dulwich/dulwich/client.py

# client.py -- Implementation of the client side git protocols
# Copyright (C) 2008-2013 Jelmer Vernooij <jelmer@jelmer.uk>
#
# Dulwich is dual-licensed under the Apache License, Version 2.0 and the GNU
# General Public License as public by the Free Software Foundation; version 2.0
# or (at your option) any later version. You can redistribute it and/or
# modify it under the terms of either of these two licenses.
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#
# You should have received a copy of the licenses; if not, see
# <http://www.gnu.org/licenses/> for a copy of the GNU General Public License
# and <http://www.apache.org/licenses/LICENSE-2.0> for a copy of the Apache
# License, Version 2.0.
#

"""Client side support for the Git protocol.

The Dulwich client supports the following capabilities:

 * thin-pack
 * multi_ack_detailed
 * multi_ack
 * side-band-64k
 * ofs-delta
 * quiet
 * report-status
 * delete-refs
 * shallow

Known capabilities that are not supported:

 * no-progress
 * include-tag
"""

from contextlib import closing
from io import BytesIO, BufferedReader
import os
import select
import socket
import subprocess
import sys
from typing import Optional, Dict, Callable, Set

from urllib.parse import (
    quote as urlquote,
    unquote as urlunquote,
    urlparse,
    urljoin,
    urlunsplit,
    urlunparse,
    )

import dulwich
from dulwich.config import get_xdg_config_home_path
from dulwich.errors import (
    GitProtocolError,
    NotGitRepository,
    SendPackError,
    )
from dulwich.protocol import (
    HangupException,
    _RBUFSIZE,
    agent_string,
    capability_agent,
    extract_capability_names,
    CAPABILITY_AGENT,
    CAPABILITY_DELETE_REFS,
    CAPABILITY_INCLUDE_TAG,
    CAPABILITY_MULTI_ACK,
    CAPABILITY_MULTI_ACK_DETAILED,
    CAPABILITY_OFS_DELTA,
    CAPABILITY_QUIET,
    CAPABILITY_REPORT_STATUS,
    CAPABILITY_SHALLOW,
    CAPABILITY_SYMREF,
    CAPABILITY_SIDE_BAND_64K,
    CAPABILITY_THIN_PACK,
    CAPABILITIES_REF,
    KNOWN_RECEIVE_CAPABILITIES,
    KNOWN_UPLOAD_CAPABILITIES,
    COMMAND_DEEPEN,
    COMMAND_SHALLOW,
    COMMAND_UNSHALLOW,
    COMMAND_DONE,
    COMMAND_HAVE,
    COMMAND_WANT,
    SIDE_BAND_CHANNEL_DATA,
    SIDE_BAND_CHANNEL_PROGRESS,
    SIDE_BAND_CHANNEL_FATAL,
    PktLineParser,
    Protocol,
    ProtocolFile,
    TCP_GIT_PORT,
    ZERO_SHA,
    extract_capabilities,
    parse_capability,
    )
from dulwich.pack import (
    write_pack_data,
    write_pack_objects,
    )
from dulwich.refs import (
    read_info_refs,
    ANNOTATED_TAG_SUFFIX,
    )


class InvalidWants(Exception):
    """Invalid wants."""

    def __init__(self, wants):
        Exception.__init__(
            self,
            "requested wants not in server provided refs: %r" % wants)


class HTTPUnauthorized(Exception):
    """Raised when authentication fails."""

    def __init__(self, www_authenticate, url):
        Exception.__init__(self, "No valid credentials provided")
        self.www_authenticate = www_authenticate
        self.url = url


def _fileno_can_read(fileno):
    """Check if a file descriptor is readable.
    """
    return len(select.select([fileno], [], [], 0)[0]) > 0


def _win32_peek_avail(handle):
    """Wrapper around PeekNamedPipe to check how many bytes are available.
    """
    from ctypes import byref, wintypes, windll
    c_avail = wintypes.DWORD()
    c_message = wintypes.DWORD()
    success = windll.kernel32.PeekNamedPipe(
        handle, None, 0, None, byref(c_avail),
        byref(c_message))
    if not success:
        raise OSError(wintypes.GetLastError())
    return c_avail.value


COMMON_CAPABILITIES = [CAPABILITY_OFS_DELTA, CAPABILITY_SIDE_BAND_64K]
UPLOAD_CAPABILITIES = ([CAPABILITY_THIN_PACK, CAPABILITY_MULTI_ACK,
                        CAPABILITY_MULTI_ACK_DETAILED, CAPABILITY_SHALLOW]
                       + COMMON_CAPABILITIES)
RECEIVE_CAPABILITIES = (
    [CAPABILITY_REPORT_STATUS, CAPABILITY_DELETE_REFS]
    + COMMON_CAPABILITIES)


class ReportStatusParser(object):
    """Handle status as reported by servers with 'report-status' capability."""

    def __init__(self):
        self._done = False
        self._pack_status = None
        self._ref_statuses = []

    def check(self):
        """Check if there were any errors and, if so, raise exceptions.

        Raises:
          SendPackError: Raised when the server could not unpack
        Returns:
          iterator over refs
        """
        if self._pack_status not in (b'unpack ok', None):
            raise SendPackError(self._pack_status)
        for status in self._ref_statuses:
            try:
                status, rest = status.split(b' ', 1)
            except ValueError:
                # malformed response, move on to the next one
                continue
            if status == b'ng':
                ref, error = rest.split(b' ', 1)
                yield ref, error.decode('utf-8')
            elif status == b'ok':
                yield rest, None
            else:
                raise GitProtocolError('invalid ref status %r' % status)

    def handle_packet(self, pkt):
        """Handle a packet.

        Raises:
          GitProtocolError: Raised when packets are received after a flush
          packet.
        """
        if self._done:
            raise GitProtocolError("received more data after status report")
        if pkt is None:
            self._done = True
            return
        if self._pack_status is None:
            self._pack_status = pkt.strip()
        else:
            ref_status = pkt.strip()
            self._ref_statuses.append(ref_status)


def read_pkt_refs(proto):
    server_capabilities = None
    refs = {}
    # Receive refs from server
    for pkt in proto.read_pkt_seq():
        (sha, ref) = pkt.rstrip(b'\n').split(None, 1)
        if sha == b'ERR':
            raise GitProtocolError(ref.decode('utf-8', 'replace'))
        if server_capabilities is None:
            (ref, server_capabilities) = extract_capabilities(ref)
        refs[ref] = sha

    if len(refs) == 0:
        return {}, set([])
    if refs == {CAPABILITIES_REF: ZERO_SHA}:
        refs = {}
    return refs, set(server_capabilities)


class FetchPackResult(object):
    """Result of a fetch-pack operation.

    Attributes:
      refs: Dictionary with all remote refs
      symrefs: Dictionary with remote symrefs
      agent: User agent string
    """

    _FORWARDED_ATTRS = [
            'clear', 'copy', 'fromkeys', 'get', 'items',
            'keys', 'pop', 'popitem',
            'setdefault', 'update', 'values', 'viewitems', 'viewkeys',
            'viewvalues']

    def __init__(self, refs, symrefs, agent, new_shallow=None,
                 new_unshallow=None):
        self.refs = refs
        self.symrefs = symrefs
        self.agent = agent
        self.new_shallow = new_shallow
        self.new_unshallow = new_unshallow

    def _warn_deprecated(self):
        import warnings
        warnings.warn(
            "Use FetchPackResult.refs instead.",
            DeprecationWarning, stacklevel=3)

    def __eq__(self, other):
        if isinstance(other, dict):
            self._warn_deprecated()
            return (self.refs == other)
        return (self.refs == other.refs and
                self.symrefs == other.symrefs and
                self.agent == other.agent)

    def __contains__(self, name):
        self._warn_deprecated()
        return name in self.refs

    def __getitem__(self, name):
        self._warn_deprecated()
        return self.refs[name]

    def __len__(self):
        self._warn_deprecated()
        return len(self.refs)

    def __iter__(self):
        self._warn_deprecated()
        return iter(self.refs)

    def __getattribute__(self, name):
        if name in type(self)._FORWARDED_ATTRS:
            self._warn_deprecated()
            return getattr(self.refs, name)
        return super(FetchPackResult, self).__getattribute__(name)

    def __repr__(self):
        return "%s(%r, %r, %r)" % (
                self.__class__.__name__, self.refs, self.symrefs, self.agent)


class SendPackResult(object):
    """Result of a upload-pack operation.

