Remove payload copy in all outgoing p2p messages

contrib/epee/include/net/levin_base.h

@@ -31,6 +31,7 @@
 
 #include <cstdint>
 
+#include "byte_stream.h"
 #include "net_utils_base.h"
 #include "span.h"
 
@@ -84,10 +85,11 @@ namespace levin
 #define LEVIN_PROTOCOL_VER_0         0
 #define LEVIN_PROTOCOL_VER_1         1
 
+ 
   template<class t_connection_context = net_utils::connection_context_base>
   struct levin_commands_handler
   {
-    virtual int invoke(int command, const epee::span<const uint8_t> in_buff, byte_slice& buff_out, t_connection_context& context)=0;
+    virtual int invoke(int command, const epee::span<const uint8_t> in_buff, byte_stream& buff_out, t_connection_context& context)=0;
     virtual int notify(int command, const epee::span<const uint8_t> in_buff, t_connection_context& context)=0;
     virtual void callback(t_connection_context& context){};
 
@@ -125,12 +127,41 @@ namespace levin
     }
   }
 
+  //! Provides space for levin (p2p) header, so that payload can be sent without copy
+  class message_writer
+  {
+    byte_slice finalize(uint32_t command, uint32_t flags, uint32_t return_code, bool expect_response);
+  public:
+    using header = bucket_head2;
+
+    explicit message_writer(std::size_t reserve = 8192);
+
+    message_writer(const message_writer&) = delete;
+    message_writer(message_writer&&) = default;
+    ~message_writer() = default;
+    message_writer& operator=(const message_writer&) = delete;
+    message_writer& operator=(message_writer&&) = default;
+
+    //! \return Size of payload (excludes header size).
+    std::size_t payload_size() const noexcept
+    {
+      return buffer.size() < sizeof(header) ? 0 : buffer.size() - sizeof(header);
+    }
+
+    byte_slice finalize_invoke(uint32_t command) { return finalize(command, LEVIN_PACKET_REQUEST, 0, true); }
+    byte_slice finalize_notify(uint32_t command) { return finalize(command, LEVIN_PACKET_REQUEST, 0, false); }
+    byte_slice finalize_response(uint32_t command, uint32_t return_code)
+    {
+      return finalize(command, LEVIN_PACKET_RESPONSE, return_code, false);
+    }
+
+    //! Has space for levin header until a finalize method is used
+    byte_stream buffer;
+  };
+
   //! \return Intialized levin header.
   bucket_head2 make_header(uint32_t command, uint64_t msg_size, uint32_t flags, bool expect_response) noexcept;
 
-  //! \return A levin notification message.
-  byte_slice make_notify(int command, epee::span<const std::uint8_t> payload);
-
   /*! Generate a dummy levin message.
 
       \param noise_bytes Total size of the returned `byte_slice`.
@@ -140,12 +171,11 @@ namespace levin
 
   /*! Generate 1+ levin messages that are identical to the noise message size.
 
-   \param noise Each levin message will be identical to the size of this
+   \param noise_size Each levin message will be identical to this value.
-      message. The bytes from this message will be used for padding.
    \return `nullptr` if `noise.size()` is less than the levin header size.
       Otherwise, a levin notification message OR 2+ levin fragment messages.
       Each message is `noise.size()` in length. */
-  byte_slice make_fragmented_notify(const byte_slice& noise, int command, epee::span<const std::uint8_t> payload);
+  byte_slice make_fragmented_notify(const std::size_t noise_size, int command, message_writer message);
 }
 }
 

contrib/epee/include/net/levin_protocol_handler_async.h

@@ -51,6 +51,21 @@
 #define MIN_BYTES_WANTED	512
 #endif
 
+template<typename context_t>
+void on_levin_traffic(const context_t &context, bool initiator, bool sent, bool error, size_t bytes, const char* category)
+{
+  MCINFO("net.p2p.traffic", context << bytes << " bytes " << (sent ? "sent" : "received") << (error ? "/corrupt" : "")
+      << " for category " << category << " initiated by " << (initiator ? "us" : "peer"));
+}
+
+template<typename context_t>
+void on_levin_traffic(const context_t &context, bool initiator, bool sent, bool error, size_t bytes, int command)
+{
+  char buf[32];
+  snprintf(buf, sizeof(buf),  "command-%u", command);
+  on_levin_traffic(context, initiator, sent, error, bytes, buf);
+}
+
 namespace epee
 {
 namespace levin
@@ -88,11 +103,10 @@ public:
   uint64_t m_max_packet_size;
   uint64_t m_invoke_timeout;
 
-  int invoke(int command, const epee::span<const uint8_t> in_buff, std::string& buff_out, boost::uuids::uuid connection_id);
+  int invoke(int command, message_writer in_msg, std::string& buff_out, boost::uuids::uuid connection_id);
   template<class callback_t>
-  int invoke_async(int command, const epee::span<const uint8_t> in_buff, boost::uuids::uuid connection_id, const callback_t &cb, size_t timeout = LEVIN_DEFAULT_TIMEOUT_PRECONFIGURED);
+  int invoke_async(int command, message_writer in_msg, boost::uuids::uuid connection_id, const callback_t &cb, size_t timeout = LEVIN_DEFAULT_TIMEOUT_PRECONFIGURED);
 
-  int notify(int command, const epee::span<const uint8_t> in_buff, boost::uuids::uuid connection_id);
   int send(epee::byte_slice message, const boost::uuids::uuid& connection_id);
   bool close(boost::uuids::uuid connection_id);
   bool update_connection_context(const t_connection_context& contxt);
@@ -122,12 +136,17 @@ class async_protocol_handler
 {
   std::string m_fragment_buffer;
 
-  bool send_message(uint32_t command, epee::span<const uint8_t> in_buff, uint32_t flags, bool expect_response)
+  bool send_message(byte_slice message)
   {
-    const bucket_head2 head = make_header(command, in_buff.size(), flags, expect_response);
+    if (message.size() < sizeof(message_writer::header))
-    if(!m_pservice_endpoint->do_send(byte_slice{as_byte_span(head), in_buff}))
       return false;
 
+    message_writer::header head;
+    std::memcpy(std::addressof(head), message.data(), sizeof(head));
+    if(!m_pservice_endpoint->do_send(std::move(message)))
+      return false;
+
+    on_levin_traffic(m_connection_context, true, true, false, head.m_cb, head.m_command);
     MDEBUG(m_connection_context << "LEVIN_PACKET_SENT. [len=" << head.m_cb
         << ", flags" << head.m_flags
         << ", r?=" << head.m_have_to_return_data
@@ -523,26 +542,17 @@ public:
           {
             if(m_current_head.m_have_to_return_data)
             {
-              byte_slice return_buff;
+              levin::message_writer return_message{32 * 1024};
               const uint32_t return_code = m_config.m_pcommands_handler->invoke(
-                m_current_head.m_command, buff_to_invoke, return_buff, m_connection_context
+                m_current_head.m_command, buff_to_invoke, return_message.buffer, m_connection_context
               );
 
               // peer_id remains unset if dropped
               if (m_current_head.m_command == m_connection_context.handshake_command() && m_connection_context.handshake_complete())
                 m_max_packet_size = m_config.m_max_packet_size;
 
