commonware_storage/mmr/
mod.rs

1//! A Merkle Mountain Range (MMR) is an append-only data structure that allows for efficient
2//! verification of the inclusion of an element, or some range of consecutive elements, in a list.
3//!
4//! # Terminology
5//!
6//! An MMR is a list of perfect binary trees (aka _mountains_) of strictly decreasing height. The
7//! roots of these trees are called the _peaks_ of the MMR. Each _element_ stored in the MMR is
8//! represented by some leaf node in one of these perfect trees, storing a positioned hash of the
9//! element. Non-leaf nodes store a positioned hash of their children.
10//!
11//! The _size_ of an MMR is the total number of nodes summed over all trees.
12//!
13//! The nodes of the MMR are ordered by a post-order traversal of the MMR trees, starting from the
14//! from tallest tree to shortest. The _position_ of a node in the MMR is defined as the 0-based
15//! index of the node in this ordering. This implies the positions of elements, which are always
16//! leaves, may not be contiguous even if they were consecutively added. An element's _location_ is
17//! its 0-based index in the order of element insertion (aka its leaf index). In the example below,
18//! the right-most element has position 18 and location 10.
19//!
20//! As the MMR is an append-only data structure, node positions never change and can be used as
21//! stable identifiers.
22//!
23//! The _height_ of a node is 0 for a leaf, 1 for the parent of 2 leaves, and so on.
24//!
25//! The _root digest_ (or just _root_) of an MMR is the result of hashing together the size of the
26//! MMR and the digests of every peak in decreasing order of height.
27//!
28//! # Examples
29//!
30//! (Borrowed from <https://docs.grin.mw/wiki/chain-state/merkle-mountain-range/>): After adding 11
31//! elements to an MMR, it will have 19 nodes total with 3 peaks corresponding to 3 perfect binary
32//! trees as pictured below, with nodes identified by their positions:
33//!
34//! ```text
35//!    Height
36//!      3              14
37//!                   /    \
38//!                  /      \
39//!                 /        \
40//!                /          \
41//!      2        6            13
42//!             /   \        /    \
43//!      1     2     5      9     12     17
44//!           / \   / \    / \   /  \   /  \
45//!      0   0   1 3   4  7   8 10  11 15  16 18
46//!
47//! Location 0   1 2   3  4   5  6   7  8   9 10
48//! ```
49//!
50//! The root hash in this example is computed as:
51//!
52//! ```text
53//!
54//! Hash(19,
55//!   Hash(14,                                                  // first peak
56//!     Hash(6,
57//!       Hash(2, Hash(0, element_0), Hash(1, element_1)),
58//!       Hash(5, Hash(3, element_2), Hash(4, element_4))
59//!     )
60//!     Hash(13,
61//!       Hash(9, Hash(7, element_7), Hash(8, element_8)),
62//!       Hash(12, Hash(10, element_10), Hash(11, element_11))
63//!     )
64//!   )
65//!   Hash(17, Hash(15, element_15), Hash(16, element_16))      // second peak
66//!   Hash(18, element_18)                                      // third peak
67//! )
68//! ```
69
70pub mod hasher;
71pub mod iterator;
72pub mod location;
73pub mod mem;
74pub mod position;
75pub mod proof;
76pub mod stability;
77
78cfg_if::cfg_if! {
79    if #[cfg(feature = "std")] {
80        pub mod bitmap;
81        pub mod grafting;
82        pub mod journaled;
83        pub mod storage;
84        pub mod verification;
85    }
86}
87
88pub use hasher::Standard as StandardHasher;
89pub use location::{Location, LocationError, MAX_LOCATION};
90pub use position::{Position, MAX_POSITION};
91pub use proof::Proof;
92use thiserror::Error;
93
94/// Errors that can occur when interacting with an MMR.
95#[derive(Error, Debug)]
96pub enum Error {
97    #[cfg(feature = "std")]
98    #[error("metadata error: {0}")]
99    MetadataError(#[from] crate::metadata::Error),
100    #[cfg(feature = "std")]
101    #[error("journal error: {0}")]
102    JournalError(#[from] crate::journal::Error),
103    #[cfg(feature = "std")]
104    #[error("runtime error: {0}")]
105    Runtime(#[from] commonware_runtime::Error),
106    #[error("missing node: {0}")]
107    MissingNode(Position),
108    #[error("invalid proof")]
109    InvalidProof,
110    #[error("root mismatch")]
111    RootMismatch,
112    #[error("element pruned: {0}")]
113    ElementPruned(Position),
114    #[error("position is not a leaf: {0}")]
115    PositionNotLeaf(Position),
116    #[error("invalid position: {0}")]
117    InvalidPosition(Position),
118    #[error("missing digest: {0}")]
119    MissingDigest(Position),
120    #[error("missing grafted digest for leaf: {0}")]
121    MissingGraftedDigest(Location),
122    #[error("invalid proof length")]
123    InvalidProofLength,
124    #[error("invalid size: {0}")]
125    InvalidSize(u64),
126    #[error("empty")]
127    Empty,
128    #[error("pruned chunks causes u64 overflow")]
129    PrunedChunksOverflow,
130    #[error("location {0} > MAX_LOCATION")]
131    LocationOverflow(Location),
132    #[error("range out of bounds: end location {0} exceeds MMR size")]
133    RangeOutOfBounds(Location),
134    #[error("bitmap has unmerkleized updates")]
135    DirtyState,
136    #[error("bit offset {0} out of bounds (size: {1})")]
137    BitOutOfBounds(u64, u64),
138    #[error("invalid pinned nodes")]
139    InvalidPinnedNodes,
140    #[error("data corrupted: {0}")]
141    DataCorrupted(&'static str),
142}
commonware_storage/mmr/mod.rs

commonware_storage/mmr/
mod.rs
