ISSUE:
Proxy authentication bug
<!-- Summary. -->

When using proxies in python 3.8.12, I get an error 407. Using any other version of python works fine. I am assuming it could be to do with this https://docs.python.org/3/whatsnew/3.8.html#notable-changes-in-python-3-8-12.

<!-- What you expected. -->

I should get a status of 200.

<!-- What happened instead. -->

I get a status code of 407.

```python
import requests


r = requests.get('https://example.org/', proxies=proxies) # You will need a proxy to test with, I am using a paid service.
print(r.status_code)

```

## System Information

```json
{
  "chardet": {
    "version": null
  },
  "charset_normalizer": {
    "version": "2.0.9"
  },
  "cryptography": {
    "version": ""
  },
  "idna": {
    "version": "3.3"
  },
  "implementation": {
    "name": "CPython",
    "version": "3.8.12"
  },
  "platform": {
    "release": "5.13.0-7620-generic",
    "system": "Linux"
  },
  "pyOpenSSL": {
    "openssl_version": "",
    "version": null
  },
  "requests": {
    "version": "2.27.0"
  },
  "system_ssl": {
    "version": "101010cf"
  },
  "urllib3": {
    "version": "1.26.7"
  },
  "using_charset_normalizer": true,
  "using_pyopenssl": false
}
```


Hi @flameaway, it’s hard to tell what exactly is happening here without more info. Could you verify this issue occurs in both Requests 2.26.0 and urllib3 1.25.11?

It could very well be related to the ipaddress change, I’d just like to rule out other potential factors before we start down that path.
Requests 2.26.0 returns status 200. Either version of urllib (1.25.11, 1.26.7) work with it. Requests 2.27.0 returns the 407 error with either urllib version.
Thanks for confirming that! It sounds like this may be localized to today's release (2.27.0) We made some minor refactorings to how we handle proxies on redirects in https://github.com/psf/requests/pull/5924. I'm not seeing anything off immediately, so this will need some digging. For the meantime, using 2.26.0 is likely the short term solution.

I just want to clarify one more comment.

> When using proxies in python 3.8.12, I get an error 407. Using any other version of python works fine.

Does this mean 2.27.0 works on all other Python versions besides 3.8.12, or did you only test 2.27.0 with 3.8.12? I want to confirm we're not dealing with a requests release issue AND a python release issue.
> Does this mean 2.27.0 works on all other Python versions besides 3.8.12, or did you only test 2.27.0 with 3.8.12? I want to confirm we're not dealing with a requests release issue AND a python release issue.

It seems to only be having issues on 2.27.0. I didn't realize, but python 3.9.7 defaulted to installing requests 2.26.0. 
Confirming that this error also occurs with requests 2.27.0 and Python 3.8.9
To be clear, there is way too little information in here as it stands to be able to debug this from our end.
Did a bisect and found: 
```
ef59aa0227bf463f0ed3d752b26db9b3acc64afb is the first bad commit
commit ef59aa0227bf463f0ed3d752b26db9b3acc64afb
Author: Nate Prewitt <Nate.Prewitt@gmail.com>
Date:   Thu Aug 26 22:06:48 2021 -0700

    Move from urlparse to parse_url for prepending schemes

 requests/utils.py   | 21 +++++++++++++++------
 tests/test_utils.py |  1 +
 2 files changed, 16 insertions(+), 6 deletions(-)
```

I'm using a proxy from QuotaGuard, so it has auth.
So after doing some digging, in my case the params passed to `urlunparse` in `prepend_scheme_if_needed` went from:
scheme: `http`
netloc: `user:pwd@host:port`
To:
scheme: `http`
netloc: `host:port`
So the auth is lost from netloc here. The auth is still parsed and stored in the auth var, however.

Adding this to `prepend_scheme_if_needed` resolves, but unaware of any other issues that might cause:
```
if auth:
    netloc = '@'.join([auth, netloc])
```
Same issue here.
Since 2.27.0 with Python 3.8

I confirm @adamp01 investigation with mine. `user:pwd` seem to be lost during proxy parsing. I always get a 
`Tunnel connection failed: 407 Proxy Authentication Required`
Thanks for confirming @racam and @adamp01. We switched to using urllib3’s parser for proxies because of some recent changes to the standard lib `urlparse` around schemes. It looks like the two differ on their definition of `netloc`. I’m working on a patch to try to get this resolved.
Thank you for helping debug this @racam and @adamp01

