fix(eth): release the state reference when stateAtTransaction gives up

[gzliudan]

stateAtTransaction obtains the parent state with StateAtBlock(..., readOnly=true), which takes a real reference on the live trie database whenever the state is available there, and hands a release function to its caller. Every path that gives up after that returns a nil release instead of calling it, so the reference is dropped rather than released:

• message build failure (base eth/state_accessor.go:249, now :261)
• replay failure (base :255, now :267)
• transaction index out of range (base :261, now :273)

The out of range path is the easiest one to hit: debug_traceTransaction with a bad index replays the whole block and then returns an error, leaking the reference taken on the live trie database. Nothing observes the leak — it is pure reference accounting, with no log, no panic and no failing assertion.

Fix

Take the release handle behind a guard that defaults to releasing and is cancelled only on the paths that hand the release over to the caller:

handedOff := false
defer func() {
    if !handedOff {
        release()
    }
}()

Only the two paths that return the state set handedOff = true, so a newly added error path cannot leak again.

Upstream

Historical issue rather than one introduced on top of the base: geth's stateAtTransaction (ethereum/go-ethereum@854fbb8ce, eth/state_accessor.go:232-277) drops the release on the same three error paths, so there is no upstream fix to port and no geth PR to reference.

Tests

TestStateAtTransactionGiveUpReturnsNoState drives the out of range path and pins what is observable from outside: the call returns nothing half-initialised (no transaction, no state and no release function). Whether the reference is actually released is deliberately not asserted — the release function is created inside StateAtBlock and cannot be observed or injected — so that part of the fix rests on the deferred block being executed, not on an assertion.

make all, go test ./eth/ -run TestStateAtTransaction, make quick-test, make test and gofmt are clean.

Relation to other work

A companion branch #2579 changes the replay inside this same function so that it follows the block processing routing. Both branches touch eth/state_accessor.go; merging this one first keeps the other a trivial rebase.

[coderabbitai]

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[Copilot]

🟡 Changes recommended

The regression test does not verify that the release callback executes and would pass without the fix.

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Pull request overview

Fixes leaked trie-state references when transaction-state replay exits with an error.

Changes:

• Releases acquired state unless ownership is returned to the caller.
• Adds an out-of-range transaction test.

File summaries

File	Description
eth/state_accessor.go	Guards state-reference ownership and cleanup.
eth/state_accessor_test.go	Exercises the out-of-range error path.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 1
• Review effort level: Balanced

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[Copilot]

🟢 Approval recommended

The focused guard correctly covers all post-acquisition error paths while preserving successful ownership transfer.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 0 new
• Review effort level: Balanced