mining: add tx lookup IPC methods and integration coverage

Add Mining interface methods getTransactionsByTxID and
getTransactionsByWitnessID to the capnp schema.

Expand integration tests to call both methods with empty inputs, a real
mempool transaction id and witness id, and unknown ids, verifying serialized
transaction bytes for hits and empty results for misses.

Author: Sjors

capnp/mining.capnp

@@ -24,6 +24,8 @@ interface Mining $Proxy.wrap("interfaces::Mining") {
     checkBlock @5 (context :Proxy.Context, block: Data, options: BlockCheckOptions) -> (reason: Text, debug: Text, result: Bool);
     interrupt @6 () -> ();
     submitBlock @7 (context :Proxy.Context, block: Data) -> (reason: Text, debug: Text, result: Bool);
+    getTransactionsByTxID @8 (context :Proxy.Context, txids: List(Data)) -> (result: List(Data));
+    getTransactionsByWitnessID @9 (context :Proxy.Context, wtxids: List(Data)) -> (result: List(Data));
 }
 
 interface BlockTemplate $Proxy.wrap("interfaces::BlockTemplate") {

tests/test.rs

@@ -1,4 +1,5 @@
 use bitcoin_capnp_types::mining_capnp;
+use encoding::encode_to_vec;
 
 #[path = "util/bitcoin_core.rs"]
 mod bitcoin_core_util;
@@ -268,6 +269,100 @@ async fn mining_submit_block() {
     .await;
 }
 
+/// getTransactionsByTxID and getTransactionsByWitnessID with empty lists and
+/// with a non-existent txid/wtxid.
+#[tokio::test]
+// Serialized because this test may mine blocks to recover wallet funding.
+#[serial_test::serial]
+async fn mining_get_transactions() {
+    with_mining_client(|_client, thread, mining| async move {
+        let wallet = bitcoin_test_wallet();
+        ensure_wallet_loaded_and_funded(&wallet);
+
+        let real_tx = create_mempool_self_transfer(&wallet);
+        let real_txid = real_tx.compute_txid().to_byte_array();
+        let real_wtxid = real_tx.compute_wtxid().to_byte_array();
+        let real_raw_tx = encode_to_vec(&real_tx);
+
+        // getTransactionsByTxID — empty list should return empty list.
+        let mut req = mining.get_transactions_by_tx_i_d_request();
+        req.get().get_context().unwrap().set_thread(thread.clone());
+        req.get().init_txids(0);
+        let resp = req.send().promise.await.unwrap();
+        let results = resp.get().unwrap().get_result().unwrap();
+        assert_eq!(
+            results.len(),
+            0,
+            "empty txid list should return empty results"
+        );
+
+        // getTransactionsByTxID — return real mempool tx and empty for unknown id.
+        let fake_txid = [0x42u8; 32];
+        let mut req = mining.get_transactions_by_tx_i_d_request();
+        req.get().get_context().unwrap().set_thread(thread.clone());
+        {
+            let mut txids = req.get().init_txids(2);
+            txids.set(0, &real_txid);
+            txids.set(1, &fake_txid);
+        }
+        let resp = req.send().promise.await.unwrap();
+        let results = resp.get().unwrap().get_result().unwrap();
+        assert_eq!(
+            results.len(),
+            2,
+            "should return one entry per requested txid, including misses"
+        );
+        assert_eq!(
+            results.get(0).unwrap(),
+            real_raw_tx.as_slice(),
+            "known txid should return serialized transaction"
+        );
+        assert!(
+            results.get(1).unwrap().is_empty(),
+            "non-existent txid should return empty data"
+        );
+
+        // getTransactionsByWitnessID — empty list should return empty list.
+        let mut req = mining.get_transactions_by_witness_i_d_request();
+        req.get().get_context().unwrap().set_thread(thread.clone());
+        req.get().init_wtxids(0);
+        let resp = req.send().promise.await.unwrap();
+        let results = resp.get().unwrap().get_result().unwrap();
+        assert_eq!(
+            results.len(),
+            0,
+            "empty wtxid list should return empty results"
+        );
+
+        // getTransactionsByWitnessID — return real mempool tx and empty for unknown id.
+        let fake_wtxid = [0x43u8; 32];
+        let mut req = mining.get_transactions_by_witness_i_d_request();
+        req.get().get_context().unwrap().set_thread(thread.clone());
+        {
+            let mut wtxids = req.get().init_wtxids(2);
+            wtxids.set(0, &real_wtxid);
+            wtxids.set(1, &fake_wtxid);
+        }
+        let resp = req.send().promise.await.unwrap();
+        let results = resp.get().unwrap().get_result().unwrap();
+        assert_eq!(
+            results.len(),
+            2,
+            "should return one entry per requested wtxid, including misses"
+        );
+        assert_eq!(
+            results.get(0).unwrap(),
+            real_raw_tx.as_slice(),
+            "known wtxid should return serialized transaction"
+        );
+        assert!(
+            results.get(1).unwrap().is_empty(),
+            "non-existent wtxid should return empty data"
+        );
+    })
+    .await;
+}
+
 /// checkBlock with a template block payload, and interrupt.
 #[tokio::test]
 // Serialized because interrupt() can affect other in-flight mining waits.