import os, struct from itertools import islice from zope.interface import implements from twisted.internet import defer from twisted.python import failure from foolscap.eventual import eventually from allmydata.interfaces import IMutableFileNode, IMutableFileURI from allmydata.util import base32, hashutil, mathutil, idlib, log from allmydata.uri import WriteableSSKFileURI from allmydata import hashtree, codec, storage from allmydata.encode import NotEnoughPeersError from pycryptopp.publickey import rsa from pycryptopp.cipher.aes import AES class NotMutableError(Exception): pass class NeedMoreDataError(Exception): def __init__(self, needed_bytes, encprivkey_offset, encprivkey_length): Exception.__init__(self) self.needed_bytes = needed_bytes # up through EOF self.encprivkey_offset = encprivkey_offset self.encprivkey_length = encprivkey_length def __str__(self): return "" % self.needed_bytes class UncoordinatedWriteError(Exception): def __repr__(self): return "<%s -- You, oh user, tried to change a file or directory at the same time as another process was trying to change it. To avoid data loss, don't do this. Please see docs/write_coordination.html for details.>" % (self.__class__.__name__,) class CorruptShareError(Exception): def __init__(self, peerid, shnum, reason): self.args = (peerid, shnum, reason) self.peerid = peerid self.shnum = shnum self.reason = reason def __str__(self): short_peerid = idlib.nodeid_b2a(self.peerid)[:8] return "= HEADER_LENGTH o = {} prefix = data[:struct.calcsize(SIGNED_PREFIX)] (version, seqnum, root_hash, IV, k, N, segsize, datalen, o['signature'], o['share_hash_chain'], o['block_hash_tree'], o['share_data'], o['enc_privkey'], o['EOF']) = struct.unpack(HEADER, data[:HEADER_LENGTH]) assert version == 0 if len(data) < o['share_hash_chain']: raise NeedMoreDataError(o['share_hash_chain'], o['enc_privkey'], o['EOF']-o['enc_privkey']) pubkey_s = data[HEADER_LENGTH:o['signature']] signature = data[o['signature']:o['share_hash_chain']] return (seqnum, root_hash, IV, k, N, segsize, datalen, pubkey_s, signature, prefix) def unpack_share(data): assert len(data) >= HEADER_LENGTH o = {} (version, seqnum, root_hash, IV, k, N, segsize, datalen, o['signature'], o['share_hash_chain'], o['block_hash_tree'], o['share_data'], o['enc_privkey'], o['EOF']) = struct.unpack(HEADER, data[:HEADER_LENGTH]) assert version == 0 if len(data) < o['EOF']: raise NeedMoreDataError(o['EOF'], o['enc_privkey'], o['EOF']-o['enc_privkey']) pubkey = data[HEADER_LENGTH:o['signature']] signature = data[o['signature']:o['share_hash_chain']] share_hash_chain_s = data[o['share_hash_chain']:o['block_hash_tree']] share_hash_format = ">H32s" hsize = struct.calcsize(share_hash_format) assert len(share_hash_chain_s) % hsize == 0, len(share_hash_chain_s) share_hash_chain = [] for i in range(0, len(share_hash_chain_s), hsize): chunk = share_hash_chain_s[i:i+hsize] (hid, h) = struct.unpack(share_hash_format, chunk) share_hash_chain.append( (hid, h) ) share_hash_chain = dict(share_hash_chain) block_hash_tree_s = data[o['block_hash_tree']:o['share_data']] assert len(block_hash_tree_s) % 32 == 0, len(block_hash_tree_s) block_hash_tree = [] for i in range(0, len(block_hash_tree_s), 32): block_hash_tree.append(block_hash_tree_s[i:i+32]) share_data = data[o['share_data']:o['enc_privkey']] enc_privkey = data[o['enc_privkey']:o['EOF']] return (seqnum, root_hash, IV, k, N, segsize, datalen, pubkey, signature, share_hash_chain, block_hash_tree, share_data, enc_privkey) def pack_checkstring(seqnum, root_hash, IV): return struct.pack(PREFIX, 0, # version, seqnum, root_hash, IV) def unpack_checkstring(checkstring): cs_len = struct.calcsize(PREFIX) version, seqnum, root_hash, IV = struct.unpack(PREFIX, checkstring[:cs_len]) assert version == 0 # TODO: just ignore the share return (seqnum, root_hash, IV) def pack_prefix(seqnum, root_hash, IV, required_shares, total_shares, segment_size, data_length): prefix = struct.pack(SIGNED_PREFIX, 0, # version, seqnum, root_hash, IV, required_shares, total_shares, segment_size, data_length, ) return prefix def pack_offsets(verification_key_length, signature_length, share_hash_chain_length, block_hash_tree_length, share_data_length, encprivkey_length): post_offset = HEADER_LENGTH offsets = {} o1 = offsets['signature'] = post_offset + verification_key_length o2 = offsets['share_hash_chain'] = o1 + signature_length o3 = offsets['block_hash_tree'] = o2 + share_hash_chain_length o4 = offsets['share_data'] = o3 + block_hash_tree_length o5 = offsets['enc_privkey'] = o4 + share_data_length o6 = offsets['EOF'] = o5 + encprivkey_length return struct.pack(">LLLLQQ", offsets['signature'], offsets['share_hash_chain'], offsets['block_hash_tree'], offsets['share_data'], offsets['enc_privkey'], offsets['EOF']) def pack_share(prefix, verification_key, signature, share_hash_chain, block_hash_tree, share_data, encprivkey): share_hash_chain_s = "".join([struct.pack(">H32s", i, share_hash_chain[i]) for i in sorted(share_hash_chain.keys())]) for h in block_hash_tree: assert len(h) == 32 block_hash_tree_s = "".join(block_hash_tree) offsets = pack_offsets(len(verification_key), len(signature), len(share_hash_chain_s), len(block_hash_tree_s), len(share_data), len(encprivkey)) final_share = "".join([prefix, offsets, verification_key, signature, share_hash_chain_s, block_hash_tree_s, share_data, encprivkey]) return final_share class Retrieve: def __init__(self, filenode): self._node = filenode self._contents = None # if the filenode already has a copy of the pubkey, use it. Otherwise # we'll grab a copy from the first peer we talk to. self._pubkey = filenode.get_pubkey() self._storage_index = filenode.get_storage_index() self._readkey = filenode.get_readkey() self._last_failure = None self._log_number = None self._log_prefix = prefix = storage.si_b2a(self._storage_index)[:5] num = self._node._client.log("Retrieve(%s): starting" % prefix) self._log_number = num def log(self, msg, **kwargs): prefix = self._log_prefix num = self._node._client.log("Retrieve(%s): %s" % (prefix, msg), parent=self._log_number, **kwargs) return num def log_err(self, f): num = log.err(f, parent=self._log_number) return num def retrieve(self): """Retrieve the filenode's current contents. Returns a Deferred that fires with a string when the contents have been retrieved.""" # 1: make a guess as to how many peers we should send requests to. We # want to hear from k+EPSILON (k because we have to, EPSILON extra # because that helps us resist rollback attacks). [TRADEOFF: # EPSILON>0 means extra work] [TODO: implement EPSILON>0] # 2: build the permuted peerlist, taking the first k+E peers # 3: send readv requests to all of them in parallel, asking for the # first 2KB of data from all shares # 4: when the first of the responses comes back, extract information: # 4a: extract the pubkey, hash it, compare against the URI. If this # check fails, log a WEIRD and ignore the peer. # 4b: extract the prefix (seqnum, roothash, k, N, segsize, datalength) # and verify the signature on it. If this is wrong, log a WEIRD # and ignore the peer. Save the prefix string in a dict that's # keyed by (seqnum,roothash) and has (prefixstring, sharemap) as # values. We'll use the prefixstring again later to avoid doing # multiple signature checks # 4c: extract the share size (offset of the last byte of sharedata). # if it is larger than 2k, send new readv requests to pull down # the extra data # 4d: if the extracted 'k' is more than we guessed, rebuild a larger # permuted peerlist and send out more readv requests. # 5: as additional responses come back, extract the prefix and compare # against the ones we've already seen. If they match, add the # peerid to the corresponing sharemap dict # 6: [TRADEOFF]: if EPSILON==0, when we get k responses for the # same (seqnum,roothash) key, attempt to reconstruct that data. # if EPSILON>0, wait for k+EPSILON responses, then attempt to # reconstruct the most popular version.. If we do not have enough # shares and there are still requests outstanding, wait. If there # are not still requests outstanding (todo: configurable), send # more requests. Never send queries to more than 2*N servers. If # we've run out of servers, fail. # 7: if we discover corrupt shares during the reconstruction process, # remove that share from the sharemap. and start step#6 again. initial_query_count = 5 self._read_size = 2000 # we might not know how many shares we need yet. self._required_shares = self._node.get_required_shares() self._total_shares = self._node.get_total_shares() # self._valid_versions is a dictionary in which the keys are # 'verinfo' tuples (seqnum, root_hash, IV). Every time we hear about # a new potential version of the file, we check its signature, and # the valid ones are added to this dictionary. The values of the # dictionary are (prefix, sharemap) tuples, where 'prefix' is just # the first part of the share (containing the serialized verinfo), # for easier comparison. 'sharemap' is a DictOfSets, in which the # keys are sharenumbers, and the values are sets of (peerid, data) # tuples. There is a (peerid, data) tuple for every instance of a # given share that we've seen. The 'data' in this tuple is a full # copy of the SDMF share, starting with the \x00 version byte and # continuing through the last byte of sharedata. self._valid_versions = {} # self._valid_shares is a dict mapping (peerid,data) tuples to # validated sharedata strings. Each time we examine the hash chains # inside a share and validate them against a signed root_hash, we add # the share to self._valid_shares . We use this to avoid re-checking # the hashes over and over again. self._valid_shares = {} self._done_deferred = defer.Deferred() d = defer.succeed(initial_query_count) d.addCallback(self._choose_initial_peers) d.addCallback(self._send_initial_requests) d.addCallback(self._wait_for_finish) return d def _wait_for_finish(self, res): return self._done_deferred def _choose_initial_peers(self, numqueries): n = self._node full_peerlist = n._client.get_permuted_peers("storage", self._storage_index) # _peerlist is a list of (peerid,conn) tuples for peers that are # worth talking too. This starts with the first numqueries in the # permuted list. If that's not enough to get us a recoverable # version, we expand this to include the first 2*total_shares peerids # (assuming we learn what total_shares is from one of the first # numqueries peers) self._peerlist = [p for p in islice(full_peerlist, numqueries)] # _peerlist_limit is the query limit we used to build this list. If # we later increase this limit, it may be useful to re-scan the # permuted list. self._peerlist_limit = numqueries return self._peerlist def _send_initial_requests(self, peerlist): self._bad_peerids = set() self._running = True self._queries_outstanding = set() self._used_peers = set() self._sharemap = DictOfSets() # shnum -> [(peerid, seqnum, R)..] dl = [] for (peerid, ss) in peerlist: self._queries_outstanding.add(peerid) self._do_query(ss, peerid, self._storage_index, self._read_size) # control flow beyond this point: state machine. Receiving responses # from queries is the input. We might send out more queries, or we # might produce a result. return None def _do_query(self, ss, peerid, storage_index, readsize): self._queries_outstanding.add(peerid) d = ss.callRemote("slot_readv", storage_index, [], [(0, readsize)]) d.addCallback(self._got_results, peerid, readsize, (ss, storage_index)) d.addErrback(self._query_failed, peerid) # errors that aren't handled by _query_failed (and errors caused by # _query_failed) get logged, but we still want to check for doneness. d.addErrback(log.err) d.addBoth(self._check_for_done) return d def _deserialize_pubkey(self, pubkey_s): verifier = rsa.create_verifying_key_from_string(pubkey_s) return verifier def _got_results(self, datavs, peerid, readsize, stuff): self._queries_outstanding.discard(peerid) self._used_peers.add(peerid) if not self._running: return for shnum,datav in datavs.items(): data = datav[0] try: self._got_results_one_share(shnum, data, peerid) except NeedMoreDataError, e: # ah, just re-send the query then. self._read_size = max(self._read_size, e.needed_bytes) # TODO: for MDMF, sanity-check self._read_size: don't let one # server cause us to try to read gigabytes of data from all # other servers. (ss, storage_index) = stuff self._do_query(ss, peerid, storage_index, self._read_size) return except CorruptShareError, e: # log it and give the other shares a chance to be processed f = failure.Failure() self.log("bad share: %s %s" % (f, f.value), level=log.WEIRD) self._bad_peerids.add(peerid) self._last_failure = f pass # all done! def _got_results_one_share(self, shnum, data, peerid): self.log("_got_results: got shnum #%d from peerid %s" % (shnum, idlib.shortnodeid_b2a(peerid))) (seqnum, root_hash, IV, k, N, segsize, datalength, # this might raise NeedMoreDataError, in which case the rest of # the shares are probably short too. _query_failed() will take # responsiblity for re-issuing the queries with a new length. pubkey_s, signature, prefix) = unpack_prefix_and_signature(data) if not self._pubkey: fingerprint = hashutil.ssk_pubkey_fingerprint_hash(pubkey_s) assert len(fingerprint) == 32 if fingerprint != self._node._fingerprint: raise CorruptShareError(peerid, shnum, "pubkey doesn't match fingerprint") self._pubkey = self._deserialize_pubkey(pubkey_s) self._node._populate_pubkey(self._pubkey) verinfo = (seqnum, root_hash, IV, segsize, datalength) if verinfo not in self._valid_versions: # it's a new pair. Verify the signature. valid = self._pubkey.verify(prefix, signature) if not valid: raise CorruptShareError(peerid, shnum, "signature is invalid") # ok, it's a valid verinfo. Add it to the list of validated # versions. self.log(" found valid version %d-%s from %s-sh%d: %d-%d/%d/%d" % (seqnum, base32.b2a(root_hash)[:4], idlib.shortnodeid_b2a(peerid), shnum, k, N, segsize, datalength)) self._valid_versions[verinfo] = (prefix, DictOfSets()) # and make a note of the other parameters we've just learned # NOTE: Retrieve needs to be refactored to put k,N in the verinfo # along with seqnum/etc, to make sure we don't co-mingle shares # from differently-encoded versions of the same file. if self._required_shares is None: self._required_shares = k self._node._populate_required_shares(k) if self._total_shares is None: self._total_shares = N self._node._populate_total_shares(N) # reject shares that don't match our narrow-minded ideas of what # encoding we're going to use. This addresses the immediate needs of # ticket #312, by turning the data corruption into unavailability. To # get back the availability (i.e. make sure that one weird-encoding # share that happens to come back first doesn't make us ignore the # rest of the shares), we need to implement the refactoring mentioned # above. if k != self._required_shares: raise CorruptShareError(peerid, shnum, "share has k=%d, we want k=%d" % (k, self._required_shares)) if N != self._total_shares: raise CorruptShareError(peerid, shnum, "share has N=%d, we want N=%d" % (N, self._total_shares)) # we've already seen this pair, and checked the signature so we # know it's a valid candidate. Accumulate the share info, if # there's enough data present. If not, raise NeedMoreDataError, # which will trigger a re-fetch. _ignored = unpack_share(data) self.log(" found enough data to add share contents") self._valid_versions[verinfo][1].add(shnum, (peerid, data)) def _query_failed(self, f, peerid): if not self._running: return self._queries_outstanding.discard(peerid) self._used_peers.add(peerid) self._last_failure = f self._bad_peerids.add(peerid) self.log("error during query: %s %s" % (f, f.value), level=log.WEIRD) def _check_for_done(self, res): if not self._running: self.log("ODD: _check_for_done but we're not running") return share_prefixes = {} versionmap = DictOfSets() for verinfo, (prefix, sharemap) in self._valid_versions.items(): # sharemap is a dict that maps shnums to sets of (peerid,data). # len(sharemap) is the number of distinct shares that appear to # be available. if len(sharemap) >= self._required_shares: # this one looks retrievable. TODO: our policy of decoding # the first version that we can get is a bit troublesome: in # a small grid with a large expansion factor, a single # out-of-date server can cause us to retrieve an older # version. Fixing this is equivalent to protecting ourselves # against a rollback attack, and the best approach is # probably to say that we won't do _attempt_decode until: # (we've received at least k+EPSILON shares or # we've received at least k shares and ran out of servers) # in that case, identify the verinfos that are decodeable and # attempt the one with the highest (seqnum,R) value. If the # highest seqnum can't be recovered, only then might we fall # back to an older version. d = defer.maybeDeferred(self._attempt_decode, verinfo, sharemap) def _problem(f): self._last_failure = f if f.check(CorruptShareError): self.log("saw corrupt share, rescheduling", level=log.WEIRD) # _attempt_decode is responsible for removing the bad # share, so we can just try again eventually(self._check_for_done, None) return return f d.addCallbacks(self._done, _problem) # TODO: create an errback-routing mechanism to make sure that # weird coding errors will cause the retrieval to fail rather # than hanging forever. Any otherwise-unhandled exceptions # should follow this path. A simple way to test this is to # raise BadNameError in _validate_share_and_extract_data . return # we don't have enough shares yet. Should we send out more queries? if self._queries_outstanding: # there are some running, so just wait for them to come back. # TODO: if our initial guess at k was too low, waiting for these # responses before sending new queries will increase our latency, # so we could speed things up by sending new requests earlier. self.log("ROUTINE: %d queries outstanding" % len(self._queries_outstanding)) return # no more queries are outstanding. Can we send out more? First, # should we be looking at more peers? self.log("need more peers: N=%s, peerlist=%d peerlist_limit=%d" % (self._total_shares, len(self._peerlist), self._peerlist_limit), level=log.UNUSUAL) if self._total_shares is not None: search_distance = self._total_shares * 2 else: search_distance = 20 self.log("search_distance=%d" % search_distance, level=log.UNUSUAL) if self._peerlist_limit < search_distance: # we might be able to get some more peers from the list peers = self._node._client.get_permuted_peers("storage", self._storage_index) self._peerlist = [p for p in islice(peers, search_distance)] self._peerlist_limit = search_distance self.log("added peers, peerlist=%d, peerlist_limit=%d" % (len(self._peerlist), self._peerlist_limit), level=log.UNUSUAL) # are there any peers on the list that we haven't used? new_query_peers = [] for (peerid, ss) in self._peerlist: if peerid not in self._used_peers: new_query_peers.append( (peerid, ss) ) if len(new_query_peers) > 5: # only query in batches of 5. TODO: this is pretty # arbitrary, really I want this to be something like # k - max(known_version_sharecounts) + some extra break if