~bzr-pqm/bzr/bzr.dev : contents of bzrlib/knit.py at revision 3368.2.29

~bzr-pqm/bzr/bzr.dev : (revision 3368.2.29)
# Copyright (C) 2005, 2006, 2007 Canonical Ltd
#
# 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; either version 2 of the License, or
# (at your option) any later version.
#
# 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., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

"""Knit versionedfile implementation.

A knit is a versioned file implementation that supports efficient append only
updates.

Knit file layout:
lifeless: the data file is made up of "delta records".  each delta record has a delta header 
that contains; (1) a version id, (2) the size of the delta (in lines), and (3)  the digest of 
the -expanded data- (ie, the delta applied to the parent).  the delta also ends with a 
end-marker; simply "end VERSION"

delta can be line or full contents.a
... the 8's there are the index number of the annotation.
version robertc@robertcollins.net-20051003014215-ee2990904cc4c7ad 7 c7d23b2a5bd6ca00e8e266cec0ec228158ee9f9e
59,59,3
8
8         if ie.executable:
8             e.set('executable', 'yes')
130,130,2
8         if elt.get('executable') == 'yes':
8             ie.executable = True
end robertc@robertcollins.net-20051003014215-ee2990904cc4c7ad 


whats in an index:
09:33 < jrydberg> lifeless: each index is made up of a tuple of; version id, options, position, size, parents
09:33 < jrydberg> lifeless: the parents are currently dictionary compressed
09:33 < jrydberg> lifeless: (meaning it currently does not support ghosts)
09:33 < lifeless> right
09:33 < jrydberg> lifeless: the position and size is the range in the data file


so the index sequence is the dictionary compressed sequence number used
in the deltas to provide line annotation

"""

# TODOS:
# 10:16 < lifeless> make partial index writes safe
# 10:16 < lifeless> implement 'knit.check()' like weave.check()
# 10:17 < lifeless> record known ghosts so we can detect when they are filled in rather than the current 'reweave 
#                    always' approach.
# move sha1 out of the content so that join is faster at verifying parents
# record content length ?
                  

from cStringIO import StringIO
from itertools import izip, chain
import operator
import os

from bzrlib.lazy_import import lazy_import
lazy_import(globals(), """
from bzrlib import (
    annotate,
    debug,
    diff,
    graph as _mod_graph,
    index as _mod_index,
    lru_cache,
    pack,
    progress,
    trace,
    tsort,
    tuned_gzip,
    )
""")
from bzrlib import (
    errors,
    osutils,
    patiencediff,
    )
from bzrlib.errors import (
    FileExists,
    NoSuchFile,
    KnitError,
    InvalidRevisionId,
    KnitCorrupt,
    KnitHeaderError,
    RevisionNotPresent,
    RevisionAlreadyPresent,
    )
from bzrlib.osutils import (
    contains_whitespace,
    contains_linebreaks,
    sha_string,
    sha_strings,
    split_lines,
    )
from bzrlib.versionedfile import (
    AbsentContentFactory,
    adapter_registry,
    ConstantMapper,
    ContentFactory,
    FulltextContentFactory,
    VersionedFile,
    VersionedFiles,
    )


# TODO: Split out code specific to this format into an associated object.

# TODO: Can we put in some kind of value to check that the index and data
# files belong together?

# TODO: accommodate binaries, perhaps by storing a byte count

# TODO: function to check whole file

# TODO: atomically append data, then measure backwards from the cursor
# position after writing to work out where it was located.  we may need to
# bypass python file buffering.

DATA_SUFFIX = '.knit'
INDEX_SUFFIX = '.kndx'


class KnitAdapter(object):
    """Base class for knit record adaption."""

    def __init__(self, basis_vf):
        """Create an adapter which accesses full texts from basis_vf.
        
        :param basis_vf: A versioned file to access basis texts of deltas from.
            May be None for adapters that do not need to access basis texts.
        """
        self._data = KnitVersionedFiles(None, None)
        self._annotate_factory = KnitAnnotateFactory()
        self._plain_factory = KnitPlainFactory()
        self._basis_vf = basis_vf


class FTAnnotatedToUnannotated(KnitAdapter):
    """An adapter from FT annotated knits to unannotated ones."""

    def get_bytes(self, factory, annotated_compressed_bytes):
        rec, contents = \
            self._data._parse_record_unchecked(annotated_compressed_bytes)
        content = self._annotate_factory.parse_fulltext(contents, rec[1])
        size, bytes = self._data._record_to_data((rec[1],), rec[3], content.text())
        return bytes


class DeltaAnnotatedToUnannotated(KnitAdapter):
    """An adapter for deltas from annotated to unannotated."""

    def get_bytes(self, factory, annotated_compressed_bytes):
        rec, contents = \
            self._data._parse_record_unchecked(annotated_compressed_bytes)
        delta = self._annotate_factory.parse_line_delta(contents, rec[1],
            plain=True)
        contents = self._plain_factory.lower_line_delta(delta)
        size, bytes = self._data._record_to_data((rec[1],), rec[3], contents)
        return bytes


class FTAnnotatedToFullText(KnitAdapter):
    """An adapter from FT annotated knits to unannotated ones."""

    def get_bytes(self, factory, annotated_compressed_bytes):
        rec, contents = \
            self._data._parse_record_unchecked(annotated_compressed_bytes)
        content, delta = self._annotate_factory.parse_record(factory.key[-1],
            contents, factory._build_details, None)
        return ''.join(content.text())


class DeltaAnnotatedToFullText(KnitAdapter):
    """An adapter for deltas from annotated to unannotated."""

    def get_bytes(self, factory, annotated_compressed_bytes):
        rec, contents = \
            self._data._parse_record_unchecked(annotated_compressed_bytes)
        delta = self._annotate_factory.parse_line_delta(contents, rec[1],
            plain=True)
        compression_parent = factory.parents[0]
        basis_entry = self._basis_vf.get_record_stream(
            [compression_parent], 'unordered', True).next()
        if basis_entry.storage_kind == 'absent':
            raise errors.RevisionNotPresent(compression_parent, self._basis_vf)
        basis_lines = split_lines(basis_entry.get_bytes_as('fulltext'))
        # Manually apply the delta because we have one annotated content and
        # one plain.
        basis_content = PlainKnitContent(basis_lines, compression_parent)
        basis_content.apply_delta(delta, rec[1])
        basis_content._should_strip_eol = factory._build_details[1]
        return ''.join(basis_content.text())


class FTPlainToFullText(KnitAdapter):
    """An adapter from FT plain knits to unannotated ones."""

    def get_bytes(self, factory, compressed_bytes):
        rec, contents = \
            self._data._parse_record_unchecked(compressed_bytes)
        content, delta = self._plain_factory.parse_record(factory.key[-1],
            contents, factory._build_details, None)
        return ''.join(content.text())


class DeltaPlainToFullText(KnitAdapter):
    """An adapter for deltas from annotated to unannotated."""

    def get_bytes(self, factory, compressed_bytes):
        rec, contents = \
            self._data._parse_record_unchecked(compressed_bytes)
        delta = self._plain_factory.parse_line_delta(contents, rec[1])
        compression_parent = factory.parents[0]
        # XXX: string splitting overhead.
        basis_entry = self._basis_vf.get_record_stream(
            [compression_parent], 'unordered', True).next()
        if basis_entry.storage_kind == 'absent':
            raise errors.RevisionNotPresent(compression_parent, self._basis_vf)
        basis_lines = split_lines(basis_entry.get_bytes_as('fulltext'))
        basis_content = PlainKnitContent(basis_lines, compression_parent)
        # Manually apply the delta because we have one annotated content and
        # one plain.
        content, _ = self._plain_factory.parse_record(rec[1], contents,
            factory._build_details, basis_content)
        return ''.join(content.text())


class KnitContentFactory(ContentFactory):
    """Content factory for streaming from knits.
    
    :seealso ContentFactory:
    """

    def __init__(self, key, parents, build_details, sha1, raw_record,
        annotated, knit=None):
        """Create a KnitContentFactory for key.
        
        :param key: The key.
        :param parents: The parents.
        :param build_details: The build details as returned from
            get_build_details.
        :param sha1: The sha1 expected from the full text of this object.
        :param raw_record: The bytes of the knit data from disk.
        :param annotated: True if the raw data is annotated.
        """
        ContentFactory.__init__(self)
        self.sha1 = sha1
        self.key = key
        self.parents = parents
        if build_details[0] == 'line-delta':
            kind = 'delta'
        else:
            kind = 'ft'
        if annotated:
            annotated_kind = 'annotated-'
        else:
            annotated_kind = ''
        self.storage_kind = 'knit-%s%s-gz' % (annotated_kind, kind)
        self._raw_record = raw_record
        self._build_details = build_details
        self._knit = knit

    def get_bytes_as(self, storage_kind):
        if storage_kind == self.storage_kind:
            return self._raw_record
        if storage_kind == 'fulltext' and self._knit is not None:
            return self._knit.get_text(self.key[0])
        else:
            raise errors.UnavailableRepresentation(self.key, storage_kind,
                self.storage_kind)


class KnitContent(object):
    """Content of a knit version to which deltas can be applied.
    
    This is always stored in memory as a list of lines with \n at the end,
    plus a flag saying if the final ending is really there or not, because that 
    corresponds to the on-disk knit representation.
    """

    def __init__(self):
        self._should_strip_eol = False

    def apply_delta(self, delta, new_version_id):
        """Apply delta to this object to become new_version_id."""
        raise NotImplementedError(self.apply_delta)

    def line_delta_iter(self, new_lines):
        """Generate line-based delta from this content to new_lines."""
        new_texts = new_lines.text()
        old_texts = self.text()
        s = patiencediff.PatienceSequenceMatcher(None, old_texts, new_texts)
        for tag, i1, i2, j1, j2 in s.get_opcodes():
            if tag == 'equal':
                continue
            # ofrom, oto, length, data
            yield i1, i2, j2 - j1, new_lines._lines[j1:j2]

    def line_delta(self, new_lines):
        return list(self.line_delta_iter(new_lines))

    @staticmethod
    def get_line_delta_blocks(knit_delta, source, target):
        """Extract SequenceMatcher.get_matching_blocks() from a knit delta"""
        target_len = len(target)
        s_pos = 0
        t_pos = 0
        for s_begin, s_end, t_len, new_text in knit_delta:
            true_n = s_begin - s_pos
            n = true_n
            if n > 0:
                # knit deltas do not provide reliable info about whether the
                # last line of a file matches, due to eol handling.
                if source[s_pos + n -1] != target[t_pos + n -1]:
                    n-=1
                if n > 0:
                    yield s_pos, t_pos, n
            t_pos += t_len + true_n
            s_pos = s_end
        n = target_len - t_pos
        if n > 0:
            if source[s_pos + n -1] != target[t_pos + n -1]:
                n-=1
            if n > 0:
                yield s_pos, t_pos, n
        yield s_pos + (target_len - t_pos), target_len, 0


class AnnotatedKnitContent(KnitContent):
    """Annotated content."""

    def __init__(self, lines):
        KnitContent.__init__(self)
        self._lines = lines

    def annotate(self):
        """Return a list of (origin, text) for each content line."""
        lines = self._lines[:]
        if self._should_strip_eol:
            origin, last_line = lines[-1]
            lines[-1] = (origin, last_line.rstrip('\n'))
        return lines

    def apply_delta(self, delta, new_version_id):
        """Apply delta to this object to become new_version_id."""
        offset = 0
        lines = self._lines
        for start, end, count, delta_lines in delta:
            lines[offset+start:offset+end] = delta_lines
            offset = offset + (start - end) + count

    def text(self):
        try:
            lines = [text for origin, text in self._lines]
        except ValueError, e:
            # most commonly (only?) caused by the internal form of the knit
            # missing annotation information because of a bug - see thread
            # around 20071015
            raise KnitCorrupt(self,
                "line in annotated knit missing annotation information: %s"
                % (e,))
        if self._should_strip_eol:
            lines[-1] = lines[-1].rstrip('\n')
        return lines

    def copy(self):
        return AnnotatedKnitContent(self._lines[:])


class PlainKnitContent(KnitContent):
    """Unannotated content.
    
