Adding ZMQ/Pub support for txpool_add and chain_main events

ZMQ.md

@@ -0,0 +1,61 @@
+# The Current/Future Status of ZMQ in Monero
+
+## ZMQ Pub/Sub
+Client `ZMQ_SUB` sockets must "subscribe" to topics before it receives any data.
+This allows filtering on the server side, so network traffic is reduced. Monero
+allows for filtering on: (1) format, (2) context, and (3) event.
+
+ * **format** refers to the _wire_ format (i.e. JSON) used to send event
+   information.
+ * **context** allows for a reduction in fields for the event, so the
+   daemon doesn't waste cycles serializing fields that get ignored.
+ * **event** refers to status changes occurring within the daemon (i.e. new
+   block to main chain).
+
+ * Formats:
+   * `json`
+ * Contexts:
+   * `full` - the entire block or transaction is transmitted (the hash can be
+     computed remotely).
+   * `minimal` - the bare minimum for a remote client to react to an event is
+     sent.
+ * Events:
+   * `chain_main` - changes to the primary/main blockchain.
+   * `txpool_add` - new _publicly visible_ transactions in the mempool.
+     Includes previously unseen transactions in a block but _not_ the
+     `miner_tx`. Does not "re-publish" after a reorg. Includes `do_not_relay`
+     transactions.
+
+The subscription topics are formatted as `format-context-event`, with prefix
+matching supported by both Monero and ZMQ. The `format`, `context` and `event`
+will _never_ have hyphens or colons in their name. For example, subscribing to
+`json-minimal-chain_main` will send minimal information in JSON when changes
+to the main/primary blockchain occur. Whereas, subscribing to `json-minimal`
+will send minimal information in JSON on all available events supported by the
+daemon.
+
+The Monero daemon will ensure that events prefixed by `chain` will be sent in
+"chain-order" - the `prev_id` (hash) field will _always_ refer to a previous
+block. On rollbacks/reorgs, the event will reference an earlier block in the
+chain instead of the last block. The Monero daemon also ensures that
+`txpool_add` events are sent before `chain_*` events - the `chain_*` messages
+will only serialize miner transactions since the other transactions were
+previously published via `txpool_add`. This prevents transactions from being
+serialized twice, even when the transaction was first observed in a block.
+
+ZMQ Pub/Sub will drop messages if the network is congested, so the above rules
+for send order are used for detecting lost messages. A missing gap in `height`
+or `prev_id` for `chain_*` events indicates a lost pub message. Missing
+`txpool_add` messages can only be detected at the next `chain_` message.
+
+Since blockchain events can be dropped, clients will likely want to have a
+timeout against `chain_main` events. The `GetLastBlockHeader` RPC is useful
+for checking the current chain state. Dropped messages should be rare in most
+conditions.
+
+The Monero daemon will send a `txpool_add` pub exactly once for each
+transaction, even after a reorg or restarts. Clients should use the
+`GetTransactionPool` after a reorg to get all transactions that have been put
+back into the tx pool or been invalidated due to a double-spend.
+
+

src/common/notify.cpp

@@ -62,7 +62,7 @@ static void replace(std::vector<std::string> &v, const char *tag, const char *s)
     boost::replace_all(str, tag, s);
 }
 
-int Notify::notify(const char *tag, const char *s, ...)
+int Notify::notify(const char *tag, const char *s, ...) const
 {
   std::vector<std::string> margs = args;
 

src/common/notify.h

@@ -38,8 +38,12 @@ class Notify
 {
 public:
   Notify(const char *spec);
+  Notify(const Notify&) = default;
+  Notify(Notify&&) = default;
+  Notify& operator=(const Notify&) = default;
+  Notify& operator=(Notify&&) = default;
 
-  int notify(const char *tag, const char *s, ...);
+  int notify(const char *tag, const char *s, ...) const;
 
 private:
   std::string filename;
@@ -47,3 +51,4 @@ private:
 };
 
 }
+

src/cryptonote_basic/events.h

@@ -0,0 +1,46 @@
+// Copyright (c) 2020, The Monero Project
+//
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without modification, are
+// permitted provided that the following conditions are met:
+//
+// 1. Redistributions of source code must retain the above copyright notice, this list of
+//    conditions and the following disclaimer.
+//
+// 2. Redistributions in binary form must reproduce the above copyright notice, this list
+//    of conditions and the following disclaimer in the documentation and/or other
+//    materials provided with the distribution.
+//
+// 3. Neither the name of the copyright holder nor the names of its contributors may be
+//    used to endorse or promote products derived from this software without specific
+//    prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
+// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
+// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
+// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#pragma once
+
+#include "crypto/hash.h"
+#include "cryptonote_basic/cryptonote_basic.h"
+
+namespace cryptonote
+{
+  /*! Transactions are expensive to move or copy (lots of 32-byte internal
+      buffers). This allows `cryptonote::core` to do a single notification for
+      a vector of transactions, without having to move/copy duplicate or invalid
+      transactions. */
+  struct txpool_event
+  {
+    cryptonote::transaction tx;
+    crypto::hash hash;
+    bool res; //!< Listeners must ignore `tx` when this is false.
+  };
+}

src/cryptonote_basic/fwd.h

@@ -0,0 +1,36 @@
+// Copyright (c) 2020, The Monero Project
+//
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without modification, are
+// permitted provided that the following conditions are met:
+//
+// 1. Redistributions of source code must retain the above copyright notice, this list of
+//    conditions and the following disclaimer.
+//
+// 2. Redistributions in binary form must reproduce the above copyright notice, this list
+//    of conditions and the following disclaimer in the documentation and/or other
+//    materials provided with the distribution.
+//
+// 3. Neither the name of the copyright holder nor the names of its contributors may be
+//    used to endorse or promote products derived from this software without specific
+//    prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
+// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
+// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
+// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#pragma once
+
+namespace cryptonote
+{
+  struct block;
+  class transaction;
+  struct txpool_event;
+}

src/cryptonote_core/blockchain.cpp

@@ -1234,10 +1234,15 @@ bool Blockchain::switch_to_alternative_blockchain(std::list<block_extended_info>
     reorg_notify->notify("%s", std::to_string(split_height).c_str(), "%h", std::to_string(m_db->height()).c_str(),
         "%n", std::to_string(m_db->height() - split_height).c_str(), "%d", std::to_string(discarded_blocks).c_str(), NULL);
 
-  std::shared_ptr<tools::Notify> block_notify = m_block_notify;
+  for (const auto& notifier : m_block_notifiers)
-  if (block_notify)
+  {
-    for (const auto &bei: alt_chain)
+    std::size_t notify_height = split_height;
-      block_notify->notify("%s", epee::string_tools::pod_to_hex(get_block_hash(bei.bl)).c_str(), NULL);
+    for (const auto& bei: alt_chain)
+    {
+      notifier(notify_height, {std::addressof(bei.bl), 1});
+      ++notify_height;
+    }
+  }
 
   MGINFO_GREEN("REORGANIZE SUCCESS! on height: " << split_height << ", new blockchain size: " << m_db->height());
   return true;
@@ -4236,12 +4241,9 @@ leave:
   get_difficulty_for_next_block(); // just to cache it
   invalidate_block_template_cache();
 
-  if (notify)
+
-  {
+  for (const auto& notifier: m_block_notifiers)
-    std::shared_ptr<tools::Notify> block_notify = m_block_notify;
+    notifier(new_height - 1, {std::addressof(bl), 1});
-    if (block_notify)
-      block_notify->notify("%s", epee::string_tools::pod_to_hex(id).c_str(), NULL);
-  }
 
   return true;
 }
@@ -5132,6 +5134,15 @@ void Blockchain::set_user_options(uint64_t maxthreads, bool sync_on_blocks, uint
   m_max_prepare_blocks_threads = maxthreads;
 }
 
+void Blockchain::add_block_notify(boost::function<void(std::uint64_t, epee::span<const block>)>&& notify)
+{
+  if (notify)
+  {
+    CRITICAL_REGION_LOCAL(m_blockchain_lock);
+    m_block_notifiers.push_back(std::move(notify));
+  }
+}
+
 void Blockchain::safesyncmode(const bool onoff)
 {
   /* all of this is no-op'd if the user set a specific

src/cryptonote_core/blockchain.h

@@ -30,6 +30,7 @@
 
 #pragma once
 #include <boost/asio/io_service.hpp>
+#include <boost/function/function_fwd.hpp>
 #include <boost/serialization/serialization.hpp>
 #include <boost/serialization/version.hpp>
 #include <boost/serialization/list.hpp>
@@ -764,7 +765,7 @@ namespace cryptonote
      *
      * @param notify the notify object to call at every new block
      */
-    void set_block_notify(const std::shared_ptr<tools::Notify> &notify) { m_block_notify = notify; }
+    void add_block_notify(boost::function<void(std::uint64_t, epee::span<const block>)> &&notify);
 
     /**
      * @brief sets a reorg notify object to call for every reorg
@@ -1125,7 +1126,11 @@ namespace cryptonote
 
     bool m_batch_success;
 
-    std::shared_ptr<tools::Notify> m_block_notify;
+    /* `boost::function` is used because the implementation never allocates if
+       the callable object has a single `std::shared_ptr` or `std::weap_ptr`
+       internally. Whereas, the libstdc++ `std::function` will allocate. */
+
+    std::vector<boost::function<void(std::uint64_t, epee::span<const block>)>> m_block_notifiers;
     std::shared_ptr<tools::Notify> m_reorg_notify;
 
     // for prepare_handle_incoming_blocks

src/cryptonote_core/cryptonote_core.cpp

@@ -41,6 +41,7 @@ using namespace epee;
 #include "common/download.h"
 #include "common/threadpool.h"
 #include "common/command_line.h"
+#include "cryptonote_basic/events.h"
 #include "warnings.h"
 #include "crypto/crypto.h"
 #include "cryptonote_config.h"
@@ -51,6 +52,7 @@ using namespace epee;
 #include "ringct/rctTypes.h"
 #include "blockchain_db/blockchain_db.h"
 #include "ringct/rctSigs.h"
+#include "rpc/zmq_pub.h"
 #include "common/notify.h"
 #include "hardforks/hardforks.h"
 #include "version.h"
@@ -262,6 +264,13 @@ namespace cryptonote
   {
     m_blockchain_storage.set_enforce_dns_checkpoints(enforce_dns);
   }
+  //-----------------------------------------------------------------------------------
+  void core::set_txpool_listener(boost::function<void(std::vector<txpool_event>)> zmq_pub)
+  {
+    CRITICAL_REGION_LOCAL(m_incoming_tx_lock);
+    m_zmq_pub = std::move(zmq_pub);
+  }
+
   //-----------------------------------------------------------------------------------------------
   bool core::update_checkpoints(const bool skip_dns /* = false */)
   {
@@ -614,7 +623,20 @@ namespace cryptonote
     try
     {
       if (!command_line::is_arg_defaulted(vm, arg_block_notify))
-        m_blockchain_storage.set_block_notify(std::shared_ptr<tools::Notify>(new tools::Notify(command_line::get_arg(vm, arg_block_notify).c_str())));
+      {
+        struct hash_notify
+        {
+          tools::Notify cmdline;
+
+          void operator()(std::uint64_t, epee::span<const block> blocks) const
+          {
+            for (const block bl : blocks)
+              cmdline.notify("%s", epee::string_tools::pod_to_hex(get_block_hash(bl)).c_str(), NULL);
+          }
+        };
+
+        m_blockchain_storage.add_block_notify(hash_notify{{command_line::get_arg(vm, arg_block_notify).c_str()}});
+      }
     }
     catch (const std::exception &e)
     {
@@ -957,8 +979,7 @@ namespace cryptonote
       return false;
     }
 