-              bucket_head2 head = make_header(m_current_head.m_command, return_buff.size(), LEVIN_PACKET_RESPONSE, false);
+              if(!send_message(return_message.finalize_response(m_current_head.m_command, return_code)))
-              head.m_return_code = SWAP32LE(return_code);
-
-              if(!m_pservice_endpoint->do_send(byte_slice{{epee::as_byte_span(head), epee::to_span(return_buff)}}))
                 return false;
-
-              MDEBUG(m_connection_context << "LEVIN_PACKET_SENT. [len=" << head.m_cb
-                << ", flags" << head.m_flags
-                << ", r?=" << head.m_have_to_return_data
-                <<", cmd = " << head.m_command
-                << ", ver=" << head.m_protocol_version);
             }
             else
               m_config.m_pcommands_handler->notify(m_current_head.m_command, buff_to_invoke, m_connection_context);
@@ -619,7 +629,7 @@ public:
   }
 
   template<class callback_t>
-  bool async_invoke(int command, const epee::span<const uint8_t> in_buff, const callback_t &cb, size_t timeout = LEVIN_DEFAULT_TIMEOUT_PRECONFIGURED)
+  bool async_invoke(int command, message_writer in_msg, const callback_t &cb, size_t timeout = LEVIN_DEFAULT_TIMEOUT_PRECONFIGURED)
   {
     misc_utils::auto_scope_leave_caller scope_exit_handler = misc_utils::create_scope_leave_handler(
       boost::bind(&async_protocol_handler::finish_outer_call, this));
@@ -638,7 +648,7 @@ public:
       if (command == m_connection_context.handshake_command())
         m_max_packet_size = m_config.m_max_packet_size;
 
-      if(!send_message(command, in_buff, LEVIN_PACKET_REQUEST, true))
+      if(!send_message(in_msg.finalize_invoke(command)))
       {
         LOG_ERROR_CC(m_connection_context, "Failed to do_send");
         err_code = LEVIN_ERROR_CONNECTION;
@@ -664,7 +674,7 @@ public:
     return true;
   }
 
-  int invoke(int command, const epee::span<const uint8_t> in_buff, std::string& buff_out)
+  int invoke(int command, message_writer in_msg, std::string& buff_out)
   {
     misc_utils::auto_scope_leave_caller scope_exit_handler = misc_utils::create_scope_leave_handler(
                                       boost::bind(&async_protocol_handler::finish_outer_call, this));
@@ -676,7 +686,7 @@ public:
     if (command == m_connection_context.handshake_command())
       m_max_packet_size = m_config.m_max_packet_size;
 
-    if (!send_message(command, in_buff, LEVIN_PACKET_REQUEST, true))
+    if (!send_message(in_msg.finalize_invoke(command)))
     {
       LOG_ERROR_CC(m_connection_context, "Failed to send request");
       return LEVIN_ERROR_CONNECTION;
@@ -713,25 +723,9 @@ public:
     return m_invoke_result_code;
   }
 
-  int notify(int command, const epee::span<const uint8_t> in_buff)
+  /*! Sends `message` without adding a levin header. The message must have been
-  {
+      created with `make_noise_notify`, `make_fragmented_notify`, or
-    misc_utils::auto_scope_leave_caller scope_exit_handler = misc_utils::create_scope_leave_handler(
+      `message_writer::finalize_notify`. See additional instructions for
-                          boost::bind(&async_protocol_handler::finish_outer_call, this));
-
-    CRITICAL_REGION_LOCAL(m_call_lock);
-
-    if (!send_message(command, in_buff, LEVIN_PACKET_REQUEST, false))
-    {
-      LOG_ERROR_CC(m_connection_context, "Failed to send notify message");
-      return -1;
-    }
-
-    return 1;
-  }
-
-  /*! Sends `message` without adding a levin header. The message must have
-      been created with `make_notify`, `make_noise_notify` or
-      `make_fragmented_notify`. See additional instructions for
       `make_fragmented_notify`.
 
       \return 1 on success */
@@ -741,14 +735,11 @@ public:
       boost::bind(&async_protocol_handler::finish_outer_call, this)
     );
 
-    const std::size_t length = message.size();
+    if (!send_message(std::move(message)))
-    if (!m_pservice_endpoint->do_send(std::move(message)))
     {
       LOG_ERROR_CC(m_connection_context, "Failed to send message, dropping it");
       return -1;
     }
-
-    MDEBUG(m_connection_context << "LEVIN_PACKET_SENT. [len=" << (length - sizeof(bucket_head2)) << ", r?=0]");
     return 1;
   }
   //------------------------------------------------------------------------------------------
@@ -842,19 +833,19 @@ int async_protocol_handler_config<t_connection_context>::find_and_lock_connectio
 }
 //------------------------------------------------------------------------------------------
 template<class t_connection_context>
-int async_protocol_handler_config<t_connection_context>::invoke(int command, const epee::span<const uint8_t> in_buff, std::string& buff_out, boost::uuids::uuid connection_id)
+int async_protocol_handler_config<t_connection_context>::invoke(int command, message_writer in_msg, std::string& buff_out, boost::uuids::uuid connection_id)
 {
   async_protocol_handler<t_connection_context>* aph;
   int r = find_and_lock_connection(connection_id, aph);
-  return LEVIN_OK == r ? aph->invoke(command, in_buff, buff_out) : r;
+  return LEVIN_OK == r ? aph->invoke(command, std::move(in_msg), buff_out) : r;
 }
 //------------------------------------------------------------------------------------------
 template<class t_connection_context> template<class callback_t>
-int async_protocol_handler_config<t_connection_context>::invoke_async(int command, const epee::span<const uint8_t> in_buff, boost::uuids::uuid connection_id, const callback_t &cb, size_t timeout)
+int async_protocol_handler_config<t_connection_context>::invoke_async(int command, message_writer in_msg, boost::uuids::uuid connection_id, const callback_t &cb, size_t timeout)
 {
   async_protocol_handler<t_connection_context>* aph;
   int r = find_and_lock_connection(connection_id, aph);
-  return LEVIN_OK == r ? aph->async_invoke(command, in_buff, cb, timeout) : r;
+  return LEVIN_OK == r ? aph->async_invoke(command, std::move(in_msg), cb, timeout) : r;
 }
 //------------------------------------------------------------------------------------------
 template<class t_connection_context> template<class callback_t>
@@ -935,14 +926,6 @@ void async_protocol_handler_config<t_connection_context>::set_handler(levin_comm
 }
 //------------------------------------------------------------------------------------------
 template<class t_connection_context>
-int async_protocol_handler_config<t_connection_context>::notify(int command, const epee::span<const uint8_t> in_buff, boost::uuids::uuid connection_id)
-{
-  async_protocol_handler<t_connection_context>* aph;
-  int r = find_and_lock_connection(connection_id, aph);
-  return LEVIN_OK == r ? aph->notify(command, in_buff) : r;
-}
-//------------------------------------------------------------------------------------------
-template<class t_connection_context>
 int async_protocol_handler_config<t_connection_context>::send(byte_slice message, const boost::uuids::uuid& connection_id)
 {
   async_protocol_handler<t_connection_context>* aph;

contrib/epee/include/storages/levin_abstract_invoke2.h

@@ -37,21 +37,14 @@
 #undef MONERO_DEFAULT_LOG_CATEGORY
 #define MONERO_DEFAULT_LOG_CATEGORY "net"
 
