dulwich/dulwich/repo.py

# repo.py -- For dealing with git repositories.
# Copyright (C) 2007 James Westby <jw+debian@jameswestby.net>
# Copyright (C) 2008-2009 Jelmer Vernooij <jelmer@samba.org>
#
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU General Public License
# as published by the Free Software Foundation; version 2
# of the License or (at your option) any later version of
# the License.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
# MA  02110-1301, USA.


"""Repository access.

This module contains the base class for git repositories
(BaseRepo) and an implementation which uses a repository on
local disk (Repo).

"""

from cStringIO import StringIO
import errno
import os

from dulwich.errors import (
    NoIndexPresent,
    NotBlobError,
    NotCommitError,
    NotGitRepository,
    NotTreeError,
    NotTagError,
    PackedRefsException,
    CommitError,
    RefFormatError,
    HookError,
    )
from dulwich.file import (
    ensure_dir_exists,
    GitFile,
    )
from dulwich.object_store import (
    DiskObjectStore,
    MemoryObjectStore,
    )
from dulwich.objects import (
    Blob,
    Commit,
    ShaFile,
    Tag,
    Tree,
    hex_to_sha,
    )

from dulwich.hooks import (
    PreCommitShellHook,
    PostCommitShellHook,
    CommitMsgShellHook,
)

import warnings


OBJECTDIR = 'objects'
SYMREF = 'ref: '
REFSDIR = 'refs'
REFSDIR_TAGS = 'tags'
REFSDIR_HEADS = 'heads'
INDEX_FILENAME = "index"

BASE_DIRECTORIES = [
    ["branches"],
    [REFSDIR],
    [REFSDIR, REFSDIR_TAGS],
    [REFSDIR, REFSDIR_HEADS],
    ["hooks"],
    ["info"]
    ]


def read_info_refs(f):
    ret = {}
    for l in f.readlines():
        (sha, name) = l.rstrip("\r\n").split("\t", 1)
        ret[name] = sha
    return ret


def check_ref_format(refname):
    """Check if a refname is correctly formatted.

    Implements all the same rules as git-check-ref-format[1].

    [1] http://www.kernel.org/pub/software/scm/git/docs/git-check-ref-format.html

    :param refname: The refname to check
    :return: True if refname is valid, False otherwise
    """
    # These could be combined into one big expression, but are listed separately
    # to parallel [1].
    if '/.' in refname or refname.startswith('.'):
        return False
    if '/' not in refname:
        return False
    if '..' in refname:
        return False
    for c in refname:
        if ord(c) < 040 or c in '\177 ~^:?*[':
            return False
    if refname[-1] in '/.':
        return False
    if refname.endswith('.lock'):
        return False
    if '@{' in refname:
        return False
    if '\\' in refname:
        return False
    return True


class RefsContainer(object):
    """A container for refs."""

    def set_ref(self, name, other):
        warnings.warn("RefsContainer.set_ref() is deprecated."
            "Use set_symblic_ref instead.",
            category=DeprecationWarning, stacklevel=2)
        return self.set_symbolic_ref(name, other)

    def set_symbolic_ref(self, name, other):
        """Make a ref point at another ref.

        :param name: Name of the ref to set
        :param other: Name of the ref to point at
        """
        raise NotImplementedError(self.set_symbolic_ref)

    def get_packed_refs(self):
        """Get contents of the packed-refs file.

        :return: Dictionary mapping ref names to SHA1s

        :note: Will return an empty dictionary when no packed-refs file is
            present.
        """
        raise NotImplementedError(self.get_packed_refs)

    def get_peeled(self, name):
        """Return the cached peeled value of a ref, if available.

        :param name: Name of the ref to peel
        :return: The peeled value of the ref. If the ref is known not point to a
            tag, this will be the SHA the ref refers to. If the ref may point to
            a tag, but no cached information is available, None is returned.
        """
        return None

    def import_refs(self, base, other):
        for name, value in other.iteritems():
            self["%s/%s" % (base, name)] = value

    def allkeys(self):
        """All refs present in this container."""
        raise NotImplementedError(self.allkeys)

    def keys(self, base=None):
        """Refs present in this container.

        :param base: An optional base to return refs under.
        :return: An unsorted set of valid refs in this container, including
            packed refs.
        """
        if base is not None:
            return self.subkeys(base)
        else:
            return self.allkeys()

    def subkeys(self, base):
        """Refs present in this container under a base.

        :param base: The base to return refs under.
        :return: A set of valid refs in this container under the base; the base
            prefix is stripped from the ref names returned.
        """
        keys = set()
        base_len = len(base) + 1
        for refname in self.allkeys():
            if refname.startswith(base):
                keys.add(refname[base_len:])
        return keys

    def as_dict(self, base=None):
        """Return the contents of this container as a dictionary.

        """
        ret = {}
        keys = self.keys(base)
        if base is None:
            base = ""
        for key in keys:
            try:
                ret[key] = self[("%s/%s" % (base, key)).strip("/")]
            except KeyError:
                continue  # Unable to resolve

        return ret

    def _check_refname(self, name):
        """Ensure a refname is valid and lives in refs or is HEAD.

        HEAD is not a valid refname according to git-check-ref-format, but this
        class needs to be able to touch HEAD. Also, check_ref_format expects
        refnames without the leading 'refs/', but this class requires that
        so it cannot touch anything outside the refs dir (or HEAD).

        :param name: The name of the reference.
        :raises KeyError: if a refname is not HEAD or is otherwise not valid.
        """
        if name in ('HEAD', 'refs/stash'):
            return
        if not name.startswith('refs/') or not check_ref_format(name[5:]):
            raise RefFormatError(name)

    def read_ref(self, refname):
        """Read a reference without following any references.

