wallet: bracket WriteHDMaster in a SQLite runtime transaction

The SQLite runtime wrote each record as its own autocommit, so a group
that must land together -- hdmaster and hdchaincode, the two halves of an
HD seed -- could be left half-written by a failure or crash between them,
the incomplete-seed state -walletstoragecheck exists to catch. Berkeley DB
was no worse (it is not transactional here either) but no better.

Add WalletSQLiteRuntimeBeginTxn/CommitTxn/RollbackTxn -- no-ops that
succeed when the SQLite backend is not active, so Berkeley DB keeps its
existing per-write behaviour -- and wrap WriteHDMaster in them so the seed
lands all-or-nothing under SQLite. The one BDB-atomic wallet rewrite, the
encrypt path, is already matched by its own transaction in the SQLite
encrypt branch; every other wallet multi-write is ordering-based on both
backends by design.

wallet-sqlite self-test now proves the bracket: a rolled-back runtime
write leaves no record, a committed one persists, and WriteHDMaster lands
both halves of the seed.

3 files changed, 89 insertions, 2 deletions

diff --git a/src/db.cpp b/src/db.cpp
index 86f6dd7..c16edb4 100644
--- a/src/db.cpp
+++ b/src/db.cpp
@@ -164,6 +164,40 @@ bool WalletSQLiteRuntimeEraseRecord(const vector<unsigned char>& vchKey)
     return pWalletSQLiteRuntime->EraseRecord(vchKey, strError);
 }
 
+// Transaction bracket for the SQLite runtime. When the SQLite backend is not
+// active these are no-ops that succeed, so a caller can wrap a group of related
+// writes and Berkeley DB keeps its existing per-write behaviour unchanged while
+// SQLite gets all-or-nothing.
+bool WalletSQLiteRuntimeBeginTxn()
+{
+    if (!pWalletSQLiteRuntime)
+        return true;
+    string strError;
+    if (pWalletSQLiteRuntime->BeginTransaction(strError))
+        return true;
+    printf("WalletSQLiteRuntimeBeginTxn() : %s\n", strError.c_str());
+    return false;
+}
+
+bool WalletSQLiteRuntimeCommitTxn()
+{
+    if (!pWalletSQLiteRuntime)
+        return true;
+    string strError;
+    if (pWalletSQLiteRuntime->CommitTransaction(strError))
+        return true;
+    printf("WalletSQLiteRuntimeCommitTxn() : %s\n", strError.c_str());
+    return false;
+}
+
+void WalletSQLiteRuntimeRollbackTxn()
+{
+    if (!pWalletSQLiteRuntime)
+        return;
+    string strError;
+    pWalletSQLiteRuntime->RollbackTransaction(strError);
+}
+
 
 CDB::CDB(const char* pszFile, const char* pszMode, bool fTxn) : pdb(NULL)
 {
diff --git a/src/db.h b/src/db.h
index fee5a82..1a272b9 100644
--- a/src/db.h
+++ b/src/db.h
@@ -365,6 +365,9 @@ bool WalletSQLiteRuntimeWriteRecord(const vector<unsigned char>& vchKey,
                                     const vector<unsigned char>& vchValue,
                                     bool fOverwrite);
 bool WalletSQLiteRuntimeEraseRecord(const vector<unsigned char>& vchKey);
+bool WalletSQLiteRuntimeBeginTxn();
+bool WalletSQLiteRuntimeCommitTxn();
+void WalletSQLiteRuntimeRollbackTxn();
 
 
 
@@ -531,8 +534,21 @@ public:
 
     bool WriteHDMaster(const vector<unsigned char>& vchMaster, const vector<unsigned char>& vchChainCode)
     {
-        return WriteWalletRecord(string("hdmaster"), vchMaster)
-            && WriteWalletRecord(string("hdchaincode"), vchChainCode);
+        // hdmaster and hdchaincode are halves of one seed: a wallet with one but
+        // not the other is an incomplete HD wallet (-walletstoragecheck flags
+        // exactly that). Under the SQLite runtime write them in one transaction
+        // so a failure or crash between the two cannot leave that half-state.
+        // Berkeley DB keeps its existing per-write behaviour -- the bracket is a
+        // no-op there.
+        if (!WalletSQLiteRuntimeBeginTxn())
+            return false;
+        if (!WriteWalletRecord(string("hdmaster"), vchMaster) ||
+            !WriteWalletRecord(string("hdchaincode"), vchChainCode))
+        {
+            WalletSQLiteRuntimeRollbackTxn();
+            return false;
+        }
+        return WalletSQLiteRuntimeCommitTxn();
     }
 
     bool WriteWalletMinVersion(int nVersion)
diff --git a/src/selftest.cpp b/src/selftest.cpp
index fc10947..7ad5a53 100644
--- a/src/selftest.cpp
+++ b/src/selftest.cpp
@@ -1231,6 +1231,43 @@ static int RunWalletSQLiteSelfTest()
                 nFail += Check(!FileExists((strRuntimeDir + "/wallet.dat").c_str()),
                                "active SQLite runtime does not create wallet.dat") ? 0 : 1;
 
+                // Transaction bracket: a rolled-back group leaves nothing, a
+                // committed group persists. This is the all-or-nothing that
+                // WriteHDMaster relies on so a half-written seed cannot survive
+                // a failure between its two records.
+                bool fTxnBegan = WalletSQLiteRuntimeBeginTxn();
+                bool fTxnWrote = fTxnBegan &&
+                    CWalletDB().WriteSetting("runtime-txn-rollback", (int64)111);
+                if (fTxnBegan)
+                    WalletSQLiteRuntimeRollbackTxn();
+                nFail += Check(fTxnBegan && fTxnWrote,
+                               "a SQLite runtime transaction opens and rolls back") ? 0 : 1;
+                int64 nRolledBack = 0;
+                nFail += Check(!CWalletDB("r").ReadSetting("runtime-txn-rollback",
+                                                           nRolledBack),
+                               "a rolled-back SQLite runtime write leaves no record") ? 0 : 1;
+
+                bool fCommitOk = WalletSQLiteRuntimeBeginTxn() &&
+                    CWalletDB().WriteSetting("runtime-txn-commit", (int64)222) &&
+                    WalletSQLiteRuntimeCommitTxn();
+                int64 nCommitted = 0;
+                nFail += Check(fCommitOk &&
+                               CWalletDB("r").ReadSetting("runtime-txn-commit",
+                                                          nCommitted) &&
+                               nCommitted == 222,
+                               "a committed SQLite runtime write persists") ? 0 : 1;
+
+                // WriteHDMaster brackets its two records in that transaction;
+                // both halves of the seed must land.
+                vector<unsigned char> vchTxnMaster(32, 0x5a);
+                vector<unsigned char> vchTxnChainCode(32, 0xa5);
+                vector<unsigned char> vchReadMaster, vchReadChainCode;
+                nFail += Check(CWalletDB().WriteHDMaster(vchTxnMaster, vchTxnChainCode) &&
+                               CWalletDB("r").ReadHDMaster(vchReadMaster, vchReadChainCode) &&
+                               vchReadMaster == vchTxnMaster &&
+                               vchReadChainCode == vchTxnChainCode,
+                               "WriteHDMaster commits both halves of the seed under SQLite") ? 0 : 1;
+
                 // Durability: close the backend (checkpoints the WAL), reopen
                 // the same file, and confirm what CWalletDB wrote is still
                 // there. This is the write-survives-a-restart property the real