KPN/tests/test_channel.cpp

#include <string>
#include <catch2/catch_test_macros.hpp>
#include <catch2/catch_approx.hpp>
#include <kpn/channel.hpp>
#include <thread>
#include <vector>

using namespace kpn;

TEST_CASE("channel storage policy: small trivial type by value", "[channel]") {
    STATIC_REQUIRE(channel_storage_policy<int>::by_value);
    STATIC_REQUIRE(channel_storage_policy<float>::by_value);
}

TEST_CASE("channel storage policy: large type by shared_ptr", "[channel]") {
    struct Big { char data[64]; };
    STATIC_REQUIRE(!channel_storage_policy<Big>::by_value);
}

TEST_CASE("push and pop single value", "[channel]") {
    Channel<int> ch(5);
    ch.push(42);
    REQUIRE(ch.pop() == 42);
}

TEST_CASE("channel respects capacity", "[channel]") {
    Channel<int> ch(2);
    ch.push(1);
    ch.push(2);
    REQUIRE_THROWS_AS(ch.push(3), ChannelOverflowError);
}

TEST_CASE("pop blocks until value available", "[channel]") {
    Channel<int> ch(5);
    int result = 0;
    std::thread producer([&] {
        std::this_thread::sleep_for(std::chrono::milliseconds(20));
        ch.push(99);
    });
    result = ch.pop();
    producer.join();
    REQUIRE(result == 99);
}

TEST_CASE("try_pop returns false on timeout", "[channel]") {
    Channel<int> ch(5);
    int out = 0;
    REQUIRE_FALSE(ch.try_pop(out, std::chrono::milliseconds(10)));
}

TEST_CASE("try_pop succeeds when value present", "[channel]") {
    Channel<int> ch(5);
    ch.push(7);
    int out = 0;
    REQUIRE(ch.try_pop(out, std::chrono::milliseconds(10)));
    REQUIRE(out == 7);
}

TEST_CASE("disable unblocks waiting pop", "[channel]") {
    Channel<int> ch(5);
    std::thread disabler([&] {
        std::this_thread::sleep_for(std::chrono::milliseconds(20));
        ch.disable();
    });
    REQUIRE_THROWS_AS(ch.pop(), ChannelClosedError);
    disabler.join();
}

TEST_CASE("push to disabled channel is silently dropped", "[channel]") {
    Channel<int> ch(5);
    ch.disable();
    ch.push(99);  // must not throw, must not enqueue
    REQUIRE(ch.size() == 0);
}

TEST_CASE("disable stops accepting and unblocks pop", "[channel]") {
    // With the SPSC lock-free ring, disable() does not drain the ring immediately;
    // items are freed when the Channel is destroyed. What it must do is:
    //  1. reject further pushes (drops silently)
    //  2. unblock any waiting pop() (throws ChannelClosedError)
    Channel<int> ch(5);
    ch.push(1);
    ch.push(2);
    REQUIRE(ch.size() == 2);
    ch.disable();
    // Further pushes are dropped
    ch.push(3);
    REQUIRE(ch.size() <= 2);
    // pop() must throw even though items remain in the ring
    REQUIRE_THROWS_AS(ch.pop(), ChannelClosedError);
}

TEST_CASE("enable re-accepts pushes after disable", "[channel]") {
    Channel<int> ch(5);
    ch.disable();
    ch.push(1);
    REQUIRE(ch.size() == 0);
    ch.enable();
    ch.push(42);
    REQUIRE(ch.pop() == 42);
}

TEST_CASE("large type stored as shared_ptr — no copy on pop", "[channel]") {
    struct Big { char data[64]; int tag; };
    Channel<Big> ch(5);
    Big b{}; b.tag = 123;
    ch.push(b);
    auto out = ch.pop();
    REQUIRE(out.tag == 123);
}

// ── ChannelDataSize / bytes_pushed tests ─────────────────────────────────────

TEST_CASE("bytes_pushed uses sizeof(T) by default for POD type", "[channel][bandwidth]") {
    Channel<int> ch(10);
    ch.push(1);
    ch.push(2);
    ch.push(3);
    ch.pop(); ch.pop(); ch.pop();

    auto snap = ch.snapshot("test");
    REQUIRE(snap.pushes == 3);
    REQUIRE(snap.bytes_pushed == 3 * sizeof(int));
}