        :param refname: The name of the reference
        :return: The contents of the ref file, or None if it does
            not exist.
        """
        contents = self.read_loose_ref(refname)
        if not contents:
            contents = self.get_packed_refs().get(refname, None)
        return contents

    def read_loose_ref(self, name):
        """Read a loose reference and return its contents.

        :param name: the refname to read
        :return: The contents of the ref file, or None if it does
            not exist.
        """
        raise NotImplementedError(self.read_loose_ref)

    def _follow(self, name):
        """Follow a reference name.

        :return: a tuple of (refname, sha), where refname is the name of the
            last reference in the symbolic reference chain
        """
        contents = SYMREF + name
        depth = 0
        while contents.startswith(SYMREF):
            refname = contents[len(SYMREF):]
            contents = self.read_ref(refname)
            if not contents:
                break
            depth += 1
            if depth > 5:
                raise KeyError(name)
        return refname, contents

    def __contains__(self, refname):
        if self.read_ref(refname):
            return True
        return False

    def __getitem__(self, name):
        """Get the SHA1 for a reference name.

        This method follows all symbolic references.
        """
        _, sha = self._follow(name)
        if sha is None:
            raise KeyError(name)
        return sha

    def set_if_equals(self, name, old_ref, new_ref):
        """Set a refname to new_ref only if it currently equals old_ref.

        This method follows all symbolic references if applicable for the
        subclass, and can be used to perform an atomic compare-and-swap
        operation.

        :param name: The refname to set.
        :param old_ref: The old sha the refname must refer to, or None to set
            unconditionally.
        :param new_ref: The new sha the refname will refer to.
        :return: True if the set was successful, False otherwise.
        """
        raise NotImplementedError(self.set_if_equals)

    def add_if_new(self, name, ref):
        """Add a new reference only if it does not already exist."""
        raise NotImplementedError(self.add_if_new)

    def __setitem__(self, name, ref):
        """Set a reference name to point to the given SHA1.

        This method follows all symbolic references if applicable for the
        subclass.

        :note: This method unconditionally overwrites the contents of a
            reference. To update atomically only if the reference has not
            changed, use set_if_equals().
        :param name: The refname to set.
        :param ref: The new sha the refname will refer to.
        """
        self.set_if_equals(name, None, ref)

    def remove_if_equals(self, name, old_ref):
        """Remove a refname only if it currently equals old_ref.

        This method does not follow symbolic references, even if applicable for
        the subclass. It can be used to perform an atomic compare-and-delete
        operation.

        :param name: The refname to delete.
        :param old_ref: The old sha the refname must refer to, or None to delete
            unconditionally.
        :return: True if the delete was successful, False otherwise.
        """
        raise NotImplementedError(self.remove_if_equals)

    def __delitem__(self, name):
        """Remove a refname.

        This method does not follow symbolic references, even if applicable for
        the subclass.

        :note: This method unconditionally deletes the contents of a reference.
            To delete atomically only if the reference has not changed, use
            remove_if_equals().

        :param name: The refname to delete.
        """
        self.remove_if_equals(name, None)


class DictRefsContainer(RefsContainer):
    """RefsContainer backed by a simple dict.

    This container does not support symbolic or packed references and is not
    threadsafe.
    """

    def __init__(self, refs):
        self._refs = refs
        self._peeled = {}

    def allkeys(self):
        return self._refs.keys()

    def read_loose_ref(self, name):
        return self._refs.get(name, None)

    def get_packed_refs(self):
        return {}

    def set_symbolic_ref(self, name, other):
        self._refs[name] = SYMREF + other

    def set_if_equals(self, name, old_ref, new_ref):
        if old_ref is not None and self._refs.get(name, None) != old_ref:
            return False
        realname, _ = self._follow(name)
        self._check_refname(realname)
        self._refs[realname] = new_ref
        return True

    def add_if_new(self, name, ref):
        if name in self._refs:
            return False
        self._refs[name] = ref
        return True

    def remove_if_equals(self, name, old_ref):
        if old_ref is not None and self._refs.get(name, None) != old_ref:
            return False
        del self._refs[name]
        return True

    def get_peeled(self, name):
        return self._peeled.get(name)

    def _update(self, refs):
        """Update multiple refs; intended only for testing."""
        # TODO(dborowitz): replace this with a public function that uses
        # set_if_equal.
        self._refs.update(refs)

    def _update_peeled(self, peeled):
        """Update cached peeled refs; intended only for testing."""
        self._peeled.update(peeled)


class InfoRefsContainer(RefsContainer):
    """Refs container that reads refs from a info/refs file."""

    def __init__(self, f):
        self._refs = {}
        self._peeled = {}
        for l in f.readlines():
            sha, name = l.rstrip("\n").split("\t")
            if name.endswith("^{}"):
                name = name[:-3]
                if not check_ref_format(name):
                    raise ValueError("invalid ref name '%s'" % name)
                self._peeled[name] = sha
            else:
                if not check_ref_format(name):
                    raise ValueError("invalid ref name '%s'" % name)
                self._refs[name] = sha

    def allkeys(self):
        return self._refs.keys()

    def read_loose_ref(self, name):
        return self._refs.get(name, None)

    def get_packed_refs(self):
        return {}

    def get_peeled(self, name):
        try:
            return self._peeled[name]
        except KeyError:
            return self._refs[name]


class DiskRefsContainer(RefsContainer):
    """Refs container that reads refs from disk."""

