source: trunk/src/allmydata/dirnode.py

"""Directory Node implementation.

Ported to Python 3.
"""

from past.builtins import unicode

import time

from zope.interface import implementer
from twisted.internet import defer
from foolscap.api import fireEventually

from allmydata.crypto import aes
from allmydata.deep_stats import DeepStats
from allmydata.mutable.common import NotWriteableError
from allmydata.mutable.filenode import MutableFileNode
from allmydata.unknown import UnknownNode, strip_prefix_for_ro
from allmydata.interfaces import IFilesystemNode, IDirectoryNode, IFileNode, \
     ExistingChildError, NoSuchChildError, ICheckable, IDeepCheckable, \
     MustBeDeepImmutableError, CapConstraintError, ChildOfWrongTypeError
from allmydata.check_results import DeepCheckResults, \
     DeepCheckAndRepairResults
from allmydata.monitor import Monitor
from allmydata.util import hashutil, base32, log, jsonbytes as json
from allmydata.util.encodingutil import quote_output, normalize
from allmydata.util.assertutil import precondition
from allmydata.util.netstring import netstring, split_netstring
from allmydata.util.consumer import download_to_data
from allmydata.uri import wrap_dirnode_cap
from allmydata.util.dictutil import AuxValueDict

from eliot import (
    ActionType,
    Field,
)
from eliot.twisted import (
    DeferredContext,
)

NAME = Field.for_types(
    u"name",
    # Make sure this works on Python 2; with str, it gets Future str which
    # breaks Eliot.
    [unicode],
    u"The name linking the parent to this node.",
)

METADATA = Field.for_types(
    u"metadata",
    [dict],
    u"Data about a node.",
)

OVERWRITE = Field.for_types(
    u"overwrite",
    [bool],
    u"True to replace an existing file of the same name, "
    u"false to fail with a collision error.",
)

ADD_FILE = ActionType(
    u"dirnode:add-file",
    [NAME, METADATA, OVERWRITE],
    [],
    u"Add a new file as a child of a directory.",
)


class _OnlyFiles(object):
    """Marker for replacement option of only replacing files."""

ONLY_FILES = _OnlyFiles()


def update_metadata(metadata, new_metadata, now):
    """Updates 'metadata' in-place with the information in 'new_metadata'.

    Timestamps are set according to the time 'now'.
    """

    if metadata is None:
        metadata = {}

    old_ctime = None
    if 'ctime' in metadata:
        old_ctime = metadata['ctime']

    if new_metadata is not None:
        # Overwrite all metadata.
        newmd = new_metadata.copy()

        # Except 'tahoe'.
        if 'tahoe' in newmd:
            del newmd['tahoe']
        if 'tahoe' in metadata:
            newmd['tahoe'] = metadata['tahoe']

        metadata = newmd

    # update timestamps
    sysmd = metadata.get('tahoe', {})
    if 'linkcrtime' not in sysmd:
        # In Tahoe < 1.4.0 we used the word 'ctime' to mean what Tahoe >= 1.4.0
        # calls 'linkcrtime'. This field is only used if it was in the old metadata,
        # and 'tahoe:linkcrtime' was not.
        if old_ctime is not None:
            sysmd['linkcrtime'] = old_ctime
        else:
            sysmd['linkcrtime'] = now

    sysmd['linkmotime'] = now
    metadata['tahoe'] = sysmd

    return metadata


# TODO: {Deleter,MetadataSetter,Adder}.modify all start by unpacking the
# contents and end by repacking them. It might be better to apply them to
# the unpacked contents.

class Deleter(object):
    def __init__(self, node, namex, must_exist=True, must_be_directory=False, must_be_file=False):
        self.node = node
        self.name = normalize(namex)
        self.must_exist = must_exist
        self.must_be_directory = must_be_directory
        self.must_be_file = must_be_file

    def modify(self, old_contents, servermap, first_time):
        children = self.node._unpack_contents(old_contents)
        if self.name not in children:
            if first_time and self.must_exist:
                raise NoSuchChildError(self.name)
            self.old_child = None
            return None
        self.old_child, metadata = children[self.name]

