diff venv/lib/python2.7/site-packages/pip/download.py @ 0:d67268158946 draft

planemo upload commit a3f181f5f126803c654b3a66dd4e83a48f7e203b

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/venv/lib/python2.7/site-packages/pip/download.py	Mon Oct 12 17:43:33 2015 -0400
@@ -0,0 +1,913 @@
+from __future__ import absolute_import
+
+import cgi
+import email.utils
+import hashlib
+import getpass
+import json
+import logging
+import mimetypes
+import os
+import platform
+import re
+import shutil
+import sys
+import tempfile
+
+from pip._vendor.six.moves.urllib import parse as urllib_parse
+from pip._vendor.six.moves.urllib import request as urllib_request
+
+import pip
+
+from pip.exceptions import InstallationError, HashMismatch
+from pip.models import PyPI
+from pip.utils import (splitext, rmtree, format_size, display_path,
+                       backup_dir, ask_path_exists, unpack_file,
+                       call_subprocess)
+from pip.utils.filesystem import check_path_owner
+from pip.utils.logging import indent_log
+from pip.utils.ui import DownloadProgressBar, DownloadProgressSpinner
+from pip.locations import write_delete_marker_file
+from pip.vcs import vcs
+from pip._vendor import requests, six
+from pip._vendor.requests.adapters import BaseAdapter, HTTPAdapter
+from pip._vendor.requests.auth import AuthBase, HTTPBasicAuth
+from pip._vendor.requests.models import Response
+from pip._vendor.requests.structures import CaseInsensitiveDict
+from pip._vendor.requests.packages import urllib3
+from pip._vendor.cachecontrol import CacheControlAdapter
+from pip._vendor.cachecontrol.caches import FileCache
+from pip._vendor.lockfile import LockError
+from pip._vendor.six.moves import xmlrpc_client
+
+
+__all__ = ['get_file_content',
+           'is_url', 'url_to_path', 'path_to_url',
+           'is_archive_file', 'unpack_vcs_link',
+           'unpack_file_url', 'is_vcs_url', 'is_file_url',
+           'unpack_http_url', 'unpack_url']
+
+
+logger = logging.getLogger(__name__)
+
+
+def user_agent():
+    """
+    Return a string representing the user agent.
+    """
+    data = {
+        "installer": {"name": "pip", "version": pip.__version__},
+        "python": platform.python_version(),
+        "implementation": {
+            "name": platform.python_implementation(),
+        },
+    }
+
+    if data["implementation"]["name"] == 'CPython':
+        data["implementation"]["version"] = platform.python_version()
+    elif data["implementation"]["name"] == 'PyPy':
+        if sys.pypy_version_info.releaselevel == 'final':
+            pypy_version_info = sys.pypy_version_info[:3]
+        else:
+            pypy_version_info = sys.pypy_version_info
+        data["implementation"]["version"] = ".".join(
+            [str(x) for x in pypy_version_info]
+        )
+    elif data["implementation"]["name"] == 'Jython':
+        # Complete Guess
+        data["implementation"]["version"] = platform.python_version()
+    elif data["implementation"]["name"] == 'IronPython':
+        # Complete Guess
+        data["implementation"]["version"] = platform.python_version()
+
+    if sys.platform.startswith("linux"):
+        distro = dict(filter(
+            lambda x: x[1],
+            zip(["name", "version", "id"], platform.linux_distribution()),
+        ))
+        libc = dict(filter(
+            lambda x: x[1],
+            zip(["lib", "version"], platform.libc_ver()),
+        ))
+        if libc:
+            distro["libc"] = libc
+        if distro:
+            data["distro"] = distro
+
+    if sys.platform.startswith("darwin") and platform.mac_ver()[0]:
+        data["distro"] = {"name": "OS X", "version": platform.mac_ver()[0]}
+
+    if platform.system():
+        data.setdefault("system", {})["name"] = platform.system()
+
+    if platform.release():
+        data.setdefault("system", {})["release"] = platform.release()
+
+    if platform.machine():
+        data["cpu"] = platform.machine()
+
+    return "{data[installer][name]}/{data[installer][version]} {json}".format(
+        data=data,
+        json=json.dumps(data, separators=(",", ":"), sort_keys=True),
+    )
+
+
+class MultiDomainBasicAuth(AuthBase):
+
+    def __init__(self, prompting=True):
+        self.prompting = prompting
+        self.passwords = {}
+
+    def __call__(self, req):
+        parsed = urllib_parse.urlparse(req.url)
+
+        # Get the netloc without any embedded credentials
+        netloc = parsed.netloc.rsplit("@", 1)[-1]
+
+        # Set the url of the request to the url without any credentials