TEST_CASE("bytes_pushed uses sizeof(T) by default for large struct", "[channel][bandwidth]") {
    struct Blob { char data[256]; };
    Channel<Blob> ch(10);
    ch.push(Blob{});
    ch.push(Blob{});

    auto snap = ch.snapshot("test");
    REQUIRE(snap.bytes_pushed == 2 * sizeof(Blob));
}

// A fake heap-owning type whose logical payload size differs from sizeof.
struct FakeFrame {
    std::vector<uint8_t> pixels;
};

// Specialise ChannelDataSize so the channel counts actual pixel bytes.
template<>
struct kpn::ChannelDataSize<FakeFrame> {
    static std::size_t bytes(const FakeFrame& f) { return f.pixels.size(); }
};

TEST_CASE("bytes_pushed uses ChannelDataSize specialisation for heap-owning type", "[channel][bandwidth]") {
    Channel<FakeFrame> ch(10);
    ch.push(FakeFrame{std::vector<uint8_t>(1000)});
    ch.push(FakeFrame{std::vector<uint8_t>(2000)});

    auto snap = ch.snapshot("test");
    REQUIRE(snap.pushes == 2);
    REQUIRE(snap.bytes_pushed == 3000);
    // item_bytes is still sizeof(FakeFrame) — the struct header
    REQUIRE(snap.item_bytes == sizeof(FakeFrame));
}

TEST_CASE("bandwidth_mbs is non-zero and correct for heap-owning type", "[channel][bandwidth]") {
    Channel<FakeFrame> ch(10);
    // Push 10 frames of 1 MB each
    for (int i = 0; i < 10; ++i)
        ch.push(FakeFrame{std::vector<uint8_t>(1'000'000)});

    auto snap = ch.snapshot("test");
    // 10 MB over 1 second => 10.0 MB/s
    REQUIRE(snap.bandwidth_mbs(1.0) == Catch::Approx(10.0).epsilon(1e-6));
    // Without the fix (using sizeof), this would have been ~40 bytes/s ≈ 0.00004 MB/s.
    REQUIRE(snap.bandwidth_mbs(1.0) > 1.0);
}

TEST_CASE("bandwidth_mbs returns 0 when elapsed_s is zero or negative", "[channel][bandwidth]") {
    Channel<int> ch(5);
    ch.push(42);
    auto snap = ch.snapshot("test");
    REQUIRE(snap.bandwidth_mbs(0.0) == 0.0);
    REQUIRE(snap.bandwidth_mbs(-1.0) == 0.0);
}

TEST_CASE("push_sentinel never overflows even on a full channel", "[channel][sentinel]") {
    Channel<int> ch(2);
    ch.push(1);
    ch.push(2);   // channel full — a plain push(3) would throw ChannelOverflowError

    // The sentinel is stored out-of-band, so it neither throws nor blocks the
    // caller — the exact property an EOF token needs under backpressure. This
    // returns immediately with the ring still full.
    REQUIRE(ch.push_sentinel(99));
    REQUIRE(ch.size() == 2);   // sentinel did not consume ring capacity
}

TEST_CASE("push_sentinel is delivered after all ring data, in order", "[channel][sentinel]") {
    Channel<int> ch(4);
    ch.push(1);
    ch.push(2);
    ch.push_sentinel(99);   // enqueue EOF while data is still buffered

    // Data drains first; the sentinel arrives only once the ring is empty.
    REQUIRE(ch.pop() == 1);
    REQUIRE(ch.pop() == 2);
    REQUIRE(ch.pop() == 99);
}

TEST_CASE("push_sentinel wakes a blocked pop", "[channel][sentinel]") {
    Channel<int> ch(2);   // empty
    std::thread producer([&] {
        std::this_thread::sleep_for(std::chrono::milliseconds(20));
        ch.push_sentinel(99);   // must wake a consumer parked on an empty ring
    });
    REQUIRE(ch.pop() == 99);
    producer.join();
}

TEST_CASE("approx_size counts a pending sentinel so consumers stay schedulable",
          "[channel][sentinel]") {
    Channel<int> ch(4);
    REQUIRE(ch.approx_size() == 0);
    ch.push_sentinel(99);
    // Node readiness checks call approx_size(); it must report the out-of-band
    // sentinel as consumable work even though it holds no ring slot.
    REQUIRE(ch.approx_size() == 1);
    REQUIRE(ch.size() == 0);       // ...but the ring itself is still empty
    int out = 0;
    REQUIRE(ch.try_pop_now(out));
    REQUIRE(out == 99);
    REQUIRE(ch.approx_size() == 0);
}

