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https://github.com/tahoe-lafs/tahoe-lafs.git
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185 lines
8.2 KiB
Python
185 lines
8.2 KiB
Python
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from zope.interface import implementer
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from twisted.internet import defer
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from allmydata.interfaces import IFilesystemNode, MustNotBeUnknownRWError, \
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MustBeDeepImmutableError
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from allmydata import uri
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from allmydata.uri import ALLEGED_READONLY_PREFIX, ALLEGED_IMMUTABLE_PREFIX
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# See ticket #833 for design rationale of UnknownNodes.
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def strip_prefix_for_ro(ro_uri, deep_immutable):
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"""Strip prefixes when storing an URI in a ro_uri slot."""
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# It is possible for an alleged-immutable URI to be put into a
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# mutable directory. In that case the ALLEGED_IMMUTABLE_PREFIX
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# should not be stripped. In other cases, the prefix can safely
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# be stripped because it is implied by the context.
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if ro_uri.startswith(ALLEGED_IMMUTABLE_PREFIX):
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if not deep_immutable:
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return ro_uri
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return ro_uri[len(ALLEGED_IMMUTABLE_PREFIX):]
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elif ro_uri.startswith(ALLEGED_READONLY_PREFIX):
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return ro_uri[len(ALLEGED_READONLY_PREFIX):]
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else:
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return ro_uri
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@implementer(IFilesystemNode)
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class UnknownNode(object):
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def __init__(self, given_rw_uri, given_ro_uri, deep_immutable=False,
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name=u"<unknown name>"):
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assert given_rw_uri is None or isinstance(given_rw_uri, str)
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assert given_ro_uri is None or isinstance(given_ro_uri, str)
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given_rw_uri = given_rw_uri or None
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given_ro_uri = given_ro_uri or None
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# We don't raise errors when creating an UnknownNode; we instead create an
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# opaque node (with rw_uri and ro_uri both None) that records the error.
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# This avoids breaking operations that never store the opaque node.
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# Note that this means that if a stored dirnode has only a rw_uri, it
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# might be dropped. Any future "write-only" cap formats should have a dummy
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# unusable readcap to stop that from happening.
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self.error = None
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self.rw_uri = self.ro_uri = None
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if given_rw_uri:
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if deep_immutable:
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if given_rw_uri.startswith(ALLEGED_IMMUTABLE_PREFIX) and not given_ro_uri:
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# We needed an immutable cap, and were given one. It was given in the
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# rw_uri slot, but that's fine; we'll move it to ro_uri below.
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pass
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elif not given_ro_uri:
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self.error = MustNotBeUnknownRWError("cannot attach unknown rw cap as immutable child",
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name, True)
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return # node will be opaque
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else:
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# We could report either error, but this probably makes more sense.
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self.error = MustBeDeepImmutableError("cannot attach unknown rw cap as immutable child",
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name)
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return # node will be opaque
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if not given_ro_uri:
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# We were given a single cap argument, or a rw_uri with no ro_uri.
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if not (given_rw_uri.startswith(ALLEGED_READONLY_PREFIX)
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or given_rw_uri.startswith(ALLEGED_IMMUTABLE_PREFIX)):
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# If the single cap is unprefixed, then we cannot tell whether it is a
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# writecap, and we don't know how to diminish it to a readcap if it is one.
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# If it didn't *already* have at least an ALLEGED_READONLY_PREFIX, then
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# prefixing it would be a bad idea because we have been given no reason
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# to believe that it is a readcap, so we might be letting a client
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# inadvertently grant excess write authority.
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self.error = MustNotBeUnknownRWError("cannot attach unknown rw cap as child",
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name, False)
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return # node will be opaque
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# OTOH, if the single cap already had a prefix (which is of the required
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# strength otherwise an error would have been thrown above), then treat it
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# as though it had been given in the ro_uri slot. This has a similar effect
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# to the use for known caps of 'bigcap = writecap or readcap' in
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# nodemaker.py: create_from_cap. It enables copying of unknown readcaps to
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# work in as many cases as we can securely allow.
