~bzr-pqm/bzr/bzr.dev

# Copyright (C) 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

"""Indexing facilities."""

__all__ = [
    'CombinedGraphIndex',
    'GraphIndex',
    'GraphIndexBuilder',
    'GraphIndexPrefixAdapter',
    'InMemoryGraphIndex',
    ]

from cStringIO import StringIO
import re

from bzrlib.lazy_import import lazy_import
lazy_import(globals(), """
from bzrlib import trace
from bzrlib.trace import mutter
""")
from bzrlib import debug, errors

_OPTION_KEY_ELEMENTS = "key_elements="
_OPTION_LEN = "len="
_OPTION_NODE_REFS = "node_ref_lists="
_SIGNATURE = "Bazaar Graph Index 1\n"


_whitespace_re = re.compile('[\t\n\x0b\x0c\r\x00 ]')
_newline_null_re = re.compile('[\n\0]')


class GraphIndexBuilder(object):
    """A builder that can build a GraphIndex.
    
    The resulting graph has the structure:
    
    _SIGNATURE OPTIONS NODES NEWLINE
    _SIGNATURE     := 'Bazaar Graph Index 1' NEWLINE
    OPTIONS        := 'node_ref_lists=' DIGITS NEWLINE
    NODES          := NODE*
    NODE           := KEY NULL ABSENT? NULL REFERENCES NULL VALUE NEWLINE
    KEY            := Not-whitespace-utf8
    ABSENT         := 'a'
    REFERENCES     := REFERENCE_LIST (TAB REFERENCE_LIST){node_ref_lists - 1}
    REFERENCE_LIST := (REFERENCE (CR REFERENCE)*)?
    REFERENCE      := DIGITS  ; digits is the byte offset in the index of the
                              ; referenced key.
    VALUE          := no-newline-no-null-bytes
    """

    def __init__(self, reference_lists=0, key_elements=1):
        """Create a GraphIndex builder.

        :param reference_lists: The number of node references lists for each
            entry.
        :param key_elements: The number of bytestrings in each key.
        """
        self.reference_lists = reference_lists
        self._keys = set()
        self._nodes = {}
        self._nodes_by_key = {}
        self._key_length = key_elements

    def _check_key(self, key):
        """Raise BadIndexKey if key is not a valid key for this index."""
        if type(key) != tuple:
            raise errors.BadIndexKey(key)
        if self._key_length != len(key):
            raise errors.BadIndexKey(key)
        for element in key:
            if not element or _whitespace_re.search(element) is not None:
                raise errors.BadIndexKey(element)

    def add_node(self, key, value, references=()):
        """Add a node to the index.

        :param key: The key. keys are non-empty tuples containing
            as many whitespace-free utf8 bytestrings as the key length
            defined for this index.
        :param references: An iterable of iterables of keys. Each is a
            reference to another key.
        :param value: The value to associate with the key. It may be any
            bytes as long as it does not contain \0 or \n.
        """
        self._check_key(key)
        if _newline_null_re.search(value) is not None:
            raise errors.BadIndexValue(value)
        if len(references) != self.reference_lists:
            raise errors.BadIndexValue(references)
        node_refs = []
        for reference_list in references:
            for reference in reference_list:
                self._check_key(reference)
                if reference not in self._nodes:
                    self._nodes[reference] = ('a', (), '')
            node_refs.append(tuple(reference_list))
        if key in self._nodes and self._nodes[key][0] == '':
            raise errors.BadIndexDuplicateKey(key, self)
        self._nodes[key] = ('', tuple(node_refs), value)
        self._keys.add(key)
        if self._key_length > 1:
            key_dict = self._nodes_by_key
            if self.reference_lists:
                key_value = key, value, tuple(node_refs)
            else:
                key_value = key, value
            # possibly should do this on-demand, but it seems likely it is 
            # always wanted
            # For a key of (foo, bar, baz) create
            # _nodes_by_key[foo][bar][baz] = key_value
            for subkey in key[:-1]:
                key_dict = key_dict.setdefault(subkey, {})
            key_dict[key[-1]] = key_value

