspace for Chinese characters（one char of 2 bytes）

[jonnyliang]

Describe the bug
Chinese （one char of 2 bytes ） input support is not very good when using Backspace key,
pelases check the eraseNPreviousChars in the file “/sshd/terminal)/terminal.go”,
I guess the n is wrong as below, because it real moved two place，so there n should be 2 not 1，

405 for i := 0; i < n; i++ {
406 t.queue(space)
407 }
408 t.advanceCursor(n)

Versions

• Client version: CentOS Linux release 7.9.2009 (Core)
• Server version:CentOS Linux release 7.9.2009 (Core)
• Latest server version available: [v1.11-rc5]

To Reproduce
Steps to reproduce the behavior:

1. login in
2. Enter any Chinese characters，For example：啊飒飒的
3. press Backspace key ， you will see the problem

thank you for you sharing，it is help for my work！

[sleibrock]

This might not be entirely supported yet, since the EraseNPreviousChars(n) function erases N amount of characters at a time. You can see how the backspace function is implemented a few lines down on that file here

ssh-chat/sshd/terminal/terminal.go

Lines 491 to 495 in 0eebb64

	case keyBackspace:
	if t.pos == 0 {
	return
	}
	t.eraseNPreviousChars(1)

I am not super familiar enough with the keyboard I/O code personally, but I don't think ssh-chat is contextually aware of what your user locale is going to be exactly. The server side is responsible for key inputs and rendering the readline functionality, but its probable that ssh-chat doesn't have enough contextual information for each user to be able to do this. To ssh-chat, when you enter a 2-byte character, ssh-chat sees exactly 2-bytes. It doesn't process whether or not that might be a rune, it only handles it at an individual byte level.

[shazow]

Hi @jonnyliang, I'm not able to reproduce this. It may be an issue with your terminal, or compatibility between your terminal and how we handle unicode character width counting:

What terminal are you using? Could you try a modern terminal like kitty or alacritty?

[sheng-ri]

I reproduce it. That is terminal compatibility issue.
In alacritty,it works perfect.
In cmd/powershell/windows temiernal, It will leave char after chinese in buffer(I guess)

(Delete chinese from the end of input)

(Delete chinese from the middle of input.And enf of input " g g" is display after delete)

Versions

Client version: Ubuntu 22.04
Server version:Windows 11
ssh-chat version: 1.10,1.11-rc5

[shazow]

Yea, that's a terminal issue unfortunately, they don't count character width the same way as modern terminals. There's no way to support both.

[jonnyliang]

Hi @jonnyliang, I'm not able to reproduce this. It may be an issue with your terminal, or compatibility between your terminal and how we handle unicode character width counting:

What terminal are you using? Could you try a modern terminal like kitty or alacritty?

You are right, this a terminal issue unfortunately, it will leave half of a char when I using XSHELL 5. it work by using alacritty! thanks！

[jonnyliang]

Yea, that's a terminal issue unfortunately, they don't count character width the same way as modern terminals. There's no way to support both.
By the way, I fixed the problem on my local code as below, it seems work well on alacritty and XSHELL，but I not sure its ok.

//
_, _, left, _ := t.moveCursorToPos(t.pos)
copy(t.line[t.pos:], t.line[n+t.pos:])
t.line = t.line[:len(t.line)-n]
if t.echo {
t.writeLine(t.line[t.pos:])
for i := 0; i < left; i++ {
t.queue(space)
}
t.advanceCursor(left)
....

[jonnyliang]

reproduce on alacritty~!

[shazow]

If you have a patch that fixes this and doesn't break other things, please make a PR and I'll take a look. :)

[jonnyliang]

I just modified content of two functions，Hope for better solution！

ssh-chat/sshd/terminal/terminal.go

func (t *Terminal) moveCursorToPos(pos int) (up, down, left, right int) {
  ...
  return up, down, left, right
}

func` (t *Terminal) eraseNPreviousChars(n int) {
        if n == 0 {
                return
        }

        if t.pos < n {
                n = t.pos
        }
        t.pos -= n
        //t.moveCursorToPos(t.pos)
       //-----------fixed begin------------------------------ 
        up, _, left, _ := t.moveCursorToPos(t.pos) 
        if left ==0{
            if up == 1{left =up}
        }
        //-----------fixed end------------------------------ 
        copy(t.line[t.pos:], t.line[n+t.pos:])
        t.line = t.line[:len(t.line)-n]
        if t.echo {
                t.writeLine(t.line[t.pos:])
                for i := 0; i < left; i++ { // left  replace n 
                        t.queue(space)
                }
                t.advanceCursor(left)
                t.moveCursorToPos(t.pos)
        }
}