Change to Tx diffusion (Dandelion++ fluff) instead of flooding

src/cryptonote_protocol/levin_notify.cpp

@@ -33,6 +33,7 @@
 #include <chrono>
 #include <deque>
 #include <stdexcept>
+#include <utility>
 
 #include "common/expect.h"
 #include "common/varint.h"
@@ -57,6 +58,37 @@ namespace levin
     constexpr const std::chrono::seconds noise_min_delay{CRYPTONOTE_NOISE_MIN_DELAY};
     constexpr const std::chrono::seconds noise_delay_range{CRYPTONOTE_NOISE_DELAY_RANGE};
 
+    /* A custom duration is used for the poisson distribution because of the
+       variance. If 5 seconds is given to `std::poisson_distribution`, 95% of
+       the values fall between 1-9s in 1s increments (not granular enough). If
+       5000 milliseconds is given, 95% of the values fall between 4859ms-5141ms
+       in 1ms increments (not enough time variance). Providing 20 quarter
+       seconds yields 95% of the values between 3s-7.25s in 1/4s increments. */
+    using fluff_stepsize = std::chrono::duration<std::chrono::milliseconds::rep, std::ratio<1, 4>>;
+    constexpr const std::chrono::seconds fluff_average_in{CRYPTONOTE_DANDELIONPP_FLUSH_AVERAGE};
+
+    /*! Bitcoin Core is using 1/2 average seconds for outgoing connections
+        compared to incoming. The thinking is that the user controls outgoing
+        connections (Dandelion++ makes similar assumptions in its stem
+        algorithm). The randomization yields 95% values between 1s-4s in
+	1/4s increments. */
+    constexpr const fluff_stepsize fluff_average_out{fluff_stepsize{fluff_average_in} / 2};
+
+    class random_poisson
+    {
+      std::poisson_distribution<fluff_stepsize::rep> dist;
+    public:
+      explicit random_poisson(fluff_stepsize average)
+        : dist(average.count() < 0 ? 0 : average.count())
+      {}
+
+      fluff_stepsize operator()()
+      {
+        crypto::random_device rand{};
+        return fluff_stepsize{dist(rand)};
+      }
+    };
+
     /*! Select a randomized duration from 0 to `range`. The precision will be to
         the systems `steady_clock`. As an example, supplying 3 seconds to this
         function will select a duration from [0, 3] seconds, and the increments
@@ -129,6 +161,12 @@ namespace levin
       return fullBlob;
     }
 
+    bool make_payload_send_txs(connections& p2p, std::vector<blobdata>&& txs, const boost::uuids::uuid& destination, const bool pad)
+    {
+      const cryptonote::blobdata blob = make_tx_payload(std::move(txs), pad);
+      return p2p.notify(NOTIFY_NEW_TRANSACTIONS::ID, epee::strspan<std::uint8_t>(blob), destination);
+    }
+
     /* The current design uses `asio::strand`s. The documentation isn't as clear
        as it should be - a `strand` has an internal `mutex` and `bool`. The
        `mutex` synchronizes thread access and the `bool` is set when a thread is
@@ -187,15 +225,18 @@ namespace levin
   {
     struct zone
     {
-      explicit zone(boost::asio::io_service& io_service, std::shared_ptr<connections> p2p, epee::byte_slice noise_in, bool is_public)
+      explicit zone(boost::asio::io_service& io_service, std::shared_ptr<connections> p2p, epee::byte_slice noise_in, bool is_public, bool pad_txs)
         : p2p(std::move(p2p)),
           noise(std::move(noise_in)),
           next_epoch(io_service),
+          flush_txs(io_service),
           strand(io_service),
           map(),
           channels(),
+          flush_time(std::chrono::steady_clock::time_point::max()),
           connection_count(0),
-          is_public(is_public)
+          is_public(is_public),
+          pad_txs(pad_txs)
       {
         for (std::size_t count = 0; !noise.empty() && count < CRYPTONOTE_NOISE_CHANNELS; ++count)
           channels.emplace_back(io_service);
@@ -204,11 +245,14 @@ namespace levin
       const std::shared_ptr<connections> p2p;
       const epee::byte_slice noise; //!< `!empty()` means zone is using noise channels
       boost::asio::steady_timer next_epoch;
+      boost::asio::steady_timer flush_txs;
       boost::asio::io_service::strand strand;
       net::dandelionpp::connection_map map;//!< Tracks outgoing uuid's for noise channels or Dandelion++ stems
       std::deque<noise_channel> channels;  //!< Never touch after init; only update elements on `noise_channel.strand`
+      std::chrono::steady_clock::time_point flush_time; //!< Next expected Dandelion++ fluff flush
       std::atomic<std::size_t> connection_count; //!< Only update in strand, can be read at any time
       const bool is_public;                      //!< Zone is public ipv4/ipv6 connections
+      const bool pad_txs;                        //!< Pad txs to the next boundary for privacy
     };
   } // detail
 