CODE CONTEXT:
TOP-1 FULL FILE requests/__init__.py:
# -*- coding: utf-8 -*-

#   __
#  /__)  _  _     _   _ _/   _
# / (   (- (/ (/ (- _)  /  _)
#          /

"""
Requests HTTP Library
~~~~~~~~~~~~~~~~~~~~~

Requests is an HTTP library, written in Python, for human beings.
Basic GET usage:

   >>> import requests
   >>> r = requests.get('https://www.python.org')
   >>> r.status_code
   200
   >>> b'Python is a programming language' in r.content
   True

... or POST:

   >>> payload = dict(key1='value1', key2='value2')
   >>> r = requests.post('https://httpbin.org/post', data=payload)
   >>> print(r.text)
   {
     ...
     "form": {
       "key1": "value1",
       "key2": "value2"
     },
     ...
   }

The other HTTP methods are supported - see `requests.api`. Full documentation
is at <https://requests.readthedocs.io>.

:copyright: (c) 2017 by Kenneth Reitz.
:license: Apache 2.0, see LICENSE for more details.
"""

import urllib3
import warnings
from .exceptions import RequestsDependencyWarning

try:
    from charset_normalizer import __version__ as charset_normalizer_version
except ImportError:
    charset_normalizer_version = None

try:
    from chardet import __version__ as chardet_version
except ImportError:
    chardet_version = None

def check_compatibility(urllib3_version, chardet_version, charset_normalizer_version):
    urllib3_version = urllib3_version.split('.')
    assert urllib3_version != ['dev']  # Verify urllib3 isn't installed from git.

    # Sometimes, urllib3 only reports its version as 16.1.
    if len(urllib3_version) == 2:
        urllib3_version.append('0')

    # Check urllib3 for compatibility.
    major, minor, patch = urllib3_version  # noqa: F811
    major, minor, patch = int(major), int(minor), int(patch)
    # urllib3 >= 1.21.1, <= 1.26
    assert major == 1
    assert minor >= 21
    assert minor <= 26

    # Check charset_normalizer for compatibility.
    if chardet_version:
        major, minor, patch = chardet_version.split('.')[:3]
        major, minor, patch = int(major), int(minor), int(patch)
        # chardet_version >= 3.0.2, < 5.0.0
        assert (3, 0, 2) <= (major, minor, patch) < (5, 0, 0)
    elif charset_normalizer_version:
        major, minor, patch = charset_normalizer_version.split('.')[:3]
        major, minor, patch = int(major), int(minor), int(patch)
        # charset_normalizer >= 2.0.0 < 3.0.0
        assert (2, 0, 0) <= (major, minor, patch) < (3, 0, 0)
    else:
        raise Exception("You need either charset_normalizer or chardet installed")

def _check_cryptography(cryptography_version):
    # cryptography < 1.3.4
    try:
        cryptography_version = list(map(int, cryptography_version.split('.')))
    except ValueError:
        return

    if cryptography_version < [1, 3, 4]:
        warning = 'Old version of cryptography ({}) may cause slowdown.'.format(cryptography_version)
        warnings.warn(warning, RequestsDependencyWarning)

# Check imported dependencies for compatibility.
try:
    check_compatibility(urllib3.__version__, chardet_version, charset_normalizer_version)
except (AssertionError, ValueError):
    warnings.warn("urllib3 ({}) or chardet ({})/charset_normalizer ({}) doesn't match a supported "
                  "version!".format(urllib3.__version__, chardet_version, charset_normalizer_version),
                  RequestsDependencyWarning)

# Attempt to enable urllib3's fallback for SNI support
# if the standard library doesn't support SNI or the
# 'ssl' library isn't available.
try:
    try:
        import ssl
    except ImportError:
        ssl = None

    if not getattr(ssl, "HAS_SNI", False):
        from urllib3.contrib import pyopenssl
        pyopenssl.inject_into_urllib3()

        # Check cryptography version
        from cryptography import __version__ as cryptography_version
        _check_cryptography(cryptography_version)
except ImportError:
    pass

# urllib3's DependencyWarnings should be silenced.
from urllib3.exceptions import DependencyWarning
warnings.simplefilter('ignore', DependencyWarning)

from .__version__ import __title__, __description__, __url__, __version__
from .__version__ import __build__, __author__, __author_email__, __license__
from .__version__ import __copyright__, __cake__

from . import utils
from . import packages
from .models import Request, Response, PreparedRequest
from .api import request, get, head, post, patch, put, delete, options
from .sessions import session, Session
from .status_codes import codes
from .exceptions import (
    RequestException, Timeout, URLRequired,
    TooManyRedirects, HTTPError, ConnectionError,
    FileModeWarning, ConnectTimeout, ReadTimeout, JSONDecodeError
)

# Set default logging handler to avoid "No handler found" warnings.
import logging
from logging import NullHandler

logging.getLogger(__name__).addHandler(NullHandler())

# FileModeWarnings go off per the default.
warnings.simplefilter('default', FileModeWarning, append=True)


requests/__init__.py:
# -*- coding: utf-8 -*-

#   __
#  /__)  _  _     _   _ _/   _
# / (   (- (/ (/ (- _)  /  _)
#          /

"""
Requests HTTP Library
~~~~~~~~~~~~~~~~~~~~~