        # Unknown children can be removed regardless of must_be_directory or must_be_file.
        if self.must_be_directory and IFileNode.providedBy(self.old_child):
            raise ChildOfWrongTypeError("delete required a directory, not a file")
        if self.must_be_file and IDirectoryNode.providedBy(self.old_child):
            raise ChildOfWrongTypeError("delete required a file, not a directory")

        del children[self.name]
        new_contents = self.node._pack_contents(children)
        return new_contents


class MetadataSetter(object):
    def __init__(self, node, namex, metadata, create_readonly_node=None):
        self.node = node
        self.name = normalize(namex)
        self.metadata = metadata
        self.create_readonly_node = create_readonly_node

    def modify(self, old_contents, servermap, first_time):
        children = self.node._unpack_contents(old_contents)
        name = self.name
        if name not in children:
            raise NoSuchChildError(name)

        now = time.time()
        child = children[name][0]

        metadata = update_metadata(children[name][1].copy(), self.metadata, now)
        if self.create_readonly_node and metadata.get('no-write', False):
            child = self.create_readonly_node(child, name)

        children[name] = (child, metadata)
        new_contents = self.node._pack_contents(children)
        return new_contents


class Adder(object):
    def __init__(self, node, entries=None, overwrite=True, create_readonly_node=None):
        """
        :param overwrite: Either True (allow overwriting anything existing),
            False (don't allow overwriting), or ONLY_FILES (only files can be
            overwritten).
        """
        self.node = node
        if entries is None:
            entries = {}
        precondition(isinstance(entries, dict), entries)
        precondition(overwrite in (True, False, ONLY_FILES), overwrite)
        # keys of 'entries' may not be normalized.
        self.entries = entries
        self.overwrite = overwrite
        self.create_readonly_node = create_readonly_node

    def set_node(self, namex, node, metadata):
        precondition(IFilesystemNode.providedBy(node), node)
        self.entries[namex] = (node, metadata)

    def modify(self, old_contents, servermap, first_time):
        children = self.node._unpack_contents(old_contents)
        now = time.time()
        for (namex, (child, new_metadata)) in list(self.entries.items()):
            name = normalize(namex)
            precondition(IFilesystemNode.providedBy(child), child)

            # Strictly speaking this is redundant because we would raise the
            # error again in _pack_normalized_children.
            child.raise_error()

            metadata = None
            if name in children:
                if not self.overwrite:
                    raise ExistingChildError("child %s already exists" % quote_output(name, encoding='utf-8'))

                if self.overwrite == ONLY_FILES and IDirectoryNode.providedBy(children[name][0]):
                    raise ExistingChildError("child %s already exists as a directory" % quote_output(name, encoding='utf-8'))
                metadata = children[name][1].copy()

            metadata = update_metadata(metadata, new_metadata, now)
            if self.create_readonly_node and metadata.get('no-write', False):
                child = self.create_readonly_node(child, name)

            children[name] = (child, metadata)
        new_contents = self.node._pack_contents(children)
        return new_contents

def _encrypt_rw_uri(writekey, rw_uri):
    precondition(isinstance(rw_uri, bytes), rw_uri)
    precondition(isinstance(writekey, bytes), writekey)

    salt = hashutil.mutable_rwcap_salt_hash(rw_uri)
    key = hashutil.mutable_rwcap_key_hash(salt, writekey)
    encryptor = aes.create_encryptor(key)
    crypttext = aes.encrypt_data(encryptor, rw_uri)
    mac = hashutil.hmac(key, salt + crypttext)
    assert len(mac) == 32
    return salt + crypttext + mac
    # The MAC is not checked by readers in Tahoe >= 1.3.0, but we still
    # produce it for the sake of older readers.

def pack_children(childrenx, writekey, deep_immutable=False):
    # initial_children must have metadata (i.e. {} instead of None)
    children = {}
    for (namex, (node, metadata)) in list(childrenx.items()):
        precondition(isinstance(metadata, dict),
                     "directory creation requires metadata to be a dict, not None", metadata)
        children[normalize(namex)] = (node, metadata)

    return _pack_normalized_children(children, writekey=writekey, deep_immutable=deep_immutable)


ZERO_LEN_NETSTR=netstring(b'')
def _pack_normalized_children(children, writekey, deep_immutable=False):
    """Take a dict that maps:
         children[unicode_nfc_name] = (IFileSystemNode, metadata_dict)
    and pack it into a single string, for use as the contents of the backing
    file. This is the same format as is returned by _unpack_contents. I also
    accept an AuxValueDict, in which case I'll use the auxilliary cached data
    as the pre-packed entry, which is faster than re-packing everything each
    time.

