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."""

from cStringIO import StringIO
import errno
import os

from dulwich.errors import (
    MissingCommitError,
    NoIndexPresent,
    NotBlobError,
    NotCommitError,
    NotGitRepository,
    NotTreeError,
    NotTagError,
    PackedRefsException,
    CommitError,
    )
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,
    object_class,
    )
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 == 'HEAD':
            return
        if not name.startswith('refs/') or not check_ref_format(name[5:]):
            raise KeyError(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
        """
        self._check_refname(name)
        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

    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._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


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.
        """
        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):
        self.object_store = object_store
        self.refs = refs

    def _init_files(self):
        """Initialize a default set of named files."""
        self._put_named_file('description', "Unnamed repository")
        self._put_named_file('config', ('[core]\n'
                                        'repositoryformatversion = 0\n'
                                        'filemode = true\n'
                                        'bare = false\n'
                                        'logallrefupdates = true\n'))
        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-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.
        """
        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.

        :raises NoIndexPresent: If no index is present
        :return: Index instance
        """
        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 not wants:
            return []
        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):
        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."""
        return self.refs[name]

    def get_refs(self):
        """Get dictionary with all refs."""
        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):
        return self.object_store[sha]

    def get_parents(self, sha):
        return self.commit(sha).parents

    def get_config(self):
        import ConfigParser
        p = ConfigParser.RawConfigParser()
        p.read(os.path.join(self._controldir, 'config'))
        return dict((section, dict(p.items(section)))
                    for section in p.sections())

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

        Returns a list of commit objects. the first of which will be the commit
        of head, then following theat will be the parents.

        Raises NotCommitError if any no commits are referenced, including if the
        head parameter isn't the sha of a commit.

        XXX: work out how to handle merges.
        """
        # We build the list backwards, as parents are more likely to be older
        # than children
        pending_commits = [head]
        history = []
        while pending_commits != []:
            head = pending_commits.pop(0)
            try:
                commit = self[head]
            except KeyError:
                raise MissingCommitError(head)
            if type(commit) != Commit:
                raise NotCommitError(commit)
            if commit in history:
                continue
            i = 0
            for known_commit in history:
                if known_commit.commit_time > commit.commit_time:
                    break
                i += 1
            history.insert(i, commit)
            pending_commits += commit.parents
        history.reverse()
        return history

    def __getitem__(self, name):
        if len(name) in (20, 40):
            try:
                return self.object_store[name]
            except KeyError:
                pass
        return self.object_store[self.refs[name]]

    def __contains__(self, 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):
        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):
        if name.startswith("refs") or name == "HEAD":
            del self.refs[name]
        raise ValueError(name)

    def do_commit(self, message, committer=None,
                  author=None, commit_timestamp=None,
                  commit_timezone=None, author_timestamp=None,
                  author_timezone=None, tree=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).
        :return: New commit SHA1
        """
        import time
        index = self.open_index()
        c = Commit()
        if tree is None:
            c.tree = index.commit(self.object_store)
        else:
            c.tree = tree
        # TODO: Allow username to be missing, and get it from .git/config
        if committer is None:
            raise ValueError("committer not set")
        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
        c.message = message
        try:
            old_head = self.refs["HEAD"]
            c.parents = [old_head]
            self.object_store.add_object(c)
            ok = self.refs.set_if_equals("HEAD", old_head, c.id)
        except KeyError:
            c.parents = []
            self.object_store.add_object(c)
            ok = self.refs.add_if_new("HEAD", c.id)
        if not ok:
            # Fail if the atomic compare-and-swap failed, leaving the commit and
            # all its objects as garbage.
            raise CommitError("HEAD changed during commit")

        return c.id


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

    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
        else:
            raise NotGitRepository(root)
        self.path = root
        object_store = DiskObjectStore(os.path.join(self.controldir(),
                                                    OBJECTDIR))
        refs = DiskRefsContainer(self.controldir())
        BaseRepo.__init__(self, object_store, refs)

    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-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.
        """
        # 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."""
        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
        """
        from dulwich.index import cleanup_mode
        index = self.open_index()
        for path in paths:
            full_path = os.path.join(self.path, path)
            blob = Blob()
            try:
                st = os.stat(full_path)
            except OSError:
                # File no longer exists
                try:
                    del index[path]
                except KeyError:
                    pass  # Doesn't exist in the index either
            else:
                f = open(full_path, 'rb')
                try:
                    blob.data = f.read()
                finally:
                    f.close()
                self.object_store.add_object(blob)
                # XXX: Cleanup some of the other file properties as well?
                index[path] = (st.st_ctime, st.st_mtime, st.st_dev, st.st_ino,
                    cleanup_mode(st.st_mode), st.st_uid, st.st_gid, st.st_size,
                    blob.id, 0)
        index.write()

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

    @classmethod
    def init(cls, path, mkdir=True):
        controldir = os.path.join(path, ".git")
        os.mkdir(controldir)
        cls.init_bare(controldir)
        return cls(path)

    @classmethod
    def init_bare(cls, path, mkdir=True):
        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()
        return ret

    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()

    @classmethod
    def init_bare(cls, objects, refs):
        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()
        return ret