Requests is an HTTP library, written in Python, for human beings.
Basic GET usage:

   >>> import requests
   >>> r = requests.get('https://www.python.org')
   >>> r.status_code
   200
   >>> b'Python is a programming language' in r.content
   True

... or POST:

   >>> payload = dict(key1='value1', key2='value2')
   >>> r = requests.post('https://httpbin.org/post', data=payload)
   >>> print(r.text)
   {
     ...
     "form": {
       "key1": "value1",
       "key2": "value2"
     },
     ...
   }

The other HTTP methods are supported - see `requests.api`. Full documentation
is at <https://requests.readthedocs.io>.

:copyright: (c) 2017 by Kenneth Reitz.
:license: Apache 2.0, see LICENSE for more details.
"""

import urllib3
import warnings
from .exceptions import RequestsDependencyWarning

try:
    from charset_normalizer import __version__ as charset_normalizer_version
except ImportError:
    charset_normalizer_version = None

try:
    from chardet import __version__ as chardet_version
except ImportError:
    chardet_version = None

def check_compatibility(urllib3_version, chardet_version, charset_normalizer_version):
    urllib3_version = urllib3_version.split('.')
    assert urllib3_version != ['dev']  # Verify urllib3 isn't installed from git.

    # Sometimes, urllib3 only reports its version as 16.1.
    if len(urllib3_version) == 2:
        urllib3_version.append('0')

    # Check urllib3 for compatibility.
    major, minor, patch = urllib3_version  # noqa: F811
    major, minor, patch = int(major), int(minor), int(patch)
    # urllib3 >= 1.21.1, <= 1.26
    assert major == 1
    assert minor >= 21
    assert minor <= 26

    # Check charset_normalizer for compatibility.
    if chardet_version:
        major, minor, patch = chardet_version.split('.')[:3]
        major, minor, patch = int(major), int(minor), int(patch)
        # chardet_version >= 3.0.2, < 5.0.0
        assert (3, 0, 2) <= (major, minor, patch) < (5, 0, 0)
    elif charset_normalizer_version:
        major, minor, patch = charset_normalizer_version.split('.')[:3]
        major, minor, patch = int(major), int(minor), int(patch)
        # charset_normalizer >= 2.0.0 < 3.0.0
        assert (2, 0, 0) <= (major, minor, patch) < (3, 0, 0)
    else:
        raise Exception("You need either charset_normalizer or chardet installed")

def _check_cryptography(cryptography_version):
    # cryptography < 1.3.4
    try:
        cryptography_version = list(map(int, cryptography_version.split('.')))
    except ValueError:
        return

    if cryptography_version < [1, 3, 4]:
        warning = 'Old version of cryptography ({}) may cause slowdown.'.format(cryptography_version)
        warnings.warn(warning, RequestsDependencyWarning)

# Check imported dependencies for compatibility.
try:
    check_compatibility(urllib3.__version__, chardet_version, charset_normalizer_version)
except (AssertionError, ValueError):
    warnings.warn("urllib3 ({}) or chardet ({})/charset_normalizer ({}) doesn't match a supported "
                  "version!".format(urllib3.__version__, chardet_version, charset_normalizer_version),
                  RequestsDependencyWarning)

# Attempt to enable urllib3's fallback for SNI support
# if the standard library doesn't support SNI or the
# 'ssl' library isn't available.
try:
    try:
        import ssl
    except ImportError:
        ssl = None

    if not getattr(ssl, "HAS_SNI", False):
        from urllib3.contrib import pyopenssl
        pyopenssl.inject_into_urllib3()

        # Check cryptography version
        from cryptography import __version__ as cryptography_version
        _check_cryptography(cryptography_version)
except ImportError:
    pass

