From 125697521d8a4a7683588c90d392414cca5d68fc Mon Sep 17 00:00:00 2001
From: evoskuil <eric@voskuil.org>
Date: Sun, 9 Jun 2024 16:50:49 -0400
Subject: [PATCH] Add block/header.get_hash() to avoid hash copy when cached.

---
 include/bitcoin/system/chain/block.hpp       | 3 +++
 include/bitcoin/system/chain/header.hpp      | 3 +++
 include/bitcoin/system/chain/transaction.hpp | 2 +-
 src/chain/block.cpp                          | 6 ++++++
 src/chain/header.cpp                         | 8 ++++++++
 5 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/include/bitcoin/system/chain/block.hpp b/include/bitcoin/system/chain/block.hpp
index c8ced5e269..c63d689c85 100644
--- a/include/bitcoin/system/chain/block.hpp
+++ b/include/bitcoin/system/chain/block.hpp
@@ -99,6 +99,9 @@ class BC_API block
     size_t serialized_size(bool witness) const NOEXCEPT;
     size_t signature_operations(bool bip16, bool bip141) const NOEXCEPT;
 
+    /// Reference used to avoid copy, sets cache if not set (not thread safe).
+    const hash_digest& get_hash() const NOEXCEPT;
+
     /// Computed malleation properties.
     bool is_malleable() const NOEXCEPT;
     bool is_malleable64() const NOEXCEPT;
diff --git a/include/bitcoin/system/chain/header.hpp b/include/bitcoin/system/chain/header.hpp
index b2d2a9f97f..bfc359ee92 100644
--- a/include/bitcoin/system/chain/header.hpp
+++ b/include/bitcoin/system/chain/header.hpp
@@ -105,6 +105,9 @@ class BC_API header
     /// Cache (this overrides hash() computation).
     void set_hash(hash_digest&& hash) const NOEXCEPT;
 
+    /// Reference used to avoid copy, sets cache if not set (not thread safe).
+    const hash_digest& get_hash() const NOEXCEPT;
+
     /// Validation.
     /// -----------------------------------------------------------------------
     /// Checkpoints and previous_block_hash are chain validation (not here).
diff --git a/include/bitcoin/system/chain/transaction.hpp b/include/bitcoin/system/chain/transaction.hpp
index 32c4fb41e2..db25b4bc78 100644
--- a/include/bitcoin/system/chain/transaction.hpp
+++ b/include/bitcoin/system/chain/transaction.hpp
@@ -119,7 +119,7 @@ class BC_API transaction
     /// This need not be set if the transaction is not segmented.
     void set_witness_hash(hash_digest&& hash) const NOEXCEPT;
 
-    /// Reference used to avoid copy, sets cache if not set.
+    /// Reference used to avoid copy, sets cache if not set (not thread safe).
     const hash_digest& get_hash(bool witness) const NOEXCEPT;
 
     /// Methods.
diff --git a/src/chain/block.cpp b/src/chain/block.cpp
index 455780fa60..c6d9bceeea 100644
--- a/src/chain/block.cpp
+++ b/src/chain/block.cpp
@@ -254,6 +254,12 @@ hash_digest block::hash() const NOEXCEPT
     return header_->hash();
 }
 
+// computed
+const hash_digest& block::get_hash() const NOEXCEPT
+{
+    return header_->get_hash();
+}
+
 // static/private
 block::sizes block::serialized_size(
     const chain::transaction_cptrs& txs) NOEXCEPT
diff --git a/src/chain/header.cpp b/src/chain/header.cpp
index ccbbc17c1d..1a461c886d 100644
--- a/src/chain/header.cpp
+++ b/src/chain/header.cpp
@@ -251,6 +251,14 @@ hash_digest header::hash() const NOEXCEPT
     return digest;
 }
 
+const hash_digest& header::get_hash() const NOEXCEPT
+{
+    if (!hash_)
+        set_hash(hash());
+
+    return *hash_;
+}
+
 // static
 uint256_t header::proof(uint32_t bits) NOEXCEPT
 {