    def finish(self):
        lines = [_SIGNATURE]
        lines.append(_OPTION_NODE_REFS + str(self.reference_lists) + '\n')
        lines.append(_OPTION_KEY_ELEMENTS + str(self._key_length) + '\n')
        lines.append(_OPTION_LEN + str(len(self._keys)) + '\n')
        prefix_length = sum(len(x) for x in lines)
        # references are byte offsets. To avoid having to do nasty
        # polynomial work to resolve offsets (references to later in the 
        # file cannot be determined until all the inbetween references have
        # been calculated too) we pad the offsets with 0's to make them be
        # of consistent length. Using binary offsets would break the trivial
        # file parsing.
        # to calculate the width of zero's needed we do three passes:
        # one to gather all the non-reference data and the number of references.
        # one to pad all the data with reference-length and determine entry
        # addresses.
        # One to serialise.
        
        # forward sorted by key. In future we may consider topological sorting,
        # at the cost of table scans for direct lookup, or a second index for
        # direct lookup
        nodes = sorted(self._nodes.items())
        # if we do not prepass, we don't know how long it will be up front.
        expected_bytes = None
        # we only need to pre-pass if we have reference lists at all.
        if self.reference_lists:
            key_offset_info = []
            non_ref_bytes = prefix_length
            total_references = 0
            # TODO use simple multiplication for the constants in this loop.
            for key, (absent, references, value) in nodes:
                # record the offset known *so far* for this key:
                # the non reference bytes to date, and the total references to
                # date - saves reaccumulating on the second pass
                key_offset_info.append((key, non_ref_bytes, total_references))
                # key is literal, value is literal, there are 3 null's, 1 NL
                # key is variable length tuple, \x00 between elements
                non_ref_bytes += sum(len(element) for element in key)
                if self._key_length > 1:
                    non_ref_bytes += self._key_length - 1
                # value is literal bytes, there are 3 null's, 1 NL.
                non_ref_bytes += len(value) + 3 + 1
                # one byte for absent if set.
                if absent:
                    non_ref_bytes += 1
                elif self.reference_lists:
                    # (ref_lists -1) tabs
                    non_ref_bytes += self.reference_lists - 1
                    # (ref-1 cr's per ref_list)
                    for ref_list in references:
                        # how many references across the whole file?
                        total_references += len(ref_list)
                        # accrue reference separators
                        if ref_list:
                            non_ref_bytes += len(ref_list) - 1
            # how many digits are needed to represent the total byte count?
            digits = 1
            possible_total_bytes = non_ref_bytes + total_references*digits
            while 10 ** digits < possible_total_bytes:
                digits += 1
                possible_total_bytes = non_ref_bytes + total_references*digits
            expected_bytes = possible_total_bytes + 1 # terminating newline
            # resolve key addresses.
            key_addresses = {}
            for key, non_ref_bytes, total_references in key_offset_info:
                key_addresses[key] = non_ref_bytes + total_references*digits
            # serialise
            format_string = '%%0%sd' % digits
        for key, (absent, references, value) in nodes:
            flattened_references = []
            for ref_list in references:
                ref_addresses = []
                for reference in ref_list:
                    ref_addresses.append(format_string % key_addresses[reference])
                flattened_references.append('\r'.join(ref_addresses))
            string_key = '\x00'.join(key)
            lines.append("%s\x00%s\x00%s\x00%s\n" % (string_key, absent,
                '\t'.join(flattened_references), value))
        lines.append('\n')
        result = StringIO(''.join(lines))
        if expected_bytes and len(result.getvalue()) != expected_bytes:
            raise errors.BzrError('Failed index creation. Internal error:'
                ' mismatched output length and expected length: %d %d' %
                (len(result.getvalue()), expected_bytes))
        return StringIO(''.join(lines))


class GraphIndex(object):
    """An index for data with embedded graphs.
 
    The index maps keys to a list of key reference lists, and a value.
    Each node has the same number of key reference lists. Each key reference
    list can be empty or an arbitrary length. The value is an opaque NULL
    terminated string without any newlines. The storage of the index is 
    hidden in the interface: keys and key references are always tuples of
    bytestrings, never the internal representation (e.g. dictionary offsets).

