Merge bitcoin/bitcoin#26690: wallet: Refactor database cursor into its own object with proper return codes

4aebd832a405090c2608e4b60bb4f34501bcea61 db: Change DatabaseCursor::Next to return status enum (Andrew Chow)
d79e8dcf2981ef1964a2fde8c472b5de1ca1c963 wallet: Have cursor users use DatabaseCursor directly (Andrew Chow)
7a198bba0a1d0a0f0fd4ca947955cb52b84bdd4b wallet: Introduce DatabaseCursor RAII class for managing cursor (Andrew Chow)
69efbc011bb74fcd8dd9ed2a8a5d31bc9e323c10 Move SafeDbt out of BerkeleyBatch (Andrew Chow)

Pull request description:

  Instead of having database cursors be tied to a particular `DatabaseBatch` object and requiring its setup and teardown be separate functions in that batch, we can have cursors be separate RAII classes. This makes it easier to create and destroy cursors as well as having cursors that have slightly different behaviors.

  Additionally, since reading data from a cursor is a tri-state, this PR changes the return value of the `Next` function (formerly `ReadAtCursor`) to return an Enum rather than the current system of 2 booleans. This greatly simplifies and unifies the code that deals with cursors as now there is no confusion as to what the function returns when there are no records left to be read.

  Extracted from #24914

ACKs for top commit:
  furszy:
    diff ACK 4aebd83
  theStack:
    Code-review ACK 4aebd832a405090c2608e4b60bb4f34501bcea61

Tree-SHA512: 5d0be56a18de5b08c777dd5a73ba5a6ef1e696fdb07d1dca952a88ded07887b7c5c04342f9a76feb2f6fe24a45dc31f094f1f5d9500e6bdf4a44f4edb66dcaa1

1 files changed, 26 insertions, 22 deletions

diff --git a/src/wallet/sqlite.cpp b/src/wallet/sqlite.cpp
index f2b9909851..7a0c4b1806 100644
--- a/src/wallet/sqlite.cpp
+++ b/src/wallet/sqlite.cpp
@@ -125,7 +125,6 @@ void SQLiteBatch::SetupSQLStatements()
         {&m_insert_stmt, "INSERT INTO main VALUES(?, ?)"},
         {&m_overwrite_stmt, "INSERT or REPLACE into main values(?, ?)"},
         {&m_delete_stmt, "DELETE FROM main WHERE key = ?"},
-        {&m_cursor_stmt, "SELECT key, value FROM main"},
     };
 
     for (const auto& [stmt_prepared, stmt_text] : statements) {
@@ -374,7 +373,6 @@ void SQLiteBatch::Close()
         {&m_insert_stmt, "insert"},
         {&m_overwrite_stmt, "overwrite"},
         {&m_delete_stmt, "delete"},
-        {&m_cursor_stmt, "cursor"},
     };
 
     for (const auto& [stmt_prepared, stmt_description] : statements) {
@@ -472,28 +470,15 @@ bool SQLiteBatch::HasKey(CDataStream&& key)
     return res == SQLITE_ROW;
 }
 
-bool SQLiteBatch::StartCursor()
+DatabaseCursor::Status SQLiteCursor::Next(CDataStream& key, CDataStream& value)
 {
-    assert(!m_cursor_init);
-    if (!m_database.m_db) return false;
-    m_cursor_init = true;
-    return true;
-}
-
-bool SQLiteBatch::ReadAtCursor(CDataStream& key, CDataStream& value, bool& complete)
-{
-    complete = false;
-
-    if (!m_cursor_init) return false;
-
     int res = sqlite3_step(m_cursor_stmt);
     if (res == SQLITE_DONE) {
-        complete = true;
-        return true;
+        return Status::DONE;
     }
     if (res != SQLITE_ROW) {
-        LogPrintf("SQLiteBatch::ReadAtCursor: Unable to execute cursor step: %s\n", sqlite3_errstr(res));
-        return false;
+        LogPrintf("%s: Unable to execute cursor step: %s\n", __func__, sqlite3_errstr(res));
+        return Status::FAIL;
     }
 
     // Leftmost column in result is index 0
@@ -503,13 +488,32 @@ bool SQLiteBatch::ReadAtCursor(CDataStream& key, CDataStream& value, bool& compl
     const std::byte* value_data{AsBytePtr(sqlite3_column_blob(m_cursor_stmt, 1))};
     size_t value_data_size(sqlite3_column_bytes(m_cursor_stmt, 1));
     value.write({value_data, value_data_size});
-    return true;
+    return Status::MORE;
 }
 
-void SQLiteBatch::CloseCursor()
+SQLiteCursor::~SQLiteCursor()
 {
     sqlite3_reset(m_cursor_stmt);
-    m_cursor_init = false;
+    int res = sqlite3_finalize(m_cursor_stmt);
+    if (res != SQLITE_OK) {
+        LogPrintf("%s: cursor closed but could not finalize cursor statement: %s\n",
+                  __func__, sqlite3_errstr(res));
+    }
+}
+
+std::unique_ptr<DatabaseCursor> SQLiteBatch::GetNewCursor()
+{
+    if (!m_database.m_db) return nullptr;
+    auto cursor = std::make_unique<SQLiteCursor>();
+
+    const char* stmt_text = "SELECT key, value FROM main";
+    int res = sqlite3_prepare_v2(m_database.m_db, stmt_text, -1, &cursor->m_cursor_stmt, nullptr);
+    if (res != SQLITE_OK) {
+        throw std::runtime_error(strprintf(
+            "%s: Failed to setup cursor SQL statement: %s\n", __func__, sqlite3_errstr(res)));
+    }
+
+    return cursor;
 }
 
 bool SQLiteBatch::TxnBegin()