new_query_peers: self.log("sending %d new queries (read %d bytes)" % (len(new_query_peers), self._read_size), level=log.UNUSUAL) for (peerid, ss) in new_query_peers: self._do_query(ss, peerid, self._storage_index, self._read_size) # we'll retrigger when those queries come back return # we've used up all the peers we're allowed to search. Failure. self.log("ran out of peers", level=log.WEIRD) e = NotEnoughPeersError("last failure: %s" % self._last_failure) return self._done(failure.Failure(e)) def _attempt_decode(self, verinfo, sharemap): # sharemap is a dict which maps shnum to [(peerid,data)..] sets. (seqnum, root_hash, IV, segsize, datalength) = verinfo assert len(sharemap) >= self._required_shares, len(sharemap) shares_s = [] for shnum in sorted(sharemap.keys()): for shareinfo in sharemap[shnum]: shares_s.append("#%d" % shnum) shares_s = ",".join(shares_s) self.log("_attempt_decode: version %d-%s, shares: %s" % (seqnum, base32.b2a(root_hash)[:4], shares_s)) # first, validate each share that we haven't validated yet. We use # self._valid_shares to remember which ones we've already checked. shares = {} for shnum, shareinfos in sharemap.items(): assert len(shareinfos) > 0 for shareinfo in shareinfos: # have we already validated the hashes on this share? if shareinfo not in self._valid_shares: # nope: must check the hashes and extract the actual data (peerid,data) = shareinfo try: # The (seqnum+root_hash+IV) tuple for this share was # already verified: specifically, all shares in the # sharemap have a (seqnum+root_hash+IV) pair that was # present in a validly signed prefix. The remainder # of the prefix for this particular share has *not* # been validated, but we don't care since we don't # use it. self._validate_share() is required to check # the hashes on the share data (and hash chains) to # make sure they match root_hash, but is not required # (and is in fact prohibited, because we don't # validate the prefix on all shares) from using # anything else in the share. validator = self._validate_share_and_extract_data sharedata = validator(peerid, root_hash, shnum, data) assert isinstance(sharedata, str) except CorruptShareError, e: self.log("share was corrupt: %s" % e, level=log.WEIRD) sharemap[shnum].discard(shareinfo) if not sharemap[shnum]: # remove the key so the test in _check_for_done # can accurately decide that we don't have enough # shares to try again right now. del sharemap[shnum] # If there are enough remaining shares, # _check_for_done() will try again raise # share is valid: remember it so we won't need to check # (or extract) it again self._valid_shares[shareinfo] = sharedata # the share is now in _valid_shares, so just copy over the # sharedata shares[shnum] = self._valid_shares[shareinfo] # now that the big loop is done, all shares in the sharemap are # valid, and they're all for the same seqnum+root_hash version, so # it's now down to doing FEC and decrypt. assert len(shares) >= self._required_shares, len(shares) d = defer.maybeDeferred(self._decode, shares, segsize, datalength) d.addCallback(self._decrypt, IV, seqnum, root_hash) return d def _validate_share_and_extract_data(self, peerid, root_hash, shnum, data): # 'data' is the whole SMDF share self.log("_validate_share_and_extract_data[%d]" % shnum) assert data[0] == "\x00" pieces = unpack_share(data) (seqnum, root_hash_copy, IV, k, N, segsize, datalen, pubkey, signature, share_hash_chain, block_hash_tree, share_data, enc_privkey) = pieces assert isinstance(share_data, str) # build the block hash tree. SDMF has only one leaf. leaves = [hashutil.block_hash(share_data)] t = hashtree.HashTree(leaves) if list(t) != block_hash_tree: raise CorruptShareError(peerid, shnum, "block hash tree failure") share_hash_leaf = t[0] t2 = hashtree.IncompleteHashTree(N) # root_hash was checked by the signature t2.set_hashes({0: root_hash}) try: t2.set_hashes(hashes=share_hash_chain, leaves={shnum: share_hash_leaf}) except (hashtree.BadHashError, hashtree.NotEnoughHashesError), e: msg = "corrupt hashes: %s" % (e,) raise CorruptShareError(peerid, shnum, msg) self.log(" data valid! len=%d" % len(share_data)) return share_data def _decode(self, shares_dict, segsize, datalength): # we ought to know these values by now assert self._required_shares is not None assert self._total_shares is not None # shares_dict is a dict mapping shnum to share data, but the codec # wants two lists. shareids = []; shares = [] for shareid, share in shares_dict.items(): shareids.append(shareid) shares.append(share) assert len(shareids) >= self._required_shares, len(shareids) # zfec really doesn't want extra shares shareids = shareids[:self._required_shares] shares = shares[:self._required_shares] fec = codec.CRSDecoder() params = "%d-%d-%d" % (segsize, self._required_shares, self._total_shares) fec.set_serialized_params(params) self.log("params %s, we have %d shares" % (params, len(shares))) self.log("about to decode, shareids=%s" % (shareids,)) d = defer.maybeDeferred(fec.decode, shares, shareids) def _done(buffers): self.log(" decode done, %d buffers" % len(buffers)) segment = "".join(buffers) self.log(" joined length %d, datalength %d" % (len(segment), datalength)) segment = segment[:datalength] self.log(" segment len=%d" % len(segment)) return segment def _err(f): self.log(" decode failed: %s" % f) return f d.addCallback(_done) d.addErrback(_err) return d def _decrypt(self, crypttext, IV, seqnum, root_hash): key = hashutil.ssk_readkey_data_hash(IV, self._readkey) decryptor = AES(key) plaintext = decryptor.process(crypttext) # it worked, so record the seqnum and root_hash for next time self._node._populate_seqnum(seqnum) self._node._populate_root_hash(root_hash) return plaintext def _done(self, contents): self.log("DONE") self._running = False eventually(self._done_deferred.callback, contents) class DictOfSets(dict): def add(self, key, value): if key in self: self[key].add(value) else: self[key] = set([value]) class Publish: """I represent a single act of publishing the mutable file to the grid.""" def __init__(self, filenode): self._node = filenode self._storage_index = self._node.get_storage_index() self._log_prefix = prefix = storage.si_b2a(self._storage_index)[:5] num = self._node._client.log("Publish(%s): starting" % prefix) self._log_number = num def log(self, *args, **kwargs): if 'parent' not in kwargs: kwargs['parent'] = self._log_number num = log.msg(*args, **kwargs) return