Re: [Buildroot] [PATCH v2 1/3] support/testing/infra/emulator.py: change the shell prompt before running tests

["Yann E. MORIN" <yann.morin.1998@free.fr>]

Julien, All,

On 2023-06-11 12:45 +0200, Julien Olivain spake thusly:
> If a program has the string '# ' (i.e. the default shell prompt) in
> its output, the test execution in the Buildroot runtime test infra is
> failing.
> 
> This can be reproduced by adding a single line in a package test
> script:
>     self.assertRunOk("echo ### this is a string with hashes ###")

The most obvious issue is when testing the environment of the shell with
env, which will output PS1 itself... There is not easy way around to fix
that, of course... :-/

I was beaten by this when adding a test for bash. I eventually solved it
in another way, but took a note to find a better solution "for later"...
;-)

> Since the string "# " is quite common, this patch changes the prompt
> after the emulator.login(), by setting the PS1 variable to a string
> which is less likely to appear in a normal program output. A small
> caveat: since there is a command echo, the command setting the new
> prompt needs to be protected to make sure it will not be detected as
> an actual shell prompt. The prompt is encoded by single-quoting
> each character (e.g. abc -> 'a''b''c').

That's not really what join() will do. E.g. with your code:

    >>> s = "#BRTEST# "
    >>> "''".join(s)
    "#''B''R''T''E''S''T''#'' "

But we don;t really care because it is then quite improbable that some
random program will output exactly this...

I was on my side thinking about using ANSI escape sequences to carry the
information that the command was actually fnished, something along the
lines of:

    export PS1="\x1B_BR_COMMAND_FINISHED\x1B\\# "

  - \x1B_ is APC (Application Program Command),
  - \x1B\\ is ST (String Terminator), which terminates APC

Instead of APC, we could use any of:

  - \x1BP DCS, Device Control String
  - \x1BX SOS, Start Of String
  - \x1B^ PM, Privacy Message
  - or even \x1B] OSC, Operating System Command

But maybe that is a bit overkill in the end...

Anyway, your patch at least breaks tests.package.test_bash...

Regards,
Yann E. MORIN.

> Signed-off-by: Julien Olivain <ju.o@free.fr>
> ---
> Changes v1 -> v2:
> - reworded commit log, to mention this issue was also seen while writing
>   a test for the dmidecode package
> - the patch series also introduce the new test for dmidecode
> ---
>  support/testing/infra/emulator.py | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/support/testing/infra/emulator.py b/support/testing/infra/emulator.py
> index 02cf486128..390c582e9d 100644
> --- a/support/testing/infra/emulator.py
> +++ b/support/testing/infra/emulator.py
> @@ -13,6 +13,7 @@ class Emulator(object):
>          # can take a long time to run the emulator. Use a timeout multiplier
>          # when running the tests to avoid sporadic failures.
>          self.timeout_multiplier = timeout_multiplier
> +        self.shell_prompt = "#BRTEST# "
>  
>      # Start Qemu to boot the system
>      #
> @@ -100,6 +101,15 @@ class Emulator(object):
>          index = self.qemu.expect(["# ", pexpect.TIMEOUT])
>          if index != 0:
>              raise SystemError("Cannot login")
> +        # Set a special shell prompt while testing. Since the standard
> +        # prompt '# ' is quite generic, a normal process output could
> +        # contain that string and confuse expect. When changing the
> +        # prompt, we also need to encode or escape it in some way to
> +        # make sure the command echo will not be seen as a prompt
> +        # itself. The prompt is encoded by single-quoting each
> +        # character (e.g. abc -> 'a''b''c').
> +        encoded_prompt = "''".join(self.shell_prompt)
> +        self.run("export PS1='{}'".format(encoded_prompt))
>          self.run("dmesg -n 1")
>          # Prevent the shell from wrapping the commands at 80 columns.
>          self.run("stty columns 29999")
> @@ -110,13 +120,13 @@ class Emulator(object):
>          self.qemu.sendline(cmd)
>          if timeout != -1:
>              timeout *= self.timeout_multiplier
> -        self.qemu.expect("# ", timeout=timeout)
> +        self.qemu.expect(self.shell_prompt, timeout=timeout)
>          # Remove double carriage return from qemu stdout so str.splitlines()
>          # works as expected.
>          output = self.qemu.before.replace("\r\r", "\r").splitlines()[1:]
>  
>          self.qemu.sendline("echo $?")
> -        self.qemu.expect("# ")
> +        self.qemu.expect(self.shell_prompt)
>          exit_code = self.qemu.before.splitlines()[2]
>          exit_code = int(exit_code)
>  
> -- 
> 2.41.0
> 
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