-    struct result { bool res; cryptonote::transaction tx; crypto::hash hash; };
+    std::vector<txpool_event> results(tx_blobs.size());
-    std::vector<result> results(tx_blobs.size());
 
     CRITICAL_REGION_LOCAL(m_incoming_tx_lock);
 
@@ -1023,6 +1044,7 @@ namespace cryptonote
     if (!tx_info.empty())
       handle_incoming_tx_accumulated_batch(tx_info, tx_relay == relay_method::block);
 
+    bool valid_events = false;
     bool ok = true;
     it = tx_blobs.begin();
     for (size_t i = 0; i < tx_blobs.size(); i++, ++it) {
@@ -1045,10 +1067,18 @@ namespace cryptonote
       {MERROR_VER("Transaction verification impossible: " << results[i].hash);}
 
       if(tvc[i].m_added_to_pool)
+      {
         MDEBUG("tx added: " << results[i].hash);
+        valid_events = true;
+      }
+      else
+        results[i].res = false;
     }
-    return ok;
 
+    if (valid_events && m_zmq_pub && matches_category(tx_relay, relay_category::legacy))
+      m_zmq_pub(std::move(results));
+
+    return ok;
     CATCH_ENTRY_L0("core::handle_incoming_txs()", false);
   }
   //-----------------------------------------------------------------------------------------------

src/cryptonote_core/cryptonote_core.h

@@ -32,9 +32,11 @@
 
 #include <ctime>
 
+#include <boost/function.hpp>
 #include <boost/program_options/options_description.hpp>
 #include <boost/program_options/variables_map.hpp>
 
+#include "cryptonote_basic/fwd.h"
 #include "cryptonote_core/i_core_events.h"
 #include "cryptonote_protocol/cryptonote_protocol_handler_common.h"
 #include "cryptonote_protocol/enums.h"
@@ -48,6 +50,7 @@
 #include "warnings.h"
 #include "crypto/hash.h"
 #include "span.h"
+#include "rpc/fwd.h"
 
 PUSH_WARNINGS
 DISABLE_VS_WARNINGS(4355)
@@ -445,6 +448,13 @@ namespace cryptonote
       */
      void set_enforce_dns_checkpoints(bool enforce_dns);
 
+     /**
+      * @brief set a listener for txes being added to the txpool
+      *
+      * @param callable to notify, or empty function to disable.
+      */
+     void set_txpool_listener(boost::function<void(std::vector<txpool_event>)> zmq_pub);
+
      /**
       * @brief set whether or not to enable or disable DNS checkpoints
       *
@@ -1098,7 +1108,12 @@ namespace cryptonote
      bool m_fluffy_blocks_enabled;
      bool m_offline;
 
+    /* `boost::function` is used because the implementation never allocates if
+       the callable object has a single `std::shared_ptr` or `std::weap_ptr`
+       internally. Whereas, the libstdc++ `std::function` will allocate. */
+
      std::shared_ptr<tools::Notify> m_block_rate_notify;
+     boost::function<void(std::vector<txpool_event>)> m_zmq_pub;
    };
 }
 

src/daemon/command_line_args.h

@@ -121,6 +121,10 @@ namespace daemon_args
       return val;
     }
   };
+  const command_line::arg_descriptor<std::vector<std::string>> arg_zmq_pub = {
+    "zmq-pub"
+  , "Address for ZMQ pub - tcp://ip:port or ipc://path"
+  };
 
   const command_line::arg_descriptor<bool> arg_zmq_rpc_disabled = {
     "no-zmq"

src/daemon/daemon.cpp

@@ -34,10 +34,12 @@
 #include "misc_log_ex.h"
 #include "daemon/daemon.h"
 #include "rpc/daemon_handler.h"
+#include "rpc/zmq_pub.h"
 #include "rpc/zmq_server.h"
 
 #include "common/password.h"
 #include "common/util.h"
+#include "cryptonote_basic/events.h"
 #include "daemon/core.h"
 #include "daemon/p2p.h"
 #include "daemon/protocol.h"
@@ -56,6 +58,17 @@ using namespace epee;
 
 namespace daemonize {
 
+struct zmq_internals
+{
+  explicit zmq_internals(t_core& core, t_p2p& p2p)
+    : rpc_handler{core.get(), p2p.get()}
+    , server{rpc_handler}
+  {}
+
+  cryptonote::rpc::DaemonHandler rpc_handler;
+  cryptonote::rpc::ZmqServer server;
+};
+
 struct t_internals {
 private:
   t_protocol protocol;
@@ -63,6 +76,7 @@ public:
   t_core core;
   t_p2p p2p;
   std::vector<std::unique_ptr<t_rpc>> rpcs;
+  std::unique_ptr<zmq_internals> zmq;
 
   t_internals(
       boost::program_options::variables_map const & vm
@@ -70,6 +84,7 @@ public:
     : core{vm}
     , protocol{vm, core, command_line::get_arg(vm, cryptonote::arg_offline)}
     , p2p{vm, protocol}
+    , zmq{nullptr}
   {
     // Handle circular dependencies
     protocol.set_p2p_endpoint(p2p.get());
@@ -86,6 +101,28 @@ public:
       auto restricted_rpc_port = command_line::get_arg(vm, restricted_rpc_port_arg);
       rpcs.emplace_back(new t_rpc{vm, core, p2p, true, restricted_rpc_port, "restricted", true});
     }
+
+    if (!command_line::get_arg(vm, daemon_args::arg_zmq_rpc_disabled))
+    {
+      zmq.reset(new zmq_internals{core, p2p});
+
+      const std::string zmq_port = command_line::get_arg(vm, daemon_args::arg_zmq_rpc_bind_port);
+      const std::string zmq_address = command_line::get_arg(vm, daemon_args::arg_zmq_rpc_bind_ip);
+
+      if (!zmq->server.init_rpc(zmq_address, zmq_port))
+        throw std::runtime_error{"Failed to add TCP socket(" + zmq_address + ":" + zmq_port + ") to ZMQ RPC Server"};
+
+      std::shared_ptr<cryptonote::listener::zmq_pub> shared;
+      const std::vector<std::string> zmq_pub = command_line::get_arg(vm, daemon_args::arg_zmq_pub);
+      if (!zmq_pub.empty() && !(shared = zmq->server.init_pub(epee::to_span(zmq_pub))))
+        throw std::runtime_error{"Failed to initialize zmq_pub"};
+
+      if (shared)
+      {
+        core.get().get_blockchain_storage().add_block_notify(cryptonote::listener::zmq_pub::chain_main{shared});
+        core.get().set_txpool_listener(cryptonote::listener::zmq_pub::txpool_add{shared});
+      }
+    }
   }
 };
 
@@ -103,9 +140,6 @@ t_daemon::t_daemon(
   : mp_internals{new t_internals{vm}},
   public_rpc_port(public_rpc_port)
 {
-  zmq_rpc_bind_port = command_line::get_arg(vm, daemon_args::arg_zmq_rpc_bind_port);
-  zmq_rpc_bind_address = command_line::get_arg(vm, daemon_args::arg_zmq_rpc_bind_ip);
-  zmq_rpc_disabled = command_line::get_arg(vm, daemon_args::arg_zmq_rpc_disabled);
 }
 
 t_daemon::~t_daemon() = default;
@@ -169,31 +203,8 @@ bool t_daemon::run(bool interactive)
       rpc_commands->start_handling(std::bind(&daemonize::t_daemon::stop_p2p, this));
     }
 
-    cryptonote::rpc::DaemonHandler rpc_daemon_handler(mp_internals->core.get(), mp_internals->p2p.get());
+    if (mp_internals->zmq)
-    cryptonote::rpc::ZmqServer zmq_server(rpc_daemon_handler);
+      mp_internals->zmq->server.run();
-
-    if (!zmq_rpc_disabled)
-    {
-      if (!zmq_server.addTCPSocket(zmq_rpc_bind_address, zmq_rpc_bind_port))
-      {
-        LOG_ERROR(std::string("Failed to add TCP Socket (") + zmq_rpc_bind_address
-            + ":" + zmq_rpc_bind_port + ") to ZMQ RPC Server");
-
-        if (rpc_commands)
-          rpc_commands->stop_handling();
-
-        for(auto& rpc : mp_internals->rpcs)
-          rpc->stop();
-
-        return false;
-      }
-
-      MINFO("Starting ZMQ server...");
-      zmq_server.run();
-
-      MINFO(std::string("ZMQ server started at ") + zmq_rpc_bind_address
-            + ":" + zmq_rpc_bind_port + ".");
-    }
     else
       MINFO("ZMQ server disabled");
 
@@ -208,8 +219,8 @@ bool t_daemon::run(bool interactive)
     if (rpc_commands)
       rpc_commands->stop_handling();
 
-    if (!zmq_rpc_disabled)
+    if (mp_internals->zmq)
-      zmq_server.stop();
+      mp_internals->zmq->server.stop();
 
     for(auto& rpc : mp_internals->rpcs)
       rpc->stop();

src/daemon/daemon.h

@@ -44,9 +44,6 @@ private:
 private:
   std::unique_ptr<t_internals> mp_internals;
   uint16_t public_rpc_port;
-  std::string zmq_rpc_bind_address;
-  std::string zmq_rpc_bind_port;
-  bool zmq_rpc_disabled;
 public:
   t_daemon(
       boost::program_options::variables_map const & vm,

src/daemon/main.cpp

@@ -154,6 +154,7 @@ int main(int argc, char const * argv[])
       command_line::add_arg(core_settings, daemon_args::arg_public_node);
       command_line::add_arg(core_settings, daemon_args::arg_zmq_rpc_bind_ip);
       command_line::add_arg(core_settings, daemon_args::arg_zmq_rpc_bind_port);
+      command_line::add_arg(core_settings, daemon_args::arg_zmq_pub);
       command_line::add_arg(core_settings, daemon_args::arg_zmq_rpc_disabled);
 
       daemonizer::init_options(hidden_options, visible_options);

src/net/zmq.cpp

@@ -158,20 +158,6 @@ namespace zmq
                 return unsigned(max_out) < added ? max_out : int(added);
             }
         };
-
-        template<typename F, typename... T>
-        expect<void> retry_op(F op, T&&... args) noexcept(noexcept(op(args...)))
-        {
-            for (;;)
-            {
-                if (0 <= op(args...))
-                    return success();
-
-                const int error = zmq_errno();
-                if (error != EINTR)
-                    return make_error_code(error);
-            }
-        }
     } // anonymous
 
     expect<std::string> receive(void* const socket, const int flags)

src/net/zmq.h

@@ -26,6 +26,8 @@
 // STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
 // THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
+#pragma once
+
 #include <memory>
 #include <string>
 #include <system_error>
@@ -105,6 +107,26 @@ namespace zmq
     //! Unique ZMQ socket handle, calls `zmq_close` on destruction.
     using socket = std::unique_ptr<void, close>;
 
+  /*! Retry a ZMQ function on `EINTR` errors. `F` must return an int with
+      values less than 0 on error.
+
+      \param op The ZMQ function to execute + retry
+      \param args Forwarded to `op`. Must be resuable in case of retry.
+      \return All errors except for `EINTR`. */
+    template<typename F, typename... T>
+    expect<void> retry_op(F op, T&&... args) noexcept(noexcept(op(args...)))
+    {
+      for (;;)
+      {
+        if (0 <= op(args...))
+          return success();
+
+        const int error = zmq_errno();
+        if (error != EINTR)
+          return make_error_code(error);
+      }
+    }
+
     /*! Read all parts of the next message on `socket`. Blocks until the entire
         next message (all parts) are read, or until `zmq_term` is called on the
         `zmq_context` associated with `socket`. If the context is terminated,

src/rpc/CMakeLists.txt

@@ -45,8 +45,11 @@ set(daemon_messages_sources
   message.cpp
   daemon_messages.cpp)
 