    If writekey is provided then I will superencrypt the child's writecap with
    writekey.

    If deep_immutable is True, I will require that all my children are deeply
    immutable, and will raise a MustBeDeepImmutableError if not.
    """
    precondition((writekey is None) or isinstance(writekey, bytes), writekey)

    has_aux = isinstance(children, AuxValueDict)
    entries = []
    for name in sorted(children.keys()):
        assert isinstance(name, str)
        entry = None
        (child, metadata) = children[name]
        child.raise_error()
        if deep_immutable and not child.is_allowed_in_immutable_directory():
            raise MustBeDeepImmutableError(
                "child %r is not allowed in an immutable directory" % (name,),
                name)
        if has_aux:
            entry = children.get_aux(name)
        if not entry:
            assert IFilesystemNode.providedBy(child), (name,child)
            assert isinstance(metadata, dict)
            rw_uri = child.get_write_uri()
            if rw_uri is None:
                rw_uri = b""
            assert isinstance(rw_uri, bytes), rw_uri

            # should be prevented by MustBeDeepImmutableError check above
            assert not (rw_uri and deep_immutable)

            ro_uri = child.get_readonly_uri()
            if ro_uri is None:
                ro_uri = b""
            assert isinstance(ro_uri, bytes), ro_uri
            if writekey is not None:
                writecap = netstring(_encrypt_rw_uri(writekey, rw_uri))
            else:
                writecap = ZERO_LEN_NETSTR
            entry = b"".join([netstring(name.encode("utf-8")),
                             netstring(strip_prefix_for_ro(ro_uri, deep_immutable)),
                             writecap,
                             netstring(json.dumps(metadata).encode("utf-8"))])
        entries.append(netstring(entry))
    return b"".join(entries)

@implementer(IDirectoryNode, ICheckable, IDeepCheckable)
class DirectoryNode(object):
    filenode_class = MutableFileNode

    def __init__(self, filenode, nodemaker, uploader):
        assert IFileNode.providedBy(filenode), filenode
        assert not IDirectoryNode.providedBy(filenode), filenode
        self._node = filenode
        filenode_cap = filenode.get_cap()
        self._uri = wrap_dirnode_cap(filenode_cap)
        self._nodemaker = nodemaker
        self._uploader = uploader

    def __repr__(self):
        return "<%s %s-%s %s>" % (self.__class__.__name__,
                                  self.is_readonly() and "RO" or "RW",
                                  self.is_mutable() and "MUT" or "IMM",
                                  hasattr(self, '_uri') and str(self._uri.abbrev(), "utf-8"))

    def get_size(self):
        """Return the size of our backing mutable file, in bytes, if we've
        fetched it. Otherwise return None. This returns synchronously."""
        return self._node.get_size()

    def get_current_size(self):
        """Calculate the size of our backing mutable file, in bytes. Returns
        a Deferred that fires with the result."""
        return self._node.get_current_size()

    def _read(self):
        if self._node.is_mutable():
            # use the IMutableFileNode API.
            d = self._node.download_best_version()
        else:
            d = download_to_data(self._node)
        d.addCallback(self._unpack_contents)
        return d

    def _decrypt_rwcapdata(self, encwrcap):
        salt = encwrcap[:16]
        crypttext = encwrcap[16:-32]
        key = hashutil.mutable_rwcap_key_hash(salt, self._node.get_writekey())
        encryptor = aes.create_decryptor(key)
        plaintext = aes.decrypt_data(encryptor, crypttext)
        return plaintext

    def _create_and_validate_node(self, rw_uri, ro_uri, name):
        # name is just for error reporting
        node = self._nodemaker.create_from_cap(rw_uri, ro_uri,
                                               deep_immutable=not self.is_mutable(),
                                               name=name)
        node.raise_error()
        return node

