log: introduce LogRateLimiter, LogLimitStats, Status

LogRateLimiter will be used to keep track of source locations and our
current time-based logging window. It contains an unordered_map and a
m_suppressions_active bool to track source locations. The map is keyed
by std::source_location, so a custom Hash function (SourceLocationHasher)
and custom KeyEqual function (SourceLocationEqual) is provided.
SourceLocationHasher uses CSipHasher(0,0) under the hood to get a
uniform distribution.

A public Reset method is provided so that a scheduler (e.g. the
"b-scheduler" thread) can periodically reset LogRateLimiter's state when
the time window has elapsed.

The LogRateLimiter::Consume method checks if we have enough available
bytes in our rate limiting budget to log an additional string. It
returns a Status enum that denotes the rate limiting status and can
be used by the caller to emit a warning, skip logging, etc.

The Status enum has three states:
- UNSUPPRESSED     (logging was successful)
- NEWLY_SUPPRESSED (logging was succcesful, next log will be suppressed)
- STILL_SUPPRESSED (logging was unsuccessful)

LogLimitStats counts the available bytes left for logging per source
location for the current logging window. It does not track actual source
locations; it is used as a value in m_source_locations.

Also exposes a SuppressionsActive() method so the logger can use
that in a later commit to prefix [*] to logs whenenever suppressions
are active.

Co-Authored-By: Niklas Gogge <n.goeggi@gmail.com>
Co-Authored-By: stickies-v <stickies-v@protonmail.com>

src/test/logging_tests.cpp

@@ -5,11 +5,13 @@
 #include <init/common.h>
 #include <logging.h>
 #include <logging/timer.h>
+#include <scheduler.h>
 #include <test/util/setup_common.h>
 #include <util/string.h>
 
 #include <chrono>
 #include <fstream>
+#include <future>
 #include <iostream>
 #include <unordered_map>
 #include <utility>
@@ -276,4 +278,79 @@ BOOST_FIXTURE_TEST_CASE(logging_Conf, LogSetup)
     }
 }
 
+void MockForwardAndSync(CScheduler& scheduler, std::chrono::seconds duration)
+{
+    scheduler.MockForward(duration);
+    std::promise<void> promise;
+    scheduler.scheduleFromNow([&promise] { promise.set_value(); }, 0ms);
+    promise.get_future().wait();
+}
+
+BOOST_AUTO_TEST_CASE(logging_log_rate_limiter)
+{
+    CScheduler scheduler{};
+    scheduler.m_service_thread = std::thread([&scheduler] { scheduler.serviceQueue(); });
+    uint64_t max_bytes{1024};
+    auto reset_window{1min};
+    auto sched_func = [&scheduler](auto func, auto window) { scheduler.scheduleEvery(std::move(func), window); };
+    BCLog::LogRateLimiter limiter{sched_func, max_bytes, reset_window};
+
+    using Status = BCLog::LogRateLimiter::Status;
+    auto source_loc_1{std::source_location::current()};
+    auto source_loc_2{std::source_location::current()};
+
+    // A fresh limiter should not have any suppressions
+    BOOST_CHECK(!limiter.SuppressionsActive());
+
+    // Resetting an unused limiter is fine
+    limiter.Reset();
+    BOOST_CHECK(!limiter.SuppressionsActive());
+
+    // No suppression should happen until more than max_bytes have been consumed
+    BOOST_CHECK_EQUAL(limiter.Consume(source_loc_1, std::string(max_bytes - 1, 'a')), Status::UNSUPPRESSED);
+    BOOST_CHECK_EQUAL(limiter.Consume(source_loc_1, "a"), Status::UNSUPPRESSED);
+    BOOST_CHECK(!limiter.SuppressionsActive());
+    BOOST_CHECK_EQUAL(limiter.Consume(source_loc_1, "a"), Status::NEWLY_SUPPRESSED);
+    BOOST_CHECK(limiter.SuppressionsActive());
+    BOOST_CHECK_EQUAL(limiter.Consume(source_loc_1, "a"), Status::STILL_SUPPRESSED);
+    BOOST_CHECK(limiter.SuppressionsActive());
+
+    // Location 2  should not be affected by location 1's suppression
+    BOOST_CHECK_EQUAL(limiter.Consume(source_loc_2, std::string(max_bytes, 'a')), Status::UNSUPPRESSED);
+    BOOST_CHECK_EQUAL(limiter.Consume(source_loc_2, "a"), Status::NEWLY_SUPPRESSED);
+    BOOST_CHECK(limiter.SuppressionsActive());
+
+    // After reset_window time has passed, all suppressions should be cleared.
+    MockForwardAndSync(scheduler, reset_window);
+
+    BOOST_CHECK(!limiter.SuppressionsActive());
+    BOOST_CHECK_EQUAL(limiter.Consume(source_loc_1, std::string(max_bytes, 'a')), Status::UNSUPPRESSED);
+    BOOST_CHECK_EQUAL(limiter.Consume(source_loc_2, std::string(max_bytes, 'a')), Status::UNSUPPRESSED);
+
+    scheduler.stop();
+}
+
+BOOST_AUTO_TEST_CASE(logging_log_limit_stats)
+{
+    BCLog::LogLimitStats counter{BCLog::RATELIMIT_MAX_BYTES};
+
+    // Check that counter gets initialized correctly.
+    BOOST_CHECK_EQUAL(counter.GetAvailableBytes(), BCLog::RATELIMIT_MAX_BYTES);
+    BOOST_CHECK_EQUAL(counter.GetDroppedBytes(), 0ull);
+
+    const uint64_t MESSAGE_SIZE{512 * 1024};
+    BOOST_CHECK(counter.Consume(MESSAGE_SIZE));
+    BOOST_CHECK_EQUAL(counter.GetAvailableBytes(), BCLog::RATELIMIT_MAX_BYTES - MESSAGE_SIZE);
+    BOOST_CHECK_EQUAL(counter.GetDroppedBytes(), 0ull);
+
+    BOOST_CHECK(counter.Consume(MESSAGE_SIZE));
+    BOOST_CHECK_EQUAL(counter.GetAvailableBytes(), BCLog::RATELIMIT_MAX_BYTES - MESSAGE_SIZE * 2);
+    BOOST_CHECK_EQUAL(counter.GetDroppedBytes(), 0ull);
+
+    // Consuming more bytes after already having consumed 1MB should fail.
+    BOOST_CHECK(!counter.Consume(500));
+    BOOST_CHECK_EQUAL(counter.GetAvailableBytes(), 0ull);
+    BOOST_CHECK_EQUAL(counter.GetDroppedBytes(), 500ull);
+}
+
 BOOST_AUTO_TEST_SUITE_END()