+set(rpc_pub_sources zmq_pub.cpp)
+
 set(daemon_rpc_server_sources
   daemon_handler.cpp
+  zmq_pub.cpp
   zmq_server.cpp)
 
 
@@ -59,8 +62,9 @@ set(rpc_headers
   rpc_version_str.h
   rpc_handler.h)
 
-set(daemon_rpc_server_headers)
+set(rpc_pub_headers zmq_pub.h)
 
+set(daemon_rpc_server_headers)
 
 set(rpc_daemon_private_headers
   bootstrap_daemon.h
@@ -83,6 +87,8 @@ set(daemon_rpc_server_private_headers
 monero_private_headers(rpc
   ${rpc_private_headers})
 
+set(rpc_pub_private_headers)
+
 monero_private_headers(daemon_rpc_server
   ${daemon_rpc_server_private_headers})
 
@@ -97,6 +103,11 @@ monero_add_library(rpc
   ${rpc_headers}
   ${rpc_private_headers})
 
+monero_add_library(rpc_pub
+  ${rpc_pub_sources}
+  ${rpc_pub_headers}
+  ${rpc_pub_private_headers})
+
 monero_add_library(daemon_messages
   ${daemon_messages_sources}
   ${daemon_messages_headers}
@@ -131,6 +142,14 @@ target_link_libraries(rpc
   PRIVATE
     ${EXTRA_LIBRARIES})
 
+target_link_libraries(rpc_pub
+  PUBLIC
+    epee
+    net
+    cryptonote_basic
+    serialization
+    ${Boost_THREAD_LIBRARY})
+
 target_link_libraries(daemon_messages
   LINK_PRIVATE
     cryptonote_core
@@ -142,6 +161,7 @@ target_link_libraries(daemon_messages
 target_link_libraries(daemon_rpc_server
   LINK_PRIVATE
     rpc
+    rpc_pub
     cryptonote_core
     cryptonote_protocol
     version

src/rpc/fwd.h

@@ -0,0 +1,37 @@
+// Copyright (c) 2019-2020, The Monero Project
+//
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without modification, are
+// permitted provided that the following conditions are met:
+//
+// 1. Redistributions of source code must retain the above copyright notice, this list of
+//    conditions and the following disclaimer.
+//
+// 2. Redistributions in binary form must reproduce the above copyright notice, this list
+//    of conditions and the following disclaimer in the documentation and/or other
+//    materials provided with the distribution.
+//
+// 3. Neither the name of the copyright holder nor the names of its contributors may be
+//    used to endorse or promote products derived from this software without specific
+//    prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
+// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
+// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
+// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#pragma once
+
+namespace cryptonote
+{
+  namespace listener
+  {
+    class zmq_pub;
+  }
+}

src/rpc/zmq_pub.cpp

@@ -0,0 +1,478 @@
+// Copyright (c) 2020, The Monero Project
+//
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without modification, are
+// permitted provided that the following conditions are met:
+//
+// 1. Redistributions of source code must retain the above copyright notice, this list of
+//    conditions and the following disclaimer.
+//
+// 2. Redistributions in binary form must reproduce the above copyright notice, this list
+//    of conditions and the following disclaimer in the documentation and/or other
+//    materials provided with the distribution.
+//
+// 3. Neither the name of the copyright holder nor the names of its contributors may be
+//    used to endorse or promote products derived from this software without specific
+//    prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
+// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
+// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
+// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#include "zmq_pub.h"
+
+#include <algorithm>
+#include <boost/range/adaptor/filtered.hpp>
+#include <boost/range/adaptor/transformed.hpp>
+#include <boost/thread/locks.hpp>
+#include <cassert>
+#include <cstdint>
+#include <cstring>
+#include <rapidjson/document.h>
+#include <rapidjson/stringbuffer.h>
+#include <rapidjson/writer.h>
+#include <stdexcept>
+#include <string>
+#include <utility>
+
+#include "common/expect.h"
+#include "crypto/crypto.h"
+#include "cryptonote_basic/cryptonote_format_utils.h"
+#include "cryptonote_basic/events.h"
+#include "misc_log_ex.h"
+#include "serialization/json_object.h"
+
+#undef MONERO_DEFAULT_LOG_CATEGORY
+#define MONERO_DEFAULT_LOG_CATEGORY "net.zmq"
+
+namespace
+{
+  constexpr const char txpool_signal[] = "tx_signal";
+
+  using chain_writer =  void(epee::byte_stream&, std::uint64_t, epee::span<const cryptonote::block>);
+  using txpool_writer = void(epee::byte_stream&, epee::span<const cryptonote::txpool_event>);
+
+  template<typename F>
+  struct context
+  {
+    char const* const name;
+    F* generate_pub;
+  };
+
+  template<typename T>
+  bool operator<(const context<T>& lhs, const context<T>& rhs) noexcept
+  {
+    return std::strcmp(lhs.name, rhs.name) < 0;
+  }
+
+  template<typename T>
+  bool operator<(const context<T>& lhs, const boost::string_ref rhs) noexcept
+  {
+    return lhs.name < rhs;
+  }
+
+  struct is_valid
+  {
+    bool operator()(const cryptonote::txpool_event& event) const noexcept
+    {
+      return event.res;
+    }
+  };
+
+  template<typename T, std::size_t N>
+  void verify_sorted(const std::array<context<T>, N>& elems, const char* name)
+  {
+    auto unsorted = std::is_sorted_until(elems.begin(), elems.end());
+    if (unsorted != elems.end())
+      throw std::logic_error{name + std::string{" array is not properly sorted, see: "} + unsorted->name};
+  }
+
+  void write_header(epee::byte_stream& buf, const boost::string_ref name)
+  {
+    buf.write(name.data(), name.size());
+    buf.put(':');
+  }
+
+  //! \return `name:...` where `...` is JSON and `name` is directly copied (no quotes - not JSON).
+  template<typename T>
+  void json_pub(epee::byte_stream& buf, const T value)
+  {
+    rapidjson::Writer<epee::byte_stream> dest{buf};
+    using cryptonote::json::toJsonValue;
+    toJsonValue(dest, value);
+  }
+
+  //! Object for "minimal" block serialization
+  struct minimal_chain
+  {
+    const std::uint64_t height;
+    const epee::span<const cryptonote::block> blocks;
+  };
+
+  //! Object for "minimal" tx serialization
+  struct minimal_txpool
+  {
+    const cryptonote::transaction& tx;
+  };
+
+  void toJsonValue(rapidjson::Writer<epee::byte_stream>& dest, const minimal_chain self)
+  {
+    namespace adapt = boost::adaptors;
+
+    const auto to_block_id = [](const cryptonote::block& bl)
+    {
+      crypto::hash id;
+      if (!get_block_hash(bl, id))
+        MERROR("ZMQ/Pub failure: get_block_hash");
+      return id;
+    };
+
+    assert(!self.blocks.empty()); // checked in zmq_pub::send_chain_main
+
+    dest.StartObject();
+    INSERT_INTO_JSON_OBJECT(dest, first_height, self.height);
+    INSERT_INTO_JSON_OBJECT(dest, first_prev_id, self.blocks[0].prev_id);
+    INSERT_INTO_JSON_OBJECT(dest, ids, (self.blocks | adapt::transformed(to_block_id)));
+    dest.EndObject();
+  }
+
+  void toJsonValue(rapidjson::Writer<epee::byte_stream>& dest, const minimal_txpool self)
+  {
+    crypto::hash id{};
+    std::size_t blob_size = 0;
+    if (!get_transaction_hash(self.tx, id, blob_size))
+    {
+      MERROR("ZMQ/Pub failure: get_transaction_hash");
+      return;
+    }
+
+    dest.StartObject();
+    INSERT_INTO_JSON_OBJECT(dest, id, id);
+    INSERT_INTO_JSON_OBJECT(dest, blob_size, blob_size);
+    dest.EndObject();
+  }
+
+  void json_full_chain(epee::byte_stream& buf, const std::uint64_t height, const epee::span<const cryptonote::block> blocks)
+  {
+    json_pub(buf, blocks);
+  }
+
+  void json_minimal_chain(epee::byte_stream& buf, const std::uint64_t height, const epee::span<const cryptonote::block> blocks)
+  {
+    json_pub(buf, minimal_chain{height, blocks});
+  }
+
+  // boost::adaptors are in place "views" - no copy/move takes place
+  // moving transactions (via sort, etc.), is expensive!
+
+  void json_full_txpool(epee::byte_stream& buf, epee::span<const cryptonote::txpool_event> txes)
+  {
+    namespace adapt = boost::adaptors;
+    const auto to_full_tx = [](const cryptonote::txpool_event& event)
+    {
+      return event.tx;
+    };
+    json_pub(buf, (txes | adapt::filtered(is_valid{}) | adapt::transformed(to_full_tx)));
+  }
+
+  void json_minimal_txpool(epee::byte_stream& buf, epee::span<const cryptonote::txpool_event> txes)
+  {
+    namespace adapt = boost::adaptors;
+    const auto to_minimal_tx = [](const cryptonote::txpool_event& event)
+    {
+      return minimal_txpool{event.tx};
+    };
+    json_pub(buf, (txes | adapt::filtered(is_valid{}) | adapt::transformed(to_minimal_tx)));
+  }
+
+  constexpr const std::array<context<chain_writer>, 2> chain_contexts =
+  {{
+    {u8"json-full-chain_main", json_full_chain},
+    {u8"json-minimal-chain_main", json_minimal_chain}
+  }};
+
+  constexpr const std::array<context<txpool_writer>, 2> txpool_contexts =
+  {{
+    {u8"json-full-txpool_add", json_full_txpool},
+    {u8"json-minimal-txpool_add", json_minimal_txpool}
+  }};
+
+  template<typename T, std::size_t N>
+  epee::span<const context<T>> get_range(const std::array<context<T>, N>& contexts, const boost::string_ref value)
+  {
+    const auto not_prefix = [](const boost::string_ref lhs, const context<T>& rhs)
+    {
+      return !(boost::string_ref{rhs.name}.starts_with(lhs));
+    };
+
+    const auto lower = std::lower_bound(contexts.begin(), contexts.end(), value);
+    const auto upper = std::upper_bound(lower, contexts.end(), value, not_prefix);
+    return {lower, std::size_t(upper - lower)};
+  }
+
+  template<std::size_t N, typename T>
+  void add_subscriptions(std::array<std::size_t, N>& subs, const epee::span<const context<T>> range, context<T> const* const first)
+  {
+    assert(range.size() <= N);
+    assert(range.begin() - first <= N - range.size());
+
+    for (const auto& ctx : range)
+    {
+      const std::size_t i = std::addressof(ctx) - first;
+      subs[i] = std::min(std::numeric_limits<std::size_t>::max() - 1, subs[i]) + 1;
+    }
+  }
+
+  template<std::size_t N, typename T>
+  void remove_subscriptions(std::array<std::size_t, N>& subs, const epee::span<const context<T>> range, context<T> const* const first)
+  {
+    assert(range.size() <= N);
+    assert(range.begin() - first <= N - range.size());
+
+    for (const auto& ctx : range)
+    {
+      const std::size_t i = std::addressof(ctx) - first;
+      subs[i] = std::max(std::size_t(1), subs[i]) - 1;
+    }
+  }
+
+  template<std::size_t N, typename T, typename... U>
+  std::array<epee::byte_slice, N> make_pubs(const std::array<std::size_t, N>& subs, const std::array<context<T>, N>& contexts, U&&... args)
+  {
+    epee::byte_stream buf{};
+
+    std::size_t last_offset = 0;
+    std::array<std::size_t, N> offsets{{}};
+    for (std::size_t i = 0; i < N; ++i)
+    {
+      if (subs[i])
+      {
+        write_header(buf, contexts[i].name);
+        contexts[i].generate_pub(buf, std::forward<U>(args)...);
+        offsets[i] = buf.size() - last_offset;
+        last_offset = buf.size();
+      }
+    }
+
+    epee::byte_slice bytes{std::move(buf)};
+    std::array<epee::byte_slice, N> out;
+    for (std::size_t i = 0; i < N; ++i)
+      out[i] = bytes.take_slice(offsets[i]);
+
+    return out;
+  }
+
+  template<std::size_t N>
+  std::size_t send_messages(void* const socket, std::array<epee::byte_slice, N>& messages)
+  {
+    std::size_t count = 0;
+    for (epee::byte_slice& message : messages)
+    {
+      if (!message.empty())
+      {
+        const expect<void> sent = net::zmq::send(std::move(message), socket, ZMQ_DONTWAIT);
+        if (!sent)
+          MERROR("Failed to send ZMQ/Pub message: " << sent.error().message());
+        else
+          ++count;
+      }
+    }
+    return count;
+  }
+
+  expect<bool> relay_block_pub(void* const relay, void* const pub) noexcept
+  {
+    zmq_msg_t msg;
+    zmq_msg_init(std::addressof(msg));
+    MONERO_CHECK(net::zmq::retry_op(zmq_msg_recv, std::addressof(msg), relay, ZMQ_DONTWAIT));
+
+    const boost::string_ref payload{
+      reinterpret_cast<const char*>(zmq_msg_data(std::addressof(msg))),
+      zmq_msg_size(std::addressof(msg))
+    };
+
+    if (payload == txpool_signal)
+    {
+      zmq_msg_close(std::addressof(msg));
+      return false;
+    }
+
+    // forward block messages (serialized on P2P thread for now)
+    const expect<void> sent = net::zmq::retry_op(zmq_msg_send, std::addressof(msg), pub, ZMQ_DONTWAIT);
+    if (!sent)
+    {
+      zmq_msg_close(std::addressof(msg));
+      return sent.error();
+    }
+    return true;
+  }
+} // anonymous
+
+namespace cryptonote { namespace listener
+{
+
+zmq_pub::zmq_pub(void* context)
+  : relay_(),
+    chain_subs_{{0}},
+    txpool_subs_{{0}},
+    sync_()
+{
+  if (!context)
+    throw std::logic_error{"ZMQ context cannot be NULL"};
+
+  verify_sorted(chain_contexts, "chain_contexts");
+  verify_sorted(txpool_contexts, "txpool_contexts");
+
+  relay_.reset(zmq_socket(context, ZMQ_PAIR));
+  if (!relay_)
+    MONERO_ZMQ_THROW("Failed to create relay socket");
+  if (zmq_connect(relay_.get(), relay_endpoint()) != 0)
+    MONERO_ZMQ_THROW("Failed to connect relay socket");
+}
+
+zmq_pub::~zmq_pub()
+{}
+
+bool zmq_pub::sub_request(boost::string_ref message)
+{
+  if (!message.empty())
+  {
+    const char tag = message[0];
+    message.remove_prefix(1);
+
+    const auto chain_range = get_range(chain_contexts, message);
+    const auto txpool_range = get_range(txpool_contexts, message);
+
+    if (!chain_range.empty() || !txpool_range.empty())
+    {
+      MDEBUG("Client " << (tag ? "subscribed" : "unsubscribed") << " to " <<
+             chain_range.size() << " chain topic(s) and " << txpool_range.size() << " txpool topic(s)");
+
+      const boost::lock_guard<boost::mutex> lock{sync_};
+      switch (tag)
+      {
+      case 0:
+        remove_subscriptions(chain_subs_, chain_range, chain_contexts.begin());
+        remove_subscriptions(txpool_subs_, txpool_range, txpool_contexts.begin());
+        return true;
+      case 1:
+        add_subscriptions(chain_subs_, chain_range, chain_contexts.begin());
+        add_subscriptions(txpool_subs_, txpool_range, txpool_contexts.begin());
+        return true;
+      default:
+        break;
+      }
+    }
+  }
+  MERROR("Invalid ZMQ/Sub message");
+  return false;
+}
+
+bool zmq_pub::relay_to_pub(void* const relay, void* const pub)
+{
+  const expect<bool> relayed = relay_block_pub(relay, pub);
+  if (!relayed)
+  {
+    MERROR("Error relaying ZMQ/Pub: " << relayed.error().message());
+    return false;
+  }
+
+  if (!*relayed)
+  {
+    std::array<std::size_t, 2> subs;
+    std::vector<cryptonote::txpool_event> events;
+    {
+      const boost::lock_guard<boost::mutex> lock{sync_};
+      if (txes_.empty())
+        return false;
+
+      subs = txpool_subs_;
+      events = std::move(txes_.front());
+      txes_.pop_front();
+    }
+    auto messages = make_pubs(subs, txpool_contexts, epee::to_span(events));
+    send_messages(pub, messages);
+    MDEBUG("Sent txpool ZMQ/Pub");
+  }
+  else
+    MDEBUG("Sent chain_main ZMQ/Pub");
+
+  return true;
+}
+
+std::size_t zmq_pub::send_chain_main(const std::uint64_t height, const epee::span<const cryptonote::block> blocks)
+{
+  if (blocks.empty())
+    return 0;
+
+  /* Block format only sends one block at a time - multiple block notifications
+     are less common and only occur on rollbacks. */
+
+  boost::unique_lock<boost::mutex> guard{sync_};
+
+  const auto subs_copy = chain_subs_;
+  guard.unlock();
+
+  for (const std::size_t sub : subs_copy)
+  {
+    if (sub)
+    {
+      /* cryptonote_core/blockchain.cpp cannot "give" us the block like core
+         does for txpool events. Since copying the block is expensive anyway,
+         serialization is done right here on the p2p thread (for now). */
+
+        auto messages = make_pubs(subs_copy, chain_contexts, height, blocks);
+        guard.lock();
+        return send_messages(relay_.get(), messages);
+    }
+  }
+  return 0;
+}
+
+std::size_t zmq_pub::send_txpool_add(std::vector<txpool_event> txes)
+{
+  if (txes.empty())
+    return 0;
+
+  const boost::lock_guard<boost::mutex> lock{sync_};
+  for (const std::size_t sub : txpool_subs_)
+  {
+    if (sub)
+    {
+      const expect<void> sent = net::zmq::retry_op(zmq_send_const, relay_.get(), txpool_signal, sizeof(txpool_signal) - 1, ZMQ_DONTWAIT);
+      if (sent)
+        txes_.emplace_back(std::move(txes));
+      else
+        MERROR("ZMQ/Pub failure, relay queue error: " << sent.error().message());
+      return bool(sent);
+    }
+  }
+  return 0;
+}
+
+void zmq_pub::chain_main::operator()(const std::uint64_t height, epee::span<const cryptonote::block> blocks) const
+{
+  const std::shared_ptr<zmq_pub> self = self_.lock();
+  if (self)
+    self->send_chain_main(height, blocks);
+  else
+    MERROR("Unable to send ZMQ/Pub - ZMQ server destroyed");
+}
+
+void zmq_pub::txpool_add::operator()(std::vector<cryptonote::txpool_event> txes) const
+{
+  const std::shared_ptr<zmq_pub> self = self_.lock();
+  if (self)
+      self->send_txpool_add(std::move(txes));
+  else
+    MERROR("Unable to send ZMQ/Pub - ZMQ server destroyed");
+}
+
+}}

