From 6ed6220a01f578aa7497ca4116aa1df2390fd0db Mon Sep 17 00:00:00 2001
From: Eric Voskuil <eric@voskuil.org>
Date: Sun, 9 Aug 2026 14:36:15 -0400
Subject: [PATCH] Fix merkle_block::size() ternary grouping.

---
 src/messages/peer/detail/merkle_block.cpp  |  2 +-
 test/messages/peer/detail/merkle_block.cpp | 42 ++++++++++++++++++++++
 2 files changed, 43 insertions(+), 1 deletion(-)

diff --git a/src/messages/peer/detail/merkle_block.cpp b/src/messages/peer/detail/merkle_block.cpp
index d245e7788..a55fd2ecd 100644
--- a/src/messages/peer/detail/merkle_block.cpp
+++ b/src/messages/peer/detail/merkle_block.cpp
@@ -100,7 +100,7 @@ void merkle_block::serialize(uint32_t BC_DEBUG_ONLY(version),
 
 size_t merkle_block::size(uint32_t) const NOEXCEPT
 {
-    return header ? header->serialized_size() : zero
+    return (header ? header->serialized_size() : zero)
         + sizeof(uint32_t)
         + variable_size(hashes.size()) + (hashes.size() * hash_size)
         + variable_size(flags.size()) + flags.size();
diff --git a/test/messages/peer/detail/merkle_block.cpp b/test/messages/peer/detail/merkle_block.cpp
index d0289a69a..293ad9c5e 100644
--- a/test/messages/peer/detail/merkle_block.cpp
+++ b/test/messages/peer/detail/merkle_block.cpp
@@ -20,6 +20,7 @@
 
 BOOST_AUTO_TEST_SUITE(p2p_merkle_block_tests)
 
+using namespace bc::system;
 using namespace network::messages::peer;
 
 BOOST_AUTO_TEST_CASE(merkle_block__properties__always__expected)
@@ -40,4 +41,45 @@ BOOST_AUTO_TEST_CASE(merkle_block__size__default__expected)
     BOOST_REQUIRE_EQUAL(merkle_block{}.size(level::canonical), expected);
 }
 
+// With a header present, size() must include the tx count, hashes, and flags,
+// not just the header (the terms trail a ternary and require grouping).
+BOOST_AUTO_TEST_CASE(merkle_block__size__with_header__includes_all_fields)
+{
+    const hashes branch{ one_hash, one_hash };
+    const data_chunk flags{ 0x1d };
+    const merkle_block instance
+    {
+        to_shared<chain::header>(), 42_u32, branch, flags
+    };
+
+    const auto expected = chain::header::serialized_size()
+        + sizeof(uint32_t)
+        + variable_size(branch.size()) + (branch.size() * hash_size)
+        + variable_size(flags.size()) + flags.size();
+
+    BOOST_REQUIRE_EQUAL(instance.size(level::canonical), expected);
+}
+
+// A populated merkle_block round-trips through its own wire form.
+BOOST_AUTO_TEST_CASE(merkle_block__serialize__with_header__round_trips)
+{
+    const hashes branch{ one_hash, one_hash };
+    const data_chunk flags{ 0x1d };
+    const merkle_block instance
+    {
+        to_shared<chain::header>(), 42_u32, branch, flags
+    };
+
+    const auto version = merkle_block::version_maximum;
+    data_chunk data(instance.size(version));
+    BOOST_REQUIRE(instance.serialize(version, data));
+
+    const auto message = merkle_block::deserialize(version, data);
+    BOOST_REQUIRE(message);
+    BOOST_REQUIRE(message->header);
+    BOOST_REQUIRE_EQUAL(message->transactions, 42_u32);
+    BOOST_REQUIRE_EQUAL(message->hashes, branch);
+    BOOST_REQUIRE_EQUAL(message->flags, flags);
+}
+
 BOOST_AUTO_TEST_SUITE_END()