def _get_nodes_for_exploration(self) -> Iterator[Tuple[NodeID, int]]:
candidates = self._get_ordered_candidates()
candidate_triplets = sliding_window(
3, caboose(cons(None, candidates), None))
for left_id, node_id, right_id in candidate_triplets:
# Filter out nodes that have already been queried
if node_id in self.queried:
continue
elif node_id in self.in_flight:
continue
# By looking at the two closest *sibling* nodes we can determine
# how much of their routing table we need to query. We consider
# the maximum logarithmic distance to either neighbor which
# guarantees that we look up the region of the network that this
# node knows the most about, but avoid querying buckets for which
# other nodes are going to have a more complete view.
if left_id is None:
left_distance = 256
else:
left_distance = compute_log_distance(node_id, left_id)
if right_id is None:
right_distance = 256
else:
right_distance = compute_log_distance(node_id, right_id)
# We use the maximum distance to ensure that we cover every part of
# the address space.
yield node_id, max(left_distance, right_distance)
def initialize_scenario(
validator_set_contract: Contract,
transition_heights: Sequence[int] = None
) -> Tuple[List[ValidatorDefinitionRange], List[Union[Type[Contract],
Contract]]]:
_transition_heights: List[Union[int, None]] = (
list(transition_heights) if transition_heights is not None else [])
w3 = validator_set_contract.web3
validator_definition_ranges = []
contracts: List[Union[Type[Contract], Contract]] = []
for enter_height, leave_height in sliding_window(
2, _transition_heights + [None]):
deployment_tx_hash = validator_set_contract.constructor().transact()
deployment_receipt: TxReceipt = w3.eth.waitForTransactionReceipt(
deployment_tx_hash)
contract = w3.eth.contract(
address=deployment_receipt["contractAddress"],
abi=validator_set_contract.abi,
)
contracts.append(contract)
validator_definition_ranges.append(
ValidatorDefinitionRange(
enter_height=enter_height,
leave_height=leave_height,
is_contract=True,
contract_address=contracts[-1].address,
validators=None,
))
return validator_definition_ranges, contracts
def _introduce_collisions(all_attestations_by_index, block_producer, state,
config):
"""
Find some attestations for later epochs for the validators
that are currently attesting in each source of attestation.
"""
collisions = (all_attestations_by_index[0], )
for src, dst in sliding_window(2, all_attestations_by_index):
if not src:
# src can be empty at low validator count
collisions += (dst, )
continue
src_index = random.choice(list(src.keys()))
src_val = src[src_index]
src_slot, _ = src_val
src_epoch = compute_epoch_at_slot(src_slot, config.SLOTS_PER_EPOCH)
dst_epoch = src_epoch + 1
collision = _find_collision(
state,
config,
validator_index=src_index,
epoch=dst_epoch,
block_producer=block_producer,
)
collisions += (merge(dst, collision), )
return collisions
async def _find_newest_matching_skeleton_header(self, peer: TChainPeer) -> BlockHeader:
start_num = await self.wait(self._launch_strategy.get_starting_block_number())
# after returning this header, we request the next gap, and prefer that one header
# is new to us, which may be the next header in this mini-skeleton. (hence the -1 below)
skip = MAX_HEADERS_FETCH - 1
skeleton_launch_headers = await self._fetch_headers_from(peer, start_num, skip=skip)
if len(skeleton_launch_headers) == 0:
raise ValidationError(
f"{peer} gave 0 headers when seeking common skeleton ancestors from {start_num}"
)
# check the first returned value
first = skeleton_launch_headers[0]
first_is_present = await self.wait(self._db.coro_header_exists(first.hash))
if not first_is_present:
await self._log_ancester_failure(peer, first)
raise ValidationError(f"No common ancestor with {peer}, who started with {first}")
elif len(skeleton_launch_headers) == 1:
return skeleton_launch_headers[0]
else:
for parent, child in sliding_window(2, skeleton_launch_headers):
is_present = await self.wait(self._db.coro_header_exists(child.hash))
if not is_present:
return parent
else:
# All headers are present, probably the canonical head updated recently
# Return the newest one
return skeleton_launch_headers[-1]
def validate_chain(cls,
root: BlockHeader,
descendants: Tuple[BlockHeader, ...],
seal_check_random_sample_rate: int = 1) -> None:
"""
Validate that all of the descendents are valid, given that the root header is valid.
