Batch minting

[StanChe]

A finalized version of the Bubblegum update for batch minting

Batch operations

As was observed, minting of assets constitutes over 90% of all operations pertaining to digital assets. In order to reduce the number of transactions and optimize the time and cost it takes to put your tree on-chain during the Solana heavy load events Metaplex has introduced the batch-mint operations. The batch extension to the Bubblegum program introduces offline Merkle tree creation, enabling users to prepare and manage Merkle trees offline before finalizing them on-chain. The resulting trees are fully compatible with the regular trees. The snapshot of the tree created is required to be stored off-chain so the replay of the tree creation is possible on any indexer.

Batch-Mint Operations

Introduction

The latest extension to the Bubblegum contract introduces batch-mint operations, allowing users to mint multiple cNFTs in just several transactions, which significantly reduces on-chain overhead and optimizes minting processes for large collections.

How It Works

With the batch-mint operations, users can prepare an entire set of NFTs off-chain, populate them within a Merkle tree structure, and then mint them to the tree in a small number of transactions. This process is designed to handle large-scale NFT collections more efficiently.

Steps to Perform a Batch-Mint

In order to simplify the Merkle tree creation and interactions we recommend using the SDK.

To understand the batch-mint flow, let's recall the structure of a tree data account:

+--------+----------------------+-----------------+
| Header |     Tree body        |     Canopy      |
+--------+----------------------+-----------------+
   56      depends on the tree    (2ⁿ⁺¹ - 2) * 32
  bytes    depth and buffer size       bytes

where n is the depth of the canopy.

1. Prepare Tree

• Invoke the prepare_tree method to initialize an account with a tree header and an empty tree body and empty canopy buffer.
• The tree is set up with initial parameters (tree size and canopy if required) but remains empty, allowing offline filling.

2. Fill Tree Offline

• User populates the tree offline, ensuring all necessary leaves are in place.
• If the canopy is required, then canopy leaf nodes are populated in the process of adding asset leaves to tree.
• The final root, proof, and last leaf are prepared for submission.

3. Serialize and Upload the Tree

• The offline tree is serialized and uploaded to an IPFS-like service, such as Arweave, ensuring public access.

4. Adding canopy (for a tree with a canopy)

• To transfer canopy leaf nodes from offline tree to the solana tree data account the add_canopy method is invoked, tree body at this stage stays empty

5. Finalize Tree

• To finalize the tree the methods finalize_tree_with_root for a tree without verified collections or finalize_tree_with_root_and_collection for a tree with one verified collection are used. Signatures from both the tree owner and a designated staker are required.
• The staker is responsible for ensuring the data's availability and consistency, verifying it before signing off.

6. Manage the Tree
   • Once the batch minting process is complete, you can manage the tree and its NFTs using all the standard Bubblegum operations.
   • You can also mint additional assets into a batch-minted tree as if it's a regular tree.

📄 prepare_tree

Prepare a tree structure that will be used to hold multiple NFTs in a batch-mint operation. This step initializes the tree and allocates the necessary resources for subsequent operations.

Accounts

Name	Writable	Signer	Optional	Description
tree_authority	✅			The TreeConfig PDA account that is initialized by this instruction.
merkle_tree	✅			Unchecked account representing the Merkle tree, must be zero-initialized.
payer	✅	✅		The account responsible for paying the transaction fees.
tree_creator		✅		The creator of the tree, who must sign the transaction.
log_wrapper				The Solana Program Library Wrapper (spl-noop) program ID for logging.
compression_program				The Solana Program Library spl-account-compression program ID.
system_program				The Solana System Program ID.

Arguments

Argument	Offset	Size	Description
max_depth	0	4	The maximum depth of the Merkle tree.
max_buffer_size	4	4	The maximum buffer size for the Merkle tree.
public	8	1	An optional boolean indicating if the tree is public.

📄 add_canopy

Add an optional canopy to the tree structure. A canopy is used to optimize the verification process for the tree, making it easier to validate NFT ownership.