    When annotate[_iter] is called on this content, the same version is reported
    for all lines. Generally, annotate[_iter] is not useful on PlainKnitContent
    objects.
    """

    def __init__(self, lines, version_id):
        KnitContent.__init__(self)
        self._lines = lines
        self._version_id = version_id

    def annotate(self):
        """Return a list of (origin, text) for each content line."""
        return [(self._version_id, line) for line in self._lines]

    def apply_delta(self, delta, new_version_id):
        """Apply delta to this object to become new_version_id."""
        offset = 0
        lines = self._lines
        for start, end, count, delta_lines in delta:
            lines[offset+start:offset+end] = delta_lines
            offset = offset + (start - end) + count
        self._version_id = new_version_id

    def copy(self):
        return PlainKnitContent(self._lines[:], self._version_id)

    def text(self):
        lines = self._lines
        if self._should_strip_eol:
            lines = lines[:]
            lines[-1] = lines[-1].rstrip('\n')
        return lines


class _KnitFactory(object):
    """Base class for common Factory functions."""

    def parse_record(self, version_id, record, record_details,
                     base_content, copy_base_content=True):
        """Parse a record into a full content object.

        :param version_id: The official version id for this content
        :param record: The data returned by read_records_iter()
        :param record_details: Details about the record returned by
            get_build_details
        :param base_content: If get_build_details returns a compression_parent,
            you must return a base_content here, else use None
        :param copy_base_content: When building from the base_content, decide
            you can either copy it and return a new object, or modify it in
            place.
        :return: (content, delta) A Content object and possibly a line-delta,
            delta may be None
        """
        method, noeol = record_details
        if method == 'line-delta':
            if copy_base_content:
                content = base_content.copy()
            else:
                content = base_content
            delta = self.parse_line_delta(record, version_id)
            content.apply_delta(delta, version_id)
        else:
            content = self.parse_fulltext(record, version_id)
            delta = None
        content._should_strip_eol = noeol
        return (content, delta)


class KnitAnnotateFactory(_KnitFactory):
    """Factory for creating annotated Content objects."""

    annotated = True

    def make(self, lines, version_id):
        num_lines = len(lines)
        return AnnotatedKnitContent(zip([version_id] * num_lines, lines))

    def parse_fulltext(self, content, version_id):
        """Convert fulltext to internal representation

        fulltext content is of the format
        revid(utf8) plaintext\n
        internal representation is of the format:
        (revid, plaintext)
        """
        # TODO: jam 20070209 The tests expect this to be returned as tuples,
        #       but the code itself doesn't really depend on that.
        #       Figure out a way to not require the overhead of turning the
        #       list back into tuples.
        lines = [tuple(line.split(' ', 1)) for line in content]
        return AnnotatedKnitContent(lines)

    def parse_line_delta_iter(self, lines):
        return iter(self.parse_line_delta(lines))

    def parse_line_delta(self, lines, version_id, plain=False):
        """Convert a line based delta into internal representation.

        line delta is in the form of:
        intstart intend intcount
        1..count lines:
        revid(utf8) newline\n
        internal representation is
        (start, end, count, [1..count tuples (revid, newline)])

        :param plain: If True, the lines are returned as a plain
            list without annotations, not as a list of (origin, content) tuples, i.e.
            (start, end, count, [1..count newline])
        """
        result = []
        lines = iter(lines)
        next = lines.next

        cache = {}
        def cache_and_return(line):
            origin, text = line.split(' ', 1)
            return cache.setdefault(origin, origin), text

        # walk through the lines parsing.
        # Note that the plain test is explicitly pulled out of the
        # loop to minimise any performance impact
        if plain:
            for header in lines:
                start, end, count = [int(n) for n in header.split(',')]
                contents = [next().split(' ', 1)[1] for i in xrange(count)]
                result.append((start, end, count, contents))
        else:
            for header in lines:
                start, end, count = [int(n) for n in header.split(',')]
                contents = [tuple(next().split(' ', 1)) for i in xrange(count)]
                result.append((start, end, count, contents))
        return result

    def get_fulltext_content(self, lines):
        """Extract just the content lines from a fulltext."""
        return (line.split(' ', 1)[1] for line in lines)

    def get_linedelta_content(self, lines):
        """Extract just the content from a line delta.

        This doesn't return all of the extra information stored in a delta.
        Only the actual content lines.
        """
        lines = iter(lines)
        next = lines.next
        for header in lines:
            header = header.split(',')
            count = int(header[2])
            for i in xrange(count):
                origin, text = next().split(' ', 1)
                yield text

    def lower_fulltext(self, content):
        """convert a fulltext content record into a serializable form.

        see parse_fulltext which this inverts.
        """
        # TODO: jam 20070209 We only do the caching thing to make sure that
        #       the origin is a valid utf-8 line, eventually we could remove it
        return ['%s %s' % (o, t) for o, t in content._lines]

    def lower_line_delta(self, delta):
        """convert a delta into a serializable form.

        See parse_line_delta which this inverts.
        """
        # TODO: jam 20070209 We only do the caching thing to make sure that
        #       the origin is a valid utf-8 line, eventually we could remove it
        out = []
        for start, end, c, lines in delta:
            out.append('%d,%d,%d\n' % (start, end, c))
            out.extend(origin + ' ' + text
                       for origin, text in lines)
        return out

    def annotate(self, knit, key):
        content = knit._get_content(key)
        # adjust for the fact that serialised annotations are only key suffixes
        # for this factory.
        if type(key) == tuple:
            prefix = key[:-1]
            origins = content.annotate()
            result = []
            for origin, line in origins:
                result.append((prefix + (origin,), line))
            return result
        else:
            # XXX: This smells a bit.  Why would key ever be a non-tuple here?
            # Aren't keys defined to be tuples?  -- spiv 20080618
            return content.annotate()


class KnitPlainFactory(_KnitFactory):
    """Factory for creating plain Content objects."""

    annotated = False

    def make(self, lines, version_id):
        return PlainKnitContent(lines, version_id)

    def parse_fulltext(self, content, version_id):
        """This parses an unannotated fulltext.

        Note that this is not a noop - the internal representation
        has (versionid, line) - its just a constant versionid.
        """
        return self.make(content, version_id)

    def parse_line_delta_iter(self, lines, version_id):
        cur = 0
        num_lines = len(lines)
        while cur < num_lines:
            header = lines[cur]
            cur += 1
            start, end, c = [int(n) for n in header.split(',')]
            yield start, end, c, lines[cur:cur+c]
            cur += c

    def parse_line_delta(self, lines, version_id):
        return list(self.parse_line_delta_iter(lines, version_id))

    def get_fulltext_content(self, lines):
        """Extract just the content lines from a fulltext."""
        return iter(lines)

    def get_linedelta_content(self, lines):
        """Extract just the content from a line delta.

        This doesn't return all of the extra information stored in a delta.
        Only the actual content lines.
        """
        lines = iter(lines)
        next = lines.next
        for header in lines:
            header = header.split(',')
            count = int(header[2])
            for i in xrange(count):
                yield next()

    def lower_fulltext(self, content):
        return content.text()

    def lower_line_delta(self, delta):
        out = []
        for start, end, c, lines in delta:
            out.append('%d,%d,%d\n' % (start, end, c))
            out.extend(lines)
        return out

    def annotate(self, knit, key):
        annotator = _KnitAnnotator(knit)
        return annotator.annotate(key)



def make_file_factory(annotated, mapper):
    """Create a factory for creating a file based KnitVersionedFiles.

    This is only functional enough to run interface tests, it doesn't try to
    provide a full pack environment.
    
    :param annotated: knit annotations are wanted.
    :param mapper: The mapper from keys to paths.
    """
    def factory(transport):
        index = _KndxIndex(transport, mapper, lambda:None, lambda:True, lambda:True)
        access = _KnitKeyAccess(transport, mapper)
        return KnitVersionedFiles(index, access, annotated=annotated)
    return factory


def make_pack_factory(graph, delta, keylength):
    """Create a factory for creating a pack based VersionedFiles.

    This is only functional enough to run interface tests, it doesn't try to
    provide a full pack environment.
    
    :param graph: Store a graph.
    :param delta: Delta compress contents.
    :param keylength: How long should keys be.
    """
    def factory(transport):
        parents = graph or delta
        ref_length = 0
        if graph:
            ref_length += 1
        if delta:
            ref_length += 1
            max_delta_chain = 200
        else:
            max_delta_chain = 0
        graph_index = _mod_index.InMemoryGraphIndex(reference_lists=ref_length,
            key_elements=keylength)
        stream = transport.open_write_stream('newpack')
        writer = pack.ContainerWriter(stream.write)
        writer.begin()
        index = _KnitGraphIndex(graph_index, lambda:True, parents=parents,
            deltas=delta, add_callback=graph_index.add_nodes)
        access = _DirectPackAccess({})
        access.set_writer(writer, graph_index, (transport, 'newpack'))
        result = KnitVersionedFiles(index, access,
            max_delta_chain=max_delta_chain)
        result.stream = stream
        result.writer = writer
        return result
    return factory


def cleanup_pack_knit(versioned_files):
    versioned_files.stream.close()
    versioned_files.writer.end()


class KnitVersionedFiles(VersionedFiles):
    """Storage for many versioned files using knit compression.

    Backend storage is managed by indices and data objects.
    """

    def __init__(self, index, data_access, max_delta_chain=200,
        annotated=False):
        """Create a KnitVersionedFiles with index and data_access.

        :param index: The index for the knit data.
        :param data_access: The access object to store and retrieve knit
            records.
        :param max_delta_chain: The maximum number of deltas to permit during
            insertion. Set to 0 to prohibit the use of deltas.
        :param annotated: Set to True to cause annotations to be calculated and
            stored during insertion.
        """
        self._index = index
        self._access = data_access
        self._max_delta_chain = max_delta_chain
        if annotated:
            self._factory = KnitAnnotateFactory()
        else:
            self._factory = KnitPlainFactory()
        self._fallback_vfs = []

    def add_fallback_versioned_files(self, a_versioned_files):
        """Add a source of texts for texts not present in this knit.