    It is presumed that the index will not be mutated - it is static data.

    Successive iter_all_entries calls will read the entire index each time.
    Additionally, iter_entries calls will read the index linearly until the
    desired keys are found. XXX: This must be fixed before the index is
    suitable for production use. :XXX
    """

    def __init__(self, transport, name):
        """Open an index called name on transport.

        :param transport: A bzrlib.transport.Transport.
        :param name: A path to provide to transport API calls.
        """
        self._transport = transport
        self._name = name
        self._nodes = None
        self._key_count = None
        self._keys_by_offset = None
        self._nodes_by_key = None

    def _buffer_all(self):
        """Buffer all the index data.

        Mutates self._nodes and self.keys_by_offset.
        """
        if 'index' in debug.debug_flags:
            mutter('Reading entire index %s', self._transport.abspath(self._name))
        stream = self._transport.get(self._name)
        self._read_prefix(stream)
        expected_elements = 3 + self._key_length
        line_count = 0
        # raw data keyed by offset
        self._keys_by_offset = {}
        # ready-to-return key:value or key:value, node_ref_lists
        self._nodes = {}
        self._nodes_by_key = {}
        trailers = 0
        pos = stream.tell()
        for line in stream.readlines():
            if line == '\n':
                trailers += 1
                continue
            elements = line.split('\0')
            if len(elements) != expected_elements:
                raise errors.BadIndexData(self)
            # keys are tuples
            key = tuple(elements[:self._key_length])
            absent, references, value = elements[-3:]
            value = value[:-1] # remove the newline
            ref_lists = []
            for ref_string in references.split('\t'):
                ref_lists.append(tuple([
                    int(ref) for ref in ref_string.split('\r') if ref
                    ]))
            ref_lists = tuple(ref_lists)
            self._keys_by_offset[pos] = (key, absent, ref_lists, value)
            pos += len(line)
        for key, absent, references, value in self._keys_by_offset.itervalues():
            if absent:
                continue
            # resolve references:
            if self.node_ref_lists:
                node_refs = []
                for ref_list in references:
                    node_refs.append(tuple([self._keys_by_offset[ref][0] for ref in ref_list]))
                node_value = (value, tuple(node_refs))
            else:
                node_value = value
            self._nodes[key] = node_value
            if self._key_length > 1:
                subkey = list(reversed(key[:-1]))
                key_dict = self._nodes_by_key
                if self.node_ref_lists:
                    key_value = key, node_value[0], node_value[1]
                else:
                    key_value = key, node_value
                # possibly should do this on-demand, but it seems likely it is 
                # always wanted
                # For a key of (foo, bar, baz) create
                # _nodes_by_key[foo][bar][baz] = key_value
                for subkey in key[:-1]:
                    key_dict = key_dict.setdefault(subkey, {})
                key_dict[key[-1]] = key_value
        # cache the keys for quick set intersections
        self._keys = set(self._nodes)
        if trailers != 1:
            # there must be one line - the empty trailer line.
            raise errors.BadIndexData(self)

    def iter_all_entries(self):
        """Iterate over all keys within the index.

        :return: An iterable of (key, value) or (key, value, reference_lists).
            The former tuple is used when there are no reference lists in the
            index, making the API compatible with simple key:value index types.
            There is no defined order for the result iteration - it will be in
            the most efficient order for the index.
        """
        if 'evil' in debug.debug_flags:
            trace.mutter_callsite(2,
                "iter_all_entries scales with size of history.")
        if self._nodes is None:
            self._buffer_all()
        if self.node_ref_lists:
            for key, (value, node_ref_lists) in self._nodes.iteritems():
                yield self, key, value, node_ref_lists
        else:
            for key, value in self._nodes.iteritems():
                yield self, key, value

