[rpc/node] check for high fee before ATMP in clients

Check absurd fee in BroadcastTransaction and RPC,
return TransactionError::MAX_FEE_EXCEEDED instead
of TxValidationResult::TX_NOT_STANDARD because this
is client preference, not a node-wide policy.

1 files changed, 27 insertions, 11 deletions

diff --git a/src/node/transaction.cpp b/src/node/transaction.cpp
index 9ae4700743..8162b79a0b 100644
--- a/src/node/transaction.cpp
+++ b/src/node/transaction.cpp
@@ -13,6 +13,18 @@
 
 #include <future>
 
+static TransactionError HandleATMPError(const TxValidationState& state, std::string& err_string_out) {
+    err_string_out = state.ToString();
+    if (state.IsInvalid()) {
+        if (state.GetResult() == TxValidationResult::TX_MISSING_INPUTS) {
+            return TransactionError::MISSING_INPUTS;
+        }
+        return TransactionError::MEMPOOL_REJECTED;
+    } else {
+        return TransactionError::MEMPOOL_ERROR;
+    }
+}
+
 TransactionError BroadcastTransaction(NodeContext& node, const CTransactionRef tx, std::string& err_string, const CAmount& max_tx_fee, bool relay, bool wait_callback)
 {
     // BroadcastTransaction can be called by either sendrawtransaction RPC or wallet RPCs.
@@ -36,20 +48,24 @@ TransactionError BroadcastTransaction(NodeContext& node, const CTransactionRef t
         if (!existingCoin.IsSpent()) return TransactionError::ALREADY_IN_CHAIN;
     }
     if (!node.mempool->exists(hashTx)) {
-        // Transaction is not already in the mempool. Submit it.
+        // Transaction is not already in the mempool.
         TxValidationState state;
-        if (!AcceptToMemoryPool(*node.mempool, state, tx,
-                                nullptr /* plTxnReplaced */, false /* bypass_limits */, max_tx_fee)) {
-            err_string = state.ToString();
-            if (state.IsInvalid()) {
-                if (state.GetResult() == TxValidationResult::TX_MISSING_INPUTS) {
-                    return TransactionError::MISSING_INPUTS;
-                }
-                return TransactionError::MEMPOOL_REJECTED;
-            } else {
-                return TransactionError::MEMPOOL_ERROR;
+        CAmount fee{0};
+        if (max_tx_fee) {
+            // First, call ATMP with test_accept and check the fee. If ATMP
+            // fails here, return error immediately.
+            if (!AcceptToMemoryPool(*node.mempool, state, tx,
+                nullptr /* plTxnReplaced */, false /* bypass_limits */, /* absurdfee*/ 0, /* test_accept */ true, &fee)) {
+                return HandleATMPError(state, err_string);
+            } else if (fee > max_tx_fee) {
+                return TransactionError::MAX_FEE_EXCEEDED;
             }
         }
+        // Try to submit the transaction to the mempool.
+        if (!AcceptToMemoryPool(*node.mempool, state, tx,
+                nullptr /* plTxnReplaced */, false /* bypass_limits */, max_tx_fee)) {
+            return HandleATMPError(state, err_string);
+        }
 
         // Transaction was accepted to the mempool.