+template<typename context_t>
+void on_levin_traffic(const context_t &context, bool initiator, bool sent, bool error, size_t bytes, const char *category);
+
+template<typename context_t>
+void on_levin_traffic(const context_t &context, bool initiator, bool sent, bool error, size_t bytes, int command);
+
 namespace
 {
-  template<typename context_t>
-  void on_levin_traffic(const context_t &context, bool initiator, bool sent, bool error, size_t bytes, const char *category)
-  {
-    MCINFO("net.p2p.traffic", context << bytes << " bytes " << (sent ? "sent" : "received") << (error ? "/corrupt" : "")
-        << " for category " << category << " initiated by " << (initiator ? "us" : "peer"));
-  }
-  template<typename context_t>
-  void on_levin_traffic(const context_t &context, bool initiator, bool sent, bool error, size_t bytes, int command)
-  {
-    char buf[32];
-    snprintf(buf, sizeof(buf),  "command-%u", command);
-    return on_levin_traffic(context, initiator, sent, error, bytes, buf);
-  }
   static const constexpr epee::serialization::portable_storage::limits_t default_levin_limits = {
     8192, // objects
     16384, // fields
@@ -117,12 +110,11 @@ namespace epee
       const boost::uuids::uuid &conn_id = context.m_connection_id;
       typename serialization::portable_storage stg;
       out_struct.store(stg);
-      byte_slice buff_to_send;
+      levin::message_writer to_send{16 * 1024};
       std::string buff_to_recv;
-      stg.store_to_binary(buff_to_send, 16 * 1024);
+      stg.store_to_binary(to_send.buffer);
 
-      on_levin_traffic(context, true, true, false, buff_to_send.size(), command);
+      int res = transport.invoke(command, std::move(to_send), buff_to_recv, conn_id);
-      int res = transport.invoke(command, boost::string_ref{reinterpret_cast<const char*>(buff_to_send.data()), buff_to_send.size()}, buff_to_recv, conn_id);
       if( res <=0 )
       {
         LOG_PRINT_L1("Failed to invoke command " << command << " return code " << res);
@@ -145,10 +137,9 @@ namespace epee
       const boost::uuids::uuid &conn_id = context.m_connection_id;
       typename serialization::portable_storage stg;
       const_cast<t_arg&>(out_struct).store(stg);//TODO: add true const support to searilzation
-      byte_slice buff_to_send;
+      levin::message_writer to_send{16 * 1024};
-      stg.store_to_binary(buff_to_send, 16 * 1024);
+      stg.store_to_binary(to_send.buffer);
-      on_levin_traffic(context, true, true, false, buff_to_send.size(), command);
+      int res = transport.invoke_async(command, std::move(to_send), conn_id, [cb, command](int code, const epee::span<const uint8_t> buff, typename t_transport::connection_context& context)->bool
-      int res = transport.invoke_async(command, epee::to_span(buff_to_send), conn_id, [cb, command](int code, const epee::span<const uint8_t> buff, typename t_transport::connection_context& context)->bool
       {
         t_result result_struct = AUTO_VAL_INIT(result_struct);
         if( code <=0 )
@@ -192,11 +183,10 @@ namespace epee
       const boost::uuids::uuid &conn_id = context.m_connection_id;
       serialization::portable_storage stg;
       out_struct.store(stg);
-      byte_slice buff_to_send;
+      levin::message_writer to_send;
-      stg.store_to_binary(buff_to_send);
+      stg.store_to_binary(to_send.buffer);
 
-      on_levin_traffic(context, true, true, false, buff_to_send.size(), command);
+      int res = transport.send(to_send.finalize_notify(command), conn_id);
-      int res = transport.notify(command, epee::to_span(buff_to_send), conn_id);
       if(res <=0 )
       {
         MERROR("Failed to notify command " << command << " return code " << res);
@@ -207,7 +197,7 @@ namespace epee
     //----------------------------------------------------------------------------------------------------
     //----------------------------------------------------------------------------------------------------
     template<class t_owner, class t_in_type, class t_out_type, class t_context, class callback_t>
-    int buff_to_t_adapter(int command, const epee::span<const uint8_t> in_buff, byte_slice& buff_out, callback_t cb, t_context& context )
+    int buff_to_t_adapter(int command, const epee::span<const uint8_t> in_buff, byte_stream& buff_out, callback_t cb, t_context& context )
     {
       serialization::portable_storage strg;
       if(!strg.load_from_binary(in_buff, &default_levin_limits))
@@ -230,12 +220,11 @@ namespace epee
       serialization::portable_storage strg_out;
       static_cast<t_out_type&>(out_struct).store(strg_out);
 
-      if(!strg_out.store_to_binary(buff_out, 32 * 1024))
+      if(!strg_out.store_to_binary(buff_out))
       {
         LOG_ERROR("Failed to store_to_binary in command" << command);
         return -1;
       }
-      on_levin_traffic(context, false, true, false, buff_out.size(), command);
 
       return res;
     }
@@ -262,7 +251,7 @@ namespace epee
     }
 
 #define CHAIN_LEVIN_INVOKE_MAP2(context_type) \
-  int invoke(int command, const epee::span<const uint8_t> in_buff, epee::byte_slice& buff_out, context_type& context) \
+  int invoke(int command, const epee::span<const uint8_t> in_buff, epee::byte_stream& buff_out, context_type& context) \
   { \
   bool handled = false; \
   return handle_invoke_map(false, command, in_buff, buff_out, context, handled); \
@@ -271,13 +260,13 @@ namespace epee
 #define CHAIN_LEVIN_NOTIFY_MAP2(context_type) \
   int notify(int command, const epee::span<const uint8_t> in_buff, context_type& context) \
   { \
-  bool handled = false; epee::byte_slice fake_str; \
+    bool handled = false; epee::byte_stream fake_str; \
     return handle_invoke_map(true, command, in_buff, fake_str, context, handled); \
   } 
 
 
 #define CHAIN_LEVIN_INVOKE_MAP() \
-  int invoke(int command, const epee::span<const uint8_t> in_buff, epee::byte_slice& buff_out, epee::net_utils::connection_context_base& context) \
+  int invoke(int command, const epee::span<const uint8_t> in_buff, epee::byte_stream& buff_out, epee::net_utils::connection_context_base& context) \
   { \
   bool handled = false; \
   return handle_invoke_map(false, command, in_buff, buff_out, context, handled); \
@@ -297,7 +286,7 @@ namespace epee
   } 
 
 #define BEGIN_INVOKE_MAP2(owner_type) \
-  template <class t_context> int handle_invoke_map(bool is_notify, int command, const epee::span<const uint8_t> in_buff, epee::byte_slice& buff_out, t_context& context, bool& handled) \
+  template <class t_context> int handle_invoke_map(bool is_notify, int command, const epee::span<const uint8_t> in_buff, epee::byte_stream& buff_out, t_context& context, bool& handled) \
   { \
   try { \
   typedef owner_type internal_owner_type_name;

contrib/epee/include/storages/portable_storage.h

@@ -34,6 +34,7 @@
 namespace epee
 {
   class byte_slice;
+  class byte_stream;
   namespace serialization
   {
     /************************************************************************/
@@ -83,8 +84,13 @@ namespace epee
 
