wallet-core: Add input module

- Add algorithm for picking notes
- Re-export some commonly used types

wallet-core/Cargo.toml

@@ -15,7 +15,7 @@ sha2 = { version = "0.10", default-features = false }
 rand = { version = "0.8", default-features = false }
 ff = { version = "0.13", default-features = false }
 poseidon-merkle = { version = "0.7", features = ["rkyv-impl"] }
-execution-core = { version = "0.1", path = "../execution-core/" }
+execution-core = { version = "0.1", path = "../execution-core/", default-features = false }
 
 [target.'cfg(target_family = "wasm")'.dependencies]
 dlmalloc = { version = "0.2", features = ["global"] }

wallet-core/src/ffi.rs

@@ -4,8 +4,7 @@
 //
 // Copyright (c) DUSK NETWORK. All rights reserved.
 
-use crate::keys::{derive_bls_pk, derive_phoenix_pk};
-use crate::RNG_SEED;
+use crate::keys::{derive_bls_pk, derive_phoenix_pk, RNG_SEED};
 use core::ptr;
 use dusk_bytes::Serializable;
 use execution_core::{

wallet-core/src/input.rs

@@ -0,0 +1,128 @@
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+//
+// Copyright (c) DUSK NETWORK. All rights reserved.
+
+//! Helper functions for working with notes.
+
+use alloc::vec::Vec;
+
+use super::{alloc, Note};
+
+use execution_core::BlsScalar;
+
+/// The maximum amount of input notes that can be spend in one
+/// phoenix-transaction
+pub const MAX_INPUT_NOTES: usize = 4;
+
+/// Pick the notes to be used in a transaction from a vector of notes.
+///
+/// The resulting array is only 4 notes long, the argument of this function can
+/// be arbitary amount of notes.
+///
+/// # Errors
+///
+/// If the target sum is greater than the sum of the notes then an error is
+/// returned. If the notes vector is empty then an error is returned.
+///
+/// See `InputNotesError` type for possible errors
+/// this function can yield.
+#[must_use]
+pub fn try_input_notes(
+    nodes: Vec<(Note, u64, BlsScalar)>,
+    target_sum: u64,
+) -> Vec<(Note, BlsScalar)> {
+    if nodes.is_empty() {
+        return Vec::new();
+    }
+
+    let mut i = 0;
+    let mut sum = 0;
+    while sum < target_sum && i < nodes.len() {
+        sum = sum.saturating_add(nodes[i].1);
+        i += 1;
+    }
+
+    if sum < target_sum {
+        return Vec::new();
+    }
+
+    pick_notes(target_sum, nodes)
+}
+
+/// Pick the notes to be used in a transaction from a vector of notes.
+///
+/// The notes are picked in a way to maximize the number of notes used,
+/// while minimizing the value employed. To do this we sort the notes in
+/// ascending value order, and go through each combination in a
+/// lexicographic order until we find the first combination whose sum is
+/// larger or equal to the given value. If such a slice is not found, an
+/// empty vector is returned.
+///
+/// Note: it is presupposed that the input notes contain enough balance to
+/// cover the given `value`.
+fn pick_notes(
+    value: u64,
+    notes_and_values: Vec<(Note, u64, BlsScalar)>,
+) -> Vec<(Note, BlsScalar)> {
+    let mut notes_and_values = notes_and_values;
+    let len = notes_and_values.len();
+
+    if len <= MAX_INPUT_NOTES {
+        return notes_and_values
+            .into_iter()
+            .map(|(note, _, b)| (note, b))
+            .collect();
+    }
+
+    notes_and_values.sort_by(|(_, aval, _), (_, bval, _)| aval.cmp(bval));
+    pick_lexicographic(notes_and_values.len(), |indices| {
+        indices
+            .iter()
+            .map(|index| notes_and_values[*index].1)
+            .sum::<u64>()
+            >= value
+    })
+    .map(|index| notes_and_values[index].clone())
+    .map(|(n, _, b)| (n, b))
+    .to_vec()
+}
+
+fn pick_lexicographic<F: Fn(&[usize; MAX_INPUT_NOTES]) -> bool>(
+    max_len: usize,
+    is_valid: F,
+) -> [usize; MAX_INPUT_NOTES] {
+    let mut indices = [0; MAX_INPUT_NOTES];
+    indices
+        .iter_mut()
+        .enumerate()
+        .for_each(|(i, index)| *index = i);
+
+    loop {
+        if is_valid(&indices) {
+            return indices;
+        }
+
+        let mut i = MAX_INPUT_NOTES - 1;
+
+        while indices[i] == i + max_len - MAX_INPUT_NOTES {
+            if i > 0 {
+                i -= 1;
+            } else {
+                break;
+            }
+        }
+
+        indices[i] += 1;
+        for j in i + 1..MAX_INPUT_NOTES {
+            indices[j] = indices[j - 1] + 1;
+        }
+
+        if indices[MAX_INPUT_NOTES - 1] == max_len {
+            break;
+        }
+    }
+
+    [0; MAX_INPUT_NOTES]
+}