+        req.url = urllib_parse.urlunparse(parsed[:1] + (netloc,) + parsed[2:])
+
+        # Use any stored credentials that we have for this netloc
+        username, password = self.passwords.get(netloc, (None, None))
+
+        # Extract credentials embedded in the url if we have none stored
+        if username is None:
+            username, password = self.parse_credentials(parsed.netloc)
+
+        if username or password:
+            # Store the username and password
+            self.passwords[netloc] = (username, password)
+
+            # Send the basic auth with this request
+            req = HTTPBasicAuth(username or "", password or "")(req)
+
+        # Attach a hook to handle 401 responses
+        req.register_hook("response", self.handle_401)
+
+        return req
+
+    def handle_401(self, resp, **kwargs):
+        # We only care about 401 responses, anything else we want to just
+        #   pass through the actual response
+        if resp.status_code != 401:
+            return resp
+
+        # We are not able to prompt the user so simple return the response
+        if not self.prompting:
+            return resp
+
+        parsed = urllib_parse.urlparse(resp.url)
+
+        # Prompt the user for a new username and password
+        username = six.moves.input("User for %s: " % parsed.netloc)
+        password = getpass.getpass("Password: ")
+
+        # Store the new username and password to use for future requests
+        if username or password:
+            self.passwords[parsed.netloc] = (username, password)
+
+        # Consume content and release the original connection to allow our new
+        #   request to reuse the same one.
+        resp.content
+        resp.raw.release_conn()
+
+        # Add our new username and password to the request
+        req = HTTPBasicAuth(username or "", password or "")(resp.request)
+
+        # Send our new request
+        new_resp = resp.connection.send(req, **kwargs)
+        new_resp.history.append(resp)
+
+        return new_resp
+
+    def parse_credentials(self, netloc):
+        if "@" in netloc:
+            userinfo = netloc.rsplit("@", 1)[0]
+            if ":" in userinfo:
+                return userinfo.split(":", 1)
+            return userinfo, None
+        return None, None
+
+
+class LocalFSAdapter(BaseAdapter):
+
+    def send(self, request, stream=None, timeout=None, verify=None, cert=None,
+             proxies=None):
+        pathname = url_to_path(request.url)
+
+        resp = Response()
+        resp.status_code = 200
+        resp.url = request.url
+
+        try:
+            stats = os.stat(pathname)
+        except OSError as exc:
+            resp.status_code = 404
+            resp.raw = exc
+        else:
+            modified = email.utils.formatdate(stats.st_mtime, usegmt=True)
+            content_type = mimetypes.guess_type(pathname)[0] or "text/plain"
+            resp.headers = CaseInsensitiveDict({
+                "Content-Type": content_type,
+                "Content-Length": stats.st_size,
+                "Last-Modified": modified,
+            })
+
+            resp.raw = open(pathname, "rb")
+            resp.close = resp.raw.close
+
+        return resp
+
+    def close(self):
+        pass
+
+
+class SafeFileCache(FileCache):
+    """
+    A file based cache which is safe to use even when the target directory may
+    not be accessible or writable.
+    """
+
+    def __init__(self, *args, **kwargs):
+        super(SafeFileCache, self).__init__(*args, **kwargs)
+
+        # Check to ensure that the directory containing our cache directory
+        # is owned by the user current executing pip. If it does not exist
+        # we will check the parent directory until we find one that does exist.
+        # If it is not owned by the user executing pip then we will disable
+        # the cache and log a warning.
+        if not check_path_owner(self.directory):
+            logger.warning(
+                "The directory '%s' or its parent directory is not owned by "
+                "the current user and the cache has been disabled. Please "
+                "check the permissions and owner of that directory. If "
+                "executing pip with sudo, you may want sudo's -H flag.",
+                self.directory,
+            )
+
+            # Set our directory to None to disable the Cache
+            self.directory = None
+
+    def get(self, *args, **kwargs):
+        # If we don't have a directory, then the cache should be a no-op.
