Test loadtxoutset RPC method

Testing loadtxoutset on regtest requires a deterministic chain that
produces a state matching the hardcoded assumeutxo entry in Bitcoin
Core’s chainparams. Without this alignment, a standard dump-and-load
cycle on a random regtest chain will always be rejected.

Replicate Bitcoin Core's C++ TestChain100Setup deterministic chain
(mocktime 1598887952, P2PK coinbase to compressed pubkey of private key
0x01, 110 blocks) so the resulting block hash matches the assumeutxo
entry. Dump the UTXO set from the miner node, feed headers to a fresh
node via submitheader, then load the snapshot and verify the model.

Wire the load_tx_out_set client macro into v27 through v30, which were
missing the call.

Author: Abeeujah

client/src/client_sync/v27/mod.rs

@@ -54,6 +54,7 @@ crate::impl_client_v17__get_tx_out_proof!();
 crate::impl_client_v26__get_tx_out_set_info!();
 crate::impl_client_v24__get_tx_spending_prevout!();
 crate::impl_client_v26__import_mempool!();
+crate::impl_client_v26__load_tx_out_set!();
 crate::impl_client_v17__precious_block!();
 crate::impl_client_v17__prune_blockchain!();
 crate::impl_client_v23__save_mempool!();

client/src/client_sync/v28/mod.rs

@@ -55,6 +55,7 @@ crate::impl_client_v17__get_tx_out_proof!();
 crate::impl_client_v26__get_tx_out_set_info!();
 crate::impl_client_v24__get_tx_spending_prevout!();
 crate::impl_client_v26__import_mempool!();
+crate::impl_client_v26__load_tx_out_set!();
 crate::impl_client_v17__precious_block!();
 crate::impl_client_v17__prune_blockchain!();
 crate::impl_client_v23__save_mempool!();

client/src/client_sync/v29/mod.rs

@@ -59,6 +59,7 @@ crate::impl_client_v17__get_tx_out_proof!();
 crate::impl_client_v26__get_tx_out_set_info!();
 crate::impl_client_v24__get_tx_spending_prevout!();
 crate::impl_client_v26__import_mempool!();
+crate::impl_client_v26__load_tx_out_set!();
 crate::impl_client_v17__precious_block!();
 crate::impl_client_v17__prune_blockchain!();
 crate::impl_client_v23__save_mempool!();

client/src/client_sync/v30/mod.rs

@@ -57,6 +57,7 @@ crate::impl_client_v17__get_tx_out_proof!();
 crate::impl_client_v26__get_tx_out_set_info!();
 crate::impl_client_v24__get_tx_spending_prevout!();
 crate::impl_client_v26__import_mempool!();
+crate::impl_client_v26__load_tx_out_set!();
 crate::impl_client_v17__precious_block!();
 crate::impl_client_v17__prune_blockchain!();
 crate::impl_client_v23__save_mempool!();

integration_test/tests/blockchain.rs

@@ -34,6 +34,102 @@ fn blockchain__dump_tx_out_set__modelled() {
     assert!(dump.coins_written.to_sat() > 0);
 }
 
+#[test]
+#[cfg(not(feature = "v25_and_below"))]
+fn blockchain__load_tx_out_set__modelled() {
+    // Regtest `loadtxoutset` requires replicating Bitcoin Core's C++
+    // TestChain100Setup to produce the exact chain whose height at `110`
+    // assumeutxo snapshot hash is hardcoded in chainparams.
+    //
+    // The C++ test framework uses:
+    //   - SetMockTime(1598887952), incrementing by 1 after each block
+    //   - P2PK coinbase output to compressed pubkey of private key 0x01
+    //   - 110 coinbase-only blocks (no wallet transactions)
+    //
+    // Matching these exactly helps us arrive at the expected hash at snapshot
+
+    #[cfg(feature = "v29_and_below")]
+    let expected_block_hash = "696e92821f65549c7ee134edceeeeaaa4105647a3c4fd9f298c0aec0ab50425c";
+    #[cfg(not(feature = "v29_and_below"))]
+    let expected_block_hash = "6affe030b7965ab538f820a56ef56c8149b7dc1d1c144af57113be080db7c397";
+
+    let snapshot_height = 110;
+
+    // Compressed public key for private key 0x01
+    let coinbase_descriptor =
+        "pk(0279be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798)";
+
+    let exe = node::exe_path().expect("failed to get bitcoind executable");
+    let mut conf_a = node::Conf::default();
+    conf_a.p2p = node::P2P::Yes;
+    let node_a = Node::with_conf(&exe, &conf_a).expect("failed to create miner node");
+
+    // TestChain100Setup mocktime matched to the exact
+    const MOCK_TIME_START: u64 = 1598887952;
+    for i in 0..snapshot_height {
+        let mock_time = MOCK_TIME_START + i;
+        let _: node::serde_json::Value = node_a
+            .client
+            .call("setmocktime", &[node::serde_json::json!(mock_time)])
+            .expect("setmocktime");
+        node_a.client.generate_to_descriptor(1, coinbase_descriptor).expect("generatetodescriptor");
+    }
+
+    let hash_at_height = node_a
+        .client
+        .get_block_hash(snapshot_height)
+        .expect("getblockhash")
+        .block_hash()
+        .expect("parse block hash");
+    assert_eq!(
+        hash_at_height.to_string(),
+        expected_block_hash,
+        "block hash at height {} does not match hardcoded assumeutxo entry",
+        snapshot_height
+    );
+
+    let temp_path = integration_test::random_tmp_file();
+    let dump_path = temp_path.to_str().expect("temp path should be valid UTF-8");
+    #[cfg(feature = "v28_and_below")]
+    {
+        let _: DumpTxOutSet = node_a.client.dump_tx_out_set(dump_path).expect("dumptxoutset");
+    }
+    #[cfg(not(feature = "v28_and_below"))]
+    {
+        let _: DumpTxOutSet =
+            node_a.client.dump_tx_out_set(dump_path, "latest").expect("dumptxoutset");
+    }
+    let mut conf_b = node::Conf::default();
+    conf_b.wallet = None;
+    conf_b.p2p = node::P2P::No;
+    let node_b = Node::with_conf(&exe, &conf_b).expect("failed to create loader node");
+
+    for h in 1..=snapshot_height {
+        let bh = node_a
+            .client
+            .get_block_hash(h)
+            .expect("getblockhash")
+            .block_hash()
+            .expect("parse block hash");
+        let header = node_a
+            .client
+            .get_block_header(&bh)
+            .expect("getblockheader")
+            .block_header()
+            .expect("parse block header");
+        node_b.client.submit_header(&header).expect("submitheader");
+    }
+
+    let json: LoadTxOutSet =
+        node_b.client.load_tx_out_set(dump_path).expect("loadtxoutset should succeed");
+    let model: Result<mtype::LoadTxOutSet, LoadTxOutSetError> = json.into_model();
+    let model = model.unwrap();
+
+    assert_eq!(model.base_height, snapshot_height as u32);
+    assert_eq!(model.tip_hash, hash_at_height);
+    assert_eq!(model.coins_loaded, bitcoin::Amount::from_btc(110.0).unwrap());
+}
+
 #[test]
 fn blockchain__get_best_block_hash__modelled() {
     let node = Node::with_wallet(Wallet::None, &[]);