# urllib3's DependencyWarnings should be silenced.
from urllib3.exceptions import DependencyWarning
warnings.simplefilter('ignore', DependencyWarning)

from .__version__ import __title__, __description__, __url__, __version__
from .__version__ import __build__, __author__, __author_email__, __license__
from .__version__ import __copyright__, __cake__

from . import utils
from . import packages
from .models import Request, Response, PreparedRequest
from .api import request, get, head, post, patch, put, delete, options
from .sessions import session, Session
from .status_codes import codes
from .exceptions import (
    RequestException, Timeout, URLRequired,
    TooManyRedirects, HTTPError, ConnectionError,
    FileModeWarning, ConnectTimeout, ReadTimeout, JSONDecodeError
)

# Set default logging handler to avoid "No handler found" warnings.
import logging
from logging import NullHandler

logging.getLogger(__name__).addHandler(NullHandler())

# FileModeWarnings go off per the default.
warnings.simplefilter('default', FileModeWarning, append=True)


requests/help.py:
"""Module containing bug report helper(s)."""
from __future__ import print_function

import json
import platform
import sys
import ssl

import idna
import urllib3

from . import __version__ as requests_version

try:
    import charset_normalizer
except ImportError:
    charset_normalizer = None

try:
    import chardet
except ImportError:
    chardet = None

try:
    from urllib3.contrib import pyopenssl
except ImportError:
    pyopenssl = None
    OpenSSL = None
    cryptography = None
else:
    import OpenSSL
    import cryptography


def _implementation():
    """Return a dict with the Python implementation and version.

    Provide both the name and the version of the Python implementation
    currently running. For example, on CPython 2.7.5 it will return
    {'name': 'CPython', 'version': '2.7.5'}.

    This function works best on CPython and PyPy: in particular, it probably
    doesn't work for Jython or IronPython. Future investigation should be done
    to work out the correct shape of the code for those platforms.
    """
    implementation = platform.python_implementation()

    if implementation == 'CPython':
        implementation_version = platform.python_version()
    elif implementation == 'PyPy':
        implementation_version = '%s.%s.%s' % (sys.pypy_version_info.major,
                                               sys.pypy_version_info.minor,
                                               sys.pypy_version_info.micro)
        if sys.pypy_version_info.releaselevel != 'final':
            implementation_version = ''.join([
                implementation_version, sys.pypy_version_info.releaselevel
            ])
    elif implementation == 'Jython':
        implementation_version = platform.python_version()  # Complete Guess
    elif implementation == 'IronPython':
        implementation_version = platform.python_version()  # Complete Guess
    else:
        implementation_version = 'Unknown'

    return {'name': implementation, 'version': implementation_version}


def info():
    """Generate information for a bug report."""
    try:
        platform_info = {
            'system': platform.system(),
            'release': platform.release(),
        }
    except IOError:
        platform_info = {
            'system': 'Unknown',
            'release': 'Unknown',
        }

    implementation_info = _implementation()
    urllib3_info = {'version': urllib3.__version__}
    charset_normalizer_info = {'version': None}
    chardet_info = {'version': None}
    if charset_normalizer:
        charset_normalizer_info = {'version': charset_normalizer.__version__}
    if chardet:
        chardet_info = {'version': chardet.__version__}

    pyopenssl_info = {
        'version': None,
        'openssl_version': '',
    }
    if OpenSSL:
        pyopenssl_info = {
            'version': OpenSSL.__version__,
            'openssl_version': '%x' % OpenSSL.SSL.OPENSSL_VERSION_NUMBER,
        }
    cryptography_info = {
        'version': getattr(cryptography, '__version__', ''),
    }
    idna_info = {
        'version': getattr(idna, '__version__', ''),
    }

    system_ssl = ssl.OPENSSL_VERSION_NUMBER
    system_ssl_info = {
        'version': '%x' % system_ssl if system_ssl is not None else ''
    }

    return {
        'platform': platform_info,
        'implementation': implementation_info,
        'system_ssl': system_ssl_info,
        'using_pyopenssl': pyopenssl is not None,
        'using_charset_normalizer': chardet is None,
        'pyOpenSSL': pyopenssl_info,
        'urllib3': urllib3_info,
        'chardet': chardet_info,
        'charset_normalizer': charset_normalizer_info,
        'cryptography': cryptography_info,
        'idna': idna_info,
        'requests': {
            'version': requests_version,
        },
    }


def main():
    """Pretty-print the bug information as JSON."""
    print(json.dumps(info(), sort_keys=True, indent=2))


