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

[John Snow]

On Tue, Nov 8, 2022 at 4:26 AM Alex Bennée <alex.bennee@linaro.org> 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.

Hm, yeah. I'm not too sure. I guess if it works, it works -- I don't
have better suggestions for you here. I need to rewrite a good bit of
how machine.py works, and time will tell if we still need this kind of
workaround when I do. I guess if it doesn't hurt anything, go for it.

*shrug*

>
> 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')):
> +                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
> +
>
>  def _console_interaction(test, success_message, failure_message,
>                           send_string, keep_sending=False, vm=None):
> @@ -139,17 +191,52 @@ def _console_interaction(test, success_message, 
> failure_message,
>          vm = test.vm
>      console = vm.console_socket.makefile(mode='rb', encoding='utf-8')
>      console_logger = logging.getLogger('console')
> +
> +    # Establish the minimum number of bytes we would need to
> +    # potentially match against success_message
> +    if success_message is not None:
> +        min_match = len(success_message)
> +    else:
> +        min_match = 0
> +
> +    console_logger.debug("looking for %d:(%s), sending %s (always=%s)",
> +                         min_match, success_message, send_string, 
> keep_sending)
> +
>      while True:
> +        msg = None
> +
> +        # First send our string, optionally repeating the send next
> +        # cycle.
>          if send_string:
>              vm.console_socket.sendall(send_string.encode())
>              if not keep_sending:
>                  send_string = None # send only once
> +
> +        # If the console has no data to read we briefly
> +        # sleep before continuing.
> +        if not console.readable():
> +            time.sleep(0.1)
> +            continue
> +
>          try:
> -            msg = console.readline().decode().strip()
> +
> +            # First we shall peek ahead for a potential match to cover 
> waiting
> +            # for lines without any newlines.
> +            if min_match > 0:
> +                msg = _peek_ahead(console, min_match, success_message)
> +
> +            # otherwise we block here for a full line
> +            if not msg:
> +                msg = console.readline().decode().strip()
> +
>          except UnicodeDecodeError:
> +            console_logger.debug("skipped unicode error")
>              msg = None
> +
> +        # if nothing came out we continue and try again
>          if not msg:
>              continue
> +
>          console_logger.debug(msg)
>          if success_message is None or success_message in msg:
>              break
> --
> 2.34.1
>
>