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

2 files changed, 42 insertions, 0 deletions

diff --git a/src/net/zmq.cpp b/src/net/zmq.cpp
index d02a22983..7ea80b907 100644
--- a/src/net/zmq.cpp
+++ b/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
 
diff --git a/src/net/zmq.h b/src/net/zmq.h
index c6a7fd743..65560b62e 100644
--- a/src/net/zmq.h
+++ b/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