Merge #122: Add utility to validate GetMerkleRes

54fd52d Add test coverage for `validate_merkle_proof` (Elias Rohrer)
fe33e19 Add utility for validating a Merkle inclusion proof (Elias Rohrer)
dd872d6 Make response types `Clone` (Elias Rohrer)

Pull request description:

  I recently needed to validate a Merkle inclusion proof as retrieved via `transaction_get_merkle`.

  As I figured it might be useful to other people, too, we add it here as a simple utility method.

ACKs for top commit:
  notmandatory:
    ACK 54fd52d

Tree-SHA512: aac12160d5b91a011988f45013eb92924c2dfb244c1720e73dc5bcb731e69065c38e022502c756100d8ee6c9af06efa0de9bbfbb2b9e3c2e34d3223539206e1c

src/lib.rs

@@ -61,6 +61,7 @@ mod config;
 pub mod raw_client;
 mod stream;
 mod types;
+pub mod utils;
 
 pub use api::ElectrumApi;
 pub use batch::Batch;

src/raw_client.rs

@@ -1079,6 +1079,8 @@ impl<T: Read + Write> ElectrumApi for RawClient<T> {
 mod test {
     use std::str::FromStr;
 
+    use crate::utils;
+
     use super::RawClient;
     use api::ElectrumApi;
 
@@ -1300,23 +1302,43 @@ mod test {
 
         let client = RawClient::new(get_test_server(), None).unwrap();
 
-        let resp = client
-            .transaction_get_merkle(
-                &Txid::from_str("cc2ca076fd04c2aeed6d02151c447ced3d09be6fb4d4ef36cb5ed4e7a3260566")
-                    .unwrap(),
-                630000,
-            )
-            .unwrap();
+        let txid =
+            Txid::from_str("1f7ff3c407f33eabc8bec7d2cc230948f2249ec8e591bcf6f971ca9366c8788d")
+                .unwrap();
+        let resp = client.transaction_get_merkle(&txid, 630000).unwrap();
         assert_eq!(resp.block_height, 630000);
-        assert_eq!(resp.pos, 0);
+        assert_eq!(resp.pos, 68);
         assert_eq!(resp.merkle.len(), 12);
         assert_eq!(
             resp.merkle[0],
             [
-                30, 10, 161, 245, 132, 125, 136, 198, 186, 138, 107, 216, 92, 22, 145, 81, 130,
-                126, 200, 65, 121, 158, 105, 111, 38, 151, 38, 147, 144, 224, 5, 218
+                34, 65, 51, 64, 49, 139, 115, 189, 185, 246, 70, 225, 168, 193, 217, 195, 47, 66,
+                179, 240, 153, 24, 114, 215, 144, 196, 212, 41, 39, 155, 246, 25
             ]
         );
+
+        // Check we can verify the merkle proof validity, but fail if we supply wrong data.
+        let block_header = client.block_header(resp.block_height).unwrap();
+        assert!(utils::validate_merkle_proof(
+            &txid,
+            &block_header.merkle_root,
+            &resp
+        ));
+
+        let mut fail_resp = resp.clone();
+        fail_resp.pos = 13;
+        assert!(!utils::validate_merkle_proof(
+            &txid,
+            &block_header.merkle_root,
+            &fail_resp
+        ));
+
+        let fail_block_header = client.block_header(resp.block_height + 1).unwrap();
+        assert!(!utils::validate_merkle_proof(
+            &txid,
+            &fail_block_header.merkle_root,
+            &resp
+        ));
     }
 
     #[test]

src/types.rs

@@ -161,7 +161,7 @@ where
 }
 
 /// Response to a [`script_get_history`](../client/struct.Client.html#method.script_get_history) request.
-#[derive(Debug, Deserialize)]
+#[derive(Clone, Debug, Deserialize)]
 pub struct GetHistoryRes {
     /// Confirmation height of the transaction. 0 if unconfirmed, -1 if unconfirmed while some of
     /// its inputs are unconfirmed too.
@@ -173,7 +173,7 @@ pub struct GetHistoryRes {
 }
 
 /// Response to a [`script_list_unspent`](../client/struct.Client.html#method.script_list_unspent) request.
-#[derive(Debug, Deserialize)]
+#[derive(Clone, Debug, Deserialize)]
 pub struct ListUnspentRes {
     /// Confirmation height of the transaction that created this output.
     pub height: usize,
@@ -186,7 +186,7 @@ pub struct ListUnspentRes {
 }
 
 /// Response to a [`server_features`](../client/struct.Client.html#method.server_features) request.
-#[derive(Debug, Deserialize)]
+#[derive(Clone, Debug, Deserialize)]
 pub struct ServerFeaturesRes {
     /// Server version reported.
     pub server_version: String,
@@ -204,7 +204,7 @@ pub struct ServerFeaturesRes {
 }
 
 /// Response to a [`server_features`](../client/struct.Client.html#method.server_features) request.
-#[derive(Debug, Deserialize)]
+#[derive(Clone, Debug, Deserialize)]
 pub struct GetHeadersRes {
     /// Maximum number of headers returned in a single response.
     pub max: usize,
@@ -219,7 +219,7 @@ pub struct GetHeadersRes {
 }
 
 /// Response to a [`script_get_balance`](../client/struct.Client.html#method.script_get_balance) request.
-#[derive(Debug, Deserialize)]
+#[derive(Clone, Debug, Deserialize)]
 pub struct GetBalanceRes {
     /// Confirmed balance in Satoshis for the address.
     pub confirmed: u64,
@@ -230,7 +230,7 @@ pub struct GetBalanceRes {
 }
 
 /// Response to a [`transaction_get_merkle`](../client/struct.Client.html#method.transaction_get_merkle) request.
-#[derive(Debug, Deserialize)]
+#[derive(Clone, Debug, Deserialize)]
 pub struct GetMerkleRes {
     /// Height of the block that confirmed the transaction
     pub block_height: usize,
@@ -242,7 +242,7 @@ pub struct GetMerkleRes {
 }
 
 /// Notification of a new block header
-#[derive(Debug, Deserialize)]
+#[derive(Clone, Debug, Deserialize)]
 pub struct HeaderNotification {
     /// New block height.
     pub height: usize,
@@ -252,7 +252,7 @@ pub struct HeaderNotification {
 }
 
 /// Notification of a new block header with the header encoded as raw bytes
-#[derive(Debug, Deserialize)]
+#[derive(Clone, Debug, Deserialize)]
 pub struct RawHeaderNotification {
     /// New block height.
     pub height: usize,
@@ -273,7 +273,7 @@ impl TryFrom<RawHeaderNotification> for HeaderNotification {
 }
 
 /// Notification of the new status of a script
-#[derive(Debug, Deserialize)]
+#[derive(Clone, Debug, Deserialize)]
 pub struct ScriptNotification {
     /// Address that generated this notification.
     pub scripthash: ScriptHash,

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()
+}