Introduce CoinFilterParams

This begins work on the `wallet::coin_control` module. The idea is to
filter coins, and determine which coins are fit for coin selection.

`Wallet::avaliable_utxos` is introduced to use `CoinFilterParams`.

Author: evanlinjin

src/wallet/coin_control.rs

@@ -0,0 +1,69 @@
+// Bitcoin Dev Kit
+// Written in 2020 by Alekos Filini <[email protected]>
+//
+// Copyright (c) 2020-2021 Bitcoin Dev Kit Developers
+//
+// This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
+// or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
+// You may not use this file except in accordance with one or both of these
+// licenses.
+
+//! Coin control
+//!
+//! This module defines how coins are to be sorted and/or grouped before coin selection.
+
+use std::collections::HashMap;
+
+use bitcoin::OutPoint;
+
+use crate::TransactionDetails;
+
+use super::COINBASE_MATURITY;
+
+/// Parameters to determine which coins/outputs to filter.
+pub struct CoinFilterParams {
+    /// Outpoints to manually keep (`true`) or skip (`false`). This overrides all other parameters.
+    pub manual: HashMap<OutPoint, bool>,
+
+    /// Whether we should filter out unconfirmed transactions.
+    /// TODO: Use minimum confirmations instead.
+    pub filter_unconfirmed: bool,
+
+    /// Whether we should filter out immature coinbase outputs.
+    /// Coinbase transaction outputs need to be at least 100 blocks deep before being spendable.
+    /// If this is set, but `current_height == None`, all coinbase outputs will be filtered out.
+    pub filter_immature_coinbase: bool,
+
+    /// Current block height.
+    pub current_height: Option<u32>,
+}
+
+impl CoinFilterParams {
+    /// Returns true if coin is to be kept, false if coin is to be filtered out.
+    pub(crate) fn keep(&self, tx: &TransactionDetails, outpoint: &OutPoint) -> bool {
+        let raw_tx = tx.transaction.as_ref().expect("failed to obtain raw tx");
+
+        if let Some(&keep) = self.manual.get(outpoint) {
+            if keep {
+                return true;
+            } else {
+                return false;
+            }
+        }
+
+        if self.filter_unconfirmed && tx.confirmation_time.is_none() {
+            return false;
+        }
+
+        // https://github.com/bitcoin/bitcoin/blob/c5e67be03bb06a5d7885c55db1f016fbf2333fe3/src/validation.cpp#L373-L375
+        if self.filter_immature_coinbase
+            && raw_tx.is_coin_base()
+            && !matches!((self.current_height, &tx.confirmation_time), (Some(tip), Some(conf)) if tip.saturating_sub(conf.height) >= COINBASE_MATURITY)
+        {
+            return false;
+        }
+
+        return true;
+    }
+}

src/wallet/mod.rs

@@ -38,6 +38,7 @@ use miniscript::ToPublicKey;
 use log::{debug, error, info, trace};
 
 pub mod address_validator;
+pub mod coin_control;
 pub mod coin_selection;
 pub mod export;
 pub mod signer;
@@ -79,6 +80,8 @@ use crate::testutils;
 use crate::types::*;
 use crate::wallet::coin_selection::Excess::{Change, NoChange};
 
+use self::coin_control::CoinFilterParams;
+
 const CACHE_ADDR_BATCH_SIZE: u32 = 100;
 const COINBASE_MATURITY: u32 = 100;
 
@@ -1454,6 +1457,22 @@ where
             .collect())
     }
 
+    /// Yes, we can!
+    pub fn available_utxos(
+        &self,
+        params: CoinFilterParams,
+    ) -> Result<impl Iterator<Item = LocalUtxo> + '_, Error> {
+        let db = self.database.borrow();
+
+        Ok(self.iter_unspent()?.filter(move |utxo| {
+            if let Ok(Some(tx)) = db.get_tx(&utxo.outpoint.txid, true) {
+                params.keep(&tx, &utxo.outpoint)
+            } else {
+                false
+            }
+        }))
+    }
+
     /// Given the options returns the list of utxos that must be used to form the
     /// transaction and any further that may be used if needed.
     #[allow(clippy::type_complexity)]
@@ -1464,7 +1483,7 @@ where
         unspendable: &HashSet<OutPoint>,
         manually_selected: Vec<WeightedUtxo>,
         must_use_all_available: bool,
-        manual_only: bool,
+        manual_only: bool, // We can just manually call `CoinSelector::select`, then `CoinSelector::finish`
         must_only_use_confirmed_tx: bool,
         current_height: Option<u32>,
     ) -> Result<(Vec<WeightedUtxo>, Vec<WeightedUtxo>), Error> {