Re: [PATCH 13/15] tests/functional: rewrite console handling to be bytewise

[Paolo Bonzini <pbonzini@redhat.com>]

On 11/19/24 16:05, Daniel P. Berrangé wrote:
> The console interaction that waits for predicted strings uses
> readline(), and thus is only capable of waiting for strings
> that are followed by a newline.
> 
> This is inconvenient when needing to match on some things,
> particularly login prompts, or shell prompts, causing tests
> to use time.sleep(...) instead, which is unreliable.
> 
> Switch to reading the console 1 byte at a time, comparing
> against the success/failure messages until we see a match,
> regardless of whether a newline is encountered.
> 
> The success/failure comparisons are done with the python bytes
> type, rather than strings, to avoid the problem of needing to
> decode partially received multibyte utf8 characters.
> 
> Heavily inspired by a patch proposed by Cédric, but written
> again to work in bytes, rather than strings.
> 
> Co-developed-by: Cédric Le Goater <clg@redhat.com>
> Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
> ---
>   tests/functional/qemu_test/cmd.py | 63 +++++++++++++++++++++++--------
>   1 file changed, 48 insertions(+), 15 deletions(-)
> 
> diff --git a/tests/functional/qemu_test/cmd.py b/tests/functional/qemu_test/cmd.py
> index 76a48064cd..91267a087f 100644
> --- a/tests/functional/qemu_test/cmd.py
> +++ b/tests/functional/qemu_test/cmd.py
> @@ -78,15 +78,58 @@ def run_cmd(args):
>   def is_readable_executable_file(path):
>       return os.path.isfile(path) and os.access(path, os.R_OK | os.X_OK)
>   
> +def _console_readline(test, vm, success, failure):
> +    msg = bytes([])
> +    done = False
> +    while True:
> +        c = vm.console_socket.recv(1)
> +        if c is None:
> +            done = True
> +            test.fail(
> +                f"EOF in console, expected '{success}'")
> +            break
> +        msg += c
> +
> +        if success is None or success in msg:

As an optimization, you could use msg.endswith(success) and 
msg.endswith(failure), which would avoid the most blatant cases of 
O(n^2) behavior.

More important, I think "if success is None" should not be here, because 
it will exit after one char.  Instead...

> +            done = True
> +            break
> +        if failure and failure in msg:
> +            done = True
> +            vm.console_socket.close()
> +            test.fail(
> +                f"'{failure}' found in console, expected '{success}'")
> +
> +        if c == b'\n':

Here you can put

                done = success is None

Paolo

> +            break
> +
> +    console_logger = logging.getLogger('console')
> +    try:
> +        console_logger.debug(msg.decode().strip())
> +    except:
> +        console_logger.debug(msg)
> +
> +    return done
> +
>   def _console_interaction(test, success_message, failure_message,
>                            send_string, keep_sending=False, vm=None):
>       assert not keep_sending or send_string
>       if vm is None:
>           vm = test.vm
> -    console = vm.console_file
> -    console_logger = logging.getLogger('console')
> +
>       test.log.debug(f"Console interaction success:'{success_message}' " +
>                      f"failure:'{failure_message}' send:'{send_string}'")
> +
> +    # We'll process console in bytes, to avoid having to
> +    # deal with unicode decode errors from receiving
> +    # partial utf8 byte sequences
> +    success_message_b = None
> +    if success_message is not None:
> +        success_message_b = success_message.encode()
> +
> +    failure_message_b = None
> +    if failure_message is not None:
> +        failure_message_b = failure_message.encode()
> +
>       while True:
>           if send_string:
>               vm.console_socket.sendall(send_string.encode())
> @@ -99,20 +142,10 @@ def _console_interaction(test, success_message, failure_message,
>                   break
>               continue
>   
> -        try:
> -            msg = console.readline().decode().strip()
> -        except UnicodeDecodeError:
> -            msg = None
> -        if not msg:
> -            continue
> -        console_logger.debug(msg)
> -        if success_message is None or success_message in msg:
> +        if _console_readline(test, vm,
> +                             success_message_b,
> +                             failure_message_b):
>               break
> -        if failure_message and failure_message in msg:
> -            console.close()
> -            fail = 'Failure message found in console: "%s". Expected: "%s"' % \
> -                    (failure_message, success_message)
> -            test.fail(fail)
>   
>   def interrupt_interactive_console_until_pattern(test, success_message,
>                                                   failure_message=None,