Reduced Data Temporary Softfork, implemented as a modified BIP9 temporary UASF #238

dathonohm · 2025-11-24T22:13:14Z

This PR re-implements #234 as a UASF rather than an MASF. That is, it adds:

a max_activation_height which is mutually exclusive with timeout, and
a BIP148/BIP8-style mandatory signaling period leading up to lock-in.

Commits prior to "Add DEPLOYMENT_REDUCED_DATA as temporary BIP9 UASF" do not compile; this is intentional to preserve all REDUCED_DATA commits precisely after dropping the original BuriedDeployment commits.

Commits prior to "Add mainnet configuration for REDUCED_DATA deployment" have failing unit tests.

Functional tests are passing on all commits.

Not eligibile for merge until the following are complete:

Rebase on v29.2.knots20251110
Fix CI failures

GregTonoski · 2025-11-25T12:46:41Z

Let me suggest adding a note that OP_RETURN is deprecated in help texts, please.

src/validation.cpp

src/script/interpreter.cpp

cal-gooo · 2025-11-30T14:33:49Z

what's the timeline to get this merged so the signaling can use this implementation?

dathonohm · 2025-12-01T15:34:54Z

There is no specific timeline to get this merged into Knots, as it is not confirmed that it will be eligible for merging, even when complete. However, I am aiming to have this draft ready for review in the next few days.

Miner signaling can still use this deployment if the activation client is released after the start of the signaling period (which is today, so this will definitely happen).

dathonohm · 2025-12-02T21:52:52Z

All comments from #234 are now addressed.

Undrafting since the code is relatively stable now.

Still needs rebase.

dathonohm · 2025-12-02T22:05:06Z

@GregTonoski

Let me suggest adding a note that OP_RETURN is deprecated in help texts, please.

OP_RETURN is not deprecated; it is merely limited to 83 bytes in consensus.

…logic

…to reduce data push size limit to 256 bytes (except for P2SH redeemScript push)

…TA (still unused)

… (still unused)

…ill unused)

…DUCED_DATA (still unused)

…ATA is active (still never)

…o cap output scripts at 83 bytes

…l never), limit non-OP_RETURN scripts to 34 bytes

… p2pkh

…to expected memory usage

…r than exceed MAX_OP_RETURN_RELAY

…T_REDUCED_DATA is active (never yet)

…BLE_WITNESS_PROGRAM,UPGRADABLE_TAPROOT_VERSION,OP_SUCCESS}

…AM,UPGRADABLE_TAPROOT_VERSION,OP_SUCCESS} on blocks when DEPLOYMENT_REDUCED_DATA is active (never yet)

Add NODE_BIP444 flag to GetDesirableServiceFlags assertions in peerman_tests and to service flags in denialofservice_tests and net_tests peer setup. NODE_BIP444 (bit 27) signals BIP444/REDUCED_DATA enforcement and is now included in desirable service flags alongside NODE_NETWORK and NODE_WITNESS for peer connections.

dathonohm · 2025-12-03T05:39:45Z

Rebased on v29.2.knots20251110.

Ready for review.

stackingsaunter · 2025-12-03T20:03:23Z

Concept NACK

There shouldn't be any emergency softfork to address spam without at least a sketeched out permanent solution

dathonohm · 2025-12-03T20:44:32Z

@stackingsaunter Please keep conceptual discussion to the BIP PR. This PR is for code review only.

src/script/interpreter.cpp

src/validation.cpp

src/script/interpreter.cpp

src/validation.cpp

src/kernel/chainparams.cpp

src/deploymentstatus.h

src/validation.cpp

kwsantiago · 2025-12-03T20:55:50Z

src/deploymentstatus.h

+    if (ThresholdState::ACTIVE != versionbitscache.State(index.pprev, params, dep)) return false;
+
+    const auto& deployment = params.vDeployments[dep];
+    // Permanent deployment (never expires)
+    if (deployment.active_duration == std::numeric_limits<int>::max()) return true;
+
+    const int activation_height = versionbitscache.StateSinceHeight(index.pprev, params, dep);
+    return index.nHeight < activation_height + deployment.active_duration;


StateSinceHeight() is called even when State() returns ACTIVE. If the deployment transitions from ACTIVE back to some other state (due to code changes or reorg), StateSinceHeight may return unexpected values.

Should we be caching the state check result and passing it to avoid redundant cache lookups?

Can you elaborate on your concern here? StateSinceHeight() is only called when State() returns ACTIVE. In the scenario where the state is ACTIVE then later not active, locks should guarantee that the versionbits cache doesn't change between these two calls.

