def _build_new_node_from_last_branch(self, branches):
""" Combines nibble of the only branch left with underlying node and creates new node. """
# Find the index of the only stored branch.
idx = 0
for i in range(len(branches)):
if len(branches[i]) > 0:
idx = i
break
# Path in leaf will contain one nibble (at this step).
prefix_nibble = NibblePath([idx], offset=1)
child = self._get_node(branches[idx])
path = None
node = None
# Build new node.
# If next node is leaf or extension, merge it.
# If next node is branch, create an extension node with one nibble in path.
if type(child) == Node.Leaf:
path = NibblePath.combine(prefix_nibble, child.path)
node = Node.Leaf(path, child.data)
elif type(child) == Node.Extension:
path = NibblePath.combine(prefix_nibble, child.path)
node = Node.Extension(path, child.next_ref)
elif type(child) == Node.Branch:
path = prefix_nibble
node = Node.Extension(path, branches[idx])
reference = self._store_node(node)
return MerklePatriciaTrie._DeleteAction.USELESS_BRANCH, (path,
reference)
def _create_branch_extension(self, path, next_ref, branches):
"""
If needed, creates an extension node and stores reference in appropriate branch.
Otherwise just stores provided reference.
"""
assert len(
path
) >= 1, "Path for extension node should contain at least one nibble"
if len(path) == 1:
branches[path.at(0)] = next_ref
else:
idx = path.at(0)
reference = self._store_node(
Node.Extension(path.consume(1), next_ref))
branches[idx] = reference
def _delete(self, node_ref, path):
""" Delete method helper """
node = self._get_node(node_ref)
if type(node) == Node.Leaf:
# If it's leaf node, then it's either node we need or incorrect key provided.
if path == node.path:
return MerklePatriciaTrie._DeleteAction.DELETED, None
else:
raise KeyError
elif type(node) == Node.Extension:
# Extension node can't be removed directly, it passes delete request to the next node.
# After that several options are possible:
# 1. Next node was deleted. Then this node should be deleted too.
# 2. Next node was updated. Then we should update stored reference.
# 3. Next node was useless branch. Then we have to update our node depending on the next node type.
if not path.starts_with(node.path):
raise KeyError
action, info = self._delete(node.next_ref,
path.consume(len(node.path)))
if action == MerklePatriciaTrie._DeleteAction.DELETED:
# Next node was deleted. This node should be deleted also.
return action, None
elif action == MerklePatriciaTrie._DeleteAction.UPDATED:
# Next node was updated. Update this node too.
child_ref = info
new_ref = self._store_node(Node.Extension(
node.path, child_ref))
return action, new_ref
elif action == MerklePatriciaTrie._DeleteAction.USELESS_BRANCH:
# Next node was useless branch.
stored_path, stored_ref = info
child = self._get_node(stored_ref)
new_node = None
if type(child) == Node.Leaf:
# If next node is the leaf, our node is unnecessary.
# Concat our path with leaf path and return reference to the leaf.
path = NibblePath.combine(node.path, child.path)
new_node = Node.Leaf(path, child.data)
elif type(child) == Node.Extension:
# If next node is the extension, merge this and next node into one.
path = NibblePath.combine(node.path, child.path)
new_node = Node.Extension(path, child.next_ref)
elif type(child) == Node.Branch:
# If next node is the branch, concatenate paths and update stored reference.
path = NibblePath.combine(node.path, stored_path)
new_node = Node.Extension(path, stored_ref)
new_reference = self._store_node(new_node)
return MerklePatriciaTrie._DeleteAction.UPDATED, new_reference
elif type(node) == Node.Branch:
