From 04f270b4358417fc2827b9f91717816062b1864e Mon Sep 17 00:00:00 2001
From: David Gumberg <davidzgumberg@gmail.com>
Date: Tue, 18 Oct 2022 19:59:58 -0700
Subject: Add test for unspendable transactions and parameter 'maxburnamount'
 to sendrawtransaction.

'maxburnamount' sets a maximum value for outputs heuristically deemed unspendable including datacarrier scripts that begin with `OP_RETURN`.
---
 src/rpc/client.cpp  |  1 +
 src/rpc/mempool.cpp | 16 +++++++++++++++-
 2 files changed, 16 insertions(+), 1 deletion(-)

(limited to 'src/rpc')

diff --git a/src/rpc/client.cpp b/src/rpc/client.cpp
index 5fe914f0a1..eb91a151b5 100644
--- a/src/rpc/client.cpp
+++ b/src/rpc/client.cpp
@@ -114,6 +114,7 @@ static const CRPCConvertParam vRPCConvertParams[] =
     { "signrawtransactionwithkey", 2, "prevtxs" },
     { "signrawtransactionwithwallet", 1, "prevtxs" },
     { "sendrawtransaction", 1, "maxfeerate" },
+    { "sendrawtransaction", 2, "maxburnamount" },
     { "testmempoolaccept", 0, "rawtxs" },
     { "testmempoolaccept", 1, "maxfeerate" },
     { "submitpackage", 0, "package" },
diff --git a/src/rpc/mempool.cpp b/src/rpc/mempool.cpp
index 44f7435a26..0e202a963d 100644
--- a/src/rpc/mempool.cpp
+++ b/src/rpc/mempool.cpp
@@ -18,6 +18,7 @@
 #include <rpc/server.h>
 #include <rpc/server_util.h>
 #include <rpc/util.h>
+#include <script/standard.h>
 #include <txmempool.h>
 #include <univalue.h>
 #include <util/moneystr.h>
@@ -44,7 +45,11 @@ static RPCHelpMan sendrawtransaction()
             {"hexstring", RPCArg::Type::STR_HEX, RPCArg::Optional::NO, "The hex string of the raw transaction"},
             {"maxfeerate", RPCArg::Type::AMOUNT, RPCArg::Default{FormatMoney(DEFAULT_MAX_RAW_TX_FEE_RATE.GetFeePerK())},
              "Reject transactions whose fee rate is higher than the specified value, expressed in " + CURRENCY_UNIT +
-                 "/kvB.\nSet to 0 to accept any fee rate.\n"},
+                 "/kvB.\nSet to 0 to accept any fee rate."},
+            {"maxburnamount", RPCArg::Type::AMOUNT, RPCArg::Default{FormatMoney(0)},
+             "Reject transactions with provably unspendable outputs (e.g. 'datacarrier' outputs that use the OP_RETURN opcode) greater than the specified value, expressed in " + CURRENCY_UNIT + ".\n"
+             "If burning funds through unspendable outputs is desired, increase this value.\n"
+             "This check is based on heuristics and does not guarantee spendability of outputs.\n"},
         },
         RPCResult{
             RPCResult::Type::STR_HEX, "", "The transaction hash in hex"
@@ -61,10 +66,19 @@ static RPCHelpMan sendrawtransaction()
                 },
         [&](const RPCHelpMan& self, const JSONRPCRequest& request) -> UniValue
         {
+            const CAmount max_burn_amount = request.params[2].isNull() ? 0 : AmountFromValue(request.params[2]);
+
             CMutableTransaction mtx;
             if (!DecodeHexTx(mtx, request.params[0].get_str())) {
                 throw JSONRPCError(RPC_DESERIALIZATION_ERROR, "TX decode failed. Make sure the tx has at least one input.");
             }
+
+            for (const auto& out : mtx.vout) {
+                if((out.scriptPubKey.IsUnspendable() || !out.scriptPubKey.HasValidOps()) && out.nValue > max_burn_amount) {
+                    throw JSONRPCTransactionError(TransactionError::MAX_BURN_EXCEEDED);
+                }
+            }
+
             CTransactionRef tx(MakeTransactionRef(std::move(mtx)));
 
             const CFeeRate max_raw_tx_fee_rate = request.params[1].isNull() ?
-- 
cgit v1.2.3