Let me know if I'm misunderstanding your question.

src/chainparams.cpp

…_data.py

DEBUG=1 in depends is already tested in the CI job "previous releases, depends DEBUG". Testing with DEBUG=1 is considered equivalent in these two CI jobs in Bitcoin Core PR bitcoin#32560, which thus does effectively the reverse of this commit.

luke-jr

Review not complete yet

src/deploymentstatus.h

luke-jr · 2025-12-13T11:50:52Z

src/rpc/blockchain.cpp

        {RPCResult::Type::NUM_TIME, "start_time", "the minimum median time past of a block at which the bit gains its meaning"},
        {RPCResult::Type::NUM_TIME, "timeout", "the median time past of a block at which the deployment is considered failed if not yet locked in"},
        {RPCResult::Type::NUM, "min_activation_height", "minimum height of blocks for which the rules may be enforced"},
+        {RPCResult::Type::NUM, "max_activation_height", "height at which the deployment will activate (2147483647 if not set)"},


Seems like it would be better to omit the field entirely, rather than return maxint when unused.

Will change this field only to be populated when used.

luke-jr · 2025-12-13T11:51:05Z

src/rpc/blockchain.cpp

        {RPCResult::Type::NUM_TIME, "start_time", "the minimum median time past of a block at which the bit gains its meaning"},
        {RPCResult::Type::NUM_TIME, "timeout", "the median time past of a block at which the deployment is considered failed if not yet locked in"},
        {RPCResult::Type::NUM, "min_activation_height", "minimum height of blocks for which the rules may be enforced"},
+        {RPCResult::Type::NUM, "max_activation_height", "height at which the deployment will activate (2147483647 if not set)"},


nit: "not set" is phrased poorly IMO

How's this: "height at which the deployment will unconditionally activate", and the parameter is now marked as optional?

luke-jr · 2025-12-13T11:52:19Z

src/rpc/blockchain.cpp

+    bip9.pushKV("max_activation_height", chainman.GetConsensus().vDeployments[id].max_activation_height);

    // BIP9 status
    bip9.pushKV("status", get_state_name(current_state));


I think "status_next" (below) won't work correctly for expiring softforks.

Yes, currently the BIP9 state machine treats this deployment as permanently active, even though in practice the rules stop being enforced at the expiry height.

I can add an "EXPIRED" state to the next version of the activation code, if you think this is a good idea. It just seemed unnecessary for this version.

luke-jr · 2025-12-13T11:53:06Z

src/rpc/blockchain.cpp

+    bip9.pushKV("max_activation_height", chainman.GetConsensus().vDeployments[id].max_activation_height);

    // BIP9 status
    bip9.pushKV("status", get_state_name(current_state));


Suggest adding a "height_end" with the final enforcement block height, for temporary softforks.

Added in the next update

luke-jr · 2025-12-20T19:45:25Z

src/versionbits.cpp

+                    // Overrides timeout to guarantee activation
                    stateNext = ThresholdState::LOCKED_IN;
                } else if (pindexPrev->GetMedianTimePast() >= nTimeTimeout) {
+                    // Timeout without activation (only if max_activation_height not set)


This comment is wrong. If nTimeTimeout is set, it can still trigger a failure if it's reached before max_activation_height - nPeriod

max_activation_height is intended to be mutually exclusive with timeout. Currently there is no validation code to check this for mainnet deployments, but I can add it if you think this is necessary.

See: #238 (comment)

luke-jr · 2025-12-20T20:09:54Z

src/chainparams.cpp

                options.version_bits_parameters[Consensus::DeploymentPos(j)] = vbparams;
                found = true;
-                LogPrintf("Setting version bits activation parameters for %s to start=%ld, timeout=%ld, min_activation_height=%d\n", vDeploymentParams[0], vbparams.start_time, vbparams.timeout, vbparams.min_activation_height);
+                LogPrintf("Setting version bits activation parameters for %s to start=%ld, timeout=%ld, min_activation_height=%d, max_activation_height=%d\n", vDeploymentParams[0], vbparams.start_time, vbparams.timeout, vbparams.min_activation_height, vbparams.max_activation_height);


Should probably include duration?

…duration

…_data to 55%

…ensus limit; add reduced_data deployment name to allow regtest RPC access for testing

…YMENT_REDUCED_DATA); adapt 6 tests to NODE_BIP148 service flag; add assert_equal_without_usage helper for testmempoolaccept results

dathonohm · 2026-01-03T03:01:27Z

All review comments are now addressed.

CI is now fully passing (except for the "test each commit" job).

A tag has been created for the current version, RC2 (identical to this branch except for the last commit, which updates the UA string for BIP-110).

Next I will make a release for RC2, and clean up the commit history here.

dathonohm mentioned this pull request Nov 24, 2025

ReducedData Temporary Softfork #234

Closed

kwsantiago reviewed Nov 25, 2025

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dathonohm mentioned this pull request Nov 26, 2025