    def _read_prefix(self, stream):
        signature = stream.read(len(self._signature()))
        if not signature == self._signature():
            raise errors.BadIndexFormatSignature(self._name, GraphIndex)
        options_line = stream.readline()
        if not options_line.startswith(_OPTION_NODE_REFS):
            raise errors.BadIndexOptions(self)
        try:
            self.node_ref_lists = int(options_line[len(_OPTION_NODE_REFS):-1])
        except ValueError:
            raise errors.BadIndexOptions(self)
        options_line = stream.readline()
        if not options_line.startswith(_OPTION_KEY_ELEMENTS):
            raise errors.BadIndexOptions(self)
        try:
            self._key_length = int(options_line[len(_OPTION_KEY_ELEMENTS):-1])
        except ValueError:
            raise errors.BadIndexOptions(self)
        options_line = stream.readline()
        if not options_line.startswith(_OPTION_LEN):
            raise errors.BadIndexOptions(self)
        try:
            self._key_count = int(options_line[len(_OPTION_LEN):-1])
        except ValueError:
            raise errors.BadIndexOptions(self)

    def iter_entries(self, keys):
        """Iterate over keys within the index.

        :param keys: An iterable providing the keys to be retrieved.
        :return: An iterable as per iter_all_entries, but restricted to the
            keys supplied. No additional keys will be returned, and every
            key supplied that is in the index will be returned.
        """
        keys = set(keys)
        if not keys:
            return
        if self._nodes is None:
            self._buffer_all()
        keys = keys.intersection(self._keys)
        if self.node_ref_lists:
            for key in keys:
                value, node_refs = self._nodes[key]
                yield self, key, value, node_refs
        else:
            for key in keys:
                yield self, key, self._nodes[key]

    def iter_entries_prefix(self, keys):
        """Iterate over keys within the index using prefix matching.

        Prefix matching is applied within the tuple of a key, not to within
        the bytestring of each key element. e.g. if you have the keys ('foo',
        'bar'), ('foobar', 'gam') and do a prefix search for ('foo', None) then
        only the former key is returned.

        :param keys: An iterable providing the key prefixes to be retrieved.
            Each key prefix takes the form of a tuple the length of a key, but
            with the last N elements 'None' rather than a regular bytestring.
            The first element cannot be 'None'.
        :return: An iterable as per iter_all_entries, but restricted to the
            keys with a matching prefix to those supplied. No additional keys
            will be returned, and every match that is in the index will be
            returned.
        """
        keys = set(keys)
        if not keys:
            return
        # load data - also finds key lengths
        if self._nodes is None:
            self._buffer_all()
        if self._key_length == 1:
            for key in keys:
                # sanity check
                if key[0] is None:
                    raise errors.BadIndexKey(key)
                if len(key) != self._key_length:
                    raise errors.BadIndexKey(key)
                if self.node_ref_lists:
                    value, node_refs = self._nodes[key]
                    yield self, key, value, node_refs
                else:
                    yield self, key, self._nodes[key]
            return
        for key in keys:
            # sanity check
            if key[0] is None:
                raise errors.BadIndexKey(key)
            if len(key) != self._key_length:
                raise errors.BadIndexKey(key)
            # find what it refers to:
            key_dict = self._nodes_by_key
            elements = list(key)
            # find the subdict whose contents should be returned.
            try:
                while len(elements) and elements[0] is not None:
                    key_dict = key_dict[elements[0]]
                    elements.pop(0)
            except KeyError:
                # a non-existant lookup.
                continue
            if len(elements):
                dicts = [key_dict]
                while dicts:
                    key_dict = dicts.pop(-1)
                    # can't be empty or would not exist
                    item, value = key_dict.iteritems().next()
                    if type(value) == dict:
                        # push keys 
                        dicts.extend(key_dict.itervalues())
                    else:
                        # yield keys
                        for value in key_dict.itervalues():
                            # each value is the key:value:node refs tuple
                            # ready to yield.
                            yield (self, ) + value
            else:
                # the last thing looked up was a terminal element
                yield (self, ) + key_dict

    def key_count(self):
        """Return an estimate of the number of keys in this index.
        
        For GraphIndex the estimate is exact.
        """
        if self._key_count is None:
            # really this should just read the prefix
            self._buffer_all()
        return self._key_count

    def _signature(self):
        """The file signature for this index type."""
        return _SIGNATURE

    def validate(self):
        """Validate that everything in the index can be accessed."""
        # iter_all validates completely at the moment, so just do that.
        for node in self.iter_all_entries():
            pass


class CombinedGraphIndex(object):
    """A GraphIndex made up from smaller GraphIndices.
    