+        if self.directory is None:
+            return
+
+        try:
+            return super(SafeFileCache, self).get(*args, **kwargs)
+        except (LockError, OSError, IOError):
+            # We intentionally silence this error, if we can't access the cache
+            # then we can just skip caching and process the request as if
+            # caching wasn't enabled.
+            pass
+
+    def set(self, *args, **kwargs):
+        # If we don't have a directory, then the cache should be a no-op.
+        if self.directory is None:
+            return
+
+        try:
+            return super(SafeFileCache, self).set(*args, **kwargs)
+        except (LockError, OSError, IOError):
+            # We intentionally silence this error, if we can't access the cache
+            # then we can just skip caching and process the request as if
+            # caching wasn't enabled.
+            pass
+
+    def delete(self, *args, **kwargs):
+        # If we don't have a directory, then the cache should be a no-op.
+        if self.directory is None:
+            return
+
+        try:
+            return super(SafeFileCache, self).delete(*args, **kwargs)
+        except (LockError, OSError, IOError):
+            # We intentionally silence this error, if we can't access the cache
+            # then we can just skip caching and process the request as if
+            # caching wasn't enabled.
+            pass
+
+
+class InsecureHTTPAdapter(HTTPAdapter):
+
+    def cert_verify(self, conn, url, verify, cert):
+        conn.cert_reqs = 'CERT_NONE'
+        conn.ca_certs = None
+
+
+class PipSession(requests.Session):
+
+    timeout = None
+
+    def __init__(self, *args, **kwargs):
+        retries = kwargs.pop("retries", 0)
+        cache = kwargs.pop("cache", None)
+        insecure_hosts = kwargs.pop("insecure_hosts", [])
+
+        super(PipSession, self).__init__(*args, **kwargs)
+
+        # Attach our User Agent to the request
+        self.headers["User-Agent"] = user_agent()
+
+        # Attach our Authentication handler to the session
+        self.auth = MultiDomainBasicAuth()
+
+        # Create our urllib3.Retry instance which will allow us to customize
+        # how we handle retries.
+        retries = urllib3.Retry(
+            # Set the total number of retries that a particular request can
+            # have.
+            total=retries,
+
+            # A 503 error from PyPI typically means that the Fastly -> Origin
+            # connection got interupted in some way. A 503 error in general
+            # is typically considered a transient error so we'll go ahead and
+            # retry it.
+            status_forcelist=[503],
+
+            # Add a small amount of back off between failed requests in
+            # order to prevent hammering the service.
+            backoff_factor=0.25,
+        )
+
+        # We want to _only_ cache responses on securely fetched origins. We do
+        # this because we can't validate the response of an insecurely fetched
+        # origin, and we don't want someone to be able to poison the cache and
+        # require manual evication from the cache to fix it.
+        if cache:
+            secure_adapter = CacheControlAdapter(
+                cache=SafeFileCache(cache),
+                max_retries=retries,
+            )
+        else:
+            secure_adapter = HTTPAdapter(max_retries=retries)
+
+        # Our Insecure HTTPAdapter disables HTTPS validation. It does not
+        # support caching (see above) so we'll use it for all http:// URLs as
+        # well as any https:// host that we've marked as ignoring TLS errors
+        # for.
+        insecure_adapter = InsecureHTTPAdapter(max_retries=retries)
+
+        self.mount("https://", secure_adapter)
+        self.mount("http://", insecure_adapter)
+
+        # Enable file:// urls
+        self.mount("file://", LocalFSAdapter())
+
+        # We want to use a non-validating adapter for any requests which are
+        # deemed insecure.
+        for host in insecure_hosts:
+            self.mount("https://{0}/".format(host), insecure_adapter)
+
+    def request(self, method, url, *args, **kwargs):
+        # Allow setting a default timeout on a session
+        kwargs.setdefault("timeout", self.timeout)
+
+        # Dispatch the actual request
+        return super(PipSession, self).request(method, url, *args, **kwargs)
+
+
+def get_file_content(url, comes_from=None, session=None):
+    """Gets the content of a file; it may be a filename, file: URL, or
+    http: URL.  Returns (location, content).  Content is unicode."""
