Merge #19308: wallet: BerkeleyBatch Handle cursor internally

ca24edfbc1941ed0a3c9586416dae4e84794eb66 walletdb: Handle cursor internally (Andrew Chow)

Pull request description:

  Instead of returning a Dbc (BDB cursor object) and having the caller deal with the cursor, make BerkeleyBatch handle the cursor internally.

  Split from #18971

ACKs for top commit:
  ryanofsky:
    Code review ACK ca24edfbc1941ed0a3c9586416dae4e84794eb66. Changes since last review: StartCursor rename, moving CloseCursor calls near returns
  promag:
    Code review ACK ca24edfbc1941ed0a3c9586416dae4e84794eb66.

Tree-SHA512: f029b498c7f275aedca53ce7ade7cb99c82975fd6cad17346a4990fb3bcc54e2a5309b32053bd13def9ee464d331b036ac79abb8fc4fa561170c6cfc85283447

3 files changed, 50 insertions, 35 deletions

diff --git a/src/wallet/bdb.cpp b/src/wallet/bdb.cpp
index 125bf004e4..24954f4a02 100644
--- a/src/wallet/bdb.cpp
+++ b/src/wallet/bdb.cpp
@@ -335,7 +335,7 @@ void BerkeleyEnvironment::CheckpointLSN(const std::string& strFile)
 }
 
 
-BerkeleyBatch::BerkeleyBatch(BerkeleyDatabase& database, const char* pszMode, bool fFlushOnCloseIn) : pdb(nullptr), activeTxn(nullptr)
+BerkeleyBatch::BerkeleyBatch(BerkeleyDatabase& database, const char* pszMode, bool fFlushOnCloseIn) : pdb(nullptr), activeTxn(nullptr), m_cursor(nullptr)
 {
     fReadOnly = (!strchr(pszMode, '+') && !strchr(pszMode, 'w'));
     fFlushOnClose = fFlushOnCloseIn;
@@ -442,6 +442,7 @@ void BerkeleyBatch::Close()
         activeTxn->abort();
     activeTxn = nullptr;
     pdb = nullptr;
+    CloseCursor();
 
     if (fFlushOnClose)
         Flush();
@@ -528,17 +529,15 @@ bool BerkeleyBatch::Rewrite(BerkeleyDatabase& database, const char* pszSkip)
                         fSuccess = false;
                     }
 
-                    Dbc* pcursor = db.GetCursor();
-                    if (pcursor)
+                    if (db.StartCursor()) {
                         while (fSuccess) {
                             CDataStream ssKey(SER_DISK, CLIENT_VERSION);
                             CDataStream ssValue(SER_DISK, CLIENT_VERSION);
-                            int ret1 = db.ReadAtCursor(pcursor, ssKey, ssValue);
-                            if (ret1 == DB_NOTFOUND) {
-                                pcursor->close();
+                            bool complete;
+                            bool ret1 = db.ReadAtCursor(ssKey, ssValue, complete);
+                            if (complete) {
                                 break;
-                            } else if (ret1 != 0) {
-                                pcursor->close();
+                            } else if (!ret1) {
                                 fSuccess = false;
                                 break;
                             }
@@ -556,6 +555,8 @@ bool BerkeleyBatch::Rewrite(BerkeleyDatabase& database, const char* pszSkip)
                             if (ret2 > 0)
                                 fSuccess = false;
                         }
+                        db.CloseCursor();
+                    }
                     if (fSuccess) {
                         db.Close();
                         env->CloseDb(strFile);
@@ -738,27 +739,30 @@ void BerkeleyDatabase::ReloadDbEnv()
     }
 }
 
-Dbc* BerkeleyBatch::GetCursor()
+bool BerkeleyBatch::StartCursor()
 {
+    assert(!m_cursor);
     if (!pdb)
-        return nullptr;
-    Dbc* pcursor = nullptr;
-    int ret = pdb->cursor(nullptr, &pcursor, 0);
-    if (ret != 0)
-        return nullptr;
-    return pcursor;
+        return false;
+    int ret = pdb->cursor(nullptr, &m_cursor, 0);
+    return ret == 0;
 }
 
-int BerkeleyBatch::ReadAtCursor(Dbc* pcursor, CDataStream& ssKey, CDataStream& ssValue)
+bool BerkeleyBatch::ReadAtCursor(CDataStream& ssKey, CDataStream& ssValue, bool& complete)
 {
+    complete = false;
+    if (m_cursor == nullptr) return false;
     // Read at cursor
     SafeDbt datKey;
     SafeDbt datValue;
-    int ret = pcursor->get(datKey, datValue, DB_NEXT);
+    int ret = m_cursor->get(datKey, datValue, DB_NEXT);
+    if (ret == DB_NOTFOUND) {
+        complete = true;
+    }
     if (ret != 0)
-        return ret;
+        return false;
     else if (datKey.get_data() == nullptr || datValue.get_data() == nullptr)
-        return 99999;
+        return false;
 