       //-------------------------------------------------------------------------------
       bool		store_to_binary(byte_slice& target, std::size_t initial_buffer_size = 8192);
-      bool		load_from_binary(const epee::span<const uint8_t> target, const limits_t *limits = NULL);
+      bool		store_to_binary(byte_stream& ss);
-      bool		load_from_binary(const std::string& target, const limits_t *limits = NULL);
+      bool		load_from_binary(const epee::span<const uint8_t> target, const limits_t *limits = nullptr);
+      bool		load_from_binary(const std::string& target, const limits_t *limits = nullptr)
+      {
+        return load_from_binary(epee::strspan<uint8_t>(target), limits);
+      }
+
       template<class trace_policy>
       bool		  dump_as_xml(std::string& targetObj, const std::string& root_name = "");
       bool		  dump_as_json(std::string& targetObj, size_t indent = 0, bool insert_newlines = true);

contrib/epee/include/storages/portable_storage_template_helper.h

@@ -36,6 +36,8 @@
 
 namespace epee
 {
+  class byte_stream;
+
   namespace serialization
   {
     //-----------------------------------------------------------------------------------------------------------
@@ -127,5 +129,14 @@ namespace epee
       store_t_to_binary(str_in, binary_buff, initial_buffer_size);
       return binary_buff;
     }
+    //-----------------------------------------------------------------------------------------------------------
+    template<class t_struct>
+    bool store_t_to_binary(t_struct& str_in, byte_stream& binary_buff)
+    {
+      portable_storage ps;
+      str_in.store(ps);
+      return ps.store_to_binary(binary_buff);
+    }
+
   }
 }

contrib/epee/src/levin_base.cpp

@@ -34,6 +34,25 @@ namespace epee
 {
 namespace levin
 {
+  message_writer::message_writer(const std::size_t reserve)
+    : buffer()
+  {
+    buffer.reserve(reserve);
+    buffer.put_n(0, sizeof(header));
+  }
+
+  byte_slice message_writer::finalize(const uint32_t command, const uint32_t flags, const uint32_t return_code, const bool expect_response)
+  {
+    if (buffer.size() < sizeof(header))
+      throw std::runtime_error{"levin_writer::finalize already called"};
+
+    header head = make_header(command, payload_size(), flags, expect_response);
+    head.m_return_code = SWAP32LE(return_code);
+
+    std::memcpy(buffer.tellp() - buffer.size(), std::addressof(head), sizeof(head));
+    return byte_slice{std::move(buffer)};
+  }
+
   bucket_head2 make_header(uint32_t command, uint64_t msg_size, uint32_t flags, bool expect_response) noexcept
   {
     bucket_head2 head = {0};
@@ -47,12 +66,6 @@ namespace levin
     return head;
   }
 
-  byte_slice make_notify(int command, epee::span<const std::uint8_t> payload)
-  {
-    const bucket_head2 head = make_header(command, payload.size(), LEVIN_PACKET_REQUEST, false);
-    return byte_slice{epee::as_byte_span(head), payload};
-  }
-
   byte_slice make_noise_notify(const std::size_t noise_bytes)
   {
     static constexpr const std::uint32_t flags =
@@ -68,46 +81,40 @@ namespace levin
     return byte_slice{std::move(buffer)};
   }
 
-  byte_slice make_fragmented_notify(const byte_slice& noise_message, int command, epee::span<const std::uint8_t> payload)
+  byte_slice make_fragmented_notify(const std::size_t noise_size, const int command, message_writer message)
   {
-    const size_t noise_size = noise_message.size();
     if (noise_size < sizeof(bucket_head2) * 2)
       return nullptr;
 
-    if (payload.size() <= noise_size - sizeof(bucket_head2))
+    if (message.buffer.size() <= noise_size)
     {
       /* The entire message can be sent at once, and the levin binary parser
          will ignore extra bytes. So just pad with zeroes and otherwise send
          a "normal", not fragmented message. */
-      const size_t padding = noise_size - sizeof(bucket_head2) - payload.size();
-      const span<const uint8_t> padding_bytes{noise_message.end() - padding, padding};
 
-      const bucket_head2 head = make_header(command, noise_size - sizeof(bucket_head2), LEVIN_PACKET_REQUEST, false);
+      message.buffer.put_n(0, noise_size - message.buffer.size());
-      return byte_slice{as_byte_span(head), payload, padding_bytes};
+      return message.finalize_notify(command);
     }
 
     // fragment message
+    const byte_slice payload_bytes = message.finalize_notify(command);
+    span<const std::uint8_t> payload = to_span(payload_bytes);
+
     const size_t payload_space = noise_size - sizeof(bucket_head2);
     const size_t expected_fragments = ((payload.size() - 2) / payload_space) + 1;
 
-    std::string buffer{};
+    byte_stream buffer{};
-    buffer.reserve((expected_fragments + 1) * noise_size); // +1 here overselects for internal bucket_head2 value
+    buffer.reserve(expected_fragments * noise_size);
 
-    bucket_head2 head = make_header(0, noise_size - sizeof(bucket_head2), LEVIN_PACKET_BEGIN, false);
+    bucket_head2 head = make_header(0, payload_space, LEVIN_PACKET_BEGIN, false);
-    buffer.append(reinterpret_cast<const char*>(&head), sizeof(head));
+    buffer.write(as_byte_span(head));
 
-    head.m_command = command;
+    // internal levin header is in payload already
-    head.m_flags = LEVIN_PACKET_REQUEST;
-    head.m_cb = payload.size();
-    buffer.append(reinterpret_cast<const char*>(&head), sizeof(head));
 
-    size_t copy_size = payload.remove_prefix(payload_space - sizeof(bucket_head2));
+    size_t copy_size = payload.remove_prefix(payload_space);
-    buffer.append(reinterpret_cast<const char*>(payload.data()) - copy_size, copy_size);
+    buffer.write(payload.data() - copy_size, copy_size);
 
-    head.m_command = 0;
     head.m_flags = 0;
-    head.m_cb = noise_size - sizeof(bucket_head2);
-
     while (!payload.empty())
     {
       copy_size = payload.remove_prefix(payload_space);
@@ -115,12 +122,12 @@ namespace levin
       if (payload.empty())
         head.m_flags = LEVIN_PACKET_END;
 
-      buffer.append(reinterpret_cast<const char*>(&head), sizeof(head));
+      buffer.write(as_byte_span(head));
-      buffer.append(reinterpret_cast<const char*>(payload.data()) - copy_size, copy_size);
+      buffer.write(payload.data() - copy_size, copy_size);
     }
 
     const size_t padding = noise_size - copy_size - sizeof(bucket_head2);
-    buffer.append(reinterpret_cast<const char*>(noise_message.end()) - padding, padding);
+    buffer.put_n(0, padding);
 
     return byte_slice{std::move(buffer)};
   }

contrib/epee/src/portable_storage.cpp

@@ -48,15 +48,23 @@ namespace serialization
     TRY_ENTRY();
     byte_stream ss;
     ss.reserve(initial_buffer_size);
+    store_to_binary(ss);
+    target = epee::byte_slice{std::move(ss)};
+    return true;
+    CATCH_ENTRY("portable_storage::store_to_binary", false);
+  }
+
+  bool portable_storage::store_to_binary(byte_stream& ss)
+  {
+    TRY_ENTRY();
     storage_block_header sbh{};
     sbh.m_signature_a = SWAP32LE(PORTABLE_STORAGE_SIGNATUREA);
     sbh.m_signature_b = SWAP32LE(PORTABLE_STORAGE_SIGNATUREB);
     sbh.m_ver = PORTABLE_STORAGE_FORMAT_VER;
     ss.write(epee::as_byte_span(sbh));
     pack_entry_to_buff(ss, m_root);
-    target = epee::byte_slice{std::move(ss)};
     return true;
-    CATCH_ENTRY("portable_storage::store_to_binary", false)
+    CATCH_ENTRY("portable_storage::store_to_binary", false);
   }
 
     bool portable_storage::dump_as_json(std::string& buff, size_t indent, bool insert_newlines)
@@ -76,11 +84,6 @@ namespace serialization
       CATCH_ENTRY("portable_storage::load_from_json", false)
     }
 