+    if session is None:
+        raise TypeError(
+            "get_file_content() missing 1 required keyword argument: 'session'"
+        )
+
+    match = _scheme_re.search(url)
+    if match:
+        scheme = match.group(1).lower()
+        if (scheme == 'file' and comes_from and
+                comes_from.startswith('http')):
+            raise InstallationError(
+                'Requirements file %s references URL %s, which is local'
+                % (comes_from, url))
+        if scheme == 'file':
+            path = url.split(':', 1)[1]
+            path = path.replace('\\', '/')
+            match = _url_slash_drive_re.match(path)
+            if match:
+                path = match.group(1) + ':' + path.split('|', 1)[1]
+            path = urllib_parse.unquote(path)
+            if path.startswith('/'):
+                path = '/' + path.lstrip('/')
+            url = path
+        else:
+            # FIXME: catch some errors
+            resp = session.get(url)
+            resp.raise_for_status()
+
+            if six.PY3:
+                return resp.url, resp.text
+            else:
+                return resp.url, resp.content
+    try:
+        with open(url) as f:
+            content = f.read()
+    except IOError as exc:
+        raise InstallationError(
+            'Could not open requirements file: %s' % str(exc)
+        )
+    return url, content
+
+
+_scheme_re = re.compile(r'^(http|https|file):', re.I)
+_url_slash_drive_re = re.compile(r'/*([a-z])\|', re.I)
+
+
+def is_url(name):
+    """Returns true if the name looks like a URL"""
+    if ':' not in name:
+        return False
+    scheme = name.split(':', 1)[0].lower()
+    return scheme in ['http', 'https', 'file', 'ftp'] + vcs.all_schemes
+
+
+def url_to_path(url):
+    """
+    Convert a file: URL to a path.
+    """
+    assert url.startswith('file:'), (
+        "You can only turn file: urls into filenames (not %r)" % url)
+
+    _, netloc, path, _, _ = urllib_parse.urlsplit(url)
+
+    # if we have a UNC path, prepend UNC share notation
+    if netloc:
+        netloc = '\\\\' + netloc
+
+    path = urllib_request.url2pathname(netloc + path)
+    return path
+
+
+def path_to_url(path):
+    """
+    Convert a path to a file: URL.  The path will be made absolute and have
+    quoted path parts.
+    """
+    path = os.path.normpath(os.path.abspath(path))
+    url = urllib_parse.urljoin('file:', urllib_request.pathname2url(path))
+    return url
+
+
+def is_archive_file(name):
+    """Return True if `name` is a considered as an archive file."""
+    archives = (
+        '.zip', '.tar.gz', '.tar.bz2', '.tgz', '.tar', '.whl'
+    )
+    ext = splitext(name)[1].lower()
+    if ext in archives:
+        return True
+    return False
+
+
+def unpack_vcs_link(link, location, only_download=False):
+    vcs_backend = _get_used_vcs_backend(link)
+    if only_download:
+        vcs_backend.export(location)
+    else:
+        vcs_backend.unpack(location)
+
+
+def _get_used_vcs_backend(link):
+    for backend in vcs.backends:
+        if link.scheme in backend.schemes:
+            vcs_backend = backend(link.url)
+            return vcs_backend
+
+
+def is_vcs_url(link):
+    return bool(_get_used_vcs_backend(link))
+
+
+def is_file_url(link):
+    return link.url.lower().startswith('file:')
+
+
+def _check_hash(download_hash, link):
+    if download_hash.digest_size != hashlib.new(link.hash_name).digest_size:
+        logger.critical(
+            "Hash digest size of the package %d (%s) doesn't match the "
+            "expected hash name %s!",
+            download_hash.digest_size, link, link.hash_name,
+        )
+        raise HashMismatch('Hash name mismatch for package %s' % link)
+    if download_hash.hexdigest() != link.hash:
+        logger.critical(
+            "Hash of the package %s (%s) doesn't match the expected hash %s!",
+            link, download_hash.hexdigest(), link.hash,
+        )
+        raise HashMismatch(
+            'Bad %s hash for package %s' % (link.hash_name, link)
+        )
+
+
+def _get_hash_from_file(target_file, link):
+    try:
+        download_hash = hashlib.new(link.hash_name)
+    except (ValueError, TypeError):
+        logger.warning(
+            "Unsupported hash name %s for package %s", link.hash_name, link,
+        )
+        return None
+
+    with open(target_file, 'rb') as fp:
+        while True:
+            chunk = fp.read(4096)
+            if not chunk:
+                break
+            download_hash.update(chunk)
+    return download_hash
+
+
+def _progress_indicator(iterable, *args, **kwargs):
+    return iterable
+
+
+def _download_url(resp, link, content_file):
+    download_hash = None
+    if link.hash and link.hash_name:
+        try:
+            download_hash = hashlib.new(link.hash_name)
+        except ValueError:
+            logger.warning(
+                "Unsupported hash name %s for package %s",
+                link.hash_name, link,
+            )
+
+    try:
+        total_length = int(resp.headers['content-length'])
+    except (ValueError, KeyError, TypeError):
+        total_length = 0
+
+    cached_resp = getattr(resp, "from_cache", False)
+
+    if logger.getEffectiveLevel() > logging.INFO:
+        show_progress = False
+    elif cached_resp:
+        show_progress = False
+    elif total_length > (40 * 1000):
+        show_progress = True
+    elif not total_length:
+        show_progress = True
+    else:
+        show_progress = False
+
+    show_url = link.show_url
+
+    def resp_read(chunk_size):
+        try:
+            # Special case for urllib3.