        :param a_versioned_files: A VersionedFiles object.
        """
        self._fallback_vfs.append(a_versioned_files)

    def add_lines(self, key, parents, lines, parent_texts=None,
        left_matching_blocks=None, nostore_sha=None, random_id=False,
        check_content=True):
        """See VersionedFiles.add_lines()."""
        self._index._check_write_ok()
        self._check_add(key, lines, random_id, check_content)
        if parents is None:
            # The caller might pass None if there is no graph data, but kndx
            # indexes can't directly store that, so we give them
            # an empty tuple instead.
            parents = ()
        return self._add(key, lines, parents,
            parent_texts, left_matching_blocks, nostore_sha, random_id)

    def _add(self, key, lines, parents, parent_texts,
        left_matching_blocks, nostore_sha, random_id):
        """Add a set of lines on top of version specified by parents.

        Any versions not present will be converted into ghosts.
        """
        # first thing, if the content is something we don't need to store, find
        # that out.
        line_bytes = ''.join(lines)
        digest = sha_string(line_bytes)
        if nostore_sha == digest:
            raise errors.ExistingContent

        present_parents = []
        if parent_texts is None:
            parent_texts = {}
        # Do a single query to ascertain parent presence.
        present_parent_map = self.get_parent_map(parents)
        for parent in parents:
            if parent in present_parent_map:
                present_parents.append(parent)

        # Currently we can only compress against the left most present parent.
        if (len(present_parents) == 0 or
            present_parents[0] != parents[0]):
            delta = False
        else:
            # To speed the extract of texts the delta chain is limited
            # to a fixed number of deltas.  This should minimize both
            # I/O and the time spend applying deltas.
            delta = self._check_should_delta(present_parents[0])

        text_length = len(line_bytes)
        options = []
        if lines:
            if lines[-1][-1] != '\n':
                # copy the contents of lines.
                lines = lines[:]
                options.append('no-eol')
                lines[-1] = lines[-1] + '\n'
                line_bytes += '\n'

        for element in key:
            if type(element) != str:
                raise TypeError("key contains non-strings: %r" % (key,))
        # Knit hunks are still last-element only
        version_id = key[-1]
        content = self._factory.make(lines, version_id)
        if 'no-eol' in options:
            # Hint to the content object that its text() call should strip the
            # EOL.
            content._should_strip_eol = True
        if delta or (self._factory.annotated and len(present_parents) > 0):
            # Merge annotations from parent texts if needed.
            delta_hunks = self._merge_annotations(content, present_parents,
                parent_texts, delta, self._factory.annotated,
                left_matching_blocks)

        if delta:
            options.append('line-delta')
            store_lines = self._factory.lower_line_delta(delta_hunks)
            size, bytes = self._record_to_data(key, digest,
                store_lines)
        else:
            options.append('fulltext')
            # isinstance is slower and we have no hierarchy.
            if self._factory.__class__ == KnitPlainFactory:
                # Use the already joined bytes saving iteration time in
                # _record_to_data.
                size, bytes = self._record_to_data(key, digest,
                    lines, [line_bytes])
            else:
                # get mixed annotation + content and feed it into the
                # serialiser.
                store_lines = self._factory.lower_fulltext(content)
                size, bytes = self._record_to_data(key, digest,
                    store_lines)

        access_memo = self._access.add_raw_records([(key, size)], bytes)[0]
        self._index.add_records(
            ((key, options, access_memo, parents),),
            random_id=random_id)
        return digest, text_length, content

    def annotate(self, key):
        """See VersionedFiles.annotate."""
        return self._factory.annotate(self, key)

    def check(self, progress_bar=None):
        """See VersionedFiles.check()."""
        # This doesn't actually test extraction of everything, but that will
        # impact 'bzr check' substantially, and needs to be integrated with
        # care. However, it does check for the obvious problem of a delta with
        # no basis.
        keys = self._index.keys()
        parent_map = self.get_parent_map(keys)
        for key in keys:
            if self._index.get_method(key) != 'fulltext':
                compression_parent = parent_map[key][0]
                if compression_parent not in parent_map:
                    raise errors.KnitCorrupt(self,
                        "Missing basis parent %s for %s" % (
                        compression_parent, key))
        for fallback_vfs in self._fallback_vfs:
            fallback_vfs.check()

    def _check_add(self, key, lines, random_id, check_content):
        """check that version_id and lines are safe to add."""
        version_id = key[-1]
        if contains_whitespace(version_id):
            raise InvalidRevisionId(version_id, self)
        self.check_not_reserved_id(version_id)
        # TODO: If random_id==False and the key is already present, we should
        # probably check that the existing content is identical to what is
        # being inserted, and otherwise raise an exception.  This would make
        # the bundle code simpler.
        if check_content:
            self._check_lines_not_unicode(lines)
            self._check_lines_are_lines(lines)

    def _check_header(self, key, line):
        rec = self._split_header(line)
        self._check_header_version(rec, key[-1])
        return rec

    def _check_header_version(self, rec, version_id):
        """Checks the header version on original format knit records.
        
        These have the last component of the key embedded in the record.
        """
        if rec[1] != version_id:
            raise KnitCorrupt(self,
                'unexpected version, wanted %r, got %r' % (version_id, rec[1]))

    def _check_should_delta(self, parent):
        """Iterate back through the parent listing, looking for a fulltext.

        This is used when we want to decide whether to add a delta or a new
        fulltext. It searches for _max_delta_chain parents. When it finds a
        fulltext parent, it sees if the total size of the deltas leading up to
        it is large enough to indicate that we want a new full text anyway.

        Return True if we should create a new delta, False if we should use a
        full text.
        """
        delta_size = 0
        fulltext_size = None
        for count in xrange(self._max_delta_chain):
            # XXX: Collapse these two queries:
            try:
                method = self._index.get_method(parent)
            except RevisionNotPresent:
                # Some basis is not locally present: always delta
                return False
            index, pos, size = self._index.get_position(parent)
            if method == 'fulltext':
                fulltext_size = size
                break
            delta_size += size
            # We don't explicitly check for presence because this is in an
            # inner loop, and if it's missing it'll fail anyhow.
            # TODO: This should be asking for compression parent, not graph
            # parent.
            parent = self._index.get_parent_map([parent])[parent][0]
        else:
            # We couldn't find a fulltext, so we must create a new one
            return False
        # Simple heuristic - if the total I/O wold be greater as a delta than
        # the originally installed fulltext, we create a new fulltext.
        return fulltext_size > delta_size

    def _build_details_to_components(self, build_details):
        """Convert a build_details tuple to a position tuple."""
        # record_details, access_memo, compression_parent
        return build_details[3], build_details[0], build_details[1]

    def _get_components_positions(self, keys, allow_missing=False):
        """Produce a map of position data for the components of keys.

        This data is intended to be used for retrieving the knit records.

        A dict of key to (record_details, index_memo, next, parents) is
        returned.
        method is the way referenced data should be applied.
        index_memo is the handle to pass to the data access to actually get the
            data
        next is the build-parent of the version, or None for fulltexts.
        parents is the version_ids of the parents of this version

        :param allow_missing: If True do not raise an error on a missing component,
            just ignore it.
        """
        component_data = {}
        pending_components = keys
        while pending_components:
            build_details = self._index.get_build_details(pending_components)
            current_components = set(pending_components)
            pending_components = set()
            for key, details in build_details.iteritems():
                (index_memo, compression_parent, parents,
                 record_details) = details
                method = record_details[0]
                if compression_parent is not None:
                    pending_components.add(compression_parent)
                component_data[key] = self._build_details_to_components(details)
            missing = current_components.difference(build_details)
            if missing and not allow_missing:
                raise errors.RevisionNotPresent(missing.pop(), self)
        return component_data
       
    def _get_content(self, key, parent_texts={}):
        """Returns a content object that makes up the specified
        version."""
        cached_version = parent_texts.get(key, None)
        if cached_version is not None:
            # Ensure the cache dict is valid.
            if not self.get_parent_map([key]):
                raise RevisionNotPresent(key, self)
            return cached_version
        text_map, contents_map = self._get_content_maps([key])
        return contents_map[key]

    def _get_content_maps(self, keys, nonlocal_keys=None):
        """Produce maps of text and KnitContents
        
        :param keys: The keys to produce content maps for.
        :param nonlocal_keys: An iterable of keys(possibly intersecting keys)
            which are known to not be in this knit, but rather in one of the
            fallback knits.
        :return: (text_map, content_map) where text_map contains the texts for
            the requested versions and content_map contains the KnitContents.
        """
        # FUTURE: This function could be improved for the 'extract many' case
        # by tracking each component and only doing the copy when the number of
        # children than need to apply delta's to it is > 1 or it is part of the
        # final output.
        keys = list(keys)
        multiple_versions = len(keys) != 1
        record_map = self._get_record_map(keys, allow_missing=True)

        text_map = {}
        content_map = {}
        final_content = {}
        if nonlocal_keys is None:
            nonlocal_keys = set()
        else:
            nonlocal_keys = frozenset(nonlocal_keys)
        missing_keys = set(nonlocal_keys)
        for source in self._fallback_vfs:
            if not missing_keys:
                break
            for record in source.get_record_stream(missing_keys,
                'unordered', True):
                if record.storage_kind == 'absent':
                    continue
                missing_keys.remove(record.key)
                lines = split_lines(record.get_bytes_as('fulltext'))
                text_map[record.key] = lines
                content_map[record.key] = PlainKnitContent(lines, record.key)
                if record.key in keys:
                    final_content[record.key] = content_map[record.key]
        for key in keys:
            if key in nonlocal_keys:
                # already handled
                continue
            components = []
            cursor = key
            while cursor is not None:
                try:
                    record, record_details, digest, next = record_map[cursor]
                except KeyError:
                    raise RevisionNotPresent(cursor, self)
                components.append((cursor, record, record_details, digest))
                cursor = next
                if cursor in content_map:
                    # no need to plan further back
                    components.append((cursor, None, None, None))
                    break

            content = None
            for (component_id, record, record_details,
                 digest) in reversed(components):
                if component_id in content_map:
                    content = content_map[component_id]
                else:
                    content, delta = self._factory.parse_record(key[-1],
                        record, record_details, content,
                        copy_base_content=multiple_versions)
                    if multiple_versions:
                        content_map[component_id] = content

            final_content[key] = content

            # digest here is the digest from the last applied component.
            text = content.text()
            actual_sha = sha_strings(text)
            if actual_sha != digest:
                raise KnitCorrupt(self,
                    '\n  sha-1 %s'
                    '\n  of reconstructed text does not match'
                    '\n  expected %s'
                    '\n  for version %s' %
                    (actual_sha, digest, key))
            text_map[key] = text
        return text_map, final_content

    def get_parent_map(self, keys):
        """Get a map of the graph parents of keys.

