-fn get_dust_value(output_script: &Script) -> u64 {
- //TODO: This belongs in rust-bitcoin (https://github.com/rust-bitcoin/rust-bitcoin/pull/566)
- if output_script.is_op_return() {
- 0
- } else if output_script.is_witness_program() {
- 294
- } else {
- 546
- }
-}
-
/// Possibly adds a change output to the given transaction, always doing so if there are excess
/// funds available beyond the requested feerate.
/// Assumes at least one input will have a witness (ie spends a segwit output).
/// Returns an Err(()) if the requested feerate cannot be met.
/// Possibly adds a change output to the given transaction, always doing so if there are excess
/// funds available beyond the requested feerate.
/// Assumes at least one input will have a witness (ie spends a segwit output).
/// Returns an Err(()) if the requested feerate cannot be met.
-pub(crate) fn maybe_add_change_output(tx: &mut Transaction, input_value: u64, witness_max_weight: usize, feerate_sat_per_1000_weight: u32, change_destination_script: Script) -> Result<(), ()> {
+/// Returns the expected maximum weight of the fully signed transaction on success.
+pub(crate) fn maybe_add_change_output(tx: &mut Transaction, input_value: u64, witness_max_weight: usize, feerate_sat_per_1000_weight: u32, change_destination_script: Script) -> Result<usize, ()> {
let mut output_value = 0;
for output in tx.output.iter() {
output_value += output.value;
if output_value >= input_value { return Err(()); }
}
let mut output_value = 0;
for output in tx.output.iter() {
output_value += output.value;
if output_value >= input_value { return Err(()); }
}
let mut change_output = TxOut {
script_pubkey: change_destination_script,
value: 0,
};
let change_len = change_output.consensus_encode(&mut sink()).unwrap();
let mut change_output = TxOut {
script_pubkey: change_destination_script,
value: 0,
};
let change_len = change_output.consensus_encode(&mut sink()).unwrap();
// Include any extra bytes required to push an extra output.
weight_with_change += (VarInt(tx.output.len() as u64 + 1).len() - VarInt(tx.output.len() as u64).len()) as i64 * 4;
// When calculating weight, add two for the flag bytes
let change_value: i64 = (input_value - output_value) as i64 - weight_with_change * feerate_sat_per_1000_weight as i64 / 1000;
// Include any extra bytes required to push an extra output.
weight_with_change += (VarInt(tx.output.len() as u64 + 1).len() - VarInt(tx.output.len() as u64).len()) as i64 * 4;
// When calculating weight, add two for the flag bytes
let change_value: i64 = (input_value - output_value) as i64 - weight_with_change * feerate_sat_per_1000_weight as i64 / 1000;
use bitcoin::blockdata::transaction::{Transaction, TxOut, TxIn, OutPoint};
use bitcoin::blockdata::script::{Script, Builder};
use bitcoin::blockdata::transaction::{Transaction, TxOut, TxIn, OutPoint};
use bitcoin::blockdata::script::{Script, Builder};
// Check that we never add dust outputs
let mut tx = Transaction { version: 2, lock_time: 0, input: Vec::new(), output: Vec::new() };
let orig_wtxid = tx.wtxid();
// Check that we never add dust outputs
let mut tx = Transaction { version: 2, lock_time: 0, input: Vec::new(), output: Vec::new() };
let orig_wtxid = tx.wtxid();
// 9 sats isn't enough to pay fee on a dummy transaction...
assert_eq!(tx.get_weight() as u64, 40); // ie 10 vbytes
// 9 sats isn't enough to pay fee on a dummy transaction...
assert_eq!(tx.get_weight() as u64, 40); // ie 10 vbytes
- assert!(maybe_add_change_output(&mut tx, 9, 0, 253, Script::new()).is_err());
+ assert!(maybe_add_change_output(&mut tx, 9, 0, 250, output_spk.clone()).is_err());
assert_eq!(tx.wtxid(), orig_wtxid); // Failure doesn't change the transaction
// but 10-564 is, just not enough to add a change output...
assert_eq!(tx.wtxid(), orig_wtxid); // Failure doesn't change the transaction
// but 10-564 is, just not enough to add a change output...