if __name__ == '__main__':
    main()


requests/utils.py:
# -*- coding: utf-8 -*-

"""
requests.utils
~~~~~~~~~~~~~~

This module provides utility functions that are used within Requests
that are also useful for external consumption.
"""

import codecs
import contextlib
import io
import os
import re
import socket
import struct
import sys
import tempfile
import warnings
import zipfile
from collections import OrderedDict
from urllib3.util import make_headers
from urllib3.util import parse_url

from .__version__ import __version__
from . import certs
# to_native_string is unused here, but imported here for backwards compatibility
from ._internal_utils import to_native_string
from .compat import parse_http_list as _parse_list_header
from .compat import (
    quote, urlparse, bytes, str, unquote, getproxies,
    proxy_bypass, urlunparse, basestring, integer_types, is_py3,
    proxy_bypass_environment, getproxies_environment, Mapping)
from .cookies import cookiejar_from_dict
from .structures import CaseInsensitiveDict
from .exceptions import (
    InvalidURL, InvalidHeader, FileModeWarning, UnrewindableBodyError)

NETRC_FILES = ('.netrc', '_netrc')

DEFAULT_CA_BUNDLE_PATH = certs.where()

DEFAULT_PORTS = {'http': 80, 'https': 443}

# Ensure that ', ' is used to preserve previous delimiter behavior.
DEFAULT_ACCEPT_ENCODING = ", ".join(
    re.split(r",\s*", make_headers(accept_encoding=True)["accept-encoding"])
)


if sys.platform == 'win32':
    # provide a proxy_bypass version on Windows without DNS lookups

    def proxy_bypass_registry(host):
        try:
            if is_py3:
                import winreg
            else:
                import _winreg as winreg
        except ImportError:
            return False

        try:
            internetSettings = winreg.OpenKey(winreg.HKEY_CURRENT_USER,
                r'Software\Microsoft\Windows\CurrentVersion\Internet Settings')
            # ProxyEnable could be REG_SZ or REG_DWORD, normalizing it
            proxyEnable = int(winreg.QueryValueEx(internetSettings,
                                              'ProxyEnable')[0])
            # ProxyOverride is almost always a string
            proxyOverride = winreg.QueryValueEx(internetSettings,
                                                'ProxyOverride')[0]
        except OSError:
            return False
        if not proxyEnable or not proxyOverride:
            return False

        # make a check value list from the registry entry: replace the
        # '<local>' string by the localhost entry and the corresponding
        # canonical entry.
        proxyOverride = proxyOverride.split(';')
        # now check if we match one of the registry values.
        for test in proxyOverride:
            if test == '<local>':
                if '.' not in host:
                    return True
            test = test.replace(".", r"\.")     # mask dots
            test = test.replace("*", r".*")     # change glob sequence
            test = test.replace("?", r".")      # change glob char
            if re.match(test, host, re.I):
                return True
        return False

    def proxy_bypass(host):  # noqa
        """Return True, if the host should be bypassed.

        Checks proxy settings gathered from the environment, if specified,
        or the registry.
        """
        if getproxies_environment():
            return proxy_bypass_environment(host)
        else:
            return proxy_bypass_registry(host)


def dict_to_sequence(d):
    """Returns an internal sequence dictionary update."""

    if hasattr(d, 'items'):
        d = d.items()

    return d


def super_len(o):
    total_length = None
    current_position = 0

    if hasattr(o, '__len__'):
        total_length = len(o)

    elif hasattr(o, 'len'):
        total_length = o.len

    elif hasattr(o, 'fileno'):
        try:
            fileno = o.fileno()
        except (io.UnsupportedOperation, AttributeError):
            # AttributeError is a surprising exception, seeing as how we've just checked
            # that `hasattr(o, 'fileno')`.  It happens for objects obtained via
            # `Tarfile.extractfile()`, per issue 5229.
            pass
        else:
            total_length = os.fstat(fileno).st_size

            # Having used fstat to determine the file length, we need to
            # confirm that this file was opened up in binary mode.
            if 'b' not in o.mode:
                warnings.warn((
                    "Requests has determined the content-length for this "
                    "request using the binary size of the file: however, the "
                    "file has been opened in text mode (i.e. without the 'b' "
                    "flag in the mode). This may lead to an incorrect "
                    "content-length. In Requests 3.0, support will be removed "
                    "for files in text mode."),
                    FileModeWarning
                )

    if hasattr(o, 'tell'):
        try:
            current_position = o.tell()
        except (OSError, IOError):
            # This can happen in some weird situations, such as when the file
            # is actually a special file descriptor like stdin. In this
            # instance, we don't know what the length is, so set it to zero and
            # let requests chunk it instead.
            if total_length is not None:
                current_position = total_length
        else:
            if hasattr(o, 'seek') and total_length is None:
                # StringIO and BytesIO have seek but no usable fileno
                try:
                    # seek to end of file
                    o.seek(0, 2)
                    total_length = o.tell()

                    # seek back to current position to support
                    # partially read file-like objects
                    o.seek(current_position or 0)
                except (OSError, IOError):
                    total_length = 0

    if total_length is None:
        total_length = 0

    return max(0, total_length - current_position)


def get_netrc_auth(url, raise_errors=False):
    """Returns the Requests tuple auth for a given url from netrc."""

    netrc_file = os.environ.get('NETRC')
    if netrc_file is not None:
        netrc_locations = (netrc_file,)
    else:
        netrc_locations = ('~/{}'.format(f) for f in NETRC_FILES)

    try:
        from netrc import netrc, NetrcParseError

        netrc_path = None

        for f in netrc_locations:
            try:
                loc = os.path.expanduser(f)
            except KeyError:
                # os.path.expanduser can fail when $HOME is undefined and
                # getpwuid fails. See https://bugs.python.org/issue20164 &
                # https://github.com/psf/requests/issues/1846
                return

            if os.path.exists(loc):
                netrc_path = loc
                break

        # Abort early if there isn't one.
        if netrc_path is None:
            return

        ri = urlparse(url)

        # Strip port numbers from netloc. This weird `if...encode`` dance is
        # used for Python 3.2, which doesn't support unicode literals.
        splitstr = b':'
        if isinstance(url, str):
            splitstr = splitstr.decode('ascii')
        host = ri.netloc.split(splitstr)[0]

        try:
            _netrc = netrc(netrc_path).authenticators(host)
            if _netrc:
                # Return with login / password
                login_i = (0 if _netrc[0] else 1)
                return (_netrc[login_i], _netrc[2])
        except (NetrcParseError, IOError):
            # If there was a parsing error or a permissions issue reading the file,
            # we'll just skip netrc auth unless explicitly asked to raise errors.
            if raise_errors:
                raise

    # App Engine hackiness.
    except (ImportError, AttributeError):
        pass


def guess_filename(obj):
    """Tries to guess the filename of the given object."""
    name = getattr(obj, 'name', None)
  

requests/sessions.py:
# -*- coding: utf-8 -*-

"""
requests.sessions
~~~~~~~~~~~~~~~~~

