mempool: persist with XOR

doc/release-notes-28207.md

@@ -0,0 +1,7 @@
+mempool.dat compatibility
+========================
+
+The `mempool.dat` file created by -persistmempool or the savemempool RPC will
+be written in a new format, which can not be read by previous software
+releases. To allow for a downgrade, a temporary setting `-persistmempoolv1` has
+been added to fall back to the legacy format.

src/init.cpp

@@ -458,6 +458,11 @@ void SetupServerArgs(ArgsManager& argsman)
     argsman.AddArg("-par=<n>", strprintf("Set the number of script verification threads (%u to %d, 0 = auto, <0 = leave that many cores free, default: %d)",
         -GetNumCores(), MAX_SCRIPTCHECK_THREADS, DEFAULT_SCRIPTCHECK_THREADS), ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
     argsman.AddArg("-persistmempool", strprintf("Whether to save the mempool on shutdown and load on restart (default: %u)", DEFAULT_PERSIST_MEMPOOL), ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
+    argsman.AddArg("-persistmempoolv1",
+                   strprintf("Whether a mempool.dat file created by -persistmempool or the savemempool RPC will be written in the legacy format "
+                             "(version 1) or the current format (version 2). This temporary option will be removed in the future. (default: %u)",
+                             DEFAULT_PERSIST_V1_DAT),
+                   ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
     argsman.AddArg("-pid=<file>", strprintf("Specify pid file. Relative paths will be prefixed by a net-specific datadir location. (default: %s)", BITCOIN_PID_FILENAME), ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
     argsman.AddArg("-prune=<n>", strprintf("Reduce storage requirements by enabling pruning (deleting) of old blocks. This allows the pruneblockchain RPC to be called to delete specific blocks and enables automatic pruning of old blocks if a target size in MiB is provided. This mode is incompatible with -txindex. "
             "Warning: Reverting this setting requires re-downloading the entire blockchain. "

src/kernel/mempool_options.h

@@ -23,6 +23,8 @@ static constexpr unsigned int DEFAULT_BLOCKSONLY_MAX_MEMPOOL_SIZE_MB{5};
 static constexpr unsigned int DEFAULT_MEMPOOL_EXPIRY_HOURS{336};
 /** Default for -mempoolfullrbf, if the transaction replaceability signaling is ignored */
 static constexpr bool DEFAULT_MEMPOOL_FULL_RBF{false};
+/** Whether to fall back to legacy V1 serialization when writing mempool.dat */
+static constexpr bool DEFAULT_PERSIST_V1_DAT{false};
 /** Default for -acceptnonstdtxn */
 static constexpr bool DEFAULT_ACCEPT_NON_STD_TXN{false};
 
@@ -56,6 +58,7 @@ struct MemPoolOptions {
     bool permit_bare_multisig{DEFAULT_PERMIT_BAREMULTISIG};
     bool require_standard{true};
     bool full_rbf{DEFAULT_MEMPOOL_FULL_RBF};
+    bool persist_v1_dat{DEFAULT_PERSIST_V1_DAT};
     MemPoolLimits limits{};
 };
 } // namespace kernel

src/kernel/mempool_persist.cpp

@@ -8,6 +8,7 @@
 #include <consensus/amount.h>
 #include <logging.h>
 #include <primitives/transaction.h>
+#include <random.h>
 #include <serialize.h>
 #include <streams.h>
 #include <sync.h>
@@ -34,14 +35,14 @@ using fsbridge::FopenFn;
 
 namespace kernel {
 
-static const uint64_t MEMPOOL_DUMP_VERSION = 1;
+static const uint64_t MEMPOOL_DUMP_VERSION_NO_XOR_KEY{1};
+static const uint64_t MEMPOOL_DUMP_VERSION{2};
 
 bool LoadMempool(CTxMemPool& pool, const fs::path& load_path, Chainstate& active_chainstate, ImportMempoolOptions&& opts)
 {
     if (load_path.empty()) return false;
 
