Struct exonum_merkledb::indexes::proof_list::ProofListIndex

pub struct ProofListIndex<T: RawAccess, V> { /* fields omitted */ }

A Merkelized version of an array list that provides proofs of existence for the list items.

ProofListIndex implements a Merkle tree, storing elements as leaves and using u64 as an index. ProofListIndex requires that elements implement the BinaryValue trait.

Safety

A ProofListIndex may contain at most 2 ** 56 elements (which is approximately 7.2e16), not 2 ** 64 as ListIndex. Since this amount is still astronomically large, an index overflow is treated similar to an integer overflow; extend and push methods will panic if the index size exceeds 2 ** 56. (Unlike integer overflows, the panic will occur in any compile mode, regardless of whether debug assertions are on.) For added safety, the application may check that an overflow does not occur before performing these operations. However, this check will be redundant in most realistic scenarios: even if 10,000,000 elements are added to a ProofListIndex every second, it will take ~228 years to overflow it.

Using readonly methods such as get, iter_from and get_proof is safe for all index values; it is unnecessary to check on the calling side whether the index exceeds 2 ** 56 - 1 .

Methods

impl<T, V> ProofListIndex<T, V> where
    T: RawAccess,
    V: BinaryValue, 

pub fn get(&self, index: u64) -> Option<V>

Returns the element at the indicated position or None if the indicated position is out of bounds.

Examples

use exonum_merkledb::{access::CopyAccessExt, TemporaryDB, Database, ProofListIndex};

let db = TemporaryDB::new();
let fork = db.fork();
let mut index = fork.get_proof_list("name");
assert_eq!(None, index.get(0));

index.push(10);
assert_eq!(Some(10), index.get(0));

pub fn last(&self) -> Option<V>

Returns the last element of the proof list or None if it is empty.

Examples

use exonum_merkledb::{access::CopyAccessExt, TemporaryDB, Database, ProofListIndex};

let db = TemporaryDB::new();
let fork = db.fork();
let mut index = fork.get_proof_list("name");
assert_eq!(None, index.last());

index.push(1);
assert_eq!(Some(1), index.last());

pub fn is_empty(&self) -> bool

Returns true if the proof list contains no elements.

Examples

use exonum_merkledb::{access::CopyAccessExt, TemporaryDB, Database, ProofListIndex};

let db = TemporaryDB::new();
let fork = db.fork();
let mut index = fork.get_proof_list("name");
assert!(index.is_empty());

index.push(10);
assert!(!index.is_empty());

pub fn len(&self) -> u64

Returns the number of elements in the proof list.

Examples

use exonum_merkledb::{access::CopyAccessExt, TemporaryDB, Database, ProofListIndex};

let db = TemporaryDB::new();
let fork = db.fork();
let mut index = fork.get_proof_list("name");
assert_eq!(0, index.len());

index.push(1);
assert_eq!(1, index.len());

pub fn height(&self) -> u8

Returns the height of the Merkle tree built based on the list.

The height of the empty list is 0; otherwise, the height is computed as ceil(log2(l)) + 1, where l is the list length.

Examples

use exonum_merkledb::{access::CopyAccessExt, TemporaryDB, Database, ProofListIndex};

let db = TemporaryDB::new();
let fork = db.fork();
let mut index = fork.get_proof_list("name");
assert_eq!(0, index.height());
index.push(1);
assert_eq!(1, index.height());
index.push(1);
assert_eq!(2, index.height());

pub fn get_proof(&self, index: u64) -> ListProof<V>

Returns a proof of existence for the list element at the specified position.

Returns a proof of absence if the list doesn't contain an element with the specified index.

Examples

use exonum_merkledb::{access::CopyAccessExt, TemporaryDB, Database, ProofListIndex};

let db = TemporaryDB::new();
let fork = db.fork();
let mut index = fork.get_proof_list("name");

index.push(1);
let proof = index.get_proof(0);
let proof_of_absence = index.get_proof(1);

pub fn get_range_proof<R: RangeBounds<u64>>(&self, range: R) -> ListProof<V>

Returns the proof of existence for the list elements in the specified range.

