fuzz: share a single mocked steady clock across FuzzedSock instances #35536

1. 
   HowHsu commented at 4:05 PM on June 15, 2026: contributor

   This is a follow-up of #35478 (comment), inspired by maflcko .

   Each FuzzedSock used to own its mocked steady clock and call MockableSteadyClock::SetMockTime() directly. Hold the clock by reference to an externally provided SteadyClockContext instead, so that several FuzzedSock instances sharing a test case (e.g. one per peer, or one created via Accept()) advance a single mocked clock, and the mocking goes through the SteadyClockContext RAII helper that resets mocktime on destruction.

   SteadyClockContext is a LimitOne type, so each fuzz target constructs one instance per iteration and passes it to ConsumeSock / ConsumeNode / the FuzzedSock constructor.

2. DrahtBot added the label Fuzzing on Jun 15, 2026
3. 
   DrahtBot commented at 4:05 PM on June 15, 2026: contributor

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   Code Coverage & Benchmarks

   For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/35536.

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   Conflicts

   Reviewers, this pull request conflicts with the following ones:

   • #35482 (fuzz: exercise the transaction-handling path in process_message(s) by HowHsu)

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4. in src/test/fuzz/util/net.h:187 in 45f690bc45

    183 | +     * Externally-provided context used to mock the steady clock in methods
    184 | +     * waiting for a given duration. It is a reference (rather than an owned
    185 | +     * member) so that several FuzzedSock instances sharing a test case (e.g.
    186 | +     * one per peer, or one created from Accept()) advance a single mocked
    187 | +     * clock: SteadyClockContext is a LimitOne type and may not be
    188 | +     * instantiated more than once at a time.
   

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   maflcko commented at 7:11 AM on June 16, 2026:

   LimitOne is an implementation detail, and I think the last sentence can be removed. Otherwise, all use-sites can explain what LimitOne means. If you want to explain it further, a better place would be SteadyClockContext itself, so that the docs are only in a single place, instead of spread out.

   The underlying reason is that time is read/written from/to a single global variable. Holding several time contexts for different objects and advancing them independently is simply impossible without changing non-test code. LimitOne is just an implementation detail to serve as a linter to avoid violations here and explicitly disallow several time contexts at runtime.

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   HowHsu commented at 8:38 AM on June 16, 2026:

   Updated

5. maflcko approved
6. 
   maflcko commented at 7:12 AM on June 16, 2026: member

   lgtm, but the new docs could be shortened.

7. 
   maflcko commented at 7:16 AM on June 16, 2026: member

   A bit unrelated, but I wonder if there should be a scripted-diff to rename SteadyClockContext to FakeSteadyClock, so that the naming follows FakeNodeClock. Otherwise, there are two naming schemes for two types of the same concept.

8. fuzz: share a single mocked steady clock across FuzzedSock instances

   Each FuzzedSock used to own its mocked steady clock and call
   MockableSteadyClock::SetMockTime() directly. Hold the clock by reference
   to an externally provided SteadyClockContext instead, so that several
   FuzzedSock instances sharing a test case (e.g. one per peer, or one
   created via Accept()) advance a single mocked clock, and the mocking goes
   through the SteadyClockContext RAII helper that resets mocktime on
   destruction.
   
   SteadyClockContext is a LimitOne type, so each fuzz target constructs one
   instance per iteration and passes it to ConsumeSock / ConsumeNode / the
   FuzzedSock constructor.

   0a270ea4ac
9. HowHsu force-pushed on Jun 16, 2026
10. 
    fanquake commented at 9:56 AM on June 17, 2026: member

    cc @marcofleon

11. 
    HowHsu commented at 7:56 AM on June 18, 2026: contributor

    A bit unrelated, but I wonder if there should be a scripted-diff to rename SteadyClockContext to FakeSteadyClock, so that the naming follows FakeNodeClock. Otherwise, there are two naming schemes for two types of the same concept.

    Checked the code and agree. Submitted a PR: https://github.com/bitcoin/bitcoin/pull/35559

12. HowHsu requested review from maflcko on Jun 18, 2026

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