    def __init__(self, path):
        self.path = path
        self._packed_refs = None
        self._peeled_refs = None

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

    def subkeys(self, base):
        keys = set()
        path = self.refpath(base)
        for root, dirs, files in os.walk(path):
            dir = root[len(path):].strip(os.path.sep).replace(os.path.sep, "/")
            for filename in files:
                refname = ("%s/%s" % (dir, filename)).strip("/")
                # check_ref_format requires at least one /, so we prepend the
                # base before calling it.
                if check_ref_format("%s/%s" % (base, refname)):
                    keys.add(refname)
        for key in self.get_packed_refs():
            if key.startswith(base):
                keys.add(key[len(base):].strip("/"))
        return keys

    def allkeys(self):
        keys = set()
        if os.path.exists(self.refpath("HEAD")):
            keys.add("HEAD")
        path = self.refpath("")
        for root, dirs, files in os.walk(self.refpath("refs")):
            dir = root[len(path):].strip(os.path.sep).replace(os.path.sep, "/")
            for filename in files:
                refname = ("%s/%s" % (dir, filename)).strip("/")
                if check_ref_format(refname):
                    keys.add(refname)
        keys.update(self.get_packed_refs())
        return keys

    def refpath(self, name):
        """Return the disk path of a ref.

        """
        if os.path.sep != "/":
            name = name.replace("/", os.path.sep)
        return os.path.join(self.path, name)

    def get_packed_refs(self):
        """Get contents of the packed-refs file.

        :return: Dictionary mapping ref names to SHA1s

        :note: Will return an empty dictionary when no packed-refs file is
            present.
        """
        # TODO: invalidate the cache on repacking
        if self._packed_refs is None:
            # set both to empty because we want _peeled_refs to be
            # None if and only if _packed_refs is also None.
            self._packed_refs = {}
            self._peeled_refs = {}
            path = os.path.join(self.path, 'packed-refs')
            try:
                f = GitFile(path, 'rb')
            except IOError, e:
                if e.errno == errno.ENOENT:
                    return {}
                raise
            try:
                first_line = iter(f).next().rstrip()
                if (first_line.startswith("# pack-refs") and " peeled" in
                        first_line):
                    for sha, name, peeled in read_packed_refs_with_peeled(f):
                        self._packed_refs[name] = sha
                        if peeled:
                            self._peeled_refs[name] = peeled
                else:
                    f.seek(0)
                    for sha, name in read_packed_refs(f):
                        self._packed_refs[name] = sha
            finally:
                f.close()
        return self._packed_refs

    def get_peeled(self, name):
        """Return the cached peeled value of a ref, if available.

        :param name: Name of the ref to peel
        :return: The peeled value of the ref. If the ref is known not point to a
            tag, this will be the SHA the ref refers to. If the ref may point to
            a tag, but no cached information is available, None is returned.
        """
        self.get_packed_refs()
        if self._peeled_refs is None or name not in self._packed_refs:
            # No cache: no peeled refs were read, or this ref is loose
            return None
        if name in self._peeled_refs:
            return self._peeled_refs[name]
        else:
            # Known not peelable
            return self[name]

    def read_loose_ref(self, name):
        """Read a reference file and return its contents.

        If the reference file a symbolic reference, only read the first line of
        the file. Otherwise, only read the first 40 bytes.

        :param name: the refname to read, relative to refpath
        :return: The contents of the ref file, or None if the file does not
            exist.
        :raises IOError: if any other error occurs
        """
        filename = self.refpath(name)
        try:
            f = GitFile(filename, 'rb')
            try:
                header = f.read(len(SYMREF))
                if header == SYMREF:
                    # Read only the first line
                    return header + iter(f).next().rstrip("\r\n")
                else:
                    # Read only the first 40 bytes
                    return header + f.read(40 - len(SYMREF))
            finally:
                f.close()
        except IOError, e:
            if e.errno == errno.ENOENT:
                return None
            raise

    def _remove_packed_ref(self, name):
        if self._packed_refs is None:
            return
        filename = os.path.join(self.path, 'packed-refs')
        # reread cached refs from disk, while holding the lock
        f = GitFile(filename, 'wb')
        try:
            self._packed_refs = None
            self.get_packed_refs()

            if name not in self._packed_refs:
                return

            del self._packed_refs[name]
            if name in self._peeled_refs:
                del self._peeled_refs[name]
            write_packed_refs(f, self._packed_refs, self._peeled_refs)
            f.close()
        finally:
            f.abort()

    def set_symbolic_ref(self, name, other):
        """Make a ref point at another ref.

        :param name: Name of the ref to set
        :param other: Name of the ref to point at
        """
        self._check_refname(name)
        self._check_refname(other)
        filename = self.refpath(name)
        try:
            f = GitFile(filename, 'wb')
            try:
                f.write(SYMREF + other + '\n')
            except (IOError, OSError):
                f.abort()
                raise
        finally:
            f.close()

    def set_if_equals(self, name, old_ref, new_ref):
        """Set a refname to new_ref only if it currently equals old_ref.

        This method follows all symbolic references, and can be used to perform
        an atomic compare-and-swap operation.

