refactor + document coin selection strategy

Co-authored-by: Xekyo <murch@murch.one>
glozow · Apr 22, 2021 · 04817b0 · 04817b0
1 parent 3663a03
commit 04817b0
Showing 1 changed file with 41 additions and 8 deletions.
diff --git a/src/wallet/wallet.cpp b/src/wallet/wallet.cpp
@@ -2502,15 +2502,48 @@ bool CWallet::SelectCoins(const std::vector<COutput>& vAvailableCoins, const CAm
         // explicitly shuffling the outputs before processing
         Shuffle(vCoins.begin(), vCoins.end(), FastRandomContext());
     }
-    bool res = value_to_select <= 0 ||
-        SelectCoinsMinConf(value_to_select, CoinEligibilityFilter(1, 6, 0), vCoins, setCoinsRet, nValueRet, coin_selection_params, bnb_used) ||
-        SelectCoinsMinConf(value_to_select, CoinEligibilityFilter(1, 1, 0), vCoins, setCoinsRet, nValueRet, coin_selection_params, bnb_used) ||
-        (m_spend_zero_conf_change && SelectCoinsMinConf(value_to_select, CoinEligibilityFilter(0, 1, 2), vCoins, setCoinsRet, nValueRet, coin_selection_params, bnb_used)) ||
-        (m_spend_zero_conf_change && SelectCoinsMinConf(value_to_select, CoinEligibilityFilter(0, 1, std::min((size_t)4, max_ancestors/3), std::min((size_t)4, max_descendants/3)), vCoins, setCoinsRet, nValueRet, coin_selection_params, bnb_used)) ||
-        (m_spend_zero_conf_change && SelectCoinsMinConf(value_to_select, CoinEligibilityFilter(0, 1, max_ancestors/2, max_descendants/2), vCoins, setCoinsRet, nValueRet, coin_selection_params, bnb_used)) ||
-        (m_spend_zero_conf_change && SelectCoinsMinConf(value_to_select, CoinEligibilityFilter(0, 1, max_ancestors-1, max_descendants-1, true /* include_partial_groups */), vCoins, setCoinsRet, nValueRet, coin_selection_params, bnb_used)) ||
-        (m_spend_zero_conf_change && !fRejectLongChains && SelectCoinsMinConf(value_to_select, CoinEligibilityFilter(0, 1, std::numeric_limits<uint64_t>::max(), std::numeric_limits<uint64_t>::max(), true /* include_partial_groups */), vCoins, setCoinsRet, nValueRet, coin_selection_params, bnb_used));
 
+    // Attempt to select coins from a pool of available Coins, applying a CoinEligibilityFilter. If an attempt fails, continue with a more permissive filter.
+    const bool res = [&] {
+        if (value_to_select <= 0) return true;
+
+        // If possible, fund the transaction with confirmed UTXOs only. Prefer at least six confirmations on outputs received from other wallets.
+        if (SelectCoinsMinConf(value_to_select, CoinEligibilityFilter(1, 6, 0), vCoins, setCoinsRet, nValueRet, coin_selection_params, bnb_used)) return true;
+        if (SelectCoinsMinConf(value_to_select, CoinEligibilityFilter(1, 1, 0), vCoins, setCoinsRet, nValueRet, coin_selection_params, bnb_used)) return true;
+
+        // Fall back to using zero confirmation change if we cannot fund the transaction otherwise.
+        // We never spend unconfirmed outputs received from other wallets.
+        if (m_spend_zero_conf_change) {
+            if (SelectCoinsMinConf(value_to_select, CoinEligibilityFilter(0, 1, 2), vCoins, setCoinsRet, nValueRet, coin_selection_params, bnb_used)) return true;
+            if (SelectCoinsMinConf(value_to_select, CoinEligibilityFilter(0, 1, std::min((size_t)4, max_ancestors/3), std::min((size_t)4, max_descendants/3)),
+                                   vCoins, setCoinsRet, nValueRet, coin_selection_params, bnb_used)) {
+                return true;
+            }
+            if (SelectCoinsMinConf(value_to_select, CoinEligibilityFilter(0, 1, max_ancestors/2, max_descendants/2),
+                                   vCoins, setCoinsRet, nValueRet, coin_selection_params, bnb_used)) {
+                return true;
+            }
+            // Relax the requirement of spending OutputGroups (groups of UTXOs sent to the same 
+            // address, which are obviously controlled by a single wallet) in their entirety.
+            if (SelectCoinsMinConf(value_to_select, CoinEligibilityFilter(0, 1, max_ancestors-1, max_descendants-1, true /* include_partial_groups */),
+                                   vCoins, setCoinsRet, nValueRet, coin_selection_params, bnb_used)) {
+                return true;
+            }
+            // Try with unlimited ancestors/descendants. Note that the tx will still need to 
+            // meet mempool ancestor/descendant policy to be broadcasted.
+            if (!fRejectLongChains &&
+                SelectCoinsMinConf(value_to_select,
+                                   CoinEligibilityFilter(0, 1, std::numeric_limits<uint64_t>::max(),
+                                                         std::numeric_limits<uint64_t>::max(),
+                                                         true /* include_partial_groups */),
+                                   vCoins, setCoinsRet, nValueRet, coin_selection_params, bnb_used)) {
+                return true;
+            }
+        }
+        // Coin Selection failed.
+        return false;
+    }();
+
     // because SelectCoinsMinConf clears the setCoinsRet, we now add the possible inputs to the coinset
     util::insert(setCoinsRet, setPresetCoins);