forked from mimblewimble/grin
/
selection.rs
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/
selection.rs
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// Copyright 2018 The Grin Developers
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//! Selection of inputs for building transactions
use crate::core::core::{amount_to_hr_string, Transaction};
use crate::core::libtx::{build, slate::Slate, tx_fee};
use crate::keychain::{Identifier, Keychain};
use crate::libwallet::error::{Error, ErrorKind};
use crate::libwallet::internal::keys;
use crate::libwallet::types::*;
use std::collections::HashMap;
/// Initialize a transaction on the sender side, returns a corresponding
/// libwallet transaction slate with the appropriate inputs selected,
/// and saves the private wallet identifiers of our selected outputs
/// into our transaction context
pub fn build_send_tx_slate<T: ?Sized, C, K>(
wallet: &mut T,
num_participants: usize,
amount: u64,
current_height: u64,
minimum_confirmations: u64,
lock_height: u64,
max_outputs: usize,
change_outputs: usize,
selection_strategy_is_use_all: bool,
parent_key_id: Identifier,
) -> Result<
(
Slate,
Context,
impl FnOnce(&mut T, &Transaction) -> Result<(), Error>,
),
Error,
>
where
T: WalletBackend<C, K>,
C: NodeClient,
K: Keychain,
{
let (elems, inputs, change_amounts_derivations, amount, fee) = select_send_tx(
wallet,
amount,
current_height,
minimum_confirmations,
lock_height,
max_outputs,
change_outputs,
selection_strategy_is_use_all,
&parent_key_id,
)?;
// Create public slate
let mut slate = Slate::blank(num_participants);
slate.amount = amount;
slate.height = current_height;
slate.lock_height = lock_height;
slate.fee = fee;
let slate_id = slate.id.clone();
let keychain = wallet.keychain().clone();
let blinding = slate.add_transaction_elements(&keychain, elems)?;
// Create our own private context
let mut context = Context::new(
wallet.keychain().secp(),
blinding.secret_key(&keychain.secp()).unwrap(),
);
// Store our private identifiers for each input
for input in inputs {
context.add_input(&input.key_id, &input.mmr_index);
}
let mut commits: HashMap<Identifier, Option<String>> = HashMap::new();
// Store change output(s) and cached commits
for (change_amount, id, mmr_index) in &change_amounts_derivations {
context.add_output(&id, &mmr_index);
commits.insert(id.clone(), wallet.cached_commit(*change_amount, &id)?);
}
let lock_inputs = context.get_inputs().clone();
let _lock_outputs = context.get_outputs().clone();
// Return a closure to acquire wallet lock and lock the coins being spent
// so we avoid accidental double spend attempt.
let update_sender_wallet_fn = move |wallet: &mut T, tx: &Transaction| {
let tx_entry = {
let mut batch = wallet.batch()?;
let log_id = batch.next_tx_log_id(&parent_key_id)?;
let mut t = TxLogEntry::new(parent_key_id.clone(), TxLogEntryType::TxSent, log_id);
t.tx_slate_id = Some(slate_id);
let filename = format!("{}.grintx", slate_id);
t.stored_tx = Some(filename);
t.fee = Some(fee);
let mut amount_debited = 0;
t.num_inputs = lock_inputs.len();
for id in lock_inputs {
let mut coin = batch.get(&id.0, &id.1).unwrap();
coin.tx_log_entry = Some(log_id);
amount_debited = amount_debited + coin.value;
batch.lock_output(&mut coin)?;
}
t.amount_debited = amount_debited;
// write the output representing our change
for (change_amount, id, _) in &change_amounts_derivations {
t.num_outputs += 1;
t.amount_credited += change_amount;
let commit = commits.get(&id).unwrap().clone();
batch.save(OutputData {
root_key_id: parent_key_id.clone(),
key_id: id.clone(),
n_child: id.to_path().last_path_index(),
commit: commit,
mmr_index: None,
value: change_amount.clone(),
status: OutputStatus::Unconfirmed,
height: current_height,
lock_height: 0,
is_coinbase: false,
tx_log_entry: Some(log_id),
})?;
}
batch.save_tx_log_entry(t.clone(), &parent_key_id)?;
batch.commit()?;
t
};
wallet.store_tx(&format!("{}", tx_entry.tx_slate_id.unwrap()), tx)?;
Ok(())
};
Ok((slate, context, update_sender_wallet_fn))
}
/// Creates a new output in the wallet for the recipient,
/// returning the key of the fresh output and a closure
/// that actually performs the addition of the output to the
/// wallet
pub fn build_recipient_output_with_slate<T: ?Sized, C, K>(
wallet: &mut T,
slate: &mut Slate,
parent_key_id: Identifier,
) -> Result<
(
Identifier,
Context,
impl FnOnce(&mut T) -> Result<(), Error>,
),
Error,
>
where
T: WalletBackend<C, K>,
C: NodeClient,
K: Keychain,
{
// Create a potential output for this transaction
let key_id = keys::next_available_key(wallet).unwrap();
let keychain = wallet.keychain().clone();
