Merge #19339: validation: re-delegate absurd fee checking from mempool to clients

b048b275d9711f70847afaea5450f17a0f7e673a [validation] Remove absurdfee from accepttomempool (John Newbery)
932564b9cfda8446a957649c2316a52e868ad5d4 scripted-diff: update max-fee-exceeded error message to include RPC (gzhao408)
8f1290c60159a3171c27250bc95687548c5c1b84 [rpc/node] check for high fee before ATMP in clients (gzhao408)

Pull request description:

  Picked up from #15810. Add separate fee-checking logic for clients that need to enforce max fee rates, then remove the `absurdFee` logic from ATMP.

  ATMP's `nAbsurdFee` argument is used to enforce user-specific behavior (it is not policy since it isn't applied consistently: it is only ever used in RPC and wallet, and set to 0 everywhere else internally). It should be removed from `AcceptToMemoryPool` because (1) validation results/mempool behavior should not be user-specific and (2) enforcing a max fee rate should be the responsibility of the client instead of the mempool.

  Note: this PR does not intend to _remove_ protection from high fees, just re-delegate the responsibility to clients.

ACKs for top commit:
  jnewbery:
    utACK b048b275d9711f70847afaea5450f17a0f7e673a
  LarryRuane:
    re-ACK b048b275d9711f70847afaea5450f17a0f7e673a
  MarcoFalke:
    re-ACK b048b275d9 , only change is squashing one commit 🏦
  instagibbs:
    utACK https://github.com/bitcoin/bitcoin/pull/19339/commits/b048b275d9711f70847afaea5450f17a0f7e673a

Tree-SHA512: 57c17ba16d230a4cae2896dd6a64c924f307757824e35784bf96da7b10aff2d8ea910710edf35e981035623a155f8766209a92a0fdb856549fde78bc3eaae4d2

1 files changed, 10 insertions, 2 deletions

diff --git a/src/rpc/rawtransaction.cpp b/src/rpc/rawtransaction.cpp
index e60e0a2d90..7a6b605ec3 100644
--- a/src/rpc/rawtransaction.cpp
+++ b/src/rpc/rawtransaction.cpp
@@ -947,11 +947,19 @@ static RPCHelpMan testmempoolaccept()
 
     TxValidationState state;
     bool test_accept_res;
-    CAmount fee;
+    CAmount fee{0};
     {
         LOCK(cs_main);
         test_accept_res = AcceptToMemoryPool(mempool, state, std::move(tx),
-            nullptr /* plTxnReplaced */, false /* bypass_limits */, max_raw_tx_fee, /* test_accept */ true, &fee);
+            nullptr /* plTxnReplaced */, false /* bypass_limits */, /* test_accept */ true, &fee);
+    }
+
+    // Check that fee does not exceed maximum fee
+    if (test_accept_res && max_raw_tx_fee && fee > max_raw_tx_fee) {
+        result_0.pushKV("allowed", false);
+        result_0.pushKV("reject-reason", "max-fee-exceeded");
+        result.push_back(std::move(result_0));
+        return result;
     }
     result_0.pushKV("allowed", test_accept_res);