wallet: encrypt atomically under the SQLite backend

EncryptWallet() had only a Berkeley DB path: it rebuilt a wallet.dat temp
file and swapped it in. Under -walletbackend=sqlite that was wrong -- it
would leave the live wallet.sqlite unencrypted and write a divergent
wallet.dat instead. Add a SQLite persistence branch that rebuilds a fresh
wallet.sqlite in one transaction (public records copied from the live
store, encrypted key material serialized byte-for-byte the way the BDB
path writes it), checkpoints it, and swaps it in with a .before-encrypt
backup, mirroring the BDB rename dance. A fresh file rather than an
in-place rewrite keeps the change atomic and leaves no plaintext key in a
freed page.

CmdEncryptWallet skips PurgeDbEnvironmentLogs under SQLite (no Berkeley DB
environment behind the wallet) and reports the backend it used.

New wallet-sqlite-encrypt self-test drives the real command path in child
processes: export a wallet to SQLite, encrypt it through
-walletbackend=sqlite, and prove it comes out encrypted, unlockable with
the right passphrase, refusing the wrong one, with its recovery phrase
intact and the original wallet.dat left untouched.

1 files changed, 14 insertions, 1 deletions

diff --git a/src/walletcmd.cpp b/src/walletcmd.cpp
index 4dda8dd..374b2cc 100644
--- a/src/walletcmd.cpp
+++ b/src/walletcmd.cpp
@@ -1365,6 +1365,11 @@ int CmdEncryptWallet(const std::string& strPassphrase)
 {
     AttachTerminal();
 
+    // Capture the backend now: under SQLite, EncryptWallet() closes the runtime
+    // store to swap the file, so WalletSQLiteRuntimeActive() reads false by the
+    // time we would decide whether to purge Berkeley DB logs below.
+    bool fSQLiteBackend = WalletSQLiteRuntimeActive();
+
     string strBackup;
     string strError;
     if (!EncryptWallet(strPassphrase, strBackup, strError))
@@ -1375,6 +1380,8 @@ int CmdEncryptWallet(const std::string& strPassphrase)
     }
 
     printf("Wallet encrypted.\n");
+    if (fSQLiteBackend)
+        printf("Wallet backend: SQLite (wallet.sqlite).\n");
     printf("The old unencrypted wallet was moved to:\n");
     printf("  %s\n", strBackup.c_str());
     printf("That backup still contains private keys in plain text. Move it offline or\n");
@@ -1387,7 +1394,13 @@ int CmdEncryptWallet(const std::string& strPassphrase)
     // them. Closing the environment and dropping the logs is the last step of
     // encrypting, not an optimisation -- our own backup advice is to copy the
     // whole directory, and following it otherwise carries the keys along.
-    PurgeDbEnvironmentLogs();
+    //
+    // The SQLite backend has no Berkeley DB environment behind the wallet, and
+    // EncryptWallet() already closed and swapped the SQLite store; there is
+    // nothing to purge, and calling into the environment here would only open
+    // one needlessly.
+    if (!fSQLiteBackend)
+        PurgeDbEnvironmentLogs();
     return 0;
 }