    Attributes:
      refs: Dictionary with all remote refs
      agent: User agent string
      ref_status: Optional dictionary mapping ref name to error message (if it
        failed to update), or None if it was updated successfully
    """

    _FORWARDED_ATTRS = [
            'clear', 'copy', 'fromkeys', 'get', 'items',
            'keys', 'pop', 'popitem',
            'setdefault', 'update', 'values', 'viewitems', 'viewkeys',
            'viewvalues']

    def __init__(self, refs, agent=None, ref_status=None):
        self.refs = refs
        self.agent = agent
        self.ref_status = ref_status

    def _warn_deprecated(self):
        import warnings
        warnings.warn(
            "Use SendPackResult.refs instead.",
            DeprecationWarning, stacklevel=3)

    def __eq__(self, other):
        if isinstance(other, dict):
            self._warn_deprecated()
            return self.refs == other
        return self.refs == other.refs and self.agent == other.agent

    def __contains__(self, name):
        self._warn_deprecated()
        return name in self.refs

    def __getitem__(self, name):
        self._warn_deprecated()
        return self.refs[name]

    def __len__(self):
        self._warn_deprecated()
        return len(self.refs)

    def __iter__(self):
        self._warn_deprecated()
        return iter(self.refs)

    def __getattribute__(self, name):
        if name in type(self)._FORWARDED_ATTRS:
            self._warn_deprecated()
            return getattr(self.refs, name)
        return super(SendPackResult, self).__getattribute__(name)

    def __repr__(self):
        return "%s(%r, %r)" % (
                self.__class__.__name__, self.refs, self.agent)


def _read_shallow_updates(proto):
    new_shallow = set()
    new_unshallow = set()
    for pkt in proto.read_pkt_seq():
        cmd, sha = pkt.split(b' ', 1)
        if cmd == COMMAND_SHALLOW:
            new_shallow.add(sha.strip())
        elif cmd == COMMAND_UNSHALLOW:
            new_unshallow.add(sha.strip())
        else:
            raise GitProtocolError('unknown command %s' % pkt)
    return (new_shallow, new_unshallow)


# TODO(durin42): this doesn't correctly degrade if the server doesn't
# support some capabilities. This should work properly with servers
# that don't support multi_ack.
class GitClient(object):
    """Git smart server client."""

    def __init__(self, thin_packs=True, report_activity=None, quiet=False,
                 include_tags=False):
        """Create a new GitClient instance.

        Args:
          thin_packs: Whether or not thin packs should be retrieved
          report_activity: Optional callback for reporting transport
            activity.
          include_tags: send annotated tags when sending the objects they point
            to
        """
        self._report_activity = report_activity
        self._report_status_parser = None
        self._fetch_capabilities = set(UPLOAD_CAPABILITIES)
        self._fetch_capabilities.add(capability_agent())
        self._send_capabilities = set(RECEIVE_CAPABILITIES)
        self._send_capabilities.add(capability_agent())
        if quiet:
            self._send_capabilities.add(CAPABILITY_QUIET)
        if not thin_packs:
            self._fetch_capabilities.remove(CAPABILITY_THIN_PACK)
        if include_tags:
            self._fetch_capabilities.add(CAPABILITY_INCLUDE_TAG)

    def get_url(self, path):
        """Retrieves full url to given path.

        Args:
          path: Repository path (as string)

        Returns:
          Url to path (as string)

        """
        raise NotImplementedError(self.get_url)

    @classmethod
    def from_parsedurl(cls, parsedurl, **kwargs):
        """Create an instance of this client from a urlparse.parsed object.

        Args:
          parsedurl: Result of urlparse()

        Returns:
          A `GitClient` object
        """
        raise NotImplementedError(cls.from_parsedurl)

    def send_pack(self, path, update_refs, generate_pack_data,
                  progress=None):
        """Upload a pack to a remote repository.

        Args:
          path: Repository path (as bytestring)
          update_refs: Function to determine changes to remote refs. Receive
            dict with existing remote refs, returns dict with
            changed refs (name -> sha, where sha=ZERO_SHA for deletions)
          generate_pack_data: Function that can return a tuple
            with number of objects and list of pack data to include
          progress: Optional progress function

        Returns:
          SendPackResult object

        Raises:
          SendPackError: if server rejects the pack data

        """
        raise NotImplementedError(self.send_pack)

    def fetch(self, path, target, determine_wants=None, progress=None,
              depth=None):
        """Fetch into a target repository.

        Args:
          path: Path to fetch from (as bytestring)
          target: Target repository to fetch into
          determine_wants: Optional function to determine what refs to fetch.
            Receives dictionary of name->sha, should return
            list of shas to fetch. Defaults to all shas.
          progress: Optional progress function
          depth: Depth to fetch at

        Returns:
          Dictionary with all remote refs (not just those fetched)

        """
        if determine_wants is None:
            determine_wants = target.object_store.determine_wants_all
        if CAPABILITY_THIN_PACK in self._fetch_capabilities:
            # TODO(jelmer): Avoid reading entire file into memory and
            # only processing it after the whole file has been fetched.
            f = BytesIO()

            def commit():
                if f.tell():
                    f.seek(0)
                    target.object_store.add_thin_pack(f.read, None)

            def abort():
                pass
        else:
            f, commit, abort = target.object_store.add_pack()
        try:
            result = self.fetch_pack(
                path, determine_wants, target.get_graph_walker(), f.write,
                progress=progress, depth=depth)
        except BaseException:
            abort()
            raise
        else:
            commit()
        target.update_shallow(result.new_shallow, result.new_unshallow)
        return result

    def fetch_pack(self, path, determine_wants, graph_walker, pack_data,
                   progress=None, depth=None):
        """Retrieve a pack from a git smart server.

        Args:
          path: Remote path to fetch from
          determine_wants: Function determine what refs
        to fetch. Receives dictionary of name->sha, should return
        list of shas to fetch.
          graph_walker: Object with next() and ack().
          pack_data: Callback called for each bit of data in the pack
          progress: Callback for progress reports (strings)
          depth: Shallow fetch depth

        Returns:
          FetchPackResult object

        """
        raise NotImplementedError(self.fetch_pack)

    def get_refs(self, path):
        """Retrieve the current refs from a git smart server.

        Args:
          path: Path to the repo to fetch from. (as bytestring)

        Returns:

        """
        raise NotImplementedError(self.get_refs)

    def _read_side_band64k_data(self, proto, channel_callbacks):
        """Read per-channel data.

        This requires the side-band-64k capability.