By default, check the seal validity (Proof-of-Work on Ethereum 1.x mainnet) of all headers.
This can be expensive. Instead, check a random sample of seals using
seal_check_random_sample_rate.
"""
all_indices = range(len(descendants))
if seal_check_random_sample_rate == 1:
indices_to_check_seal = set(all_indices)
else:
sample_size = len(all_indices) // seal_check_random_sample_rate
indices_to_check_seal = set(random.sample(all_indices,
sample_size))
header_pairs = sliding_window(2, concatv([root], descendants))
for index, (parent, child) in enumerate(header_pairs):
if child.parent_hash != parent.hash:
raise ValidationError(
"Invalid header chain; {} has parent {}, but expected {}".
format(child, child.parent_hash, parent.hash))
should_check_seal = index in indices_to_check_seal
vm_class = cls.get_vm_class_for_block_number(child.block_number)
vm_class.validate_header(child,
parent,
check_seal=should_check_seal)
def validate_chain(
self,
root: BlockHeaderAPI,
descendants: Tuple[BlockHeaderAPI, ...],
seal_check_random_sample_rate: int = 1) -> None:
all_indices = range(len(descendants))
if seal_check_random_sample_rate == 1:
indices_to_check_seal = set(all_indices)
elif seal_check_random_sample_rate == 0:
indices_to_check_seal = set()
else:
sample_size = len(all_indices) // seal_check_random_sample_rate
indices_to_check_seal = set(random.sample(all_indices, sample_size))
header_pairs = sliding_window(2, concatv([root], descendants))
for index, (parent, child) in enumerate(header_pairs):
if child.parent_hash != parent.hash:
raise ValidationError(
f"Invalid header chain; {child} has parent {encode_hex(child.parent_hash)},"
f" but expected {encode_hex(parent.hash)}"
)
should_check_seal = index in indices_to_check_seal
vm = self.get_vm(child)
try:
vm.validate_header(child, parent)
except ValidationError as exc:
raise ValidationError(
f"{child} is not a valid child of {parent}: {exc}"
) from exc
if should_check_seal:
vm.validate_seal(child)
def _get_blocks(self,
start_block: BaseBeaconBlock,
max_blocks: int) -> Iterable[BaseBeaconBlock]:
if max_blocks < 0:
raise Exception("Invariant: max blocks cannot be negative")
if max_blocks == 0:
return
yield start_block
blocks_generator = cons(start_block, (
self.db.get_canonical_block_by_slot(slot)
for slot in itertools.count(start_block.slot + 1)
))
max_blocks_generator = take(max_blocks, blocks_generator)
try:
# ensure only a connected chain is returned (breaks might occur if the start block is
# not part of the canonical chain or if the canonical chain changes during execution)
for parent, child in sliding_window(2, max_blocks_generator):
if child.parent_root == parent.hash:
yield child
else:
break
except BlockNotFound:
return
def validate_validator_definition_order(
validator_definition_ranges: Sequence[ValidatorDefinitionRange]
) -> None:
for current_range, next_range in sliding_window(
2, validator_definition_ranges):
if current_range.leave_height != next_range.enter_height:
raise ValueError("Missing validator definition range")
def _persist_header_chain(
cls, db: BaseDB, headers: Iterable[BlockHeader]
) -> Tuple[Tuple[BlockHeader, ...], Tuple[BlockHeader, ...]]:
headers_iterator = iter(headers)
try:
first_header = first(headers_iterator)
except StopIteration:
return tuple(), tuple()
is_genesis = first_header.parent_hash == GENESIS_PARENT_HASH
if not is_genesis and not cls._header_exists(db,
first_header.parent_hash):
raise ParentNotFound(
"Cannot persist block header ({}) with unknown parent ({})".