        :param name: The refname to set.
        :param old_ref: The old sha the refname must refer to, or None to set
            unconditionally.
        :param new_ref: The new sha the refname will refer to.
        :return: True if the set was successful, False otherwise.
        """
        self._check_refname(name)
        try:
            realname, _ = self._follow(name)
        except KeyError:
            realname = name
        filename = self.refpath(realname)
        ensure_dir_exists(os.path.dirname(filename))
        f = GitFile(filename, 'wb')
        try:
            if old_ref is not None:
                try:
                    # read again while holding the lock
                    orig_ref = self.read_loose_ref(realname)
                    if orig_ref is None:
                        orig_ref = self.get_packed_refs().get(realname, None)
                    if orig_ref != old_ref:
                        f.abort()
                        return False
                except (OSError, IOError):
                    f.abort()
                    raise
            try:
                f.write(new_ref + "\n")
            except (OSError, IOError):
                f.abort()
                raise
        finally:
            f.close()
        return True

    def add_if_new(self, name, ref):
        """Add a new reference only if it does not already exist.

        This method follows symrefs, and only ensures that the last ref in the
        chain does not exist.

        :param name: The refname to set.
        :param ref: The new sha the refname will refer to.
        :return: True if the add was successful, False otherwise.
        """
        try:
            realname, contents = self._follow(name)
            if contents is not None:
                return False
        except KeyError:
            realname = name
        self._check_refname(realname)
        filename = self.refpath(realname)
        ensure_dir_exists(os.path.dirname(filename))
        f = GitFile(filename, 'wb')
        try:
            if os.path.exists(filename) or name in self.get_packed_refs():
                f.abort()
                return False
            try:
                f.write(ref + "\n")
            except (OSError, IOError):
                f.abort()
                raise
        finally:
            f.close()
        return True

    def remove_if_equals(self, name, old_ref):
        """Remove a refname only if it currently equals old_ref.

        This method does not follow symbolic references. It can be used to
        perform an atomic compare-and-delete operation.

        :param name: The refname to delete.
        :param old_ref: The old sha the refname must refer to, or None to delete
            unconditionally.
        :return: True if the delete was successful, False otherwise.
        """
        self._check_refname(name)
        filename = self.refpath(name)
        ensure_dir_exists(os.path.dirname(filename))
        f = GitFile(filename, 'wb')
        try:
            if old_ref is not None:
                orig_ref = self.read_loose_ref(name)
                if orig_ref is None:
                    orig_ref = self.get_packed_refs().get(name, None)
                if orig_ref != old_ref:
                    return False
            # may only be packed
            try:
                os.remove(filename)
            except OSError, e:
                if e.errno != errno.ENOENT:
                    raise
            self._remove_packed_ref(name)
        finally:
            # never write, we just wanted the lock
            f.abort()
        return True


def _split_ref_line(line):
    """Split a single ref line into a tuple of SHA1 and name."""
    fields = line.rstrip("\n").split(" ")
    if len(fields) != 2:
        raise PackedRefsException("invalid ref line '%s'" % line)
    sha, name = fields
    try:
        hex_to_sha(sha)
    except (AssertionError, TypeError), e:
        raise PackedRefsException(e)
    if not check_ref_format(name):
        raise PackedRefsException("invalid ref name '%s'" % name)
    return (sha, name)


def read_packed_refs(f):
    """Read a packed refs file.

    :param f: file-like object to read from
    :return: Iterator over tuples with SHA1s and ref names.
    """
    for l in f:
        if l[0] == "#":
            # Comment
            continue
        if l[0] == "^":
            raise PackedRefsException(
              "found peeled ref in packed-refs without peeled")
        yield _split_ref_line(l)


def read_packed_refs_with_peeled(f):
    """Read a packed refs file including peeled refs.

    Assumes the "# pack-refs with: peeled" line was already read. Yields tuples
    with ref names, SHA1s, and peeled SHA1s (or None).

    :param f: file-like object to read from, seek'ed to the second line
    """
    last = None
    for l in f:
        if l[0] == "#":
            continue
        l = l.rstrip("\r\n")
        if l[0] == "^":
            if not last:
                raise PackedRefsException("unexpected peeled ref line")
            try:
                hex_to_sha(l[1:])
            except (AssertionError, TypeError), e:
                raise PackedRefsException(e)
            sha, name = _split_ref_line(last)
            last = None
            yield (sha, name, l[1:])
        else:
            if last:
                sha, name = _split_ref_line(last)
                yield (sha, name, None)
            last = l
    if last:
        sha, name = _split_ref_line(last)
        yield (sha, name, None)


def write_packed_refs(f, packed_refs, peeled_refs=None):
    """Write a packed refs file.

    :param f: empty file-like object to write to
    :param packed_refs: dict of refname to sha of packed refs to write
    :param peeled_refs: dict of refname to peeled value of sha
    """
    if peeled_refs is None:
        peeled_refs = {}
    else:
        f.write('# pack-refs with: peeled\n')
    for refname in sorted(packed_refs.iterkeys()):
        f.write('%s %s\n' % (packed_refs[refname], refname))
        if refname in peeled_refs:
            f.write('^%s\n' % peeled_refs[refname])


class BaseRepo(object):
    """Base class for a git repository.

    :ivar object_store: Dictionary-like object for accessing
        the objects
    :ivar refs: Dictionary-like object with the refs in this
        repository
    """

    def __init__(self, object_store, refs):
        """Open a repository.

        This shouldn't be called directly, but rather through one of the
        base classes, such as MemoryRepo or Repo.

        :param object_store: Object store to use
        :param refs: Refs container to use
        """
        self.object_store = object_store
        self.refs = refs

        self.hooks = {}

    def _init_files(self, bare):
        """Initialize a default set of named files."""
        from dulwich.config import ConfigFile
        self._put_named_file('description', "Unnamed repository")
        f = StringIO()
        cf = ConfigFile()
        cf.set("core", "repositoryformatversion", "0")
        cf.set("core", "filemode", "true")
        cf.set("core", "bare", str(bare).lower())
        cf.set("core", "logallrefupdates", "true")
        cf.write_to_file(f)
        self._put_named_file('config', f.getvalue())
        self._put_named_file(os.path.join('info', 'exclude'), '')

    def get_named_file(self, path):
        """Get a file from the control dir with a specific name.