    The backing indices must implement GraphIndex, and are presumed to be
    static data.

    Queries against the combined index will be made against the first index,
    and then the second and so on. The order of index's can thus influence
    performance significantly. For example, if one index is on local disk and a
    second on a remote server, the local disk index should be before the other
    in the index list.
    """

    def __init__(self, indices):
        """Create a CombinedGraphIndex backed by indices.

        :param indices: An ordered list of indices to query for data.
        """
        self._indices = indices

    def insert_index(self, pos, index):
        """Insert a new index in the list of indices to query.

        :param pos: The position to insert the index.
        :param index: The index to insert.
        """
        self._indices.insert(pos, index)

    def iter_all_entries(self):
        """Iterate over all keys within the index

        Duplicate keys across child indices are presumed to have the same
        value and are only reported once.

        :return: An iterable of (key, reference_lists, value). There is no
            defined order for the result iteration - it will be in the most
            efficient order for the index.
        """
        seen_keys = set()
        for index in self._indices:
            for node in index.iter_all_entries():
                if node[1] not in seen_keys:
                    yield node
                    seen_keys.add(node[1])

    def iter_entries(self, keys):
        """Iterate over keys within the index.

        Duplicate keys across child indices are presumed to have the same
        value and are only reported once.

        :param keys: An iterable providing the keys to be retrieved.
        :return: An iterable of (key, reference_lists, value). There is no
            defined order for the result iteration - it will be in the most
            efficient order for the index.
        """
        keys = set(keys)
        for index in self._indices:
            if not keys:
                return
            for node in index.iter_entries(keys):
                keys.remove(node[1])
                yield node

    def iter_entries_prefix(self, keys):
        """Iterate over keys within the index using prefix matching.

        Duplicate keys across child indices are presumed to have the same
        value and are only reported once.

        Prefix matching is applied within the tuple of a key, not to within
        the bytestring of each key element. e.g. if you have the keys ('foo',
        'bar'), ('foobar', 'gam') and do a prefix search for ('foo', None) then
        only the former key is returned.

        :param keys: An iterable providing the key prefixes to be retrieved.
            Each key prefix takes the form of a tuple the length of a key, but
            with the last N elements 'None' rather than a regular bytestring.
            The first element cannot be 'None'.
        :return: An iterable as per iter_all_entries, but restricted to the
            keys with a matching prefix to those supplied. No additional keys
            will be returned, and every match that is in the index will be
            returned.
        """
        keys = set(keys)
        if not keys:
            return
        seen_keys = set()
        for index in self._indices:
            for node in index.iter_entries_prefix(keys):
                if node[1] in seen_keys:
                    continue
                seen_keys.add(node[1])
                yield node

    def key_count(self):
        """Return an estimate of the number of keys in this index.
        
        For CombinedGraphIndex this is approximated by the sum of the keys of
        the child indices. As child indices may have duplicate keys this can
        have a maximum error of the number of child indices * largest number of
        keys in any index.
        """
        return sum((index.key_count() for index in self._indices), 0)

    def validate(self):
        """Validate that everything in the index can be accessed."""
        for index in self._indices:
            index.validate()


class InMemoryGraphIndex(GraphIndexBuilder):
    """A GraphIndex which operates entirely out of memory and is mutable.

    This is designed to allow the accumulation of GraphIndex entries during a
    single write operation, where the accumulated entries need to be immediately
    available - for example via a CombinedGraphIndex.
    """

    def add_nodes(self, nodes):
        """Add nodes to the index.