format(encode_hex(first_header.hash),
encode_hex(first_header.parent_hash)))
if is_genesis:
score = 0
else:
score = cls._get_score(db, first_header.parent_hash)
curr_chain_head = first_header
db.set(
curr_chain_head.hash,
rlp.encode(curr_chain_head),
)
score = cls._set_hash_scores_to_db(db, curr_chain_head, score)
orig_headers_seq = concat([(first_header, ), headers_iterator])
for parent, child in sliding_window(2, orig_headers_seq):
if parent.hash != child.parent_hash:
raise ValidationError(
"Non-contiguous chain. Expected {} to have {} as parent but was {}"
.format(
encode_hex(child.hash),
encode_hex(parent.hash),
encode_hex(child.parent_hash),
))
curr_chain_head = child
db.set(
curr_chain_head.hash,
rlp.encode(curr_chain_head),
)
score = cls._set_hash_scores_to_db(db, curr_chain_head, score)
try:
previous_canonical_head = cls._get_canonical_head(db).hash
head_score = cls._get_score(db, previous_canonical_head)
except CanonicalHeadNotFound:
return cls._set_as_canonical_chain_head(db, curr_chain_head.hash)
if score > head_score:
return cls._set_as_canonical_chain_head(db, curr_chain_head.hash)
return tuple(), tuple()
def _persist_header_chain(
cls,
db: DatabaseAPI,
headers: Iterable[BlockHeaderAPI],
genesis_parent_hash: Hash32,
) -> Tuple[Tuple[BlockHeaderAPI, ...], Tuple[BlockHeaderAPI, ...]]:
headers_iterator = iter(headers)
try:
first_header = first(headers_iterator)
except StopIteration:
return tuple(), tuple()
is_genesis = first_header.parent_hash == genesis_parent_hash
if not is_genesis and not cls._header_exists(db, first_header.parent_hash):
raise ParentNotFound(
f"Cannot persist block header ({encode_hex(first_header.hash)}) "
f"with unknown parent ({encode_hex(first_header.parent_hash)})"
)
if is_genesis:
score = 0
else:
score = cls._get_score(db, first_header.parent_hash)
curr_chain_head = first_header
db.set(
curr_chain_head.hash,
rlp.encode(curr_chain_head),
)
score = cls._set_hash_scores_to_db(db, curr_chain_head, score)
orig_headers_seq = concat([(first_header,), headers_iterator])
for parent, child in sliding_window(2, orig_headers_seq):
if parent.hash != child.parent_hash:
raise ValidationError(
f"Non-contiguous chain. Expected {encode_hex(child.hash)} "
f"to have {encode_hex(parent.hash)} as parent "
f"but was {encode_hex(child.parent_hash)}"
)
curr_chain_head = child
db.set(
curr_chain_head.hash,
rlp.encode(curr_chain_head),
)
score = cls._set_hash_scores_to_db(db, curr_chain_head, score)
try:
previous_canonical_head = cls._get_canonical_head_hash(db)
head_score = cls._get_score(db, previous_canonical_head)
except CanonicalHeadNotFound:
return cls._set_as_canonical_chain_head(db, curr_chain_head, genesis_parent_hash)
if score > head_score:
return cls._set_as_canonical_chain_head(db, curr_chain_head, genesis_parent_hash)
return tuple(), tuple()
def _find_breakpoints(*values: int) -> Iterable[int]:
yield 0
for index, (left, right) in enumerate(sliding_window(2, values), 1):
if left + 1 == right:
continue
else:
yield index
yield len(values)
def _load_state_machines(
sm_configuration: StateMachineConfiguration
) -> Iterable[Tuple[Container[int], MedallaStateMachineFast]]:
sm_configuration += ((FAR_FUTURE_SLOT, None), )
for (first_fork, second_fork) in toolz.sliding_window(2, sm_configuration):
valid_range = range(first_fork[0], second_fork[0])
valid_sm = first_fork[1]()
yield (valid_range, valid_sm)
def _load_state_machines(
sm_configuration: StateMachineConfiguration, chain_db: BaseBeaconChainDB
) -> Iterable[Tuple[Container[int], "BaseBeaconStateMachine"]]:
sm_configuration += ((FAR_FUTURE_SLOT, None),)
for (first_fork, second_fork) in toolz.sliding_window(2, sm_configuration):
valid_range = range(first_fork[0], second_fork[0])
valid_sm = first_fork[1](chain_db)
yield (valid_range, valid_sm)
def test_enr_partitioning(sizes, max_size):
partitions = partition_enr_indices_by_size(sizes, max_size)
indices = [index for partition in partitions for index in partition]
dropped_indices = tuple(index for index, size in enumerate(sizes)
if size > max_size)
assert len(indices) == len(set(indices))
assert set(indices) == set(range(len(sizes))) - set(dropped_indices)
assert all(index1 < index2
for index1, index2 in sliding_window(2, indices))
partitioned_sizes = tuple(
tuple(sizes[index] for index in partition) for partition in partitions)
assert all(sum(partition) <= max_size for partition in partitioned_sizes)
assert all(
sum(partition) + next_partition[0] > max_size
for partition, next_partition in sliding_window(2, partitioned_sizes))
def ensure_branch(block_dicts):
"""make sure we really have a branch, i.e. each block is the parent block
of the following block
raises ValueError if block_dicts is not a branch.