    def _create_readonly_node(self, node, name):
        # name is just for error reporting
        if not node.is_unknown() and node.is_readonly():
            return node
        return self._create_and_validate_node(None, node.get_readonly_uri(), name=name)

    def _unpack_contents(self, data):
        # the directory is serialized as a list of netstrings, one per child.
        # Each child is serialized as a list of four netstrings: (name, ro_uri,
        # rwcapdata, metadata), in which the name, ro_uri, metadata are in
        # cleartext. The 'name' is UTF-8 encoded, and should be normalized to NFC.
        # The rwcapdata is formatted as:
        # pack("16ss32s", iv, AES(H(writekey+iv), plaintext_rw_uri), mac)
        assert isinstance(data, bytes), (repr(data), type(data))
        # an empty directory is serialized as an empty string
        if data == b"":
            return AuxValueDict()
        writeable = not self.is_readonly()
        mutable = self.is_mutable()
        children = AuxValueDict()
        position = 0
        while position < len(data):
            entries, position = split_netstring(data, 1, position)
            entry = entries[0]
            (namex_utf8, ro_uri, rwcapdata, metadata_s), subpos = split_netstring(entry, 4)
            if not mutable and len(rwcapdata) > 0:
                raise ValueError("the rwcapdata field of a dirnode in an immutable directory was not empty")

            # A name containing characters that are unassigned in one version of Unicode might
            # not be normalized wrt a later version. See the note in section 'Normalization Stability'
            # at <http://unicode.org/policies/stability_policy.html>.
            # Therefore we normalize names going both in and out of directories.
            name = normalize(namex_utf8.decode("utf-8"))

            rw_uri = b""
            if writeable:
                rw_uri = self._decrypt_rwcapdata(rwcapdata)

            # Since the encryption uses CTR mode, it currently leaks the length of the
            # plaintext rw_uri -- and therefore whether it is present, i.e. whether the
            # dirnode is writeable (ticket #925). By stripping trailing spaces in
            # Tahoe >= 1.6.0, we may make it easier for future versions to plug this leak.
            # ro_uri is treated in the same way for consistency.
            # rw_uri and ro_uri will be either None or a non-empty string.

            rw_uri = rw_uri.rstrip(b' ') or None
            ro_uri = ro_uri.rstrip(b' ') or None

            try:
                child = self._create_and_validate_node(rw_uri, ro_uri, name)
                if mutable or child.is_allowed_in_immutable_directory():
                    metadata = json.loads(metadata_s)
                    assert isinstance(metadata, dict)
                    children[name] = (child, metadata)
                    children.set_with_aux(name, (child, metadata), auxilliary=entry)
                else:
                    log.msg(format="mutable cap for child %(name)s unpacked from an immutable directory",
                            name=quote_output(name, encoding='utf-8'),
                            facility="tahoe.webish", level=log.UNUSUAL)
            except CapConstraintError as e:
                log.msg(format="unmet constraint on cap for child %(name)s unpacked from a directory:\n"
                               "%(message)s", message=e.args[0], name=quote_output(name, encoding='utf-8'),
                               facility="tahoe.webish", level=log.UNUSUAL)

        return children

    def _pack_contents(self, children):
        # expects children in the same format as _unpack_contents returns
        return _pack_normalized_children(children, self._node.get_writekey())

    def is_readonly(self):
        return self._node.is_readonly()

    def is_mutable(self):
        return self._node.is_mutable()

    def is_unknown(self):
        return False

    def is_allowed_in_immutable_directory(self):
        return not self._node.is_mutable()

    def raise_error(self):
        pass

    def get_uri(self):
        return self._uri.to_string()

    def get_write_uri(self):
        if self.is_readonly():
            return None
        return self._uri.to_string()

    def get_readonly_uri(self):
        return self._uri.get_readonly().to_string()

    def get_cap(self):
        return self._uri

    def get_readcap(self):
        return self._uri.get_readonly()

    def get_verify_cap(self):
        return self._uri.get_verify_cap()