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given_ro_uri = given_rw_uri
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given_rw_uri = None
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elif given_ro_uri.startswith(ALLEGED_IMMUTABLE_PREFIX):
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# Strange corner case: we were given a cap in both slots, with the ro_uri
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# alleged to be immutable. A real immutable object wouldn't have a writecap.
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self.error = MustBeDeepImmutableError("cannot accept a child entry that specifies "
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"both rw_uri, and ro_uri with an imm. prefix",
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name)
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return # node will be opaque
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# If the ro_uri definitely fails the constraint, it should be treated as opaque and
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# the error recorded.
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if given_ro_uri:
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read_cap = uri.from_string(given_ro_uri, deep_immutable=deep_immutable, name=name)
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if isinstance(read_cap, uri.UnknownURI):
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self.error = read_cap.get_error()
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if self.error:
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assert self.rw_uri is None and self.ro_uri is None
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return
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if deep_immutable:
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assert self.rw_uri is None
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# strengthen the constraint on ro_uri to ALLEGED_IMMUTABLE_PREFIX
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if given_ro_uri:
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if given_ro_uri.startswith(ALLEGED_IMMUTABLE_PREFIX):
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self.ro_uri = given_ro_uri
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elif given_ro_uri.startswith(ALLEGED_READONLY_PREFIX):
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self.ro_uri = ALLEGED_IMMUTABLE_PREFIX + given_ro_uri[len(ALLEGED_READONLY_PREFIX):]
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else:
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self.ro_uri = ALLEGED_IMMUTABLE_PREFIX + given_ro_uri
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else:
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# not immutable, so a writecap is allowed
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self.rw_uri = given_rw_uri
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# strengthen the constraint on ro_uri to ALLEGED_READONLY_PREFIX
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if given_ro_uri:
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if (given_ro_uri.startswith(ALLEGED_READONLY_PREFIX) or
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given_ro_uri.startswith(ALLEGED_IMMUTABLE_PREFIX)):
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self.ro_uri = given_ro_uri
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else:
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self.ro_uri = ALLEGED_READONLY_PREFIX + given_ro_uri
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def get_cap(self):
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return uri.UnknownURI(self.rw_uri or self.ro_uri)
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def get_readcap(self):
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return uri.UnknownURI(self.ro_uri)
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def is_readonly(self):
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raise AssertionError("an UnknownNode might be either read-only or "
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"read/write, so we shouldn't be calling is_readonly")
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def is_mutable(self):
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raise AssertionError("an UnknownNode might be either mutable or immutable, "
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"so we shouldn't be calling is_mutable")
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def is_unknown(self):
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return True
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def is_allowed_in_immutable_directory(self):
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# An UnknownNode consisting only of a ro_uri is allowed in an
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# immutable directory, even though we do not know that it is
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# immutable (or even read-only), provided that no error was detected.
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return not self.error and not self.rw_uri
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def is_alleged_immutable(self):
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return not self.error and not self.rw_uri and (not self.ro_uri or self.ro_uri.startswith(ALLEGED_IMMUTABLE_PREFIX))
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def raise_error(self):
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if self.error is not None:
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raise self.error
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def get_uri(self):
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return self.rw_uri or self.ro_uri
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def get_write_uri(self):
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return self.rw_uri
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def get_readonly_uri(self):
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return self.ro_uri
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def get_storage_index(self):
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return None
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def get_verify_cap(self):
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return None
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def get_repair_cap(self):
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return None
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def get_size(self):
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return None
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def get_current_size(self):
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return defer.succeed(None)
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def check(self, monitor, verify, add_lease):
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return defer.succeed(None)
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def check_and_repair(self, monitor, verify, add_lease):
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return defer.succeed(None)
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