wallet: Add DatabaseBatch::ErasePrefix method

This new function is not used yet this commit, but next commit adds usages and
test coverage for both BDB and sqlite.

1 files changed, 23 insertions, 2 deletions

diff --git a/src/wallet/bdb.cpp b/src/wallet/bdb.cpp
index dd425c1160..6daf0f47a5 100644
--- a/src/wallet/bdb.cpp
+++ b/src/wallet/bdb.cpp
@@ -665,12 +665,14 @@ void BerkeleyDatabase::ReloadDbEnv()
     env->ReloadDbEnv();
 }
 
-BerkeleyCursor::BerkeleyCursor(BerkeleyDatabase& database)
+BerkeleyCursor::BerkeleyCursor(BerkeleyDatabase& database, BerkeleyBatch* batch)
 {
     if (!database.m_db.get()) {
         throw std::runtime_error(STR_INTERNAL_BUG("BerkeleyDatabase does not exist"));
     }
-    int ret = database.m_db->cursor(nullptr, &m_cursor, 0);
+    // Transaction argument to cursor is only needed when using the cursor to
+    // write to the database. Read-only cursors do not need a txn pointer.
+    int ret = database.m_db->cursor(batch ? batch->txn() : nullptr, &m_cursor, 0);
     if (ret != 0) {
         throw std::runtime_error(STR_INTERNAL_BUG(strprintf("BDB Cursor could not be created. Returned %d", ret)));
     }
@@ -817,6 +819,25 @@ bool BerkeleyBatch::HasKey(DataStream&& key)
     return ret == 0;
 }
 
+bool BerkeleyBatch::ErasePrefix(Span<const std::byte> prefix)
+{
+    if (!TxnBegin()) return false;
+    auto cursor{std::make_unique<BerkeleyCursor>(m_database, this)};
+    // const_cast is safe below even though prefix_key is an in/out parameter,
+    // because we are not using the DB_DBT_USERMEM flag, so BDB will allocate
+    // and return a different output data pointer
+    Dbt prefix_key{const_cast<std::byte*>(prefix.data()), static_cast<uint32_t>(prefix.size())}, prefix_value{};
+    int ret{cursor->dbc()->get(&prefix_key, &prefix_value, DB_SET_RANGE)};
+    for (int flag{DB_CURRENT}; ret == 0; flag = DB_NEXT) {
+        SafeDbt key, value;
+        ret = cursor->dbc()->get(key, value, flag);
+        if (ret != 0 || key.get_size() < prefix.size() || memcmp(key.get_data(), prefix.data(), prefix.size()) != 0) break;
+        ret = cursor->dbc()->del(0);
+    }
+    cursor.reset();
+    return TxnCommit() && (ret == 0 || ret == DB_NOTFOUND);
+}
+
 void BerkeleyDatabase::AddRef()
 {
     LOCK(cs_db);