dulwich/dulwich/refs.py

# refs.py -- For dealing with git refs
# Copyright (C) 2008-2013 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.


"""Ref handling.

"""
import errno
import os

from dulwich.errors import (
    PackedRefsException,
    RefFormatError,
    )
from dulwich.objects import (
    hex_to_sha,
    )
from dulwich.file import (
    GitFile,
    ensure_dir_exists,
    )


SYMREF = 'ref: '


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) < 0o40 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_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 as e:
                if e.errno == errno.ENOENT:
                    return {}
                raise
            try:
                first_line = next(iter(f)).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 + next(iter(f)).rstrip("\r\n")
                else:
                    # Read only the first 40 bytes
                    return header + f.read(40 - len(SYMREF))
            finally:
                f.close()
        except IOError as 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 as 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) as 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) as 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])


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 write_info_refs(refs, store):
    """Generate info refs."""
    for name, sha in sorted(refs.items()):
        # get_refs() includes HEAD as a special case, but we don't want to
        # advertise it
        if name == 'HEAD':
            continue
        try:
            o = store[sha]
        except KeyError:
            continue
        peeled = store.peel_sha(sha)
        yield '%s\t%s\n' % (o.id, name)
        if o.id != peeled.id:
            yield '%s\t%s^{}\n' % (peeled.id, name)