    def get_repair_cap(self):
        if self._node.is_readonly():
            return None # readonly (mutable) dirnodes are not yet repairable
        return self._uri

    def get_storage_index(self):
        return self._uri.get_storage_index()

    def check(self, monitor, verify=False, add_lease=False):
        """Perform a file check. See IChecker.check for details."""
        return self._node.check(monitor, verify, add_lease)
    def check_and_repair(self, monitor, verify=False, add_lease=False):
        return self._node.check_and_repair(monitor, verify, add_lease)

    def list(self):
        """I return a Deferred that fires with a dictionary mapping child
        name to a tuple of (IFilesystemNode, metadata)."""
        return self._read()

    def has_child(self, namex):
        """I return a Deferred that fires with a boolean, True if there
        exists a child of the given name, False if not."""
        name = normalize(namex)
        d = self._read()
        d.addCallback(lambda children: name in children)
        return d

    def _get(self, children, name):
        child = children.get(name)
        if child is None:
            raise NoSuchChildError(name)
        return child[0]

    def _get_with_metadata(self, children, name):
        child = children.get(name)
        if child is None:
            raise NoSuchChildError(name)
        return child

    def get(self, namex):
        """I return a Deferred that fires with the named child node,
        which is an IFilesystemNode."""
        name = normalize(namex)
        d = self._read()
        d.addCallback(self._get, name)
        return d

    def get_child_and_metadata(self, namex):
        """I return a Deferred that fires with the (node, metadata) pair for
        the named child. The node is an IFilesystemNode, and the metadata
        is a dictionary."""
        name = normalize(namex)
        d = self._read()
        d.addCallback(self._get_with_metadata, name)
        return d

    def get_metadata_for(self, namex):
        name = normalize(namex)
        d = self._read()
        d.addCallback(lambda children: children[name][1])
        return d

    def set_metadata_for(self, namex, metadata):
        name = normalize(namex)
        if self.is_readonly():
            return defer.fail(NotWriteableError())
        assert isinstance(metadata, dict)
        s = MetadataSetter(self, name, metadata,
                           create_readonly_node=self._create_readonly_node)
        d = self._node.modify(s.modify)
        d.addCallback(lambda res: self)
        return d

    def get_child_at_path(self, pathx):
        """Transform a child path into an IFilesystemNode.

        I perform a recursive series of 'get' operations to find the named
        descendant node. I return a Deferred that fires with the node, or
        errbacks with IndexError if the node could not be found.

        The path can be either a single string (slash-separated) or a list of
        path-name elements.
        """
        d = self.get_child_and_metadata_at_path(pathx)
        d.addCallback(lambda node_and_metadata: node_and_metadata[0])
        return d

    def get_child_and_metadata_at_path(self, pathx):
        """Transform a child path into an IFilesystemNode and
        a metadata dictionary from the last edge that was traversed.
        """

        if not pathx:
            return defer.succeed((self, {}))
        if isinstance(pathx, (list, tuple)):
            pass
        else:
            pathx = pathx.split("/")
        for p in pathx:
            assert isinstance(p, str), p
        childnamex = pathx[0]
        remaining_pathx = pathx[1:]
        if remaining_pathx:
            d = self.get(childnamex)
            d.addCallback(lambda node:
                          node.get_child_and_metadata_at_path(remaining_pathx))
            return d
        d = self.get_child_and_metadata(childnamex)
        return d

    def set_uri(self, namex, writecap, readcap=None, metadata=None, overwrite=True):
        precondition(isinstance(writecap, (bytes, type(None))), writecap)
        precondition(isinstance(readcap, (bytes, type(None))), readcap)

        # We now allow packing unknown nodes, provided they are valid
        # for this type of directory.
        child_node = self._create_and_validate_node(writecap, readcap, namex)
        d = self.set_node(namex, child_node, metadata, overwrite)
        d.addCallback(lambda res: child_node)
        return d

    def set_children(self, entries, overwrite=True):
        # this takes URIs
        a = Adder(self, overwrite=overwrite,
                  create_readonly_node=self._create_readonly_node)
        for (namex, e) in entries.items():
            assert isinstance(namex, str), namex
            if len(e) == 2:
                writecap, readcap = e
                metadata = None
            else:
                assert len(e) == 3
                writecap, readcap, metadata = e
            precondition(isinstance(writecap, (bytes,type(None))), writecap)
            precondition(isinstance(readcap, (bytes,type(None))), readcap)

