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 load options, or import blocks
from a single specified file path.

src/kernel/bitcoinkernel.cpp

@@ -791,6 +791,25 @@ 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);
+        btck_ChainstateManager::get(chainman).m_chainman->ActiveChainstate().ForceFlushStateToDisk();
+    } 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

@@ -732,7 +732,9 @@ 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.
@@ -787,6 +789,22 @@ 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 option was previously set for
+ * the chainstate and block 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 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, 2);
+
 /**
  * @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

@@ -699,6 +699,20 @@ 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

@@ -580,6 +580,9 @@ 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)
@@ -587,6 +590,10 @@ 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)