        :param nodes: An iterable of (key, node_refs, value) entries to add.
        """
        if self.reference_lists:
            for (key, value, node_refs) in nodes:
                self.add_node(key, value, node_refs)
        else:
            for (key, value) in nodes:
                self.add_node(key, value)

    def iter_all_entries(self):
        """Iterate over all keys within the index

        :return: An iterable of (key, reference_lists, value). There is no
            defined order for the result iteration - it will be in the most
            efficient order for the index (in this case dictionary hash order).
        """
        if 'evil' in debug.debug_flags:
            trace.mutter_callsite(2,
                "iter_all_entries scales with size of history.")
        if self.reference_lists:
            for key, (absent, references, value) in self._nodes.iteritems():
                if not absent:
                    yield self, key, value, references
        else:
            for key, (absent, references, value) in self._nodes.iteritems():
                if not absent:
                    yield self, key, value

    def iter_entries(self, keys):
        """Iterate over keys within the index.

        :param keys: An iterable providing the keys to be retrieved.
        :return: An iterable of (key, reference_lists, value). There is no
            defined order for the result iteration - it will be in the most
            efficient order for the index (keys iteration order in this case).
        """
        keys = set(keys)
        if self.reference_lists:
            for key in keys.intersection(self._keys):
                node = self._nodes[key]
                if not node[0]:
                    yield self, key, node[2], node[1]
        else:
            for key in keys.intersection(self._keys):
                node = self._nodes[key]
                if not node[0]:
                    yield self, key, node[2]

    def iter_entries_prefix(self, keys):
        """Iterate over keys within the index using prefix matching.

        Prefix matching is applied within the tuple of a key, not to within
        the bytestring of each key element. e.g. if you have the keys ('foo',
        'bar'), ('foobar', 'gam') and do a prefix search for ('foo', None) then
        only the former key is returned.

        :param keys: An iterable providing the key prefixes to be retrieved.
            Each key prefix takes the form of a tuple the length of a key, but
            with the last N elements 'None' rather than a regular bytestring.
            The first element cannot be 'None'.
        :return: An iterable as per iter_all_entries, but restricted to the
            keys with a matching prefix to those supplied. No additional keys
            will be returned, and every match that is in the index will be
            returned.
        """
        # XXX: To much duplication with the GraphIndex class; consider finding
        # a good place to pull out the actual common logic.
        keys = set(keys)
        if not keys:
            return
        if self._key_length == 1:
            for key in keys:
                # sanity check
                if key[0] is None:
                    raise errors.BadIndexKey(key)
                if len(key) != self._key_length:
                    raise errors.BadIndexKey(key)
                node = self._nodes[key]
                if node[0]:
                    continue 
                if self.reference_lists:
                    yield self, key, node[2], node[1]
                else:
                    yield self, key, node[2]
            return
        for key in keys:
            # sanity check
            if key[0] is None:
                raise errors.BadIndexKey(key)
            if len(key) != self._key_length:
                raise errors.BadIndexKey(key)
            # find what it refers to:
            key_dict = self._nodes_by_key
            elements = list(key)
            # find the subdict to return
            try:
                while len(elements) and elements[0] is not None:
                    key_dict = key_dict[elements[0]]
                    elements.pop(0)
            except KeyError:
                # a non-existant lookup.
                continue
            if len(elements):
                dicts = [key_dict]
                while dicts:
                    key_dict = dicts.pop(-1)
                    # can't be empty or would not exist
                    item, value = key_dict.iteritems().next()
                    if type(value) == dict:
                        # push keys 
                        dicts.extend(key_dict.itervalues())
                    else:
                        # yield keys
                        for value in key_dict.itervalues():
                            yield (self, ) + value
            else:
                yield (self, ) + key_dict

    def key_count(self):
        """Return an estimate of the number of keys in this index.
        
        For InMemoryGraphIndex the estimate is exact.
        """
        return len(self._keys)

    def validate(self):
        """In memory index's have no known corruption at the moment."""


class GraphIndexPrefixAdapter(object):
    """An adapter between GraphIndex with different key lengths.

    Queries against this will emit queries against the adapted Graph with the
    prefix added, queries for all items use iter_entries_prefix. The returned
    nodes will have their keys and node references adjusted to remove the 
    prefix. Finally, an add_nodes_callback can be supplied - when called the
    nodes and references being added will have prefix prepended.
    """

    def __init__(self, adapted, prefix, missing_key_length,
        add_nodes_callback=None):
        """Construct an adapter against adapted with prefix."""
        self.adapted = adapted
        self.prefix_key = prefix + (None,)*missing_key_length
        self.prefix = prefix
        self.prefix_len = len(prefix)
        self.add_nodes_callback = add_nodes_callback

    def add_nodes(self, nodes):
        """Add nodes to the index.

