Function SimulationTest

src/test/fuzz/p2p_transport_serialization.cpp:108–332

template<RandomNumberGenerator R>
void SimulationTest(Transport& initiator, Transport& responder, R& rng, FuzzedDataProvider& provider)
{
    // Simulation test with two Transport objects, which send messages to each other, with
    // sending and receiving fragmented into multiple pieces that may be interleaved. It primarily
    // verifies that the sending and receiving side are compatible with each other, plus a few
    // sanity checks. It does not attempt to introduce errors in the communicated data.

    // Put the transports in an array for by-index access.
    const std::array<Transport*, 2> transports = {&initiator, &responder};

    // Two vectors representing in-flight bytes. inflight[i] is from transport[i] to transport[!i].
    std::array<std::vector<uint8_t>, 2> in_flight;

    // Two queues with expected messages. expected[i] is expected to arrive in transport[!i].
    std::array<std::deque<CSerializedNetMsg>, 2> expected;

    // Vectors with bytes last returned by GetBytesToSend() on transport[i].
    std::array<std::vector<uint8_t>, 2> to_send;

    // Last returned 'more' values (if still relevant) by transport[i]->GetBytesToSend(), for
    // both have_next_message false and true.
    std::array<std::optional<bool>, 2> last_more, last_more_next;

    // Whether more bytes to be sent are expected on transport[i], before and after
    // SetMessageToSend().
    std::array<std::optional<bool>, 2> expect_more, expect_more_next;

    // Function to consume a message type.
    auto msg_type_fn = [&]() {
        uint8_t v = provider.ConsumeIntegral<uint8_t>();
        if (v == 0xFF) {
            // If v is 0xFF, construct a valid (but possibly unknown) message type from the fuzz
            // data.
            std::string ret;
            while (ret.size() < CMessageHeader::MESSAGE_TYPE_SIZE) {
                char c = provider.ConsumeIntegral<char>();
                // Match the allowed characters in CMessageHeader::IsMessageTypeValid(). Any other
                // character is interpreted as end.
                if (c < ' ' || c > 0x7E) break;
                ret += c;
            }
            return ret;
        } else {
            // Otherwise, use it as index into the list of known messages.
            return g_all_messages[v % g_all_messages.size()];
        }
    };

    // Function to construct a CSerializedNetMsg to send.
    auto make_msg_fn = [&](bool first) {
        CSerializedNetMsg msg;
        if (first) {
            // Always send a "version" message as first one.
            msg.m_type = "version";
        } else {
            msg.m_type = msg_type_fn();
        }
        // Determine size of message to send (limited to 75 kB for performance reasons).