src/rpc/zmq_pub.h

@@ -0,0 +1,110 @@
+// Copyright (c) 2020, The Monero Project
+//
+// All rights reserved.
+ //
+// Redistribution and use in source and binary forms, with or without modification, are
+// permitted provided that the following conditions are met:
+//
+// 1. Redistributions of source code must retain the above copyright notice, this list of
+//    conditions and the following disclaimer.
+//
+// 2. Redistributions in binary form must reproduce the above copyright notice, this list
+//    of conditions and the following disclaimer in the documentation and/or other
+//    materials provided with the distribution.
+//
+// 3. Neither the name of the copyright holder nor the names of its contributors may be
+//    used to endorse or promote products derived from this software without specific
+//    prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
+// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
+// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
+// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#pragma once
+
+#include <array>
+#include <boost/thread/mutex.hpp>
+#include <boost/utility/string_ref.hpp>
+#include <cstdint>
+#include <deque>
+#include <memory>
+#include <vector>
+
+#include "cryptonote_basic/fwd.h"
+#include "net/zmq.h"
+#include "span.h"
+
+namespace cryptonote { namespace listener
+{
+/*! \brief Sends ZMQ PUB messages on cryptonote events
+
+    Clients must ensure that all transaction(s) are notified before any blocks
+    they are contained in, and must ensure that each block is notified in chain
+    order. An external lock **must** be held by clients during the entire
+    txpool check and notification sequence and (a possibly second) lock is held
+    during the entire block check and notification sequence. Otherwise, events
+    could be sent in a different order than processed. */
+class zmq_pub
+{
+  /* Each socket has its own internal queue. So we can only use one socket, else
+     the messages being published are not guaranteed to be in the same order
+     pushed. */
+
+    net::zmq::socket relay_;
+    std::deque<std::vector<txpool_event>> txes_;
+    std::array<std::size_t, 2> chain_subs_;
+    std::array<std::size_t, 2> txpool_subs_;
+    boost::mutex sync_; //!< Synchronizes counts in `*_subs_` arrays.
+
+  public:
+    //! \return Name of ZMQ_PAIR endpoint for pub notifications
+    static constexpr const char* relay_endpoint() noexcept { return "inproc://pub_relay"; }
+
+    explicit zmq_pub(void* context);
+
+    zmq_pub(const zmq_pub&) = delete;
+    zmq_pub(zmq_pub&&) = delete;
+
+    ~zmq_pub();
+
+    zmq_pub& operator=(const zmq_pub&) = delete;
+    zmq_pub& operator=(zmq_pub&&) = delete;
+
+    //! Process a client subscription request (from XPUB sockets). Thread-safe.
+    bool sub_request(const boost::string_ref message);
+
+    /*! Forward ZMQ messages sent to `relay` via `send_chain_main` or
+      `send_txpool_add` to `pub`. Used by `ZmqServer`. */
+    bool relay_to_pub(void* relay, void* pub);
+
+    /*! Send a `ZMQ_PUB` notification for a change to the main chain.
+        Thread-safe.
+        \return Number of ZMQ messages sent to relay. */
+    std::size_t send_chain_main(std::uint64_t height, epee::span<const cryptonote::block> blocks);
+
+    /*! Send a `ZMQ_PUB` notification for new tx(es) being added to the local
+        pool. Thread-safe.
+        \return Number of ZMQ messages sent to relay. */
+    std::size_t send_txpool_add(std::vector<cryptonote::txpool_event> txes);
+
+    //! Callable for `send_chain_main` with weak ownership to `zmq_pub` object.
+    struct chain_main
+    {
+      std::weak_ptr<zmq_pub> self_;
+      void operator()(std::uint64_t height, epee::span<const cryptonote::block> blocks) const;
+    };
+
+    //! Callable for `send_txpool_add` with weak ownership to `zmq_pub` object.
+    struct txpool_add
+    {
+      std::weak_ptr<zmq_pub> self_;
+      void operator()(std::vector<cryptonote::txpool_event> txes) const;
+    };
+  };
+}}

src/rpc/zmq_server.cpp

@@ -29,10 +29,16 @@
 #include "zmq_server.h"
 
