Transaction Fields

Every transaction submitted to the Bullet exchange is wrapped in an UnsignedTransaction containing the call message, a uniqueness value, transaction details, and an optional address_override. This guide covers the uniqueness, details, and address override fields.

Uniqueness

The UniquenessData field prevents transaction replay. Bullet supports three modes:

#![allow(unused)]
fn main() {
enum UniquenessData {
    Nonce(u64) = 0,
    Generation(u64) = 1,
    Window(u64) = 2,
}
}

Window mode (recommended)

The uniqueness value can be whatever you want — it just needs to be unique per key within an increasing block window of 1000 nonces. We recommend using millisecond timestamps.

Compared to the strictly monotonic Nonce variant multiple transactions can be in-flight concurrently.

Best practice: use SystemTime::now() in milliseconds. Avoid reusing values — if you submit multiple transactions in a tight loop, ensure each is distinct.

Nonce mode

Use Nonce(u64) for strict sequential ordering. The nonce must be exactly current_nonce + 1 for the credential. This mode is simpler but only allows one in-flight transaction at a time.

TxDetails

#![allow(unused)]
fn main() {
struct TxDetails {
    max_priority_fee_bips: u64,
    max_fee: Amount,
    gas_limit: Option<[u64; 2]>,
    chain_hash_fragment: u64,
}
}

These fields are required in every transaction. We recommend using the values below.

Field	Type	Description
`chain_hash_fragment`	`u64`	First 8 bytes of the chain hash (`GET /fapi/v1/exchangeInfo` → `chainHash`) as a little-endian `u64`; see `chain_hash_fragment`
`max_fee`	`Amount(u128)`	Maximum fee the sender is willing to pay
`gas_limit`	`Option<[u64; 2]>`	2D gas limit: `[compute, storage]`. `None` defaults to block limit
`max_priority_fee_bips`	`u64`	Priority fee tip in basis points

The fragment lets the exchange pick the chain hash a transaction was signed over when more than one is valid during a chain-hash rotation. It replaces the former chain_id field.

Gas model

Bullet uses a 2D gas model with separate compute and storage dimensions. The gas_limit field caps how much of each resource a transaction may consume.

Paymaster

Gas fees are covered by a paymaster — users do not pay gas out of pocket. The fields are still required for transaction validity.

Recommended Values

Field	Recommended value	Notes
`uniqueness`	`Window(timestamp_ms())`	Millisecond timestamp
`max_priority_fee_bips`	`0`
`max_fee`	`1 << 48`
`gas_limit`	`None`	Defaults to block limit. Use `[5_000_000, 5_000_000]` for order placement or `[500_000, 500_000]` for simpler ops if you want explicit caps
`chain_hash_fragment`	`chain_hash_fragment(&chain_hash)`	Derived from the `chainHash` you sign with
`address_override`	`None`	Execute as your own address. Only set it to act on another account that explicitly authorized your key

See the default_tx_details helper for a ready-to-use implementation.

Address override

UnsignedTransaction.address_override is an Option<[u8; 32]> and is part of the signed bytes. Leave it None: the transaction then executes as the account the exchange resolves for the signing credential, which is the key’s own account or, for a registered delegate key, the delegator’s main account (see Delegate Accounts; delegation needs no override). Some(address) executes as that account instead and is only admitted when the account has explicitly authorized the signing credential; otherwise the transaction is skipped before execution.

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