"""
for parent, child in sliding_window(2, block_dicts):
if child.parentHash != parent.hash:
raise ValueError("Given branch is not connected")
def partition_advertisements(
advertisements: Sequence[Advertisement],
max_payload_size: int,
) -> Iterable[Tuple[Advertisement, ...]]:
encoded_sizes = tuple(
len(advertisement.content_key) + ADVERTISEMENT_FIXED_SIZE
for advertisement in advertisements)
partition_indices = _get_partition_indices(encoded_sizes, max_payload_size)
for left, right in sliding_window(2, partition_indices):
yield tuple(advertisements[left:right])
def _get_partition_indices(encoded_sizes: Sequence[int],
max_payload_size: int) -> Iterable[int]:
cumulative_sizes = accumulate(operator.add, encoded_sizes)
offset = 0
yield 0
for idx, (last_size,
size) in enumerate(sliding_window(2, cons(0, cumulative_sizes))):
if size - offset > max_payload_size:
offset = last_size
yield idx
yield len(encoded_sizes)
def first_nonconsecutive_header(headers: Sequence[BlockHeader]) -> int:
"""
:return: index of first child that does not match parent header, or a number
past the end if all are consecutive
"""
for index, (parent, child) in enumerate(sliding_window(2, headers)):
if child.parent_hash != parent.hash:
return index + 1
# return an index off the end to indicate that all headers are consecutive
return len(headers)
def _validate_sequence(self, blocks: Tuple[BaseBeaconBlock, ...]) -> None:
# workaround for https://github.com/pytoolz/cytoolz/issues/123#issuecomment-432905716
if not blocks:
return
for parent, child in sliding_window(2, blocks):
# check that the received blocks form a sequence of descendents connected by parent
# hashes, starting with the oldest ancestor
if child.parent_root != parent.signing_root:
raise ValidationError(
"Returned blocks are not a connected branch")
def _extract_integer_ranges(*values: int) -> Iterable[Tuple[int, int]]:
"""
Take a sequence of integers which is expected to be ordered and return the
most concise definition of the sequence in terms of integer ranges.
- fn(1, 2, 3) -> ((1, 3),)
- fn(1, 2, 3, 7, 8, 9) -> ((1, 3), (7, 9))
- fn(1, 7, 8, 9) -> ((1, 1), (7, 9))
"""
for left, right in sliding_window(2, _find_breakpoints(*values)):
chunk = values[left:right]
yield chunk[0], chunk[-1]
def _validate_gap_invariants(gaps):
# 1. gaps are sorted
for low, high in gaps[0]:
assert high >= low, gaps
# 2. gaps are not overrlapping
for low_range, high_range in sliding_window(2, gaps[0]):
# the top of the low range must not be sequential with the bottom of the high range
assert low_range[1] + 1 < high_range[0], gaps
# 3. final gap does not overlap with the tail
if len(gaps[0]):
final_gap_range = gaps[0][-1]
assert final_gap_range[1] + 1 < gaps[1], gaps
def deserialize_variable_size_parts(self,
offset_pairs: Tuple[Tuple[int, TSedes], ...],
stream: IO[bytes]) -> Iterable[Any]:
offsets, fields = zip(*offset_pairs)
*head_fields, last_field = fields
for sedes, (left_offset, right_offset) in zip(head_fields, sliding_window(2, offsets)):
field_length = right_offset - left_offset
field_data = read_exact(field_length, stream)
yield sedes.deserialize(field_data)
# simply reading to the end of the current stream gives us all of the final element data
final_field_data = stream.read()
yield last_field.deserialize(final_field_data)
def filter_overlapping_paths(*paths: TreePath) -> Iterable[TreePath]:
"""
Filter out any paths that are a prefix of another path.