Returns a proof of absence for a range of values, if either or both its bounds exceed the list state.

Panics

Panics if the range bounds are illegal.

Examples

use exonum_merkledb::{access::CopyAccessExt, TemporaryDB, Database, ProofListIndex};

let db = TemporaryDB::new();
let fork = db.fork();
let mut index = fork.get_proof_list("name");
index.extend(vec![1, 2, 3, 4, 5]);

let range_proof = index.get_range_proof(1..3);
assert!(range_proof.indexes_unchecked().eq(vec![1, 2]));
// This proof will contain only 4 elements with indexes 1..5.
let intersection_proof = index.get_range_proof(1..10);
assert!(intersection_proof.indexes_unchecked().eq(1..5));
// This proof does not contain any elements at all.
let empty_proof = index.get_range_proof(100..10000);
assert!(empty_proof.entries_unchecked().is_empty());

pub fn iter(&self) -> Values<V>

Returns an iterator over the list values.

Examples

use exonum_merkledb::{access::CopyAccessExt, TemporaryDB, Database, ProofListIndex};

let db = TemporaryDB::new();
let fork = db.fork();
let index = fork.get_proof_list::<_, u8>("name");

for val in index.iter() {
    println!("{}", val);
}

pub fn iter_from(&self, from: u64) -> Values<V>

Returns an iterator over the list values starting from the specified position.

Examples

use exonum_merkledb::{access::CopyAccessExt, TemporaryDB, Database, ProofListIndex};

let db = TemporaryDB::new();
let fork = db.fork();
let index = fork.get_proof_list::<_, u8>("name");

for val in index.iter_from(1) {
    println!("{}", val);
}

impl<T, V> ProofListIndex<T, V> where
    T: RawAccessMut,
    V: BinaryValue, 

pub fn push(&mut self, value: V)

Appends an element to the back of the proof list.

Examples

use exonum_merkledb::{access::CopyAccessExt, TemporaryDB, Database, ProofListIndex};

let db = TemporaryDB::new();
let fork = db.fork();
let mut index = fork.get_proof_list("name");

index.push(1);
assert!(!index.is_empty());

pub fn extend<I>(&mut self, iter: I) where
    I: IntoIterator<Item = V>, 

Extends the proof list with the contents of an iterator.

Examples

use exonum_merkledb::{access::CopyAccessExt, TemporaryDB, Database, ProofListIndex};

let db = TemporaryDB::new();
let fork = db.fork();
let mut index = fork.get_proof_list("name");

index.extend([1, 2, 3].iter().cloned());
assert_eq!(3, index.len());

pub fn set(&mut self, index: u64, value: V)

Changes a value at the specified position.

Panics

Panics if index is equal or greater than the current state of the proof list.

Examples

use exonum_merkledb::{access::CopyAccessExt, TemporaryDB, Database, ProofListIndex};

let db = TemporaryDB::new();
let fork = db.fork();
let mut index = fork.get_proof_list("name");

index.push(1);
assert_eq!(Some(1), index.get(0));

index.set(0, 100);
assert_eq!(Some(100), index.get(0));

pub fn truncate(&mut self, new_length: u64)

Shortens the list, keeping the indicated number of first len elements and dropping the rest.

If len is greater than the current state of the list, this has no effect.

Examples

use exonum_merkledb::{access::CopyAccessExt, TemporaryDB, Database, ProofListIndex};

let db = TemporaryDB::new();
let fork = db.fork();
let mut index = fork.get_proof_list("name");

index.extend([1, 2, 3, 4, 5].iter().cloned());
assert_eq!(5, index.len());
index.truncate(3);
assert!(index.iter().eq(vec![1, 2, 3]));

pub fn pop(&mut self) -> Option<V>

Removes the last element from the list and returns it, or returns None if the list is empty.

