kernel: Move MessageStartChars to its own file

The protocol.h file contains many non-consensus related definitions and
should thus not be part of the libbitcoinkernel. This commit makes
protocol.h no longer a required include for users of the
libbitcoinkernel.

This commit is part of the libbitcoinkernel project, namely its stage 1
step 3: Decouple most non-consensus headers from libbitcoinkernel.

Co-Authored-By: Cory Fields <cory-nospam-@coryfields.com>

Author: TheCharlatan

src/Makefile.am

@@ -191,6 +191,7 @@ BITCOIN_CORE_H = \
   kernel/mempool_options.h \
   kernel/mempool_persist.h \
   kernel/mempool_removal_reason.h \
+  kernel/messagestartchars.h \
   kernel/notifications_interface.h \
   kernel/validation_cache_sizes.h \
   key.h \

src/addrdb.cpp

@@ -90,7 +90,7 @@ void DeserializeDB(Stream& stream, Data&& data, bool fCheckSum = true)
 {
     HashVerifier verifier{stream};
     // de-serialize file header (network specific magic number) and ..
-    CMessageHeader::MessageStartChars pchMsgTmp;
+    MessageStartChars pchMsgTmp;
     verifier >> pchMsgTmp;
     // ... verify the network matches ours
     if (pchMsgTmp != Params().MessageStart()) {

src/kernel/chainparams.cpp

@@ -10,6 +10,7 @@
 #include <consensus/merkle.h>
 #include <consensus/params.h>
 #include <hash.h>
+#include <kernel/messagestartchars.h>
 #include <logging.h>
 #include <primitives/block.h>
 #include <primitives/transaction.h>

src/kernel/chainparams.h

@@ -7,9 +7,9 @@
 #define BITCOIN_KERNEL_CHAINPARAMS_H
 
 #include <consensus/params.h>
+#include <kernel/messagestartchars.h>
 #include <netaddress.h>
 #include <primitives/block.h>
-#include <protocol.h>
 #include <uint256.h>
 #include <util/chaintype.h>
 #include <util/hash_type.h>
@@ -87,7 +87,7 @@ class CChainParams
     };
 
     const Consensus::Params& GetConsensus() const { return consensus; }
-    const CMessageHeader::MessageStartChars& MessageStart() const { return pchMessageStart; }
+    const MessageStartChars& MessageStart() const { return pchMessageStart; }
     uint16_t GetDefaultPort() const { return nDefaultPort; }
     uint16_t GetDefaultPort(Network net) const
     {
@@ -165,7 +165,7 @@ class CChainParams
     CChainParams() {}
 
     Consensus::Params consensus;
-    CMessageHeader::MessageStartChars pchMessageStart;
+    MessageStartChars pchMessageStart;
     uint16_t nDefaultPort;
     uint64_t nPruneAfterHeight;
     uint64_t m_assumed_blockchain_size;

src/kernel/messagestartchars.h

@@ -0,0 +1,13 @@
+// Copyright (c) 2023 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_KERNEL_MESSAGESTARTCHARS_H
+#define BITCOIN_KERNEL_MESSAGESTARTCHARS_H
+
+#include <array>
+#include <cstdint>
+
+using MessageStartChars = std::array<uint8_t, 4>;
+
+#endif // BITCOIN_KERNEL_MESSAGESTARTCHARS_H

src/net.cpp

@@ -1144,7 +1144,7 @@ bool V2Transport::ProcessReceivedKeyBytes() noexcept
     // they receive our uniformly random key and garbage, but detecting this case specially
     // means we can log it.
     static constexpr std::array<uint8_t, 12> MATCH = {'v', 'e', 'r', 's', 'i', 'o', 'n', 0, 0, 0, 0, 0};
-    static constexpr size_t OFFSET = std::tuple_size_v<CMessageHeader::MessageStartChars>;
+    static constexpr size_t OFFSET = std::tuple_size_v<MessageStartChars>;
     if (!m_initiating && m_recv_buffer.size() >= OFFSET + MATCH.size()) {
         if (std::equal(MATCH.begin(), MATCH.end(), m_recv_buffer.begin() + OFFSET)) {
             LogPrint(BCLog::NET, "V2 transport error: V1 peer with wrong MessageStart %s\n",

src/net.h

@@ -10,15 +10,16 @@
 #include <chainparams.h>
 #include <common/bloom.h>
 #include <compat/compat.h>
-#include <node/connection_types.h>
 #include <consensus/amount.h>
 #include <crypto/siphash.h>
 #include <hash.h>
 #include <i2p.h>
+#include <kernel/messagestartchars.h>
 #include <net_permissions.h>
 #include <netaddress.h>
 #include <netbase.h>
 #include <netgroup.h>
+#include <node/connection_types.h>
 #include <policy/feerate.h>
 #include <protocol.h>
 #include <random.h>
@@ -360,7 +361,7 @@ class Transport {
 class V1Transport final : public Transport
 {
 private:
-    CMessageHeader::MessageStartChars m_magic_bytes;
+    MessageStartChars m_magic_bytes;
     const NodeId m_node_id; // Only for logging
     mutable Mutex m_recv_mutex; //!< Lock for receive state
     mutable CHash256 hasher GUARDED_BY(m_recv_mutex);

src/node/blockstorage.cpp

@@ -11,6 +11,7 @@
 #include <flatfile.h>
 #include <hash.h>
 #include <kernel/chainparams.h>
+#include <kernel/messagestartchars.h>
 #include <logging.h>
 #include <pow.h>
 #include <reverse_iterator.h>
@@ -927,7 +928,7 @@ bool BlockManager::ReadRawBlockFromDisk(std::vector<uint8_t>& block, const FlatF
     }
 
     try {
-        CMessageHeader::MessageStartChars blk_start;
+        MessageStartChars blk_start;
         unsigned int blk_size;
 
         filein >> blk_start >> blk_size;

src/node/blockstorage.h

@@ -11,7 +11,7 @@
 #include <kernel/blockmanager_opts.h>
 #include <kernel/chainparams.h>
 #include <kernel/cs_main.h>
-#include <protocol.h>
+#include <kernel/messagestartchars.h>
 #include <sync.h>
 #include <util/fs.h>
 #include <util/hasher.h>
@@ -73,7 +73,7 @@ static const unsigned int UNDOFILE_CHUNK_SIZE = 0x100000; // 1 MiB
 static const unsigned int MAX_BLOCKFILE_SIZE = 0x8000000; // 128 MiB
 
 /** Size of header written by WriteBlockToDisk before a serialized CBlock */
-static constexpr size_t BLOCK_SERIALIZATION_HEADER_SIZE = std::tuple_size_v<CMessageHeader::MessageStartChars> + sizeof(unsigned int);
+static constexpr size_t BLOCK_SERIALIZATION_HEADER_SIZE = std::tuple_size_v<MessageStartChars> + sizeof(unsigned int);
 
 extern std::atomic_bool fReindex;
 

src/protocol.h

@@ -6,6 +6,7 @@
 #ifndef BITCOIN_PROTOCOL_H
 #define BITCOIN_PROTOCOL_H
 
+#include <kernel/messagestartchars.h> // IWYU pragma: export
 #include <netaddress.h>
 #include <primitives/transaction.h>
 #include <serialize.h>
@@ -27,7 +28,6 @@
 class CMessageHeader
 {
 public:
-    using MessageStartChars = std::array<uint8_t, 4>;
     static constexpr size_t COMMAND_SIZE = 12;
     static constexpr size_t MESSAGE_SIZE_SIZE = 4;
     static constexpr size_t CHECKSUM_SIZE = 4;