fix: assert in signing_shares for quorums with 3 members but 2 nodes only

[knst]

Issue being fixed or feature implemented

Currently we have several quorums which have size 3 with threshold 2 nodes: llmq_test_instantsend, llmq_test_platform, llmq_test and they are used on RegTest.

For extreme case when only 2 nodes exist the assert happens:

  AssertionError: Unexpected stderr dashd: llmq/signing_shares.cpp:812: static CDeterministicMNCPtr llmq::CSigSharesManager::SelectMemberForRecovery(const llmq::CQuorumCPtr&, const uint256&, size_t): Assertion `size_t(attempt) < quorum->members.size()' failed.
  Posix Signal: Aborted
     0#: (0x5BF40CE70DA2) stl_vector.h:115       - std::_Vector_base<unsigned long, std::allocator<unsigned long> >::_Vector_impl_data::_M_copy_data(std::_Vector_base<unsigned long, std::allocator<unsigned long> >::_Vector_impl_data const&)
     1#: (0x5BF40CE70DA2) stl_vector.h:127       - std::_Vector_base<unsigned long, std::allocator<unsigned long> >::_Vector_impl_data::_M_swap_data(std::_Vector_base<unsigned long, std::allocator<unsigned long> >::_Vector_impl_data&)
     2#: (0x5BF40CE70DA2) stl_vector.h:1962      - std::vector<unsigned long, std::allocator<unsigned long> >::_M_move_assign(std::vector<unsigned long, std::allocator<unsigned long> >&&, std::integral_constant<bool, true>)
     3#: (0x5BF40CE70DA2) stl_vector.h:771       - std::vector<unsigned long, std::allocator<unsigned long> >::operator=(std::vector<unsigned long, std::allocator<unsigned long> >&&)
     4#: (0x5BF40CE70DA2) stacktraces.cpp:777    - HandlePosixSignal
     5#: (0x7664C9245320) libc_sigaction.c       - ???
     6#: (0x7664C929EB1C) pthread_kill.c:44      - __pthread_kill_implementation
     7#: (0x7664C929EB1C) pthread_kill.c:78      - __pthread_kill_internal
     8#: (0x7664C929EB1C) pthread_kill.c:89      - __GI___pthread_kill
     9#: (0x7664C924526E) raise.c:27             - __GI_raise
    10#: (0x7664C92288FF) abort.c:81             - __GI_abort
    11#: (0x7664C922881B) loadmsgcat.c:1177      - _nl_load_domain
    12#: (0x7664C923B507) <unknown-file>         - ???
    13#: (0x5BF40C6E88C8) signing_shares.cpp:823 - llmq::CSigSharesManager::SelectMemberForRecovery(std::shared_ptr<llmq::CQuorum const> const&, uint256 const&, unsigned long)
    14#: (0x5BF40C94A285) quorums.cpp:737        - operator()
    15#: (0x5BF40C94A514) std_function.h:292     - _M_invoke
    16#: (0x5BF40CE082C6) util.cpp:510           - RPCHelpMan::HandleRequest(JSONRPCRequest const&) const
    17#: (0x5BF40C89824A) univalue.h:17          - UniValue::operator=(UniValue&&)
    18#: (0x5BF40C89824A) server.h:108           - CRPCCommand::CRPCCommand(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, RPCHelpMan (*)())::{lambda(JSONRPCRequest const&, UniValue&, bool)#1}::operator()(JSONRPCRequest const&, UniValue&, bool) const
    19#: (0x5BF40C9976F4) std_function.h:591     - std::function<bool (JSONRPCRequest const&, UniValue&, bool)>::operator()(JSONRPCRequest const&, UniValue&, bool) const
    20#: (0x5BF40C9976F4) server.cpp:622         - ExecuteCommand
    21#: (0x5BF40C99879F) server.cpp:511         - ExecuteCommands
    22#: (0x5BF40C99879F) server.cpp:543         - CRPCTable::execute(JSONRPCRequest const&) const
    23#: (0x5BF40CB75F24) httprpc.cpp:247        - HTTPReq_JSONRPC

Discovered during implementation of https://github.com/dashpay/dash-issues/issues/77

What was done?

Changed condition in assert, implemented special case of using Nth element from array size N for SelectMemberForRecovery, added test for this case.

How Has This Been Tested?

Improved functional test feature_asset_locks.py to test this corner case for quorum llmq_test_instantsend and llmq_test_platform

Breaking Changes

N/A

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated relevant unit/integration/functional/e2e tests
• I have made corresponding changes to the documentation
• I have assigned this pull request to a milestone

[UdjinM6]

Interesting. However if we are going to allow attempt to wrap around then quorum->members.size() is actually irrelevant here imo, attempt should be limited by recoveryMembers instead.

From src/llmq/params.h:

    // How many members should we try to send all sigShares to before we give up.
    int recoveryMembers;

Pls consider 8ff9ba1.

[UdjinM6]

utACK f44edde

[UdjinM6]

nit: clang format complains

Suggested change

	CDeterministicMNCPtr CSigSharesManager::SelectMemberForRecovery(const CQuorumCPtr& quorum, const uint256 &id, int attempt)
	CDeterministicMNCPtr CSigSharesManager::SelectMemberForRecovery(const CQuorumCPtr& quorum, const uint256& id, int attempt)

[knst]

I will fix it if need to force-push again.

[PastaPastaPasta]

utACK f44edde