        Args:
          proto: Protocol object to read from
          channel_callbacks: Dictionary mapping channels to packet
            handlers to use. None for a callback discards channel data.
        """
        for pkt in proto.read_pkt_seq():
            channel = ord(pkt[:1])
            pkt = pkt[1:]
            try:
                cb = channel_callbacks[channel]
            except KeyError:
                raise AssertionError('Invalid sideband channel %d' % channel)
            else:
                if cb is not None:
                    cb(pkt)

    @staticmethod
    def _should_send_pack(new_refs):
        # The packfile MUST NOT be sent if the only command used is delete.
        return any(sha != ZERO_SHA for sha in new_refs.values())

    def _handle_receive_pack_head(self, proto, capabilities, old_refs,
                                  new_refs):
        """Handle the head of a 'git-receive-pack' request.

        Args:
          proto: Protocol object to read from
          capabilities: List of negotiated capabilities
          old_refs: Old refs, as received from the server
          new_refs: Refs to change

        Returns:
          (have, want) tuple
        """
        want = []
        have = [x for x in old_refs.values() if not x == ZERO_SHA]
        sent_capabilities = False

        for refname in new_refs:
            if not isinstance(refname, bytes):
                raise TypeError('refname is not a bytestring: %r' % refname)
            old_sha1 = old_refs.get(refname, ZERO_SHA)
            if not isinstance(old_sha1, bytes):
                raise TypeError('old sha1 for %s is not a bytestring: %r' %
                                (refname, old_sha1))
            new_sha1 = new_refs.get(refname, ZERO_SHA)
            if not isinstance(new_sha1, bytes):
                raise TypeError('old sha1 for %s is not a bytestring %r' %
                                (refname, new_sha1))

            if old_sha1 != new_sha1:
                if sent_capabilities:
                    proto.write_pkt_line(old_sha1 + b' ' + new_sha1 + b' ' +
                                         refname)
                else:
                    proto.write_pkt_line(
                        old_sha1 + b' ' + new_sha1 + b' ' + refname + b'\0' +
                        b' '.join(sorted(capabilities)))
                    sent_capabilities = True
            if new_sha1 not in have and new_sha1 != ZERO_SHA:
                want.append(new_sha1)
        proto.write_pkt_line(None)
        return (have, want)

    def _negotiate_receive_pack_capabilities(self, server_capabilities):
        negotiated_capabilities = (
            self._send_capabilities & server_capabilities)
        agent = None
        for capability in server_capabilities:
            k, v = parse_capability(capability)
            if k == CAPABILITY_AGENT:
                agent = v
        unknown_capabilities = (  # noqa: F841
            extract_capability_names(server_capabilities) -
            KNOWN_RECEIVE_CAPABILITIES)
        # TODO(jelmer): warn about unknown capabilities
        return negotiated_capabilities, agent

    def _handle_receive_pack_tail(
            self, proto: Protocol, capabilities: Set[bytes],
            progress: Callable[[bytes], None] = None
            ) -> Optional[Dict[bytes, Optional[str]]]:
        """Handle the tail of a 'git-receive-pack' request.

        Args:
          proto: Protocol object to read from
          capabilities: List of negotiated capabilities
          progress: Optional progress reporting function

        Returns:
          dict mapping ref name to:
            error message if the ref failed to update
            None if it was updated successfully
        """
        if CAPABILITY_SIDE_BAND_64K in capabilities:
            if progress is None:
                def progress(x):
                    pass
            channel_callbacks = {2: progress}
            if CAPABILITY_REPORT_STATUS in capabilities:
                channel_callbacks[1] = PktLineParser(
                    self._report_status_parser.handle_packet).parse
            self._read_side_band64k_data(proto, channel_callbacks)
        else:
            if CAPABILITY_REPORT_STATUS in capabilities:
                for pkt in proto.read_pkt_seq():
                    self._report_status_parser.handle_packet(pkt)
        if self._report_status_parser is not None:
            return dict(self._report_status_parser.check())

        return None

    def _negotiate_upload_pack_capabilities(self, server_capabilities):
        unknown_capabilities = (  # noqa: F841
            extract_capability_names(server_capabilities) -
            KNOWN_UPLOAD_CAPABILITIES)
        # TODO(jelmer): warn about unknown capabilities
        symrefs = {}
        agent = None
        for capability in server_capabilities:
            k, v = parse_capability(capability)
            if k == CAPABILITY_SYMREF:
                (src, dst) = v.split(b':', 1)
                symrefs[src] = dst
            if k == CAPABILITY_AGENT:
                agent = v

        negotiated_capabilities = (
            self._fetch_capabilities & server_capabilities)
        return (negotiated_capabilities, symrefs, agent)

    def _handle_upload_pack_head(self, proto, capabilities, graph_walker,
                                 wants, can_read, depth):
        """Handle the head of a 'git-upload-pack' request.

        Args:
          proto: Protocol object to read from
          capabilities: List of negotiated capabilities
          graph_walker: GraphWalker instance to call .ack() on
          wants: List of commits to fetch
          can_read: function that returns a boolean that indicates
        whether there is extra graph data to read on proto
          depth: Depth for request

        Returns:

        """
        assert isinstance(wants, list) and isinstance(wants[0], bytes)
        proto.write_pkt_line(COMMAND_WANT + b' ' + wants[0] + b' ' +
                             b' '.join(sorted(capabilities)) + b'\n')
        for want in wants[1:]:
            proto.write_pkt_line(COMMAND_WANT + b' ' + want + b'\n')
        if depth not in (0, None) or getattr(graph_walker, 'shallow', None):
            if CAPABILITY_SHALLOW not in capabilities:
                raise GitProtocolError(
                    "server does not support shallow capability required for "
                    "depth")
            for sha in graph_walker.shallow:
                proto.write_pkt_line(COMMAND_SHALLOW + b' ' + sha + b'\n')
            if depth is not None:
                proto.write_pkt_line(COMMAND_DEEPEN + b' ' +
                                     str(depth).encode('ascii') + b'\n')
            proto.write_pkt_line(None)
            if can_read is not None:
                (new_shallow, new_unshallow) = _read_shallow_updates(proto)
            else:
                new_shallow = new_unshallow = None
        else:
            new_shallow = new_unshallow = set()
            proto.write_pkt_line(None)
        have = next(graph_walker)
        while have:
            proto.write_pkt_line(COMMAND_HAVE + b' ' + have + b'\n')
            if can_read is not None and can_read():
                pkt = proto.read_pkt_line()
                parts = pkt.rstrip(b'\n').split(b' ')
                if parts[0] == b'ACK':
                    graph_walker.ack(parts[1])
                    if parts[2] in (b'continue', b'common'):
                        pass
                    elif parts[2] == b'ready':
                        break
                    else:
                        raise AssertionError(
                            "%s not in ('continue', 'ready', 'common)" %
                            parts[2])
            have = next(graph_walker)
        proto.write_pkt_line(COMMAND_DONE + b'\n')
        return (new_shallow, new_unshallow)

    def _handle_upload_pack_tail(self, proto, capabilities, graph_walker,
                                 pack_data, progress=None, rbufsize=_RBUFSIZE):
        """Handle the tail of a 'git-upload-pack' request.

        Args:
          proto: Protocol object to read from
          capabilities: List of negotiated capabilities
          graph_walker: GraphWalker instance to call .ack() on
          pack_data: Function to call with pack data
          progress: Optional progress reporting function
          rbufsize: Read buffer size

        Returns:

        """
        pkt = proto.read_pkt_line()
        while pkt:
            parts = pkt.rstrip(b'\n').split(b' ')
            if parts[0] == b'ACK':
                graph_walker.ack(parts[1])
            if len(parts) < 3 or parts[2] not in (
                    b'ready', b'continue', b'common'):
                break
            pkt = proto.read_pkt_line()
        if CAPABILITY_SIDE_BAND_64K in capabilities:
            if progress is None:
                # Just ignore progress data

                def progress(x):
                    pass
            self._read_side_band64k_data(proto, {
                SIDE_BAND_CHANNEL_DATA: pack_data,
                SIDE_BAND_CHANNEL_PROGRESS: progress}
            )
        else:
            while True:
                data = proto.read(rbufsize)
                if data == b"":
                    break
                pack_data(data)


def check_wants(wants, refs):
    """Check that a set of wants is valid.

