Re: [PATCH 2/4] python/console_socket: accept existing FD in initializer

[John Snow]

On Thu, Jul 20, 2023 at 10:01 AM Daniel P. Berrangé <berrange@redhat.com> wrote:
>
> On Thu, Jul 20, 2023 at 09:04:46AM -0400, John Snow wrote:
> > Useful if we want to use ConsoleSocket() for a socket created by
> > socketpair().
> >
> > Signed-off-by: John Snow <jsnow@redhat.com>
> > ---
> >  python/qemu/machine/console_socket.py | 11 +++++++----
> >  1 file changed, 7 insertions(+), 4 deletions(-)
> >
> > diff --git a/python/qemu/machine/console_socket.py 
> > b/python/qemu/machine/console_socket.py
> > index 4e28ba9bb2..42bfa12411 100644
> > --- a/python/qemu/machine/console_socket.py
> > +++ b/python/qemu/machine/console_socket.py
> > @@ -17,7 +17,7 @@
> >  import socket
> >  import threading
> >  import time
> > -from typing import Deque, Optional
> > +from typing import Deque, Optional, Union
> >
> >
> >  class ConsoleSocket(socket.socket):
> > @@ -30,13 +30,16 @@ class ConsoleSocket(socket.socket):
> >      Optionally a file path can be passed in and we will also
> >      dump the characters to this file for debugging purposes.
> >      """
> > -    def __init__(self, address: str, file: Optional[str] = None,
> > +    def __init__(self, address: Union[str, int], file: Optional[str] = 
> > None,
> >                   drain: bool = False):
>
> IMHO calling the pre-opened FD an "address" is pushing the
> interpretation a bit.
>

You're right.

> It also makes the behaviour non-obvious from a caller. Seeing a
> caller, you have to work backwards to find out what type it has,
> to figure out the semantics of the method call.
>
> IOW, I'd prefer to see
>
>    address: Optional[str], sock_fd: Optional[int]
>
> and then just do a check
>
>    if (address is not None and sock_fd is not None) or
>       (address is None and sock_fd is None):
>       raise Exception("either 'address' or 'sock_fd' is required")
>
> thus when you see
>
>    ConsoleSocket(sock_fd=xxx)
>
> it is now obvious it has different behaviour to
>
>    ConsoleSocket(address=yyy)
>

Yeah, that's just a little harder to type - in the sense that it
appears as though you could omit either argument by just observing the
signature. One thing I like about "one mandatory argument that takes
many forms" is that it's obvious you need to give it *something* from
the signature.

You're right that the name is now very silly, though.

The "obvious it has different behavior" is a good argument, I'll change it.

--js

>
> >          self._recv_timeout_sec = 300.0
> >          self._sleep_time = 0.5
> >          self._buffer: Deque[int] = deque()
> > -        socket.socket.__init__(self, socket.AF_UNIX, socket.SOCK_STREAM)
> > -        self.connect(address)
> > +        if isinstance(address, str):
> > +            socket.socket.__init__(self, socket.AF_UNIX, 
> > socket.SOCK_STREAM)
> > +            self.connect(address)
> > +        else:
> > +            socket.socket.__init__(self, fileno=address)
> >          self._logfile = None
> >          if file:
> >              # pylint: disable=consider-using-with
> > --
> > 2.41.0
> >
>
> With regards,
> Daniel
> --
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>