Examples

use exonum_merkledb::{access::CopyAccessExt, TemporaryDB, Database, ProofListIndex};

let db = TemporaryDB::new();
let fork = db.fork();
let mut index = fork.get_proof_list("name");
assert_eq!(None, index.pop());
index.push(1);
assert_eq!(Some(1), index.pop());

pub fn clear(&mut self)

Clears the proof list, removing all values.

Notes

Currently, this method is not optimized to delete a large set of data. During the execution of this method, the amount of allocated memory is linearly dependent on the number of elements in the index.

Examples

use exonum_merkledb::{access::CopyAccessExt, TemporaryDB, Database, ProofListIndex};

let db = TemporaryDB::new();
let fork = db.fork();
let mut index = fork.get_proof_list("name");
index.push(1);
assert!(!index.is_empty());
index.clear();
assert!(index.is_empty());

Trait Implementations

impl<T: Debug + RawAccess, V: Debug> Debug for ProofListIndex<T, V>

fn fmt(&self, f: &mut Formatter) -> Result

Formats the value using the given formatter.

impl<T, V> FromAccess<T> for ProofListIndex<T::Base, V> where
    T: Access,
    V: BinaryValue, 

fn from_access(access: T, addr: IndexAddress) -> Result<Self, AccessError>

Constructs the object at the given address.

fn from_root(access: T) -> Result<Self, AccessError>

Constructs the object from the root of the access.

impl<T, V> IndexIterator for ProofListIndex<T, V> where
    T: RawAccess,
    V: BinaryValue, 

type Key = u64

Type encompassing index keys.

type Value = V

Type encompassing index values.

fn index_iter(&self, from: Option<&u64>) -> Entries<u64, V>

Continues iteration from the specified position. If from is None, starts the iteration from scratch.

impl<'a, T, V> IntoIterator for &'a ProofListIndex<T, V> where
    T: RawAccess,
    V: BinaryValue, 

type Item = V

The type of the elements being iterated over.

type IntoIter = Values<'a, V>

Which kind of iterator are we turning this into?

fn into_iter(self) -> Self::IntoIter

Creates an iterator from a value.

impl<T, V> ObjectHash for ProofListIndex<T, V> where
    T: RawAccess,
    V: BinaryValue, 

object_hash for a list depends on all list items. It explicitly commits to the list length in order to be able to more easily prove absence of elements and to prevent second pre-image attacks.

Specification

The object_hash is calculated as follows:

h = sha256( HashTag::ListNode || u64_LE(len) || root_hash )

Here, u64_LE is the 8-byte little-endian serialization of an integer. In particular, for an empty list

h = sha256( HashTag::ListNode || 0 || Hash::zero() )

root_hash is defined recursively based on the binary Merkle tree corresponding to the list. The tree is built so that left children at each level are filled up first, and the depth of each leaf node is the same. For example, here's the structure of a tree with 6 leaves:

      root (0..6)
     /        \
   0..4      4..6
  /    \       |
0..2  2..4   4..6
/  \  /  \   /  \
0  1  2  3   4  5

For branch nodes of the tree,

node_hash = sha256( HashTag::ListBranchNode || left_hash || right_hash? )

where left_hash is the hash of the left child and right_hash is the optional hash of the right child, which may be absent if the tree is not balanced.

For leaves, the hash is

leaf_hash = sha256( HashTag::Blob || serialized_value ).

Examples

let db = TemporaryDB::new();
let fork = db.fork();
let mut index = fork.get_proof_list("name");

let default_hash = index.object_hash();
assert_eq!(HashTag::empty_list_hash(), default_hash);
index.push(1);
let hash = index.object_hash();
assert_ne!(hash, default_hash);

fn object_hash(&self) -> Hash

Returns a hash of the value.