term: add examples for ReadPassword

[codesoap]

These examples demonstrate how to use ReadPassword for interactive password input from the terminal. They highlight how to use the function, even if standard input is not a terminal (e.g. when it is a pipe). The example for Windows is especially interesting, because there seems to be a bug where CONIN$ cannot be used unless opened with the write flag.

This contribution was suggested to me at golang/go#46164.

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This PR (HEAD: 1712572) has been imported to Gerrit for code review.

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This PR (HEAD: b2824fc) has been imported to Gerrit for code review.

Please visit https://go-review.googlesource.com/c/term/+/324829 to see it.

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[codesoap]

@alexbrainman said in golang/go#46164 (comment) that he would rather use the Windows API for opening CONIN$, than to use OpenFile with the os.O_RDWR flag. I have no preference, but am open to changing the Windows example, if using the Windows API directly is preferred.

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Message from Richard Ulmer:

Patch Set 2:

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Patch Set 2: Code-Review+1

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Patch Set 2:

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[ghost]

Thank you for contributing this example! Unfortunately when I try to use your technique in my program I get:

panic: open /dev/tty: no such device or address

[codesoap]

@acnodal-tc What operating system are you using and which of the three examples did you try?

[ghost]

I'm on Debian 11:

$ \cat /etc/os-release 
PRETTY_NAME="Debian GNU/Linux 11 (bullseye)"
NAME="Debian GNU/Linux"
VERSION_ID="11"
VERSION="11 (bullseye)"
VERSION_CODENAME=bullseye
ID=debian
HOME_URL="https://www.debian.org/"
SUPPORT_URL="https://www.debian.org/support"
BUG_REPORT_URL="https://bugs.debian.org/"

I integrated the code from ExampleReadPassword_unix() into my program, and it works great when I run it locally but if I run it using ssh it crashes:

~/work/Code/epic/epicctl$ ssh localhost "~/work/Code/epic/epicctl/epicctl create api-user user3 root" <<PASSWORD
password1
password1
PASSWORD
panic: open /dev/tty: no such device or address

[codesoap]

@acnodal-tc The ReadPassword function is not designed for what you are trying to do. If you pass "command argument" to ssh ("~/work/Code/epic/epicctl/epicctl create api-user user3 root"), ssh will not open a terminal. ReadPassword is meant to read passwords from a terminal, not from a pipe.

[ghost]

Ah, thank you. Perhaps this comment isn't accurate, then: "If standard input is not bound to the terminal, a password can still be read from it."

[codesoap]

The "it" in "a password can still be read from it" refers to the terminal, not the standard input. To read from standard input, you don't need the golang.org/x/term package at all.

[ghost]

Gotcha. Thank you!