            # We now allow packing unknown nodes, provided they are valid
            # for this type of directory.
            child_node = self._create_and_validate_node(writecap, readcap, namex)
            a.set_node(namex, child_node, metadata)
        d = self._node.modify(a.modify)
        d.addCallback(lambda ign: self)
        return d

    def set_node(self, namex, child, metadata=None, overwrite=True):
        """I add a child at the specific name. I return a Deferred that fires
        when the operation finishes. This Deferred will fire with the child
        node that was just added. I will replace any existing child of the
        same name.

        If this directory node is read-only, the Deferred will errback with a
        NotWriteableError."""

        precondition(IFilesystemNode.providedBy(child), child)

        if self.is_readonly():
            return defer.fail(NotWriteableError())
        assert IFilesystemNode.providedBy(child), child
        a = Adder(self, overwrite=overwrite,
                  create_readonly_node=self._create_readonly_node)
        a.set_node(namex, child, metadata)
        d = self._node.modify(a.modify)
        d.addCallback(lambda res: child)
        return d

    def set_nodes(self, entries, overwrite=True):
        precondition(isinstance(entries, dict), entries)
        if self.is_readonly():
            return defer.fail(NotWriteableError())
        a = Adder(self, entries, overwrite=overwrite,
                  create_readonly_node=self._create_readonly_node)
        d = self._node.modify(a.modify)
        d.addCallback(lambda res: self)
        return d


    def add_file(self, namex, uploadable, metadata=None, overwrite=True):
        """I upload a file (using the given IUploadable), then attach the
        resulting FileNode to the directory at the given name. I return a
        Deferred that fires (with the IFileNode of the uploaded file) when
        the operation completes."""
        with ADD_FILE(name=namex, metadata=metadata, overwrite=overwrite).context():
            name = normalize(namex)
            if self.is_readonly():
                d = DeferredContext(defer.fail(NotWriteableError()))
            else:
                # XXX should pass reactor arg
                d = DeferredContext(self._uploader.upload(uploadable))
                d.addCallback(lambda results:
                              self._create_and_validate_node(results.get_uri(), None,
                                                             name))
                d.addCallback(lambda node:
                              self.set_node(name, node, metadata, overwrite))

        return d.addActionFinish()

    def delete(self, namex, must_exist=True, must_be_directory=False, must_be_file=False):
        """I remove the child at the specific name. I return a Deferred that
        fires (with the node just removed) when the operation finishes."""
        if self.is_readonly():
            return defer.fail(NotWriteableError())
        deleter = Deleter(self, namex, must_exist=must_exist,
                          must_be_directory=must_be_directory, must_be_file=must_be_file)
        d = self._node.modify(deleter.modify)
        d.addCallback(lambda res: deleter.old_child)
        return d

    # XXX: Too many arguments? Worthwhile to break into mutable/immutable?
    def create_subdirectory(self, namex, initial_children=None, overwrite=True,
                            mutable=True, mutable_version=None, metadata=None):
        if initial_children is None:
            initial_children = {}
        name = normalize(namex)
        if self.is_readonly():
            return defer.fail(NotWriteableError())
        if mutable:
            if mutable_version:
                d = self._nodemaker.create_new_mutable_directory(initial_children,
                                                                 version=mutable_version)
            else:
                d = self._nodemaker.create_new_mutable_directory(initial_children)
        else:
            # mutable version doesn't make sense for immmutable directories.
            assert mutable_version is None
            d = self._nodemaker.create_immutable_directory(initial_children)
        def _created(child):
            entries = {name: (child, metadata)}
            a = Adder(self, entries, overwrite=overwrite,
                      create_readonly_node=self._create_readonly_node)
            d = self._node.modify(a.modify)
            d.addCallback(lambda res: child)
            return d
        d.addCallback(_created)
        return d

    def move_child_to(self, current_child_namex, new_parent,
                      new_child_namex=None, overwrite=True):
        """
        I take one of my child links and move it to a new parent. The child
        link is referenced by name. In the new parent, the child link will live
        at 'new_child_namex', which defaults to 'current_child_namex'. I return
        a Deferred that fires when the operation finishes.
        'new_child_namex' and 'current_child_namex' need not be normalized.

