Transaction Mass

Transaction mass limits

Transaction mass is a value calculated from the transaction by applying different weights to transaction metrics. These metrics include the mass per transaction byte, mass per script public key byte, and mass per signing operation. Theese costs are network-specific and for the Mainnet have the following parameters:

#![allow(unused)]
fn main() {
pub const MAINNET_PARAMS: Params = Params {
    mass_per_tx_byte: 1,
    mass_per_script_pub_key_byte: 10,
    mass_per_sig_op: 1000,
    ...
}
}

The maximum allowed transaction mass is 100_000 mass.

#![allow(unused)]
fn main() {
const MAXIMUM_STANDARD_TRANSACTION_MASS: u64 = 100_000;
}

Calculating transaction mass

SigOps mass

#![allow(unused)]
fn main() {
let total_sigops: u64 = tx.inputs.iter().map(|input| input.sig_op_count as u64).sum();
let total_sigops_mass = total_sigops * self.mass_per_sig_op;

}

Input mass

one input mass = (input-size * mass_per_tx_byte) + (input-sig-op-count * mass_per_sig_op)

input-size = outpoint-size + u64 (storage for length of signature script) + signature script length + u64 (sequence)

so one input mass = ((36 + 8 + 66^* + 8) * 1) + (1 * 1000) = 1118

*here value "66" is not fixed but depends on signature script length; see size += input.signature_script.len() as u64; line in the transaction_input_estimated_serialized_size() function below.

Transaction mass

transaction mass = 
    ( tx-size * mass_per_tx_byte ) + 
    ( total-ouput-script-size * mass_per_script_pub_key_byte ) + 
    ( total-input-sigops * mass_per_sig_op )

#![allow(unused)]
fn main() {
let size = transaction_estimated_serialized_size(tx);
let mass_for_size = size * self.mass_per_tx_byte;
let total_script_public_key_size: u64 = tx
    .outputs
    .iter()
    .map(|output| 2 /* script public key version (u16) */ + output.script_public_key.script().len() as u64)
    .sum();
let total_script_public_key_mass = total_script_public_key_size * self.mass_per_script_pub_key_byte;

let total_sigops: u64 = tx.inputs.iter().map(|input| input.sig_op_count as u64).sum();
let total_sigops_mass = total_sigops * self.mass_per_sig_op;

let transaction_mass = mass_for_size + total_script_public_key_mass + total_sigops_mass
}

Other resources

Mass calculation code can be found here: https://github.com/aspectron/rusty-kaspa/blob/wasm-bindings/consensus/core/src/mass/mod.rs#L59-L89

TODO - change the URL after PR merge to this: https://github.com/kaspanet/rusty-kaspa/blob/master/consensus/core/src/mass/mod.rs