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add fee_for_output to txbuilder (#60)
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@SebastienGllmt
SebastienGllmt authored Aug 26, 2020
1 parent 0c063c3 commit 35e4ee2
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Showing 2 changed files with 194 additions and 10 deletions.
14 changes: 14 additions & 0 deletions rust/pkg/cardano_serialization_lib.js.flow
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Original file line number Diff line number Diff line change
Expand Up @@ -574,6 +574,13 @@ declare export class ByronAddress {
*/
static from_bytes(bytes: Uint8Array): ByronAddress;

/**
* returns the byron protocol magic embedded in the address, or mainnet id if none is present
* note: for bech32 addresses, you need to use network_id instead
* @returns {number}
*/
byron_protocol_magic(): number;

/**
* @returns {number}
*/
Expand Down Expand Up @@ -3041,6 +3048,13 @@ declare export class TransactionBuilder {
*/
add_output(output: TransactionOutput): void;

/**
* calculates how much the fee would increase if you added a given output
* @param {TransactionOutput} output
* @returns {BigNum}
*/
fee_for_output(output: TransactionOutput): BigNum;

/**
* @param {BigNum} fee
*/
Expand Down
190 changes: 180 additions & 10 deletions rust/src/tx_builder.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -168,6 +168,23 @@ impl TransactionBuilder {
}
}

/// calculates how much the fee would increase if you added a given output
pub fn fee_for_output(&mut self, output: &TransactionOutput) -> Result<Coin, JsValue> {
let mut self_copy = self.clone();

// we need some value for these for it to be a a valid transaction
// but since we're only calculating the different between the fee of two transactions
// it doesn't matter what these are set as, since it cancels out
self_copy.set_ttl(0);
self_copy.set_fee(&Coin::new(0));

let fee_before = min_fee(&self_copy)?;

self_copy.add_output(&output)?;
let fee_after = min_fee(&self_copy)?;
fee_after.checked_sub(&fee_before)
}

pub fn set_fee(&mut self, fee: &Coin) {
self.fee = Some(fee.clone())
}
Expand Down Expand Up @@ -272,32 +289,31 @@ impl TransactionBuilder {
Some(_x) => return Err(JsValue::from_str("Cannot calculate change if fee was explicitly specified")),
}?;
let input_total = self.get_explicit_input()?.checked_add(&self.get_implicit_input()?)?;
let output_total = self.get_explicit_output()?;
let deposit = self.get_deposit()?;
match input_total.unwrap() > output_total.checked_add(&fee)?.unwrap() {
let output_total = self.get_explicit_output()?.checked_add(&self.get_deposit()?)?;
match input_total.unwrap() >= output_total.checked_add(&fee)?.unwrap() {
false => return Err(JsValue::from_str("Insufficient input in transaction")),
true => {
let mut copy = self.clone();
copy.add_output(&TransactionOutput {
// check how much the fee would increase if we added a change output
let fee_for_change = self.fee_for_output(&TransactionOutput {
address: address.clone(),
// maximum possible output to maximize fee from adding this output
// this may over-estimate the fee by a few bytes but that's okay
amount: Coin::new(0x1_00_00_00_00),
})?;
let new_fee = copy.min_fee()?;
let new_fee = fee.checked_add(&fee_for_change)?;
// needs to have at least minimum_utxo_val leftover for the change to be a valid UTXO entry
match input_total > output_total.checked_add(&deposit)?.checked_add(&new_fee)?.checked_add(&self.minimum_utxo_val)? {
match input_total >= output_total.checked_add(&new_fee)?.checked_add(&self.minimum_utxo_val)? {
false => {
// recall: we originally assumed the fee was the maximum possible so we definitely have enough input to cover whatever fee it ends up being
self.set_fee(&input_total.checked_sub(&output_total)?.checked_sub(&deposit)?);
self.set_fee(&input_total.checked_sub(&output_total)?);
return Ok(false) // not enough input to covert the extra fee from adding an output so we just burn whatever is left
},
true => {
// recall: we originally assumed the fee was the maximum possible so we definitely have enough input to cover whatever fee it ends up being
self.set_fee(&new_fee);
self.add_output(&TransactionOutput {
address: address.clone(),
amount: input_total.checked_sub(&output_total)?.checked_sub(&new_fee)?.checked_sub(&deposit)?,
amount: input_total.checked_sub(&output_total)?.checked_sub(&new_fee)?,
})?;
},
};
Expand Down Expand Up @@ -487,7 +503,6 @@ mod tests {
.derive(0)
.to_public();

let spend_cred = StakeCredential::from_keyhash(&spend.to_raw_key().hash());
let stake_cred = StakeCredential::from_keyhash(&stake.to_raw_key().hash());
tx_builder.add_key_input(
&spend.to_raw_key().hash(),
Expand Down Expand Up @@ -522,4 +537,159 @@ mod tests {
);
let _final_tx = tx_builder.build(); // just test that it doesn't throw
}