        Although the filename should be interpreted as a filename relative to
        the control dir in a disk-based Repo, the object returned need not be
        pointing to a file in that location.

        :param path: The path to the file, relative to the control dir.
        :return: An open file object, or None if the file does not exist.
        """
        raise NotImplementedError(self.get_named_file)

    def _put_named_file(self, path, contents):
        """Write a file to the control dir with the given name and contents.

        :param path: The path to the file, relative to the control dir.
        :param contents: A string to write to the file.
        """
        raise NotImplementedError(self._put_named_file)

    def open_index(self):
        """Open the index for this repository.

        :raise NoIndexPresent: If no index is present
        :return: The matching `Index`
        """
        raise NotImplementedError(self.open_index)

    def fetch(self, target, determine_wants=None, progress=None):
        """Fetch objects into another repository.

        :param target: The target repository
        :param determine_wants: Optional function to determine what refs to
            fetch.
        :param progress: Optional progress function
        """
        if determine_wants is None:
            determine_wants = lambda heads: heads.values()
        target.object_store.add_objects(
          self.fetch_objects(determine_wants, target.get_graph_walker(),
                             progress))
        return self.get_refs()

    def fetch_objects(self, determine_wants, graph_walker, progress,
                      get_tagged=None):
        """Fetch the missing objects required for a set of revisions.

        :param determine_wants: Function that takes a dictionary with heads
            and returns the list of heads to fetch.
        :param graph_walker: Object that can iterate over the list of revisions
            to fetch and has an "ack" method that will be called to acknowledge
            that a revision is present.
        :param progress: Simple progress function that will be called with
            updated progress strings.
        :param get_tagged: Function that returns a dict of pointed-to sha -> tag
            sha for including tags.
        :return: iterator over objects, with __len__ implemented
        """
        wants = determine_wants(self.get_refs())
        if wants is None:
            # TODO(dborowitz): find a way to short-circuit that doesn't change
            # this interface.
            return None
        haves = self.object_store.find_common_revisions(graph_walker)
        return self.object_store.iter_shas(
          self.object_store.find_missing_objects(haves, wants, progress,
                                                 get_tagged))

    def get_graph_walker(self, heads=None):
        """Retrieve a graph walker.

        A graph walker is used by a remote repository (or proxy)
        to find out which objects are present in this repository.

        :param heads: Repository heads to use (optional)
        :return: A graph walker object
        """
        if heads is None:
            heads = self.refs.as_dict('refs/heads').values()
        return self.object_store.get_graph_walker(heads)

    def ref(self, name):
        """Return the SHA1 a ref is pointing to.

        :param name: Name of the ref to look up
        :raise KeyError: when the ref (or the one it points to) does not exist
        :return: SHA1 it is pointing at
        """
        return self.refs[name]

    def get_refs(self):
        """Get dictionary with all refs.

        :return: A ``dict`` mapping ref names to SHA1s
        """
        return self.refs.as_dict()

    def head(self):
        """Return the SHA1 pointed at by HEAD."""
        return self.refs['HEAD']

    def _get_object(self, sha, cls):
        assert len(sha) in (20, 40)
        ret = self.get_object(sha)
        if not isinstance(ret, cls):
            if cls is Commit:
                raise NotCommitError(ret)
            elif cls is Blob:
                raise NotBlobError(ret)
            elif cls is Tree:
                raise NotTreeError(ret)
            elif cls is Tag:
                raise NotTagError(ret)
            else:
                raise Exception("Type invalid: %r != %r" % (
                  ret.type_name, cls.type_name))
        return ret

    def get_object(self, sha):
        """Retrieve the object with the specified SHA.

        :param sha: SHA to retrieve
        :return: A ShaFile object
        :raise KeyError: when the object can not be found
        """
        return self.object_store[sha]

    def get_parents(self, sha):
        """Retrieve the parents of a specific commit.

        :param sha: SHA of the commit for which to retrieve the parents
        :return: List of parents
        """
        return self.commit(sha).parents

    def get_config(self):
        """Retrieve the config object.

        :return: `ConfigFile` object for the ``.git/config`` file.
        """
        raise NotImplementedError(self.get_config)

    def get_config_stack(self):
        """Return a config stack for this repository.

        This stack accesses the configuration for both this repository
        itself (.git/config) and the global configuration, which usually
        lives in ~/.gitconfig.

        :return: `Config` instance for this repository
        """
        from dulwich.config import StackedConfig
        backends = [self.get_config()] + StackedConfig.default_backends()
        return StackedConfig(backends, writable=backends[0])

    def commit(self, sha):
        """Retrieve the commit with a particular SHA.

        :param sha: SHA of the commit to retrieve
        :raise NotCommitError: If the SHA provided doesn't point at a Commit
        :raise KeyError: If the SHA provided didn't exist
        :return: A `Commit` object
        """
        warnings.warn("Repo.commit(sha) is deprecated. Use Repo[sha] instead.",
            category=DeprecationWarning, stacklevel=2)
        return self._get_object(sha, Commit)

    def tree(self, sha):
        """Retrieve the tree with a particular SHA.

