proposal: x/term: expose tcflush functionality

[gdamore]

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

$ go version
go version go1.14.2 linux/amd64

Does this issue reproduce with the latest release?

Yes

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

go env Output

$ go env

I'm the developer of the popular github.com/gdamore/tcell package.

I'm skipping the rest of this questionaire as I think it's not terribly relevant to this feature request.

Essentially, I'd like golang.org/x/term to expose a method to flush I/O on the tty. This would permit us to ensure that we can pause the text UI, and not wind up sucking in a bunch of I/O when restoring back to raw mode.

Alternatively, having a version of term.MakeRaw (and probably also term.Restore) that let me specify TCSFLUSH behavior would also work.

[ianlancetaylor]

It will help us if you can suggest a specific function or method, with documentation. Thanks.

Also, it seems like there is quite a lot of Unix termios functionality that is not in golang.org/x/term. Do we want to just add stuff piecemeal?

[gdamore]

The easiest thing to do would be to just add a "tcflush" API. Sort of like here: https://www.ibm.com/support/knowledgecenter/en/SSLTBW_2.3.0/com.ibm.zos.v2r3.bpxbd00/rttcfu.htm

An alternative idea would be to create either an extended version of MakeRaw (say MakeRawExt()) that takes an "op" operation argument with one of the value Flush, Drain, or Now. This could also be added as optional argument to MakeRaw via an ...Options kind of varargs.

To be honest I think "tcflush" (call it TcFlush I guess) is the most flexible and powerful. I can then call that right before the other options, and you could support both flushing and draining on either input or output.