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Assets on Polkadot

The Polkadot Relay Chain does not natively support assets beyond DOT This functionality exists in parachains. On Polkadot, this parachain is called Statemint, and on Kusama it is called Statemine. All information in this guide applies equally to Kusama/Statemine.

Statemint provides a first-class interface for creating, managing, and using both fungible and non-fungible assets. The fungible interface is similar to Ethereum's ERC-20 standard. However, the data structures and stateful operations are encoded directly into the chain's runtime, making operations fast and fee-efficient.

Beyond merely supporting assets, integrating Statemint into your systems has several benefits for infrastructure providers and users:

  • Support for on-chain assets.
  • Significantly lower transaction fees (about 1/10) than the Relay Chain.
  • Significantly lower deposits (1/10) than the Relay Chain. This includes the existential deposit and deposits for proxy/multisig operations.
  • Ability to pay transaction fees in certain assets. As in, accounts would not need DOT in order to exist on-chain nor to pay fees.

Statemint will use DOT as its native currency. Users can transfer DOT from the Relay Chain into Statemint and use it natively. The Relay Chain will also accept DOT transfers from Statemint back to the Relay Chain to use for staking, governance, or any other activity taking place there.

Using Statemint for DOT/KSM balance transfers will be much more efficient than the Relay Chain and is highly recommended. Until domain specific parachains are built, the Relay Chain will still need to be used for staking and governance.

Assets Basics​

See the Assets pallet for the most up-to-date info and reference documentation.

Assets are stored as a map from an ID to information about the asset, including a management team, total supply, total number of accounts, its sufficiency for account existence, and more. Additionally, the asset owner can register metadata like the name, symbol, and number of decimals for representation.

Some assets, as determined by on-chain governance, are regarded as “sufficient”. Sufficiency means that the asset balance is enough to create the account on-chain, with no need for the DOT/KSM existential deposit. Likewise, you cannot send a non-sufficient asset to an account that does not exist. Sufficient assets can be used to pay transaction fees (i.e. there is no need to hold DOT/KSM on the account).

Assets do have a minimum balance (set by the creator), and if an account drops below that balance, the dust is lost.

Asset Operations​

The Assets pallet has its own interface for dealing with assets. See the Integration section below for how to fetch information and construct transactions.

The main functions you will probably interact with are transfer and transfer_keep_alive. These functions transfer some amount (balance) of an AssetId (a u32, not a contract address) to another account.

The Assets pallet also provides an approve_transfer, cancel_approval, and transfer_approved interface for non-custodial operations.

Asset transfers will result in an assets.transferred event. The same instructions for monitoring events and not transactions applies to asset transfers.

Note that you can use the same addresses (except anonymous proxies!) on Statemint that you use on the Relay Chain. The SS58 encodings are the same, only the chain information (genesis hash, etc.) will change on transaction construction.

Integration​

Statemint will come with the same tooling suite that Parity Technologies provides for the Relay Chain, namely API Sidecar and TxWrapper Polkadot. If you have a technical question or issue about how to use one of the integration tools please file a GitHub issue so a developer can help.

Parachain Node​

Using Statemint will require running a parachain node to sync the chain. This is very similar to running a Polkadot node, with the addition of some extra flags. The basic format looks like this:

./statemint $STATEMINT_CLI_ARGS --collator -- $POLKADOT_CLI_ARGS

where both $STATEMINT_CLI_ARGS and $POLKADOT_CLI_ARGS consist of regular Polkadot node flags. Flags can be used twice, one for the collating component and one for the Relay Chain component. Additional ports that will be used are (by default) 9934, 9616, and 30334 (Relay Chain RPC, Prometheus endpoint, and libp2p respectively). As usual, any of these ports can be adjusted through flags. To deploy a Statemint RPC node, one would use the same flags as a Polkadot RPC node in place of $STATEMINT_CLI_ARGS. The node will keep both the database for Polkadot and for Statemint in its database directory, so provision disks accordingly.

Sidecar​

API Sidecar is a REST service for Relay Chain and parachain nodes; It comes with endpoints to query info about assets and asset balances on Statemint.

  • Asset lookups will always use the AssetId to refer to an asset class. On-chain metadata is subject to change and thus not suitable as a canonical index.
  • Please refer to docs for full usage information. Details on options like how to make a historical query are not included here.

Tx Wrapper Polkadot​

TxWrapper Polkadot is a library designed to facilitate transaction construction and signing in offline environments; it comes with a set of asset-specific functions to use on Statemint. When constructing parachain transactions, you can use txwrapper-polkadot exactly as on the Relay Chain, but would construct transactions with the appropriate parachain metadata like genesis hash, spec version, and type registry.