Use byte_slice for sending zmq messages - removes data copy within zmq

contrib/epee/include/byte_slice.h

@@ -42,7 +42,12 @@ namespace epee
 
   struct release_byte_slice
   {
-    void operator()(byte_slice_data*) const noexcept;
+    //! For use with `zmq_message_init_data`, use second arg for buffer pointer.
+    static void call(void*, void* ptr) noexcept;
+    void operator()(byte_slice_data* ptr) const noexcept
+    {
+      call(nullptr, ptr);
+    }
   };
 
   /*! Inspired by slices in golang. Storage is thread-safe reference counted,
@@ -140,6 +145,9 @@ namespace epee
         \throw std::out_of_range If `size() < end`.
         \return Slice starting at `data() + begin` of size `end - begin`. */
     byte_slice get_slice(std::size_t begin, std::size_t end) const;
+
+    //! \post `empty()` \return Ownership of ref-counted buffer.
+    std::unique_ptr<byte_slice_data, release_byte_slice> take_buffer() noexcept;
   };
 } // epee
 

contrib/epee/src/byte_slice.cpp

@@ -49,12 +49,16 @@ namespace epee
     std::atomic<std::size_t> ref_count;
   };
 
-  void release_byte_slice::operator()(byte_slice_data* ptr) const noexcept
+  void release_byte_slice::call(void*, void* ptr) noexcept
   {
-    if (ptr && --(ptr->ref_count) == 0)
+    if (ptr)
     {
-      ptr->~byte_slice_data();
+      byte_slice_data* self = static_cast<byte_slice_data*>(ptr);
-      free(ptr);
+      if (--(self->ref_count) == 0)
+      {
+        self->~byte_slice_data();
+        free(self);
+      }
     }
   }
 
@@ -206,4 +210,11 @@ namespace epee
       return {};
     return {storage_.get(), {portion_.begin() + begin, end - begin}};
   }
+
+  std::unique_ptr<byte_slice_data, release_byte_slice> byte_slice::take_buffer() noexcept
+  {
+    std::unique_ptr<byte_slice_data, release_byte_slice> out{std::move(storage_)};
+    portion_ = nullptr;
+    return out;
+  }
 } // epee

src/net/zmq.cpp

@@ -33,6 +33,8 @@
 #include <limits>
 #include <utility>
 
+#include "byte_slice.h"
+
 namespace net
 {
 namespace zmq
@@ -183,6 +185,22 @@ namespace zmq
     {
         return retry_op(zmq_send, socket, payload.data(), payload.size(), flags);
     }
+
+    expect<void> send(epee::byte_slice&& payload, void* socket, int flags) noexcept
+    {
+        void* const data = const_cast<std::uint8_t*>(payload.data());
+        const std::size_t size = payload.size();
+        auto buffer = payload.take_buffer(); // clears `payload` from callee
+
+        zmq_msg_t msg{};
+        MONERO_ZMQ_CHECK(zmq_msg_init_data(std::addressof(msg), data, size, epee::release_byte_slice::call, buffer.get()));
+        buffer.release(); // zmq will now decrement byte_slice ref-count
+
+        expect<void> sent = retry_op(zmq_msg_send, std::addressof(msg), socket, flags);
+        if (!sent) // beware if removing `noexcept` from this function - possible leak here
+            zmq_msg_close(std::addressof(msg));
+        return sent;
+    }
 } // zmq
 } // net
 

src/net/zmq.h

@@ -53,6 +53,11 @@
 #define MONERO_ZMQ_THROW(msg)                         \
     MONERO_THROW( ::net::zmq::get_error_code(), msg )
 
+namespace epee
+{
+    class byte_slice;
+}
+
 namespace net
 {
 namespace zmq
@@ -132,5 +137,24 @@ namespace zmq
         \param flags See `zmq_send` for possible flags.
         \return `success()` if sent, otherwise ZMQ error. */
     expect<void> send(epee::span<const std::uint8_t> payload, void* socket, int flags = 0) noexcept;
+
+    /*! Sends `payload` on `socket`. Blocks until the entire message is queued
+        for sending, or until `zmq_term` is called on the `zmq_context`
+        associated with `socket`. If the context is terminated,
+        `make_error_code(ETERM)` is returned.
+
+        \note This will automatically retry on `EINTR`, so exiting on
+            interrupts requires context termination.
+        \note If non-blocking behavior is requested on `socket` or by `flags`,
+            then `net::zmq::make_error_code(EAGAIN)` will be returned if this
+            would block.
+
+        \param payload sent as one message on `socket`.
+        \param socket Handle created with `zmq_socket`.
+        \param flags See `zmq_msg_send` for possible flags.
+
+        \post `payload.emtpy()` - ownership is transferred to zmq.
+        \return `success()` if sent, otherwise ZMQ error. */
+    expect<void> send(epee::byte_slice&& payload, void* socket, int flags = 0) noexcept;
 } // zmq
 } // net

