wallet: Add GetPrefixCursor to DatabaseBatch

In order to get records beginning with a prefix, we will need a cursor
specifically for that prefix. So add a GetPrefixCursor function and
DatabaseCursor classes for dealing with those prefixes.

Tested on each supported db engine.

1) Write two different key->value elements to db.
2) Create a new prefix cursor and walk-through every returned element,
   verifying that it gets parsed properly.
3) Try to move the cursor outside the filtered range: expect failure
   and flag complete=true.

Co-Authored-By: Ryan Ofsky <ryan@ofsky.org>
Co-Authored-By: furszy <matiasfurszyfer@protonmail.com>

1 files changed, 6 insertions, 1 deletions

diff --git a/src/wallet/bdb.h b/src/wallet/bdb.h
index e8a57e8a5e..8cc03692d6 100644
--- a/src/wallet/bdb.h
+++ b/src/wallet/bdb.h
@@ -190,9 +190,13 @@ class BerkeleyCursor : public DatabaseCursor
 {
 private:
     Dbc* m_cursor;
+    std::vector<std::byte> m_key_prefix;
+    bool m_first{true};
 
 public:
-    explicit BerkeleyCursor(BerkeleyDatabase& database, const BerkeleyBatch& batch);
+    // Constructor for cursor for records matching the prefix
+    // To match all records, an empty prefix may be provided.
+    explicit BerkeleyCursor(BerkeleyDatabase& database, const BerkeleyBatch& batch, Span<const std::byte> prefix = {});
     ~BerkeleyCursor() override;
 
     Status Next(DataStream& key, DataStream& value) override;
@@ -229,6 +233,7 @@ public:
     void Close() override;
 
     std::unique_ptr<DatabaseCursor> GetNewCursor() override;
+    std::unique_ptr<DatabaseCursor> GetNewPrefixCursor(Span<const std::byte> prefix) override;
     bool TxnBegin() override;
     bool TxnCommit() override;
     bool TxnAbort() override;