Re: input characters echoing is broken

[Kerin Millar]

On Fri, 16 Feb 2024 15:27:28 +0100
Rubén Gonzalez <rgonzalez@fluendo.com> wrote:

> Hello
> 
> I am a maintainer of Fluster, an open-source testing framework for video
> decoder conformance.
> 
> After researching a bug reported [1], we could create a simple Python
> script that breaks bash input characters echoing.
> 
> The Python script is in the GitHub issues. As I can not reproduce the issue
> with other shells, I imagine it is related to bash. Can you help me with
> the next steps to check? Or ideas to research?
> 
> Thank you very much,
> Ruben
> 
> [1] https://github.com/fluendo/fluster/issues/147

Bash should not be involved in any capacity because you execute 
subprocess.run() method without setting shell=True, although you could still 
execute bash in the case that the value of command is ["bash", "-c", "shell 
code goes here"].

Regardless, any application run in a terminal - including ffmpeg - is free to 
print escape sequences that might alter the behaviour of the terminal. 
Applications may also use the standard termios(3) interface to alter the 
behaviour of the terminal. As an example, try running "stty -echo" in your 
shell. You'll find that, henceforth, your keyboard input is no longer echoed. 
That happens because stty(1) is being instructed to use said interface to 
disable ECHO for your terminal's input mode. It has nothing to do with the 
shell.

In the issue, you claim that the terminal behaviour is altered even in the case 
that STDOUT and STDERR are redirected to /dev/null. That makes it somewhat 
unlikely that escape sequences are to blame, though it's still possible for an 
application to open and write to /dev/tty directly. As an experiment, you could 
try redirecting STDIN with </dev/null. Perhaps the behaviour of whatever it is 
that you are executing will vary based on whether the standard input is found 
to be a tty or not. You could also wrap the application with a tracing utility 
- such as strace - to get a better understanding of what it is doing.

-- 
Kerin Millar