 #include <chrono>
-#include <cstdint>
+#include <cstring>
+#include <utility>
+#include <stdexcept>
 #include <system_error>
 
 #include "byte_slice.h"
+#include "rpc/zmq_pub.h"
+
+#undef MONERO_DEFAULT_LOG_CATEGORY
+#define MONERO_DEFAULT_LOG_CATEGORY "net.zmq"
 
 namespace cryptonote
 {
@@ -42,14 +48,57 @@ namespace
   constexpr const int num_zmq_threads = 1;
   constexpr const std::int64_t max_message_size = 10 * 1024 * 1024; // 10 MiB
   constexpr const std::chrono::seconds linger_timeout{2}; // wait period for pending out messages
-}
+
+  net::zmq::socket init_socket(void* context, int type, epee::span<const std::string> addresses)
+  {
+    if (context == nullptr)
+      throw std::logic_error{"NULL context provided"};
+
+    net::zmq::socket out{};
+    out.reset(zmq_socket(context, type));
+    if (!out)
+    {
+      MONERO_LOG_ZMQ_ERROR("Failed to create ZMQ socket");
+      return nullptr;
+    }
+
+    if (zmq_setsockopt(out.get(), ZMQ_MAXMSGSIZE, std::addressof(max_message_size), sizeof(max_message_size)) != 0)
+    {
+      MONERO_LOG_ZMQ_ERROR("Failed to set maximum incoming message size");
+      return nullptr;
+    }
+
+    static constexpr const int linger_value = std::chrono::milliseconds{linger_timeout}.count();
+    if (zmq_setsockopt(out.get(), ZMQ_LINGER, std::addressof(linger_value), sizeof(linger_value)) != 0)
+    {
+      MONERO_LOG_ZMQ_ERROR("Failed to set linger timeout");
+      return nullptr;
+    }
+
+    for (const std::string& address : addresses)
+    {
+      if (zmq_bind(out.get(), address.c_str()) < 0)
+      {
+        MONERO_LOG_ZMQ_ERROR("ZMQ bind failed");
+        return nullptr;
+      }
+      MINFO("ZMQ now listening at " << address);
+    }
+
+    return out;
+  }
+} // anonymous
 
 namespace rpc
 {
 
 ZmqServer::ZmqServer(RpcHandler& h) :
     handler(h),
-    context(zmq_init(num_zmq_threads))
+    context(zmq_init(num_zmq_threads)),
+    rep_socket(nullptr),
+    pub_socket(nullptr),
+    relay_socket(nullptr),
+    shared_state(nullptr)
 {
     if (!context)
         MONERO_ZMQ_THROW("Unable to create ZMQ context");
@@ -64,22 +113,59 @@ void ZmqServer::serve()
   try
   {
     // socket must close before `zmq_term` will exit.
-    const net::zmq::socket socket = std::move(rep_socket);
+    const net::zmq::socket rep = std::move(rep_socket);
-    if (!socket)
+    const net::zmq::socket pub = std::move(pub_socket);
+    const net::zmq::socket relay = std::move(relay_socket);
+    const std::shared_ptr<listener::zmq_pub> state = std::move(shared_state);
+
+    const unsigned init_count = unsigned(bool(pub)) + bool(relay) + bool(state);
+    if (!rep || (init_count && init_count != 3))
     {
-      MERROR("ZMQ RPC server reply socket is null");
+      MERROR("ZMQ RPC server socket is null");
       return;
     }
 
+    MINFO("ZMQ Server started");
+
+    const int read_flags = pub ? ZMQ_DONTWAIT : 0;
+    std::array<zmq_pollitem_t, 3> sockets =
+    {{
+      {relay.get(), 0, ZMQ_POLLIN, 0},
+      {pub.get(), 0, ZMQ_POLLIN, 0},
+      {rep.get(), 0, ZMQ_POLLIN, 0}
+    }};
+
+    /* This uses XPUB to watch for subscribers, to reduce CPU cycles for
+       serialization when the data will be dropped. This is important for block
+       serialization, which is done on the p2p threads currently (see
+       zmq_pub.cpp).
+
+       XPUB sockets are not thread-safe, so the p2p thread cannot write into
+       the socket while we read here for subscribers. A ZMQ_PAIR socket is
+       used for inproc notification. No data is every copied to kernel, it is
+       all userspace messaging. */
+
     while (1)
     {
-      const std::string message = MONERO_UNWRAP(net::zmq::receive(socket.get()));
+      if (pub)
+        MONERO_UNWRAP(net::zmq::retry_op(zmq_poll, sockets.data(), sockets.size(), -1));
+
+      if (sockets[0].revents)
+        state->relay_to_pub(relay.get(), pub.get());
+
+      if (sockets[1].revents)
+        state->sub_request(MONERO_UNWRAP(net::zmq::receive(pub.get(), ZMQ_DONTWAIT)));
+
+      if (!pub || sockets[2].revents)
+      {
+        const std::string message = MONERO_UNWRAP(net::zmq::receive(rep.get(), read_flags));
         MDEBUG("Received RPC request: \"" << message << "\"");
         epee::byte_slice response = handler.handle(message);
 
         const boost::string_ref response_view{reinterpret_cast<const char*>(response.data()), response.size()};
         MDEBUG("Sending RPC reply: \"" << response_view << "\"");
-      MONERO_UNWRAP(net::zmq::send(std::move(response), socket.get()));
+        MONERO_UNWRAP(net::zmq::send(std::move(response), rep.get()));
+      }
     }
   }
   catch (const std::system_error& e)
@@ -97,38 +183,12 @@ void ZmqServer::serve()
   }
 }
 
-bool ZmqServer::addIPCSocket(const boost::string_ref address, const boost::string_ref port)
+void* ZmqServer::init_rpc(boost::string_ref address, boost::string_ref port)
-{
-  MERROR("ZmqServer::addIPCSocket not yet implemented!");
-  return false;
-}
-
-bool ZmqServer::addTCPSocket(boost::string_ref address, boost::string_ref port)
 {
   if (!context)
   {
     MERROR("ZMQ RPC Server already shutdown");
-    return false;
+    return nullptr;
-  }
-
-  rep_socket.reset(zmq_socket(context.get(), ZMQ_REP));
-  if (!rep_socket)
-  {
-    MONERO_LOG_ZMQ_ERROR("ZMQ RPC Server socket create failed");
-    return false;
-  }
-
-  if (zmq_setsockopt(rep_socket.get(), ZMQ_MAXMSGSIZE, std::addressof(max_message_size), sizeof(max_message_size)) != 0)
-  {
-    MONERO_LOG_ZMQ_ERROR("Failed to set maximum incoming message size");
-    return false;
-  }
-
-  static constexpr const int linger_value = std::chrono::milliseconds{linger_timeout}.count();
-  if (zmq_setsockopt(rep_socket.get(), ZMQ_LINGER, std::addressof(linger_value), sizeof(linger_value)) != 0)
-  {
-    MONERO_LOG_ZMQ_ERROR("Failed to set linger timeout");
-    return false;
   }
 
   if (address.empty())
@@ -141,12 +201,34 @@ bool ZmqServer::addTCPSocket(boost::string_ref address, boost::string_ref port)
   bind_address += ":";
   bind_address.append(port.data(), port.size());
 
-  if (zmq_bind(rep_socket.get(), bind_address.c_str()) < 0)
+  rep_socket = init_socket(context.get(), ZMQ_REP, {std::addressof(bind_address), 1});
+  return bool(rep_socket) ? context.get() : nullptr;
+}
+
+std::shared_ptr<listener::zmq_pub> ZmqServer::init_pub(epee::span<const std::string> addresses)
+{
+  try
   {
-    MONERO_LOG_ZMQ_ERROR("ZMQ RPC Server bind failed");
+    shared_state = std::make_shared<listener::zmq_pub>(context.get());
-    return false;
+    pub_socket = init_socket(context.get(), ZMQ_XPUB, addresses);
+    if (!pub_socket)
+      throw std::runtime_error{"Unable to initialize ZMQ_XPUB socket"};
+
+    const std::string relay_address[] = {listener::zmq_pub::relay_endpoint()};
+    relay_socket = init_socket(context.get(), ZMQ_PAIR, relay_address);
+    if (!relay_socket)
+      throw std::runtime_error{"Unable to initialize ZMQ_PAIR relay"};
   }
-  return true;
+  catch (const std::runtime_error& e)
+  {
+    shared_state = nullptr;
+    pub_socket = nullptr;
+    relay_socket = nullptr;
+    MERROR("Failed to create ZMQ/Pub listener: " << e.what());
+    return nullptr;
+  }
+
+  return shared_state;
 }
 
 void ZmqServer::run()
@@ -163,7 +245,6 @@ void ZmqServer::stop()
   run_thread.join();
 }
 
-
 }  // namespace cryptonote
 
 }  // namespace rpc

src/rpc/zmq_server.h

@@ -30,10 +30,16 @@
 
 #include <boost/thread/thread.hpp>
 #include <boost/utility/string_ref.hpp>
+#include <cstdint>
+#include <memory>
+#include <string>
 
 #include "common/command_line.h"
+#include "cryptonote_basic/fwd.h"
 #include "net/zmq.h"
-#include "rpc_handler.h"
+#include "rpc/fwd.h"
+#include "rpc/rpc_handler.h"
+#include "span.h"
 
 namespace cryptonote
 {
@@ -41,7 +47,7 @@ namespace cryptonote
 namespace rpc
 {
 
-class ZmqServer
+class ZmqServer final
 {
   public:
 
@@ -49,12 +55,13 @@ class ZmqServer
 
     ~ZmqServer();
 
-    static void init_options(boost::program_options::options_description& desc);
-
     void serve();
 
-    bool addIPCSocket(boost::string_ref address, boost::string_ref port);
+    //! \return ZMQ context on success, `nullptr` on failure
-    bool addTCPSocket(boost::string_ref address, boost::string_ref port);
+    void* init_rpc(boost::string_ref address, boost::string_ref port);
+
+    //! \return `nullptr` on errors.
+    std::shared_ptr<listener::zmq_pub> init_pub(epee::span<const std::string> addresses);
 
     void run();
     void stop();
@@ -67,9 +74,11 @@ class ZmqServer
     boost::thread run_thread;
 
     net::zmq::socket rep_socket;
+    net::zmq::socket pub_socket;
+    net::zmq::socket relay_socket;
+    std::shared_ptr<listener::zmq_pub> shared_state;
 };
 
-
 }  // namespace cryptonote
 
 }  // namespace rpc

src/serialization/json_object.h

@@ -356,7 +356,7 @@ inline typename std::enable_if<sfinae::is_vector_like<Vec>::value, void>::type t
   dest.StartArray();
   for (const auto& t : vec)
     toJsonValue(dest, t);
-  dest.EndArray(vec.size());
+  dest.EndArray();
 }
 
 template <typename Vec>

tests/unit_tests/CMakeLists.txt

@@ -109,6 +109,7 @@ target_link_libraries(unit_tests
     cryptonote_protocol
     cryptonote_core
     daemon_messages
+    daemon_rpc_server
     blockchain_db
     lmdb_lib
     rpc

tests/unit_tests/json_serialization.cpp

@@ -15,7 +15,7 @@
 #include "serialization/json_object.h"
 
