Merge bitcoin#30592: Remove mempoolfullrbf

c189eec doc: release note for mempoolrullrbf removal (Greg Sanders)
d47297c rpc: Mark fullrbf and bip125-replaceable as deprecated (Greg Sanders)
04a5dce docs: remove requirement to signal bip125 (Greg Sanders)
111a23d Remove -mempoolfullrbf option (Greg Sanders)

Pull request description:

  Given bitcoin#30493 and the related discussion on network uptake it's probably not helpful to have an option for a feature that will not be respected by the network in any meaningful way.

  Wallet changes can be done in another PR on its own cadence to account for possible fingerprinting, waiting for fullrbf logic to permeate the network, etc.

ACKs for top commit:
  stickies-v:
    re-ACK c189eec
  achow101:
    ACK c189eec
  murchandamus:
    ACK c189eec
  rkrux:
    reACK c189eec

Tree-SHA512: 9447f88f8f291c56c5bde70af0a91b0a4f5163aaaf173370fbfdaa3c3fd0b44120b14d3a1977f7ee10e27ffe9453f8a70dd38aad0ffb8c39cf145049d2550730

doc/bips.md

@@ -34,7 +34,6 @@ BIPs that are implemented by Bitcoin Core:
 * [`BIP 111`](https://github.com/bitcoin/bips/blob/master/bip-0111.mediawiki): `NODE_BLOOM` service bit added, and enforced for all peer versions as of **v0.13.0** ([PR #6579](https://github.com/bitcoin/bitcoin/pull/6579) and [PR #6641](https://github.com/bitcoin/bitcoin/pull/6641)).
 * [`BIP 112`](https://github.com/bitcoin/bips/blob/master/bip-0112.mediawiki): The CHECKSEQUENCEVERIFY opcode has been implemented since **v0.12.1** ([PR #7524](https://github.com/bitcoin/bitcoin/pull/7524)), and has been *buried* since **v0.19.0** ([PR #16060](https://github.com/bitcoin/bitcoin/pull/16060)).
 * [`BIP 113`](https://github.com/bitcoin/bips/blob/master/bip-0113.mediawiki): Median time past lock-time calculations have been implemented since **v0.12.1** ([PR #6566](https://github.com/bitcoin/bitcoin/pull/6566)), and has been *buried* since **v0.19.0** ([PR #16060](https://github.com/bitcoin/bitcoin/pull/16060)).
-* [`BIP 125`](https://github.com/bitcoin/bips/blob/master/bip-0125.mediawiki): Opt-in full replace-by-fee partially implemented: signaling is enforced if configured. For other replacement rules, see doc/policy/mempool-replacements.md.
 * [`BIP 130`](https://github.com/bitcoin/bips/blob/master/bip-0130.mediawiki): direct headers announcement is negotiated with peer versions `>=70012` as of **v0.12.0** ([PR 6494](https://github.com/bitcoin/bitcoin/pull/6494)).
 * [`BIP 133`](https://github.com/bitcoin/bips/blob/master/bip-0133.mediawiki): feefilter messages are respected and sent for peer versions `>=70013` as of **v0.13.0** ([PR 7542](https://github.com/bitcoin/bitcoin/pull/7542)).
 * [`BIP 141`](https://github.com/bitcoin/bips/blob/master/bip-0141.mediawiki): Segregated Witness (Consensus Layer) as of **v0.13.0** ([PR 8149](https://github.com/bitcoin/bitcoin/pull/8149)), defined for mainnet as of **v0.13.1** ([PR 8937](https://github.com/bitcoin/bitcoin/pull/8937)), and *buried* since **v0.19.0** ([PR #16060](https://github.com/bitcoin/bitcoin/pull/16060)).

doc/policy/mempool-replacements.md

@@ -10,12 +10,7 @@ A transaction ("replacement transaction") may replace its directly conflicting t
 their in-mempool descendants (together, "original transactions") if, in addition to passing all
 other consensus and policy rules, each of the following conditions are met:
 
-1. If `-mempoolfullrbf=0` (the value is 1 by default), the directly conflicting transactions all signal replaceability explicitly. A transaction is
-   signaling BIP125 replaceability if any of its inputs have an nSequence number less than (0xffffffff - 1).
-   A transaction also signals replaceability if its version field is set to 3.
-
-   *Rationale*: See [BIP125
-   explanation](https://github.com/bitcoin/bips/blob/master/bip-0125.mediawiki#motivation).
+1. (Removed)
 
 2. The replacement transaction only include an unconfirmed input if that input was included in
    one of the directly conflicting transactions. An unconfirmed input spends an output from a
@@ -80,3 +75,5 @@ This set of rules is similar but distinct from BIP125.
   #25353](https://github.com/bitcoin/bitcoin/pull/25353)).
 