This module provides a Session object to manage and persist settings across
requests (cookies, auth, proxies).
"""
import os
import sys
import time
from datetime import timedelta
from collections import OrderedDict

from .auth import _basic_auth_str
from .compat import cookielib, is_py3, urljoin, urlparse, Mapping
from .cookies import (
    cookiejar_from_dict, extract_cookies_to_jar, RequestsCookieJar, merge_cookies)
from .models import Request, PreparedRequest, DEFAULT_REDIRECT_LIMIT
from .hooks import default_hooks, dispatch_hook
from ._internal_utils import to_native_string
from .utils import to_key_val_list, default_headers, DEFAULT_PORTS
from .exceptions import (
    TooManyRedirects, InvalidSchema, ChunkedEncodingError, ContentDecodingError)

from .structures import CaseInsensitiveDict
from .adapters import HTTPAdapter

from .utils import (
    requote_uri, get_environ_proxies, get_netrc_auth, should_bypass_proxies,
    get_auth_from_url, rewind_body, resolve_proxies
)

from .status_codes import codes

# formerly defined here, reexposed here for backward compatibility
from .models import REDIRECT_STATI

# Preferred clock, based on which one is more accurate on a given system.
if sys.platform == 'win32':
    try:  # Python 3.4+
        preferred_clock = time.perf_counter
    except AttributeError:  # Earlier than Python 3.
        preferred_clock = time.clock
else:
    preferred_clock = time.time


def merge_setting(request_setting, session_setting, dict_class=OrderedDict):
    """Determines appropriate setting for a given request, taking into account
    the explicit setting on that request, and the setting in the session. If a
    setting is a dictionary, they will be merged together using `dict_class`
    """

    if session_setting is None:
        return request_setting

    if request_setting is None:
        return session_setting

    # Bypass if not a dictionary (e.g. verify)
    if not (
            isinstance(session_setting, Mapping) and
            isinstance(request_setting, Mapping)
    ):
        return request_setting

    merged_setting = dict_class(to_key_val_list(session_setting))
    merged_setting.update(to_key_val_list(request_setting))

    # Remove keys that are set to None. Extract keys first to avoid altering
    # the dictionary during iteration.
    none_keys = [k for (k, v) in merged_setting.items() if v is None]
    for key in none_keys:
        del merged_setting[key]

    return merged_setting


def merge_hooks(request_hooks, session_hooks, dict_class=OrderedDict):
    """Properly merges both requests and session hooks.