"""
if not paths:
return
sorted_paths = sorted(paths)
for left, right in sliding_window(2, sorted_paths):
if right[:len(left)] == left:
continue
else:
yield left
# Because of the use of `sliding_window` we need to manually yield the last
# path
yield sorted_paths[-1]
def merklize_elements(elements: Sequence[ProofElement]) -> Hash32:
"""
Given a set of `ProofElement` compute the `hash_tree_root`.
This also verifies that the proof is both "well-formed" and "minimal".
"""
elements_by_depth = groupby(operator.attrgetter("depth"), elements)
max_depth = max(elements_by_depth.keys())
for depth in range(max_depth, 0, -1):
try:
elements_at_depth = sorted(elements_by_depth.pop(depth))
except KeyError:
continue
# Verify that all of the paths at this level are unique
paths = set(el.path for el in elements_at_depth)
if len(paths) != len(elements_at_depth):
raise BrokenTree(
f"Duplicate paths detected: depth={depth} elements={elements_at_depth}"
)
sibling_pairs = tuple(
(left, right)
for left, right in sliding_window(2, elements_at_depth)
if left.path[:-1] == right.path[:-1])
# Check to see if any of the elements didn't have a sibling which
# indicates either a missing sibling, or a duplicate node.
orphans = set(elements_at_depth).difference(
itertools.chain(*sibling_pairs))
if orphans:
raise BrokenTree(
f"Orphaned tree elements: dept={depth} orphans={orphans}")
parents = tuple(
ProofElement(path=left.path[:-1],
value=hash_eth2(left.value + right.value))
for left, right in sibling_pairs)
if not elements_by_depth and len(parents) == 1:
return parents[0].value
else:
elements_by_depth.setdefault(depth - 1, [])
elements_by_depth[depth - 1].extend(parents)
else:
raise BrokenTree("Unable to fully collapse tree within 32 rounds")
def test_enr_partitioning(num_enr_records, max_payload_size):
enrs = ENRFactory.create_batch(num_enr_records)
batches = partition_enrs(enrs, max_payload_size)
assert sum(len(batch) for batch in batches) == len(enrs)
assert set(itertools.chain(*batches)) == set(enrs)
for batch in batches:
encoded_batch = rlp.encode(batch,
sedes=rlp.sedes.CountableList(ENRSedes))
assert len(encoded_batch) <= max_payload_size
for batch, next_batch in sliding_window(2, batches):
overfull_batch = tuple(batch) + (next_batch[0], )
encoded_batch = rlp.encode(overfull_batch,
sedes=rlp.sedes.CountableList(ENRSedes))
assert len(encoded_batch) > max_payload_size
def _deserialize_stream_to_tuple(
self, stream: IO[bytes]) -> Iterable[TDeserialized]:
if self.element_sedes.is_fixed_sized:
element_size = self.element_sedes.get_fixed_size()
data = stream.read()
if len(data) % element_size != 0:
raise DeserializationError(
f"Invalid max_length. List is comprised of a fixed size sedes "
f"but total serialized data is not an even multiple of the "
f"element size. data max_length: {len(data)} element size: "
f"{element_size}")
for start_idx in range(0, len(data), element_size):
segment = data[start_idx:start_idx + element_size]
yield self.element_sedes.deserialize(segment)
else:
stream_zero_loc = stream.tell()
try:
first_offset = s_decode_offset(stream)
except DeserializationError:
if stream.tell() == stream_zero_loc:
# Empty list
return
else:
raise
num_remaining_offset_bytes = first_offset - stream.tell()
if num_remaining_offset_bytes % OFFSET_SIZE != 0:
raise DeserializationError(
f"Offset bytes was not a multiple of {OFFSET_SIZE}. Got "
f"{num_remaining_offset_bytes}")
num_remaining_offsets = num_remaining_offset_bytes // OFFSET_SIZE
tail_offsets = tuple(
s_decode_offset(stream) for _ in range(num_remaining_offsets))
offsets = tuple(cons(first_offset, tail_offsets))
for left_offset, right_offset in sliding_window(2, offsets):
element_length = right_offset - left_offset
element_data = read_exact(element_length, stream)
yield self.element_sedes.deserialize(element_data)
# simply reading to the end of the current stream gives us all of the final element data
final_element_data = stream.read()
yield self.element_sedes.deserialize(final_element_data)
def _compute_gas_price(probabilities: Sequence[Probability],
desired_probability: float) -> Wei:
"""
Given a sorted range of ``Probability`` named-tuples returns a gas price
computed based on where the ``desired_probability`` would fall within the
range.