 * Full replace-by-fee is the default policy as of **v28.0** ([PR #30493](https://github.com/bitcoin/bitcoin/pull/30493)).
+
+* Signaling for replace-by-fee is no longer required as of [PR 30592](https://github.com/bitcoin/bitcoin/pull/30592).

doc/policy/packages.md

@@ -38,8 +38,6 @@ The following rules are enforced for all packages:
 
 * Only limited package replacements are currently considered. (#28984)
 
-   - If `-mempoolfullrbf=0` (the value is 1 by default), all direct conflicts must signal replacement.
-
    - Packages are 1-parent-1-child, with no in-mempool ancestors of the package.
 
    - All conflicting clusters (connected components of mempool transactions) must be clusters of up to size 2.

doc/release-notes-30592.md

@@ -0,0 +1,7 @@
+Full Replace-By-Fee
+===================
+
+Starting with v28.0, the `mempoolfullrbf` startup option was set to
+default to `1`. With widespread adoption of this policy, users no longer
+benefit from disabling it, so the option has been removed, making full
+replace-by-fee the standard behavior. (#30592)

src/init.cpp

@@ -637,7 +637,6 @@ void SetupServerArgs(ArgsManager& argsman, bool can_listen_ipc)
                              "is of this size or less (default: %u)",
                              MAX_OP_RETURN_RELAY),
                    ArgsManager::ALLOW_ANY, OptionsCategory::NODE_RELAY);
-    argsman.AddArg("-mempoolfullrbf", strprintf("(DEPRECATED) Accept transaction replace-by-fee without requiring replaceability signaling (default: %u)", DEFAULT_MEMPOOL_FULL_RBF), ArgsManager::ALLOW_ANY, OptionsCategory::NODE_RELAY);
     argsman.AddArg("-permitbaremultisig", strprintf("Relay transactions creating non-P2SH multisig outputs (default: %u)", DEFAULT_PERMIT_BAREMULTISIG), ArgsManager::ALLOW_ANY,
                    OptionsCategory::NODE_RELAY);
     argsman.AddArg("-minrelaytxfee=<amt>", strprintf("Fees (in %s/kvB) smaller than this are considered zero fee for relaying, mining and transaction creation (default: %s)",

src/kernel/mempool_options.h

@@ -21,8 +21,6 @@ static constexpr unsigned int DEFAULT_MAX_MEMPOOL_SIZE_MB{300};
 static constexpr unsigned int DEFAULT_BLOCKSONLY_MAX_MEMPOOL_SIZE_MB{5};
 /** Default for -mempoolexpiry, expiration time for mempool transactions in hours */
 static constexpr unsigned int DEFAULT_MEMPOOL_EXPIRY_HOURS{336};
-/** Default for -mempoolfullrbf, if the transaction replaceability signaling is ignored */
-static constexpr bool DEFAULT_MEMPOOL_FULL_RBF{true};
 /** Whether to fall back to legacy V1 serialization when writing mempool.dat */
 static constexpr bool DEFAULT_PERSIST_V1_DAT{false};
 /** Default for -acceptnonstdtxn */
@@ -55,7 +53,6 @@ struct MemPoolOptions {
     std::optional<unsigned> max_datacarrier_bytes{DEFAULT_ACCEPT_DATACARRIER ? std::optional{MAX_OP_RETURN_RELAY} : std::nullopt};
     bool permit_bare_multisig{DEFAULT_PERMIT_BAREMULTISIG};
     bool require_standard{true};
-    bool full_rbf{DEFAULT_MEMPOOL_FULL_RBF};
     bool persist_v1_dat{DEFAULT_PERSIST_V1_DAT};
     MemPoolLimits limits{};
 

src/node/mempool_args.cpp

@@ -92,11 +92,6 @@ util::Result<void> ApplyArgsManOptions(const ArgsManager& argsman, const CChainP
         return util::Error{strprintf(Untranslated("acceptnonstdtxn is not currently supported for %s chain"), chainparams.GetChainTypeString())};
     }
 
-    mempool_opts.full_rbf = argsman.GetBoolArg("-mempoolfullrbf", mempool_opts.full_rbf);
-    if (!mempool_opts.full_rbf) {
-        LogInfo("Warning: mempoolfullrbf=0 set but deprecated and will be removed in a future release\n");
-    }
-
     mempool_opts.persist_v1_dat = argsman.GetBoolArg("-persistmempoolv1", mempool_opts.persist_v1_dat);
 
