Many edge cases exist when parents in a child-with-parents package can
spend each other. However, this pattern should also be uncommon in
normal use cases.
While allowing submitted packages to be slightly larger than what
may be allowed in the mempool to allow simpler reasoning
about contextual-less checks vs chain limits.
32c1dd1ad6 [test] mempool coins disappearing mid-package evaluation (glozow)
a67f460c3f [refactor] split setup in mempool_limit test (glozow)
d08696120e [test framework] add ability to spend only confirmed utxos (glozow)
3ea71feb11 [validation] don't LimitMempoolSize in any subpackage submissions (glozow)
d227b7234c [validation] return correct result when already-in-mempool tx gets evicted (glozow)
9698b81828 [refactor] back-fill results in AcceptPackage (glozow)
8ad7ad3392 [validation] make PackageMempoolAcceptResult members mutable (glozow)
03b87c11ca [validation] add AcceptSubPackage to delegate Accept* calls and clean up m_view (glozow)
3f01a3dab1 [CCoinsViewMemPool] track non-base coins and allow Reset (glozow)
7d7f7a1189 [policy] check for duplicate txids in package (glozow)
Pull request description:
While we are evaluating a package, we split it into "subpackages" for evaluation (currently subpackages all have size 1 except the last one). If a subpackage has size 1, we may add a tx to mempool and call `LimitMempoolSize()`, which evicts transactions if the mempool gets full. We handle the case where the just-submitted transaction is evicted immediately, but we don't handle the case in which a transaction from a previous subpackage (either just submitted or already in mempool) is evicted. Mainly, since the coins created by the evicted transaction are cached in `m_view`, we don't realize the UTXO has disappeared until `CheckInputsFromMempoolAndCache` asserts that they exist. Also, the returned `PackageMempoolAcceptResult` reports that the transaction is in mempool even though it isn't anymore.
Fix this by not calling `LimitMempoolSize()` until the very end, and editing the results map with "mempool full" if things fall out.
Pointed out by instagibbs in faeed687e5 on top of the v3 PR.
ACKs for top commit:
instagibbs:
reACK 32c1dd1ad6
Tree-SHA512: 61e7f69db4712e5e5bfa27d037ab66bdd97f1bf60a8d9ffb96adb1f0609af012c810d681102ee5c7baec7b5fe8cb7c304a60c63ccc445d00d86a2b7f0e7ddb90
(1) Call AcceptSingleTransaction when there is only 1 transaction in the
subpackage. This avoids calling PackageMempoolChecks() which enforces
rules that don't need to be applied for a single transaction, i.e.
disabling CPFP carve out.
There is a slight change in the error type returned, as shown in the
txpackage_tests change. When a transaction is the last one left in the
package and its fee is too low, this returns a PCKG_TX instead of
PCKG_POLICY. This interface is clearer; "package-fee-too-low" for 1
transaction would be a bit misleading.
(2) Clean up m_view and m_viewmempool so that coins created in this
sub-package evaluation are not available for other sub-package
evaluations. The contents of the mempool may change, so coins that are
available now might not be later.
Duplicates of normal transactions would be found by looking for
conflicting inputs, but this doesn't catch identical empty transactions.
These wouldn't be valid but exiting early is good and AcceptPackage's
result sanity checks assume non-duplicate transactions.
Avoid adding transactions below min relay feerate because, even if they
were bumped through CPFP when entering the mempool, we do not have a
DoS-resistant way of ensuring they always remain bumped. In the future,
this rule can be relaxed (e.g. to allow packages to bump 0-fee
transactions) if we find a way to do so.
This makes the interface more predictable and useful. The caller
understands one or more transactions failed, and can learn what happened
with each transaction. We already have this information, so we might as
well return it.
It doesn't make sense to do this for other PackageValidationResult
values because:
- PCKG_RESULT_UNSET: this means everything succeeded, so the individual
failures are no longer accurate.
- PCKG_MEMPOOL_ERROR: something went wrong with the mempool logic;
transaction failures might not be meaningful.
- PCKG_POLICY: this means something was wrong with the package as a
whole. The caller should use the PackageValidationState to find the
error, rather than looking at individual MempoolAcceptResults.
This value creates an extremely confusing interface as its existence is
dependent upon implementation details (whether something was submitted
on its own, etc). MempoolAcceptResult::m_effective_feerate is much more
helpful, as it always exists for submitted transactions.
Makes the test more minimal. We're just trying to test that our package
sanitization logic is correct. Now that this code lives in its own
function (rather than inside of AcceptMultipleTransactions), there's no
need to call ProcessNewPackage to test this.