        The overwrite parameter may be True (overwrite any existing child),
        False (error if the new child link already exists), or ONLY_FILES
        (error if the new child link exists and points to a directory).
        """
        if self.is_readonly() or new_parent.is_readonly():
            return defer.fail(NotWriteableError())

        current_child_name = normalize(current_child_namex)
        if new_child_namex is None:
            new_child_name = current_child_name
        else:
            new_child_name = normalize(new_child_namex)

        from_uri = self.get_write_uri()
        if new_parent.get_write_uri() == from_uri and new_child_name == current_child_name:
            # needed for correctness, otherwise we would delete the child
            return defer.succeed("redundant rename/relink")

        d = self.get_child_and_metadata(current_child_name)
        def _got_child(child_and_metadata):
            (child, metadata) = child_and_metadata
            return new_parent.set_node(new_child_name, child, metadata,
                                       overwrite=overwrite)
        d.addCallback(_got_child)
        d.addCallback(lambda child: self.delete(current_child_name))
        return d


    def deep_traverse(self, walker):
        """Perform a recursive walk, using this dirnode as a root, notifying
        the 'walker' instance of everything I encounter.

        I call walker.enter_directory(parent, children) once for each dirnode
        I visit, immediately after retrieving the list of children. I pass in
        the parent dirnode and the dict of childname->(childnode,metadata).
        This function should *not* traverse the children: I will do that.
        enter_directory() is most useful for the deep-stats number that
        counts how large a directory is.

        I call walker.add_node(node, path) for each node (both files and
        directories) I can reach. Most work should be done here.

        I avoid loops by keeping track of verifier-caps and refusing to call
        walker.add_node() or traverse a node that I've seen before. This
        means that any file or directory will only be given to the walker
        once. If files or directories are referenced multiple times by a
        directory structure, this may appear to under-count or miss some of
        them.

        I return a Monitor which can be used to wait for the operation to
        finish, learn about its progress, or cancel the operation.
        """

        # this is just a tree-walker, except that following each edge
        # requires a Deferred. We used to use a ConcurrencyLimiter to limit
        # fanout to 10 simultaneous operations, but the memory load of the
        # queued operations was excessive (in one case, with 330k dirnodes,
        # it caused the process to run into the 3.0GB-ish per-process 32bit
        # linux memory limit, and crashed). So we use a single big Deferred
        # chain, and do a strict depth-first traversal, one node at a time.
        # This can be slower, because we aren't pipelining directory reads,
        # but it brought the memory footprint down by roughly 50%.

        monitor = Monitor()
        walker.set_monitor(monitor)

        found = set([self.get_verify_cap()])
        d = self._deep_traverse_dirnode(self, [], walker, monitor, found)
        d.addCallback(lambda ignored: walker.finish())
        d.addBoth(monitor.finish)
        d.addErrback(lambda f: None)

        return monitor

    def _deep_traverse_dirnode(self, node, path, walker, monitor, found):
        # process this directory, then walk its children
        monitor.raise_if_cancelled()
        d = defer.maybeDeferred(walker.add_node, node, path)
        d.addCallback(lambda ignored: node.list())
        d.addCallback(self._deep_traverse_dirnode_children, node, path,
                      walker, monitor, found)
        return d