     ApplyArgsManOptions(argsman, mempool_opts.limits);

src/rpc/mempool.cpp

@@ -277,7 +277,7 @@ static std::vector<RPCResult> MempoolEntryDescription()
             {RPCResult{RPCResult::Type::STR_HEX, "transactionid", "parent transaction id"}}},
         RPCResult{RPCResult::Type::ARR, "spentby", "unconfirmed transactions spending outputs from this transaction",
             {RPCResult{RPCResult::Type::STR_HEX, "transactionid", "child transaction id"}}},
-        RPCResult{RPCResult::Type::BOOL, "bip125-replaceable", "Whether this transaction signals BIP125 replaceability or has an unconfirmed ancestor signaling BIP125 replaceability.\n"},
+        RPCResult{RPCResult::Type::BOOL, "bip125-replaceable", "Whether this transaction signals BIP125 replaceability or has an unconfirmed ancestor signaling BIP125 replaceability. (DEPRECATED)\n"},
         RPCResult{RPCResult::Type::BOOL, "unbroadcast", "Whether this transaction is currently unbroadcast (initial broadcast not yet acknowledged by any peers)"},
     };
 }
@@ -682,7 +682,7 @@ UniValue MempoolInfoToJSON(const CTxMemPool& pool)
     ret.pushKV("minrelaytxfee", ValueFromAmount(pool.m_opts.min_relay_feerate.GetFeePerK()));
     ret.pushKV("incrementalrelayfee", ValueFromAmount(pool.m_opts.incremental_relay_feerate.GetFeePerK()));
     ret.pushKV("unbroadcastcount", uint64_t{pool.GetUnbroadcastTxs().size()});
-    ret.pushKV("fullrbf", pool.m_opts.full_rbf);
+    ret.pushKV("fullrbf", true);
     return ret;
 }
 
@@ -704,7 +704,7 @@ static RPCHelpMan getmempoolinfo()
                 {RPCResult::Type::STR_AMOUNT, "minrelaytxfee", "Current minimum relay fee for transactions"},
                 {RPCResult::Type::NUM, "incrementalrelayfee", "minimum fee rate increment for mempool limiting or replacement in " + CURRENCY_UNIT + "/kvB"},
                 {RPCResult::Type::NUM, "unbroadcastcount", "Current number of transactions that haven't passed initial broadcast yet"},
-                {RPCResult::Type::BOOL, "fullrbf", "True if the mempool accepts RBF without replaceability signaling inspection"},
+                {RPCResult::Type::BOOL, "fullrbf", "True if the mempool accepts RBF without replaceability signaling inspection (DEPRECATED)"},
             }},
         RPCExamples{
             HelpExampleCli("getmempoolinfo", "")

src/validation.cpp

@@ -816,30 +816,10 @@ bool MemPoolAccept::PreChecks(ATMPArgs& args, Workspace& ws)
         const CTransaction* ptxConflicting = m_pool.GetConflictTx(txin.prevout);
         if (ptxConflicting) {
             if (!args.m_allow_replacement) {
-                // Transaction conflicts with a mempool tx, but we're not allowing replacements.
+                // Transaction conflicts with a mempool tx, but we're not allowing replacements in this context.
                 return state.Invalid(TxValidationResult::TX_MEMPOOL_POLICY, "bip125-replacement-disallowed");
             }
-            if (!ws.m_conflicts.count(ptxConflicting->GetHash()))
-            {
-                // Transactions that don't explicitly signal replaceability are
-                // *not* replaceable with the current logic, even if one of their
-                // unconfirmed ancestors signals replaceability. This diverges
-                // from BIP125's inherited signaling description (see CVE-2021-31876).
-                // Applications relying on first-seen mempool behavior should
-                // check all unconfirmed ancestors; otherwise an opt-in ancestor
-                // might be replaced, causing removal of this descendant.
-                //
-                // All TRUC transactions are considered replaceable.
-                //
-                // Replaceability signaling of the original transactions may be
-                // ignored due to node setting.
-                const bool allow_rbf{m_pool.m_opts.full_rbf || SignalsOptInRBF(*ptxConflicting) || ptxConflicting->version == TRUC_VERSION};
-                if (!allow_rbf) {
-                    return state.Invalid(TxValidationResult::TX_MEMPOOL_POLICY, "txn-mempool-conflict");
-                }
-
-                ws.m_conflicts.insert(ptxConflicting->GetHash());
-            }
+            ws.m_conflicts.insert(ptxConflicting->GetHash());
         }
     }