num def log_err(self, *args, **kwargs): if 'parent' not in kwargs: kwargs['parent'] = self._log_number num = log.err(*args, **kwargs) return num def publish(self, newdata): """Publish the filenode's current contents. Returns a Deferred that fires (with None) when the publish has done as much work as it's ever going to do, or errbacks with ConsistencyError if it detects a simultaneous write. """ # 1: generate shares (SDMF: files are small, so we can do it in RAM) # 2: perform peer selection, get candidate servers # 2a: send queries to n+epsilon servers, to determine current shares # 2b: based upon responses, create target map # 3: send slot_testv_and_readv_and_writev messages # 4: as responses return, update share-dispatch table # 4a: may need to run recovery algorithm # 5: when enough responses are back, we're done self.log("starting publish, datalen is %s" % len(newdata)) self._writekey = self._node.get_writekey() assert self._writekey, "need write capability to publish" old_roothash = self._node._current_roothash old_seqnum = self._node._current_seqnum assert old_seqnum is not None, "must read before replace" self._new_seqnum = old_seqnum + 1 # read-before-replace also guarantees these fields are available readkey = self._node.get_readkey() required_shares = self._node.get_required_shares() total_shares = self._node.get_total_shares() self._pubkey = self._node.get_pubkey() # these two may not be, we might have to get them from the first peer self._privkey = self._node.get_privkey() self._encprivkey = self._node.get_encprivkey() IV = os.urandom(16) # we read only 1KB because all we generally care about is the seqnum # ("prefix") info, so we know which shares are where. We need to get # the privkey from somebody, which means reading more like 3KB, but # the code in _obtain_privkey will ensure that we manage that even if # we need an extra roundtrip. TODO: arrange to read 3KB from one peer # who is likely to hold a share (like, say, ourselves), so we can # avoid the latency of that extra roundtrip. self._read_size = 1000 d = defer.succeed(total_shares) d.addCallback(self._query_peers) d.addCallback(self._obtain_privkey) d.addCallback(self._encrypt_and_encode, newdata, readkey, IV, required_shares, total_shares) d.addCallback(self._generate_shares, self._new_seqnum, IV) d.addCallback(self._send_shares, IV) d.addCallback(self._maybe_recover) d.addCallback(lambda res: None) return d def _query_peers(self, total_shares): self.log("_query_peers") storage_index = self._storage_index # In 0.7.0, we went through extra work to make sure that we include # ourselves in the peerlist, mainly to match Retrieve (which did the # same thing. With the post-0.7.0 Introducer refactoring, we got rid # of the include-myself flags, and standardized on the # uploading/downloading node not being special. # One nice feature of the old approach was that by putting a share on # the local storage server, we're more likely to be able to retrieve # a copy of the encrypted private key (even if all the old servers # have gone away), so we can regenerate new shares even if we can't # retrieve the old contents. This need will eventually go away when # we switch to DSA-based mutable files (which store the private key # in the URI). peerlist = self._node._client.get_permuted_peers("storage", storage_index) current_share_peers = DictOfSets() reachable_peers = {} # list of (peerid, shnum, offset, length) where the encprivkey might # be found self._encprivkey_shares = [] EPSILON = total_shares / 2 #partial_peerlist = islice(peerlist, total_shares + EPSILON) partial_peerlist = peerlist[:total_shares+EPSILON] self._storage_servers = {} dl = [] for permutedid, (peerid, ss) in enumerate(partial_peerlist): self._storage_servers[peerid] = ss d = self._do_query(ss, peerid, storage_index) d.addCallback(self._got_query_results, peerid, permutedid, reachable_peers, current_share_peers) dl.append(d) d = defer.DeferredList(dl) d.addCallback(self._got_all_query_results, total_shares, reachable_peers, current_share_peers) # TODO: add an errback to, probably to ignore that peer # TODO: if we can't get a privkey from these servers, consider # looking farther afield. Be aware of the old 0.7.0 behavior that # causes us to create our initial directory before we've connected to # anyone but ourselves.. those old directories may not be # retrieveable if our own server is no longer in the early part of # the permuted peerlist. return d def _do_query(self, ss, peerid, storage_index): self.log("querying %s" % idlib.shortnodeid_b2a(peerid)) d = ss.callRemote("slot_readv", storage_index, [], [(0, self._read_size)]) return d def _got_query_results(self, datavs, peerid, permutedid, reachable_peers, current_share_peers): lp = self.log(format="_got_query_results from %(peerid)s", peerid=idlib.shortnodeid_b2a(peerid)) assert isinstance(datavs, dict) reachable_peers[peerid] = permutedid if not datavs: self.log("peer has no shares", parent=lp) for shnum, datav in datavs.items(): lp2 = self.log("peer has shnum %d" % shnum, parent=lp) assert len(datav) == 1 data = datav[0] # We want (seqnum, root_hash, IV) from all servers to know what # versions we are replacing. We want the encprivkey from one # server (assuming it's valid) so we know our own private key, so # we can sign our update. SMDF: read the whole share from each # server. TODO: later we can optimize this to transfer less data. # we assume that we have enough data to extract the signature. # TODO: if this raises NeedMoreDataError, arrange to do another # read pass. r = unpack_prefix_and_signature(data) (seqnum, root_hash, IV, k, N, segsize, datalen, pubkey_s, signature, prefix) = r # self._pubkey is present because we require read-before-replace valid = self._pubkey.verify(prefix, signature) if not valid: self.log(format="bad signature from %(peerid)s shnum %(shnum)d", peerid=idlib.shortnodeid_b2a(peerid), shnum=shnum, parent=lp2, level=log.WEIRD) continue self.log(format="peer has goodsig shnum %(shnum)d seqnum %(seqnum)d", shnum=shnum, seqnum=seqnum, parent=lp2, level=log.NOISY) share = (shnum, seqnum, root_hash) current_share_peers.add(shnum, (peerid, seqnum, root_hash) ) if not self._privkey: self._try_to_extract_privkey(data, peerid, shnum) def _try_to_extract_privkey(self, data, peerid, shnum): try: r = unpack_share(data) except NeedMoreDataError, e: # this share won't help us. oh