- assert!(maybe_add_change_output(&mut tx, 10, 0, 253, Script::new()).is_ok());
+ assert!(maybe_add_change_output(&mut tx, 10, 0, 250, output_spk.clone()).is_ok());
assert_eq!(tx.output.len(), 0);
assert_eq!(tx.wtxid(), orig_wtxid); // If we don't add an output, we don't change the transaction
assert_eq!(tx.output.len(), 0);
assert_eq!(tx.wtxid(), orig_wtxid); // If we don't add an output, we don't change the transaction
- assert!(maybe_add_change_output(&mut tx, 564, 0, 253, Script::new()).is_ok());
+ assert!(maybe_add_change_output(&mut tx, 549, 0, 250, output_spk.clone()).is_ok());
assert_eq!(tx.output.len(), 0);
assert_eq!(tx.wtxid(), orig_wtxid); // If we don't add an output, we don't change the transaction
assert_eq!(tx.output.len(), 0);
assert_eq!(tx.wtxid(), orig_wtxid); // If we don't add an output, we don't change the transaction
- assert!(maybe_add_change_output(&mut tx, 565, 2, 253, Script::new()).is_ok());
+ assert!(maybe_add_change_output(&mut tx, 590, 2, 250, output_spk.clone()).is_ok());
assert_eq!(tx.output.len(), 0);
assert_eq!(tx.wtxid(), orig_wtxid); // If we don't add an output, we don't change the transaction
assert_eq!(tx.output.len(), 0);
assert_eq!(tx.wtxid(), orig_wtxid); // If we don't add an output, we don't change the transaction
- // at 565 we can afford the change output at the dust limit (546)
- assert!(maybe_add_change_output(&mut tx, 565, 0, 253, Script::new()).is_ok());
+ // at 590 we can afford the change output at the dust limit (546)
+ assert!(maybe_add_change_output(&mut tx, 590, 0, 250, output_spk.clone()).is_ok());
assert_eq!(tx.output.len(), 1);
assert_eq!(tx.output[0].value, 546);
assert_eq!(tx.output.len(), 1);
assert_eq!(tx.output[0].value, 546);
- assert_eq!(tx.output[0].script_pubkey, Script::new());
- assert_eq!(tx.get_weight() / 4, 565-546); // New weight is exactly the fee we wanted.
+ assert_eq!(tx.output[0].script_pubkey, output_spk);
+ assert_eq!(tx.get_weight() / 4, 590-546); // New weight is exactly the fee we wanted.
let orig_weight = tx.get_weight();
assert_eq!(orig_weight / 4, 61);
let orig_weight = tx.get_weight();
assert_eq!(orig_weight / 4, 61);
// Input value of the output value + fee - 1 should fail:
assert!(maybe_add_change_output(&mut tx, 1000 + 61 + 100 - 1, 400, 250, Builder::new().push_int(2).into_script()).is_err());
assert_eq!(tx.wtxid(), orig_wtxid); // Failure doesn't change the transaction
// but one more input sat should succeed, without changing the transaction
assert!(maybe_add_change_output(&mut tx, 1000 + 61 + 100, 400, 250, Builder::new().push_int(2).into_script()).is_ok());
assert_eq!(tx.wtxid(), orig_wtxid); // If we don't add an output, we don't change the transaction
// Input value of the output value + fee - 1 should fail:
assert!(maybe_add_change_output(&mut tx, 1000 + 61 + 100 - 1, 400, 250, Builder::new().push_int(2).into_script()).is_err());
assert_eq!(tx.wtxid(), orig_wtxid); // Failure doesn't change the transaction
// but one more input sat should succeed, without changing the transaction
assert!(maybe_add_change_output(&mut tx, 1000 + 61 + 100, 400, 250, Builder::new().push_int(2).into_script()).is_ok());
assert_eq!(tx.wtxid(), orig_wtxid); // If we don't add an output, we don't change the transaction
- // In order to get a change output, we need to add 546 plus the output's weight / 4 (10)...
- assert!(maybe_add_change_output(&mut tx, 1000 + 61 + 100 + 546 + 9, 400, 250, Builder::new().push_int(2).into_script()).is_ok());
+ // In order to get a change output, we need to add 474 plus the output's weight / 4 (10)...
+ assert!(maybe_add_change_output(&mut tx, 1000 + 61 + 100 + 474 + 9, 400, 250, Builder::new().push_int(2).into_script()).is_ok());
- assert!(maybe_add_change_output(&mut tx, 1000 + 61 + 100 + 546 + 10, 400, 250, Builder::new().push_int(2).into_script()).is_ok());
+ assert!(maybe_add_change_output(&mut tx, 1000 + 61 + 100 + 474 + 10, 400, 250, Builder::new().push_int(2).into_script()).is_ok());
assert_eq!(tx.output[1].script_pubkey, Builder::new().push_int(2).into_script());
assert_eq!(tx.get_weight() - orig_weight, 40); // Weight difference matches what we had to add above
tx.output.pop();
assert_eq!(tx.output[1].script_pubkey, Builder::new().push_int(2).into_script());
assert_eq!(tx.get_weight() - orig_weight, 40); // Weight difference matches what we had to add above
tx.output.pop();