BIP 110: Reduced Data Temporary Softfork bitcoin/bips#2017

Open

dathonohm marked this pull request as ready for review December 2, 2025 23:29

luke-jr added 21 commits December 2, 2025 21:32

Use TAPROOT_CONTROL_MAX_NODE_COUNT_REDUCED for non-consensus Taproot …

4726200

…logic

Policy: Enforce SCRIPT_VERIFY_REDUCED_DATA as a policy rule

f67c78c

script: Define SCRIPT_VERIFY_REDUCED_DATA verification flag (unused) …

b9eb527

…to reduce data push size limit to 256 bytes (except for P2SH redeemScript push)

script: Limit Taproot annex to 256 bytes for SCRIPT_VERIFY_REDUCED_DA…

66fa459

…TA (still unused)

script: Forbid Taproot annex entirely with SCRIPT_VERIFY_REDUCED_DATA…

973857f

… (still unused)

script: Forbid OP_IF in Tapscript with SCRIPT_VERIFY_REDUCED_DATA (st…

91225d3

…ill unused)

script: Limit Taproot control block to 257 bytes for SCRIPT_VERIFY_RE…

c99487e

…DUCED_DATA (still unused)

consensus: Enforce SCRIPT_VERIFY_REDUCED_DATA if DEPLOYMENT_REDUCED_D…

53d86cb

…ATA is active (still never)

Limit datacarriersize config to MAX_OUTPUT_DATA_SIZE (=83 B)

46c7b08

consensus: Add no-op flags to CheckTxInputs function

a9cce00

consensus: Define CheckTxInputsRules::OutputSizeLimit flag (unused) t…

afe1748

…o cap output scripts at 83 bytes

consensus: When CheckTxInputsRules::OutputSizeLimit is enforced (stil…

485948c

…l never), limit non-OP_RETURN scripts to 34 bytes

QA: rpc_getdescriptoractivity: Use RAW_OP_TRUE for test_no_address

2bf1683

QA: test_framework/wallet: Turn MiniWalletMode.RAW_P2PK into actually…

1d6b283

… p2pkh

RPC/Mempool: Provide tx memory usage in testmempoolaccept

18610e5

QA: test_framework/mempool_util: Calibrate fill_mempool bulk tx size …

9cb379b

…to expected memory usage

Bugfix: QA: mempool_limit: Use "usage" rather than "bytes"

613a4ed

QA: test_framework: Use multiple OP_RETURNs to pad transactions rathe…

3c83333

…r than exceed MAX_OP_RETURN_RELAY

consensus: Enforce CheckTxInputsRules::OutputSizeLimit when DEPLOYMEN…

b5b1d22

…T_REDUCED_DATA is active (never yet)

Policy: Do not allow user to bypass SCRIPT_VERIFY_DISCOURAGE_{UPGRADA…

ff4abbb

…BLE_WITNESS_PROGRAM,UPGRADABLE_TAPROOT_VERSION,OP_SUCCESS}

consensus: Enforce SCRIPT_VERIFY_DISCOURAGE_{UPGRADABLE_WITNESS_PROGR…

7d5242e

…AM,UPGRADABLE_TAPROOT_VERSION,OP_SUCCESS} on blocks when DEPLOYMENT_REDUCED_DATA is active (never yet)

dathonohm added 4 commits December 2, 2025 22:57

Change all BIP444 references to UASF-ReducedData

51c5bcf

Add mainnet configuration for REDUCED_DATA deployment

bebbf97

Remove UASF uacomment for mainline Knots

d699af3

dathonohm force-pushed the uasf-modified-bip9 branch from df70e59 to d699af3 Compare December 3, 2025 05:38

kwsantiago reviewed Dec 3, 2025

View reviewed changes

Retropex and others added 8 commits December 23, 2025 10:57

test: Fix fuzz for miniscript.cpp

fc34075

test: change permission and remove some f-string in logs

870fb89

test: use the correct flag for ignore_rejects in feature_uasf_reduced…

f832fd9

…_data.py

policy: Fix unsigned integer underflow in GetPriority

d529f37

test: Add retry logic to mempool_limit for i686 race condition

5af60d9

fixup! Fix interface_bitcoin_cli test to accept BIP148 service bit

d617ac6

Fix false unknown deployment warning for Taproot on mainnet

ada8116

luke-jr requested changes Dec 23, 2025

View reviewed changes

dathonohm added 4 commits December 24, 2025 14:21

fixup! Add expiry support to versionbit deployments

b47322e

fixup! Add max_activation_height for mandatory BIP9 activation

7e067c7

fixup! Add expiry support to versionbit deployments

51babbe

fixup! Support regtest vbparams for max_activation_height and active_…

74cd5c5

…duration

dathonohm requested a review from luke-jr December 27, 2025 02:59

dathonohm and others added 5 commits December 29, 2025 15:14

Add per-deployment BIP9 threshold; restore global to 90%, set reduced…

1f6e3e8

…_data to 55%

Support regtest vbparams for per-deployment threshold

9605360

fixup! test: Adapt functional tests to MAX_OUTPUT_SCRIPT_SIZE=34 cons…

e7f3b9f

…ensus limit; add reduced_data deployment name to allow regtest RPC access for testing

squash! test: Skip test_segwit_versions subtest (conflicts with DEPLO…

094701a

…YMENT_REDUCED_DATA); adapt 6 tests to NODE_BIP148 service flag; add assert_equal_without_usage helper for testmempoolaccept results

net: ask DNS seed for x8000009

5a54af7

dathonohm force-pushed the uasf-modified-bip9 branch from 994b2fe to 5a54af7 Compare January 1, 2026 01:33

Reduced Data Temporary Softfork, implemented as a modified BIP9 temporary UASF #238

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