well. offset = e.encprivkey_offset length = e.encprivkey_length self.log("shnum %d on peerid %s: share was too short (%dB) " "to get the encprivkey; [%d:%d] ought to hold it" % (shnum, idlib.shortnodeid_b2a(peerid), len(data), offset, offset+length)) # NOTE: if uncoordinated writes are taking place, someone might # change the share (and most probably move the encprivkey) before # we get a chance to do one of these reads and fetch it. This # will cause us to see a NotEnoughPeersError(unable to fetch # privkey) instead of an UncoordinatedWriteError . This is a # nuisance, but it will go away when we move to DSA-based mutable # files (since the privkey will be small enough to fit in the # write cap). self._encprivkey_shares.append( (peerid, shnum, offset, length)) return (seqnum, root_hash, IV, k, N, segsize, datalen, pubkey, signature, share_hash_chain, block_hash_tree, share_data, enc_privkey) = r return self._try_to_validate_privkey(enc_privkey, peerid, shnum) def _try_to_validate_privkey(self, enc_privkey, peerid, shnum): alleged_privkey_s = self._node._decrypt_privkey(enc_privkey) alleged_writekey = hashutil.ssk_writekey_hash(alleged_privkey_s) if alleged_writekey != self._writekey: self.log("invalid privkey from %s shnum %d" % (idlib.nodeid_b2a(peerid)[:8], shnum), level=log.WEIRD) return # it's good self.log("got valid privkey from shnum %d on peerid %s" % (shnum, idlib.shortnodeid_b2a(peerid))) self._privkey = rsa.create_signing_key_from_string(alleged_privkey_s) self._encprivkey = enc_privkey self._node._populate_encprivkey(self._encprivkey) self._node._populate_privkey(self._privkey) def _got_all_query_results(self, res, total_shares, reachable_peers, current_share_peers): self.log("_got_all_query_results") # now that we know everything about the shares currently out there, # decide where to place the new shares. # if an old share X is on a node, put the new share X there too. # TODO: 1: redistribute shares to achieve one-per-peer, by copying # shares from existing peers to new (less-crowded) ones. The # old shares must still be updated. # TODO: 2: move those shares instead of copying them, to reduce future # update work # if log.recording_noisy logmsg = [] for shnum in range(total_shares): logmsg2 = [] for oldplace in current_share_peers.get(shnum, []): (peerid, seqnum, R) = oldplace logmsg2.append("%s:#%d:R=%s" % (idlib.shortnodeid_b2a(peerid), seqnum, base32.b2a(R)[:4])) logmsg.append("sh%d on (%s)" % (shnum, "/".join(logmsg2))) self.log("sharemap: %s" % (", ".join(logmsg)), level=log.NOISY) self.log("we are planning to push new seqnum=#%d" % self._new_seqnum, level=log.NOISY) shares_needing_homes = range(total_shares) target_map = DictOfSets() # maps shnum to set((peerid,oldseqnum,oldR)) shares_per_peer = DictOfSets() for shnum in range(total_shares): for oldplace in current_share_peers.get(shnum, []): (peerid, seqnum, R) = oldplace if seqnum >= self._new_seqnum: self.log("somebody has a newer sequence number than what we were uploading", level=log.WEIRD) self.log(format="peerid=%(peerid)s, theirs=%(seqnum)d, mine=%(new_seqnum)d", peerid=idlib.shortnodeid_b2a(peerid), seqnum=seqnum, new_seqnum=self._new_seqnum) raise UncoordinatedWriteError("somebody has a newer sequence number than us") target_map.add(shnum, oldplace) shares_per_peer.add(peerid, shnum) if shnum in shares_needing_homes: shares_needing_homes.remove(shnum) # now choose homes for the remaining shares. We prefer peers with the # fewest target shares, then peers with the lowest permuted index. If # there are no shares already in place, this will assign them # one-per-peer in the normal permuted order. while shares_needing_homes: if not reachable_peers: prefix = storage.si_b2a(self._node.get_storage_index())[:5] raise NotEnoughPeersError("ran out of peers during upload of (%s); shares_needing_homes: %s, reachable_peers: %s" % (prefix, shares_needing_homes, reachable_peers,)) shnum = shares_needing_homes.pop(0) possible_homes = reachable_peers.keys() possible_homes.sort(lambda a,b: cmp( (len(shares_per_peer.get(a, [])), reachable_peers[a]), (len(shares_per_peer.get(b, [])), reachable_peers[b]) )) target_peerid = possible_homes[0] target_map.add(shnum, (target_peerid, None, None) ) shares_per_peer.add(target_peerid, shnum) assert not shares_needing_homes target_info = (target_map, shares_per_peer) return target_info def _obtain_privkey(self, target_info): # make sure we've got a copy of our private key. if self._privkey: # Must have picked it up during _query_peers. We're good to go. return target_info # Nope, we haven't managed to grab a copy, and we still need it. Ask # peers one at a time until we get a copy. Only bother asking peers # who've admitted to holding a share. target_map, shares_per_peer = target_info # pull shares from self._encprivkey_shares if not self._encprivkey_shares: raise NotEnoughPeersError("Unable to find a copy of the privkey") (peerid, shnum, offset, length) = self._encprivkey_shares.pop(0) ss = self._storage_servers[peerid] self.log("trying to obtain privkey from %s shnum %d" % (idlib.shortnodeid_b2a(peerid), shnum)) d = self._do_privkey_query(ss, peerid, shnum, offset, length) d.addErrback(self.log_err) d.addCallback(lambda res: self._obtain_privkey(target_info)) return d def _do_privkey_query(self, rref, peerid, shnum, offset, length): d = rref.callRemote("slot_readv", self._storage_index, [shnum], [(offset, length)] ) d.addCallback(self._privkey_query_response, peerid, shnum) return d def _privkey_query_response(self, datav, peerid, shnum): data = datav[shnum][0] self._try_to_validate_privkey(data, peerid, shnum) def _encrypt_and_encode(self, target_info, newdata, readkey, IV, required_shares, total_shares): self.log("_encrypt_and_encode") key = hashutil.ssk_readkey_data_hash(IV, readkey) enc = AES(key) crypttext = enc.process(newdata) assert len(crypttext) == len(newdata) # now apply FEC self.MAX_SEGMENT_SIZE = 1024*1024 data_length = len(crypttext) segment_size = min(self.MAX_SEGMENT_SIZE, len(crypttext)) # this must be a multiple of self.required_shares segment_size = mathutil.next_multiple(segment_size, required_shares) if segment_size: self.num_segments = mathutil.div_ceil(len(crypttext), segment_size) else: self.num_segments = 0 assert self.num_segments in [0, 1,] # SDMF restrictions fec = codec.CRSEncoder() fec.set_params(segment_size, required_shares, total_shares) piece_size = fec.get_block_size() crypttext_pieces = [None] * required_shares for i in range(len(crypttext_pieces)): offset = i * piece_size piece = crypttext[offset:offset+piece_size] piece = piece + "\x00"*(piece_size - len(piece)) # padding crypttext_pieces[i] = piece assert len(piece) == piece_size d = fec.encode(crypttext_pieces) d.addCallback(lambda shares_and_shareids: (shares_and_shareids, required_shares, total_shares, segment_size, data_length, target_info) ) return d def _generate_shares(self, (shares_and_shareids, required_shares, total_shares, segment_size, data_length, target_info), seqnum, IV): self.log("_generate_shares") # we should know these by now privkey = self._privkey encprivkey = self._encprivkey pubkey = self._pubkey (shares, share_ids) = shares_and_shareids assert len(shares) == len(share_ids) assert len(shares) == total_shares all_shares = {} block_hash_trees = {} share_hash_leaves = [None] * len(shares) for i in range(len(shares)): share_data = shares[i] shnum = share_ids[i] all_shares[shnum] = share_data # build the block hash tree. SDMF has only one leaf. leaves = [hashutil.block_hash(share_data)] t = hashtree.HashTree(leaves) block_hash_trees[shnum] = block_hash_tree = list(t) share_hash_leaves[shnum] = t[0] for leaf in share_hash_leaves: assert leaf is not None share_hash_tree = hashtree.HashTree(share_hash_leaves) share_hash_chain = {} for shnum in range(total_shares): needed_hashes = share_hash_tree.needed_hashes(shnum) share_hash_chain[shnum] = dict( [ (i, share_hash_tree[i]) for i in needed_hashes ] ) root_hash = share_hash_tree[0] assert len(root_hash) == 32 self.log("my new root_hash is %s" % base32.b2a(root_hash)) prefix = pack_prefix(seqnum, root_hash, IV, required_shares, total_shares, segment_size, data_length) # now pack the beginning of the share. All shares are the same up # to the signature, then they have divergent share hash chains, # then completely different block hash trees + IV + share data, # then they all share the same encprivkey at the end. The sizes # of everything are the same for all shares. signature = privkey.sign(prefix) verification_key = pubkey.serialize() final_shares = {} for shnum in range(total_shares): final_share = pack_share(prefix, verification_key, signature, share_hash_chain[shnum], block_hash_trees[shnum], all_shares[shnum], encprivkey) final_shares[shnum] = final_share return (seqnum, root_hash, final_shares, target_info) def _send_shares(self, (seqnum, root_hash, final_shares, target_info), IV): self.log("_send_shares") # we're finally ready to send out our shares. If we encounter any # surprises here, it's because somebody else is writing at the same # time. (Note: in the future, when we remove the _query_peers() step # and instead speculate about [or remember] which shares are where, # surprises here are *not* indications of UncoordinatedWriteError, # and we'll need to respond to them more gracefully.) target_map, shares_per_peer = target_info my_checkstring = pack_checkstring(seqnum, root_hash, IV) peer_messages = {} expected_old_shares = {} for shnum, peers in target_map.items(): for (peerid, old_seqnum, old_root_hash) in peers: testv = [(0, len(my_checkstring), "le", my_checkstring)] new_share = final_shares[shnum] writev = [(0, new_share)] if peerid not in peer_messages: peer_messages[peerid] = {} peer_messages[peerid][shnum] = (testv, writev, None) if peerid not in expected_old_shares: expected_old_shares[peerid] = {} expected_old_shares[peerid][shnum] = (old_seqnum, old_root_hash) read_vector = [(0, len(my_checkstring))] dl = [] # ok, send the messages! self._surprised = False dispatch_map = DictOfSets() for peerid, tw_vectors in peer_messages.items(): write_enabler = self._node.get_write_enabler(peerid) renew_secret = self._node.get_renewal_secret(peerid) cancel_secret = self._node.get_cancel_secret(peerid) secrets = (write_enabler, renew_secret, cancel_secret) d = self._do_testreadwrite(peerid, secrets, tw_vectors, read_vector) d.addCallback(self._got_write_answer, tw_vectors, my_checkstring, peerid, expected_old_shares[peerid], dispatch_map) dl.append(d) d = defer.DeferredList(dl) d.addCallback(lambda res: (self._surprised, dispatch_map)) return d def _do_testreadwrite(self, peerid, secrets, tw_vectors, read_vector): storage_index = self._node._uri.storage_index ss = self._storage_servers[peerid] d = ss.callRemote("slot_testv_and_readv_and_writev", storage_index, secrets, tw_vectors, read_vector) return d def _got_write_answer(self, answer, tw_vectors, my_checkstring, peerid, expected_old_shares, dispatch_map): lp = self.log("_got_write_answer from %s" % idlib.shortnodeid_b2a(peerid)) wrote, read_data = answer surprised = False (new_seqnum,new_root_hash,new_IV) = unpack_checkstring(my_checkstring) if wrote: for shnum in tw_vectors: dispatch_map.add(shnum, (peerid, new_seqnum, new_root_hash)) else: # surprise! our testv failed, so the write did not happen self.log("our testv failed, that write did not happen", parent=lp, level=log.WEIRD) surprised = True for shnum, (old_cs,) in read_data.items(): (old_seqnum, old_root_hash, IV) = unpack_checkstring(old_cs) if not wrote: dispatch_map.add(shnum, (peerid, old_seqnum, old_root_hash)) if shnum not in expected_old_shares: # surprise! there was a share we didn't know about self.log("they had share %d that we didn't know about" % shnum, parent=lp, level=log.WEIRD) surprised = True else: seqnum, root_hash = expected_old_shares[shnum] if seqnum is not None: if seqnum != old_seqnum or root_hash != old_root_hash: # surprise! somebody modified the share on us self.log("somebody modified the share on us:" " shnum=%d: I thought they had #%d:R=%s," " but testv reported #%d:R=%s" % (shnum, seqnum, base32.b2a(root_hash)[:4], old_seqnum, base32.b2a(old_root_hash)[:4]), parent=lp, level=log.WEIRD) surprised = True if surprised: self._surprised = True def _log_dispatch_map(self, dispatch_map): for shnum, places in dispatch_map.items(): sent_to = [(idlib.shortnodeid_b2a(peerid), seqnum, base32.b2a(root_hash)[:4]) for (peerid,seqnum,root_hash) in places] self.log(" share %d sent to: %s" % (shnum, sent_to), level=log.NOISY) def _maybe_recover(self, (surprised, dispatch_map)): self.log("_maybe_recover, surprised=%s, dispatch_map:" % surprised, level=log.NOISY) self._log_dispatch_map(dispatch_map) if not surprised: self.log(" no recovery needed") return self.log("We need recovery!", level=log.WEIRD) print "RECOVERY NOT YET IMPLEMENTED" # but dispatch_map will help us do it raise UncoordinatedWriteError("I was surprised!") # use client.create_mutable_file() to make one of these class MutableFileNode: implements(IMutableFileNode) publish_class = Publish retrieve_class = Retrieve SIGNATURE_KEY_SIZE = 2048 def __init__(self, client): self._client = client self._pubkey = None # filled in upon first read self._privkey = None # filled in if we're mutable self._required_shares = None # ditto self._total_shares = None # ditto self._sharemap = {} # known shares, shnum-to-[nodeids] self._current_data = None # SDMF: we're allowed to cache the contents self._current_roothash = None # ditto self._current_seqnum = None # ditto def __repr__(self): return "<%s %x %s %s>" % (self.