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Add support for custom sorting and deprecate BIP69 #556

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Add support for custom sorting and deprecate BIP69
Yureien Feb 27, 2022
946819f
Updated CHANGELOG
Yureien Feb 27, 2022
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1 change: 1 addition & 0 deletions CHANGELOG.md
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Expand Up @@ -8,6 +8,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0

- Removed default verification from `wallet::sync`. sync-time verification is added in `script_sync` and is activated by `verify` feature flag.
- `verify` flag removed from `TransactionDetails`.
- Deprecated `TxOrdering::Bip69Lexicographic` and added `TxOrdering::Custom`.

## [v0.16.1] - [v0.16.0]

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1 change: 1 addition & 0 deletions src/wallet/mod.rs
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Expand Up @@ -2145,6 +2145,7 @@ pub(crate) mod test {
let (wallet, _, _) = get_funded_wallet(get_test_wpkh());
let addr = wallet.get_address(New).unwrap();
let mut builder = wallet.build_tx();
#[allow(deprecated)]
builder
.add_recipient(addr.script_pubkey(), 30_000)
.add_recipient(addr.script_pubkey(), 10_000)
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36 changes: 34 additions & 2 deletions src/wallet/tx_builder.rs
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Expand Up @@ -36,11 +36,14 @@
//! # Ok::<(), bdk::Error>(())
//! ```

use std::cmp::Ordering;
use std::collections::BTreeMap;
use std::collections::HashSet;
use std::default::Default;
use std::marker::PhantomData;
use std::sync::Arc;

use bitcoin::blockdata::transaction::{TxIn, TxOut};
use bitcoin::util::psbt::{self, PartiallySignedTransaction as Psbt};
use bitcoin::{OutPoint, Script, SigHashType, Transaction};

Expand Down Expand Up @@ -646,14 +649,22 @@ impl<'a, B, D: BatchDatabase> TxBuilder<'a, B, D, DefaultCoinSelectionAlgorithm,
}

/// Ordering of the transaction's inputs and outputs
#[derive(Debug, Ord, PartialOrd, Eq, PartialEq, Hash, Clone, Copy)]
#[derive(Clone)]
pub enum TxOrdering {
/// Randomized (default)
Shuffle,
/// Unchanged
Untouched,
/// BIP69 / Lexicographic
#[deprecated = "BIP69 does not improve privacy as was the intention of the BIP"]
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I don't know if we can, but if possible I would add a link to the discussion here on github. Maybe you could make a multiline warning, first line stays the same, and in a new line something like "To know more read the discussion at: ...".

Similar to what the rust compiler does when you have an error.

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@afilini Can you give me an example in the rust lang? I can just look at their source code and implement the same way.

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I meant something like:

warning: the feature `native_link_modifiers` is incomplete and may not be safe to use and/or cause compiler crashes
 --> library/unwind/src/lib.rs:8:12
  |
8 | #![feature(native_link_modifiers)]
  |            ^^^^^^^^^^^^^^^^^^^^^
  |
  = note: `#[warn(incomplete_features)]` on by default
  = note: see issue #81490 <https://github.com/rust-lang/rust/issues/81490> for more information

I like that "note: see issue ..." at the end

Bip69Lexicographic,
/// Provide custom comparison functions for sorting
Custom {
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I think we may have to add some sort of "state" here, something that the two functions could look at to know what to do essentially. It doesn't have to be mutable, that would mess a lot of this up.

If we don't wanna add generic types we could maybe add a Box<dyn std::any::Any>, which you can then downcast to whatever you need in the functions. Obviously you would also have to add that as an extra argument to your functions.

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CC @LLFourn who proposed sorting with a shared secret. I think you would not be able to do that, unless you introduce this state.

I'm not sure what happens if you try borrowing from local variables in the two Fns, I'm guessing you are not allowed to do that because of lifetime issues. Maybe we should test this first, actually.

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@fadedcoder can you write a doc comment or a test which maybe demos how to use a secret to hash the input/output to produce the key?

Given the awkward Arc thing it might be better to have a convenience method like set_custom_ordering(i_f: impl Fn(&Txin...), o_f: impl Fn(&TxOut,..)) which would wrap the Arcs around them.

I think we may have to add some sort of "state" here, something that the two functions could look at to know what to do essentially. It doesn't have to be mutable, that would mess a lot of this up.

Just move in what you need?

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Just move in what you need?

For some reason I always instinctively think that move will only work with FnOnce because I feel like the value would be consumed at the first iteration.

So yeah, move probably works, but as you said it would be nice to have an example and more tests to verify this.

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Yeah sure, I'll add some tests or examples soon!

/// Transaction inputs sort function
input_sort: Arc<dyn Fn(&TxIn, &TxIn) -> Ordering>,
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Very minor nit, but this confused me for a second: I would just import std::cmp and then here use cmp::Ordering.

For a second I confused Ordering with TxOrdering and I couldn't figure out what was going on.

/// Transaction outputs sort function
output_sort: Arc<dyn Fn(&TxOut, &TxOut) -> Ordering>,
},
}

impl Default for TxOrdering {
Expand All @@ -662,6 +673,18 @@ impl Default for TxOrdering {
}
}

impl std::fmt::Debug for TxOrdering {
fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
match self {
TxOrdering::Shuffle => write!(f, "Randomized"),
TxOrdering::Untouched => write!(f, "Unchanged"),
#[allow(deprecated)]
TxOrdering::Bip69Lexicographic => write!(f, "BIP69 / Lexicographic"),
TxOrdering::Custom { .. } => write!(f, "Custom"),
}
}
}

impl TxOrdering {
/// Sort transaction inputs and outputs by [`TxOrdering`] variant
pub fn sort_tx(&self, tx: &mut Transaction) {
Expand All @@ -679,13 +702,21 @@ impl TxOrdering {

tx.output.shuffle(&mut rng);
}
#[allow(deprecated)]
TxOrdering::Bip69Lexicographic => {
tx.input.sort_unstable_by_key(|txin| {
(txin.previous_output.txid, txin.previous_output.vout)
});
tx.output
.sort_unstable_by_key(|txout| (txout.value, txout.script_pubkey.clone()));
}
TxOrdering::Custom {
input_sort,
output_sort,
} => {
tx.input.sort_unstable_by(|a, b| input_sort(a, b));
tx.output.sort_unstable_by(|a, b| output_sort(a, b));
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💡 I think you want sort_by_cached_key here since you might do some expensive computation why computing the key e.g. hashing.

}
}
}
}
Expand Down Expand Up @@ -769,7 +800,7 @@ mod test {

#[test]
fn test_output_ordering_default_shuffle() {
assert_eq!(TxOrdering::default(), TxOrdering::Shuffle);
assert!(std::matches!(TxOrdering::default(), TxOrdering::Shuffle));
}

#[test]
Expand Down Expand Up @@ -800,6 +831,7 @@ mod test {
let original_tx = ordering_test_tx!();
let mut tx = original_tx;

#[allow(deprecated)]
TxOrdering::Bip69Lexicographic.sort_tx(&mut tx);

assert_eq!(
Expand Down