 
-namespace
+namespace test
 {
     cryptonote::transaction
     make_miner_transaction(cryptonote::account_public_address const& to)
@@ -82,7 +82,10 @@ namespace
 
         return tx;
     }
+}
 
+namespace
+{
     template<typename T>
     T test_json(const T& value)
     {
@@ -109,7 +112,7 @@ TEST(JsonSerialization, MinerTransaction)
 {
     cryptonote::account_base acct;
     acct.generate();
-    const auto miner_tx = make_miner_transaction(acct.get_keys().m_account_address);
+    const auto miner_tx = test::make_miner_transaction(acct.get_keys().m_account_address);
 
     crypto::hash tx_hash{};
     ASSERT_TRUE(cryptonote::get_transaction_hash(miner_tx, tx_hash));
@@ -137,8 +140,8 @@ TEST(JsonSerialization, RegularTransaction)
     cryptonote::account_base acct2;
     acct2.generate();
 
-    const auto miner_tx = make_miner_transaction(acct1.get_keys().m_account_address);
+    const auto miner_tx = test::make_miner_transaction(acct1.get_keys().m_account_address);
-    const auto tx = make_transaction(
+    const auto tx = test::make_transaction(
         acct1.get_keys(), {miner_tx}, {acct2.get_keys().m_account_address}, false, false
     );
 
@@ -168,8 +171,8 @@ TEST(JsonSerialization, RingctTransaction)
     cryptonote::account_base acct2;
     acct2.generate();
 
-    const auto miner_tx = make_miner_transaction(acct1.get_keys().m_account_address);
+    const auto miner_tx = test::make_miner_transaction(acct1.get_keys().m_account_address);
-    const auto tx = make_transaction(
+    const auto tx = test::make_transaction(
         acct1.get_keys(), {miner_tx}, {acct2.get_keys().m_account_address}, true, false
     );
 
@@ -199,8 +202,8 @@ TEST(JsonSerialization, BulletproofTransaction)
     cryptonote::account_base acct2;
     acct2.generate();
 
-    const auto miner_tx = make_miner_transaction(acct1.get_keys().m_account_address);
+    const auto miner_tx = test::make_miner_transaction(acct1.get_keys().m_account_address);
-    const auto tx = make_transaction(
+    const auto tx = test::make_transaction(
         acct1.get_keys(), {miner_tx}, {acct2.get_keys().m_account_address}, true, true
     );
 

tests/unit_tests/json_serialization.h

@@ -0,0 +1,42 @@
+// Copyright (c) 2020, The Monero Project
+//
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without modification, are
+// permitted provided that the following conditions are met:
+//
+// 1. Redistributions of source code must retain the above copyright notice, this list of
+//    conditions and the following disclaimer.
+//
+// 2. Redistributions in binary form must reproduce the above copyright notice, this list
+//    of conditions and the following disclaimer in the documentation and/or other
+//    materials provided with the distribution.
+//
+// 3. Neither the name of the copyright holder nor the names of its contributors may be
+//    used to endorse or promote products derived from this software without specific
+//    prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
+// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
+// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
+// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#pragma once
+
+namespace test
+{
+  cryptonote::transaction make_miner_transaction(cryptonote::account_public_address const& to);
+
+  cryptonote::transaction
+  make_transaction(
+      cryptonote::account_keys const& from,
+      std::vector<cryptonote::transaction> const& sources,
+      std::vector<cryptonote::account_public_address> const& destinations,
+      bool rct,
+      bool bulletproof);
+}

tests/unit_tests/zmq_rpc.cpp

@@ -26,11 +26,25 @@
 // STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
 // THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
+#include <boost/preprocessor/stringize.hpp>
 #include <gtest/gtest.h>
+#include <rapidjson/document.h>
 
+#include "cryptonote_basic/account.h"
+#include "cryptonote_basic/cryptonote_basic.h"
+#include "cryptonote_basic/events.h"
+#include "cryptonote_basic/cryptonote_format_utils.h"
+#include "json_serialization.h"
+#include "net/zmq.h"
 #include "rpc/message.h"
+#include "rpc/zmq_pub.h"
+#include "rpc/zmq_server.h"
 #include "serialization/json_object.h"
 
