X-Git-Url: http://git.bitcoin.ninja/index.cgi?a=blobdiff_plain;f=lightning%2Fsrc%2Futil%2Ftransaction_utils.rs;h=4d444d7c2aba29f20aa8ad6bee4e4483e008024d;hb=a731efcb6822609b400170bce54d59addc5821c3;hp=a7c1e6bc6f78a48e15b69cf4081f0b88534b30e3;hpb=06091cee0fd29549e5e24c673bf361ab3a562529;p=rust-lightning diff --git a/lightning/src/util/transaction_utils.rs b/lightning/src/util/transaction_utils.rs index a7c1e6bc..4d444d7c 100644 --- a/lightning/src/util/transaction_utils.rs +++ b/lightning/src/util/transaction_utils.rs @@ -1,6 +1,22 @@ -use bitcoin::blockdata::transaction::TxOut; +// This file is Copyright its original authors, visible in version control +// history. +// +// This file is licensed under the Apache License, Version 2.0 or the MIT license +// , at your option. +// You may not use this file except in accordance with one or both of these +// licenses. -use std::cmp::Ordering; +use bitcoin::blockdata::transaction::{Transaction, TxOut}; +use bitcoin::blockdata::script::Script; +use bitcoin::consensus::Encodable; +use bitcoin::consensus::encode::VarInt; + +use ln::msgs::MAX_VALUE_MSAT; + +use prelude::*; +use io_extras::sink; +use core::cmp::Ordering; pub fn sort_outputs Ordering>(outputs: &mut Vec<(TxOut, T)>, tie_breaker: C) { outputs.sort_unstable_by(|a, b| { @@ -12,15 +28,60 @@ pub fn sort_outputs Ordering>(outputs: &mut Vec<(TxOut, T)> }); } +/// 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. +/// 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 { + if input_value > MAX_VALUE_MSAT / 1000 { return Err(()); } + + const WITNESS_FLAG_BYTES: i64 = 2; + + let mut output_value = 0; + for output in tx.output.iter() { + output_value += output.value; + if output_value >= input_value { return Err(()); } + } + + let dust_value = change_destination_script.dust_value(); + let mut change_output = TxOut { + script_pubkey: change_destination_script, + value: 0, + }; + let change_len = change_output.consensus_encode(&mut sink()).unwrap(); + let starting_weight = tx.get_weight() + WITNESS_FLAG_BYTES as usize + witness_max_weight; + let mut weight_with_change: i64 = starting_weight as i64 + change_len as i64 * 4; + // 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; + if change_value >= dust_value.as_sat() as i64 { + change_output.value = change_value as u64; + tx.output.push(change_output); + Ok(weight_with_change as usize) + } else if (input_value - output_value) as i64 - (starting_weight as i64) * feerate_sat_per_1000_weight as i64 / 1000 < 0 { + Err(()) + } else { + Ok(starting_weight) + } +} + #[cfg(test)] mod tests { use super::*; + use bitcoin::blockdata::transaction::{Transaction, TxOut, TxIn, OutPoint}; use bitcoin::blockdata::script::{Script, Builder}; - use bitcoin::blockdata::transaction::TxOut; + use bitcoin::hash_types::{PubkeyHash, Txid}; + + use bitcoin::hashes::sha256d::Hash as Sha256dHash; + use bitcoin::hashes::Hash; use hex::decode; + use alloc::vec; + #[test] fn sort_output_by_value() { let txout1 = TxOut { @@ -149,4 +210,82 @@ mod tests { bip69_txout_test_1: TXOUT1.to_vec(), bip69_txout_test_2: TXOUT2.to_vec(), } + + #[test] + fn test_tx_value_overrun() { + // If we have a bogus input amount or outputs valued more than inputs, we should fail + let mut tx = Transaction { version: 2, lock_time: 0, input: Vec::new(), output: vec![TxOut { + script_pubkey: Script::new(), value: 1000 + }] }; + assert!(maybe_add_change_output(&mut tx, 21_000_000_0000_0001, 0, 253, Script::new()).is_err()); + assert!(maybe_add_change_output(&mut tx, 400, 0, 253, Script::new()).is_err()); + assert!(maybe_add_change_output(&mut tx, 4000, 0, 253, Script::new()).is_ok()); + } + + #[test] + fn test_tx_change_edge() { + // 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(); + let output_spk = Script::new_p2pkh(&PubkeyHash::hash(&[0; 0])); + assert_eq!(output_spk.dust_value().as_sat(), 546); + // 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, 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!(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!(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 + // 590 is also not enough, if we anticipate 2 more weight units pushing us up to the next vbyte + // (considering the two bytes for segwit flags) + 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 + // 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[0].script_pubkey, output_spk); + assert_eq!(tx.get_weight() / 4, 590-546); // New weight is exactly the fee we wanted. + + tx.output.pop(); + assert_eq!(tx.wtxid(), orig_wtxid); // The only change is the addition of one output. + } + + #[test] + fn test_tx_extra_outputs() { + // Check that we correctly handle existing outputs + let mut tx = Transaction { version: 2, lock_time: 0, input: vec![TxIn { + previous_output: OutPoint::new(Txid::from_hash(Sha256dHash::default()), 0), script_sig: Script::new(), witness: Vec::new(), sequence: 0, + }], output: vec![TxOut { + script_pubkey: Builder::new().push_int(1).into_script(), value: 1000 + }] }; + let orig_wtxid = tx.wtxid(); + let orig_weight = tx.get_weight(); + assert_eq!(orig_weight / 4, 61); + + assert_eq!(Builder::new().push_int(2).into_script().dust_value().as_sat(), 474); + + // 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 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_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, 1000 + 61 + 100 + 474 + 10, 400, 250, Builder::new().push_int(2).into_script()).is_ok()); + assert_eq!(tx.output.len(), 2); + assert_eq!(tx.output[1].value, 474); + 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.wtxid(), orig_wtxid); // The only change is the addition of one output. + } }