+            for chunk in resp.raw.stream(
+                    chunk_size,
+                    # We use decode_content=False here because we do
+                    # want urllib3 to mess with the raw bytes we get
+                    # from the server. If we decompress inside of
+                    # urllib3 then we cannot verify the checksum
+                    # because the checksum will be of the compressed
+                    # file. This breakage will only occur if the
+                    # server adds a Content-Encoding header, which
+                    # depends on how the server was configured:
+                    # - Some servers will notice that the file isn't a
+                    #   compressible file and will leave the file alone
+                    #   and with an empty Content-Encoding
+                    # - Some servers will notice that the file is
+                    #   already compressed and will leave the file
+                    #   alone and will add a Content-Encoding: gzip
+                    #   header
+                    # - Some servers won't notice anything at all and
+                    #   will take a file that's already been compressed
+                    #   and compress it again and set the
+                    #   Content-Encoding: gzip header
+                    #
+                    # By setting this not to decode automatically we
+                    # hope to eliminate problems with the second case.
+                    decode_content=False):
+                yield chunk
+        except AttributeError:
+            # Standard file-like object.
+            while True:
+                chunk = resp.raw.read(chunk_size)
+                if not chunk:
+                    break
+                yield chunk
+
+    progress_indicator = _progress_indicator
+
+    if link.netloc == PyPI.netloc:
+        url = show_url
+    else:
+        url = link.url_without_fragment
+
+    if show_progress:  # We don't show progress on cached responses
+        if total_length:
+            logger.info(
+                "Downloading %s (%s)", url, format_size(total_length),
+            )
+            progress_indicator = DownloadProgressBar(
+                max=total_length,
+            ).iter
+        else:
+            logger.info("Downloading %s", url)
+            progress_indicator = DownloadProgressSpinner().iter
+    elif cached_resp:
+        logger.info("Using cached %s", url)
+    else:
+        logger.info("Downloading %s", url)
+
+    logger.debug('Downloading from URL %s', link)
+
+    for chunk in progress_indicator(resp_read(4096), 4096):
+        if download_hash is not None:
+            download_hash.update(chunk)
+        content_file.write(chunk)
+    if link.hash and link.hash_name:
+        _check_hash(download_hash, link)
+    return download_hash
+
+
+def _copy_file(filename, location, content_type, link):
+    copy = True
+    download_location = os.path.join(location, link.filename)
+    if os.path.exists(download_location):
+        response = ask_path_exists(
+            'The file %s exists. (i)gnore, (w)ipe, (b)ackup ' %
+            display_path(download_location), ('i', 'w', 'b'))
+        if response == 'i':
+            copy = False
+        elif response == 'w':
+            logger.warning('Deleting %s', display_path(download_location))
+            os.remove(download_location)
+        elif response == 'b':
+            dest_file = backup_dir(download_location)
+            logger.warning(
+                'Backing up %s to %s',
+                display_path(download_location),
+                display_path(dest_file),
+            )
+            shutil.move(download_location, dest_file)
+    if copy:
+        shutil.copy(filename, download_location)
+        logger.info('Saved %s', display_path(download_location))
+
+
+def unpack_http_url(link, location, download_dir=None, session=None):
+    if session is None:
+        raise TypeError(
+            "unpack_http_url() missing 1 required keyword argument: 'session'"
+        )
+
+    temp_dir = tempfile.mkdtemp('-unpack', 'pip-')
+
+    # If a download dir is specified, is the file already downloaded there?