+#define MASSERT(...)                                                      \
+  if (!(__VA_ARGS__))                                                     \
+    return testing::AssertionFailure() << BOOST_PP_STRINGIZE(__VA_ARGS__)
+
 TEST(ZmqFullMessage, InvalidRequest)
 {
   EXPECT_THROW(
@@ -53,3 +67,711 @@ TEST(ZmqFullMessage, Request)
   cryptonote::rpc::FullMessage parsed{request, true};
   EXPECT_STREQ("foo", parsed.getRequestType().c_str());
 }
+
+namespace
+{
+  using published_json = std::pair<std::string, rapidjson::Document>;
+
+  constexpr const char inproc_pub[] = "inproc://dummy_pub";
+
+  net::zmq::socket create_socket(void* ctx, const char* address)
+  {
+    net::zmq::socket sock{zmq_socket(ctx, ZMQ_PAIR)};
+    if (!sock)
+      MONERO_ZMQ_THROW("failed to create socket");
+    if (zmq_bind(sock.get(), address) != 0)
+      MONERO_ZMQ_THROW("socket bind failure");
+    return sock;
+  }
+
+  std::vector<std::string> get_messages(void* socket, int count = -1)
+  {
+    std::vector<std::string> out;
+    for ( ; count || count < 0; --count)
+    {
+      expect<std::string> next = net::zmq::receive(socket, (count < 0 ? ZMQ_DONTWAIT : 0));
+      if (next == net::zmq::make_error_code(EAGAIN))
+        return out;
+      out.push_back(std::move(*next));
+    }
+    return out;
+  }
+
+  std::vector<published_json> get_published(void* socket, int count = -1)
+  {
+    std::vector<published_json> out;
+
+    const auto messages = get_messages(socket, count);
+    out.reserve(messages.size());
+
+    for (const std::string& message : messages)
+    {
+      const char* split = std::strchr(message.c_str(), ':');
+      if (!split)
+        throw std::runtime_error{"Invalid ZMQ/Pub message"};
+
+      out.emplace_back();
+      out.back().first = {message.c_str(), split};
+      if (out.back().second.Parse(split + 1).HasParseError())
+        throw std::runtime_error{"Failed to parse ZMQ/Pub message"};
+    }
+
+    return out;
+  }
+
+  testing::AssertionResult compare_full_txpool(epee::span<const cryptonote::txpool_event> events, const published_json& pub)
+  {
+    MASSERT(pub.first == "json-full-txpool_add");
+    MASSERT(pub.second.IsArray());
+    MASSERT(pub.second.Size() <= events.size());
+
+    std::size_t i = 0;
+    for (const cryptonote::txpool_event& event : events)
+    {
+      MASSERT(i <= pub.second.Size());
+      if (!event.res)
+        continue;
+
+      cryptonote::transaction tx{};
+      cryptonote::json::fromJsonValue(pub.second[i], tx);
+
+      crypto::hash id{};
+      MASSERT(cryptonote::get_transaction_hash(event.tx, id));
+      MASSERT(cryptonote::get_transaction_hash(tx, id));
+      MASSERT(event.tx.hash == tx.hash);
+      ++i;
+    }
+    return testing::AssertionSuccess();
+  }
+
+  testing::AssertionResult compare_minimal_txpool(epee::span<const cryptonote::txpool_event> events, const published_json& pub)
+  {
+    MASSERT(pub.first == "json-minimal-txpool_add");
+    MASSERT(pub.second.IsArray());
+    MASSERT(pub.second.Size() <= events.size());
+
+    std::size_t i = 0;
+    for (const cryptonote::txpool_event& event : events)
+    {
+      MASSERT(i <= pub.second.Size());
+      if (!event.res)
+        continue;
+
+      std::size_t actual_size = 0;
+      crypto::hash actual_id{};
+
+      MASSERT(pub.second[i].IsObject());
+      GET_FROM_JSON_OBJECT(pub.second[i], actual_id, id);
+      GET_FROM_JSON_OBJECT(pub.second[i], actual_size, blob_size);
+
+      std::size_t expected_size = 0;
+      crypto::hash expected_id{};
+      MASSERT(cryptonote::get_transaction_hash(event.tx, expected_id, expected_size));
+      MASSERT(expected_size == actual_size);
+      MASSERT(expected_id == actual_id);
+      ++i;
+    }
+    return testing::AssertionSuccess();
+  }
+
+  testing::AssertionResult compare_full_block(const epee::span<const cryptonote::block> expected, const published_json& pub)
+  {
+    MASSERT(pub.first == "json-full-chain_main");
+    MASSERT(pub.second.IsArray());
+
+    std::vector<cryptonote::block> actual;
+    cryptonote::json::fromJsonValue(pub.second, actual);
+
+    MASSERT(expected.size() == actual.size());
+
+    for (std::size_t i = 0; i < expected.size(); ++i)
+    {
+      crypto::hash id;
+      MASSERT(cryptonote::get_block_hash(expected[i], id));
+      MASSERT(cryptonote::get_block_hash(actual[i], id));
+      MASSERT(expected[i].hash == actual[i].hash);
+    }
+
+    return testing::AssertionSuccess();
+  }
+
+  testing::AssertionResult compare_minimal_block(std::size_t height, const epee::span<const cryptonote::block> expected, const published_json& pub)
+  {
+    MASSERT(pub.first == "json-minimal-chain_main");
+    MASSERT(pub.second.IsObject());
+    MASSERT(!expected.empty());
+
+    std::size_t actual_height = 0;
+    crypto::hash actual_id{};
+    crypto::hash actual_prev_id{};
+    std::vector<crypto::hash> actual_ids{};
+    GET_FROM_JSON_OBJECT(pub.second, actual_height, first_height);
+    GET_FROM_JSON_OBJECT(pub.second, actual_prev_id, first_prev_id);
+    GET_FROM_JSON_OBJECT(pub.second, actual_ids, ids);
+
+    MASSERT(height == actual_height);
+    MASSERT(expected[0].prev_id == actual_prev_id);
+    MASSERT(expected.size() == actual_ids.size());
+
+    for (std::size_t i = 0; i < expected.size(); ++i)
+    {
+      crypto::hash id;
+      MASSERT(cryptonote::get_block_hash(expected[i], id));
+      MASSERT(id == actual_ids[i]);
+    }
+
+    return testing::AssertionSuccess();
+  }
+
+  struct zmq_base : public testing::Test
+  {
+    cryptonote::account_base acct;
+
+    zmq_base()
+      : testing::Test(), acct()
+    {
+      acct.generate();
+    }
+
+    cryptonote::transaction make_miner_transaction()
+    {
+      return test::make_miner_transaction(acct.get_keys().m_account_address);
+    }
+
+    cryptonote::transaction make_transaction(const std::vector<cryptonote::account_public_address>& destinations)
+    {
+      return test::make_transaction(acct.get_keys(), {make_miner_transaction()}, destinations, true, true);
+    }
+
+    cryptonote::transaction make_transaction()
+    {
+      cryptonote::account_base temp_account;
+      temp_account.generate();
+      return make_transaction({temp_account.get_keys().m_account_address});
+    }
+
+    cryptonote::block make_block()
+    {
+      cryptonote::block block{};
+      block.major_version = 1;
+      block.minor_version = 3;
+      block.timestamp = 100;
+      block.prev_id = crypto::rand<crypto::hash>();
+      block.nonce = 100;
+      block.miner_tx = make_miner_transaction();
+      return block;
+    }
+  };
+
+  struct zmq_pub : public zmq_base
+  {
+    net::zmq::context ctx;
+    net::zmq::socket relay;
+    net::zmq::socket dummy_pub;
+    net::zmq::socket dummy_client;
+    std::shared_ptr<cryptonote::listener::zmq_pub> pub;
+
+    zmq_pub()
+      : zmq_base(),
+        ctx(zmq_init(1)),
+        relay(create_socket(ctx.get(), cryptonote::listener::zmq_pub::relay_endpoint())),
+        dummy_pub(create_socket(ctx.get(), inproc_pub)),
+        dummy_client(zmq_socket(ctx.get(), ZMQ_PAIR)),
+        pub(std::make_shared<cryptonote::listener::zmq_pub>(ctx.get()))
+    {
+      if (!dummy_client)
+        MONERO_ZMQ_THROW("failed to create socket");
+      if (zmq_connect(dummy_client.get(), inproc_pub) != 0)
+        MONERO_ZMQ_THROW("failed to connect to dummy pub");
+    }
+
+    virtual void TearDown() override final
+    {
+      EXPECT_EQ(0u, get_messages(relay.get()).size());
+      EXPECT_EQ(0u, get_messages(dummy_client.get()).size());
+    }
+
+    template<std::size_t N>
+    bool sub_request(const char (&topic)[N])
+    {
+      return pub->sub_request({topic, N - 1});
+    }
+  };
+
+  struct dummy_handler final : cryptonote::rpc::RpcHandler
+  {
+    dummy_handler()
+      : cryptonote::rpc::RpcHandler()
+    {}
+
+    virtual epee::byte_slice handle(const std::string& request) override final
+    {
+      throw std::logic_error{"not implemented"};
+    }
+  };
+
+  struct zmq_server : public zmq_base
+  {
+    dummy_handler handler;
+    cryptonote::rpc::ZmqServer server;
+    std::shared_ptr<cryptonote::listener::zmq_pub> pub;
+    net::zmq::socket sub;
+
+    zmq_server()
+      : zmq_base(),
+        handler(),
+        server(handler),
+        pub(),
+        sub()
+    {
+      void* ctx = server.init_rpc({}, {});
+      if (!ctx)
+        throw std::runtime_error{"init_rpc failure"};
+
+      const std::string endpoint = inproc_pub;
+      pub = server.init_pub({std::addressof(endpoint), 1});
+      if (!pub)
+        throw std::runtime_error{"failed to initiaze zmq/pub"};
+
+      sub.reset(zmq_socket(ctx, ZMQ_SUB));
+      if (!sub)
+        MONERO_ZMQ_THROW("failed to create socket");
+      if (zmq_connect(sub.get(), inproc_pub) != 0)
+        MONERO_ZMQ_THROW("failed to connect to dummy pub");
+
+      server.run();
+    }
+
+    virtual void TearDown() override final
+    {
+      EXPECT_EQ(0u, get_messages(sub.get()).size());
+      sub.reset();
+      pub.reset();
+      server.stop();
+    }
+
+    template<std::size_t N>
+    void subscribe(const char (&topic)[N])
+    {
+      if (zmq_setsockopt(sub.get(), ZMQ_SUBSCRIBE, topic, N - 1) != 0)
+        MONERO_ZMQ_THROW("failed to subscribe");
+    }
+  };
+}
+
+TEST_F(zmq_pub, InvalidContext)
+{
+  EXPECT_THROW(cryptonote::listener::zmq_pub{nullptr}, std::logic_error);
+}
+
+TEST_F(zmq_pub, NoBlocking)
+{
+  EXPECT_FALSE(pub->relay_to_pub(relay.get(), dummy_pub.get()));
+}
+
+TEST_F(zmq_pub, DefaultDrop)
+{
+  EXPECT_EQ(0u, pub->send_txpool_add({{make_transaction(), {}, true}}));
+
+  const cryptonote::block bl = make_block();
+  EXPECT_EQ(0u,pub->send_chain_main(5, {std::addressof(bl), 1}));
+  EXPECT_NO_THROW(cryptonote::listener::zmq_pub::chain_main{pub}(5, {std::addressof(bl), 1}));
+}
+
+TEST_F(zmq_pub, JsonFullTxpool)
+{
+  static constexpr const char topic[] = "\1json-full-txpool_add";
+
+  ASSERT_TRUE(sub_request(topic));
+
+  std::vector<cryptonote::txpool_event> events
+  {
+   {make_transaction(), {}, true}, {make_transaction(), {}, true}
+  };
+
+  EXPECT_NO_THROW(pub->send_txpool_add(events));
+  EXPECT_TRUE(pub->relay_to_pub(relay.get(), dummy_pub.get()));
+
+  auto pubs = get_published(dummy_client.get());
+  EXPECT_EQ(1u, pubs.size());
+  ASSERT_LE(1u, pubs.size());
+  EXPECT_TRUE(compare_full_txpool(epee::to_span(events), pubs.front()));
+
+  EXPECT_NO_THROW(cryptonote::listener::zmq_pub::txpool_add{pub}(events));
+  EXPECT_TRUE(pub->relay_to_pub(relay.get(), dummy_pub.get()));
+
+  pubs = get_published(dummy_client.get());
+  EXPECT_EQ(1u, pubs.size());
+  ASSERT_LE(1u, pubs.size());
+  EXPECT_TRUE(compare_full_txpool(epee::to_span(events), pubs.front()));
+
+  events.at(0).res = false;
+  EXPECT_EQ(1u, pub->send_txpool_add(events));
+  EXPECT_TRUE(pub->relay_to_pub(relay.get(), dummy_pub.get()));
+
+  pubs = get_published(dummy_client.get());
+  EXPECT_EQ(1u, pubs.size());
+  ASSERT_LE(1u, pubs.size());
+  EXPECT_TRUE(compare_full_txpool(epee::to_span(events), pubs.front()));
+
+  events.at(0).res = false;
+  EXPECT_NO_THROW(cryptonote::listener::zmq_pub::txpool_add{pub}(events));
+  EXPECT_TRUE(pub->relay_to_pub(relay.get(), dummy_pub.get()));
+
+  pubs = get_published(dummy_client.get());
+  EXPECT_EQ(1u, pubs.size());
+  ASSERT_LE(1u, pubs.size());
+  EXPECT_TRUE(compare_full_txpool(epee::to_span(events), pubs.front()));
+}
+
+TEST_F(zmq_pub, JsonMinimalTxpool)
+{
+  static constexpr const char topic[] = "\1json-minimal-txpool_add";
+
+  ASSERT_TRUE(sub_request(topic));
+
+  std::vector<cryptonote::txpool_event> events
+  {
+   {make_transaction(), {}, true}, {make_transaction(), {}, true}
+  };
+
+  EXPECT_NO_THROW(pub->send_txpool_add(events));
+  EXPECT_TRUE(pub->relay_to_pub(relay.get(), dummy_pub.get()));
+
+  auto pubs = get_published(dummy_client.get());
+  EXPECT_EQ(1u, pubs.size());
+  ASSERT_LE(1u, pubs.size());
+  EXPECT_TRUE(compare_minimal_txpool(epee::to_span(events), pubs.front()));
+
