wallet: Only broadcast resubmitted transactions that were added to the mempool #36482

pull achow101 wants to merge 5 commits into bitcoin:master from achow101:broadcasttx-if-new changing 5 files +163 −65

achow101 commented at 9:48 PM on October 8, 2026: member

As discussed in #36403, one of the issues with current rebroadcast behavior is that the rebroadcast begins an unconditional relay of a transaction to peers. While this is broadcast is limited to peers that have not previously been inv'd the transaction, there is still a privacy leak in this double relay of a transaction, especially so for transactions that are still in nodes' mempools.

This PR changes the rebroadcast to only rebroadcast transactions if the transaction was not already present in our mempool. This provides some additional privacy while retaining intended rebroadcast behavior as transactions that have likely fallen out of nodes' mempools are the ones that actually need to be rebroadcast.

The wallet rebroadcast tests are additionally refactored for isolation so that their behaviors can still be tested after this change. Additionally, a test for the loading resubmission was added, as well as a test for the new behavior.
test: Refactor wallet_resendwallettransactions for test case isolation 2121d61323
test: Test wallet unconfirmed resubmission on load 858be1c447

node: Add option to relay txs only if they are added to mempool

BroadcastTransaction takes different modes of broadcasting. Add one
which will attempt to add a transaction to the mempool, and if that
succeeds, broadcast the transaction to peers. If the transaction already
exists in the mempool, it will not be rebroadcast.

4446226ea9

wallet: Only rebroadcast transactions that were re-added to the mempool 8aed98fef4
test: Check that wallet txs already in the mempool are not rebroadcast 4dbd27f37b
DrahtBot added the label Wallet on Oct 8, 2026
DrahtBot commented at 9:48 PM on October 8, 2026: contributor


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External sites
- Code coverage & benchmarks: https://corecheck.dev/bitcoin/bitcoin/pulls/36482
- Ralph review <img src=https://review.fish.foo/assets/bitcoin/bitcoin/36482.png alt="Ralph review status"> https://git.fish.foo/bitcoin/bitcoin/pulls/36482#author-ralph


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Conflicts

Reviewers, this pull request conflicts with the following ones:
- #36540 <img src="https://drahtbot.space/ack_count/bitcoin/bitcoin/36540.svg"> (mempool: remove time-based transaction expiry by ismaelsadeeq)
- #36481 <img src="https://drahtbot.space/ack_count/bitcoin/bitcoin/36481.svg"> (wallet, rpc, gui: Allow users to manually rebroadcast a wallet transaction by achow101)
- #36398 <img src="https://drahtbot.space/ack_count/bitcoin/bitcoin/36398.svg"> (wallet: only rebroadcast transactions originating from the wallet by mzumsande)
- #36330 <img src="https://drahtbot.space/ack_count/bitcoin/bitcoin/36330.svg"> (wallet: don't resubmit transactions under -privatebroadcast by instagibbs)
- #36257 <img src="https://drahtbot.space/ack_count/bitcoin/bitcoin/36257.svg"> (qa: assert_equals -> assert_true/assert_false by hodlinator)
- #19461 <img src="https://drahtbot.space/ack_count/bitcoin/bitcoin/19461.svg"> (multiprocess: Add bitcoin-gui -ipcconnect option by ryanofsky)
- #19460 <img src="https://drahtbot.space/ack_count/bitcoin/bitcoin/19460.svg"> (multiprocess: Add bitcoin-wallet -ipcconnect option by ryanofsky)
- #10102 <img src="https://drahtbot.space/ack_count/bitcoin/bitcoin/10102.svg"> (Multiprocess bitcoin by ryanofsky)
If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.
polespinasa commented at 10:24 PM on October 8, 2026: member

concept ACK
in test/functional/wallet_resendwallettransactions.py:45 in 8aed98fef4
```
  41 | @@ -42,6 +42,19 @@ def mine_empty_block(self, node):
  42 |          block.solve()
  43 |          node.submitblock(block.serialize().hex())
  44 |  
  45 | +    def evict_mempool_transaction(self, conflict_utxo, node, wallet, indep_wallet):
```
mzumsande commented at 3:32 PM on October 9, 2026:

This replacement pattern with indep_utxo is just the mechanism that an attacker could do to probe for which nodes a given address belong to, so this doesn't appear to completely solve the receiver issue from #3828.

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#36403 Rethinking Transaction Rebroadcasting

wallet: Only broadcast resubmitted transactions that were added to the mempool #36482

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