__class__.__name__, id(self), self.is_readonly() and 'RO' or 'RW', hasattr(self, '_uri') and self._uri.abbrev()) def init_from_uri(self, myuri): # we have the URI, but we have not yet retrieved the public # verification key, nor things like 'k' or 'N'. If and when someone # wants to get our contents, we'll pull from shares and fill those # in. self._uri = IMutableFileURI(myuri) if not self._uri.is_readonly(): self._writekey = self._uri.writekey self._readkey = self._uri.readkey self._storage_index = self._uri.storage_index self._fingerprint = self._uri.fingerprint # the following values are learned during Retrieval # self._pubkey # self._required_shares # self._total_shares # and these are needed for Publish. They are filled in by Retrieval # if possible, otherwise by the first peer that Publish talks to. self._privkey = None self._encprivkey = None return self def create(self, initial_contents): """Call this when the filenode is first created. This will generate the keys, generate the initial shares, wait until at least numpeers are connected, allocate shares, and upload the initial contents. Returns a Deferred that fires (with the MutableFileNode instance you should use) when it completes. """ self._required_shares = 3 self._total_shares = 10 d = defer.maybeDeferred(self._generate_pubprivkeys) def _generated( (pubkey, privkey) ): self._pubkey, self._privkey = pubkey, privkey pubkey_s = self._pubkey.serialize() privkey_s = self._privkey.serialize() self._writekey = hashutil.ssk_writekey_hash(privkey_s) self._encprivkey = self._encrypt_privkey(self._writekey, privkey_s) self._fingerprint = hashutil.ssk_pubkey_fingerprint_hash(pubkey_s) self._uri = WriteableSSKFileURI(self._writekey, self._fingerprint) self._readkey = self._uri.readkey self._storage_index = self._uri.storage_index # TODO: seqnum/roothash: really we mean "doesn't matter since # nobody knows about us yet" self._current_seqnum = 0 self._current_roothash = "\x00"*32 return self._publish(initial_contents) d.addCallback(_generated) return d def _generate_pubprivkeys(self): # RSA key generation for a 2048 bit key takes between 0.8 and 3.2 secs signer = rsa.generate(self.SIGNATURE_KEY_SIZE) verifier = signer.get_verifying_key() return verifier, signer def _publish(self, initial_contents): p = self.publish_class(self) d = p.publish(initial_contents) d.addCallback(lambda res: self) return d def _encrypt_privkey(self, writekey, privkey): enc = AES(writekey) crypttext = enc.process(privkey) return crypttext def _decrypt_privkey(self, enc_privkey): enc = AES(self._writekey) privkey = enc.process(enc_privkey) return privkey def _populate(self, stuff): # the Retrieval object calls this with values it discovers when # downloading the slot. This is how a MutableFileNode that was # created from a URI learns about its full key. pass def _populate_pubkey(self, pubkey): self._pubkey = pubkey def _populate_required_shares(self, required_shares): self._required_shares = required_shares def _populate_total_shares(self, total_shares): self._total_shares = total_shares def _populate_seqnum(self, seqnum): self._current_seqnum = seqnum def _populate_root_hash(self, root_hash): self._current_roothash = root_hash def _populate_privkey(self, privkey): self._privkey = privkey def _populate_encprivkey(self, encprivkey): self._encprivkey = encprivkey def get_write_enabler(self, peerid): assert len(peerid) == 20 return hashutil.ssk_write_enabler_hash(self._writekey, peerid) def get_renewal_secret(self, peerid): assert len(peerid) == 20 crs = self._client.get_renewal_secret() frs = hashutil.file_renewal_secret_hash(crs, self._storage_index) return hashutil.bucket_renewal_secret_hash(frs, peerid) def get_cancel_secret(self, peerid): assert len(peerid) == 20 ccs = self._client.get_cancel_secret() fcs = hashutil.file_cancel_secret_hash(ccs, self._storage_index) return hashutil.bucket_cancel_secret_hash(fcs, peerid) def get_writekey(self): return self._writekey def get_readkey(self): return self._readkey def get_storage_index(self): return self._storage_index def get_privkey(self): return self._privkey def get_encprivkey(self): return self._encprivkey def get_pubkey(self): return self._pubkey def get_required_shares(self): return self._required_shares def get_total_shares(self): return self._total_shares def get_uri(self): return self._uri.to_string() def get_size(self): return "?" # TODO: this is likely to cause problems, not being an int def get_readonly(self): if self.is_readonly(): return self ro = MutableFileNode(self._client) ro.init_from_uri(self._uri.get_readonly()) return ro def get_readonly_uri(self): return self._uri.get_readonly().to_string() def is_mutable(self): return self._uri.is_mutable() def is_readonly(self): return self._uri.is_readonly() def __hash__(self): return hash((self.__class__, self.uri)) def __cmp__(self, them): if cmp(type(self), type(them)): return cmp(type(self), type(them)) if cmp(self.__class__, them.__class__): return cmp(self.__class__, them.__class__) return cmp(self.uri, them.uri) def get_verifier(self): return IMutableFileURI(self._uri).get_verifier() def check(self): verifier = self.get_verifier() return self._client.getServiceNamed("checker").check(verifier) def download(self, target): # fake it. TODO: make this cleaner. d = self.download_to_data() def _done(data): target.open(len(data)) target.write(data) target.close() return target.finish() d.addCallback(_done) return d def download_to_data(self): r = Retrieve(self) return r.retrieve() def replace(self, newdata): r = Retrieve(self) d = r.retrieve() d.addCallback(lambda res: self._publish(newdata)) return d