bdb: Be able to make byteswapped databases

Byteswapped databases make it easier to test opening and deserializing
other endian databases.

src/wallet/bdb.cpp

@@ -65,6 +65,8 @@ RecursiveMutex cs_db;
 std::map<std::string, std::weak_ptr<BerkeleyEnvironment>> g_dbenvs GUARDED_BY(cs_db); //!< Map from directory name to db environment.
 } // namespace
 
+static constexpr auto REVERSE_BYTE_ORDER{std::endian::native == std::endian::little ? 4321 : 1234};
+
 bool WalletDatabaseFileId::operator==(const WalletDatabaseFileId& rhs) const
 {
     return memcmp(value, &rhs.value, sizeof(value)) == 0;
@@ -300,7 +302,11 @@ static Span<const std::byte> SpanFromDbt(const SafeDbt& dbt)
 }
 
 BerkeleyDatabase::BerkeleyDatabase(std::shared_ptr<BerkeleyEnvironment> env, fs::path filename, const DatabaseOptions& options) :
-    WalletDatabase(), env(std::move(env)), m_filename(std::move(filename)), m_max_log_mb(options.max_log_mb)
+    WalletDatabase(),
+    env(std::move(env)),
+    m_byteswap(options.require_format == DatabaseFormat::BERKELEY_SWAP),
+    m_filename(std::move(filename)),
+    m_max_log_mb(options.max_log_mb)
 {
     auto inserted = this->env->m_databases.emplace(m_filename, std::ref(*this));
     assert(inserted.second);
@@ -389,6 +395,10 @@ void BerkeleyDatabase::Open()
                 }
             }
 
+            if (m_byteswap) {
+                pdb_temp->set_lorder(REVERSE_BYTE_ORDER);
+            }
+
             ret = pdb_temp->open(nullptr,                             // Txn pointer
                             fMockDb ? nullptr : strFile.c_str(),      // Filename
                             fMockDb ? strFile.c_str() : "main",       // Logical db name
@@ -521,6 +531,10 @@ bool BerkeleyDatabase::Rewrite(const char* pszSkip)
                     BerkeleyBatch db(*this, true);
                     std::unique_ptr<Db> pdbCopy = std::make_unique<Db>(env->dbenv.get(), 0);
 
+                    if (m_byteswap) {
+                        pdbCopy->set_lorder(REVERSE_BYTE_ORDER);
+                    }
+
                     int ret = pdbCopy->open(nullptr,               // Txn pointer
                                             strFileRes.c_str(), // Filename
                                             "main",             // Logical db name

src/wallet/bdb.h

@@ -147,6 +147,9 @@ public:
     /** Database pointer. This is initialized lazily and reset during flushes, so it can be null. */
     std::unique_ptr<Db> m_db;
 
+    // Whether to byteswap
+    bool m_byteswap;
+
     fs::path m_filename;
     int64_t m_max_log_mb;
 

src/wallet/db.h

@@ -184,6 +184,7 @@ enum class DatabaseFormat {
     BERKELEY,
     SQLITE,
     BERKELEY_RO,
+    BERKELEY_SWAP,
 };
 
 struct DatabaseOptions {

src/wallet/dump.cpp

@@ -186,6 +186,8 @@ bool CreateFromDump(const ArgsManager& args, const std::string& name, const fs::
         data_format = DatabaseFormat::BERKELEY;
     } else if (file_format == "sqlite") {
         data_format = DatabaseFormat::SQLITE;
+    } else if (file_format == "bdb_swap") {
+        data_format = DatabaseFormat::BERKELEY_SWAP;
     } else {
         error = strprintf(_("Unknown wallet file format \"%s\" provided. Please provide one of \"bdb\" or \"sqlite\"."), file_format);
         return false;