-multi_data_permitted: Allow >1 op_return output by policy

src/chainparams.cpp

@@ -154,6 +154,7 @@ public:
         consensus.connect_genesis_outputs = false;
         anyonecanspend_aremine = false;
         enforce_pak = false;
+        multi_data_permitted = false;
 
         /**
          * The message start string is designed to be unlikely to occur in normal data.
@@ -273,6 +274,7 @@ public:
         consensus.connect_genesis_outputs = false;
         anyonecanspend_aremine = false;
         enforce_pak = false;
+        multi_data_permitted = false;
 
         pchMessageStart[0] = 0x0b;
         pchMessageStart[1] = 0x11;
@@ -367,6 +369,7 @@ public:
         consensus.connect_genesis_outputs = false;
         anyonecanspend_aremine = false;
         enforce_pak = false;
+        multi_data_permitted = false;
 
         pchMessageStart[0] = 0xfa;
         pchMessageStart[1] = 0xbf;
@@ -547,6 +550,9 @@ class CCustomParams : public CRegTestParams {
 
         enforce_pak = args.GetBoolArg("-enforce_pak", false);
 
+        // Allow multiple op_return outputs by relay policy
+        multi_data_permitted = args.GetBoolArg("-multi_data_permitted", true);
+
         // bitcoin regtest is the parent chain by default
         parentGenesisBlockHash = uint256S(args.GetArg("-parentgenesisblockhash", "0f9188f13cb7b2c71f2a335e3a4fc328bf5beb436012afca590b1a11466e2206"));
         // Either it has a parent chain or not

src/chainparams.h

@@ -88,6 +88,7 @@ public:
     bool anyonecanspend_aremine;
     const std::string& ParentBech32HRP() const { return parent_bech32_hrp; }
     bool GetEnforcePak() const { return enforce_pak; }
+    bool GetMultiDataPermitted() const { return multi_data_permitted; }
 
 protected:
     CChainParams() {}
@@ -113,6 +114,7 @@ protected:
     uint256 parentGenesisBlockHash;
     std::string parent_bech32_hrp;
     bool enforce_pak;
+    bool multi_data_permitted;
 };
 
 /**

src/chainparamsbase.cpp

@@ -39,6 +39,7 @@ void SetupChainParamsBaseOptions()
 
     gArgs.AddArg("-fedpegscript", "The script for the federated peg.", false, OptionsCategory::CHAINPARAMS);
     gArgs.AddArg("-enforce_pak", "Causes standardness checks to enforce Pegout Authorization Key(PAK) validation, and miner to include PAK commitments when configured. Can not be set when acceptnonstdtx is set to true.", false, OptionsCategory::ELEMENTS);
+    gArgs.AddArg("-multi_data_permitted", "Allow relay of multiple OP_RETURN outputs. (default: true)", false, OptionsCategory::ELEMENTS);
 }
 
 static std::unique_ptr<CBaseChainParams> globalChainBaseParams;

src/policy/policy.cpp

@@ -149,7 +149,7 @@ bool IsStandardTx(const CTransaction& tx, std::string& reason)
     }
 
     // only one OP_RETURN txout is permitted
-    if (nDataOut > 1) {
+    if (!params.GetMultiDataPermitted() && nDataOut > 1) {
         reason = "multi-op-return";
         return false;
     }

test/bitcoin_functional/functional/test_framework/util.py

@@ -311,6 +311,7 @@ def initialize_datadir(dirname, n, chain):
         f.write("anyonecanspendaremine=0\n")
         f.write("con_blockheightinheader=0\n")
         f.write("con_signed_blocks=0\n")
+        f.write("multi_data_permitted=0\n")
         f.write("walletrbf=0\n") # Default is 1 in Elements
         f.write("con_bip34height=100000000\n")
         f.write("con_bip65height=1351\n")

test/functional/mempool_accept.py

@@ -260,11 +260,12 @@ class MempoolAcceptanceTest(BitcoinTestFramework):
             result_expected=[{'txid': tx.rehash(), 'allowed': False, 'reject-reason': '64: dust'}],
             rawtxs=[bytes_to_hex_str(tx.serialize())],
         )
+        # Elements: We allow multi op_return outputs by default. This still fails because relay fee isn't met
         tx.deserialize(BytesIO(hex_str_to_bytes(raw_tx_reference)))
         tx.vout[0].scriptPubKey = CScript([OP_RETURN, b'\xff'])
         tx.vout = [tx.vout[0]] * 2
         self.check_mempool_result(
-            result_expected=[{'txid': tx.rehash(), 'allowed': False, 'reject-reason': '64: multi-op-return'}],
+                result_expected=[{'txid': tx.rehash(), 'allowed': False, 'reject-reason': '66: min relay fee not met'}],
             rawtxs=[bytes_to_hex_str(tx.serialize())],
         )