src/rpc/daemon_handler.cpp

@@ -33,6 +33,7 @@
 #include <stdexcept>
 
 #include <boost/uuid/nil_generator.hpp>
+#include <boost/utility/string_ref.hpp>
 // likely included by daemon_handler.h's includes,
 // but including here for clarity
 #include "cryptonote_core/cryptonote_core.h"
@@ -48,7 +49,7 @@ namespace rpc
 {
   namespace
   {
-    using handler_function = std::string(DaemonHandler& handler, const rapidjson::Value& id, const rapidjson::Value& msg);
+    using handler_function = epee::byte_slice(DaemonHandler& handler, const rapidjson::Value& id, const rapidjson::Value& msg);
     struct handler_map
     {
       const char* method_name;
@@ -66,7 +67,7 @@ namespace rpc
     }
 
     template<typename Message>
-    std::string handle_message(DaemonHandler& handler, const rapidjson::Value& id, const rapidjson::Value& parameters)
+    epee::byte_slice handle_message(DaemonHandler& handler, const rapidjson::Value& id, const rapidjson::Value& parameters)
     {
       typename Message::Request request{};
       request.fromJson(parameters);
@@ -903,7 +904,7 @@ namespace rpc
     return true;
   }
 
-  std::string DaemonHandler::handle(const std::string& request)
+  epee::byte_slice DaemonHandler::handle(const std::string& request)
   {
     MDEBUG("Handling RPC request: " << request);
 
@@ -916,8 +917,11 @@ namespace rpc
       if (matched_handler == std::end(handlers) || matched_handler->method_name != request_type)
         return BAD_REQUEST(request_type, req_full.getID());
 
-      std::string response = matched_handler->call(*this, req_full.getID(), req_full.getMessage());
+      epee::byte_slice response = matched_handler->call(*this, req_full.getID(), req_full.getMessage());
-      MDEBUG("Returning RPC response: " << response);
+
+      const boost::string_ref response_view{reinterpret_cast<const char*>(response.data()), response.size()};
+      MDEBUG("Returning RPC response: " << response_view);
+
       return response;
     }
     catch (const std::exception& e)

src/rpc/daemon_handler.h

@@ -28,6 +28,7 @@
 
 #pragma once
 
+#include "byte_slice.h"
 #include "daemon_messages.h"
 #include "daemon_rpc_version.h"
 #include "rpc_handler.h"
@@ -132,7 +133,7 @@ class DaemonHandler : public RpcHandler
 
     void handle(const GetOutputDistribution::Request& req, GetOutputDistribution::Response& res);
 
-    std::string handle(const std::string& request);
+    epee::byte_slice handle(const std::string& request) override final;
 
   private:
 

src/rpc/message.cpp

@@ -149,7 +149,7 @@ cryptonote::rpc::error FullMessage::getError()
   return err;
 }
 
-std::string FullMessage::getRequest(const std::string& request, const Message& message, const unsigned id)
+epee::byte_slice FullMessage::getRequest(const std::string& request, const Message& message, const unsigned id)
 {
   rapidjson::StringBuffer buffer;
   {
@@ -172,11 +172,11 @@ std::string FullMessage::getRequest(const std::string& request, const Message& m
     if (!dest.IsComplete())
       throw std::logic_error{"Invalid JSON tree generated"};
   }
-  return std::string{buffer.GetString(), buffer.GetSize()};
+  return epee::byte_slice{{buffer.GetString(), buffer.GetSize()}};
 }
 
 
-std::string FullMessage::getResponse(const Message& message, const rapidjson::Value& id)
+epee::byte_slice FullMessage::getResponse(const Message& message, const rapidjson::Value& id)
 {
   rapidjson::StringBuffer buffer;
   {
@@ -207,17 +207,17 @@ std::string FullMessage::getResponse(const Message& message, const rapidjson::Va
     if (!dest.IsComplete())
       throw std::logic_error{"Invalid JSON tree generated"};
   }
-  return std::string{buffer.GetString(), buffer.GetSize()};
+  return epee::byte_slice{{buffer.GetString(), buffer.GetSize()}};
 }
 
 // convenience functions for bad input
-std::string BAD_REQUEST(const std::string& request)
+epee::byte_slice BAD_REQUEST(const std::string& request)
 {
   rapidjson::Value invalid;
   return BAD_REQUEST(request, invalid);
 }
 
-std::string BAD_REQUEST(const std::string& request, const rapidjson::Value& id)
+epee::byte_slice BAD_REQUEST(const std::string& request, const rapidjson::Value& id)
 {
   Message fail;
   fail.status = Message::STATUS_BAD_REQUEST;
@@ -225,7 +225,7 @@ std::string BAD_REQUEST(const std::string& request, const rapidjson::Value& id)
   return FullMessage::getResponse(fail, id);
 }
 
-std::string BAD_JSON(const std::string& error_details)
+epee::byte_slice BAD_JSON(const std::string& error_details)
 {
   rapidjson::Value invalid;
   Message fail;

src/rpc/message.h

@@ -33,6 +33,7 @@
 #include <rapidjson/writer.h>
 #include <string>
 
+#include "byte_slice.h"
 #include "rpc/message_data_structs.h"
 
 namespace cryptonote
@@ -85,8 +86,8 @@ namespace rpc
 
       cryptonote::rpc::error getError();
 
