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102 lines
3.0 KiB
102 lines
3.0 KiB
3 years ago
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# Copyright (C) Dnspython Contributors, see LICENSE for text of ISC license
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import dns.exception
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# pylint: disable=unused-import
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from dns._asyncbackend import Socket, DatagramSocket, \
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StreamSocket, Backend # noqa:
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# pylint: enable=unused-import
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_default_backend = None
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_backends = {}
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# Allow sniffio import to be disabled for testing purposes
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_no_sniffio = False
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class AsyncLibraryNotFoundError(dns.exception.DNSException):
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pass
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def get_backend(name):
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"""Get the specified asynchronous backend.
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*name*, a ``str``, the name of the backend. Currently the "trio",
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"curio", and "asyncio" backends are available.
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Raises NotImplementError if an unknown backend name is specified.
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"""
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# pylint: disable=import-outside-toplevel,redefined-outer-name
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backend = _backends.get(name)
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if backend:
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return backend
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if name == 'trio':
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import dns._trio_backend
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backend = dns._trio_backend.Backend()
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elif name == 'curio':
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import dns._curio_backend
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backend = dns._curio_backend.Backend()
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elif name == 'asyncio':
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import dns._asyncio_backend
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backend = dns._asyncio_backend.Backend()
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else:
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raise NotImplementedError(f'unimplemented async backend {name}')
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_backends[name] = backend
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return backend
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def sniff():
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"""Attempt to determine the in-use asynchronous I/O library by using
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the ``sniffio`` module if it is available.
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Returns the name of the library, or raises AsyncLibraryNotFoundError
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if the library cannot be determined.
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"""
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# pylint: disable=import-outside-toplevel
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try:
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if _no_sniffio:
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raise ImportError
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import sniffio
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try:
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return sniffio.current_async_library()
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except sniffio.AsyncLibraryNotFoundError:
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raise AsyncLibraryNotFoundError('sniffio cannot determine ' +
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'async library')
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except ImportError:
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import asyncio
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try:
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asyncio.get_running_loop()
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return 'asyncio'
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except RuntimeError:
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raise AsyncLibraryNotFoundError('no async library detected')
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except AttributeError: # pragma: no cover
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# we have to check current_task on 3.6
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if not asyncio.Task.current_task():
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raise AsyncLibraryNotFoundError('no async library detected')
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return 'asyncio'
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def get_default_backend():
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"""Get the default backend, initializing it if necessary.
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"""
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if _default_backend:
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return _default_backend
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return set_default_backend(sniff())
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def set_default_backend(name):
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"""Set the default backend.
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It's not normally necessary to call this method, as
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``get_default_backend()`` will initialize the backend
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appropriately in many cases. If ``sniffio`` is not installed, or
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in testing situations, this function allows the backend to be set
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explicitly.
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"""
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global _default_backend
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_default_backend = get_backend(name)
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return _default_backend
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