Merge bitcoin/bitcoin#34846: kernel: Add API getter functions for timelock fields (nLockTime, nSequence)

9f28120a5b kernel: Add API function for getting a tx input's nSequence (Sebastian Falbesoner)
6b64b181d5 kernel: Add API function for getting a tx's nLockTime (Sebastian Falbesoner)

Pull request description:

  This PR introduces two new C API functions to libbitcoinkernel:
  * `btck_transaction_get_locktime` to access a transaction's `nLockTime` value
  * `btck_transaction_input_get_sequence` to access a transaction input's `nSequence` value

  Inspired by https://bnoc.xyz/t/forward-compatible-coinbase-locktimes-for-bip-54. After reading this I thought it would be a nice/useful showcase to check BIP54 compliance of (historical) blocks using bitcoinkernel, without having to manually deserialize the transaction (this is just about one of the four BIP54 rules though, especially the sigops limit is much more involved).

ACKs for top commit:
  sedited:
    ACK 9f28120a5b
  yuvicc:
    ACK 9f28120a5b
  stickies-v:
    ACK 9f28120a5b

Tree-SHA512: 9eae795d6e4b9b367bbfe2665b916121ef64031e8d10667c71741344b5eea4c2562862a937bdf1363cc66b67bb5d48392c9f44e52f0d92d2a5a65e10d061b703

src/kernel/bitcoinkernel.cpp

@@ -533,6 +533,11 @@ const btck_TransactionInput* btck_transaction_get_input_at(const btck_Transactio
     return btck_TransactionInput::ref(&btck_Transaction::get(transaction)->vin[input_index]);
 }
 
+uint32_t btck_transaction_get_locktime(const btck_Transaction* transaction)
+{
+    return btck_Transaction::get(transaction)->nLockTime;
+}
+
 const btck_Txid* btck_transaction_get_txid(const btck_Transaction* transaction)
 {
     return btck_Txid::ref(&btck_Transaction::get(transaction)->GetHash());
@@ -692,6 +697,11 @@ const btck_TransactionOutPoint* btck_transaction_input_get_out_point(const btck_
     return btck_TransactionOutPoint::ref(&btck_TransactionInput::get(input).prevout);
 }
 
+uint32_t btck_transaction_input_get_sequence(const btck_TransactionInput* input)
+{
+    return btck_TransactionInput::get(input).nSequence;
+}
+
 void btck_transaction_input_destroy(btck_TransactionInput* input)
 {
     delete input;

src/kernel/bitcoinkernel.h

@@ -576,6 +576,15 @@ BITCOINKERNEL_API const btck_TransactionInput* BITCOINKERNEL_WARN_UNUSED_RESULT
 BITCOINKERNEL_API size_t BITCOINKERNEL_WARN_UNUSED_RESULT btck_transaction_count_inputs(
     const btck_Transaction* transaction) BITCOINKERNEL_ARG_NONNULL(1);
 
+/**
+ * @brief Get a transaction's nLockTime value.
+ *
+ * @param[in] transaction Non-null.
+ * @return                The nLockTime value.
+ */
+BITCOINKERNEL_API uint32_t BITCOINKERNEL_WARN_UNUSED_RESULT btck_transaction_get_locktime(
+    const btck_Transaction* transaction) BITCOINKERNEL_ARG_NONNULL(1);
+
 /**
  * @brief Get the txid of a transaction. The returned txid is not owned and
  * depends on the lifetime of the transaction.
@@ -1505,6 +1514,15 @@ BITCOINKERNEL_API btck_TransactionInput* BITCOINKERNEL_WARN_UNUSED_RESULT btck_t
 BITCOINKERNEL_API const btck_TransactionOutPoint* BITCOINKERNEL_WARN_UNUSED_RESULT btck_transaction_input_get_out_point(
     const btck_TransactionInput* transaction_input) BITCOINKERNEL_ARG_NONNULL(1);
 
+/**
+ * @brief Get a transaction input's nSequence value.
+ *
+ * @param[in] transaction_input Non-null.
+ * @return                      The nSequence value.
+ */
+BITCOINKERNEL_API uint32_t BITCOINKERNEL_WARN_UNUSED_RESULT btck_transaction_input_get_sequence(
+    const btck_TransactionInput* transaction_input) BITCOINKERNEL_ARG_NONNULL(1);
+
 /**
  * Destroy the transaction input.
  */

src/kernel/bitcoinkernel_wrapper.h

@@ -551,6 +551,11 @@ public:
     {
         return OutPointView{btck_transaction_input_get_out_point(impl())};
     }
+
+    uint32_t GetSequence() const
+    {
+        return btck_transaction_input_get_sequence(impl());
+    }
 };
 
 class TransactionInputView : public View<btck_TransactionInput>, public TransactionInputApi<TransactionInputView>
@@ -596,6 +601,11 @@ public:
         return TransactionInputView{btck_transaction_get_input_at(impl(), index)};
     }
 
+    uint32_t GetLocktime() const
+    {
+        return btck_transaction_get_locktime(impl());
+    }
+
     TxidView Txid() const
     {
         return TxidView{btck_transaction_get_txid(impl())};

src/test/kernel/test_kernel.cpp

@@ -401,8 +401,11 @@ BOOST_AUTO_TEST_CASE(btck_transaction_tests)
 
     BOOST_CHECK_EQUAL(tx.CountOutputs(), 2);
     BOOST_CHECK_EQUAL(tx.CountInputs(), 1);
+    BOOST_CHECK_EQUAL(tx.GetLocktime(), 510826);
     auto broken_tx_data{std::span<std::byte>{tx_data.begin(), tx_data.begin() + 10}};
     BOOST_CHECK_THROW(Transaction{broken_tx_data}, std::runtime_error);
+    auto input{tx.GetInput(0)};
+    BOOST_CHECK_EQUAL(input.GetSequence(), 0xfffffffe);
     auto output{tx.GetOutput(tx.CountOutputs() - 1)};
     BOOST_CHECK_EQUAL(output.Amount(), 42130042);
     auto script_pubkey{output.GetScriptPubkey()};