        :param sha: SHA of the tree to retrieve
        :raise NotTreeError: If the SHA provided doesn't point at a Tree
        :raise KeyError: If the SHA provided didn't exist
        :return: A `Tree` object
        """
        warnings.warn("Repo.tree(sha) is deprecated. Use Repo[sha] instead.",
            category=DeprecationWarning, stacklevel=2)
        return self._get_object(sha, Tree)

    def tag(self, sha):
        """Retrieve the tag with a particular SHA.

        :param sha: SHA of the tag to retrieve
        :raise NotTagError: If the SHA provided doesn't point at a Tag
        :raise KeyError: If the SHA provided didn't exist
        :return: A `Tag` object
        """
        warnings.warn("Repo.tag(sha) is deprecated. Use Repo[sha] instead.",
            category=DeprecationWarning, stacklevel=2)
        return self._get_object(sha, Tag)

    def get_blob(self, sha):
        """Retrieve the blob with a particular SHA.

        :param sha: SHA of the blob to retrieve
        :raise NotBlobError: If the SHA provided doesn't point at a Blob
        :raise KeyError: If the SHA provided didn't exist
        :return: A `Blob` object
        """
        warnings.warn("Repo.get_blob(sha) is deprecated. Use Repo[sha] "
            "instead.", category=DeprecationWarning, stacklevel=2)
        return self._get_object(sha, Blob)

    def get_peeled(self, ref):
        """Get the peeled value of a ref.

        :param ref: The refname to peel.
        :return: The fully-peeled SHA1 of a tag object, after peeling all
            intermediate tags; if the original ref does not point to a tag, this
            will equal the original SHA1.
        """
        cached = self.refs.get_peeled(ref)
        if cached is not None:
            return cached
        return self.object_store.peel_sha(self.refs[ref]).id

    def get_walker(self, include=None, *args, **kwargs):
        """Obtain a walker for this repository.

        :param include: Iterable of SHAs of commits to include along with their
            ancestors. Defaults to [HEAD]
        :param exclude: Iterable of SHAs of commits to exclude along with their
            ancestors, overriding includes.
        :param order: ORDER_* constant specifying the order of results. Anything
            other than ORDER_DATE may result in O(n) memory usage.
        :param reverse: If True, reverse the order of output, requiring O(n)
            memory.
        :param max_entries: The maximum number of entries to yield, or None for
            no limit.
        :param paths: Iterable of file or subtree paths to show entries for.
        :param rename_detector: diff.RenameDetector object for detecting
            renames.
        :param follow: If True, follow path across renames/copies. Forces a
            default rename_detector.
        :param since: Timestamp to list commits after.
        :param until: Timestamp to list commits before.
        :param queue_cls: A class to use for a queue of commits, supporting the
            iterator protocol. The constructor takes a single argument, the
            Walker.
        :return: A `Walker` object
        """
        from dulwich.walk import Walker
        if include is None:
            include = [self.head()]
        return Walker(self.object_store, include, *args, **kwargs)

    def revision_history(self, head):
        """Returns a list of the commits reachable from head.

        :param head: The SHA of the head to list revision history for.
        :return: A list of commit objects reachable from head, starting with
            head itself, in descending commit time order.
        :raise MissingCommitError: if any missing commits are referenced,
            including if the head parameter isn't the SHA of a commit.
        """
        warnings.warn("Repo.revision_history() is deprecated."
            "Use dulwich.walker.Walker(repo) instead.",
            category=DeprecationWarning, stacklevel=2)
        return [e.commit for e in self.get_walker(include=[head])]

    def __getitem__(self, name):
        """Retrieve a Git object by SHA1 or ref.

        :param name: A Git object SHA1 or a ref name
        :return: A `ShaFile` object, such as a Commit or Blob
        :raise KeyError: when the specified ref or object does not exist
        """
        if len(name) in (20, 40):
            try:
                return self.object_store[name]
            except KeyError:
                pass
        try:
            return self.object_store[self.refs[name]]
        except RefFormatError:
            raise KeyError(name)

    def __contains__(self, name):
        """Check if a specific Git object or ref is present.

        :param name: Git object SHA1 or ref name
        """
        if len(name) in (20, 40):
            return name in self.object_store or name in self.refs
        else:
            return name in self.refs

    def __setitem__(self, name, value):
        """Set a ref.

        :param name: ref name
        :param value: Ref value - either a ShaFile object, or a hex sha
        """
        if name.startswith("refs/") or name == "HEAD":
            if isinstance(value, ShaFile):
                self.refs[name] = value.id
            elif isinstance(value, str):
                self.refs[name] = value
            else:
                raise TypeError(value)
        else:
            raise ValueError(name)

    def __delitem__(self, name):
        """Remove a ref.

        :param name: Name of the ref to remove
        """
        if name.startswith("refs/") or name == "HEAD":
            del self.refs[name]
        else:
            raise ValueError(name)

    def _get_user_identity(self):
        """Determine the identity to use for new commits.
        """
        config = self.get_config_stack()
        return "%s <%s>" % (
            config.get(("user", ), "name"),
            config.get(("user", ), "email"))

    def do_commit(self, message=None, committer=None,
                  author=None, commit_timestamp=None,
                  commit_timezone=None, author_timestamp=None,
                  author_timezone=None, tree=None, encoding=None,
                  ref='HEAD', merge_heads=None):
        """Create a new commit.

