Merge rust-bitcoin/rust-bitcoin#2987: Add `TxIdentifier` trait

a738754f67 Add TxIdentifier trait (Tobin C. Harding)

Pull request description:

  Add a new trait `TxIdentifier` that abstracts over the `Txid` and `Wtxid` types. We make `AsRef` a super trait so that the new trait needs no methods.

  Seal the trait so consumers of the library cannot implement it.

  Use the new trait in:

  - the `bip152` module to tighten up the `with_siphash_keys` function
  - as a trait bound on the `Leaf` associated type in the `MerkleNode` trait

ACKs for top commit:
  apoelstra:
    ACK a738754f67
  Kixunil:
    ACK a738754f67

Tree-SHA512: a7bda26a4a5107f96b24ea3c163286a7ab21a817bdec3434b3ab27d78e99c0548a7362a2271d362b89038c80d9251767c0d62e1df702ef57d9edaf141ab55cd6

bitcoin/src/bip152.rs

@@ -15,6 +15,7 @@ use io::{BufRead, Write};
 use crate::consensus::encode::{self, Decodable, Encodable, VarInt};
 use crate::internal_macros::{impl_array_newtype_stringify, impl_consensus_encoding};
 use crate::prelude::Vec;
+use crate::transaction::TxIdentifier;
 use crate::{block, Block, BlockHash, Transaction};
 
 /// A BIP-152 error
@@ -116,7 +117,7 @@ impl ShortId {
     }
 
     /// Calculates the short ID with the given (w)txid and using the provided SipHash keys.
-    pub fn with_siphash_keys<T: AsRef<[u8]>>(txid: &T, siphash_keys: (u64, u64)) -> ShortId {
+    pub fn with_siphash_keys<T: TxIdentifier>(txid: &T, siphash_keys: (u64, u64)) -> ShortId {
         // 2. Running SipHash-2-4 with the input being the transaction ID and the keys (k0/k1)
         // set to the first two little-endian 64-bit integers from the above hash, respectively.
         let hash = siphash24::Hash::hash_with_keys(siphash_keys.0, siphash_keys.1, txid.as_ref());
@@ -242,14 +243,11 @@ impl HeaderAndShortIds {
                     },
                 });
             } else {
-                short_ids.push(ShortId::with_siphash_keys(
+                match version {
-                    &match version {
+                    1 => short_ids.push(ShortId::with_siphash_keys(&tx.compute_txid(), siphash_keys)),
-                        1 => tx.compute_txid().to_raw_hash(),
+                    2 => short_ids.push(ShortId::with_siphash_keys(&tx.compute_wtxid(), siphash_keys)),
-                        2 => tx.compute_wtxid().to_raw_hash(),
+                    _ => unreachable!(),
-                        _ => unreachable!(),
+                }
-                    },
-                    siphash_keys,
-                ));
             }
         }
 

bitcoin/src/blockdata/transaction.rs

@@ -67,6 +67,18 @@ impl Wtxid {
     pub fn all_zeros() -> Self { Self::from_byte_array([0; 32]) }
 }
 
+/// Trait that abstracts over a transaction identifier i.e., `Txid` and `Wtxid`.
+pub trait TxIdentifier: sealed::Sealed + AsRef<[u8]> {}
+
+impl TxIdentifier for Txid {}
+impl TxIdentifier for Wtxid {}
+
+mod sealed {
+    pub trait Sealed {}
+    impl Sealed for super::Txid {}
+    impl Sealed for super::Wtxid {}
+}
+
 /// The marker MUST be a 1-byte zero value: 0x00. (BIP-141)
 const SEGWIT_MARKER: u8 = 0x00;
 /// The flag MUST be a 1-byte non-zero value. Currently, 0x01 MUST be used. (BIP-141)

bitcoin/src/merkle_tree/mod.rs

@@ -20,6 +20,7 @@ use hashes::{sha256d, HashEngine as _};
 
 use crate::internal_macros::impl_hashencode;
 use crate::prelude::Vec;
+use crate::transaction::TxIdentifier;
 use crate::{Txid, Wtxid};
 
 #[rustfmt::skip]
@@ -46,7 +47,7 @@ impl_hashencode!(WitnessMerkleNode);
 /// do not use this algorithm and cannot use this trait.
 pub trait MerkleNode: Copy {
     /// The hash (TXID or WTXID) of a transaciton in the tree.
-    type Leaf;
+    type Leaf: TxIdentifier;
 
     /// Convert a hash to a leaf node of the tree.
     fn from_leaf(leaf: Self::Leaf) -> Self;