# Copyright (C) Dnspython Contributors, see LICENSE for text of ISC license
from typing import Dict
import dns.exception
# pylint: disable=unused-import
from dns._asyncbackend import ( # noqa: F401 lgtm[py/unused-import]
Backend,
DatagramSocket,
Socket,
StreamSocket,
)
# pylint: enable=unused-import
_default_backend = None
_backends: Dict[str, Backend] = {}
# Allow sniffio import to be disabled for testing purposes
_no_sniffio = False
class AsyncLibraryNotFoundError(dns.exception.DNSException):
pass
def get_backend(name: str) -> Backend:
"""Get the specified asynchronous backend.
*name*, a ``str``, the name of the backend. Currently the "trio"
and "asyncio" backends are available.
Raises NotImplementedError if an unknown backend name is specified.
"""
# pylint: disable=import-outside-toplevel,redefined-outer-name
backend = _backends.get(name)
if backend:
return backend
if name == "trio":
import dns._trio_backend
backend = dns._trio_backend.Backend()
elif name == "asyncio":
import dns._asyncio_backend
backend = dns._asyncio_backend.Backend()
else:
raise NotImplementedError(f"unimplemented async backend {name}")
_backends[name] = backend
return backend
def sniff() -> str:
"""Attempt to determine the in-use asynchronous I/O library by using
the ``sniffio`` module if it is available.
Returns the name of the library, or raises AsyncLibraryNotFoundError
if the library cannot be determined.
"""
# pylint: disable=import-outside-toplevel
try:
if _no_sniffio:
raise ImportError
import sniffio
try:
return sniffio.current_async_library()
except sniffio.AsyncLibraryNotFoundError:
raise AsyncLibraryNotFoundError("sniffio cannot determine async library")
except ImportError:
import asyncio
try:
asyncio.get_running_loop()
return "asyncio"
except RuntimeError:
raise AsyncLibraryNotFoundError("no async library detected")
def get_default_backend() -> Backend:
"""Get the default backend, initializing it if necessary."""
if _default_backend:
return _default_backend
return set_default_backend(sniff())
def set_default_backend(name: str) -> Backend:
"""Set the default backend.
It's not normally necessary to call this method, as
``get_default_backend()`` will initialize the backend
appropriately in many cases. If ``sniffio`` is not installed, or
in testing situations, this function allows the backend to be set
explicitly.
"""
global _default_backend
_default_backend = get_backend(name)
return _default_backend
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