kernel: Add functions to get the block hash from a block

This is useful for a host block processing feature where having an
identifier for the block is needed. Without this, external users need to
serialize the block and calculate the hash externally, which is less
efficient.

src/kernel/bitcoinkernel.cpp

@@ -963,6 +963,24 @@ kernel_ByteArray* kernel_copy_block_pointer_data(const kernel_BlockPointer* bloc
     return byte_array;
 }
 
+kernel_BlockHash* kernel_block_get_hash(kernel_Block* block_)
+{
+    auto block{cast_cblocksharedpointer(block_)};
+    auto hash{(*block)->GetHash()};
+    auto block_hash = new kernel_BlockHash{};
+    std::memcpy(block_hash->hash, hash.begin(), sizeof(hash));
+    return block_hash;
+}
+
+kernel_BlockHash* kernel_block_pointer_get_hash(const kernel_BlockPointer* block_)
+{
+    auto block{cast_const_cblock(block_)};
+    auto hash{block->GetHash()};
+    auto block_hash = new kernel_BlockHash{};
+    std::memcpy(block_hash->hash, hash.begin(), sizeof(hash));
+    return block_hash;
+}
+
 void kernel_block_destroy(kernel_Block* block)
 {
     if (block) {

src/kernel/bitcoinkernel.h

@@ -978,6 +978,26 @@ kernel_Block* BITCOINKERNEL_WARN_UNUSED_RESULT kernel_block_create(
     const unsigned char* raw_block, size_t raw_block_len
 ) BITCOINKERNEL_ARG_NONNULL(1);
 
+/**
+ * @brief Calculate and return the hash of a block.
+ *
+ * @param[in] block Non-null.
+ * @return    The block hash.
+ */
+kernel_BlockHash* BITCOINKERNEL_WARN_UNUSED_RESULT kernel_block_get_hash(
+    kernel_Block* block
+) BITCOINKERNEL_ARG_NONNULL(1);
+
+/** @name ByteArray
+ * @brief Calculate and return the hash of a block.
+ *
+ * @param[in] block Non-null.
+ * @return    The block hash.
+ */
+kernel_BlockHash* BITCOINKERNEL_WARN_UNUSED_RESULT kernel_block_pointer_get_hash(
+    const kernel_BlockPointer* block
+) BITCOINKERNEL_ARG_NONNULL(1);
+
 /**
  * @brief Copies block data into the returned byte array.
  *

src/kernel/bitcoinkernel_wrapper.h

@@ -219,6 +219,13 @@ class KernelNotifications
     friend class ContextOptions;
 };
 
+struct BlockHashDeleter {
+    void operator()(kernel_BlockHash* ptr) const
+    {
+        kernel_block_hash_destroy(ptr);
+    }
+};
+
 class UnownedBlock
 {
 private:
@@ -232,6 +239,11 @@ class UnownedBlock
     UnownedBlock(UnownedBlock&&) = delete;
     UnownedBlock& operator=(UnownedBlock&&) = delete;
 
+    std::unique_ptr<kernel_BlockHash, BlockHashDeleter> GetHash() const noexcept
+    {
+        return std::unique_ptr<kernel_BlockHash, BlockHashDeleter>(kernel_block_pointer_get_hash(m_block));
+    }
+
     std::vector<unsigned char> GetBlockData() const noexcept
     {
         auto serialized_block{kernel_copy_block_pointer_data(m_block)};
@@ -485,6 +497,11 @@ class Block
 
     Block(kernel_Block* block) noexcept : m_block{block} {}
 
+    std::unique_ptr<kernel_BlockHash, BlockHashDeleter> GetHash() const noexcept
+    {
+        return std::unique_ptr<kernel_BlockHash, BlockHashDeleter>(kernel_block_get_hash(m_block.get()));
+    }
+
     std::vector<unsigned char> GetBlockData() const noexcept
     {
         auto serialized_block{kernel_copy_block_data(m_block.get())};
@@ -533,13 +550,6 @@ class BlockUndo
     }
 };
 
-struct BlockHashDeleter {
-    void operator()(kernel_BlockHash* ptr) const
-    {
-        kernel_block_hash_destroy(ptr);
-    }
-};
-
 class BlockIndex
 {
 private:

src/test/kernel/test_kernel.cpp

@@ -569,7 +569,8 @@ void chainman_reindex_test(TestDirectory& test_directory)
     auto tip_index{chainman->GetBlockIndexFromTip()};
     auto tip_block_string{chainman->ReadBlock(tip_index).value().GetBlockData()};
     auto second_index{chainman->GetBlockIndexByHeight(1).value()};
-    auto second_block_string{chainman->ReadBlock(second_index).value().GetBlockData()};
+    auto second_block{chainman->ReadBlock(second_index).value()};
+    auto second_block_string{second_block.GetBlockData()};
     auto second_height{second_index.GetHeight()};
     assert(second_height == 1);
     assert(next_block_string == tip_block_string);
@@ -578,6 +579,8 @@ void chainman_reindex_test(TestDirectory& test_directory)
     auto hash{second_index.GetHash()};
     auto another_second_index{chainman->GetBlockIndexByHash(hash.get())};
     auto another_second_height{another_second_index.GetHeight()};
+    auto block_hash{second_block.GetHash()};
+    assert(std::equal(std::begin(block_hash->hash), std::end(block_hash->hash), std::begin(hash->hash)));
     assert(second_height == another_second_height);
 }