    Args:
      wants: Set of object SHAs to fetch
      refs: Refs dictionary to check against

    Returns:

    """
    missing = set(wants) - {
            v for (k, v) in refs.items()
            if not k.endswith(ANNOTATED_TAG_SUFFIX)}
    if missing:
        raise InvalidWants(missing)


def _remote_error_from_stderr(stderr):
    if stderr is None:
        return HangupException()
    lines = [line.rstrip(b'\n') for line in stderr.readlines()]
    for line in lines:
        if line.startswith(b'ERROR: '):
            return GitProtocolError(
                line[len(b'ERROR: '):].decode('utf-8', 'replace'))
    return HangupException(lines)


class TraditionalGitClient(GitClient):
    """Traditional Git client."""

    DEFAULT_ENCODING = 'utf-8'

    def __init__(self, path_encoding=DEFAULT_ENCODING, **kwargs):
        self._remote_path_encoding = path_encoding
        super(TraditionalGitClient, self).__init__(**kwargs)

    def _connect(self, cmd, path):
        """Create a connection to the server.

        This method is abstract - concrete implementations should
        implement their own variant which connects to the server and
        returns an initialized Protocol object with the service ready
        for use and a can_read function which may be used to see if
        reads would block.

        Args:
          cmd: The git service name to which we should connect.
          path: The path we should pass to the service. (as bytestirng)
        """
        raise NotImplementedError()

    def send_pack(self, path, update_refs, generate_pack_data,
                  progress=None):
        """Upload a pack to a remote repository.

        Args:
          path: Repository path (as bytestring)
          update_refs: Function to determine changes to remote refs.
        Receive dict with existing remote refs, returns dict with
        changed refs (name -> sha, where sha=ZERO_SHA for deletions)
          generate_pack_data: Function that can return a tuple with
        number of objects and pack data to upload.
          progress: Optional callback called with progress updates

        Returns:
          SendPackResult

        Raises:
          SendPackError: if server rejects the pack data

        """
        proto, unused_can_read, stderr = self._connect(b'receive-pack', path)
        with proto:
            try:
                old_refs, server_capabilities = read_pkt_refs(proto)
            except HangupException:
                raise _remote_error_from_stderr(stderr)
            negotiated_capabilities, agent = \
                self._negotiate_receive_pack_capabilities(server_capabilities)
            if CAPABILITY_REPORT_STATUS in negotiated_capabilities:
                self._report_status_parser = ReportStatusParser()
            report_status_parser = self._report_status_parser

            try:
                new_refs = orig_new_refs = update_refs(dict(old_refs))
            except BaseException:
                proto.write_pkt_line(None)
                raise

            if set(new_refs.items()).issubset(set(old_refs.items())):
                proto.write_pkt_line(None)
                return SendPackResult(new_refs, agent=agent, ref_status={})

            if CAPABILITY_DELETE_REFS not in server_capabilities:
                # Server does not support deletions. Fail later.
                new_refs = dict(orig_new_refs)
                for ref, sha in orig_new_refs.items():
                    if sha == ZERO_SHA:
                        if CAPABILITY_REPORT_STATUS in negotiated_capabilities:
                            report_status_parser._ref_statuses.append(
                                b'ng ' + ref +
                                b' remote does not support deleting refs')
                            report_status_parser._ref_status_ok = False
                        del new_refs[ref]

            if new_refs is None:
                proto.write_pkt_line(None)
                return SendPackResult(old_refs, agent=agent, ref_status={})

            if len(new_refs) == 0 and len(orig_new_refs):
                # NOOP - Original new refs filtered out by policy
                proto.write_pkt_line(None)
                if report_status_parser is not None:
                    ref_status = dict(report_status_parser.check())
                else:
                    ref_status = None
                return SendPackResult(
                    old_refs, agent=agent, ref_status=ref_status)

            (have, want) = self._handle_receive_pack_head(
                proto, negotiated_capabilities, old_refs, new_refs)

            pack_data_count, pack_data = generate_pack_data(
                have, want,
                ofs_delta=(CAPABILITY_OFS_DELTA in negotiated_capabilities))

            if self._should_send_pack(new_refs):
                write_pack_data(proto.write_file(), pack_data_count, pack_data)

            ref_status = self._handle_receive_pack_tail(
                proto, negotiated_capabilities, progress)
            return SendPackResult(new_refs, agent=agent, ref_status=ref_status)

    def fetch_pack(self, path, determine_wants, graph_walker, pack_data,
                   progress=None, depth=None):
        """Retrieve a pack from a git smart server.

        Args:
          path: Remote path to fetch from
          determine_wants: Function determine what refs
        to fetch. Receives dictionary of name->sha, should return
        list of shas to fetch.
          graph_walker: Object with next() and ack().
          pack_data: Callback called for each bit of data in the pack
          progress: Callback for progress reports (strings)
          depth: Shallow fetch depth

        Returns:
          FetchPackResult object

        """
        proto, can_read, stderr = self._connect(b'upload-pack', path)
        with proto:
            try:
                refs, server_capabilities = read_pkt_refs(proto)
            except HangupException:
                raise _remote_error_from_stderr(stderr)
            negotiated_capabilities, symrefs, agent = (
                    self._negotiate_upload_pack_capabilities(
                            server_capabilities))

            if refs is None:
                proto.write_pkt_line(None)
                return FetchPackResult(refs, symrefs, agent)

            try:
                wants = determine_wants(refs)
            except BaseException:
                proto.write_pkt_line(None)
                raise
            if wants is not None:
                wants = [cid for cid in wants if cid != ZERO_SHA]
            if not wants:
                proto.write_pkt_line(None)
                return FetchPackResult(refs, symrefs, agent)
            (new_shallow, new_unshallow) = self._handle_upload_pack_head(
                proto, negotiated_capabilities, graph_walker, wants, can_read,
                depth=depth)
            self._handle_upload_pack_tail(
                proto, negotiated_capabilities, graph_walker, pack_data,
                progress)
            return FetchPackResult(
                    refs, symrefs, agent, new_shallow, new_unshallow)

    def get_refs(self, path):
        """Retrieve the current refs from a git smart server.
        """
        # stock `git ls-remote` uses upload-pack
        proto, _, stderr = self._connect(b'upload-pack', path)
        with proto:
            try:
                refs, _ = read_pkt_refs(proto)
            except HangupException:
                raise _remote_error_from_stderr(stderr)
            proto.write_pkt_line(None)
            return refs

    def archive(self, path, committish, write_data, progress=None,
                write_error=None, format=None, subdirs=None, prefix=None):
        proto, can_read, stderr = self._connect(b'upload-archive', path)
        with proto:
            if format is not None:
                proto.write_pkt_line(b"argument --format=" + format)
            proto.write_pkt_line(b"argument " + committish)
            if subdirs is not None:
                for subdir in subdirs:
                    proto.write_pkt_line(b"argument " + subdir)
            if prefix is not None:
                proto.write_pkt_line(b"argument --prefix=" + prefix)
            proto.write_pkt_line(None)
            try:
                pkt = proto.read_pkt_line()
            except HangupException:
                raise _remote_error_from_stderr(stderr)
            if pkt == b"NACK\n" or pkt == b"NACK":
                return
            elif pkt == b"ACK\n" or pkt == b"ACK":
                pass
            elif pkt.startswith(b"ERR "):
                raise GitProtocolError(
                        pkt[4:].rstrip(b"\n").decode('utf-8', 'replace'))
            else:
                raise AssertionError("invalid response %r" % pkt)
            ret = proto.read_pkt_line()
            if ret is not None:
                raise AssertionError("expected pkt tail")
            self._read_side_band64k_data(proto, {
                SIDE_BAND_CHANNEL_DATA: write_data,
                SIDE_BAND_CHANNEL_PROGRESS: progress,
                SIDE_BAND_CHANNEL_FATAL: write_error})


class TCPGitClient(TraditionalGitClient):
    """A Git Client that works over TCP directly (i.e. git://)."""

