Re: [PATCH v1 2/9] tests/avocado: improve behaviour waiting for login prompts

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

On 8/11/22 10:23, Alex Bennée wrote:
> This attempts to deal with the problem of login prompts not being
> guaranteed to be terminated with a newline. The solution to this is to
> peek at the incoming data looking to see if we see an up-coming match
> before we fall back to the old readline() logic. The reason to mostly
> rely on readline is because I am occasionally seeing the peek stalling
> despite data being there.
> 
> This seems kinda hacky and gross so I'm open to alternative approaches
> and cleaner python code.

I'd have done it the same way...

> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
> ---
>   tests/avocado/avocado_qemu/__init__.py | 89 +++++++++++++++++++++++++-
>   1 file changed, 88 insertions(+), 1 deletion(-)
> 
> diff --git a/tests/avocado/avocado_qemu/__init__.py b/tests/avocado/avocado_qemu/__init__.py
> index 910f3ba1ea..d6ff68e171 100644
> --- a/tests/avocado/avocado_qemu/__init__.py
> +++ b/tests/avocado/avocado_qemu/__init__.py
> @@ -131,6 +131,58 @@ def pick_default_qemu_bin(bin_prefix='qemu-system-', arch=None):
>               return path
>       return None
>   
> +def _peek_ahead(console, min_match, success_message):
> +    """
> +    peek ahead in the console stream keeping an eye out for the
> +    success message.
> +
> +    Returns some message to process or None, indicating the normal
> +    readline should occur.
> +    """
> +    console_logger = logging.getLogger('console')
> +    peek_len = 0
> +    retries = 0
> +
> +    while True:
> +        try:
> +            old_peek_len = peek_len
> +            peek_ahead = console.peek(min_match).decode()
> +            peek_len = len(peek_ahead)
> +
> +            # if we get stuck too long lets just fallback to readline
> +            if peek_len <= old_peek_len:
> +                retries += 1
> +                if retries > 10:
> +                    return None
> +
> +            # if we see a newline in the peek we can let safely bail
> +            # and let the normal readline() deal with it
> +            if peek_ahead.endswith(('\n', '\r', '\r\n')):

'\r\n' superfluous.

> +                return None
> +
> +            # if we haven't seen enough for the whole message but the
> +            # first part matches lets just loop again
> +            if len(peek_ahead) < min_match and \
> +               success_message[:peek_len] in peek_ahead:
> +                continue
> +
> +            # if we see the whole success_message we are done, consume
> +            # it and pass back so we can exit to the user
> +            if success_message in peek_ahead:
> +                return console.read(peek_len).decode()
> +
> +            # of course if we've seen enough then this line probably
> +            # doesn't contain what we are looking for, fallback
> +            if peek_len > min_match:
> +                return None
> +
> +        except UnicodeDecodeError:
> +            console_logger.log("error in decode of peek")
> +            return None
> +
> +    # we should never get here
> +    return None

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>