        :param message: Commit message
        :param committer: Committer fullname
        :param author: Author fullname (defaults to committer)
        :param commit_timestamp: Commit timestamp (defaults to now)
        :param commit_timezone: Commit timestamp timezone (defaults to GMT)
        :param author_timestamp: Author timestamp (defaults to commit timestamp)
        :param author_timezone: Author timestamp timezone
            (defaults to commit timestamp timezone)
        :param tree: SHA1 of the tree root to use (if not specified the
            current index will be committed).
        :param encoding: Encoding
        :param ref: Optional ref to commit to (defaults to current branch)
        :param merge_heads: Merge heads (defaults to .git/MERGE_HEADS)
        :return: New commit SHA1
        """
        import time
        c = Commit()
        if tree is None:
            index = self.open_index()
            c.tree = index.commit(self.object_store)
        else:
            if len(tree) != 40:
                raise ValueError("tree must be a 40-byte hex sha string")
            c.tree = tree

        try:
            self.hooks['pre-commit'].execute()
        except HookError, e:
            raise CommitError(e)
        except KeyError:  # no hook defined, silent fallthrough
            pass

        if merge_heads is None:
            # FIXME: Read merge heads from .git/MERGE_HEADS
            merge_heads = []
        if committer is None:
            committer = self._get_user_identity()
        c.committer = committer
        if commit_timestamp is None:
            commit_timestamp = time.time()
        c.commit_time = int(commit_timestamp)
        if commit_timezone is None:
            # FIXME: Use current user timezone rather than UTC
            commit_timezone = 0
        c.commit_timezone = commit_timezone
        if author is None:
            author = committer
        c.author = author
        if author_timestamp is None:
            author_timestamp = commit_timestamp
        c.author_time = int(author_timestamp)
        if author_timezone is None:
            author_timezone = commit_timezone
        c.author_timezone = author_timezone
        if encoding is not None:
            c.encoding = encoding
        if message is None:
            # FIXME: Try to read commit message from .git/MERGE_MSG
            raise ValueError("No commit message specified")

        try:
            c.message = self.hooks['commit-msg'].execute(message)
            if c.message is None:
                c.message = message
        except HookError, e:
            raise CommitError(e)
        except KeyError:  # no hook defined, message not modified
            c.message = message

        try:
            old_head = self.refs[ref]
            c.parents = [old_head] + merge_heads
            self.object_store.add_object(c)
            ok = self.refs.set_if_equals(ref, old_head, c.id)
        except KeyError:
            c.parents = merge_heads
            self.object_store.add_object(c)
            ok = self.refs.add_if_new(ref, c.id)
        if not ok:
            # Fail if the atomic compare-and-swap failed, leaving the commit and
            # all its objects as garbage.
            raise CommitError("%s changed during commit" % (ref,))

        try:
            self.hooks['post-commit'].execute()
        except HookError, e:  # silent failure
            warnings.warn("post-commit hook failed: %s" % e, UserWarning)
        except KeyError:  # no hook defined, silent fallthrough
            pass

        return c.id


class Repo(BaseRepo):
    """A git repository backed by local disk.

    To open an existing repository, call the contructor with
    the path of the repository.

    To create a new repository, use the Repo.init class method.
    """

    def __init__(self, root):
        if os.path.isdir(os.path.join(root, ".git", OBJECTDIR)):
            self.bare = False
            self._controldir = os.path.join(root, ".git")
        elif (os.path.isdir(os.path.join(root, OBJECTDIR)) and
              os.path.isdir(os.path.join(root, REFSDIR))):
            self.bare = True
            self._controldir = root
        elif (os.path.isfile(os.path.join(root, ".git"))):
            import re
            f = open(os.path.join(root, ".git"), 'r')
            try:
                _, path = re.match('(gitdir: )(.+$)', f.read()).groups()
            finally:
                f.close()
            self.bare = False
            self._controldir = os.path.join(root, path)
        else:
            raise NotGitRepository(
                "No git repository was found at %(path)s" % dict(path=root)
            )
        self.path = root
        object_store = DiskObjectStore(os.path.join(self.controldir(),
                                                    OBJECTDIR))
        refs = DiskRefsContainer(self.controldir())
        BaseRepo.__init__(self, object_store, refs)

        self.hooks['pre-commit'] = PreCommitShellHook(self.controldir())
        self.hooks['commit-msg'] = CommitMsgShellHook(self.controldir())
        self.hooks['post-commit'] = PostCommitShellHook(self.controldir())

    def controldir(self):
        """Return the path of the control directory."""
        return self._controldir

    def _put_named_file(self, path, contents):
        """Write a file to the control dir with the given name and contents.

        :param path: The path to the file, relative to the control dir.
        :param contents: A string to write to the file.
        """
        path = path.lstrip(os.path.sep)
        f = GitFile(os.path.join(self.controldir(), path), 'wb')
        try:
            f.write(contents)
        finally:
            f.close()

    def get_named_file(self, path):
        """Get a file from the control dir with a specific name.

        Although the filename should be interpreted as a filename relative to
        the control dir in a disk-based Repo, the object returned need not be
        pointing to a file in that location.

        :param path: The path to the file, relative to the control dir.
        :return: An open file object, or None if the file does not exist.
        """
        # TODO(dborowitz): sanitize filenames, since this is used directly by
        # the dumb web serving code.
        path = path.lstrip(os.path.sep)
        try:
            return open(os.path.join(self.controldir(), path), 'rb')
        except (IOError, OSError), e:
            if e.errno == errno.ENOENT:
                return None
            raise

    def index_path(self):
        """Return path to the index file."""
        return os.path.join(self.controldir(), INDEX_FILENAME)

    def open_index(self):
        """Open the index for this repository.

        :raise NoIndexPresent: If no index is present
        :return: The matching `Index`
        """
        from dulwich.index import Index
        if not self.has_index():
            raise NoIndexPresent()
        return Index(self.index_path())

    def has_index(self):
        """Check if an index is present."""
        # Bare repos must never have index files; non-bare repos may have a
        # missing index file, which is treated as empty.
        return not self.bare

    def stage(self, paths):
        """Stage a set of paths.

