kernel: Add import blocks function to C header

Add `btck_import_blocks` to import block data and rebuild indexes. The
function can either reindex all existing block files if the indexes were
previously wiped through the chainstate manager options, or import
blocks from specified file paths.

src/kernel/bitcoinkernel.cpp

@@ -795,6 +795,24 @@ void btck_chainstate_manager_destroy(btck_ChainstateManager* chainman)
     delete chainman;
 }
 
+int btck_chainstate_manager_import_blocks(btck_ChainstateManager* chainman, const char** block_file_paths_data, size_t* block_file_paths_lens, size_t block_file_paths_data_len)
+{
+    try {
+        std::vector<fs::path> import_files;
+        import_files.reserve(block_file_paths_data_len);
+        for (uint32_t i = 0; i < block_file_paths_data_len; i++) {
+            if (block_file_paths_data[i] != nullptr) {
+                import_files.emplace_back(std::string{block_file_paths_data[i], block_file_paths_lens[i]}.c_str());
+            }
+        }
+        node::ImportBlocks(*btck_ChainstateManager::get(chainman).m_chainman, import_files);
+    } catch (const std::exception& e) {
+        LogError("Failed to import blocks: %s", e.what());
+        return -1;
+    }
+    return 0;
+}
+
 btck_Block* btck_block_create(const void* raw_block, size_t raw_block_length)
 {
     auto block{std::make_shared<CBlock>()};

src/kernel/bitcoinkernel.h

@@ -747,7 +747,9 @@ BITCOINKERNEL_API void btck_chainstate_manager_options_set_worker_threads_num(
     int worker_threads) BITCOINKERNEL_ARG_NONNULL(1);
 
 /**
- * @brief Sets wipe db in the options.
+ * @brief Sets wipe db in the options. In combination with calling
+ * @ref btck_chainstate_manager_import_blocks this triggers either a full reindex,
+ * or a reindex of just the chainstate database.
  *
  * @param[in] chainstate_manager_options Non-null, created by @ref btck_chainstate_manager_options_create.
  * @param[in] wipe_block_tree_db         Set wipe block tree db. Should only be 1 if wipe_chainstate_db is 1 too.
@@ -802,6 +804,22 @@ BITCOINKERNEL_API void btck_chainstate_manager_options_destroy(btck_ChainstateMa
 BITCOINKERNEL_API btck_ChainstateManager* BITCOINKERNEL_WARN_UNUSED_RESULT btck_chainstate_manager_create(
     const btck_ChainstateManagerOptions* chainstate_manager_options) BITCOINKERNEL_ARG_NONNULL(1);
 
+/**
+ * @brief Triggers the start of a reindex if the wipe options were previously
+ * set for the chainstate manager. Can also import an array of existing block
+ * files selected by the user.
+ *
+ * @param[in] chainstate_manager        Non-null.
+ * @param[in] block_file_paths_data     Nullable, array of block files described by their full filesystem paths.
+ * @param[in] block_file_paths_lens     Nullable, array containing the lengths of each of the paths.
+ * @param[in] block_file_paths_data_len Length of the block_file_paths_data and block_file_paths_len arrays.
+ * @return                              0 if the import blocks call was completed successfully, non-zero otherwise.
+ */
+BITCOINKERNEL_API int BITCOINKERNEL_WARN_UNUSED_RESULT btck_chainstate_manager_import_blocks(
+    btck_ChainstateManager* chainstate_manager,
+    const char** block_file_paths_data, size_t* block_file_paths_lens,
+    size_t block_file_paths_data_len) BITCOINKERNEL_ARG_NONNULL(1);
+
 /**
  * @brief Process and validate the passed in block with the chainstate
  * manager. Processing first does checks on the block, and if these passed,

src/kernel/bitcoinkernel_wrapper.h

@@ -690,6 +690,20 @@ public:
     {
     }
 
+    bool ImportBlocks(const std::span<const std::string> paths)
+    {
+        std::vector<const char*> c_paths;
+        std::vector<size_t> c_paths_lens;
+        c_paths.reserve(paths.size());
+        c_paths_lens.reserve(paths.size());
+        for (const auto& path : paths) {
+            c_paths.push_back(path.c_str());
+            c_paths_lens.push_back(path.length());
+        }
+
+        return btck_chainstate_manager_import_blocks(get(), c_paths.data(), c_paths_lens.data(), c_paths.size()) == 0;
+    }
+
     bool ProcessBlock(const Block& block, bool* new_block)
     {
         int _new_block;

src/test/kernel/test_kernel.cpp

@@ -552,6 +552,9 @@ void chainman_reindex_test(TestDirectory& test_directory)
     auto notifications{std::make_shared<TestKernelNotifications>()};
     auto context{create_context(notifications, ChainType::MAINNET)};
     auto chainman{create_chainman(test_directory, true, false, false, false, context)};
+
+    std::vector<std::string> import_files;
+    BOOST_CHECK(chainman->ImportBlocks(import_files));
 }
 
 void chainman_reindex_chainstate_test(TestDirectory& test_directory)
@@ -559,6 +562,10 @@ void chainman_reindex_chainstate_test(TestDirectory& test_directory)
     auto notifications{std::make_shared<TestKernelNotifications>()};
     auto context{create_context(notifications, ChainType::MAINNET)};
     auto chainman{create_chainman(test_directory, false, true, false, false, context)};
+
+    std::vector<std::string> import_files;
+    import_files.push_back((test_directory.m_directory / "blocks" / "blk00000.dat").string());
+    BOOST_CHECK(chainman->ImportBlocks(import_files));
 }
 
 void chainman_mainnet_validation_test(TestDirectory& test_directory)