Update dnspython-2.2.0

lib/dns/asyncbackend.py

@@ -0,0 +1,96 @@
+# Copyright (C) Dnspython Contributors, see LICENSE for text of ISC license
+
+import dns.exception
+
+from dns._asyncbackend import Socket, DatagramSocket, \
+    StreamSocket, Backend  # noqa:
+
+
+_default_backend = None
+
+_backends = {}
+
+# Allow sniffio import to be disabled for testing purposes
+_no_sniffio = False
+
+class AsyncLibraryNotFoundError(dns.exception.DNSException):
+    pass
+
+
+def get_backend(name):
+    """Get the specified asychronous backend.
+
+    *name*, a ``str``, the name of the backend.  Currently the "trio",
+    "curio", and "asyncio" backends are available.
+
+    Raises NotImplementError if an unknown backend name is specified.
+    """
+    backend = _backends.get(name)
+    if backend:
+        return backend
+    if name == 'trio':
+        import dns._trio_backend
+        backend = dns._trio_backend.Backend()
+    elif name == 'curio':
+        import dns._curio_backend
+        backend = dns._curio_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():
+    """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.
+    """
+    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')
+        except AttributeError:  # pragma: no cover
+            # we have to check current_task on 3.6
+            if not asyncio.Task.current_task():
+                raise AsyncLibraryNotFoundError('no async library detected')
+            return 'asyncio'
+
+
+def get_default_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):
+    """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