    def __init__(self, host, port=None, **kwargs):
        if port is None:
            port = TCP_GIT_PORT
        self._host = host
        self._port = port
        super(TCPGitClient, self).__init__(**kwargs)

    @classmethod
    def from_parsedurl(cls, parsedurl, **kwargs):
        return cls(parsedurl.hostname, port=parsedurl.port, **kwargs)

    def get_url(self, path):
        netloc = self._host
        if self._port is not None and self._port != TCP_GIT_PORT:
            netloc += ":%d" % self._port
        return urlunsplit(("git", netloc, path, '', ''))

    def _connect(self, cmd, path):
        if not isinstance(cmd, bytes):
            raise TypeError(cmd)
        if not isinstance(path, bytes):
            path = path.encode(self._remote_path_encoding)
        sockaddrs = socket.getaddrinfo(
            self._host, self._port, socket.AF_UNSPEC, socket.SOCK_STREAM)
        s = None
        err = socket.error("no address found for %s" % self._host)
        for (family, socktype, proto, canonname, sockaddr) in sockaddrs:
            s = socket.socket(family, socktype, proto)
            s.setsockopt(socket.IPPROTO_TCP, socket.TCP_NODELAY, 1)
            try:
                s.connect(sockaddr)
                break
            except socket.error as e:
                err = e
                if s is not None:
                    s.close()
                s = None
        if s is None:
            raise err
        # -1 means system default buffering
        rfile = s.makefile('rb', -1)
        # 0 means unbuffered
        wfile = s.makefile('wb', 0)

        def close():
            rfile.close()
            wfile.close()
            s.close()

        proto = Protocol(rfile.read, wfile.write, close,
                         report_activity=self._report_activity)
        if path.startswith(b"/~"):
            path = path[1:]
        # TODO(jelmer): Alternative to ascii?
        proto.send_cmd(
            b'git-' + cmd, path, b'host=' + self._host.encode('ascii'))
        return proto, lambda: _fileno_can_read(s), None


class SubprocessWrapper(object):
    """A socket-like object that talks to a subprocess via pipes."""

    def __init__(self, proc):
        self.proc = proc
        self.read = BufferedReader(proc.stdout).read
        self.write = proc.stdin.write

    @property
    def stderr(self):
        return self.proc.stderr

    def can_read(self):
        if sys.platform == 'win32':
            from msvcrt import get_osfhandle
            handle = get_osfhandle(self.proc.stdout.fileno())
            return _win32_peek_avail(handle) != 0
        else:
            return _fileno_can_read(self.proc.stdout.fileno())

    def close(self):
        self.proc.stdin.close()
        self.proc.stdout.close()
        if self.proc.stderr:
            self.proc.stderr.close()
        self.proc.wait()


def find_git_command():
    """Find command to run for system Git (usually C Git)."""
    if sys.platform == 'win32':  # support .exe, .bat and .cmd
        try:  # to avoid overhead
            import win32api
        except ImportError:  # run through cmd.exe with some overhead
            return ['cmd', '/c', 'git']
        else:
            status, git = win32api.FindExecutable('git')
            return [git]
    else:
        return ['git']


class SubprocessGitClient(TraditionalGitClient):
    """Git client that talks to a server using a subprocess."""

    @classmethod
    def from_parsedurl(cls, parsedurl, **kwargs):
        return cls(**kwargs)

    git_command = None

    def _connect(self, service, path):
        if not isinstance(service, bytes):
            raise TypeError(service)
        if isinstance(path, bytes):
            path = path.decode(self._remote_path_encoding)
        if self.git_command is None:
            git_command = find_git_command()
        argv = git_command + [service.decode('ascii'), path]
        p = subprocess.Popen(argv, bufsize=0, stdin=subprocess.PIPE,
                             stdout=subprocess.PIPE,
                             stderr=subprocess.PIPE)
        pw = SubprocessWrapper(p)
        return (Protocol(pw.read, pw.write, pw.close,
                         report_activity=self._report_activity),
                pw.can_read, p.stderr)


class LocalGitClient(GitClient):
    """Git Client that just uses a local Repo."""

    def __init__(self, thin_packs=True, report_activity=None, config=None):
        """Create a new LocalGitClient instance.

        Args:
          thin_packs: Whether or not thin packs should be retrieved
          report_activity: Optional callback for reporting transport
            activity.
        """
        self._report_activity = report_activity
        # Ignore the thin_packs argument

    def get_url(self, path):
        return urlunsplit(('file', '', path, '', ''))

    @classmethod
    def from_parsedurl(cls, parsedurl, **kwargs):
        return cls(**kwargs)

    @classmethod
    def _open_repo(cls, path):
        from dulwich.repo import Repo
        if not isinstance(path, str):
            path = os.fsdecode(path)
        return closing(Repo(path))

    def send_pack(self, path, update_refs, generate_pack_data,
                  progress=None):
        """Upload a pack to a remote repository.

        Args:
          path: Repository path (as bytestring)
          update_refs: Function to determine changes to remote refs.
        Receive dict with existing remote refs, returns dict with
        changed refs (name -> sha, where sha=ZERO_SHA for deletions)
        with number of items and pack data to upload.
          progress: Optional progress function

        Returns:
          SendPackResult

        Raises:
          SendPackError: if server rejects the pack data

        """
        if not progress:
            def progress(x):
                pass

        with self._open_repo(path) as target:
            old_refs = target.get_refs()
            new_refs = update_refs(dict(old_refs))

            have = [sha1 for sha1 in old_refs.values() if sha1 != ZERO_SHA]
            want = []
            for refname, new_sha1 in new_refs.items():
                if (new_sha1 not in have and
                        new_sha1 not in want and
                        new_sha1 != ZERO_SHA):
                    want.append(new_sha1)

            if (not want and
                    set(new_refs.items()).issubset(set(old_refs.items()))):
                return SendPackResult(new_refs, ref_status={})

            target.object_store.add_pack_data(
                *generate_pack_data(have, want, ofs_delta=True))

            ref_status = {}

            for refname, new_sha1 in new_refs.items():
                old_sha1 = old_refs.get(refname, ZERO_SHA)
                if new_sha1 != ZERO_SHA:
                    if not target.refs.set_if_equals(
                            refname, old_sha1, new_sha1):
                        msg = 'unable to set %s to %s' % (refname, new_sha1)
                        progress(msg)
                        ref_status[refname] = msg
                else:
                    if not target.refs.remove_if_equals(refname, old_sha1):
                        progress('unable to remove %s' % refname)
                        ref_status[refname] = 'unable to remove'

        return SendPackResult(new_refs, ref_status=ref_status)

    def fetch(self, path, target, determine_wants=None, progress=None,
              depth=None):
        """Fetch into a target repository.