        :param keys: The keys to look up parents for.
        :return: A mapping from keys to parents. Absent keys are absent from
            the mapping.
        """
        return self._get_parent_map_with_sources(keys)[0]

    def _get_parent_map_with_sources(self, keys):
        """Get a map of the parents of keys.

        :param keys: The keys to look up parents for.
        :return: A tuple. The first element is a mapping from keys to parents.
            Absent keys are absent from the mapping. The second element is a
            list with the locations each key was found in. The first element
            is the in-this-knit parents, the second the first fallback source,
            and so on.
        """
        result = {}
        sources = [self._index] + self._fallback_vfs
        source_results = []
        missing = set(keys)
        for source in sources:
            if not missing:
                break
            new_result = source.get_parent_map(missing)
            source_results.append(new_result)
            result.update(new_result)
            missing.difference_update(set(new_result))
        return result, source_results

    def _get_record_map(self, keys, allow_missing=False):
        """Produce a dictionary of knit records.
        
        :return: {key:(record, record_details, digest, next)}
            record
                data returned from read_records
            record_details
                opaque information to pass to parse_record
            digest
                SHA1 digest of the full text after all steps are done
            next
                build-parent of the version, i.e. the leftmost ancestor.
                Will be None if the record is not a delta.
        :param keys: The keys to build a map for
        :param allow_missing: If some records are missing, rather than 
            error, just return the data that could be generated.
        """
        position_map = self._get_components_positions(keys,
            allow_missing=allow_missing)
        # key = component_id, r = record_details, i_m = index_memo, n = next
        records = [(key, i_m) for key, (r, i_m, n)
                             in position_map.iteritems()]
        record_map = {}
        for key, record, digest in \
                self._read_records_iter(records):
            (record_details, index_memo, next) = position_map[key]
            record_map[key] = record, record_details, digest, next
        return record_map

    def get_record_stream(self, keys, ordering, include_delta_closure):
        """Get a stream of records for keys.

        :param keys: The keys to include.
        :param ordering: Either 'unordered' or 'topological'. A topologically
            sorted stream has compression parents strictly before their
            children.
        :param include_delta_closure: If True then the closure across any
            compression parents will be included (in the opaque data).
        :return: An iterator of ContentFactory objects, each of which is only
            valid until the iterator is advanced.
        """
        # keys might be a generator
        keys = set(keys)
        if not keys:
            return
        if not self._index.has_graph:
            # Cannot topological order when no graph has been stored.
            ordering = 'unordered'
        if include_delta_closure:
            positions = self._get_components_positions(keys, allow_missing=True)
        else:
            build_details = self._index.get_build_details(keys)
            # map from key to
            # (record_details, access_memo, compression_parent_key)
            positions = dict((key, self._build_details_to_components(details))
                for key, details in build_details.iteritems())
        absent_keys = keys.difference(set(positions))
        # There may be more absent keys : if we're missing the basis component
        # and are trying to include the delta closure.
        if include_delta_closure:
            needed_from_fallback = set()
            # Build up reconstructable_keys dict.  key:True in this dict means
            # the key can be reconstructed.
            reconstructable_keys = {}
            for key in keys:
                # the delta chain
                try:
                    chain = [key, positions[key][2]]
                except KeyError:
                    needed_from_fallback.add(key)
                    continue
                result = True
                while chain[-1] is not None:
                    if chain[-1] in reconstructable_keys:
                        result = reconstructable_keys[chain[-1]]
                        break
                    else:
                        try:
                            chain.append(positions[chain[-1]][2])
                        except KeyError:
                            # missing basis component
                            needed_from_fallback.add(chain[-1])
                            result = True
                            break
                for chain_key in chain[:-1]:
                    reconstructable_keys[chain_key] = result
                if not result:
                    needed_from_fallback.add(key)
        # Double index lookups here : need a unified api ?
        global_map, parent_maps = self._get_parent_map_with_sources(keys)
        if ordering == 'topological':
            # Global topological sort
            present_keys = tsort.topo_sort(global_map)
            # Now group by source:
            source_keys = []
            current_source = None
            for key in present_keys:
                for parent_map in parent_maps:
                    if key in parent_map:
                        key_source = parent_map
                        break
                if current_source is not key_source:
                    source_keys.append((key_source, []))
                    current_source = key_source
                source_keys[-1][1].append(key)
        else:
            # Just group by source; remote sources first.
            present_keys = []
            source_keys = []
            for parent_map in reversed(parent_maps):
                source_keys.append((parent_map, []))
                for key in parent_map:
                    present_keys.append(key)
                    source_keys[-1][1].append(key)
        absent_keys = keys - set(global_map)
        for key in absent_keys:
            yield AbsentContentFactory(key)
        # restrict our view to the keys we can answer.
        # XXX: Memory: TODO: batch data here to cap buffered data at (say) 1MB.
        # XXX: At that point we need to consider the impact of double reads by
        # utilising components multiple times.
        if include_delta_closure:
            # XXX: get_content_maps performs its own index queries; allow state
            # to be passed in.
            text_map, _ = self._get_content_maps(present_keys,
                needed_from_fallback - absent_keys)
            for key in present_keys:
                yield FulltextContentFactory(key, global_map[key], None,
                    ''.join(text_map[key]))
        else:
            for source, keys in source_keys:
                if source is parent_maps[0]:
                    # this KnitVersionedFiles
                    records = [(key, positions[key][1]) for key in keys]
                    for key, raw_data, sha1 in self._read_records_iter_raw(records):
                        (record_details, index_memo, _) = positions[key]
                        yield KnitContentFactory(key, global_map[key],
                            record_details, sha1, raw_data, self._factory.annotated, None)
                else:
                    vf = self._fallback_vfs[parent_maps.index(source) - 1]
                    for record in vf.get_record_stream(keys, ordering,
                        include_delta_closure):
                        yield record

    def get_sha1s(self, keys):
        """See VersionedFiles.get_sha1s()."""
        missing = set(keys)
        record_map = self._get_record_map(missing, allow_missing=True)
        result = {}
        for key, details in record_map.iteritems():
            if key not in missing:
                continue
            # record entry 2 is the 'digest'.
            result[key] = details[2]
        missing.difference_update(set(result))
        for source in self._fallback_vfs:
            if not missing:
                break
            new_result = source.get_sha1s(missing)
            result.update(new_result)
            missing.difference_update(set(new_result))
        return result

    def insert_record_stream(self, stream):
        """Insert a record stream into this container.

        :param stream: A stream of records to insert. 
        :return: None
        :seealso VersionedFiles.get_record_stream:
        """
        def get_adapter(adapter_key):
            try:
                return adapters[adapter_key]
            except KeyError:
                adapter_factory = adapter_registry.get(adapter_key)
                adapter = adapter_factory(self)
                adapters[adapter_key] = adapter
                return adapter
        if self._factory.annotated:
            # self is annotated, we need annotated knits to use directly.
            annotated = "annotated-"
            convertibles = []
        else:
            # self is not annotated, but we can strip annotations cheaply.
            annotated = ""
            convertibles = set(["knit-annotated-ft-gz"])
            if self._max_delta_chain:
                convertibles.add("knit-annotated-delta-gz")
        # The set of types we can cheaply adapt without needing basis texts.
        native_types = set()
        if self._max_delta_chain:
            native_types.add("knit-%sdelta-gz" % annotated)
        native_types.add("knit-%sft-gz" % annotated)
        knit_types = native_types.union(convertibles)
        adapters = {}
        # Buffer all index entries that we can't add immediately because their
        # basis parent is missing. We don't buffer all because generating
        # annotations may require access to some of the new records. However we
        # can't generate annotations from new deltas until their basis parent
        # is present anyway, so we get away with not needing an index that
        # includes the new keys.
        # key = basis_parent, value = index entry to add
        buffered_index_entries = {}
        for record in stream:
            parents = record.parents
            # Raise an error when a record is missing.
            if record.storage_kind == 'absent':
                raise RevisionNotPresent([record.key], self)
            if record.storage_kind in knit_types:
                if record.storage_kind not in native_types:
                    try:
                        adapter_key = (record.storage_kind, "knit-delta-gz")
                        adapter = get_adapter(adapter_key)
                    except KeyError:
                        adapter_key = (record.storage_kind, "knit-ft-gz")
                        adapter = get_adapter(adapter_key)
                    bytes = adapter.get_bytes(
                        record, record.get_bytes_as(record.storage_kind))
                else:
                    bytes = record.get_bytes_as(record.storage_kind)
                options = [record._build_details[0]]
                if record._build_details[1]:
                    options.append('no-eol')
                # Just blat it across.
                # Note: This does end up adding data on duplicate keys. As
                # modern repositories use atomic insertions this should not
                # lead to excessive growth in the event of interrupted fetches.
                # 'knit' repositories may suffer excessive growth, but as a
                # deprecated format this is tolerable. It can be fixed if
                # needed by in the kndx index support raising on a duplicate
                # add with identical parents and options.
                access_memo = self._access.add_raw_records(
                    [(record.key, len(bytes))], bytes)[0]
                index_entry = (record.key, options, access_memo, parents)
                buffered = False
                if 'fulltext' not in options:
                    basis_parent = parents[0]
                    # Note that pack backed knits don't need to buffer here
                    # because they buffer all writes to the transaction level,
                    # but we don't expose that difference at the index level. If
                    # the query here has sufficient cost to show up in
                    # profiling we should do that.
                    if basis_parent not in self.get_parent_map([basis_parent]):
                        pending = buffered_index_entries.setdefault(
                            basis_parent, [])
                        pending.append(index_entry)
                        buffered = True
                if not buffered:
                    self._index.add_records([index_entry])
            elif record.storage_kind == 'fulltext':
                self.add_lines(record.key, parents,
                    split_lines(record.get_bytes_as('fulltext')))
            else:
                adapter_key = record.storage_kind, 'fulltext'
                adapter = get_adapter(adapter_key)
                lines = split_lines(adapter.get_bytes(
                    record, record.get_bytes_as(record.storage_kind)))
                try:
                    self.add_lines(record.key, parents, lines)
                except errors.RevisionAlreadyPresent:
                    pass
            # Add any records whose basis parent is now available.
            added_keys = [record.key]
            while added_keys:
                key = added_keys.pop(0)
                if key in buffered_index_entries:
                    index_entries = buffered_index_entries[key]
                    self._index.add_records(index_entries)
                    added_keys.extend(
                        [index_entry[0] for index_entry in index_entries])
                    del buffered_index_entries[key]
        # If there were any deltas which had a missing basis parent, error.
        if buffered_index_entries:
            raise errors.RevisionNotPresent(buffered_index_entries.keys()[0],
                self)

    def iter_lines_added_or_present_in_keys(self, keys, pb=None):
        """Iterate over the lines in the versioned files from keys.

        This may return lines from other keys. Each item the returned
        iterator yields is a tuple of a line and a text version that that line
        is present in (not introduced in).

        Ordering of results is in whatever order is most suitable for the
        underlying storage format.