-    FILE* filestr{opts.mockable_fopen_function(load_path, "rb")};
-    CAutoFile file{filestr, CLIENT_VERSION};
+    CAutoFile file{opts.mockable_fopen_function(load_path, "rb"), CLIENT_VERSION};
     if (file.IsNull()) {
         LogPrintf("Failed to open mempool file from disk. Continuing anyway.\n");
         return false;
@@ -57,9 +58,15 @@ bool LoadMempool(CTxMemPool& pool, const fs::path& load_path, Chainstate& active
     try {
         uint64_t version;
         file >> version;
-        if (version != MEMPOOL_DUMP_VERSION) {
+        std::vector<std::byte> xor_key;
+        if (version == MEMPOOL_DUMP_VERSION_NO_XOR_KEY) {
+            // Leave XOR-key empty
+        } else if (version == MEMPOOL_DUMP_VERSION) {
+            file >> xor_key;
+        } else {
             return false;
         }
+        file.SetXor(xor_key);
         uint64_t num;
         file >> num;
         while (num) {
@@ -151,17 +158,22 @@ bool DumpMempool(const CTxMemPool& pool, const fs::path& dump_path, FopenFn mock
 
     auto mid = SteadyClock::now();
 
-    try {
-        FILE* filestr{mockable_fopen_function(dump_path + ".new", "wb")};
-        if (!filestr) {
+    CAutoFile file{mockable_fopen_function(dump_path + ".new", "wb"), CLIENT_VERSION};
+    if (file.IsNull()) {
         return false;
     }
 
-        CAutoFile file{filestr, CLIENT_VERSION};
-
-        uint64_t version = MEMPOOL_DUMP_VERSION;
+    try {
+        const uint64_t version{pool.m_persist_v1_dat ? MEMPOOL_DUMP_VERSION_NO_XOR_KEY : MEMPOOL_DUMP_VERSION};
         file << version;
 
+        std::vector<std::byte> xor_key(8);
+        if (!pool.m_persist_v1_dat) {
+            FastRandomContext{}.fillrand(xor_key);
+            file << xor_key;
+        }
+        file.SetXor(xor_key);
+
         file << (uint64_t)vinfo.size();
         for (const auto& i : vinfo) {
             file << *(i.tx);

src/node/mempool_args.cpp

@@ -93,6 +93,8 @@ util::Result<void> ApplyArgsManOptions(const ArgsManager& argsman, const CChainP
 
     mempool_opts.full_rbf = argsman.GetBoolArg("-mempoolfullrbf", mempool_opts.full_rbf);
 
+    mempool_opts.persist_v1_dat = argsman.GetBoolArg("-persistmempoolv1", mempool_opts.persist_v1_dat);
+
     ApplyArgsManOptions(argsman, mempool_opts.limits);
 
     return {};

src/streams.h

@@ -471,7 +471,7 @@ class AutoFile
 {
 protected:
     std::FILE* m_file;
-    const std::vector<std::byte> m_xor;
+    std::vector<std::byte> m_xor;
 
 public:
     explicit AutoFile(std::FILE* file, std::vector<std::byte> data_xor={}) : m_file{file}, m_xor{std::move(data_xor)} {}
@@ -511,6 +511,9 @@ public:
      */
     bool IsNull() const { return m_file == nullptr; }
 
+    /** Continue with a different XOR key */
+    void SetXor(std::vector<std::byte> data_xor) { m_xor = data_xor; }
+
     /** Implementation detail, only used internally. */
     std::size_t detail_fread(Span<std::byte> dst);
 

src/txmempool.cpp

@@ -412,6 +412,7 @@ CTxMemPool::CTxMemPool(const Options& opts)
       m_max_datacarrier_bytes{opts.max_datacarrier_bytes},
       m_require_standard{opts.require_standard},
       m_full_rbf{opts.full_rbf},
+      m_persist_v1_dat{opts.persist_v1_dat},
       m_limits{opts.limits}
 {
 }

src/txmempool.h

@@ -446,6 +446,7 @@ public:
     const std::optional<unsigned> m_max_datacarrier_bytes;
     const bool m_require_standard;
     const bool m_full_rbf;
+    const bool m_persist_v1_dat;
 
     const Limits m_limits;
 

test/functional/mempool_compatibility.py

@@ -28,7 +28,7 @@ class MempoolCompatibilityTest(BitcoinTestFramework):
 
     def setup_network(self):
         self.add_nodes(self.num_nodes, versions=[
-            200100,  # Last release with previous mempool format
+            200100,  # Last release without unbroadcast serialization and without XOR
             None,
         ])
         self.start_nodes()
@@ -59,7 +59,7 @@ class MempoolCompatibilityTest(BitcoinTestFramework):
         old_node_mempool.rename(new_node_mempool)
 
         self.log.info("Start new node and verify mempool contains the tx")
-        self.start_node(1)
+        self.start_node(1, extra_args=["-persistmempoolv1=1"])
         assert old_tx_hash in new_node.getrawmempool()
 
         self.log.info("Add unbroadcasted tx to mempool on new node and shutdown")