`@solana/spl-account-compression`

A TypeScript library for interacting with SPL Account Compression and SPL NoOp. Docs here.

Install

npm install --save @solana/spl-account-compression @solana/web3.js

yarn add @solana/spl-account-compression @solana/web3.js

This on-chain program provides an interface for composing smart contracts to create and use SPL ConcurrentMerkleTrees. The primary application of using SPL ConcurrentMerkleTrees is to synchronize off-chain databases with on-chain updates.

SPL ConcurrentMerkleTrees are Merkle Trees that have their roots on-chain with support for fast-forwarding proofs. Fast forwarding allows multiple updates to the tree in a single block and reduces the latency burden on indexers.

In order to execute transactions that modify an SPL ConcurrentMerkleTree, an indexer will need to parse through transactions that touch the tree in order to provide up-to-date merkle proofs. For more information regarding merkle proofs, see this great explainer.

This program is targeted towards supporting Metaplex Compressed NFTs and may be subject to change.

A rough draft of the whitepaper for SPL ConcurrentMerkleTrees can be found here.

High Level Overview

Instructions

Code to interact with the on-chain instructions is auto-generated by @metaplex-foundation/solita. Exported functions to create instructions have pattern create<instructionName>Instruction.

For example, account compression's append_leaf instruction has a Solita-generated factory function called createAppendLeafInstruction.

Solita provides very low-level functions to create instructions. Thus, helper functions are provided for each instruction, denoted with the suffix ix.

For example: createReplaceLeafInstruction has a helper function createReplaceLeafIx

Modules

A merkle tree reference implementation is provided to index the on-chain trees. The MerkleTree class and its helpers are provided under src/merkle-tree.

The MerkleTree class is meant to follow a similar interface as MerkleTree from merkletreejs.

Feature	Our Tree	`merkletreejs`	Notes
updateLeaf	✅	❌	This is the unique feature of `ConcurrentMerkleTree`'s
multiProof	❌	✅	Possible to support in future version of Account Compression
addLeaf	✅	✅	Our version does this via `updateLeaf()`

If you'd like to see more features added, please create an issue with the title Account Compression and your feature request.

Examples

Create a tree

// Assume: known `payer` Keypair

// Generate a keypair for the ConcurrentMerkleTree
const cmtKeypair = Keypair.generate();

// Create a system instruction to allocate enough 
// space for the tree
const allocAccountIx = await createAllocTreeIx(
    connection,
    cmtKeypair.publicKey,
    payer.publicKey,
    { maxDepth, maxBufferSize },
    canopyDepth,
);

// Create an SPL compression instruction to initialize
// the newly created ConcurrentMerkleTree
const initTreeIx = createInitEmptyMerkleTreeIx(
    cmtKeypair.publicKey, 
    payer.publicKey, 
    { maxDepth, maxBufferSize }
);

const tx = new Transaction().add(allocAccountIx).add(initTreeIx);

await sendAndConfirmTransaction(connection, tx, [cmtKeypair, payer]);

Add a leaf to the tree

// Create a new leaf
const newLeaf: Buffer = crypto.randomBytes(32);

// Add the new leaf to the existing tree
const appendIx = createAppendIx(cmtKeypair.publicKey, payer.publicKey, newLeaf);

const tx = new Transaction().add(appendIx);

await sendAndConfirmTransaction(connection, tx, [payer]);

Replace a leaf in the tree, using the provided MerkleTree as an indexer

This example assumes that offChainTree has been indexing all previous modifying transactions involving this tree. It is okay for the indexer to be behind by a maximum of maxBufferSize transactions.

// Assume: `offChainTree` is a MerkleTree instance
// that has been indexing the `cmtKeypair.publicKey` transactions

// Get a new leaf
const newLeaf: Buffer = crypto.randomBytes(32);

// Query off-chain records for information about the leaf
// you wish to replace by its index in the tree
const leafIndex = 314;

// Replace the leaf at `leafIndex` with `newLeaf`
const replaceIx = createReplaceIx(
    cmtKeypair.publicKey,          
    payer.publicKey,
    newLeaf,
    offChainTree.getProof(leafIndex) 
);

const tx = new Transaction().add(replaceIx);

await sendAndConfirmTransaction(connection, tx, [payer]);

Replace a leaf in the tree, using a 3rd party indexer

This example assumes that some 3rd party service is indexing the the tree at cmtKeypair.publicKey for you, and providing MerkleProofs via some REST endpoint. The getProofFromAnIndexer function is a placeholder to exemplify this relationship.

// Get a new leaf
const newLeaf: Buffer = crypto.randomBytes(32);

// Query off-chain indexer for a MerkleProof
// possibly by executing GET request against a REST api
const proof = await getProofFromAnIndexer(myOldLeaf);

// Replace `myOldLeaf` with `newLeaf` at the same index in the tree
const replaceIx = createReplaceIx(
    cmtKeypair.publicKey,          
    payer.publicKey,
    newLeaf,
    proof
);

const tx = new Transaction().add(replaceIx);

await sendAndConfirmTransaction(connection, tx, [payer]);

Reference examples

Here are some examples using account compression in the wild:

Solana Program Library tests
Metaplex Program Library Compressed NFT tests

Build from Source

Install dependencies with yarn.
Generate the Solita SDK with yarn solita.
Then build the SDK with yarn build.
Run tests with yarn test. (Expect jest to detect an open handle that prevents it from exiting naturally)

@solana/spl-account-compression