        :param nodes: An iterable of (key, node_refs, value) entries to add.
        """
        # save nodes in case its an iterator
        nodes = tuple(nodes)
        translated_nodes = []
        try:
            # Add prefix_key to each reference node_refs is a tuple of tuples,
            # so split it apart, and add prefix_key to the internal reference
            for (key, value, node_refs) in nodes:
                adjusted_references = (
                    tuple(tuple(self.prefix + ref_node for ref_node in ref_list)
                        for ref_list in node_refs))
                translated_nodes.append((self.prefix + key, value,
                    adjusted_references))
        except ValueError:
            # XXX: TODO add an explicit interface for getting the reference list
            # status, to handle this bit of user-friendliness in the API more 
            # explicitly.
            for (key, value) in nodes:
                translated_nodes.append((self.prefix + key, value))
        self.add_nodes_callback(translated_nodes)

    def add_node(self, key, value, references=()):
        """Add a node to the index.

        :param key: The key. keys are non-empty tuples containing
            as many whitespace-free utf8 bytestrings as the key length
            defined for this index.
        :param references: An iterable of iterables of keys. Each is a
            reference to another key.
        :param value: The value to associate with the key. It may be any
            bytes as long as it does not contain \0 or \n.
        """
        self.add_nodes(((key, value, references), ))

    def _strip_prefix(self, an_iter):
        """Strip prefix data from nodes and return it."""
        for node in an_iter:
            # cross checks
            if node[1][:self.prefix_len] != self.prefix:
                raise errors.BadIndexData(self)
            for ref_list in node[3]:
                for ref_node in ref_list:
                    if ref_node[:self.prefix_len] != self.prefix:
                        raise errors.BadIndexData(self)
            yield node[0], node[1][self.prefix_len:], node[2], (
                tuple(tuple(ref_node[self.prefix_len:] for ref_node in ref_list)
                for ref_list in node[3]))

    def iter_all_entries(self):
        """Iterate over all keys within the index

        iter_all_entries is implemented against the adapted index using
        iter_entries_prefix.

        :return: An iterable of (key, reference_lists, value). There is no
            defined order for the result iteration - it will be in the most
            efficient order for the index (in this case dictionary hash order).
        """
        return self._strip_prefix(self.adapted.iter_entries_prefix([self.prefix_key]))

    def iter_entries(self, keys):
        """Iterate over keys within the index.

        :param keys: An iterable providing the keys to be retrieved.
        :return: An iterable of (key, reference_lists, value). There is no
            defined order for the result iteration - it will be in the most
            efficient order for the index (keys iteration order in this case).
        """
        return self._strip_prefix(self.adapted.iter_entries(
            self.prefix + key for key in keys))

    def iter_entries_prefix(self, keys):
        """Iterate over keys within the index using prefix matching.

        Prefix matching is applied within the tuple of a key, not to within
        the bytestring of each key element. e.g. if you have the keys ('foo',
        'bar'), ('foobar', 'gam') and do a prefix search for ('foo', None) then
        only the former key is returned.

        :param keys: An iterable providing the key prefixes to be retrieved.
            Each key prefix takes the form of a tuple the length of a key, but
            with the last N elements 'None' rather than a regular bytestring.
            The first element cannot be 'None'.
        :return: An iterable as per iter_all_entries, but restricted to the
            keys with a matching prefix to those supplied. No additional keys
            will be returned, and every match that is in the index will be
            returned.
        """
        return self._strip_prefix(self.adapted.iter_entries_prefix(
            self.prefix + key for key in keys))

    def key_count(self):
        """Return an estimate of the number of keys in this index.
        
        For GraphIndexPrefixAdapter this is relatively expensive - key
        iteration with the prefix is done.
        """
        return len(list(self.iter_all_entries()))

    def validate(self):
        """Call the adapted's validate."""
        self.adapted.validate()