-    bool portable_storage::load_from_binary(const std::string& target, const limits_t *limits)
-    {
-         return load_from_binary(epee::strspan<uint8_t>(target), limits);
-    }
-
     bool portable_storage::load_from_binary(const epee::span<const uint8_t> source, const limits_t *limits)
     {
       m_root.m_entries.clear();

src/cryptonote_core/blockchain.cpp

@@ -57,6 +57,7 @@
 #include "common/notify.h"
 #include "common/varint.h"
 #include "common/pruning.h"
+#include "time_helper.h"
 
 #undef MONERO_DEFAULT_LOG_CATEGORY
 #define MONERO_DEFAULT_LOG_CATEGORY "blockchain"

src/cryptonote_protocol/cryptonote_protocol_handler.h

@@ -46,6 +46,8 @@
 #include "block_queue.h"
 #include "common/perf_timer.h"
 #include "cryptonote_basic/connection_context.h"
+#include "net/levin_base.h"
+#include "p2p/net_node_common.h"
 #include <boost/circular_buffer.hpp>
 
 PUSH_WARNINGS
@@ -195,10 +197,11 @@ namespace cryptonote
       bool post_notify(typename t_parameter::request& arg, cryptonote_connection_context& context)
       {
         LOG_PRINT_L2("[" << epee::net_utils::print_connection_context_short(context) << "] post " << typeid(t_parameter).name() << " -->");
-        epee::byte_slice blob;
+
-        epee::serialization::store_t_to_binary(arg, blob, 256 * 1024); // optimize for block responses
+        epee::levin::message_writer out{256 * 1024}; // optimize for block responses
+        epee::serialization::store_t_to_binary(arg, out.buffer);
         //handler_response_blocks_now(blob.size()); // XXX
-        return m_p2p->invoke_notify_to_peer(t_parameter::ID, epee::to_span(blob), context);
+        return m_p2p->invoke_notify_to_peer(t_parameter::ID, std::move(out), context);
       }
   };
 

src/cryptonote_protocol/cryptonote_protocol_handler.inl

@@ -2699,15 +2699,15 @@ skip:
     // send fluffy ones first, we want to encourage people to run that
     if (!fluffyConnections.empty())
     {
-      epee::byte_slice fluffyBlob;
+      epee::levin::message_writer fluffyBlob{32 * 1024};
-      epee::serialization::store_t_to_binary(fluffy_arg, fluffyBlob, 32 * 1024);
+      epee::serialization::store_t_to_binary(fluffy_arg, fluffyBlob.buffer);
-      m_p2p->relay_notify_to_list(NOTIFY_NEW_FLUFFY_BLOCK::ID, epee::to_span(fluffyBlob), std::move(fluffyConnections));
+      m_p2p->relay_notify_to_list(NOTIFY_NEW_FLUFFY_BLOCK::ID, std::move(fluffyBlob), std::move(fluffyConnections));
     }
     if (!fullConnections.empty())
     {
-      epee::byte_slice fullBlob;
+      epee::levin::message_writer fullBlob{128 * 1024};
-      epee::serialization::store_t_to_binary(arg, fullBlob, 128 * 1024);
+      epee::serialization::store_t_to_binary(arg, fullBlob.buffer);
-      m_p2p->relay_notify_to_list(NOTIFY_NEW_BLOCK::ID, epee::to_span(fullBlob), std::move(fullConnections));
+      m_p2p->relay_notify_to_list(NOTIFY_NEW_BLOCK::ID, std::move(fullBlob), std::move(fullConnections));
     }
 
     return true;

src/cryptonote_protocol/cryptonote_protocol_handler_common.h

@@ -30,8 +30,8 @@
 
 #pragma once
 
-#include "p2p/net_node_common.h"
 #include "cryptonote_protocol/cryptonote_protocol_defs.h"
+#include "cryptonote_protocol/enums.h"
 #include "cryptonote_basic/connection_context.h"
 namespace cryptonote
 {

src/cryptonote_protocol/levin_notify.cpp

@@ -159,7 +159,7 @@ namespace levin
       return get_out_connections(p2p, get_blockchain_height(p2p, core));
     }
 
-    epee::byte_slice make_tx_payload(std::vector<blobdata>&& txs, const bool pad, const bool fluff)
+    epee::levin::message_writer make_tx_message(std::vector<blobdata>&& txs, const bool pad, const bool fluff)
     {
       NOTIFY_NEW_TRANSACTIONS::request request{};
       request.txs = std::move(txs);
@@ -193,21 +193,17 @@ namespace levin
         // if the size of _ moved enough, we might lose byte in size encoding, we don't care
       }
 
-      epee::byte_slice fullBlob;
+      epee::levin::message_writer out;
-      if (!epee::serialization::store_t_to_binary(request, fullBlob))
+      if (!epee::serialization::store_t_to_binary(request, out.buffer))
         throw std::runtime_error{"Failed to serialize to epee binary format"};
 
-      return fullBlob;
+      return out;
     }
 
     bool make_payload_send_txs(connections& p2p, std::vector<blobdata>&& txs, const boost::uuids::uuid& destination, const bool pad, const bool fluff)
     {
-      const epee::byte_slice blob = make_tx_payload(std::move(txs), pad, fluff);
+      epee::byte_slice blob = make_tx_message(std::move(txs), pad, fluff).finalize_notify(NOTIFY_NEW_TRANSACTIONS::ID);
-      p2p.for_connection(destination, [&blob](detail::p2p_context& context) {
+      return p2p.send(std::move(blob), destination);
-        on_levin_traffic(context, true, true, false, blob.size(), NOTIFY_NEW_TRANSACTIONS::ID);
-        return true;
-      });
-      return p2p.notify(NOTIFY_NEW_TRANSACTIONS::ID, epee::to_span(blob), destination);
     }
 
     /* The current design uses `asio::strand`s. The documentation isn't as clear
@@ -653,10 +649,6 @@ namespace levin
           else
             message = zone_->noise.clone();
 
-          zone_->p2p->for_connection(channel.connection, [&](detail::p2p_context& context) {
-            on_levin_traffic(context, true, true, false, message.size(), "noise");
-            return true;
-          });
           if (zone_->p2p->send(std::move(message), channel.connection))
           {
             if (!channel.queue.empty() && channel.active.empty())
@@ -816,9 +808,8 @@ namespace levin
 
       // Padding is not useful when using noise mode. Send as stem so receiver
       // forwards in Dandelion++ mode.
-      const epee::byte_slice payload = make_tx_payload(std::move(txs), false, false);
       epee::byte_slice message = epee::levin::make_fragmented_notify(
-        zone_->noise, NOTIFY_NEW_TRANSACTIONS::ID, epee::to_span(payload)
+        zone_->noise.size(), NOTIFY_NEW_TRANSACTIONS::ID, make_tx_message(std::move(txs), false, false)
       );
       if (CRYPTONOTE_MAX_FRAGMENTS * zone_->noise.size() < message.size())
       {

