kernel: Add block validation to C header

The added function allows the user process and validate a given block
with the chainstate manager. The *_process_block(...) function does some
preliminary checks on the block before passing it to
`ProcessNewBlock(...)`. These are similar to the checks in the
`submitblock()` rpc.

Richer processing of the block validation result will be made available
in the following commits through the validation interface.

The commits also adds a utility for deserializing a `CBlock`
(`kernel_block_create()`) that may then be passed to the library for
processing.

The tests exercise the function for both mainnet and regtest. The
commit also adds the data of 206 regtest blocks (some blocks also
contain transactions).

src/kernel/bitcoinkernel.cpp

@@ -6,6 +6,7 @@
 
 #include <kernel/bitcoinkernel.h>
 
+#include <chain.h>
 #include <consensus/amount.h>
 #include <consensus/validation.h>
 #include <kernel/caches.h>
@@ -18,6 +19,7 @@
 #include <logging.h>
 #include <node/blockstorage.h>
 #include <node/chainstate.h>
+#include <primitives/block.h>
 #include <primitives/transaction.h>
 #include <script/interpreter.h>
 #include <script/script.h>
@@ -25,6 +27,7 @@
 #include <streams.h>
 #include <sync.h>
 #include <tinyformat.h>
+#include <uint256.h>
 #include <util/fs.h>
 #include <util/result.h>
 #include <util/signalinterrupt.h>
@@ -44,8 +47,6 @@
 #include <utility>
 #include <vector>
 
-class CBlockIndex;
-
 // Define G_TRANSLATION_FUN symbol in libbitcoinkernel library so users of the
 // library aren't required to export this symbol
 extern const std::function<std::string(const char*)> G_TRANSLATION_FUN{nullptr};
@@ -133,6 +134,7 @@ struct Handle {
 } // namespace
 
 struct btck_BlockTreeEntry: Handle<btck_BlockTreeEntry, CBlockIndex> {};
+struct btck_Block : Handle<btck_Block, std::shared_ptr<const CBlock>> {};
 
 namespace {
 
@@ -761,3 +763,53 @@ void btck_chainstate_manager_destroy(btck_ChainstateManager* chainman)
 
     delete chainman;
 }
+
+btck_Block* btck_block_create(const void* raw_block, size_t raw_block_length)
+{
+    auto block{std::make_shared<CBlock>()};
+
+    DataStream stream{std::span{reinterpret_cast<const std::byte*>(raw_block), raw_block_length}};
+
+    try {
+        stream >> TX_WITH_WITNESS(*block);
+    } catch (...) {
+        LogDebug(BCLog::KERNEL, "Block decode failed.");
+        return nullptr;
+    }
+
+    return btck_Block::create(block);
+}
+
+btck_Block* btck_block_copy(const btck_Block* block)
+{
+    return btck_Block::copy(block);
+}
+
+size_t btck_block_count_transactions(const btck_Block* block)
+{
+    return btck_Block::get(block)->vtx.size();
+}
+
+const btck_Transaction* btck_block_get_transaction_at(const btck_Block* block, size_t index)
+{
+    assert(index < btck_Block::get(block)->vtx.size());
+    return btck_Transaction::ref(&btck_Block::get(block)->vtx[index]);
+}
+
+void btck_block_destroy(btck_Block* block)
+{
+    delete block;
+}
+
+int btck_chainstate_manager_process_block(
+    btck_ChainstateManager* chainman,
+    const btck_Block* block,
+    int* _new_block)
+{
+    bool new_block;
+    auto result = btck_ChainstateManager::get(chainman).m_chainman->ProcessNewBlock(btck_Block::get(block), /*force_processing=*/true, /*min_pow_checked=*/true, /*new_block=*/&new_block);
+    if (_new_block) {
+        *_new_block = new_block ? 1 : 0;
+    }
+    return result ? 0 : -1;
+}