#[test]
fn build_tx_exact_amount() {
// transactions where sum(input) == sum(output) exact should pass
let linear_fee = LinearFee::new(&Coin::new(0), &Coin::new(0));
let mut tx_builder = TransactionBuilder::new(&linear_fee, &Coin::new(1), &Coin::new(0), &Coin::new(0));
let spend = root_key_15()
.derive(harden(1852))
.derive(harden(1815))
.derive(harden(0))
.derive(0)
.derive(0)
.to_public();
let change_key = root_key_15()
.derive(harden(1852))
.derive(harden(1815))
.derive(harden(0))
.derive(1)
.derive(0)
.to_public();
let stake = root_key_15()
.derive(harden(1852))
.derive(harden(1815))
.derive(harden(0))
.derive(2)
.derive(0)
.to_public();
tx_builder.add_key_input(
&&spend.to_raw_key().hash(),
&TransactionInput::new(&genesis_id(), 0),
&Coin::new(5)
);
let spend_cred = StakeCredential::from_keyhash(&spend.to_raw_key().hash());
let stake_cred = StakeCredential::from_keyhash(&stake.to_raw_key().hash());
let addr_net_0 = BaseAddress::new(0, &spend_cred, &stake_cred).to_address();
tx_builder.add_output(&TransactionOutput::new(
&addr_net_0,
&Coin::new(5)
)).unwrap();
tx_builder.set_ttl(0);

let change_cred = StakeCredential::from_keyhash(&change_key.to_raw_key().hash());
let change_addr = BaseAddress::new(0, &change_cred, &stake_cred).to_address();
let added_change = tx_builder.add_change_if_needed(
&change_addr
).unwrap();
assert_eq!(added_change, false);
let final_tx = tx_builder.build().unwrap();
assert_eq!(final_tx.outputs().len(), 1);
}

#[test]
fn build_tx_exact_change() {
// transactions where we have exactly enough ADA to add change should pass
let linear_fee = LinearFee::new(&Coin::new(0), &Coin::new(0));
let mut tx_builder = TransactionBuilder::new(&linear_fee, &Coin::new(1), &Coin::new(0), &Coin::new(0));
let spend = root_key_15()
.derive(harden(1852))
.derive(harden(1815))
.derive(harden(0))
.derive(0)
.derive(0)
.to_public();
let change_key = root_key_15()
.derive(harden(1852))
.derive(harden(1815))
.derive(harden(0))
.derive(1)
.derive(0)
.to_public();
let stake = root_key_15()
.derive(harden(1852))
.derive(harden(1815))
.derive(harden(0))
.derive(2)
.derive(0)
.to_public();
tx_builder.add_key_input(
&&spend.to_raw_key().hash(),
&TransactionInput::new(&genesis_id(), 0),
&Coin::new(6)
);
let spend_cred = StakeCredential::from_keyhash(&spend.to_raw_key().hash());
let stake_cred = StakeCredential::from_keyhash(&stake.to_raw_key().hash());
let addr_net_0 = BaseAddress::new(0, &spend_cred, &stake_cred).to_address();
tx_builder.add_output(&TransactionOutput::new(
&addr_net_0,
&Coin::new(5)
)).unwrap();
tx_builder.set_ttl(0);

let change_cred = StakeCredential::from_keyhash(&change_key.to_raw_key().hash());
let change_addr = BaseAddress::new(0, &change_cred, &stake_cred).to_address();
let added_change = tx_builder.add_change_if_needed(
&change_addr
).unwrap();
assert_eq!(added_change, true);
let final_tx = tx_builder.build().unwrap();
assert_eq!(final_tx.outputs().len(), 2);
assert_eq!(final_tx.outputs().get(1).amount().to_str(), "1");
}

#[test]
#[should_panic]
fn build_tx_insufficient_deposit() {
// transactions should fail with insufficient fees if a deposit is required
let linear_fee = LinearFee::new(&Coin::new(0), &Coin::new(0));
let mut tx_builder = TransactionBuilder::new(&linear_fee, &Coin::new(1), &Coin::new(0), &Coin::new(5));
let spend = root_key_15()
.derive(harden(1852))
.derive(harden(1815))
.derive(harden(0))
.derive(0)
.derive(0)
.to_public();
let change_key = root_key_15()
.derive(harden(1852))
.derive(harden(1815))
.derive(harden(0))
.derive(1)
.derive(0)
.to_public();
let stake = root_key_15()
.derive(harden(1852))
.derive(harden(1815))
.derive(harden(0))
.derive(2)
.derive(0)
.to_public();
tx_builder.add_key_input(
&&spend.to_raw_key().hash(),
&TransactionInput::new(&genesis_id(), 0),
&Coin::new(5)
);
let spend_cred = StakeCredential::from_keyhash(&spend.to_raw_key().hash());
let stake_cred = StakeCredential::from_keyhash(&stake.to_raw_key().hash());
let addr_net_0 = BaseAddress::new(0, &spend_cred, &stake_cred).to_address();
tx_builder.add_output(&TransactionOutput::new(
&addr_net_0,
&Coin::new(5)
)).unwrap();
tx_builder.set_ttl(0);

// add a cert which requires a deposit
let mut certs = Certificates::new();
certs.add(&Certificate::new_stake_registration(&StakeRegistration::new(&stake_cred)));
tx_builder.set_certs(&certs);

let change_cred = StakeCredential::from_keyhash(&change_key.to_raw_key().hash());
let change_addr = BaseAddress::new(0, &change_cred, &stake_cred).to_address();

tx_builder.add_change_if_needed(
&change_addr
).unwrap();
}
}

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