    This is necessary because when request_hooks == {'response': []}, the
    merge breaks Session hooks entirely.
    """
    if session_hooks is None or session_hooks.get('response') == []:
        return request_hooks

    if request_hooks is None or request_hooks.get('response') == []:
        return session_hooks

    return merge_setting(request_hooks, session_hooks, dict_class)


class SessionRedirectMixin(object):

    def get_redirect_target(self, resp):
        """Receives a Response. Returns a redirect URI or ``None``"""
        # Due to the nature of how requests processes redirects this method will
        # be called at least once upon the original response and at least twice
        # on each subsequent redirect response (if any).
        # If a custom mixin is used to handle this logic, it may be advantageous
        # to cache the redirect location onto the response object as a private
        # attribute.
        if resp.is_redirect:
            location = resp.headers['location']
            # Currently the underlying http module on py3 decode headers
            # in latin1, but empirical evidence suggests that latin1 is very
            # rarely used with non-ASCII characters in HTTP headers.
            # It is more likely to get UTF8 header rather than latin1.
            # This causes incorrect handling of UTF8 encoded location headers.
            # To solve this, we re-encode the location in latin1.
            if is_py3:
                location = location.encode('latin1')
            return to_native_string(location, 'utf8')
        return None

    def should_strip_auth(self, old_url, new_url):
        """Decide whether Authorization header should be removed when redirecting"""
        old_parsed = urlparse(old_url)
        new_parsed = urlparse(new_url)
        if old_parsed.hostname != new_parsed.hostname:
            return True
        # Special case: allow http -> https redirect when using the standard
        # ports. This isn't specified by RFC 7235, but is kept to avoid
        # breaking backwards compatibility with older versions of requests
        # that allowed any redirects on the same host.
        if (old_parsed.scheme == 'http' and old_parsed.port in (80, None)
                and new_parsed.scheme == 'https' and new_parsed.port in (443, None)):
            return False

        # Handle default port usage corresponding to scheme.
        changed_port = old_parsed.port != new_parsed.port
        changed_scheme = old_parsed.scheme != new_parsed.scheme
        default_port = (DEFAULT_PORTS.get(old_parsed.scheme, None), None)
        if (not changed_scheme and old_parsed.port in default_port
                and new_parsed.port in default_port):
            return False

        # Standard case: root URI must match
        return changed_port or changed_scheme

    def resolve_redirects(self, resp, req, stream=False, timeout=None,
                          verify=True, cert=None, proxies=None, yield_requests=False, **adapter_kwargs):
        """Receives a Response. Returns a generator of Responses or Requests."""

        hist = []  # keep track of history

        url = self.get_redirect_target(resp)
        previous_fragment = urlparse(req.url).fragment
        while url:
            prepared_request = req.copy()

            # Update history and keep track of redirects.
            # resp.history must ignore the original request in this loop
            hist.append(resp)
            resp.history = hist[1:]

            try:
                resp.content  # Consume socket so it can be released
            except (ChunkedEncodingError, ContentDecodingError, RuntimeError):
                resp.raw.read(decode_content=False)

            if len(resp.history) >= self.max_redirects:
                raise TooManyRedirects('Exceeded {} redirects.'.format(self.max_redirects), response=resp)

            # Release the connection back into the pool.
            resp.close()

            # Handle redirection without scheme (see: RFC 1808 Section 4)
            if url.startswith('//'):
                parsed_rurl = urlparse(resp.url)
                url = ':'.join([to_native_string(parsed_rurl.scheme), url])

            # Normalize url case and attach previous fragment if needed (RFC 7231 7.1.2)
            parsed = urlparse(url)
            if parsed.fragment == '' and previous_fragment:
                parsed = parsed._replace(fragment=previous_fragment)
            elif parsed.fragment:
                previous_fragment = parsed.fragment
            url = parsed.geturl()