TEST_CASE("try_pop_now delivers a pending sentinel once the ring is empty",
          "[channel][sentinel]") {
    Channel<int> ch(2);
    ch.push(1);
    ch.push_sentinel(99);

    int out = 0;
    REQUIRE(ch.try_pop_now(out));   // ring data first
    REQUIRE(out == 1);
    REQUIRE(ch.try_pop_now(out));   // then the sentinel
    REQUIRE(out == 99);
    REQUIRE_FALSE(ch.try_pop_now(out));   // nothing left
}

// Regression: the sentinel slot holds one token and refuses a second.
//
// push_sentinel used to write eof_value_ unconditionally. Offering a second
// token before the first was taken therefore did two wrong things at once: it
// lost the first silently — and a lost EOF wedges every downstream pop forever
// — and it wrote the storage while the consumer could be moving the previous
// value out of it. For the shared_ptr storage that non-trivial types use, that
// is a torn refcount, not merely a stale read.
//
// Refusing is correct rather than queueing: two control tokens on one channel
// means the stream ended twice, which is a caller protocol error. Coalescing
// them would hide it, and there is no second value that could sensibly follow
// the end of a stream.
TEST_CASE("a second sentinel is refused, not swallowed", "[channel][sentinel]") {
    Channel<int> ch(4);

    REQUIRE(ch.push_sentinel(1));
    // Slot occupied: the first token is still undelivered.
    REQUIRE_FALSE(ch.push_sentinel(2));

    // The first survives intact — the overwrite is what used to lose it.
    int out = 0;
    REQUIRE(ch.try_pop_now(out));
    CHECK(out == 1);

    // And the slot is reusable once drained.
    REQUIRE(ch.push_sentinel(3));
    REQUIRE(ch.try_pop_now(out));
    CHECK(out == 3);
}

TEST_CASE("a refused sentinel is counted as a drop", "[channel][sentinel]") {
    // Visibility matters more here than for a dropped value: the refusal means
    // a control token went nowhere, and the only alternative to a counter is
    // for it to vanish.
    Channel<int> ch(4);
    REQUIRE(ch.push_sentinel(1));
    const auto before = ch.stats().drops.load();
    REQUIRE_FALSE(ch.push_sentinel(2));
    CHECK(ch.stats().drops.load() == before + 1);
}

TEST_CASE("try_push_sentinel leaves a refused value untouched", "[channel][sentinel]") {
    // The non-consuming form exists so a refused token is still the caller's to
    // report. The consuming push_sentinel cannot offer that, since the value is
    // already moved into its parameter.
    Channel<std::string> ch(4);
    std::string first = "eof-1", second = "eof-2";

    REQUIRE(ch.try_push_sentinel(first) == Channel<std::string>::SentinelResult::Taken);
    REQUIRE(ch.try_push_sentinel(second) == Channel<std::string>::SentinelResult::SlotBusy);
    CHECK(second == "eof-2");          // not moved from

    ch.disable();
    std::string third = "eof-3";
    CHECK(ch.try_push_sentinel(third) == Channel<std::string>::SentinelResult::Closed);
    CHECK(third == "eof-3");
}

// Regression: try_push must distinguish delivered from discarded.
//
// It returned bool, and returned *true* for a closed channel — so "the value
// arrived" and "the value was thrown away because nobody is listening" were the
// same answer. Every caller was nonetheless correct, because both cases mean
// "stop trying"; but nothing above the channel could tell the two apart, and a
// producer counting successful pushes counted discards among them. Only the
// channel's own drop counter knew, and only if someone read the diagnostics.
TEST_CASE("try_push distinguishes taken, full and closed", "[channel]") {
    Channel<int> ch(2);
    int v = 1;

    CHECK(ch.try_push(v) == Channel<int>::PushResult::Taken);
    CHECK(ch.try_push(v) == Channel<int>::PushResult::Taken);
    // Ring is full: the value is untouched and the caller keeps it.
    CHECK(ch.try_push(v) == Channel<int>::PushResult::Full);
    CHECK(v == 1);

    ch.disable();
    const auto drops_before = ch.stats().drops.load();
    CHECK(ch.try_push(v) == Channel<int>::PushResult::Closed);
    // Discarded, and recorded as such rather than reported as a delivery.
    CHECK(ch.stats().drops.load() == drops_before + 1);
}