:param probabilities: An iterable of `Probability` named-tuples sorted in reverse order.
:param desired_probability: An floating point representation of the desired
probability. (e.g. ``85% -> 0.85``)
"""
first = probabilities[0]
last = probabilities[-1]
if desired_probability >= first.prob:
return Wei(int(first.gas_price))
elif desired_probability <= last.prob:
return Wei(int(last.gas_price))
for left, right in sliding_window(2, probabilities):
if desired_probability < right.prob:
continue
elif desired_probability > left.prob:
# This code block should never be reachable as it would indicate
# that we already passed by the probability window in which our
# `desired_probability` is located.
raise Exception('Invariant')
adj_prob = desired_probability - right.prob
window_size = left.prob - right.prob
position = adj_prob / window_size
gas_window_size = left.gas_price - right.gas_price
gas_price = int(math.ceil(right.gas_price +
gas_window_size * position))
return Wei(gas_price)
else:
# The initial `if/else` clause in this function handles the case where
# the `desired_probability` is either above or below the min/max
# probability found in the `probabilities`.
#
# With these two cases handled, the only way this code block should be
# reachable would be if the `probabilities` were not sorted correctly.
# Otherwise, the `desired_probability` **must** fall between two of the
# values in the `probabilities``.
raise Exception('Invariant')
def test_advertisement_partitioning(content_keys):
advertisements = tuple(
AdvertisementFactory(
content_key=content_key, signature=keys.Signature(b"\x00" * 65)
)
for content_key in content_keys
)
batches = partition_advertisements(advertisements, 512)
for batch in batches:
ssz_payload = tuple(ad.to_sedes_payload() for ad in batch)
encoded = ssz.encode(ssz_payload, sedes=AdvertiseSedes)
assert len(encoded) <= 512
for left, right in sliding_window(2, batches):
ssz_payload = tuple(ad.to_sedes_payload() for ad in left + (right[0],))
encoded = ssz.encode(ssz_payload, sedes=AdvertiseSedes)
assert len(encoded) > 512
def get_validator_definition_ranges(
validator_definition: Dict) -> Sequence[ValidatorDefinitionRange]:
validate_validator_definition(validator_definition)
sorted_definition = sorted(
# Lambda tuple destructuring has been removed from Python 3 (https://www.python.org/dev/peps/pep-3113/) :-(
validator_definition["multi"].items(),
key=lambda item: int(item[0]),
)
result = []
# Iterate over all configurations. Add an extra empty item for the sliding window to slide to the very end.
# Alternatively we'd have to do some additional processing which would further complicate the code
for (range_height, range_config), (next_range_height, _) in sliding_window(
2, chain(sorted_definition, [[None, None]])):
[(config_type, config_data)] = range_config.items()
validators: Optional[List[bytes]] = None
if config_type == "list":
is_contract = False
validators = [
to_canonical_address(validator_address)
for validator_address in config_data
]
contract_address = None
elif config_type in ["contract", "safeContract"]:
is_contract = True
validators = None
contract_address = to_canonical_address(config_data)
else:
assert False, "Unreachable. Invalid config type."
result.append(
ValidatorDefinitionRange(
enter_height=int(range_height),
leave_height=int(next_range_height)
if next_range_height is not None else None,
is_contract=is_contract,
validators=validators,
contract_address=contract_address,
))
return result
def _deserialize_stream_to_tuple(
self, stream: IO[bytes]) -> Iterable[TDeserializedElement]:
if self.element_sedes.is_fixed_sized:
element_size = self.element_sedes.get_fixed_size()
for _ in range(self.length):
element_data = read_exact(element_size, stream)
yield self.element_sedes.deserialize(element_data)
else:
offsets = tuple(
s_decode_offset(stream) for _ in range(self.length))
for left_offset, right_offset in sliding_window(2, offsets):
element_length = right_offset - left_offset
element_data = read_exact(element_length, stream)
yield self.element_sedes.deserialize(element_data)
# simply reading to the end of the current stream gives us all of the final element data
final_element_data = stream.read()
yield self.element_sedes.deserialize(final_element_data)