+  EXPECT_NO_THROW(cryptonote::listener::zmq_pub::txpool_add{pub}(events));
+  EXPECT_TRUE(pub->relay_to_pub(relay.get(), dummy_pub.get()));
+
+  pubs = get_published(dummy_client.get());
+  EXPECT_EQ(1u, pubs.size());
+  ASSERT_LE(1u, pubs.size());
+  EXPECT_TRUE(compare_minimal_txpool(epee::to_span(events), pubs.front()));
+
+  events.at(0).res = false;
+  EXPECT_EQ(1u, pub->send_txpool_add(events));
+  EXPECT_TRUE(pub->relay_to_pub(relay.get(), dummy_pub.get()));
+
+  pubs = get_published(dummy_client.get());
+  EXPECT_EQ(1u, pubs.size());
+  ASSERT_LE(1u, pubs.size());
+  EXPECT_TRUE(compare_minimal_txpool(epee::to_span(events), pubs.front()));
+
+  events.at(0).res = false;
+  EXPECT_NO_THROW(cryptonote::listener::zmq_pub::txpool_add{pub}(events));
+  EXPECT_TRUE(pub->relay_to_pub(relay.get(), dummy_pub.get()));
+
+  pubs = get_published(dummy_client.get());
+  EXPECT_EQ(1u, pubs.size());
+  ASSERT_LE(1u, pubs.size());
+  EXPECT_TRUE(compare_minimal_txpool(epee::to_span(events), pubs.front()));
+}
+
+TEST_F(zmq_pub, JsonFullChain)
+{
+  static constexpr const char topic[] = "\1json-full-chain_main";
+
+  ASSERT_TRUE(sub_request(topic));
+
+  const std::array<cryptonote::block, 2> blocks{{make_block(), make_block()}};
+
+  EXPECT_EQ(1u, pub->send_chain_main(100, epee::to_span(blocks)));
+  EXPECT_TRUE(pub->relay_to_pub(relay.get(), dummy_pub.get()));
+
+  auto pubs = get_published(dummy_client.get());
+  EXPECT_EQ(1u, pubs.size());
+  ASSERT_LE(1u, pubs.size());
+  EXPECT_TRUE(compare_full_block(epee::to_span(blocks), pubs.front()));
+
+  EXPECT_NO_THROW(cryptonote::listener::zmq_pub::chain_main{pub}(533, epee::to_span(blocks)));
+  EXPECT_TRUE(pub->relay_to_pub(relay.get(), dummy_pub.get()));
+
+  pubs = get_published(dummy_client.get());
+  EXPECT_EQ(1u, pubs.size());
+  ASSERT_LE(1u, pubs.size());
+  EXPECT_TRUE(compare_full_block(epee::to_span(blocks), pubs.front()));
+}
+
+TEST_F(zmq_pub, JsonMinimalChain)
+{
+  static constexpr const char topic[] = "\1json-minimal-chain_main";
+
+  ASSERT_TRUE(sub_request(topic));
+
+  const std::array<cryptonote::block, 2> blocks{{make_block(), make_block()}};
+
+  EXPECT_EQ(1u, pub->send_chain_main(100, epee::to_span(blocks)));
+  EXPECT_TRUE(pub->relay_to_pub(relay.get(), dummy_pub.get()));
+
+  auto pubs = get_published(dummy_client.get());
+  EXPECT_EQ(1u, pubs.size());
+  ASSERT_LE(1u, pubs.size());
+  EXPECT_TRUE(compare_minimal_block(100, epee::to_span(blocks), pubs.front()));
+
+  EXPECT_NO_THROW(cryptonote::listener::zmq_pub::chain_main{pub}(533, epee::to_span(blocks)));
+  EXPECT_TRUE(pub->relay_to_pub(relay.get(), dummy_pub.get()));
+
+  pubs = get_published(dummy_client.get());
+  EXPECT_EQ(1u, pubs.size());
+  ASSERT_LE(1u, pubs.size());
+  EXPECT_TRUE(compare_minimal_block(533, epee::to_span(blocks), pubs.front()));
+}
+
+TEST_F(zmq_pub, JsonFullAll)
+{
+  static constexpr const char topic[] = "\1json-full";
+
+  ASSERT_TRUE(sub_request(topic));
+  {
+    std::vector<cryptonote::txpool_event> events
+    {
+     {make_transaction(), {}, true}, {make_transaction(), {}, true}
+    };
+
+    EXPECT_EQ(1u, pub->send_txpool_add(events));
+    EXPECT_TRUE(pub->relay_to_pub(relay.get(), dummy_pub.get()));
+
+    auto pubs = get_published(dummy_client.get());
+    EXPECT_EQ(1u, pubs.size());
+    ASSERT_LE(1u, pubs.size());
+    EXPECT_TRUE(compare_full_txpool(epee::to_span(events), pubs.front()));
+
+    EXPECT_NO_THROW(cryptonote::listener::zmq_pub::txpool_add{pub}(events));
+    EXPECT_TRUE(pub->relay_to_pub(relay.get(), dummy_pub.get()));
+
+    pubs = get_published(dummy_client.get());
+    EXPECT_EQ(1u, pubs.size());
+    ASSERT_LE(1u, pubs.size());
+    EXPECT_TRUE(compare_full_txpool(epee::to_span(events), pubs.front()));
+
+    events.at(0).res = false;
+    EXPECT_NO_THROW(pub->send_txpool_add(events));
+    EXPECT_TRUE(pub->relay_to_pub(relay.get(), dummy_pub.get()));
+
+    pubs = get_published(dummy_client.get());
+    EXPECT_EQ(1u, pubs.size());
+    ASSERT_LE(1u, pubs.size());
+    EXPECT_TRUE(compare_full_txpool(epee::to_span(events), pubs.front()));
+
+    events.at(0).res = false;
+    EXPECT_NO_THROW(cryptonote::listener::zmq_pub::txpool_add{pub}(events));
+    EXPECT_TRUE(pub->relay_to_pub(relay.get(), dummy_pub.get()));
+
+    pubs = get_published(dummy_client.get());
+    EXPECT_EQ(1u, pubs.size());
+    ASSERT_LE(1u, pubs.size());
+    EXPECT_TRUE(compare_full_txpool(epee::to_span(events), pubs.front()));
+  }
+  {
+    const std::array<cryptonote::block, 2> blocks{{make_block(), make_block()}};
+
+    EXPECT_EQ(1u, pub->send_chain_main(100, epee::to_span(blocks)));
+    EXPECT_TRUE(pub->relay_to_pub(relay.get(), dummy_pub.get()));
+
+    auto pubs = get_published(dummy_client.get());
+    EXPECT_EQ(1u, pubs.size());
+    ASSERT_LE(1u, pubs.size());
+    EXPECT_TRUE(compare_full_block(epee::to_span(blocks), pubs.front()));
+
+    EXPECT_NO_THROW(cryptonote::listener::zmq_pub::chain_main{pub}(533, epee::to_span(blocks)));
+    EXPECT_TRUE(pub->relay_to_pub(relay.get(), dummy_pub.get()));
+
+    pubs = get_published(dummy_client.get());
+    EXPECT_EQ(1u, pubs.size());
+    ASSERT_LE(1u, pubs.size());
+    EXPECT_TRUE(compare_full_block(epee::to_span(blocks), pubs.front()));
+  }
+}
+
+TEST_F(zmq_pub, JsonMinimalAll)
+{
+  static constexpr const char topic[] = "\1json-minimal";
+
+  ASSERT_TRUE(sub_request(topic));
+
+  {
+    std::vector<cryptonote::txpool_event> events
+    {
+     {make_transaction(), {}, true}, {make_transaction(), {}, true}
+    };
+
+    EXPECT_EQ(1u, pub->send_txpool_add(events));
+    EXPECT_TRUE(pub->relay_to_pub(relay.get(), dummy_pub.get()));
+
+    auto pubs = get_published(dummy_client.get());
+    EXPECT_EQ(1u, pubs.size());
+    ASSERT_LE(1u, pubs.size());
+    EXPECT_TRUE(compare_minimal_txpool(epee::to_span(events), pubs.front()));
+
+    EXPECT_NO_THROW(cryptonote::listener::zmq_pub::txpool_add{pub}(events));
+    EXPECT_TRUE(pub->relay_to_pub(relay.get(), dummy_pub.get()));
+
+    pubs = get_published(dummy_client.get());
+    EXPECT_EQ(1u, pubs.size());
+    ASSERT_LE(1u, pubs.size());
+    EXPECT_TRUE(compare_minimal_txpool(epee::to_span(events), pubs.front()));
+
+    events.at(0).res = false;
+    EXPECT_NO_THROW(pub->send_txpool_add(events));
+    EXPECT_TRUE(pub->relay_to_pub(relay.get(), dummy_pub.get()));
+
+    pubs = get_published(dummy_client.get());
+    EXPECT_EQ(1u, pubs.size());
+    ASSERT_LE(1u, pubs.size());
+    EXPECT_TRUE(compare_minimal_txpool(epee::to_span(events), pubs.front()));
+
+    events.at(0).res = false;
+    EXPECT_NO_THROW(cryptonote::listener::zmq_pub::txpool_add{pub}(events));
+    EXPECT_TRUE(pub->relay_to_pub(relay.get(), dummy_pub.get()));
+
+    pubs = get_published(dummy_client.get());
+    EXPECT_EQ(1u, pubs.size());
+    ASSERT_LE(1u, pubs.size());
+    EXPECT_TRUE(compare_minimal_txpool(epee::to_span(events), pubs.front()));
+  }
+  {
+    const std::array<cryptonote::block, 2> blocks{{make_block(), make_block()}};
+
+    EXPECT_EQ(1u, pub->send_chain_main(100, epee::to_span(blocks)));
+    EXPECT_TRUE(pub->relay_to_pub(relay.get(), dummy_pub.get()));
+
+    auto pubs = get_published(dummy_client.get());
+    EXPECT_EQ(1u, pubs.size());
+    ASSERT_LE(1u, pubs.size());
+    EXPECT_TRUE(compare_minimal_block(100, epee::to_span(blocks), pubs.front()));
+
+    EXPECT_NO_THROW(cryptonote::listener::zmq_pub::chain_main{pub}(533, epee::to_span(blocks)));
+    EXPECT_TRUE(pub->relay_to_pub(relay.get(), dummy_pub.get()));
+
+    pubs = get_published(dummy_client.get());
+    EXPECT_EQ(1u, pubs.size());
+    ASSERT_LE(1u, pubs.size());
+    EXPECT_TRUE(compare_minimal_block(533, epee::to_span(blocks), pubs.front()));
+  }
+}
+
+TEST_F(zmq_pub, JsonAll)
+{
+  static constexpr const char topic[] = "\1json";
+
+  ASSERT_TRUE(sub_request(topic));
+
+  {
+    std::vector<cryptonote::txpool_event> events
+    {
+     {make_transaction(), {}, true}, {make_transaction(), {}, true}
+    };
+
+    EXPECT_EQ(1u, pub->send_txpool_add(events));
+    EXPECT_TRUE(pub->relay_to_pub(relay.get(), dummy_pub.get()));
+
+    auto pubs = get_published(dummy_client.get());
+    EXPECT_EQ(2u, pubs.size());
+    ASSERT_LE(2u, pubs.size());
+    EXPECT_TRUE(compare_full_txpool(epee::to_span(events), pubs.front()));
+    EXPECT_TRUE(compare_minimal_txpool(epee::to_span(events), pubs.back()));
+
+    EXPECT_NO_THROW(cryptonote::listener::zmq_pub::txpool_add{pub}(events));
+    EXPECT_TRUE(pub->relay_to_pub(relay.get(), dummy_pub.get()));
+
+    pubs = get_published(dummy_client.get());
+    EXPECT_EQ(2u, pubs.size());
+    ASSERT_LE(2u, pubs.size());
+    EXPECT_TRUE(compare_full_txpool(epee::to_span(events), pubs.front()));
+    EXPECT_TRUE(compare_minimal_txpool(epee::to_span(events), pubs.back()));
+
+    events.at(0).res = false;
+    EXPECT_EQ(1u, pub->send_txpool_add(events));
+    EXPECT_TRUE(pub->relay_to_pub(relay.get(), dummy_pub.get()));
+
+    pubs = get_published(dummy_client.get());
+    EXPECT_EQ(2u, pubs.size());
+    ASSERT_LE(2u, pubs.size());
+    EXPECT_TRUE(compare_full_txpool(epee::to_span(events), pubs.front()));
+    EXPECT_TRUE(compare_minimal_txpool(epee::to_span(events), pubs.back()));
+
+    events.at(0).res = false;
+    EXPECT_NO_THROW(cryptonote::listener::zmq_pub::txpool_add{pub}(events));
+    EXPECT_TRUE(pub->relay_to_pub(relay.get(), dummy_pub.get()));
+
+    pubs = get_published(dummy_client.get());
+    EXPECT_EQ(2u, pubs.size());
+    ASSERT_LE(2u, pubs.size());
+    EXPECT_TRUE(compare_full_txpool(epee::to_span(events), pubs.front()));
+    EXPECT_TRUE(compare_minimal_txpool(epee::to_span(events), pubs.back()));
+  }
+  {
+    const std::array<cryptonote::block, 1> blocks{{make_block()}};
+
+    EXPECT_EQ(2u, pub->send_chain_main(100, epee::to_span(blocks)));
+    EXPECT_TRUE(pub->relay_to_pub(relay.get(), dummy_pub.get()));
+    EXPECT_TRUE(pub->relay_to_pub(relay.get(), dummy_pub.get()));
+
+    auto pubs = get_published(dummy_client.get());
+    EXPECT_EQ(2u, pubs.size());
+    ASSERT_LE(2u, pubs.size());
+    EXPECT_TRUE(compare_full_block(epee::to_span(blocks), pubs.front()));
+    EXPECT_TRUE(compare_minimal_block(100, epee::to_span(blocks), pubs.back()));
+
+    EXPECT_NO_THROW(cryptonote::listener::zmq_pub::chain_main{pub}(533, epee::to_span(blocks)));
+    EXPECT_TRUE(pub->relay_to_pub(relay.get(), dummy_pub.get()));
+    EXPECT_TRUE(pub->relay_to_pub(relay.get(), dummy_pub.get()));
+
+    pubs = get_published(dummy_client.get());
+    EXPECT_EQ(2u, pubs.size());
+    ASSERT_LE(2u, pubs.size());
+    EXPECT_TRUE(compare_full_block(epee::to_span(blocks), pubs.front()));
+    EXPECT_TRUE(compare_minimal_block(533, epee::to_span(blocks), pubs.back()));
+  }
+}
+
+TEST_F(zmq_pub, JsonChainWeakPtrSkip)
+{
+  static constexpr const char topic[] = "\1json";
+
+  ASSERT_TRUE(sub_request(topic));
+
+  const std::array<cryptonote::block, 1> blocks{{make_block()}};
+
+  pub.reset();
+  EXPECT_NO_THROW(cryptonote::listener::zmq_pub::chain_main{pub}(533, epee::to_span(blocks)));
+}
+
+TEST_F(zmq_pub, JsonTxpoolWeakPtrSkip)
+{
+  static constexpr const char topic[] = "\1json";
+
+  ASSERT_TRUE(sub_request(topic));
+
+  std::vector<cryptonote::txpool_event> events
+  {
+    {make_transaction(), {}, true}, {make_transaction(), {}, true}
+  };
+
+  pub.reset();
+  EXPECT_NO_THROW(cryptonote::listener::zmq_pub::txpool_add{pub}(std::move(events)));
+}
+
+TEST_F(zmq_server, pub)
+{
+  subscribe("json-minimal");
+
+  std::vector<cryptonote::txpool_event> events
+  {
+   {make_transaction(), {}, true}, {make_transaction(), {}, true}
+  };
+
+  const std::array<cryptonote::block, 1> blocks{{make_block()}};
+
+  ASSERT_EQ(1u, pub->send_txpool_add(events));
+  ASSERT_EQ(1u, pub->send_chain_main(200, epee::to_span(blocks)));
+
+  auto pubs = get_published(sub.get(), 2);
+  EXPECT_EQ(2u, pubs.size());
+  ASSERT_LE(2u, pubs.size());
+  EXPECT_TRUE(compare_minimal_txpool(epee::to_span(events), pubs.front()));
+  EXPECT_TRUE(compare_minimal_block(200, epee::to_span(blocks), pubs.back()));
+}