     // Convert to streams
     ssKey.SetType(SER_DISK);
@@ -767,7 +771,14 @@ int BerkeleyBatch::ReadAtCursor(Dbc* pcursor, CDataStream& ssKey, CDataStream& s
     ssValue.SetType(SER_DISK);
     ssValue.clear();
     ssValue.write((char*)datValue.get_data(), datValue.get_size());
-    return 0;
+    return true;
+}
+
+void BerkeleyBatch::CloseCursor()
+{
+    if (!m_cursor) return;
+    m_cursor->close();
+    m_cursor = nullptr;
 }
 
 bool BerkeleyBatch::TxnBegin()
diff --git a/src/wallet/bdb.h b/src/wallet/bdb.h
index c121bb4228..ee9cfa46b1 100644
--- a/src/wallet/bdb.h
+++ b/src/wallet/bdb.h
@@ -198,6 +198,7 @@ protected:
     Db* pdb;
     std::string strFile;
     DbTxn* activeTxn;
+    Dbc* m_cursor;
     bool fReadOnly;
     bool fFlushOnClose;
     BerkeleyEnvironment *env;
@@ -284,8 +285,9 @@ public:
         return HasKey(ssKey);
     }
 
-    Dbc* GetCursor();
-    int ReadAtCursor(Dbc* pcursor, CDataStream& ssKey, CDataStream& ssValue);
+    bool StartCursor();
+    bool ReadAtCursor(CDataStream& ssKey, CDataStream& ssValue, bool& complete);
+    void CloseCursor();
     bool TxnBegin();
     bool TxnCommit();
     bool TxnAbort();
diff --git a/src/wallet/walletdb.cpp b/src/wallet/walletdb.cpp
index 603887ee58..ba5087e2e1 100644
--- a/src/wallet/walletdb.cpp
+++ b/src/wallet/walletdb.cpp
@@ -700,8 +700,7 @@ DBErrors WalletBatch::LoadWallet(CWallet* pwallet)
         }
 
         // Get cursor
-        Dbc* pcursor = m_batch.GetCursor();
-        if (!pcursor)
+        if (!m_batch.StartCursor())
         {
             pwallet->WalletLogPrintf("Error getting wallet database cursor\n");
             return DBErrors::CORRUPT;
@@ -712,11 +711,14 @@ DBErrors WalletBatch::LoadWallet(CWallet* pwallet)
             // Read next record
             CDataStream ssKey(SER_DISK, CLIENT_VERSION);
             CDataStream ssValue(SER_DISK, CLIENT_VERSION);
-            int ret = m_batch.ReadAtCursor(pcursor, ssKey, ssValue);
-            if (ret == DB_NOTFOUND)
+            bool complete;
+            bool ret = m_batch.ReadAtCursor(ssKey, ssValue, complete);
+            if (complete) {
                 break;
-            else if (ret != 0)
+            }
+            else if (!ret)
             {
+                m_batch.CloseCursor();
                 pwallet->WalletLogPrintf("Error reading next record from wallet database\n");
                 return DBErrors::CORRUPT;
             }
@@ -743,10 +745,10 @@ DBErrors WalletBatch::LoadWallet(CWallet* pwallet)
             if (!strErr.empty())
                 pwallet->WalletLogPrintf("%s\n", strErr);
         }
-        pcursor->close();
     } catch (...) {
         result = DBErrors::CORRUPT;
     }
+    m_batch.CloseCursor();
 
     // Set the active ScriptPubKeyMans
     for (auto spk_man_pair : wss.m_active_external_spks) {
@@ -850,8 +852,7 @@ DBErrors WalletBatch::FindWalletTx(std::vector<uint256>& vTxHash, std::list<CWal
         }
 
         // Get cursor
-        Dbc* pcursor = m_batch.GetCursor();
-        if (!pcursor)
+        if (!m_batch.StartCursor())
         {
             LogPrintf("Error getting wallet database cursor\n");
             return DBErrors::CORRUPT;
@@ -862,11 +863,12 @@ DBErrors WalletBatch::FindWalletTx(std::vector<uint256>& vTxHash, std::list<CWal
             // Read next record
             CDataStream ssKey(SER_DISK, CLIENT_VERSION);
             CDataStream ssValue(SER_DISK, CLIENT_VERSION);
-            int ret = m_batch.ReadAtCursor(pcursor, ssKey, ssValue);
-            if (ret == DB_NOTFOUND)
+            bool complete;
+            bool ret = m_batch.ReadAtCursor(ssKey, ssValue, complete);
+            if (complete) {
                 break;
-            else if (ret != 0)
-            {
+            } else if (!ret) {
+                m_batch.CloseCursor();
                 LogPrintf("Error reading next record from wallet database\n");
                 return DBErrors::CORRUPT;
             }
@@ -881,10 +883,10 @@ DBErrors WalletBatch::FindWalletTx(std::vector<uint256>& vTxHash, std::list<CWal
                 ssValue >> vWtx.back();
             }
         }
-        pcursor->close();
     } catch (...) {
         result = DBErrors::CORRUPT;
     }
+    m_batch.CloseCursor();
 
     return result;
 }