let key_id_inner = key_id.clone();
let amount = slate.amount;
let height = slate.height;
let slate_id = slate.id.clone();
let blinding =
slate.add_transaction_elements(&keychain, vec![build::output(amount, key_id.clone())])?;
// Add blinding sum to our context
let mut context = Context::new(
keychain.secp(),
blinding
.secret_key(wallet.keychain().clone().secp())
.unwrap(),
);
context.add_output(&key_id, &None);
// Create closure that adds the output to recipient's wallet
// (up to the caller to decide when to do)
let wallet_add_fn = move |wallet: &mut T| {
let commit = wallet.cached_commit(amount, &key_id_inner)?;
let mut batch = wallet.batch()?;
let log_id = batch.next_tx_log_id(&parent_key_id)?;
let mut t = TxLogEntry::new(parent_key_id.clone(), TxLogEntryType::TxReceived, log_id);
t.tx_slate_id = Some(slate_id);
t.amount_credited = amount;
t.num_outputs = 1;
batch.save(OutputData {
root_key_id: parent_key_id.clone(),
key_id: key_id_inner.clone(),
mmr_index: None,
n_child: key_id_inner.to_path().last_path_index(),
commit: commit,
value: amount,
status: OutputStatus::Unconfirmed,
height: height,
lock_height: 0,
is_coinbase: false,
tx_log_entry: Some(log_id),
})?;
batch.save_tx_log_entry(t, &parent_key_id)?;
batch.commit()?;
Ok(())
};
Ok((key_id, context, wallet_add_fn))
}
/// Builds a transaction to send to someone from the HD seed associated with the
/// wallet and the amount to send. Handles reading through the wallet data file,
/// selecting outputs to spend and building the change.
pub fn select_send_tx<T: ?Sized, C, K>(
wallet: &mut T,
amount: u64,
current_height: u64,
minimum_confirmations: u64,
lock_height: u64,
max_outputs: usize,
change_outputs: usize,
selection_strategy_is_use_all: bool,
parent_key_id: &Identifier,
) -> Result<
(
Vec<Box<build::Append<K>>>,
Vec<OutputData>,
Vec<(u64, Identifier, Option<u64>)>, // change amounts and derivations
u64, // amount
u64, // fee
),
Error,
>
where
T: WalletBackend<C, K>,
C: NodeClient,
K: Keychain,
{
// select some spendable coins from the wallet
let (max_outputs, mut coins) = select_coins(
wallet,
amount,
current_height,
minimum_confirmations,
max_outputs,
selection_strategy_is_use_all,
parent_key_id,
);
// sender is responsible for setting the fee on the partial tx
// recipient should double check the fee calculation and not blindly trust the
// sender
// TODO - Is it safe to spend without a change output? (1 input -> 1 output)
// TODO - Does this not potentially reveal the senders private key?
//
// First attempt to spend without change
let mut fee = tx_fee(coins.len(), 1, 1, None);
let mut total: u64 = coins.iter().map(|c| c.value).sum();
let mut amount_with_fee = amount + fee;
if total == 0 {
return Err(ErrorKind::NotEnoughFunds {
available: 0,
available_disp: amount_to_hr_string(0, false),
needed: amount_with_fee as u64,
needed_disp: amount_to_hr_string(amount_with_fee as u64, false),
})?;
}
// The amount with fee is more than the total values of our max outputs
if total < amount_with_fee && coins.len() == max_outputs {
return Err(ErrorKind::NotEnoughFunds {
available: total,
available_disp: amount_to_hr_string(total, false),
needed: amount_with_fee as u64,
needed_disp: amount_to_hr_string(amount_with_fee as u64, false),
})?;
}
let num_outputs = change_outputs + 1;
// We need to add a change address or amount with fee is more than total
if total != amount_with_fee {
fee = tx_fee(coins.len(), num_outputs, 1, None);
amount_with_fee = amount + fee;
// Here check if we have enough outputs for the amount including fee otherwise
// look for other outputs and check again
while total < amount_with_fee {
// End the loop if we have selected all the outputs and still not enough funds
if coins.len() == max_outputs {
return Err(ErrorKind::NotEnoughFunds {
available: total as u64,
available_disp: amount_to_hr_string(total, false),
needed: amount_with_fee as u64,
needed_disp: amount_to_hr_string(amount_with_fee as u64, false),
})?;
}
// select some spendable coins from the wallet
coins = select_coins(
wallet,
amount_with_fee,
current_height,
minimum_confirmations,
max_outputs,
selection_strategy_is_use_all,
parent_key_id,
)
.1;
fee = tx_fee(coins.len(), num_outputs, 1, None);
total = coins.iter().map(|c| c.value).sum();
amount_with_fee = amount + fee;
}
}
// build transaction skeleton with inputs and change
let (mut parts, change_amounts_derivations) =
inputs_and_change(&coins, wallet, amount, fee, change_outputs)?;
// This is more proof of concept than anything but here we set lock_height
// on tx being sent (based on current chain height via api).