        If a progress bar is supplied, it may be used to indicate progress.
        The caller is responsible for cleaning up progress bars (because this
        is an iterator).

        NOTES:
         * Lines are normalised by the underlying store: they will all have \n
           terminators.
         * Lines are returned in arbitrary order.

        :return: An iterator over (line, key).
        """
        if pb is None:
            pb = progress.DummyProgress()
        keys = set(keys)
        total = len(keys)
        # we don't care about inclusions, the caller cares.
        # but we need to setup a list of records to visit.
        # we need key, position, length
        key_records = []
        build_details = self._index.get_build_details(keys)
        for key, details in build_details.iteritems():
            if key in keys:
                key_records.append((key, details[0]))
                keys.remove(key)
        records_iter = enumerate(self._read_records_iter(key_records))
        for (key_idx, (key, data, sha_value)) in records_iter:
            pb.update('Walking content.', key_idx, total)
            compression_parent = build_details[key][1]
            if compression_parent is None:
                # fulltext
                line_iterator = self._factory.get_fulltext_content(data)
            else:
                # Delta 
                line_iterator = self._factory.get_linedelta_content(data)
            # XXX: It might be more efficient to yield (key,
            # line_iterator) in the future. However for now, this is a simpler
            # change to integrate into the rest of the codebase. RBC 20071110
            for line in line_iterator:
                yield line, key
        for source in self._fallback_vfs:
            if not keys:
                break
            source_keys = set()
            for line, key in source.iter_lines_added_or_present_in_keys(keys):
                source_keys.add(key)
                yield line, key
            keys.difference_update(source_keys)
        if keys:
            raise RevisionNotPresent(keys, self.filename)
        pb.update('Walking content.', total, total)

    def _make_line_delta(self, delta_seq, new_content):
        """Generate a line delta from delta_seq and new_content."""
        diff_hunks = []
        for op in delta_seq.get_opcodes():
            if op[0] == 'equal':
                continue
            diff_hunks.append((op[1], op[2], op[4]-op[3], new_content._lines[op[3]:op[4]]))
        return diff_hunks

    def _merge_annotations(self, content, parents, parent_texts={},
                           delta=None, annotated=None,
                           left_matching_blocks=None):
        """Merge annotations for content and generate deltas.
        
        This is done by comparing the annotations based on changes to the text
        and generating a delta on the resulting full texts. If annotations are
        not being created then a simple delta is created.
        """
        if left_matching_blocks is not None:
            delta_seq = diff._PrematchedMatcher(left_matching_blocks)
        else:
            delta_seq = None
        if annotated:
            for parent_key in parents:
                merge_content = self._get_content(parent_key, parent_texts)
                if (parent_key == parents[0] and delta_seq is not None):
                    seq = delta_seq
                else:
                    seq = patiencediff.PatienceSequenceMatcher(
                        None, merge_content.text(), content.text())
                for i, j, n in seq.get_matching_blocks():
                    if n == 0:
                        continue
                    # this copies (origin, text) pairs across to the new
                    # content for any line that matches the last-checked
                    # parent.
                    content._lines[j:j+n] = merge_content._lines[i:i+n]
            # XXX: Robert says the following block is a workaround for a
            # now-fixed bug and it can probably be deleted. -- mbp 20080618
            if content._lines and content._lines[-1][1][-1] != '\n':
                # The copied annotation was from a line without a trailing EOL,
                # reinstate one for the content object, to ensure correct
                # serialization.
                line = content._lines[-1][1] + '\n'
                content._lines[-1] = (content._lines[-1][0], line)
        if delta:
            if delta_seq is None:
                reference_content = self._get_content(parents[0], parent_texts)
                new_texts = content.text()
                old_texts = reference_content.text()
                delta_seq = patiencediff.PatienceSequenceMatcher(
                                                 None, old_texts, new_texts)
            return self._make_line_delta(delta_seq, content)

    def _parse_record(self, version_id, data):
        """Parse an original format knit record.

        These have the last element of the key only present in the stored data.
        """
        rec, record_contents = self._parse_record_unchecked(data)
        self._check_header_version(rec, version_id)
        return record_contents, rec[3]

    def _parse_record_header(self, key, raw_data):
        """Parse a record header for consistency.

        :return: the header and the decompressor stream.
                 as (stream, header_record)
        """
        df = tuned_gzip.GzipFile(mode='rb', fileobj=StringIO(raw_data))
        try:
            # Current serialise
            rec = self._check_header(key, df.readline())
        except Exception, e:
            raise KnitCorrupt(self,
                              "While reading {%s} got %s(%s)"
                              % (key, e.__class__.__name__, str(e)))
        return df, rec

    def _parse_record_unchecked(self, data):
        # profiling notes:
        # 4168 calls in 2880 217 internal
        # 4168 calls to _parse_record_header in 2121
        # 4168 calls to readlines in 330
        df = tuned_gzip.GzipFile(mode='rb', fileobj=StringIO(data))
        try:
            record_contents = df.readlines()
        except Exception, e:
            raise KnitCorrupt(self, "Corrupt compressed record %r, got %s(%s)" %
                (data, e.__class__.__name__, str(e)))
        header = record_contents.pop(0)
        rec = self._split_header(header)
        last_line = record_contents.pop()
        if len(record_contents) != int(rec[2]):
            raise KnitCorrupt(self,
                              'incorrect number of lines %s != %s'
                              ' for version {%s} %s'
                              % (len(record_contents), int(rec[2]),
                                 rec[1], record_contents))
        if last_line != 'end %s\n' % rec[1]:
            raise KnitCorrupt(self,
                              'unexpected version end line %r, wanted %r' 
                              % (last_line, rec[1]))
        df.close()
        return rec, record_contents

    def _read_records_iter(self, records):
        """Read text records from data file and yield result.

        The result will be returned in whatever is the fastest to read.
        Not by the order requested. Also, multiple requests for the same
        record will only yield 1 response.
        :param records: A list of (key, access_memo) entries
        :return: Yields (key, contents, digest) in the order
                 read, not the order requested
        """
        if not records:
            return

        # XXX: This smells wrong, IO may not be getting ordered right.
        needed_records = sorted(set(records), key=operator.itemgetter(1))
        if not needed_records:
            return

        # The transport optimizes the fetching as well 
        # (ie, reads continuous ranges.)
        raw_data = self._access.get_raw_records(
            [index_memo for key, index_memo in needed_records])

        for (key, index_memo), data in \
                izip(iter(needed_records), raw_data):
            content, digest = self._parse_record(key[-1], data)
            yield key, content, digest

    def _read_records_iter_raw(self, records):
        """Read text records from data file and yield raw data.

        This unpacks enough of the text record to validate the id is
        as expected but thats all.

        Each item the iterator yields is (key, bytes, sha1_of_full_text).
        """
        # setup an iterator of the external records:
        # uses readv so nice and fast we hope.
        if len(records):
            # grab the disk data needed.
            needed_offsets = [index_memo for key, index_memo
                                           in records]
            raw_records = self._access.get_raw_records(needed_offsets)

        for key, index_memo in records:
            data = raw_records.next()
            # validate the header (note that we can only use the suffix in
            # current knit records).
            df, rec = self._parse_record_header(key, data)
            df.close()
            yield key, data, rec[3]

    def _record_to_data(self, key, digest, lines, dense_lines=None):
        """Convert key, digest, lines into a raw data block.
        
        :param key: The key of the record. Currently keys are always serialised
            using just the trailing component.
        :param dense_lines: The bytes of lines but in a denser form. For
            instance, if lines is a list of 1000 bytestrings each ending in \n,
            dense_lines may be a list with one line in it, containing all the
            1000's lines and their \n's. Using dense_lines if it is already
            known is a win because the string join to create bytes in this
            function spends less time resizing the final string.
        :return: (len, a StringIO instance with the raw data ready to read.)
        """
        # Note: using a string copy here increases memory pressure with e.g.
        # ISO's, but it is about 3 seconds faster on a 1.2Ghz intel machine
        # when doing the initial commit of a mozilla tree. RBC 20070921
        bytes = ''.join(chain(
            ["version %s %d %s\n" % (key[-1],
                                     len(lines),
                                     digest)],
            dense_lines or lines,
            ["end %s\n" % key[-1]]))
        if type(bytes) != str:
            raise AssertionError(
                'data must be plain bytes was %s' % type(bytes))
        if lines and lines[-1][-1] != '\n':
            raise ValueError('corrupt lines value %r' % lines)
        compressed_bytes = tuned_gzip.bytes_to_gzip(bytes)
        return len(compressed_bytes), compressed_bytes

    def _split_header(self, line):
        rec = line.split()
        if len(rec) != 4:
            raise KnitCorrupt(self,
                              'unexpected number of elements in record header')
        return rec

    def keys(self):
        """See VersionedFiles.keys."""
        if 'evil' in debug.debug_flags:
            trace.mutter_callsite(2, "keys scales with size of history")
        sources = [self._index] + self._fallback_vfs
        result = set()
        for source in sources:
            result.update(source.keys())
        return result



class _KndxIndex(object):
    """Manages knit index files

    The index is kept in memory and read on startup, to enable
    fast lookups of revision information.  The cursor of the index
    file is always pointing to the end, making it easy to append
    entries.

    _cache is a cache for fast mapping from version id to a Index
    object.

    _history is a cache for fast mapping from indexes to version ids.

    The index data format is dictionary compressed when it comes to
    parent references; a index entry may only have parents that with a
    lover index number.  As a result, the index is topological sorted.

    Duplicate entries may be written to the index for a single version id
    if this is done then the latter one completely replaces the former:
    this allows updates to correct version and parent information. 
    Note that the two entries may share the delta, and that successive
    annotations and references MUST point to the first entry.

    The index file on disc contains a header, followed by one line per knit
    record. The same revision can be present in an index file more than once.
    The first occurrence gets assigned a sequence number starting from 0. 
    
    The format of a single line is
    REVISION_ID FLAGS BYTE_OFFSET LENGTH( PARENT_ID|PARENT_SEQUENCE_ID)* :\n
    REVISION_ID is a utf8-encoded revision id
    FLAGS is a comma separated list of flags about the record. Values include 
        no-eol, line-delta, fulltext.
    BYTE_OFFSET is the ascii representation of the byte offset in the data file
        that the the compressed data starts at.
    LENGTH is the ascii representation of the length of the data file.
    PARENT_ID a utf-8 revision id prefixed by a '.' that is a parent of
        REVISION_ID.
    PARENT_SEQUENCE_ID the ascii representation of the sequence number of a
        revision id already in the knit that is a parent of REVISION_ID.
    The ' :' marker is the end of record marker.
    
    partial writes:
    when a write is interrupted to the index file, it will result in a line
    that does not end in ' :'. If the ' :' is not present at the end of a line,
    or at the end of the file, then the record that is missing it will be
    ignored by the parser.

    When writing new records to the index file, the data is preceded by '\n'
    to ensure that records always start on new lines even if the last write was
    interrupted. As a result its normal for the last line in the index to be
    missing a trailing newline. One can be added with no harmful effects.