wallet-core/src/keys.rs

@@ -21,7 +21,11 @@ use execution_core::{
     },
 };
 
-use crate::RNG_SEED;
+/// The seed bytes buffer which is used at multiple places
+pub type Seed = [u8; RNG_SEED];
+
+/// Length of the seed of the generated rng.
+pub const RNG_SEED: usize = 64;
 
 /// Generates a [`BlsSecretKey`] from a seed and index.
 ///

wallet-core/src/lib.rs

@@ -16,18 +16,18 @@ static ALLOC: dlmalloc::GlobalDlmalloc = dlmalloc::GlobalDlmalloc;
 
 extern crate alloc;
 
-pub mod keys;
-pub mod transaction;
-
 #[cfg(target_family = "wasm")]
 mod ffi;
 
-/// Length of the seed of the generated rng.
-pub const RNG_SEED: usize = 64;
+pub mod input;
+pub mod keys;
+pub mod transaction;
 
-// The maximum amount of input notes that can be spend in one
-// phoenix-transaction
-const MAX_INPUT_NOTES: usize = 4;
+pub mod prelude {
+    //! Re-export of the most commonly used types and traits.
+    pub use crate::keys;
+    pub use crate::{input::MAX_INPUT_NOTES, keys::RNG_SEED};
+}
 
 use alloc::collections::btree_map::BTreeMap;
 use alloc::vec::Vec;
@@ -77,8 +77,9 @@ where
 
     values.sort_by(|a, b| b.cmp(a));
 
-    let spendable = values.iter().take(MAX_INPUT_NOTES).sum();
-    let value = spendable + values.iter().skip(MAX_INPUT_NOTES).sum::<u64>();
+    let spendable = values.iter().take(input::MAX_INPUT_NOTES).sum();
+    let value =
+        spendable + values.iter().skip(input::MAX_INPUT_NOTES).sum::<u64>();
 
     BalanceInfo { value, spendable }
 }

wallet-core/tests/notes.rs

@@ -5,21 +5,49 @@
 // Copyright (c) DUSK NETWORK. All rights reserved.
 
 use ff::Field;
-use rand::rngs::StdRng;
-use rand::{Rng, SeedableRng};
+use rand::{rngs::StdRng, CryptoRng, RngCore, SeedableRng};
 
 use execution_core::{
     transfer::phoenix::{
         Note, NoteLeaf, PublicKey as PhoenixPublicKey,
         SecretKey as PhoenixSecretKey,
     },
-    JubJubScalar,
+    BlsScalar, JubJubScalar,
 };
 
 use wallet_core::{
-    keys::derive_multiple_phoenix_sk, map_owned, phoenix_balance, BalanceInfo,
+    input::try_input_notes, keys::derive_multiple_phoenix_sk, map_owned,
+    phoenix_balance, BalanceInfo,
 };
 