parts.push(build::with_lock_height(lock_height));
Ok((parts, coins, change_amounts_derivations, amount, fee))
}
/// Selects inputs and change for a transaction
pub fn inputs_and_change<T: ?Sized, C, K>(
coins: &Vec<OutputData>,
wallet: &mut T,
amount: u64,
fee: u64,
num_change_outputs: usize,
) -> Result<
(
Vec<Box<build::Append<K>>>,
Vec<(u64, Identifier, Option<u64>)>,
),
Error,
>
where
T: WalletBackend<C, K>,
C: NodeClient,
K: Keychain,
{
let mut parts = vec![];
// calculate the total across all inputs, and how much is left
let total: u64 = coins.iter().map(|c| c.value).sum();
parts.push(build::with_fee(fee));
// if we are spending 10,000 coins to send 1,000 then our change will be 9,000
// if the fee is 80 then the recipient will receive 1000 and our change will be
// 8,920
let change = total - amount - fee;
// build inputs using the appropriate derived key_ids
for coin in coins {
if coin.is_coinbase {
parts.push(build::coinbase_input(coin.value, coin.key_id.clone()));
} else {
parts.push(build::input(coin.value, coin.key_id.clone()));
}
}
let mut change_amounts_derivations = vec![];
if change == 0 {
debug!("No change (sending exactly amount + fee), no change outputs to build");
} else {
debug!(
"Building change outputs: total change: {} ({} outputs)",
change, num_change_outputs
);
let part_change = change / num_change_outputs as u64;
let remainder_change = change % part_change;
for x in 0..num_change_outputs {
// n-1 equal change_outputs and a final one accounting for any remainder
let change_amount = if x == (num_change_outputs - 1) {
part_change + remainder_change
} else {
part_change
};
let change_key = wallet.next_child().unwrap();
change_amounts_derivations.push((change_amount, change_key.clone(), None));
parts.push(build::output(change_amount, change_key));
}
}
Ok((parts, change_amounts_derivations))
}
/// Select spendable coins from a wallet.
/// Default strategy is to spend the maximum number of outputs (up to
/// max_outputs). Alternative strategy is to spend smallest outputs first
/// but only as many as necessary. When we introduce additional strategies
/// we should pass something other than a bool in.
/// TODO: Possibly move this into another trait to be owned by a wallet?
pub fn select_coins<T: ?Sized, C, K>(
wallet: &mut T,
amount: u64,
current_height: u64,
minimum_confirmations: u64,
max_outputs: usize,
select_all: bool,
parent_key_id: &Identifier,
) -> (usize, Vec<OutputData>)
// max_outputs_available, Outputs
where
T: WalletBackend<C, K>,
C: NodeClient,
K: Keychain,
{
// first find all eligible outputs based on number of confirmations
let mut eligible = wallet
.iter()
.filter(|out| {
out.root_key_id == *parent_key_id
&& out.eligible_to_spend(current_height, minimum_confirmations)
})
.collect::<Vec<OutputData>>();
let max_available = eligible.len();
// sort eligible outputs by increasing value
eligible.sort_by_key(|out| out.value);
// use a sliding window to identify potential sets of possible outputs to spend
// Case of amount > total amount of max_outputs(500):
// The limit exists because by default, we always select as many inputs as
// possible in a transaction, to reduce both the Output set and the fees.
// But that only makes sense up to a point, hence the limit to avoid being too
// greedy. But if max_outputs(500) is actually not enough to cover the whole
// amount, the wallet should allow going over it to satisfy what the user
// wants to send. So the wallet considers max_outputs more of a soft limit.
if eligible.len() > max_outputs {
for window in eligible.windows(max_outputs) {
let windowed_eligibles = window.iter().cloned().collect::<Vec<_>>();
if let Some(outputs) = select_from(amount, select_all, windowed_eligibles) {
return (max_available, outputs);
}
}
// Not exist in any window of which total amount >= amount.
// Then take coins from the smallest one up to the total amount of selected
// coins = the amount.
if let Some(outputs) = select_from(amount, false, eligible.clone()) {
debug!(
"Extending maximum number of outputs. {} outputs selected.",
outputs.len()
);
return (max_available, outputs);
}
} else {
if let Some(outputs) = select_from(amount, select_all, eligible.clone()) {
return (max_available, outputs);
}
}
// we failed to find a suitable set of outputs to spend,
// so return the largest amount we can so we can provide guidance on what is
// possible
eligible.reverse();
(
max_available,
eligible.iter().take(max_outputs).cloned().collect(),
)
}
fn select_from(amount: u64, select_all: bool, outputs: Vec<OutputData>) -> Option<Vec<OutputData>> {
let total = outputs.iter().fold(0, |acc, x| acc + x.value);
if total >= amount {
if select_all {
return Some(outputs.iter().cloned().collect());
} else {
let mut selected_amount = 0;
return Some(
outputs
.iter()
.take_while(|out| {
let res = selected_amount < amount;
selected_amount += out.value;
res
})
.cloned()
.collect(),
);
}
} else {
None
}
}