refactor: prepare mempool_persist for obfuscation key change

These changes are meant to simplify the diffs for the riskier optimization commits later.

Author: l0rinc

src/node/mempool_persist.cpp

@@ -60,15 +60,17 @@ bool LoadMempool(CTxMemPool& pool, const fs::path& load_path, Chainstate& active
     try {
         uint64_t version;
         file >> version;
-        std::vector<std::byte> obfuscation;
+
         if (version == MEMPOOL_DUMP_VERSION_NO_XOR_KEY) {
-            // Leave XOR-key empty
+            file.SetObfuscation({});
         } else if (version == MEMPOOL_DUMP_VERSION) {
+            std::vector<std::byte> obfuscation(Obfuscation::KEY_SIZE);
             file >> obfuscation;
+            file.SetObfuscation(obfuscation);
         } else {
             return false;
         }
-        file.SetObfuscation(obfuscation);
+
         uint64_t total_txns_to_load;
         file >> total_txns_to_load;
         uint64_t txns_tried = 0;
@@ -180,12 +182,14 @@ bool DumpMempool(const CTxMemPool& pool, const fs::path& dump_path, FopenFn mock
         const uint64_t version{pool.m_opts.persist_v1_dat ? MEMPOOL_DUMP_VERSION_NO_XOR_KEY : MEMPOOL_DUMP_VERSION};
         file << version;
 
-        std::vector<std::byte> obfuscation(Obfuscation::KEY_SIZE);
         if (!pool.m_opts.persist_v1_dat) {
+            std::vector<std::byte> obfuscation(Obfuscation::KEY_SIZE);
             FastRandomContext{}.fillrand(obfuscation);
             file << obfuscation;
+            file.SetObfuscation(obfuscation);
+        } else {
+            file.SetObfuscation({});
         }
-        file.SetObfuscation(obfuscation);
 
         uint64_t mempool_transactions_to_write(vinfo.size());
         file << mempool_transactions_to_write;