        :param paths: List of paths, relative to the repository path
        """
        if isinstance(paths, basestring):
            paths = [paths]
        from dulwich.index import index_entry_from_stat
        index = self.open_index()
        for path in paths:
            full_path = os.path.join(self.path, path)
            try:
                st = os.stat(full_path)
            except OSError:
                # File no longer exists
                try:
                    del index[path]
                except KeyError:
                    pass  # already removed
            else:
                blob = Blob()
                f = open(full_path, 'rb')
                try:
                    blob.data = f.read()
                finally:
                    f.close()
                self.object_store.add_object(blob)
                index[path] = index_entry_from_stat(st, blob.id, 0)
        index.write()

    def clone(self, target_path, mkdir=True, bare=False,
            origin="origin"):
        """Clone this repository.

        :param target_path: Target path
        :param mkdir: Create the target directory
        :param bare: Whether to create a bare repository
        :param origin: Base name for refs in target repository
            cloned from this repository
        :return: Created repository as `Repo`
        """
        if not bare:
            target = self.init(target_path, mkdir=mkdir)
        else:
            target = self.init_bare(target_path)
        self.fetch(target)
        target.refs.import_refs(
            'refs/remotes/' + origin, self.refs.as_dict('refs/heads'))
        target.refs.import_refs(
            'refs/tags', self.refs.as_dict('refs/tags'))
        try:
            target.refs.add_if_new(
                'refs/heads/master',
                self.refs['refs/heads/master'])
        except KeyError:
            pass

        # Update target head
        head, head_sha = self.refs._follow('HEAD')
        if head is not None and head_sha is not None:
            target.refs.set_symbolic_ref('HEAD', head)
            target['HEAD'] = head_sha

            if not bare:
                # Checkout HEAD to target dir
                target._build_tree()

        return target

    def _build_tree(self):
        from dulwich.index import build_index_from_tree
        config = self.get_config()
        honor_filemode = config.get_boolean('core', 'filemode', os.name != "nt")
        return build_index_from_tree(self.path, self.index_path(),
                self.object_store, self['HEAD'].tree,
                honor_filemode=honor_filemode)

    def get_config(self):
        """Retrieve the config object.

        :return: `ConfigFile` object for the ``.git/config`` file.
        """
        from dulwich.config import ConfigFile
        path = os.path.join(self._controldir, 'config')
        try:
            return ConfigFile.from_path(path)
        except (IOError, OSError), e:
            if e.errno != errno.ENOENT:
                raise
            ret = ConfigFile()
            ret.path = path
            return ret

    def __repr__(self):
        return "<Repo at %r>" % self.path

    @classmethod
    def _init_maybe_bare(cls, path, bare):
        for d in BASE_DIRECTORIES:
            os.mkdir(os.path.join(path, *d))
        DiskObjectStore.init(os.path.join(path, OBJECTDIR))
        ret = cls(path)
        ret.refs.set_symbolic_ref("HEAD", "refs/heads/master")
        ret._init_files(bare)
        return ret

    @classmethod
    def init(cls, path, mkdir=False):
        """Create a new repository.

        :param path: Path in which to create the repository
        :param mkdir: Whether to create the directory
        :return: `Repo` instance
        """
        if mkdir:
            os.mkdir(path)
        controldir = os.path.join(path, ".git")
        os.mkdir(controldir)
        cls._init_maybe_bare(controldir, False)
        return cls(path)

    @classmethod
    def init_bare(cls, path):
        """Create a new bare repository.

        ``path`` should already exist and be an emty directory.

        :param path: Path to create bare repository in
        :return: a `Repo` instance
        """
        return cls._init_maybe_bare(path, True)

    create = init_bare


class MemoryRepo(BaseRepo):
    """Repo that stores refs, objects, and named files in memory.

    MemoryRepos are always bare: they have no working tree and no index, since
    those have a stronger dependency on the filesystem.
    """

    def __init__(self):
        BaseRepo.__init__(self, MemoryObjectStore(), DictRefsContainer({}))
        self._named_files = {}
        self.bare = True

    def _put_named_file(self, path, contents):
        """Write a file to the control dir with the given name and contents.

        :param path: The path to the file, relative to the control dir.
        :param contents: A string to write to the file.
        """
        self._named_files[path] = contents

    def get_named_file(self, path):
        """Get a file from the control dir with a specific name.

        Although the filename should be interpreted as a filename relative to
        the control dir in a disk-baked Repo, the object returned need not be
        pointing to a file in that location.

        :param path: The path to the file, relative to the control dir.
        :return: An open file object, or None if the file does not exist.
        """
        contents = self._named_files.get(path, None)
        if contents is None:
            return None
        return StringIO(contents)

    def open_index(self):
        """Fail to open index for this repo, since it is bare.

        :raise NoIndexPresent: Raised when no index is present
        """
        raise NoIndexPresent()

    def get_config(self):
        """Retrieve the config object.

        :return: `ConfigFile` object.
        """
        from dulwich.config import ConfigFile
        return ConfigFile()

    @classmethod
    def init_bare(cls, objects, refs):
        """Create a new bare repository in memory.

        :param objects: Objects for the new repository,
            as iterable
        :param refs: Refs as dictionary, mapping names
            to object SHA1s
        """
        ret = cls()
        for obj in objects:
            ret.object_store.add_object(obj)
        for refname, sha in refs.iteritems():
            ret.refs[refname] = sha
        ret._init_files(bare=True)
        return ret