        Args:
          path: Path to fetch from (as bytestring)
          target: Target repository to fetch into
          determine_wants: Optional function determine what refs
        to fetch. Receives dictionary of name->sha, should return
        list of shas to fetch. Defaults to all shas.
          progress: Optional progress function
          depth: Shallow fetch depth

        Returns:
          FetchPackResult object

        """
        with self._open_repo(path) as r:
            refs = r.fetch(target, determine_wants=determine_wants,
                           progress=progress, depth=depth)
            return FetchPackResult(refs, r.refs.get_symrefs(),
                                   agent_string())

    def fetch_pack(self, path, determine_wants, graph_walker, pack_data,
                   progress=None, depth=None):
        """Retrieve a pack from a git smart server.

        Args:
          path: Remote path to fetch from
          determine_wants: Function determine what refs
        to fetch. Receives dictionary of name->sha, should return
        list of shas to fetch.
          graph_walker: Object with next() and ack().
          pack_data: Callback called for each bit of data in the pack
          progress: Callback for progress reports (strings)
          depth: Shallow fetch depth

        Returns:
          FetchPackResult object

        """
        with self._open_repo(path) as r:
            objects_iter = r.fetch_objects(
                determine_wants, graph_walker, progress=progress, depth=depth)
            symrefs = r.refs.get_symrefs()
            agent = agent_string()

            # Did the process short-circuit (e.g. in a stateless RPC call)?
            # Note that the client still expects a 0-object pack in most cases.
            if objects_iter is None:
                return FetchPackResult(None, symrefs, agent)
            protocol = ProtocolFile(None, pack_data)
            write_pack_objects(protocol, objects_iter)
            return FetchPackResult(r.get_refs(), symrefs, agent)

    def get_refs(self, path):
        """Retrieve the current refs from a git smart server.
        """

        with self._open_repo(path) as target:
            return target.get_refs()


# What Git client to use for local access
default_local_git_client_cls = LocalGitClient


class SSHVendor(object):
    """A client side SSH implementation."""

    def connect_ssh(self, host, command, username=None, port=None,
                    password=None, key_filename=None):
        # This function was deprecated in 0.9.1
        import warnings
        warnings.warn(
            "SSHVendor.connect_ssh has been renamed to SSHVendor.run_command",
            DeprecationWarning)
        return self.run_command(host, command, username=username, port=port,
                                password=password, key_filename=key_filename)

    def run_command(self, host, command, username=None, port=None,
                    password=None, key_filename=None):
        """Connect to an SSH server.

        Run a command remotely and return a file-like object for interaction
        with the remote command.

        Args:
          host: Host name
          command: Command to run (as argv array)
          username: Optional ame of user to log in as
          port: Optional SSH port to use
          password: Optional ssh password for login or private key
          key_filename: Optional path to private keyfile

        Returns:

        """
        raise NotImplementedError(self.run_command)


class StrangeHostname(Exception):
    """Refusing to connect to strange SSH hostname."""

    def __init__(self, hostname):
        super(StrangeHostname, self).__init__(hostname)


class SubprocessSSHVendor(SSHVendor):
    """SSH vendor that shells out to the local 'ssh' command."""

    def run_command(self, host, command, username=None, port=None,
                    password=None, key_filename=None):

        if password is not None:
            raise NotImplementedError(
                "Setting password not supported by SubprocessSSHVendor.")

        args = ['ssh', '-x']

        if port:
            args.extend(['-p', str(port)])

        if key_filename:
            args.extend(['-i', str(key_filename)])

        if username:
            host = '%s@%s' % (username, host)
        if host.startswith('-'):
            raise StrangeHostname(hostname=host)
        args.append(host)

        proc = subprocess.Popen(args + [command], bufsize=0,
                                stdin=subprocess.PIPE,
                                stdout=subprocess.PIPE,
                                stderr=subprocess.PIPE)
        return SubprocessWrapper(proc)


class PLinkSSHVendor(SSHVendor):
    """SSH vendor that shells out to the local 'plink' command."""

    def run_command(self, host, command, username=None, port=None,
                    password=None, key_filename=None):

        if sys.platform == 'win32':
            args = ['plink.exe', '-ssh']
        else:
            args = ['plink', '-ssh']

        if password is not None:
            import warnings
            warnings.warn(
                "Invoking PLink with a password exposes the password in the "
                "process list.")
            args.extend(['-pw', str(password)])

        if port:
            args.extend(['-P', str(port)])

        if key_filename:
            args.extend(['-i', str(key_filename)])

        if username:
            host = '%s@%s' % (username, host)
        if host.startswith('-'):
            raise StrangeHostname(hostname=host)
        args.append(host)

        proc = subprocess.Popen(args + [command], bufsize=0,
                                stdin=subprocess.PIPE,
                                stdout=subprocess.PIPE,
                                stderr=subprocess.PIPE)
        return SubprocessWrapper(proc)


def ParamikoSSHVendor(**kwargs):
    import warnings
    warnings.warn(
        "ParamikoSSHVendor has been moved to dulwich.contrib.paramiko_vendor.",
        DeprecationWarning)
    from dulwich.contrib.paramiko_vendor import ParamikoSSHVendor
    return ParamikoSSHVendor(**kwargs)


# Can be overridden by users
get_ssh_vendor = SubprocessSSHVendor


class SSHGitClient(TraditionalGitClient):

    def __init__(self, host, port=None, username=None, vendor=None,
                 config=None, password=None, key_filename=None, **kwargs):
        self.host = host
        self.port = port
        self.username = username
        self.password = password
        self.key_filename = key_filename
        super(SSHGitClient, self).__init__(**kwargs)
        self.alternative_paths = {}
        if vendor is not None:
            self.ssh_vendor = vendor
        else:
            self.ssh_vendor = get_ssh_vendor()

    def get_url(self, path):
        netloc = self.host
        if self.port is not None:
            netloc += ":%d" % self.port

        if self.username is not None:
            netloc = urlquote(self.username, '@/:') + "@" + netloc

        return urlunsplit(('ssh', netloc, path, '', ''))

    @classmethod
    def from_parsedurl(cls, parsedurl, **kwargs):
        return cls(host=parsedurl.hostname, port=parsedurl.port,
                   username=parsedurl.username, **kwargs)

    def _get_cmd_path(self, cmd):
        cmd = self.alternative_paths.get(cmd, b'git-' + cmd)
        assert isinstance(cmd, bytes)
        return cmd

    def _connect(self, cmd, path):
        if not isinstance(cmd, bytes):
            raise TypeError(cmd)
        if isinstance(path, bytes):
            path = path.decode(self._remote_path_encoding)
        if path.startswith("/~"):
            path = path[1:]
        argv = (self._get_cmd_path(cmd).decode(self._remote_path_encoding) +
                " '" + path + "'")
        kwargs = {}
        if self.password is not None:
            kwargs['password'] = self.password
        if self.key_filename is not None:
            kwargs['key_filename'] = self.key_filename
        con = self.ssh_vendor.run_command(
            self.host, argv, port=self.port, username=self.username,
            **kwargs)
        return (Protocol(con.read, con.write, con.close,
                         report_activity=self._report_activity),
                con.can_read, getattr(con, 'stderr', None))


def default_user_agent_string():
    # Start user agent with "git/", because GitHub requires this. :-( See
    # https://github.com/jelmer/dulwich/issues/562 for details.
    return "git/dulwich/%s" % ".".join([str(x) for x in dulwich.__version__])


def default_urllib3_manager(config, pool_manager_cls=None,
                            proxy_manager_cls=None, **override_kwargs):
    """Return `urllib3` connection pool manager.

    Honour detected proxy configurations.

    Args:
      config: dulwich.config.ConfigDict` instance with Git configuration.
      kwargs: Additional arguments for urllib3.ProxyManager

    Returns:
      `pool_manager_cls` (defaults to `urllib3.ProxyManager`) instance for
      proxy configurations, `proxy_manager_cls` (defaults to
      `urllib3.PoolManager`) instance otherwise.

