Add utility for validating a Merkle inclusion proof

... as retrieved via `transaction_get_merkle`.

src/lib.rs

@@ -63,6 +63,7 @@ mod config;
 pub mod raw_client;
 mod stream;
 mod types;
+pub mod utils;
 
 pub use api::ElectrumApi;
 pub use batch::Batch;

src/utils.rs

@@ -0,0 +1,43 @@
+//! Utilities helping to handle Electrum-related data.
+
+use bitcoin::hash_types::TxMerkleNode;
+use bitcoin::hashes::sha256d::Hash as Sha256d;
+use bitcoin::hashes::Hash;
+use bitcoin::Txid;
+use types::GetMerkleRes;
+
+/// Verifies a Merkle inclusion proof as retrieved via [`transaction_get_merkle`] for a transaction with the
+/// given `txid` and `merkle_root` as included in the [`BlockHeader`].
+///
+/// Returns `true` if the transaction is included in the corresponding block, and `false`
+/// otherwise.
+///
+/// [`transaction_get_merkle`]: crate::ElectrumApi::transaction_get_merkle
+/// [`BlockHeader`]: bitcoin::BlockHeader
+pub fn validate_merkle_proof(
+    txid: &Txid,
+    merkle_root: &TxMerkleNode,
+    merkle_res: &GetMerkleRes,
+) -> bool {
+    let mut index = merkle_res.pos;
+    let mut cur = txid.to_raw_hash();
+    for bytes in &merkle_res.merkle {
+        let mut reversed = [0u8; 32];
+        reversed.copy_from_slice(bytes);
+        reversed.reverse();
+        // unwrap() safety: `reversed` has len 32 so `from_slice` can never fail.
+        let next_hash = Sha256d::from_slice(&reversed).unwrap();
+
+        let (left, right) = if index % 2 == 0 {
+            (cur, next_hash)
+        } else {
+            (next_hash, cur)
+        };
+
+        let data = [&left[..], &right[..]].concat();
+        cur = Sha256d::hash(&data);
+        index /= 2;
+    }
+
+    cur == merkle_root.to_raw_hash()
+}