            # Facilitate relative 'location' headers, as allowed by RFC 7231.
            # (e.g. '/path/to/resource' instead of 'http://domain.tld/path/to/resource')
            # Compliant with RFC3986, we percent encode the url.
            if not parsed.netloc:
                url = urljoin(resp.url, requote_uri(url))
            else:
                url = requote_uri(url)

            prepared_request.url = to_native_string(url)

            self.rebuild_method(prepared_request, resp)

            # https://github.com/psf/requests/issues/1084
            if resp.status_code not in (codes.temporary_redirect, codes.permanent_redirect):
                # https://github.com/psf/requests/issues/3490
                purged_hea

setup.py:
#!/usr/bin/env python
# Learn more: https://github.com/kennethreitz/setup.py
import os
import sys

from codecs import open

from setuptools import setup
from setuptools.command.test import test as TestCommand

here = os.path.abspath(os.path.dirname(__file__))

class PyTest(TestCommand):
    user_options = [('pytest-args=', 'a', "Arguments to pass into py.test")]

    def initialize_options(self):
        TestCommand.initialize_options(self)
        try:
            from multiprocessing import cpu_count
            self.pytest_args = ['-n', str(cpu_count()), '--boxed']
        except (ImportError, NotImplementedError):
            self.pytest_args = ['-n', '1', '--boxed']

    def finalize_options(self):
        TestCommand.finalize_options(self)
        self.test_args = []
        self.test_suite = True

    def run_tests(self):
        import pytest

        errno = pytest.main(self.pytest_args)
        sys.exit(errno)

# 'setup.py publish' shortcut.
if sys.argv[-1] == 'publish':
    os.system('python setup.py sdist bdist_wheel')
    os.system('twine upload dist/*')
    sys.exit()

packages = ['requests']

requires = [
    'charset_normalizer~=2.0.0; python_version >= "3"',
    'chardet>=3.0.2,<5; python_version < "3"',
    'idna>=2.5,<3; python_version < "3"',
    'idna>=2.5,<4; python_version >= "3"',
    'urllib3>=1.21.1,<1.27',
    'certifi>=2017.4.17'

]
test_requirements = [
    'pytest-httpbin==0.0.7',
    'pytest-cov',
    'pytest-mock',
    'pytest-xdist',
    'PySocks>=1.5.6, !=1.5.7',
    'pytest>=3'
]

about = {}
with open(os.path.join(here, 'requests', '__version__.py'), 'r', 'utf-8') as f:
    exec(f.read(), about)

with open('README.md', 'r', 'utf-8') as f:
    readme = f.read()

setup(
    name=about['__title__'],
    version=about['__version__'],
    description=about['__description__'],
    long_description=readme,
    long_description_content_type='text/markdown',
    author=about['__author__'],
    author_email=about['__author_email__'],
    url=about['__url__'],
    packages=packages,
    package_data={'': ['LICENSE', 'NOTICE']},
    package_dir={'requests': 'requests'},
    include_package_data=True,
    python_requires=">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*, !=3.4.*, !=3.5.*",
    install_requires=requires,
    license=about['__license__'],
    zip_safe=False,
    classifiers=[
        'Development Status :: 5 - Production/Stable',
        'Environment :: Web Environment',
        'Intended Audience :: Developers',
        'License :: OSI Approved :: Apache Software License',
        'Natural Language :: English',
        'Operating System :: OS Independent',
        'Programming Language :: Python',
        'Programming Language :: Python :: 2',
        'Programming Language :: Python :: 2.7',
        'Programming Language :: Python :: 3',
        'Programming Language :: Python :: 3.6',
        'Programming Language :: Python :: 3.7',
        'Programming Language :: Python :: 3.8',
        'Programming Language :: Python :: 3.9',
        'Programming Language :: Python :: 3.10',
        'Programming Language :: Python :: Implementation :: CPython',
        'Programming Language :: Python :: Implementation :: PyPy',
        'Topic :: Internet :: WWW/HTTP',
        'Topic :: Software Development :: Libraries',
    ],
    cmdclass={'test': PyTest},
    tests_require=test_requirements,
    extras_require={
        'security': [],
        'socks': ['PySocks>=1.5.6, !=1.5.7'],
        'socks:sys_platform == "win32" and python_version == "2.7"': ['win_inet_pton'],
        'use_chardet_on_py3': ['chardet>=3.0.2,<5']
    },
    project_urls={
        'Documentation': 'https://requests.readthedocs.io',
        'Source': 'https://github.com/psf/requests',
    },
)