src/p2p/net_node.h

@@ -344,10 +344,9 @@ namespace nodetool
     virtual void on_connection_close(p2p_connection_context& context);
     virtual void callback(p2p_connection_context& context);
     //----------------- i_p2p_endpoint -------------------------------------------------------------
-    virtual bool relay_notify_to_list(int command, const epee::span<const uint8_t> data_buff, std::vector<std::pair<epee::net_utils::zone, boost::uuids::uuid>> connections);
+    virtual bool relay_notify_to_list(int command, epee::levin::message_writer message, std::vector<std::pair<epee::net_utils::zone, boost::uuids::uuid>> connections) final;
     virtual epee::net_utils::zone send_txs(std::vector<cryptonote::blobdata> txs, const epee::net_utils::zone origin, const boost::uuids::uuid& source, cryptonote::relay_method tx_relay);
-    virtual bool invoke_command_to_peer(int command, const epee::span<const uint8_t> req_buff, std::string& resp_buff, const epee::net_utils::connection_context_base& context);
+    virtual bool invoke_notify_to_peer(int command, epee::levin::message_writer message, const epee::net_utils::connection_context_base& context) final;
-    virtual bool invoke_notify_to_peer(int command, const epee::span<const uint8_t> req_buff, const epee::net_utils::connection_context_base& context);
     virtual bool drop_connection(const epee::net_utils::connection_context_base& context);
     virtual void request_callback(const epee::net_utils::connection_context_base& context);
     virtual void for_each_connection(std::function<bool(typename t_payload_net_handler::connection_context&, peerid_type, uint32_t)> f);

src/p2p/net_node.inl

@@ -2169,8 +2169,9 @@ namespace nodetool
   }
   //-----------------------------------------------------------------------------------
   template<class t_payload_net_handler>
-  bool node_server<t_payload_net_handler>::relay_notify_to_list(int command, const epee::span<const uint8_t> data_buff, std::vector<std::pair<epee::net_utils::zone, boost::uuids::uuid>> connections)
+  bool node_server<t_payload_net_handler>::relay_notify_to_list(int command, epee::levin::message_writer data_buff, std::vector<std::pair<epee::net_utils::zone, boost::uuids::uuid>> connections)
   {
+    epee::byte_slice message = data_buff.finalize_notify(command);
     std::sort(connections.begin(), connections.end());
     auto zone = m_network_zones.begin();
     for(const auto& c_id: connections)
@@ -2188,7 +2189,7 @@ namespace nodetool
         ++zone;
       }
       if (zone->first == c_id.first)
-        zone->second.m_net_server.get_config_object().notify(command, data_buff, c_id.second);
+        zone->second.m_net_server.get_config_object().send(message.clone(), c_id.second);
     }
     return true;
   }
@@ -2255,24 +2256,13 @@ namespace nodetool
   }
   //-----------------------------------------------------------------------------------
   template<class t_payload_net_handler>
-  bool node_server<t_payload_net_handler>::invoke_notify_to_peer(int command, const epee::span<const uint8_t> req_buff, const epee::net_utils::connection_context_base& context)
+  bool node_server<t_payload_net_handler>::invoke_notify_to_peer(const int command, epee::levin::message_writer message, const epee::net_utils::connection_context_base& context)
   {
     if(is_filtered_command(context.m_remote_address, command))
       return false;
 
     network_zone& zone = m_network_zones.at(context.m_remote_address.get_zone());
-    int res = zone.m_net_server.get_config_object().notify(command, req_buff, context.m_connection_id);
+    int res = zone.m_net_server.get_config_object().send(message.finalize_notify(command), context.m_connection_id);
-    return res > 0;
-  }
-  //-----------------------------------------------------------------------------------
-  template<class t_payload_net_handler>
-  bool node_server<t_payload_net_handler>::invoke_command_to_peer(int command, const epee::span<const uint8_t> req_buff, std::string& resp_buff, const epee::net_utils::connection_context_base& context)
-  {
-    if(is_filtered_command(context.m_remote_address, command))
-      return false;
-
-    network_zone& zone = m_network_zones.at(context.m_remote_address.get_zone());
-    int res = zone.m_net_server.get_config_object().invoke(command, req_buff, resp_buff, context.m_connection_id);
     return res > 0;
   }
   //-----------------------------------------------------------------------------------

src/p2p/net_node_common.h

@@ -40,6 +40,8 @@
 #include "net/net_utils_base.h"
 #include "p2p_protocol_defs.h"
 
+namespace epee { namespace levin { class message_writer; } }
+
 namespace nodetool
 {
 
@@ -49,10 +51,9 @@ namespace nodetool
   template<class t_connection_context>
   struct i_p2p_endpoint
   {
-    virtual bool relay_notify_to_list(int command, const epee::span<const uint8_t> data_buff, std::vector<std::pair<epee::net_utils::zone, boost::uuids::uuid>> connections)=0;
+    virtual bool relay_notify_to_list(int command, epee::levin::message_writer message, std::vector<std::pair<epee::net_utils::zone, boost::uuids::uuid>> connections)=0;
     virtual epee::net_utils::zone send_txs(std::vector<cryptonote::blobdata> txs, const epee::net_utils::zone origin, const boost::uuids::uuid& source, cryptonote::relay_method tx_relay)=0;
-    virtual bool invoke_command_to_peer(int command, const epee::span<const uint8_t> req_buff, std::string& resp_buff, const epee::net_utils::connection_context_base& context)=0;
+    virtual bool invoke_notify_to_peer(int command, epee::levin::message_writer message, const epee::net_utils::connection_context_base& context)=0;
-    virtual bool invoke_notify_to_peer(int command, const epee::span<const uint8_t> req_buff, const epee::net_utils::connection_context_base& context)=0;
     virtual bool drop_connection(const epee::net_utils::connection_context_base& context)=0;
     virtual void request_callback(const epee::net_utils::connection_context_base& context)=0;
     virtual uint64_t get_public_connections_count()=0;
@@ -71,7 +72,7 @@ namespace nodetool
   template<class t_connection_context>
   struct p2p_endpoint_stub: public i_p2p_endpoint<t_connection_context>
   {
-    virtual bool relay_notify_to_list(int command, const epee::span<const uint8_t> data_buff, std::vector<std::pair<epee::net_utils::zone, boost::uuids::uuid>> connections)
+    virtual bool relay_notify_to_list(int command, epee::levin::message_writer message, std::vector<std::pair<epee::net_utils::zone, boost::uuids::uuid>> connections)
     {
       return false;
     }
@@ -79,11 +80,7 @@ namespace nodetool
     {
       return epee::net_utils::zone::invalid;
     }
-    virtual bool invoke_command_to_peer(int command, const epee::span<const uint8_t> req_buff, std::string& resp_buff, const epee::net_utils::connection_context_base& context)
+    virtual bool invoke_notify_to_peer(int command, epee::levin::message_writer message, const epee::net_utils::connection_context_base& context)
-    {
-      return false;
-    }
-    virtual bool invoke_notify_to_peer(int command, const epee::span<const uint8_t> req_buff, const epee::net_utils::connection_context_base& context)
     {
       return true;
     }

tests/fuzz/levin.cpp

@@ -68,13 +68,13 @@ namespace
     {
     }
 
-    virtual int invoke(int command, const epee::span<const uint8_t> in_buff, epee::byte_slice& buff_out, test_levin_connection_context& context)
+    virtual int invoke(int command, const epee::span<const uint8_t> in_buff, epee::byte_stream& buff_out, test_levin_connection_context& context)
     {
       m_invoke_counter.inc();
       boost::unique_lock<boost::mutex> lock(m_mutex);
       m_last_command = command;
       m_last_in_buf = std::string((const char*)in_buff.data(), in_buff.size());
-      buff_out = m_invoke_out_buf.clone();
+      buff_out.write(epee::to_span(m_invoke_out_buf));
       return m_return_code;
     }
 

tests/net_load_tests/net_load_tests.h

@@ -67,7 +67,7 @@ namespace net_load_tests
     {
     }
 
-    virtual int invoke(int command, const epee::span<const uint8_t> in_buff, epee::byte_slice& buff_out, test_connection_context& context)
+    virtual int invoke(int command, const epee::span<const uint8_t> in_buff, epee::byte_stream& buff_out, test_connection_context& context)
     {
       //m_invoke_counter.inc();
       //std::unique_lock<std::mutex> lock(m_mutex);