-      static std::string getRequest(const std::string& request, const Message& message, unsigned id);
+      static epee::byte_slice getRequest(const std::string& request, const Message& message, unsigned id);
-      static std::string getResponse(const Message& message, const rapidjson::Value& id);
+      static epee::byte_slice getResponse(const Message& message, const rapidjson::Value& id);
     private:
 
       FullMessage() = default;
@@ -99,10 +100,10 @@ namespace rpc
 
 
   // convenience functions for bad input
-  std::string BAD_REQUEST(const std::string& request);
+  epee::byte_slice BAD_REQUEST(const std::string& request);
-  std::string BAD_REQUEST(const std::string& request, const rapidjson::Value& id);
+  epee::byte_slice BAD_REQUEST(const std::string& request, const rapidjson::Value& id);
 
-  std::string BAD_JSON(const std::string& error_details);
+  epee::byte_slice BAD_JSON(const std::string& error_details);
 
 
 }  // namespace rpc

src/rpc/rpc_handler.h

@@ -32,6 +32,7 @@
 #include <cstdint>
 #include <string>
 #include <vector>
+#include "byte_slice.h"
 #include "crypto/hash.h"
 
 namespace cryptonote
@@ -54,7 +55,7 @@ class RpcHandler
     RpcHandler() { }
     virtual ~RpcHandler() { }
 
-    virtual std::string handle(const std::string& request) = 0;
+    virtual epee::byte_slice handle(const std::string& request) = 0;
 
     static boost::optional<output_distribution_data>
       get_output_distribution(const std::function<bool(uint64_t, uint64_t, uint64_t, uint64_t&, std::vector<uint64_t>&, uint64_t&)> &f, uint64_t amount, uint64_t from_height, uint64_t to_height, const std::function<crypto::hash(uint64_t)> &get_hash, bool cumulative, uint64_t blockchain_height);

src/rpc/zmq_server.cpp

@@ -28,10 +28,13 @@
 
 #include "zmq_server.h"
 
+#include <boost/utility/string_ref.hpp>
 #include <chrono>
 #include <cstdint>
 #include <system_error>
 
+#include "byte_slice.h"
+
 namespace cryptonote
 {
 
@@ -73,10 +76,11 @@ void ZmqServer::serve()
     {
       const std::string message = MONERO_UNWRAP(net::zmq::receive(socket.get()));
       MDEBUG("Received RPC request: \"" << message << "\"");
-      const std::string& response = handler.handle(message);
+      epee::byte_slice response = handler.handle(message);
 
-      MONERO_UNWRAP(net::zmq::send(epee::strspan<std::uint8_t>(response), socket.get()));
+      const boost::string_ref response_view{reinterpret_cast<const char*>(response.data()), response.size()};
-      MDEBUG("Sent RPC reply: \"" << response << "\"");
+      MDEBUG("Sending RPC reply: \"" << response_view << "\"");
+      MONERO_UNWRAP(net::zmq::send(std::move(response), socket.get()));
     }
   }
   catch (const std::system_error& e)

tests/unit_tests/net.cpp

@@ -1702,6 +1702,45 @@ TEST(zmq, read_write)
     EXPECT_EQ(message, *received);
 }
 
+TEST(zmq, read_write_slice)
+{
+    net::zmq::context context{zmq_init(1)};
+    ASSERT_NE(nullptr, context);
+
+    net::zmq::socket send_socket{zmq_socket(context.get(), ZMQ_REQ)};
+    net::zmq::socket recv_socket{zmq_socket(context.get(), ZMQ_REP)};
+    ASSERT_NE(nullptr, send_socket);
+    ASSERT_NE(nullptr, recv_socket);
+
+    ASSERT_EQ(0u, zmq_bind(recv_socket.get(), "inproc://testing"));
+    ASSERT_EQ(0u, zmq_connect(send_socket.get(), "inproc://testing"));
+
+    std::string message;
+    message.resize(1024);
+    crypto::rand(message.size(), reinterpret_cast<std::uint8_t*>(std::addressof(message[0])));
+
+    {
+        epee::byte_slice slice_message{{epee::strspan<std::uint8_t>(message)}};
+        ASSERT_TRUE(bool(net::zmq::send(std::move(slice_message), send_socket.get())));
+        EXPECT_TRUE(slice_message.empty());
+    }
+
+    const expect<std::string> received = net::zmq::receive(recv_socket.get());
+    ASSERT_TRUE(bool(received));
+    EXPECT_EQ(message, *received);
+}
+
+TEST(zmq, write_slice_fail)
+{
+    std::string message;
+    message.resize(1024);
+    crypto::rand(message.size(), reinterpret_cast<std::uint8_t*>(std::addressof(message[0])));
+
+    epee::byte_slice slice_message{std::move(message)};
+    EXPECT_FALSE(bool(net::zmq::send(std::move(slice_message), nullptr)));
+    EXPECT_TRUE(slice_message.empty());
+}
+
 TEST(zmq, read_write_multipart)
 {
     net::zmq::context context{zmq_init(1)};