+    already_downloaded_path = None
+    if download_dir:
+        already_downloaded_path = _check_download_dir(link, download_dir)
+
+    if already_downloaded_path:
+        from_path = already_downloaded_path
+        content_type = mimetypes.guess_type(from_path)[0]
+    else:
+        # let's download to a tmp dir
+        from_path, content_type = _download_http_url(link, session, temp_dir)
+
+    # unpack the archive to the build dir location. even when only downloading
+    # archives, they have to be unpacked to parse dependencies
+    unpack_file(from_path, location, content_type, link)
+
+    # a download dir is specified; let's copy the archive there
+    if download_dir and not already_downloaded_path:
+        _copy_file(from_path, download_dir, content_type, link)
+
+    if not already_downloaded_path:
+        os.unlink(from_path)
+    rmtree(temp_dir)
+
+
+def unpack_file_url(link, location, download_dir=None):
+    """Unpack link into location.
+    If download_dir is provided and link points to a file, make a copy
+    of the link file inside download_dir."""
+
+    link_path = url_to_path(link.url_without_fragment)
+
+    # If it's a url to a local directory
+    if os.path.isdir(link_path):
+        if os.path.isdir(location):
+            rmtree(location)
+        shutil.copytree(link_path, location, symlinks=True)
+        if download_dir:
+            logger.info('Link is a directory, ignoring download_dir')
+        return
+
+    # if link has a hash, let's confirm it matches
+    if link.hash:
+        link_path_hash = _get_hash_from_file(link_path, link)
+        _check_hash(link_path_hash, link)
+
+    # If a download dir is specified, is the file already there and valid?
+    already_downloaded_path = None
+    if download_dir:
+        already_downloaded_path = _check_download_dir(link, download_dir)
+
+    if already_downloaded_path:
+        from_path = already_downloaded_path
+    else:
+        from_path = link_path
+
+    content_type = mimetypes.guess_type(from_path)[0]
+
+    # unpack the archive to the build dir location. even when only downloading
+    # archives, they have to be unpacked to parse dependencies
+    unpack_file(from_path, location, content_type, link)
+
+    # a download dir is specified and not already downloaded
+    if download_dir and not already_downloaded_path:
+        _copy_file(from_path, download_dir, content_type, link)
+
+
+def _copy_dist_from_dir(link_path, location):
+    """Copy distribution files in `link_path` to `location`.
+
+    Invoked when user requests to install a local directory. E.g.:
+
+        pip install .
+        pip install ~/dev/git-repos/python-prompt-toolkit
+
+    """
+
+    # Note: This is currently VERY SLOW if you have a lot of data in the
+    # directory, because it copies everything with `shutil.copytree`.
+    # What it should really do is build an sdist and install that.
+    # See https://github.com/pypa/pip/issues/2195
+
+    if os.path.isdir(location):
+        rmtree(location)
+
+    # build an sdist
+    setup_py = 'setup.py'
+    sdist_args = [sys.executable]
+    sdist_args.append('-c')
+    sdist_args.append(
+        "import setuptools, tokenize;__file__=%r;"
+        "exec(compile(getattr(tokenize, 'open', open)(__file__).read()"
+        ".replace('\\r\\n', '\\n'), __file__, 'exec'))" % setup_py)
+    sdist_args.append('sdist')
+    sdist_args += ['--dist-dir', location]
+    logger.info('Running setup.py sdist for %s', link_path)
+
+    with indent_log():
+        call_subprocess(sdist_args, cwd=link_path, show_stdout=False)
+
+    # unpack sdist into `location`
+    sdist = os.path.join(location, os.listdir(location)[0])
+    logger.info('Unpacking sdist %s into %s', sdist, location)
+    unpack_file(sdist, location, content_type=None, link=None)
+
+
+class PipXmlrpcTransport(xmlrpc_client.Transport):
+    """Provide a `xmlrpclib.Transport` implementation via a `PipSession`
+    object.