    """
    proxy_server = user_agent = None
    ca_certs = ssl_verify = None

    if proxy_server is None:
        for proxyname in ('https_proxy', 'http_proxy', 'all_proxy'):
            proxy_server = os.environ.get(proxyname)
            if proxy_server is not None:
                break

    if config is not None:
        if proxy_server is None:
            try:
                proxy_server = config.get(b"http", b"proxy")
            except KeyError:
                pass
        try:
            user_agent = config.get(b"http", b"useragent")
        except KeyError:
            pass

        # TODO(jelmer): Support per-host settings
        try:
            ssl_verify = config.get_boolean(b"http", b"sslVerify")
        except KeyError:
            ssl_verify = True

        try:
            ca_certs = config.get(b"http", b"sslCAInfo")
        except KeyError:
            ca_certs = None

    if user_agent is None:
        user_agent = default_user_agent_string()

    headers = {"User-agent": user_agent}

    kwargs = {}
    if ssl_verify is True:
        kwargs['cert_reqs'] = "CERT_REQUIRED"
    elif ssl_verify is False:
        kwargs['cert_reqs'] = 'CERT_NONE'
    else:
        # Default to SSL verification
        kwargs['cert_reqs'] = "CERT_REQUIRED"

    if ca_certs is not None:
        kwargs['ca_certs'] = ca_certs
    kwargs.update(override_kwargs)

    # Try really hard to find a SSL certificate path
    if 'ca_certs' not in kwargs and kwargs.get('cert_reqs') != 'CERT_NONE':
        try:
            import certifi
        except ImportError:
            pass
        else:
            kwargs['ca_certs'] = certifi.where()

    import urllib3

    if proxy_server is not None:
        if proxy_manager_cls is None:
            proxy_manager_cls = urllib3.ProxyManager
        # `urllib3` requires a `str` object in both Python 2 and 3, while
        # `ConfigDict` coerces entries to `bytes` on Python 3. Compensate.
        if not isinstance(proxy_server, str):
            proxy_server = proxy_server.decode()
        manager = proxy_manager_cls(proxy_server, headers=headers, **kwargs)
    else:
        if pool_manager_cls is None:
            pool_manager_cls = urllib3.PoolManager
        manager = pool_manager_cls(headers=headers, **kwargs)

    return manager


class HttpGitClient(GitClient):

    def __init__(self, base_url, dumb=None, pool_manager=None, config=None,
                 username=None, password=None, **kwargs):
        self._base_url = base_url.rstrip("/") + "/"
        self._username = username
        self._password = password
        self.dumb = dumb

        if pool_manager is None:
            self.pool_manager = default_urllib3_manager(config)
        else:
            self.pool_manager = pool_manager

        if username is not None:
            # No escaping needed: ":" is not allowed in username:
            # https://tools.ietf.org/html/rfc2617#section-2
            credentials = "%s:%s" % (username, password)
            import urllib3.util
            basic_auth = urllib3.util.make_headers(basic_auth=credentials)
            self.pool_manager.headers.update(basic_auth)

        GitClient.__init__(self, **kwargs)

    def get_url(self, path):
        return self._get_url(path).rstrip("/")

    @classmethod
    def from_parsedurl(cls, parsedurl, **kwargs):
        password = parsedurl.password
        if password is not None:
            kwargs['password'] = urlunquote(password)
        username = parsedurl.username
        if username is not None:
            kwargs['username'] = urlunquote(username)
        netloc = parsedurl.hostname
        if parsedurl.port:
            netloc = "%s:%s" % (netloc, parsedurl.port)
        if parsedurl.username:
            netloc = "%s@%s" % (parsedurl.username, netloc)
        parsedurl = parsedurl._replace(netloc=netloc)
        return cls(urlunparse(parsedurl), **kwargs)

    def __repr__(self):
        return "%s(%r, dumb=%r)" % (
            type(self).__name__, self._base_url, self.dumb)

    def _get_url(self, path):
        if not isinstance(path, str):
            # urllib3.util.url._encode_invalid_chars() converts the path back
            # to bytes using the utf-8 codec.
            path = path.decode('utf-8')
        return urljoin(self._base_url, path).rstrip("/") + "/"

    def _http_request(self, url, headers=None, data=None,
                      allow_compression=False):
        """Perform HTTP request.

        Args:
          url: Request URL.
          headers: Optional custom headers to override defaults.
          data: Request data.
          allow_compression: Allow GZipped communication.

        Returns:
          Tuple (`response`, `read`), where response is an `urllib3`
          response object with additional `content_type` and
          `redirect_location` properties, and `read` is a consumable read
          method for the response data.

        """
        req_headers = self.pool_manager.headers.copy()
        if headers is not None:
            req_headers.update(headers)
        req_headers["Pragma"] = "no-cache"
        if allow_compression:
            req_headers["Accept-Encoding"] = "gzip"
        else:
            req_headers["Accept-Encoding"] = "identity"

        if data is None:
            resp = self.pool_manager.request("GET", url, headers=req_headers)
        else:
            resp = self.pool_manager.request("POST", url, headers=req_headers,
                                             body=data)

        if resp.status == 404:
            raise NotGitRepository()
        if resp.status == 401:
            raise HTTPUnauthorized(resp.getheader('WWW-Authenticate'), url)
        if resp.status != 200:
            raise GitProtocolError("unexpected http resp %d for %s" %
                                   (resp.status, url))

        # TODO: Optimization available by adding `preload_content=False` to the
        # request and just passing the `read` method on instead of going via
        # `BytesIO`, if we can guarantee that the entire response is consumed
        # before issuing the next to still allow for connection reuse from the
        # pool.
        read = BytesIO(resp.data).read

        resp.content_type = resp.getheader("Content-Type")
        # Check if geturl() is available (urllib3 version >= 1.23)
        try:
            resp_url = resp.geturl()
        except AttributeError:
            # get_redirect_location() is available for urllib3 >= 1.1
            resp.redirect_location = resp.get_redirect_location()
        else:
            resp.redirect_location = resp_url if resp_url != url else ''
        return resp, read

    def _discover_references(self, service, base_url):
        assert base_url[-1] == "/"
        tail = "info/refs"
        headers = {"Accept": "*/*"}
        if self.dumb is not True:
            tail += "?service=%s" % service.decode('ascii')
        url = urljoin(base_url, tail)
        resp, read = self._http_request(url, headers, allow_compression=True)

        if resp.redirect_location:
            # Something changed (redirect!), so let's update the base URL
            if not resp.redirect_location.endswith(tail):
                raise GitProtocolError(
                        "Redirected from URL %s to URL %s without %s" % (
                            url, resp.redirect_location, tail))
            base_url = resp.redirect_location[:-len(tail)]

        try:
            self.dumb = not resp.content_type.startswith("application/x-git-")
            if not self.dumb:
                proto = Protocol(read, None)
                # The first line should mention the service
                try:
                    [pkt] = list(proto.read_pkt_seq())
                except ValueError:
                    raise GitProtocolError(
                        "unexpected number of packets received")
                if pkt.rstrip(b'\n') != (b'# service=' + service):
                    raise GitProtocolError(
                        "unexpected first line %r from smart server" % pkt)
                return read_pkt_refs(proto) + (base_url, )
            else:
                return read_info_refs(resp), set(), base_url
        finally:
            resp.close()

    def _smart_request(self, service, url, data):
        assert url[-1] == "/"
        url = urljoin(url, service)
        result_content_type = "application/x-%s-result" % service
        headers = {
            "Content-Type": "application/x-%s-request" % service,
            "Accept": result_content_type,
            "Content-Length": str(len(data)),
        }
        resp, read = self._http_request(url, headers, data)
        if resp.content_type != result_content_type:
            raise GitProtocolError("Invalid content-type from server: %s"
                                   % resp.content_type)
        return resp, read

    def send_pack(self, path, update_refs, generate_pack_data,
                  progress=None):
        """Upload a pack to a remote repository.