@@ -245,49 +289,112 @@ namespace levin
       }
     };
 
-    //! Sends a message to every active connection
-    class flood_notify
+    //! Sends txs on connections with expired timers, and queues callback for next timer expiration (if any).
+    struct fluff_flush
     {
       std::shared_ptr<detail::zone> zone_;
-      epee::byte_slice message_; // Requires manual copy
-      boost::uuids::uuid source_;
+      std::chrono::steady_clock::time_point flush_time_;
 
-    public:
-      explicit flood_notify(std::shared_ptr<detail::zone> zone, epee::byte_slice message, const boost::uuids::uuid& source)
-        : zone_(std::move(zone)), message_(message.clone()), source_(source)
-      {}
+      static void queue(std::shared_ptr<detail::zone> zone, const std::chrono::steady_clock::time_point flush_time)
+      {
+        assert(zone != nullptr);
+        assert(zone->strand.running_in_this_thread());
 
-      flood_notify(flood_notify&&) = default;
-      flood_notify(const flood_notify& source)
-        : zone_(source.zone_), message_(source.message_.clone()), source_(source.source_)
-      {}
+        detail::zone& this_zone = *zone;
+        this_zone.flush_time = flush_time;
+        this_zone.flush_txs.expires_at(flush_time);
+        this_zone.flush_txs.async_wait(this_zone.strand.wrap(fluff_flush{std::move(zone), flush_time}));
+      }
 
-      void operator()() const
+      void operator()(const boost::system::error_code error)
       {
         if (!zone_ || !zone_->p2p)
           return;
 
         assert(zone_->strand.running_in_this_thread());
 
-        /* The foreach should be quick, but then it iterates and acquires the
-           same lock for every connection. So do in a strand because two threads
-           will ping-pong each other with cacheline invalidations. Revisit if
-           algorithm changes or the locking strategy within the levin config
-           class changes. */
+        const bool timer_error = bool(error);
+        if (timer_error)
+        {
+          if (error != boost::system::errc::operation_canceled)
+            throw boost::system::system_error{error, "fluff_flush timer failed"};
 
-        std::vector<boost::uuids::uuid> connections;
-        connections.reserve(connection_id_reserve_size);
-        zone_->p2p->foreach_connection([this, &connections] (detail::p2p_context& context) {
-          /* Only send to outgoing connections when "flooding" over i2p/tor.
-             Otherwise this makes the tx linkable to a hidden service address,
-             making things linkable across connections. */
-          if (this->source_ != context.m_connection_id && (this->zone_->is_public || !context.m_is_income))
-            connections.emplace_back(context.m_connection_id);
+          // new timer canceled this one set in future
+          if (zone_->flush_time < flush_time_)
+            return;
+        }
+
+        const auto now = std::chrono::steady_clock::now();
+        auto next_flush = std::chrono::steady_clock::time_point::max();
+        std::vector<std::pair<std::vector<blobdata>, boost::uuids::uuid>> connections{};
+        zone_->p2p->foreach_connection([timer_error, now, &next_flush, &connections] (detail::p2p_context& context)
+        {
+          if (!context.fluff_txs.empty())
+          {
+            if (context.flush_time <= now || timer_error) // flush on canceled timer
+            {
+              context.flush_time = std::chrono::steady_clock::time_point::max();
+              connections.emplace_back(std::move(context.fluff_txs), context.m_connection_id);
+              context.fluff_txs.clear();
+            }
+            else // not flushing yet
+              next_flush = std::min(next_flush, context.flush_time);
+          }
+          else // nothing to flush
+            context.flush_time = std::chrono::steady_clock::time_point::max();
           return true;
         });
 