+    """
+    def __init__(self, index_url, session, use_datetime=False):
+        xmlrpc_client.Transport.__init__(self, use_datetime)
+        index_parts = urllib_parse.urlparse(index_url)
+        self._scheme = index_parts.scheme
+        self._session = session
+
+    def request(self, host, handler, request_body, verbose=False):
+        parts = (self._scheme, host, handler, None, None, None)
+        url = urllib_parse.urlunparse(parts)
+        try:
+            headers = {'Content-Type': 'text/xml'}
+            response = self._session.post(url, data=request_body,
+                                          headers=headers, stream=True)
+            response.raise_for_status()
+            self.verbose = verbose
+            return self.parse_response(response.raw)
+        except requests.HTTPError as exc:
+            logger.critical(
+                "HTTP error %s while getting %s",
+                exc.response.status_code, url,
+            )
+            raise
+
+
+def unpack_url(link, location, download_dir=None,
+               only_download=False, session=None):
+    """Unpack link.
+       If link is a VCS link:
+         if only_download, export into download_dir and ignore location
+          else unpack into location
+       for other types of link:
+         - unpack into location
+         - if download_dir, copy the file into download_dir
+         - if only_download, mark location for deletion
+    """
+    # non-editable vcs urls
+    if is_vcs_url(link):
+        unpack_vcs_link(link, location, only_download)
+
+    # file urls
+    elif is_file_url(link):
+        unpack_file_url(link, location, download_dir)
+        if only_download:
+            write_delete_marker_file(location)
+
+    # http urls
+    else:
+        if session is None:
+            session = PipSession()
+
+        unpack_http_url(
+            link,
+            location,
+            download_dir,
+            session,
+        )
+        if only_download:
+            write_delete_marker_file(location)
+
+
+def _download_http_url(link, session, temp_dir):
+    """Download link url into temp_dir using provided session"""
+    target_url = link.url.split('#', 1)[0]
+    try:
+        resp = session.get(
+            target_url,
+            # We use Accept-Encoding: identity here because requests
+            # defaults to accepting compressed responses. This breaks in
+            # a variety of ways depending on how the server is configured.
+            # - Some servers will notice that the file isn't a compressible
+            #   file and will leave the file alone and with an empty
+            #   Content-Encoding
+            # - Some servers will notice that the file is already
+            #   compressed and will leave the file alone and will add a
+            #   Content-Encoding: gzip header
+            # - Some servers won't notice anything at all and will take
+            #   a file that's already been compressed and compress it again
+            #   and set the Content-Encoding: gzip header
+            # By setting this to request only the identity encoding We're
+            # hoping to eliminate the third case. Hopefully there does not
+            # exist a server which when given a file will notice it is
+            # already compressed and that you're not asking for a
+            # compressed file and will then decompress it before sending
+            # because if that's the case I don't think it'll ever be
+            # possible to make this work.
+            headers={"Accept-Encoding": "identity"},
+            stream=True,
+        )
+        resp.raise_for_status()
+    except requests.HTTPError as exc:
+        logger.critical(
+            "HTTP error %s while getting %s", exc.response.status_code, link,
+        )
+        raise
+
+    content_type = resp.headers.get('content-type', '')
+    filename = link.filename  # fallback
+    # Have a look at the Content-Disposition header for a better guess
+    content_disposition = resp.headers.get('content-disposition')
+    if content_disposition:
+        type, params = cgi.parse_header(content_disposition)
+        # We use ``or`` here because we don't want to use an "empty" value
+        # from the filename param.
+        filename = params.get('filename') or filename
+    ext = splitext(filename)[1]
+    if not ext:
+        ext = mimetypes.guess_extension(content_type)
+        if ext:
+            filename += ext
+    if not ext and link.url != resp.url:
+        ext = os.path.splitext(resp.url)[1]
+        if ext:
+            filename += ext
+    file_path = os.path.join(temp_dir, filename)
+    with open(file_path, 'wb') as content_file:
+        _download_url(resp, link, content_file)
+    return file_path, content_type
+
+
+def _check_download_dir(link, download_dir):
+    """ Check download_dir for previously downloaded file with correct hash
+        If a correct file is found return its path else None
+    """
+    download_path = os.path.join(download_dir, link.filename)
+    if os.path.exists(download_path):
+        # If already downloaded, does its hash match?
+        logger.info('File was already downloaded %s', download_path)
+        if link.hash:
+            download_hash = _get_hash_from_file(download_path, link)
+            try:
+                _check_hash(download_hash, link)
+            except HashMismatch:
+                logger.warning(
+                    'Previously-downloaded file %s has bad hash, '
+                    're-downloading.',
+                    download_path
+                )
+                os.unlink(download_path)
+                return None
+        return download_path
+    return None