    def _deep_traverse_dirnode_children(self, children, parent, path,
                                        walker, monitor, found):
        monitor.raise_if_cancelled()
        d = defer.maybeDeferred(walker.enter_directory, parent, children)
        # we process file-like children first, so we can drop their FileNode
        # objects as quickly as possible. Tests suggest that a FileNode (held
        # in the client's nodecache) consumes about 2440 bytes. dirnodes (not
        # in the nodecache) seem to consume about 2000 bytes.
        dirkids = []
        filekids = []
        for name, (child, metadata) in sorted(children.items()):
            childpath = path + [name]
            if isinstance(child, UnknownNode):
                walker.add_node(child, childpath)
                continue
            verifier = child.get_verify_cap()
            # allow LIT files (for which verifier==None) to be processed
            if (verifier is not None) and (verifier in found):
                continue
            found.add(verifier)
            if IDirectoryNode.providedBy(child):
                dirkids.append( (child, childpath) )
            else:
                filekids.append( (child, childpath) )
        for i, (child, childpath) in enumerate(filekids):
            d.addCallback(lambda ignored, child=child, childpath=childpath:
                          walker.add_node(child, childpath))
            # to work around the Deferred tail-recursion problem
            # (specifically the defer.succeed flavor) requires us to avoid
            # doing more than 158 LIT files in a row. We insert a turn break
            # once every 100 files (LIT or CHK) to preserve some stack space
            # for other code. This is a different expression of the same
            # Twisted problem as in #237.
            if i % 100 == 99:
                d.addCallback(lambda ignored: fireEventually())
        for (child, childpath) in dirkids:
            d.addCallback(lambda ignored, child=child, childpath=childpath:
                          self._deep_traverse_dirnode(child, childpath,
                                                      walker, monitor,
                                                      found))
        return d


    def build_manifest(self):
        """Return a Monitor, with a ['status'] that will be a list of (path,
        cap) tuples, for all nodes (directories and files) reachable from
        this one."""
        walker = ManifestWalker(self)
        return self.deep_traverse(walker)

    def start_deep_stats(self):
        # Since deep_traverse tracks verifier caps, we avoid double-counting
        # children for which we've got both a write-cap and a read-cap
        return self.deep_traverse(DeepStats(self))

    def start_deep_check(self, verify=False, add_lease=False):
        return self.deep_traverse(DeepChecker(self, verify, repair=False, add_lease=add_lease))

    def start_deep_check_and_repair(self, verify=False, add_lease=False):
        return self.deep_traverse(DeepChecker(self, verify, repair=True, add_lease=add_lease))


class ManifestWalker(DeepStats):
    def __init__(self, origin):
        DeepStats.__init__(self, origin)
        self.manifest = []
        self.storage_index_strings = set()
        self.verifycaps = set()

    def add_node(self, node, path):
        self.manifest.append( (tuple(path), node.get_uri()) )
        si = node.get_storage_index()
        if si:
            self.storage_index_strings.add(base32.b2a(si))
        v = node.get_verify_cap()
        if v:
            self.verifycaps.add(v.to_string())
        return DeepStats.add_node(self, node, path)

    def get_results(self):
        stats = DeepStats.get_results(self)
        return {"manifest": self.manifest,
                "verifycaps": self.verifycaps,
                "storage-index": self.storage_index_strings,
                "stats": stats,
                }


class DeepChecker(object):
    def __init__(self, root, verify, repair, add_lease):
        root_si = root.get_storage_index()
        if root_si:
            root_si_base32 = base32.b2a(root_si)
        else:
            root_si_base32 = ""
        self._lp = log.msg(format="deep-check starting (%(si)s),"
                           " verify=%(verify)s, repair=%(repair)s",
                           si=root_si_base32, verify=verify, repair=repair)
        self._verify = verify
        self._repair = repair
        self._add_lease = add_lease
        if repair:
            self._results = DeepCheckAndRepairResults(root_si)
        else:
            self._results = DeepCheckResults(root_si)
        self._stats = DeepStats(root)

    def set_monitor(self, monitor):
        self.monitor = monitor
        monitor.set_status(self._results)

    def add_node(self, node, childpath):
        if self._repair:
            d = node.check_and_repair(self.monitor, self._verify, self._add_lease)
            d.addCallback(self._results.add_check_and_repair, childpath)
        else:
            d = node.check(self.monitor, self._verify, self._add_lease)
            d.addCallback(self._results.add_check, childpath)
        d.addCallback(lambda ignored: self._stats.add_node(node, childpath))
        return d

    def enter_directory(self, parent, children):
        return self._stats.enter_directory(parent, children)

    def finish(self):
        log.msg("deep-check done", parent=self._lp)
        self._results.update_stats(self._stats.get_results())
        return self._results


# use client.create_dirnode() to make one of these