mercurial/utils/interfaceutil.py

wireprotov2: define and use stream encoders

Now that we have basic support for defining stream encoding, it is
time to start doing something with it.

We define various classes implementing stream encoders/decoders for
the defined encoding profiles. This is relatively straightforward.

We teach the inputstream and outputstream classes how to encode,
decode, and flush data.

We then teach the clientreactor how to filter received data through
the inputstream decoder.

One of the features of the framing format is that streams can span
requests. This is a differentiating feature from say HTTP/2, which
associates streams with requests. By allowing streams to span requests,
we can reuse compression context data across requests/responses. But
in order to do this, we need a mechanism to "flush" the encoder at
logical boundaries so that receivers receive all data where it is
expected. And a "flush" event is distinct from a "finish" event from
the perspective of certain compressors because a "flush" will retain
compression context state whereas a "finish" operation will not. This
is why encoders have both a flush() and a finish() and each uses
specific flushing semantics on the underlying compressor.

The added tests verify various behavior of decoders via clientreactor.
These tests do test some compression behavior via use of outputstream.
But for all intents and purposes, server reactor support for encoding
is not yet implemented.

Differential Revision: https://phab.mercurial-scm.org/D4921

# interfaceutil.py - Utilities for declaring interfaces.
#
# Copyright 2018 Gregory Szorc <[e-mail]>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.

# zope.interface imposes a run-time cost due to module import overhead and
# bookkeeping for declaring interfaces. So, we use stubs for various
# zope.interface primitives unless instructed otherwise.

from __future__ import absolute_import

from .. import (
    encoding,
)

if encoding.environ.get('HGREALINTERFACES'):
    from ..thirdparty.zope import (
        interface as zi,
    )

    Attribute = zi.Attribute
    Interface = zi.Interface
    implementer = zi.implementer
else:
    class Attribute(object):
        def __init__(self, __name__, __doc__=''):
            pass

    class Interface(object):
        def __init__(self, name, bases=(), attrs=None, __doc__=None,
                 __module__=None):
            pass

    def implementer(*ifaces):
        def wrapper(cls):
            return cls

        return wrapper