tests/unit_tests/epee_boosted_tcp_server.cpp

@@ -153,7 +153,7 @@ TEST(test_epee_connection, test_lifetime)
       delay(delay),
       on_connection_close_f(on_connection_close_f)
     {}
-    virtual int invoke(int, const epee::span<const uint8_t>, epee::byte_slice&, context_t&) override { epee::misc_utils::sleep_no_w(delay); return {}; }
+    virtual int invoke(int, const epee::span<const uint8_t>, epee::byte_stream&, context_t&) override { epee::misc_utils::sleep_no_w(delay); return {}; }
     virtual int notify(int, const epee::span<const uint8_t>, context_t&) override { return {}; }
     virtual void callback(context_t&) override {}
     virtual void on_connection_new(context_t&) override {}
@@ -281,7 +281,7 @@ TEST(test_epee_connection, test_lifetime)
     for (auto i = 0; i < N; ++i) {
       tag = create_connection();
       ASSERT_TRUE(shared_state->get_connections_count() == 1);
-      success = shared_state->invoke_async(1, {}, tag, [](int, const epee::span<const uint8_t>, context_t&){}, TIMEOUT);
+      success = shared_state->invoke_async(1, epee::levin::message_writer{}, tag, [](int, const epee::span<const uint8_t>, context_t&){}, TIMEOUT);
       ASSERT_TRUE(success);
       while (shared_state->sock_count == 1) {
         success = shared_state->foreach_connection([&shared_state, &tag](context_t&){

tests/unit_tests/epee_levin_protocol_handler_async.cpp

@@ -59,13 +59,13 @@ namespace
     {
     }
 
-    virtual int invoke(int command, const epee::span<const uint8_t> in_buff, epee::byte_slice& buff_out, test_levin_connection_context& context)
+    virtual int invoke(int command, const epee::span<const uint8_t> in_buff, epee::byte_stream& buff_out, test_levin_connection_context& context)
     {
       m_invoke_counter.inc();
       boost::unique_lock<boost::mutex> lock(m_mutex);
       m_last_command = command;
       m_last_in_buf = std::string((const char*)in_buff.data(), in_buff.size());
-      buff_out = m_invoke_out_buf.clone();
+      buff_out.write(epee::to_span(m_invoke_out_buf));
       return m_return_code;
     }
 
@@ -434,8 +434,11 @@ TEST_F(positive_test_connection_to_levin_protocol_handler_calls, handler_process
   const int expected_command = 4673261;
   const std::string in_data(256, 'e');
 
+  epee::levin::message_writer message{};
+  message.buffer.write(epee::to_span(in_data));
+
   const epee::byte_slice noise = epee::levin::make_noise_notify(1024);
-  const epee::byte_slice notify = epee::levin::make_notify(expected_command, epee::strspan<std::uint8_t>(in_data));
+  const epee::byte_slice notify = message.finalize_notify(expected_command);
 
   test_connection_ptr conn = create_connection();
 
@@ -468,11 +471,16 @@ TEST_F(positive_test_connection_to_levin_protocol_handler_calls, handler_process
   const int expected_command = 4673261;
   const int expected_fragmented_command = 46732;
   const std::string in_data(256, 'e');
-  std::string in_fragmented_data(1024 * 4, 'c');
+
+  epee::levin::message_writer message{};
+  message.buffer.write(epee::to_span(in_data));
+
+  epee::levin::message_writer in_fragmented_data;
+  in_fragmented_data.buffer.put_n('c', 1024 * 4);
 
   const epee::byte_slice noise = epee::levin::make_noise_notify(1024);
-  const epee::byte_slice notify = epee::levin::make_notify(expected_command, epee::strspan<std::uint8_t>(in_data));
+  const epee::byte_slice notify = message.finalize_notify(expected_command);
-  epee::byte_slice fragmented = epee::levin::make_fragmented_notify(noise, expected_fragmented_command, epee::strspan<std::uint8_t>(in_fragmented_data));
+  epee::byte_slice fragmented = epee::levin::make_fragmented_notify(noise.size(), expected_fragmented_command, std::move(in_fragmented_data));
 
   EXPECT_EQ(5u, fragmented.size() / 1024);
   EXPECT_EQ(0u, fragmented.size() % 1024);
@@ -497,11 +505,13 @@ TEST_F(positive_test_connection_to_levin_protocol_handler_calls, handler_process
     ASSERT_TRUE(conn->m_protocol_handler.handle_recv(next.data(), next.size()));
   }
 
-  in_fragmented_data.resize(((1024 - sizeof(epee::levin::bucket_head2)) * 5) - sizeof(epee::levin::bucket_head2)); // add padding zeroes
+  std::string compare_buffer(1024 * 4, 'c');
+  compare_buffer.resize(((1024 - sizeof(epee::levin::bucket_head2)) * 5) - sizeof(epee::levin::bucket_head2)); // add padding zeroes
+
   ASSERT_EQ(4u, m_commands_handler.notify_counter());
   ASSERT_EQ(0u, m_commands_handler.invoke_counter());
   ASSERT_EQ(expected_fragmented_command, m_commands_handler.last_command());
-  ASSERT_EQ(in_fragmented_data, m_commands_handler.last_in_buf());
+  ASSERT_EQ(compare_buffer, m_commands_handler.last_in_buf());
   ASSERT_EQ(0u, conn->send_counter());
   ASSERT_TRUE(conn->last_send_data().empty());
 

tests/unit_tests/levin.cpp

@@ -245,9 +245,9 @@ namespace
             return out;
         }
 
-        virtual int invoke(int command, const epee::span<const uint8_t> in_buff, epee::byte_slice& buff_out, cryptonote::levin::detail::p2p_context& context) override final
+        virtual int invoke(int command, const epee::span<const uint8_t> in_buff, epee::byte_stream& buff_out, cryptonote::levin::detail::p2p_context& context) override final
         {
-            buff_out = nullptr;
+            buff_out.clear();
             invoked_.push_back(
                 {context.m_connection_id, command, std::string{reinterpret_cast<const char*>(in_buff.data()), in_buff.size()}}
             );
@@ -384,21 +384,50 @@ TEST(make_header, expect_return)
     EXPECT_EQ(0u, header1.m_flags);
 }
 
-TEST(make_notify, empty_payload)
+TEST(message_writer, invoke_with_empty_payload)
 {
-    const epee::byte_slice message = epee::levin::make_notify(443, nullptr);
+    const epee::byte_slice message = epee::levin::message_writer{}.finalize_invoke(443);
+    const epee::levin::bucket_head2 header =
+        epee::levin::make_header(443, 0, LEVIN_PACKET_REQUEST, true);
+    ASSERT_EQ(sizeof(header), message.size());
+    EXPECT_TRUE(std::memcmp(std::addressof(header), message.data(), sizeof(header)) == 0);
+}
+
+TEST(message_writer, invoke_with_payload)
+{
+    std::string bytes(100, 'a');
+    std::generate(bytes.begin(), bytes.end(), crypto::random_device{});
+
+    epee::levin::message_writer writer{};
+    writer.buffer.write(epee::to_span(bytes));
+
+    const epee::byte_slice message = writer.finalize_invoke(443);
+    const epee::levin::bucket_head2 header =
+        epee::levin::make_header(443, bytes.size(), LEVIN_PACKET_REQUEST, true);
+
+    ASSERT_EQ(sizeof(header) + bytes.size(), message.size());
+    EXPECT_TRUE(std::memcmp(std::addressof(header), message.data(), sizeof(header)) == 0);
+    EXPECT_TRUE(std::memcmp(bytes.data(), message.data() + sizeof(header), bytes.size()) == 0);
+}
+
+TEST(message_writer, notify_with_empty_payload)
+{
+    const epee::byte_slice message = epee::levin::message_writer{}.finalize_notify(443);
     const epee::levin::bucket_head2 header =
         epee::levin::make_header(443, 0, LEVIN_PACKET_REQUEST, false);
     ASSERT_EQ(sizeof(header), message.size());
     EXPECT_TRUE(std::memcmp(std::addressof(header), message.data(), sizeof(header)) == 0);
 }
 