Accounts

Name	Writable	Signer	Optional	Description
tree_authority				The TreeConfig PDA account previously initialized by prepare_tree.
merkle_tree	✅			The account representing the Merkle tree to which the canopy is being added.
tree_delegate		✅		The delegate authorized to modify the tree.
log_wrapper				The Solana Program Library Wrapper (spl-noop) program ID for logging.
compression_program				The Solana Program Library spl-account-compression program ID.
system_program				The Solana System Program ID.

Arguments

Argument	Offset	Size	Description
start_index	0	4	The starting index for the canopy nodes being added.
canopy_nodes	4	???	A vector of canopy nodes (32-byte arrays) to append to the Merkle tree.

📄 finalize_tree_with_root

Finalize the tree structure by setting the Merkle root, which represents the entire batch of NFTs. This operation completes the preparation phase and makes the tree ready for usage.

Accounts

Name	Writable	Signer	Optional	Description
tree_authority	✅			The TreeConfig PDA account previously initialized by prepare_tree.
merkle_tree	✅			The account containing the Merkle tree structure.
payer	✅	✅		The account responsible for paying the transaction fees.
tree_delegate		✅		The delegate of the tree, responsible for finalizing it.
staker		✅		The account of the staker, required to have the minimal required stake to allow batch-minting.
registrar				The account representing the registrar for managing stake accounts.
voter				The account representing the voting account.
mining				The account representing the mining account on rewards contract.
fee_receiver	✅			The account designated to receive protocol fees.
log_wrapper				The Solana Program Library Wrapper (spl-noop) program ID for logging.
compression_program				The Solana Program Library spl-account-compression program ID.
system_program				The Solana System Program ID.
remaining accounts			✅	Pubkeys(s) that are 32-byte Keccak256 hash values that represent the nodes for this cNFT's Merkle proof.

Arguments

Argument	Offset	Size	Description
root	0	32	The Merkle root hash for the tree.
rightmost_leaf	32	32	The hash of the rightmost leaf node in the tree.
rightmost_index	64	4	The index of the rightmost leaf node in the tree.
_metadata_url	68	???	A string - URL for the uploaded batch-mint json, required by indexers to fetch the tree for initialization.
_metadata_hash	???	???	A string representing a hex-encoded xxh3_128 hash of the uploaded batch-mint json-file.

📄 finalize_tree_with_root_and_collection

Finalize the tree structure by setting the Merkle root and associating it with a specific NFT collection. This operation allows having a verified collection for NFTs in the batch.

Accounts

Name	Writable	Signer	Optional	Description
tree_authority	✅			The TreeConfig PDA account previously initialized by prepare_tree.
merkle_tree	✅			The account containing the Merkle tree structure.
payer	✅	✅		The account responsible for paying the transaction fees.
tree_delegate		✅		The delegate of the tree, responsible for finalizing it.
staker		✅		The account of the staker, required to have the minimal required stake to allow batch-minting.
collection_authority		✅		Either the collection update authority or a delegate.
registrar				The account representing the registrar for managing stake accounts.
voter				The account representing the voting account.
mining				The account representing the mining authority.
fee_receiver	✅			The account designated to receive protocol fees.
collection_authority_record_pda			✅	Either a metadata delegate record PDA for a collection delegate, or a legacy collection authority record PDA.
collection_mint				The account representing the collection mint.
collection_metadata	✅			Metadata account of the collection. Modified in the case of a sized collection.
edition_account				The account representing the Master Edition account of the collection.
log_wrapper				The Solana Program Library Wrapper (spl-noop) program ID for logging.
compression_program				The Solana Program Library spl-account-compression program ID.
system_program				The Solana System Program ID.
remaining accounts			✅	Pubkeys(s) that are 32-byte Keccak256 hash values that represent the nodes for this cNFT's Merkle proof.

Arguments

Argument	Offset	Size	Description
root	0	32	The Merkle root hash for the tree.
rightmost_leaf	32	32	The hash of the rightmost leaf node in the tree.
rightmost_index	64	4	The index of the rightmost leaf node in the tree.
_metadata_url	68	???	A string - URL for the uploaded batch-mint json, required by indexers to fetch the tree for initialization.
_metadata_hash	???	???	A string representing a hex-encoded xxh3_128 hash of the uploaded batch-mint json-file.