    :ivar _kndx_cache: dict from prefix to the old state of KnitIndex objects,
        where prefix is e.g. the (fileid,) for .texts instances or () for
        constant-mapped things like .revisions, and the old state is
        tuple(history_vector, cache_dict).  This is used to prevent having an
        ABI change with the C extension that reads .kndx files.
    """

    HEADER = "# bzr knit index 8\n"

    def __init__(self, transport, mapper, get_scope, allow_writes, is_locked):
        """Create a _KndxIndex on transport using mapper."""
        self._transport = transport
        self._mapper = mapper
        self._get_scope = get_scope
        self._allow_writes = allow_writes
        self._is_locked = is_locked
        self._reset_cache()
        self.has_graph = True

    def add_records(self, records, random_id=False):
        """Add multiple records to the index.
        
        :param records: a list of tuples:
                         (key, options, access_memo, parents).
        :param random_id: If True the ids being added were randomly generated
            and no check for existence will be performed.
        """
        paths = {}
        for record in records:
            key = record[0]
            prefix = key[:-1]
            path = self._mapper.map(key) + '.kndx'
            path_keys = paths.setdefault(path, (prefix, []))
            path_keys[1].append(record)
        for path in sorted(paths):
            prefix, path_keys = paths[path]
            self._load_prefixes([prefix])
            lines = []
            orig_history = self._kndx_cache[prefix][1][:]
            orig_cache = self._kndx_cache[prefix][0].copy()

            try:
                for key, options, (_, pos, size), parents in path_keys:
                    if parents is None:
                        # kndx indices cannot be parentless.
                        parents = ()
                    line = "\n%s %s %s %s %s :" % (
                        key[-1], ','.join(options), pos, size,
                        self._dictionary_compress(parents))
                    if type(line) != str:
                        raise AssertionError(
                            'data must be utf8 was %s' % type(line))
                    lines.append(line)
                    self._cache_key(key, options, pos, size, parents)
                if len(orig_history):
                    self._transport.append_bytes(path, ''.join(lines))
                else:
                    self._init_index(path, lines)
            except:
                # If any problems happen, restore the original values and re-raise
                self._kndx_cache[prefix] = (orig_cache, orig_history)
                raise

    def _cache_key(self, key, options, pos, size, parent_keys):
        """Cache a version record in the history array and index cache.

        This is inlined into _load_data for performance. KEEP IN SYNC.
        (It saves 60ms, 25% of the __init__ overhead on local 4000 record
         indexes).
        """
        prefix = key[:-1]
        version_id = key[-1]
        # last-element only for compatibilty with the C load_data.
        parents = tuple(parent[-1] for parent in parent_keys)
        for parent in parent_keys:
            if parent[:-1] != prefix:
                raise ValueError("mismatched prefixes for %r, %r" % (
                    key, parent_keys))
        cache, history = self._kndx_cache[prefix]
        # only want the _history index to reference the 1st index entry
        # for version_id
        if version_id not in cache:
            index = len(history)
            history.append(version_id)
        else:
            index = cache[version_id][5]
        cache[version_id] = (version_id,
                                   options,
                                   pos,
                                   size,
                                   parents,
                                   index)

    def check_header(self, fp):
        line = fp.readline()
        if line == '':
            # An empty file can actually be treated as though the file doesn't
            # exist yet.
            raise errors.NoSuchFile(self)
        if line != self.HEADER:
            raise KnitHeaderError(badline=line, filename=self)

    def _check_read(self):
        if not self._is_locked():
            raise errors.ObjectNotLocked(self)
        if self._get_scope() != self._scope:
            self._reset_cache()

    def _check_write_ok(self):
        """Assert if not writes are permitted."""
        if not self._is_locked():
            raise errors.ObjectNotLocked(self)
        if self._get_scope() != self._scope:
            self._reset_cache()
        if self._mode != 'w':
            raise errors.ReadOnlyObjectDirtiedError(self)

    def get_build_details(self, keys):
        """Get the method, index_memo and compression parent for keys.

        Ghosts are omitted from the result.

        :param keys: An iterable of keys.
        :return: A dict of key:(index_memo, compression_parent, parents,
            record_details).
            index_memo
                opaque structure to pass to read_records to extract the raw
                data
            compression_parent
                Content that this record is built upon, may be None
            parents
                Logical parents of this node
            record_details
                extra information about the content which needs to be passed to
                Factory.parse_record
        """
        prefixes = self._partition_keys(keys)
        parent_map = self.get_parent_map(keys)
        result = {}
        for key in keys:
            if key not in parent_map:
                continue # Ghost
            method = self.get_method(key)
            parents = parent_map[key]
            if method == 'fulltext':
                compression_parent = None
            else:
                compression_parent = parents[0]
            noeol = 'no-eol' in self.get_options(key)
            index_memo = self.get_position(key)
            result[key] = (index_memo, compression_parent,
                                  parents, (method, noeol))
        return result

    def get_method(self, key):
        """Return compression method of specified key."""
        options = self.get_options(key)
        if 'fulltext' in options:
            return 'fulltext'
        elif 'line-delta' in options:
            return 'line-delta'
        else:
            raise errors.KnitIndexUnknownMethod(self, options)

    def get_options(self, key):
        """Return a list representing options.

        e.g. ['foo', 'bar']
        """
        prefix, suffix = self._split_key(key)
        self._load_prefixes([prefix])
        try:
            return self._kndx_cache[prefix][0][suffix][1]
        except KeyError:
            raise RevisionNotPresent(key, self)

    def get_parent_map(self, keys):
        """Get a map of the parents of keys.

        :param keys: The keys to look up parents for.
        :return: A mapping from keys to parents. Absent keys are absent from
            the mapping.
        """
        # Parse what we need to up front, this potentially trades off I/O
        # locality (.kndx and .knit in the same block group for the same file
        # id) for less checking in inner loops.
        prefixes = set(key[:-1] for key in keys)
        self._load_prefixes(prefixes)
        result = {}
        for key in keys:
            prefix = key[:-1]
            try:
                suffix_parents = self._kndx_cache[prefix][0][key[-1]][4]
            except KeyError:
                pass
            else:
                result[key] = tuple(prefix + (suffix,) for
                    suffix in suffix_parents)
        return result

    def get_position(self, key):
        """Return details needed to access the version.
        
        :return: a tuple (key, data position, size) to hand to the access
            logic to get the record.
        """
        prefix, suffix = self._split_key(key)
        self._load_prefixes([prefix])
        entry = self._kndx_cache[prefix][0][suffix]
        return key, entry[2], entry[3]

    def _init_index(self, path, extra_lines=[]):
        """Initialize an index."""
        sio = StringIO()
        sio.write(self.HEADER)
        sio.writelines(extra_lines)
        sio.seek(0)
        self._transport.put_file_non_atomic(path, sio,
                            create_parent_dir=True)
                           # self._create_parent_dir)
                           # mode=self._file_mode,
                           # dir_mode=self._dir_mode)

    def keys(self):
        """Get all the keys in the collection.
        
        The keys are not ordered.
        """
        result = set()
        # Identify all key prefixes.
        # XXX: A bit hacky, needs polish.
        if type(self._mapper) == ConstantMapper:
            prefixes = [()]
        else:
            relpaths = set()
            for quoted_relpath in self._transport.iter_files_recursive():
                path, ext = os.path.splitext(quoted_relpath)
                relpaths.add(path)
            prefixes = [self._mapper.unmap(path) for path in relpaths]
        self._load_prefixes(prefixes)
        for prefix in prefixes:
            for suffix in self._kndx_cache[prefix][1]:
                result.add(prefix + (suffix,))
        return result
    
    def _load_prefixes(self, prefixes):
        """Load the indices for prefixes."""
        self._check_read()
        for prefix in prefixes:
            if prefix not in self._kndx_cache:
                # the load_data interface writes to these variables.
                self._cache = {}
                self._history = []
                self._filename = prefix
                try:
                    path = self._mapper.map(prefix) + '.kndx'
                    fp = self._transport.get(path)
                    try:
                        # _load_data may raise NoSuchFile if the target knit is
                        # completely empty.
                        _load_data(self, fp)
                    finally:
                        fp.close()
                    self._kndx_cache[prefix] = (self._cache, self._history)
                    del self._cache
                    del self._filename
                    del self._history
                except NoSuchFile:
                    self._kndx_cache[prefix] = ({}, [])
                    if type(self._mapper) == ConstantMapper:
                        # preserve behaviour for revisions.kndx etc.
                        self._init_index(path)
                    del self._cache
                    del self._filename
                    del self._history

    def _partition_keys(self, keys):
        """Turn keys into a dict of prefix:suffix_list."""
        result = {}
        for key in keys:
            prefix_keys = result.setdefault(key[:-1], [])
            prefix_keys.append(key[-1])
        return result

    def _dictionary_compress(self, keys):
        """Dictionary compress keys.
        
        :param keys: The keys to generate references to.
        :return: A string representation of keys. keys which are present are
            dictionary compressed, and others are emitted as fulltext with a
            '.' prefix.
        """
        if not keys:
            return ''
        result_list = []
        prefix = keys[0][:-1]
        cache = self._kndx_cache[prefix][0]
        for key in keys:
            if key[:-1] != prefix:
                # kndx indices cannot refer across partitioned storage.
                raise ValueError("mismatched prefixes for %r" % keys)
            if key[-1] in cache:
                # -- inlined lookup() --
                result_list.append(str(cache[key[-1]][5]))
                # -- end lookup () --
            else:
                result_list.append('.' + key[-1])
        return ' '.join(result_list)

    def _reset_cache(self):
        # Possibly this should be a LRU cache. A dictionary from key_prefix to
        # (cache_dict, history_vector) for parsed kndx files.
        self._kndx_cache = {}
        self._scope = self._get_scope()
        allow_writes = self._allow_writes()
        if allow_writes:
            self._mode = 'w'
        else:
            self._mode = 'r'

    def _split_key(self, key):
        """Split key into a prefix and suffix."""
        return key[:-1], key[-1]


class _KnitGraphIndex(object):
    """A KnitVersionedFiles index layered on GraphIndex."""

    def __init__(self, graph_index, is_locked, deltas=False, parents=True,
        add_callback=None):
        """Construct a KnitGraphIndex on a graph_index.

        :param graph_index: An implementation of bzrlib.index.GraphIndex.
        :param is_locked: A callback to check whether the object should answer
            queries.
        :param deltas: Allow delta-compressed records.
        :param parents: If True, record knits parents, if not do not record 
            parents.
        :param add_callback: If not None, allow additions to the index and call
            this callback with a list of added GraphIndex nodes:
            [(node, value, node_refs), ...]
        :param is_locked: A callback, returns True if the index is locked and
            thus usable.
        """
        self._add_callback = add_callback
        self._graph_index = graph_index
        self._deltas = deltas
        self._parents = parents
        if deltas and not parents:
            # XXX: TODO: Delta tree and parent graph should be conceptually
            # separate.
            raise KnitCorrupt(self, "Cannot do delta compression without "
                "parent tracking.")
        self.has_graph = parents
        self._is_locked = is_locked

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

    def add_records(self, records, random_id=False):
        """Add multiple records to the index.
        