-        for (const boost::uuids::uuid& connection : connections)
-          zone_->p2p->send(message_.clone(), connection);
+        for (auto& connection : connections)
+          make_payload_send_txs(*zone_->p2p, std::move(connection.first), connection.second, zone_->pad_txs);
+
+        if (next_flush != std::chrono::steady_clock::time_point::max())
+          fluff_flush::queue(std::move(zone_), next_flush);
+        else
+          zone_->flush_time = next_flush; // signal that no timer is set
+      }
+    };
+
+    /*! The "fluff" portion of the Dandelion++ algorithm. Every tx is queued
+        per-connection and flushed with a randomized poisson timer. This
+        implementation only has one system timer per-zone, and instead tracks
+        the lowest flush time. */
+    struct fluff_notify
+    {
+      std::shared_ptr<detail::zone> zone_;
+      std::vector<blobdata> txs_;
+      boost::uuids::uuid source_;
+
+      void operator()()
+      {
+        if (!zone_ || !zone_->p2p || txs_.empty())
+          return;
+
+        assert(zone_->strand.running_in_this_thread());
+
+        const auto now = std::chrono::steady_clock::now();
+        auto next_flush = std::chrono::steady_clock::time_point::max();
+
+        random_poisson in_duration(fluff_average_in);
+        random_poisson out_duration(fluff_average_out);
+
+        zone_->p2p->foreach_connection([this, now, &in_duration, &out_duration, &next_flush] (detail::p2p_context& context)
+        {
+          if (this->source_ != context.m_connection_id && (this->zone_->is_public || !context.m_is_income))
+          {
+            if (context.fluff_txs.empty())
+              context.flush_time = now + (context.m_is_income ? in_duration() : out_duration());
+
+            next_flush = std::min(next_flush, context.flush_time);
+            context.fluff_txs.reserve(context.fluff_txs.size() + this->txs_.size());
+            for (const blobdata& tx : this->txs_)
+              context.fluff_txs.push_back(tx); // must copy instead of move (multiple conns)
+          }
+          return true;
+        });
+
+        if (next_flush < zone_->flush_time)
+          fluff_flush::queue(std::move(zone_), next_flush);
       }
     };
 
@@ -451,7 +558,7 @@ namespace levin
       }
     };
 
-    //! Prepares connections for new channel epoch and sets timer for next epoch
+    //! Prepares connections for new channel/dandelionpp epoch and sets timer for next epoch
     struct start_epoch
     {
       // Variables allow for Dandelion++ extension
@@ -481,8 +588,8 @@ namespace levin
     };
   } // anonymous
 
-  notify::notify(boost::asio::io_service& service, std::shared_ptr<connections> p2p, epee::byte_slice noise, bool is_public)
-    : zone_(std::make_shared<detail::zone>(service, std::move(p2p), std::move(noise), is_public))
+  notify::notify(boost::asio::io_service& service, std::shared_ptr<connections> p2p, epee::byte_slice noise, const bool is_public, const bool pad_txs)
+    : zone_(std::make_shared<detail::zone>(service, std::move(p2p), std::move(noise), is_public, pad_txs))
   {
     if (!zone_->p2p)
       throw std::logic_error{"cryptonote::levin::notify cannot have nullptr p2p argument"};
@@ -533,8 +640,18 @@ namespace levin
       channel.next_noise.cancel();
   }
 
-  bool notify::send_txs(std::vector<blobdata> txs, const boost::uuids::uuid& source, const bool pad_txs)
+  void notify::run_fluff()
   {
+    if (!zone_)
+      return;
+    zone_->flush_txs.cancel();
+  }
+
+  bool notify::send_txs(std::vector<blobdata> txs, const boost::uuids::uuid& source)
+  {
+    if (txs.empty())
+      return true;
+
     if (!zone_)
       return false;
 
@@ -565,12 +682,7 @@ namespace levin
     }
     else
     {
-      const std::string payload = make_tx_payload(std::move(txs), pad_txs);
-      epee::byte_slice message =
-        epee::levin::make_notify(NOTIFY_NEW_TRANSACTIONS::ID, epee::strspan<std::uint8_t>(payload));
-
-      // traditional monero send technique
-      zone_->strand.dispatch(flood_notify{zone_, std::move(message), source});
+      zone_->strand.dispatch(fluff_notify{zone_, std::move(txs), source});
     }
 
     return true;