-TEST(make_notify, with_payload)
+TEST(message_writer, notify_with_payload)
 {
     std::string bytes(100, 'a');
     std::generate(bytes.begin(), bytes.end(), crypto::random_device{});
 
-    const epee::byte_slice message = epee::levin::make_notify(443, epee::strspan<std::uint8_t>(bytes));
+    epee::levin::message_writer writer{};
+    writer.buffer.write(epee::to_span(bytes));
+
+    const epee::byte_slice message = writer.finalize_notify(443);
     const epee::levin::bucket_head2 header =
         epee::levin::make_header(443, bytes.size(), LEVIN_PACKET_REQUEST, false);
 
@@ -407,6 +436,44 @@ TEST(make_notify, with_payload)
     EXPECT_TRUE(std::memcmp(bytes.data(), message.data() + sizeof(header), bytes.size()) == 0);
 }
 
+TEST(message_writer, response_with_empty_payload)
+{
+    const epee::byte_slice message = epee::levin::message_writer{}.finalize_response(443, 1);
+    epee::levin::bucket_head2 header =
+        epee::levin::make_header(443, 0, LEVIN_PACKET_RESPONSE, false);
+    header.m_return_code = SWAP32LE(1);
+    ASSERT_EQ(sizeof(header), message.size());
+    EXPECT_TRUE(std::memcmp(std::addressof(header), message.data(), sizeof(header)) == 0);
+}
+
+TEST(message_writer, response_with_payload)
+{
+    std::string bytes(100, 'a');
+    std::generate(bytes.begin(), bytes.end(), crypto::random_device{});
+
+    epee::levin::message_writer writer{};
+    writer.buffer.write(epee::to_span(bytes));
+
+    const epee::byte_slice message = writer.finalize_response(443, 6450);
+    epee::levin::bucket_head2 header =
+        epee::levin::make_header(443, bytes.size(), LEVIN_PACKET_RESPONSE, false);
+    header.m_return_code = SWAP32LE(6450);
+
+    ASSERT_EQ(sizeof(header) + bytes.size(), message.size());
+    EXPECT_TRUE(std::memcmp(std::addressof(header), message.data(), sizeof(header)) == 0);
+    EXPECT_TRUE(std::memcmp(bytes.data(), message.data() + sizeof(header), bytes.size()) == 0);
+}
+
+TEST(message_writer, error)
+{
+    epee::levin::message_writer writer{};
+    writer.buffer.clear();
+
+    EXPECT_THROW(writer.finalize_invoke(0), std::runtime_error);
+    EXPECT_THROW(writer.finalize_notify(0), std::runtime_error);
+    EXPECT_THROW(writer.finalize_response(0, 0), std::runtime_error);
+}
+
 TEST(make_noise, invalid)
 {
     EXPECT_TRUE(epee::levin::make_noise_notify(sizeof(epee::levin::bucket_head2) - 1).empty());
@@ -428,13 +495,13 @@ TEST(make_noise, valid)
 
 TEST(make_fragment, invalid)
 {
-    EXPECT_TRUE(epee::levin::make_fragmented_notify(nullptr, 0, nullptr).empty());
+    EXPECT_TRUE(epee::levin::make_fragmented_notify(0, 0, epee::levin::message_writer{}).empty());
 }
 
 TEST(make_fragment, single)
 {
     const epee::byte_slice noise = epee::levin::make_noise_notify(1024);
-    const epee::byte_slice fragment = epee::levin::make_fragmented_notify(noise, 11, nullptr);
+    const epee::byte_slice fragment = epee::levin::make_fragmented_notify(noise.size(), 11, epee::levin::message_writer{});
     const epee::levin::bucket_head2 header =
         epee::levin::make_header(11, 1024 - sizeof(epee::levin::bucket_head2), LEVIN_PACKET_REQUEST, false);
 
@@ -449,8 +516,13 @@ TEST(make_fragment, multiple)
     std::string bytes(1024 * 3 - 150, 'a');
     std::generate(bytes.begin(), bytes.end(), crypto::random_device{});
 
+    epee::levin::message_writer message;
+    message.buffer.write(epee::to_span(bytes));
+
     const epee::byte_slice noise = epee::levin::make_noise_notify(1024);
-    epee::byte_slice fragment = epee::levin::make_fragmented_notify(noise, 114, epee::strspan<std::uint8_t>(bytes));
+    epee::byte_slice fragment = epee::levin::make_fragmented_notify(noise.size(), 114, std::move(message));
+
+    EXPECT_EQ(1024 * 3, fragment.size());
 
     epee::levin::bucket_head2 header =
         epee::levin::make_header(0, 1024 - sizeof(epee::levin::bucket_head2), LEVIN_PACKET_BEGIN, false);
@@ -497,6 +569,7 @@ TEST(make_fragment, multiple)
 
     fragment.take_slice(bytes.size());
 
+    EXPECT_EQ(18, fragment.size());
     EXPECT_EQ(18, std::count(fragment.cbegin(), fragment.cend(), 0));
 }
 
@@ -2161,20 +2234,31 @@ TEST_F(levin_notify, command_max_bytes)
 
     add_connection(true);
 
-    std::string bytes(4096, 'h');
+    std::string payload(4096, 'h');
+    epee::byte_slice bytes;
+    {
+        epee::levin::message_writer dest{};
+        dest.buffer.write(epee::to_span(payload));
+        bytes = dest.finalize_notify(ping_command);
+    }
 
-    EXPECT_EQ(1, get_connections().notify(ping_command, epee::strspan<std::uint8_t>(bytes), contexts_.front().get_id()));
+    EXPECT_EQ(1, get_connections().send(bytes.clone(), contexts_.front().get_id()));
     EXPECT_EQ(1u, contexts_.front().process_send_queue(true));
     EXPECT_EQ(1u, receiver_.notified_size());
 
     const received_message msg = receiver_.get_raw_notification();
     EXPECT_EQ(ping_command, msg.command);
     EXPECT_EQ(contexts_.front().get_id(), msg.connection);
-    EXPECT_EQ(bytes, msg.payload);
+    EXPECT_EQ(payload, msg.payload);
 
-    bytes.push_back('e');
+    {
+        payload.push_back('h');
+        epee::levin::message_writer dest{};
+        dest.buffer.write(epee::to_span(payload));
+        bytes = dest.finalize_notify(ping_command);
+    }
 
-    EXPECT_EQ(1, get_connections().notify(ping_command, epee::strspan<std::uint8_t>(bytes), contexts_.front().get_id()));
+    EXPECT_EQ(1, get_connections().send(std::move(bytes), contexts_.front().get_id()));
     EXPECT_EQ(1u, contexts_.front().process_send_queue(false));
     EXPECT_EQ(0u, receiver_.notified_size());
 }