x/crypto/ssh/terminal: GetSize returns incorrect results

[egazz]

Please answer these questions before submitting your issue. Thanks!

What version of Go are you using (go version)?

go1.11 windows/amd64

Does this issue reproduce with the latest release?

Yes (since as far as I know this is the latest release).

What operating system and processor architecture are you using (go env)?

Windows 10, amd64.

What did you do?

package main

import (
	"fmt"
	"os"
	"golang.org/x/crypto/ssh/terminal"
)

func main() {

	termID := int(os.Stdout.Fd())
	termWidth, termHeight, termSizeErr := terminal.GetSize(termID)
	
	if termSizeErr != nil {
	
		panic(termSizeErr)
		
	}
	
	fmt.Printf("Width: %v, height: %v", termWidth, termHeight)

}

What did you expect to see?

Accurate height and width of the terminal.

What did you see instead?

Height is way off. My terminal window is 30 lines tall, but this returns a height of 9001. Width was correct, however.

In addition, I noticed that this issue remains. On Windows, getting the terminal handle via os.Stdin.Fd() results in an error, while os.Stdout.Fd() results in the above. However, on Linux, using Stdin works properly.

[alexbrainman]

I think, it kind of works

There are many definitions of terminal height and width.

I looked at the code, and GetSize uses GetConsoleScreenBufferInfo Windows API. What should this package use instead? Why?

Thank you.

Alex

[egazz]

Hi, thanks for the reply.

I will say what I expected was the window size. I can imagine scenarios where one may need both, but for a basic console app, I think size of the window, i.e. the viewable area, is more important.

For example, if I wanted to know how much space I have for writing text, I'd need to know the dimensions (same thing for clearing the screen, unless there's a method that I haven't found yet....) The same is true for determining whether things need to be redrawn if the terminal window is resized.

I noticed this library uses syscall to reference TIOCGWINSZ, which according to this is part of the Linux kernel at least. I don't know if it'd work on Windows, though.

[alexbrainman]

I don't know if it'd work on Windows, though.

That code does not run on Windows - note how first line of that source file says

// +build !windows

Alex

[egazz]

That was my concern. It looks, then, like the only way to get this information is sending a command such as stty via os.Stdin?

But back to my original issue, at the least it seems like the documentation should make it clearer that GetSize in fact gets the buffer size, not the window size. It's also worth noting that this behavior is different on Linux, where on at least some terminal emulators (such as urxvt) it returns the window size.

[alexbrainman]

It looks, then, like the only way to get this information is sending a command such as stty via os.Stdin?

There is no stty command on Windows, if that is what you are suggesting.

Alex

[gopherbot]

Change https://golang.org/cl/163538 mentions this issue: ssh/terminal: fix GetSize on Windows