Initial python3 changes

Mostly just updating libraries, removing string encoding/decoding,
fixing some edge cases. No new functionality was added in this
commit.

lib/cheroot/_compat.py

@@ -0,0 +1,148 @@
+# pylint: disable=unused-import
+"""Compatibility code for using Cheroot with various versions of Python."""
+
+from __future__ import absolute_import, division, print_function
+__metaclass__ = type
+
+import os
+import platform
+import re
+
+import six
+
+try:
+    import selectors  # lgtm [py/unused-import]
+except ImportError:
+    import selectors2 as selectors  # noqa: F401  # lgtm [py/unused-import]
+
+try:
+    import ssl
+    IS_ABOVE_OPENSSL10 = ssl.OPENSSL_VERSION_INFO >= (1, 1)
+    del ssl
+except ImportError:
+    IS_ABOVE_OPENSSL10 = None
+
+# contextlib.suppress was added in Python 3.4
+try:
+    from contextlib import suppress
+except ImportError:
+    from contextlib import contextmanager
+
+    @contextmanager
+    def suppress(*exceptions):
+        """Return a context manager that suppresses the `exceptions`."""
+        try:
+            yield
+        except exceptions:
+            pass
+
+
+IS_CI = bool(os.getenv('CI'))
+IS_GITHUB_ACTIONS_WORKFLOW = bool(os.getenv('GITHUB_WORKFLOW'))
+
+
+IS_PYPY = platform.python_implementation() == 'PyPy'
+
+
+SYS_PLATFORM = platform.system()
+IS_WINDOWS = SYS_PLATFORM == 'Windows'
+IS_LINUX = SYS_PLATFORM == 'Linux'
+IS_MACOS = SYS_PLATFORM == 'Darwin'
+
+PLATFORM_ARCH = platform.machine()
+IS_PPC = PLATFORM_ARCH.startswith('ppc')
+
+
+if not six.PY2:
+    def ntob(n, encoding='ISO-8859-1'):
+        """Return the native string as bytes in the given encoding."""
+        assert_native(n)
+        # In Python 3, the native string type is unicode
+        return n.encode(encoding)
+
+    def ntou(n, encoding='ISO-8859-1'):
+        """Return the native string as Unicode with the given encoding."""
+        assert_native(n)
+        # In Python 3, the native string type is unicode
+        return n
+
+    def bton(b, encoding='ISO-8859-1'):
+        """Return the byte string as native string in the given encoding."""
+        return b.decode(encoding)
+else:
+    # Python 2
+    def ntob(n, encoding='ISO-8859-1'):
+        """Return the native string as bytes in the given encoding."""
+        assert_native(n)
+        # In Python 2, the native string type is bytes. Assume it's already
+        # in the given encoding, which for ISO-8859-1 is almost always what
+        # was intended.
+        return n
+
+    def ntou(n, encoding='ISO-8859-1'):
+        """Return the native string as Unicode with the given encoding."""
+        assert_native(n)
+        # In Python 2, the native string type is bytes.
+        # First, check for the special encoding 'escape'. The test suite uses
+        # this to signal that it wants to pass a string with embedded \uXXXX
+        # escapes, but without having to prefix it with u'' for Python 2,
+        # but no prefix for Python 3.
+        if encoding == 'escape':
+            return re.sub(
+                r'\\u([0-9a-zA-Z]{4})',
+                lambda m: six.unichr(int(m.group(1), 16)),
+                n.decode('ISO-8859-1'),
+            )
+        # Assume it's already in the given encoding, which for ISO-8859-1
+        # is almost always what was intended.
+        return n.decode(encoding)
+
+    def bton(b, encoding='ISO-8859-1'):
+        """Return the byte string as native string in the given encoding."""
+        return b
+
+
+def assert_native(n):
+    """Check whether the input is of native :py:class:`str` type.
+
+    Raises:
+        TypeError: in case of failed check
+
+    """
+    if not isinstance(n, str):
+        raise TypeError('n must be a native str (got %s)' % type(n).__name__)
+
+
+if not six.PY2:
+    """Python 3 has :py:class:`memoryview` builtin."""
+    # Python 2.7 has it backported, but socket.write() does
+    # str(memoryview(b'0' * 100)) -> <memory at 0x7fb6913a5588>
+    # instead of accessing it correctly.
+    memoryview = memoryview
+else:
+    """Link :py:class:`memoryview` to buffer under Python 2."""
+    memoryview = buffer  # noqa: F821
+
+
+def extract_bytes(mv):
+    r"""Retrieve bytes out of the given input buffer.
+
+    :param mv: input :py:func:`buffer`
+    :type mv: memoryview or bytes
+
+    :return: unwrapped bytes
+    :rtype: bytes
+
+    :raises ValueError: if the input is not one of \
+                        :py:class:`memoryview`/:py:func:`buffer` \
+                        or :py:class:`bytes`
+    """
+    if isinstance(mv, memoryview):
+        return bytes(mv) if six.PY2 else mv.tobytes()
+
+    if isinstance(mv, bytes):
+        return mv
+
+    raise ValueError(
+        'extract_bytes() only accepts bytes and memoryview/buffer',
+    )