+/// Generate a note, useful for testing purposes
+pub fn gen_note<T: RngCore + CryptoRng>(
+    rng: &mut T,
+    obfuscated_note: bool,
+    owner_pk: &PhoenixPublicKey,
+    value: u64,
+) -> Note {
+    let sender_pk = PhoenixPublicKey::from(&PhoenixSecretKey::random(rng));
+
+    let value_blinder = JubJubScalar::random(&mut *rng);
+    let sender_blinder = [
+        JubJubScalar::random(&mut *rng),
+        JubJubScalar::random(&mut *rng),
+    ];
+    if obfuscated_note {
+        Note::obfuscated(
+            rng,
+            &sender_pk,
+            owner_pk,
+            value,
+            value_blinder,
+            sender_blinder,
+        )
+    } else {
+        Note::transparent(rng, &sender_pk, owner_pk, value, sender_blinder)
+    }
+}
+
 #[test]
 fn test_map_owned() {
     // Assuming this set of notes where the number used as suffix is the
@@ -121,41 +149,59 @@ fn test_balance() {
     );
 }
 
-fn gen_note(
-    rng: &mut StdRng,
-    obfuscated_note: bool,
-    owner_pk: &PhoenixPublicKey,
-    value: u64,
-) -> NoteLeaf {
-    let sender_pk = PhoenixPublicKey::from(&PhoenixSecretKey::random(rng));
+#[test]
+fn knapsack_works() {
+    use rand::SeedableRng;
 
-    let value_blinder = JubJubScalar::random(&mut *rng);
-    let sender_blinder = [
-        JubJubScalar::random(&mut *rng),
-        JubJubScalar::random(&mut *rng),
-    ];
-    if obfuscated_note {
-        NoteLeaf {
-            note: Note::obfuscated(
-                rng,
-                &sender_pk,
-                &owner_pk,
-                value,
-                value_blinder,
-                sender_blinder,
-            ),
-            block_height: rng.gen(),
-        }
-    } else {
-        NoteLeaf {
-            note: Note::transparent(
-                rng,
-                &sender_pk,
-                &owner_pk,
-                value,
-                sender_blinder,
-            ),
-            block_height: rng.gen(),
-        }
-    }
+    let mut rng = rand_chacha::ChaCha12Rng::seed_from_u64(0xbeef);
+
+    // sanity check
+    assert_eq!(try_input_notes(vec![], 70), Vec::new(),);
+
+    let sk = PhoenixSecretKey::random(&mut rng);
+    let pk = PhoenixPublicKey::from(&sk);
+
+    // basic check
+    let note = gen_note(&mut rng, true, &pk, 100);
+    let n = note.gen_nullifier(&sk);
+    let available = vec![(note, 100, n)];
+    let inputs_notes: Vec<(Note, BlsScalar)> = available
+        .clone()
+        .into_iter()
+        .map(|(a, _, b)| (a, b))
+        .collect();
+    let input = try_input_notes(available, 70);
+    assert_eq!(input, inputs_notes);
+
+    // out of balance basic check
+    let note = gen_note(&mut rng, true, &pk, 100);
+    let available = vec![(note, 100, n)];
+    assert_eq!(try_input_notes(available, 101), Vec::new());
+
+    // multiple inputs check
+    // note: this test is checking a naive, simple order-based output
+
+    let note1 = gen_note(&mut rng, true, &pk, 100);
+    let note2 = gen_note(&mut rng, true, &pk, 500);
+    let note3 = gen_note(&mut rng, true, &pk, 300);
+
+    let available = vec![(note1, 100, n), (note2, 500, n), (note3, 300, n)];
+
+    let result: Vec<(Note, BlsScalar)> = available
+        .clone()
+        .into_iter()
+        .map(|(a, _, b)| (a, b))
+        .collect();
+
+    assert_eq!(try_input_notes(available.clone(), 600), result);
+
+    let note1 = gen_note(&mut rng, true, &pk, 100);
+    let note2 = gen_note(&mut rng, true, &pk, 500);
+    let note3 = gen_note(&mut rng, true, &pk, 300);
+
+    let n = note1.gen_nullifier(&sk);
+
+    let available = vec![(note1, 100, n), (note2, 500, n), (note3, 300, n)];
+
+    assert_eq!(try_input_notes(available, 901), Vec::new());
 }