# For branch node things are quite complicated.
# If rest of the key is empty and there is stored value, just clear value field.
# Otherwise call _delete for the appropriate branch.
# At this step we will have delete action and (possibly) index of the branch we're working with.
#
# Then, if next node was updated or was useless branch, just update reference.
# If `_DeleteAction` is `DELETED` then either the next node or value of this node was removed.
# We have to check if there is at least 2 branches or 1 branch and value still persist in this node.
# If there are no branches and no value left, delete this node completely.
# If there is a value but no branches, create leaf node with value and empty path
# and return `USELESS_BRANCH` action.
# If there is an only branch and no value, merge nibble of this branch and path of the underlying node
# and return `USELESS_BRANCH` action.
# Otherwise our branch isn't useless and was updated.
action = None
idx = None
info = None
assert len(path) != 0 or len(
node.data) != 0, "Empty path or empty branch node in _delete"
# Decide if we need to remove value of this node or go deeper.
if len(path) == 0 and len(node.data) == 0:
# This branch node has no value thus we can't delete it.
raise KeyError
elif len(path) == 0 and len(node.data) != 0:
node.data = b''
action = MerklePatriciaTrie._DeleteAction.DELETED
else:
# Store idx of the branch we're working with.
idx = path.at(0)
if len(node.branches[idx]) == 0:
raise KeyError
action, info = self._delete(node.branches[idx],
path.consume(1))
node.branches[idx] = b''
if action == MerklePatriciaTrie._DeleteAction.DELETED:
non_empty_count = sum(
map(lambda x: 1 if len(x) > 0 else 0, node.branches))
if non_empty_count == 0 and len(node.data) == 0:
# Branch node is empty, just delete it.
return MerklePatriciaTrie._DeleteAction.DELETED, None
elif non_empty_count == 0 and len(node.data) != 0:
# No branches, just value.
path = NibblePath([])
reference = self._store_node(Node.Leaf(path, node.data))
return MerklePatriciaTrie._DeleteAction.USELESS_BRANCH, (
path, reference)
elif non_empty_count == 1 and len(node.data) == 0:
# No value and one branch
return self._build_new_node_from_last_branch(node.branches)
else:
# Branch has value and 1+ branches or no value and 2+ branches.
# It isn't useless, so action is `UPDATED`.
reference = self._store_node(node)
return MerklePatriciaTrie._DeleteAction.UPDATED, reference
elif action == MerklePatriciaTrie._DeleteAction.UPDATED:
# Just update reference.
next_ref = info
node.branches[idx] = next_ref
reference = self._store_node(node)
return MerklePatriciaTrie._DeleteAction.UPDATED, reference
elif action == MerklePatriciaTrie._DeleteAction.USELESS_BRANCH:
# Just update reference.
_, next_ref = info
node.branches[idx] = next_ref
reference = self._store_node(node)
return MerklePatriciaTrie._DeleteAction.UPDATED, reference
def _update(self, node_ref, path, value):
""" Update support method """
if not node_ref:
return self._store_node(Node.Leaf(path, value))
node = self._get_node(node_ref)
if type(node) == Node.Leaf:
# If we're updating the leaf there are 2 possible ways:
# 1. Path is equals to the rest of the key. Then we should just update value of this leaf.
# 2. Path differs. Then we should split this node into several nodes.
if node.path == path:
# Path is the same. Just change the value.
node.data = value
return self._store_node(node)
# If we are here, we have to split the node.
# Find the common part of the key and leaf's path.
common_prefix = path.common_prefix(node.path)
# Cut off the common part.
path.consume(len(common_prefix))
node.path.consume(len(common_prefix))
# Create branch node to split paths.
branch_reference = self._create_branch_node(
path, value, node.path, node.data)
# If common part isn't empty, we have to create an extension node before branch node.
# Otherwise, we need just branch node.
if len(common_prefix) != 0:
return self._store_node(
Node.Extension(common_prefix, branch_reference))
else:
return branch_reference
elif type(node) == Node.Extension:
# If we're updating an extenstion there are 2 possible ways:
# 1. Key starts with the extension node's path. Then we just go ahead and all the work will be done there.
# 2. Key doesn't start with extension node's path. Then we have to split extension node.
if path.starts_with(node.path):
# Just go ahead.
new_reference = self._update(node.next_ref,
path.consume(len(node.path)),
value)
return self._store_node(
Node.Extension(node.path, new_reference))
# Split extension node.
# Find the common part of the key and extension's path.
common_prefix = path.common_prefix(node.path)
# Cut off the common part.
path.consume(len(common_prefix))
node.path.consume(len(common_prefix))
# Create an empty branch node. It may have or have not the value depending on the length
# of the rest of the key.
branches = [b''] * 16
branch_value = value if len(path) == 0 else b''
# If needed, create leaf branch for the value we're inserting.
self._create_branch_leaf(path, value, branches)
# If needed, create an extension node for the rest of the extension's path.
self._create_branch_extension(node.path, node.next_ref, branches)
branch_reference = self._store_node(
Node.Branch(branches, branch_value))
# If common part isn't empty, we have to create an extension node before branch node.
# Otherwise, we need just branch node.
if len(common_prefix) != 0:
return self._store_node(
Node.Extension(common_prefix, branch_reference))
else:
return branch_reference
elif type(node) == Node.Branch:
# For branch node things are easy.
# 1. If key is empty, just store value in this node.
# 2. If key isn't empty, just call `_update` with appropiate branch reference.
if len(path) == 0:
return self._store_node(Node.Branch(node.branches, value))
idx = path.at(0)
new_reference = self._update(node.branches[idx], path.consume(1),
value)
node.branches[idx] = new_reference
return self._store_node(node)