        This function does not insert data into the Immutable GraphIndex
        backing the KnitGraphIndex, instead it prepares data for insertion by
        the caller and checks that it is safe to insert then calls
        self._add_callback with the prepared GraphIndex nodes.

        :param records: a list of tuples:
                         (key, options, access_memo, parents).
        :param random_id: If True the ids being added were randomly generated
            and no check for existence will be performed.
        """
        if not self._add_callback:
            raise errors.ReadOnlyError(self)
        # we hope there are no repositories with inconsistent parentage
        # anymore.

        keys = {}
        for (key, options, access_memo, parents) in records:
            if self._parents:
                parents = tuple(parents)
            index, pos, size = access_memo
            if 'no-eol' in options:
                value = 'N'
            else:
                value = ' '
            value += "%d %d" % (pos, size)
            if not self._deltas:
                if 'line-delta' in options:
                    raise KnitCorrupt(self, "attempt to add line-delta in non-delta knit")
            if self._parents:
                if self._deltas:
                    if 'line-delta' in options:
                        node_refs = (parents, (parents[0],))
                    else:
                        node_refs = (parents, ())
                else:
                    node_refs = (parents, )
            else:
                if parents:
                    raise KnitCorrupt(self, "attempt to add node with parents "
                        "in parentless index.")
                node_refs = ()
            keys[key] = (value, node_refs)
        # check for dups
        if not random_id:
            present_nodes = self._get_entries(keys)
            for (index, key, value, node_refs) in present_nodes:
                if (value[0] != keys[key][0][0] or
                    node_refs != keys[key][1]):
                    raise KnitCorrupt(self, "inconsistent details in add_records"
                        ": %s %s" % ((value, node_refs), keys[key]))
                del keys[key]
        result = []
        if self._parents:
            for key, (value, node_refs) in keys.iteritems():
                result.append((key, value, node_refs))
        else:
            for key, (value, node_refs) in keys.iteritems():
                result.append((key, value))
        self._add_callback(result)
        
    def _check_read(self):
        """raise if reads are not permitted."""
        if not self._is_locked():
            raise errors.ObjectNotLocked(self)

    def _check_write_ok(self):
        """Assert if writes are not permitted."""
        if not self._is_locked():
            raise errors.ObjectNotLocked(self)

    def _compression_parent(self, an_entry):
        # return the key that an_entry is compressed against, or None
        # Grab the second parent list (as deltas implies parents currently)
        compression_parents = an_entry[3][1]
        if not compression_parents:
            return None
        if len(compression_parents) != 1:
            raise AssertionError(
                "Too many compression parents: %r" % compression_parents)
        return compression_parents[0]

    def get_build_details(self, keys):
        """Get the method, index_memo and compression parent for version_ids.

        Ghosts are omitted from the result.

        :param keys: An iterable of keys.
        :return: A dict of key:
            (index_memo, compression_parent, parents, record_details).
            index_memo
                opaque structure to pass to read_records to extract the raw
                data
            compression_parent
                Content that this record is built upon, may be None
            parents
                Logical parents of this node
            record_details
                extra information about the content which needs to be passed to
                Factory.parse_record
        """
        self._check_read()
        result = {}
        entries = self._get_entries(keys, False)
        for entry in entries:
            key = entry[1]
            if not self._parents:
                parents = ()
            else:
                parents = entry[3][0]
            if not self._deltas:
                compression_parent_key = None
            else:
                compression_parent_key = self._compression_parent(entry)
            noeol = (entry[2][0] == 'N')
            if compression_parent_key:
                method = 'line-delta'
            else:
                method = 'fulltext'
            result[key] = (self._node_to_position(entry),
                                  compression_parent_key, parents,
                                  (method, noeol))
        return result

    def _get_entries(self, keys, check_present=False):
        """Get the entries for keys.
        
        :param keys: An iterable of index key tuples.
        """
        keys = set(keys)
        found_keys = set()
        if self._parents:
            for node in self._graph_index.iter_entries(keys):
                yield node
                found_keys.add(node[1])
        else:
            # adapt parentless index to the rest of the code.
            for node in self._graph_index.iter_entries(keys):
                yield node[0], node[1], node[2], ()
                found_keys.add(node[1])
        if check_present:
            missing_keys = keys.difference(found_keys)
            if missing_keys:
                raise RevisionNotPresent(missing_keys.pop(), self)

    def get_method(self, key):
        """Return compression method of specified key."""
        return self._get_method(self._get_node(key))

    def _get_method(self, node):
        if not self._deltas:
            return 'fulltext'
        if self._compression_parent(node):
            return 'line-delta'
        else:
            return 'fulltext'

    def _get_node(self, key):
        try:
            return list(self._get_entries([key]))[0]
        except IndexError:
            raise RevisionNotPresent(key, self)

    def get_options(self, key):
        """Return a list representing options.

        e.g. ['foo', 'bar']
        """
        node = self._get_node(key)
        options = [self._get_method(node)]
        if node[2][0] == 'N':
            options.append('no-eol')
        return options

    def get_parent_map(self, keys):
        """Get a map of the parents of keys.

        :param keys: The keys to look up parents for.
        :return: A mapping from keys to parents. Absent keys are absent from
            the mapping.
        """
        self._check_read()
        nodes = self._get_entries(keys)
        result = {}
        if self._parents:
            for node in nodes:
                result[node[1]] = node[3][0]
        else:
            for node in nodes:
                result[node[1]] = None
        return result

    def get_position(self, key):
        """Return details needed to access the version.
        
        :return: a tuple (index, data position, size) to hand to the access
            logic to get the record.
        """
        node = self._get_node(key)
        return self._node_to_position(node)

    def keys(self):
        """Get all the keys in the collection.
        
        The keys are not ordered.
        """
        self._check_read()
        return [node[1] for node in self._graph_index.iter_all_entries()]
    
    def _node_to_position(self, node):
        """Convert an index value to position details."""
        bits = node[2][1:].split(' ')
        return node[0], int(bits[0]), int(bits[1])


class _KnitKeyAccess(object):
    """Access to records in .knit files."""

    def __init__(self, transport, mapper):
        """Create a _KnitKeyAccess with transport and mapper.

        :param transport: The transport the access object is rooted at.
        :param mapper: The mapper used to map keys to .knit files.
        """
        self._transport = transport
        self._mapper = mapper

    def add_raw_records(self, key_sizes, raw_data):
        """Add raw knit bytes to a storage area.

        The data is spooled to the container writer in one bytes-record per
        raw data item.

        :param sizes: An iterable of tuples containing the key and size of each
            raw data segment.
        :param raw_data: A bytestring containing the data.
        :return: A list of memos to retrieve the record later. Each memo is an
            opaque index memo. For _KnitKeyAccess the memo is (key, pos,
            length), where the key is the record key.
        """
        if type(raw_data) != str:
            raise AssertionError(
                'data must be plain bytes was %s' % type(raw_data))
        result = []
        offset = 0
        # TODO: This can be tuned for writing to sftp and other servers where
        # append() is relatively expensive by grouping the writes to each key
        # prefix.
        for key, size in key_sizes:
            path = self._mapper.map(key)
            try:
                base = self._transport.append_bytes(path + '.knit',
                    raw_data[offset:offset+size])
            except errors.NoSuchFile:
                self._transport.mkdir(osutils.dirname(path))
                base = self._transport.append_bytes(path + '.knit',
                    raw_data[offset:offset+size])
            # if base == 0:
            # chmod.
            offset += size
            result.append((key, base, size))
        return result

    def get_raw_records(self, memos_for_retrieval):
        """Get the raw bytes for a records.

        :param memos_for_retrieval: An iterable containing the access memo for
            retrieving the bytes.
        :return: An iterator over the bytes of the records.
        """
        # first pass, group into same-index request to minimise readv's issued.
        request_lists = []
        current_prefix = None
        for (key, offset, length) in memos_for_retrieval:
            if current_prefix == key[:-1]:
                current_list.append((offset, length))
            else:
                if current_prefix is not None:
                    request_lists.append((current_prefix, current_list))
                current_prefix = key[:-1]
                current_list = [(offset, length)]
        # handle the last entry
        if current_prefix is not None:
            request_lists.append((current_prefix, current_list))
        for prefix, read_vector in request_lists:
            path = self._mapper.map(prefix) + '.knit'
            for pos, data in self._transport.readv(path, read_vector):
                yield data


class _DirectPackAccess(object):
    """Access to data in one or more packs with less translation."""

    def __init__(self, index_to_packs):
        """Create a _DirectPackAccess object.

        :param index_to_packs: A dict mapping index objects to the transport
            and file names for obtaining data.
        """
        self._container_writer = None
        self._write_index = None
        self._indices = index_to_packs

    def add_raw_records(self, key_sizes, raw_data):
        """Add raw knit bytes to a storage area.

        The data is spooled to the container writer in one bytes-record per
        raw data item.

        :param sizes: An iterable of tuples containing the key and size of each
            raw data segment.
        :param raw_data: A bytestring containing the data.
        :return: A list of memos to retrieve the record later. Each memo is an
            opaque index memo. For _DirectPackAccess the memo is (index, pos,
            length), where the index field is the write_index object supplied
            to the PackAccess object.
        """
        if type(raw_data) != str:
            raise AssertionError(
                'data must be plain bytes was %s' % type(raw_data))
        result = []
        offset = 0
        for key, size in key_sizes:
            p_offset, p_length = self._container_writer.add_bytes_record(
                raw_data[offset:offset+size], [])
            offset += size
            result.append((self._write_index, p_offset, p_length))
        return result

    def get_raw_records(self, memos_for_retrieval):
        """Get the raw bytes for a records.

        :param memos_for_retrieval: An iterable containing the (index, pos, 
            length) memo for retrieving the bytes. The Pack access method
            looks up the pack to use for a given record in its index_to_pack
            map.
        :return: An iterator over the bytes of the records.
        """
        # first pass, group into same-index requests
        request_lists = []
        current_index = None
        for (index, offset, length) in memos_for_retrieval:
            if current_index == index:
                current_list.append((offset, length))
            else:
                if current_index is not None:
                    request_lists.append((current_index, current_list))
                current_index = index
                current_list = [(offset, length)]
        # handle the last entry
        if current_index is not None:
            request_lists.append((current_index, current_list))
        for index, offsets in request_lists:
            transport, path = self._indices[index]
            reader = pack.make_readv_reader(transport, path, offsets)
            for names, read_func in reader.iter_records():
                yield read_func(None)

    def set_writer(self, writer, index, transport_packname):
        """Set a writer to use for adding data."""
        if index is not None:
            self._indices[index] = transport_packname
        self._container_writer = writer
        self._write_index = index


# Deprecated, use PatienceSequenceMatcher instead
KnitSequenceMatcher = patiencediff.PatienceSequenceMatcher


def annotate_knit(knit, revision_id):
    """Annotate a knit with no cached annotations.