        Args:
          path: Repository path (as bytestring)
          update_refs: Function to determine changes to remote refs.
        Receives dict with existing remote refs, returns dict with
        changed refs (name -> sha, where sha=ZERO_SHA for deletions)
          generate_pack_data: Function that can return a tuple
        with number of elements and pack data to upload.
          progress: Optional progress function

        Returns:
          SendPackResult

        Raises:
          SendPackError: if server rejects the pack data

        """
        url = self._get_url(path)
        old_refs, server_capabilities, url = self._discover_references(
            b"git-receive-pack", url)
        negotiated_capabilities, agent = (
            self._negotiate_receive_pack_capabilities(server_capabilities))
        negotiated_capabilities.add(capability_agent())

        if CAPABILITY_REPORT_STATUS in negotiated_capabilities:
            self._report_status_parser = ReportStatusParser()

        new_refs = update_refs(dict(old_refs))
        if new_refs is None:
            # Determine wants function is aborting the push.
            return SendPackResult(old_refs, agent=agent, ref_status={})
        if set(new_refs.items()).issubset(set(old_refs.items())):
            return SendPackResult(new_refs, agent=agent, ref_status={})
        if self.dumb:
            raise NotImplementedError(self.fetch_pack)
        req_data = BytesIO()
        req_proto = Protocol(None, req_data.write)
        (have, want) = self._handle_receive_pack_head(
            req_proto, negotiated_capabilities, old_refs, new_refs)
        pack_data_count, pack_data = generate_pack_data(
                have, want,
                ofs_delta=(CAPABILITY_OFS_DELTA in negotiated_capabilities))
        if self._should_send_pack(new_refs):
            write_pack_data(req_proto.write_file(), pack_data_count, pack_data)
        resp, read = self._smart_request("git-receive-pack", url,
                                         data=req_data.getvalue())
        try:
            resp_proto = Protocol(read, None)
            ref_status = self._handle_receive_pack_tail(
                resp_proto, negotiated_capabilities, progress)
            return SendPackResult(
                new_refs, agent=agent, ref_status=ref_status)
        finally:
            resp.close()

    def fetch_pack(self, path, determine_wants, graph_walker, pack_data,
                   progress=None, depth=None):
        """Retrieve a pack from a git smart server.

        Args:
          path: Path to fetch from
          determine_wants: Callback that returns list of commits to fetch
          graph_walker: Object with next() and ack().
          pack_data: Callback called for each bit of data in the pack
          progress: Callback for progress reports (strings)
          depth: Depth for request

        Returns:
          FetchPackResult object

        """
        url = self._get_url(path)
        refs, server_capabilities, url = self._discover_references(
            b"git-upload-pack", url)
        negotiated_capabilities, symrefs, agent = (
                self._negotiate_upload_pack_capabilities(
                        server_capabilities))
        wants = determine_wants(refs)
        if wants is not None:
            wants = [cid for cid in wants if cid != ZERO_SHA]
        if not wants:
            return FetchPackResult(refs, symrefs, agent)
        if self.dumb:
            raise NotImplementedError(self.fetch_pack)
        req_data = BytesIO()
        req_proto = Protocol(None, req_data.write)
        (new_shallow, new_unshallow) = self._handle_upload_pack_head(
                req_proto, negotiated_capabilities, graph_walker, wants,
                can_read=None, depth=depth)
        resp, read = self._smart_request(
            "git-upload-pack", url, data=req_data.getvalue())
        try:
            resp_proto = Protocol(read, None)
            if new_shallow is None and new_unshallow is None:
                (new_shallow, new_unshallow) = _read_shallow_updates(
                        resp_proto)
            self._handle_upload_pack_tail(
                resp_proto, negotiated_capabilities, graph_walker, pack_data,
                progress)
            return FetchPackResult(
                    refs, symrefs, agent, new_shallow, new_unshallow)
        finally:
            resp.close()

    def get_refs(self, path):
        """Retrieve the current refs from a git smart server.
        """
        url = self._get_url(path)
        refs, _, _ = self._discover_references(
            b"git-upload-pack", url)
        return refs


def get_transport_and_path_from_url(url, config=None, **kwargs):
    """Obtain a git client from a URL.

    Args:
      url: URL to open (a unicode string)
      config: Optional config object
      thin_packs: Whether or not thin packs should be retrieved
      report_activity: Optional callback for reporting transport
        activity.

    Returns:
      Tuple with client instance and relative path.

    """
    parsed = urlparse(url)
    if parsed.scheme == 'git':
        return (TCPGitClient.from_parsedurl(parsed, **kwargs),
                parsed.path)
    elif parsed.scheme in ('git+ssh', 'ssh'):
        return SSHGitClient.from_parsedurl(parsed, **kwargs), parsed.path
    elif parsed.scheme in ('http', 'https'):
        return HttpGitClient.from_parsedurl(
            parsed, config=config, **kwargs), parsed.path
    elif parsed.scheme == 'file':
        return default_local_git_client_cls.from_parsedurl(
            parsed, **kwargs), parsed.path

    raise ValueError("unknown scheme '%s'" % parsed.scheme)


def parse_rsync_url(location):
    """Parse a rsync-style URL.
    """
    if ':' in location and '@' not in location:
        # SSH with no user@, zero or one leading slash.
        (host, path) = location.split(':', 1)
        user = None
    elif ':' in location:
        # SSH with user@host:foo.
        user_host, path = location.split(':', 1)
        if '@' in user_host:
            user, host = user_host.rsplit('@', 1)
        else:
            user = None
            host = user_host
    else:
        raise ValueError('not a valid rsync-style URL')
    return (user, host, path)


def get_transport_and_path(location, **kwargs):
    """Obtain a git client from a URL.

    Args:
      location: URL or path (a string)
      config: Optional config object
      thin_packs: Whether or not thin packs should be retrieved
      report_activity: Optional callback for reporting transport
        activity.

    Returns:
      Tuple with client instance and relative path.

    """
    # First, try to parse it as a URL
    try:
        return get_transport_and_path_from_url(location, **kwargs)
    except ValueError:
        pass

    if (sys.platform == 'win32' and
            location[0].isalpha() and location[1:3] == ':\\'):
        # Windows local path
        return default_local_git_client_cls(**kwargs), location

    try:
        (username, hostname, path) = parse_rsync_url(location)
    except ValueError:
        # Otherwise, assume it's a local path.
        return default_local_git_client_cls(**kwargs), location
    else:
        return SSHGitClient(hostname, username=username, **kwargs), path


DEFAULT_GIT_CREDENTIALS_PATHS = [
    os.path.expanduser('~/.git-credentials'),
    get_xdg_config_home_path('git', 'credentials')]


def get_credentials_from_store(scheme, hostname, username=None,
                               fnames=DEFAULT_GIT_CREDENTIALS_PATHS):
    for fname in fnames:
        try:
            with open(fname, 'rb') as f:
                for line in f:
                    parsed_line = urlparse(line.strip())
                    if (parsed_line.scheme == scheme and
                            parsed_line.hostname == hostname and
                            (username is None or
                                parsed_line.username == username)):
                        return parsed_line.username, parsed_line.password
        except FileNotFoundError:
            # If the file doesn't exist, try the next one.
            continue