    This implementation is for knits with no cached annotations.
    It will work for knits with cached annotations, but this is not
    recommended.
    """
    annotator = _KnitAnnotator(knit)
    return iter(annotator.annotate(revision_id))


class _KnitAnnotator(object):
    """Build up the annotations for a text."""

    def __init__(self, knit):
        self._knit = knit

        # Content objects, differs from fulltexts because of how final newlines
        # are treated by knits. the content objects here will always have a
        # final newline
        self._fulltext_contents = {}

        # Annotated lines of specific revisions
        self._annotated_lines = {}

        # Track the raw data for nodes that we could not process yet.
        # This maps the revision_id of the base to a list of children that will
        # annotated from it.
        self._pending_children = {}

        # Nodes which cannot be extracted
        self._ghosts = set()

        # Track how many children this node has, so we know if we need to keep
        # it
        self._annotate_children = {}
        self._compression_children = {}

        self._all_build_details = {}
        # The children => parent revision_id graph
        self._revision_id_graph = {}

        self._heads_provider = None

        self._nodes_to_keep_annotations = set()
        self._generations_until_keep = 100

    def set_generations_until_keep(self, value):
        """Set the number of generations before caching a node.

        Setting this to -1 will cache every merge node, setting this higher
        will cache fewer nodes.
        """
        self._generations_until_keep = value

    def _add_fulltext_content(self, revision_id, content_obj):
        self._fulltext_contents[revision_id] = content_obj
        # TODO: jam 20080305 It might be good to check the sha1digest here
        return content_obj.text()

    def _check_parents(self, child, nodes_to_annotate):
        """Check if all parents have been processed.

        :param child: A tuple of (rev_id, parents, raw_content)
        :param nodes_to_annotate: If child is ready, add it to
            nodes_to_annotate, otherwise put it back in self._pending_children
        """
        for parent_id in child[1]:
            if (parent_id not in self._annotated_lines):
                # This parent is present, but another parent is missing
                self._pending_children.setdefault(parent_id,
                                                  []).append(child)
                break
        else:
            # This one is ready to be processed
            nodes_to_annotate.append(child)

    def _add_annotation(self, revision_id, fulltext, parent_ids,
                        left_matching_blocks=None):
        """Add an annotation entry.

        All parents should already have been annotated.
        :return: A list of children that now have their parents satisfied.
        """
        a = self._annotated_lines
        annotated_parent_lines = [a[p] for p in parent_ids]
        annotated_lines = list(annotate.reannotate(annotated_parent_lines,
            fulltext, revision_id, left_matching_blocks,
            heads_provider=self._get_heads_provider()))
        self._annotated_lines[revision_id] = annotated_lines
        for p in parent_ids:
            ann_children = self._annotate_children[p]
            ann_children.remove(revision_id)
            if (not ann_children
                and p not in self._nodes_to_keep_annotations):
                del self._annotated_lines[p]
                del self._all_build_details[p]
                if p in self._fulltext_contents:
                    del self._fulltext_contents[p]
        # Now that we've added this one, see if there are any pending
        # deltas to be done, certainly this parent is finished
        nodes_to_annotate = []
        for child in self._pending_children.pop(revision_id, []):
            self._check_parents(child, nodes_to_annotate)
        return nodes_to_annotate

    def _get_build_graph(self, key):
        """Get the graphs for building texts and annotations.

        The data you need for creating a full text may be different than the
        data you need to annotate that text. (At a minimum, you need both
        parents to create an annotation, but only need 1 parent to generate the
        fulltext.)

        :return: A list of (key, index_memo) records, suitable for
            passing to read_records_iter to start reading in the raw data fro/
            the pack file.
        """
        if key in self._annotated_lines:
            # Nothing to do
            return []
        pending = set([key])
        records = []
        generation = 0
        kept_generation = 0
        while pending:
            # get all pending nodes
            generation += 1
            this_iteration = pending
            build_details = self._knit._index.get_build_details(this_iteration)
            self._all_build_details.update(build_details)
            # new_nodes = self._knit._index._get_entries(this_iteration)
            pending = set()
            for key, details in build_details.iteritems():
                (index_memo, compression_parent, parents,
                 record_details) = details
                self._revision_id_graph[key] = parents
                records.append((key, index_memo))
                # Do we actually need to check _annotated_lines?
                pending.update(p for p in parents
                                 if p not in self._all_build_details)
                if compression_parent:
                    self._compression_children.setdefault(compression_parent,
                        []).append(key)
                if parents:
                    for parent in parents:
                        self._annotate_children.setdefault(parent,
                            []).append(key)
                    num_gens = generation - kept_generation
                    if ((num_gens >= self._generations_until_keep)
                        and len(parents) > 1):
                        kept_generation = generation
                        self._nodes_to_keep_annotations.add(key)

            missing_versions = this_iteration.difference(build_details.keys())
            self._ghosts.update(missing_versions)
            for missing_version in missing_versions:
                # add a key, no parents
                self._revision_id_graph[missing_version] = ()
                pending.discard(missing_version) # don't look for it
        if self._ghosts.intersection(self._compression_children):
            raise KnitCorrupt(
                "We cannot have nodes which have a ghost compression parent:\n"
                "ghosts: %r\n"
                "compression children: %r"
                % (self._ghosts, self._compression_children))
        # Cleanout anything that depends on a ghost so that we don't wait for
        # the ghost to show up
        for node in self._ghosts:
            if node in self._annotate_children:
                # We won't be building this node
                del self._annotate_children[node]
        # Generally we will want to read the records in reverse order, because
        # we find the parent nodes after the children
        records.reverse()
        return records

    def _annotate_records(self, records):
        """Build the annotations for the listed records."""
        # We iterate in the order read, rather than a strict order requested
        # However, process what we can, and put off to the side things that
        # still need parents, cleaning them up when those parents are
        # processed.
        for (rev_id, record,
             digest) in self._knit._read_records_iter(records):
            if rev_id in self._annotated_lines:
                continue
            parent_ids = self._revision_id_graph[rev_id]
            parent_ids = [p for p in parent_ids if p not in self._ghosts]
            details = self._all_build_details[rev_id]
            (index_memo, compression_parent, parents,
             record_details) = details
            nodes_to_annotate = []
            # TODO: Remove the punning between compression parents, and
            #       parent_ids, we should be able to do this without assuming
            #       the build order
            if len(parent_ids) == 0:
                # There are no parents for this node, so just add it
                # TODO: This probably needs to be decoupled
                fulltext_content, delta = self._knit._factory.parse_record(
                    rev_id, record, record_details, None)
                fulltext = self._add_fulltext_content(rev_id, fulltext_content)
                nodes_to_annotate.extend(self._add_annotation(rev_id, fulltext,
                    parent_ids, left_matching_blocks=None))
            else:
                child = (rev_id, parent_ids, record)
                # Check if all the parents are present
                self._check_parents(child, nodes_to_annotate)
            while nodes_to_annotate:
                # Should we use a queue here instead of a stack?
                (rev_id, parent_ids, record) = nodes_to_annotate.pop()
                (index_memo, compression_parent, parents,
                 record_details) = self._all_build_details[rev_id]
                if compression_parent is not None:
                    comp_children = self._compression_children[compression_parent]
                    if rev_id not in comp_children:
                        raise AssertionError("%r not in compression children %r"
                            % (rev_id, comp_children))
                    # If there is only 1 child, it is safe to reuse this
                    # content
                    reuse_content = (len(comp_children) == 1
                        and compression_parent not in
                            self._nodes_to_keep_annotations)
                    if reuse_content:
                        # Remove it from the cache since it will be changing
                        parent_fulltext_content = self._fulltext_contents.pop(compression_parent)
                        # Make sure to copy the fulltext since it might be
                        # modified
                        parent_fulltext = list(parent_fulltext_content.text())
                    else:
                        parent_fulltext_content = self._fulltext_contents[compression_parent]
                        parent_fulltext = parent_fulltext_content.text()
                    comp_children.remove(rev_id)
                    fulltext_content, delta = self._knit._factory.parse_record(
                        rev_id, record, record_details,
                        parent_fulltext_content,
                        copy_base_content=(not reuse_content))
                    fulltext = self._add_fulltext_content(rev_id,
                                                          fulltext_content)
                    blocks = KnitContent.get_line_delta_blocks(delta,
                            parent_fulltext, fulltext)
                else:
                    fulltext_content = self._knit._factory.parse_fulltext(
                        record, rev_id)
                    fulltext = self._add_fulltext_content(rev_id,
                        fulltext_content)
                    blocks = None
                nodes_to_annotate.extend(
                    self._add_annotation(rev_id, fulltext, parent_ids,
                                     left_matching_blocks=blocks))

    def _get_heads_provider(self):
        """Create a heads provider for resolving ancestry issues."""
        if self._heads_provider is not None:
            return self._heads_provider
        parent_provider = _mod_graph.DictParentsProvider(
            self._revision_id_graph)
        graph_obj = _mod_graph.Graph(parent_provider)
        head_cache = _mod_graph.FrozenHeadsCache(graph_obj)
        self._heads_provider = head_cache
        return head_cache

    def annotate(self, key):
        """Return the annotated fulltext at the given key.

        :param key: The key to annotate.
        """
        if True or len(self._knit._fallback_vfs) > 0:
            # stacked knits can't use the fast path at present.
            return self._simple_annotate(key)
        records = self._get_build_graph(key)
        if key in self._ghosts:
            raise errors.RevisionNotPresent(key, self._knit)
        self._annotate_records(records)
        return self._annotated_lines[key]

    def _simple_annotate(self, key):
        """Return annotated fulltext, rediffing from the full texts.

        This is slow but makes no assumptions about the repository
        being able to produce line deltas.
        """
        # TODO: this code generates a parent maps of present ancestors; it
        # could be split out into a separate method, and probably should use
        # iter_ancestry instead. -- mbp and robertc 20080704
        graph = _mod_graph.Graph(self._knit)
        head_cache = _mod_graph.FrozenHeadsCache(graph)
        search = graph._make_breadth_first_searcher([key])
        keys = set()
        while True:
            try:
                present, ghosts = search.next_with_ghosts()
            except StopIteration:
                break
            keys.update(present)
        parent_map = self._knit.get_parent_map(keys)
        parent_cache = {}
        reannotate = annotate.reannotate
        for record in self._knit.get_record_stream(keys, 'topological', True):
            key = record.key
            fulltext = split_lines(record.get_bytes_as('fulltext'))
            parents = parent_map[key]
            if parents is not None:
                parent_lines = [parent_cache[parent] for parent in parent_map[key]]
            else:
                parent_lines = []
            parent_cache[key] = list(
                reannotate(parent_lines, fulltext, key, None, head_cache))
        try:
            return parent_cache[key]
        except KeyError, e:
            raise errors.RevisionNotPresent(key, self._knit)


try:
    from bzrlib._knit_load_data_c import _load_data_c as _load_data
except ImportError:
    from bzrlib._knit_load_data_py import _load_data_py as _load_data