TxEngine.hpp

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#ifndef DPDKLIBS_INCLUDE_DPDKLIBS_SENDER_TXENGINE_HPP_
#define DPDKLIBS_INCLUDE_DPDKLIBS_SENDER_TXENGINE_HPP_
 
#include <cstddef>
#include <cstdint>
#include <cstring>
 
namespace dunedaq::dpdklibs::sender {
 
enum class TxOutcome
{
  kSent,          // backend took ownership of the buffer
  kAllocFailed,   // no buffer was available
  kPrepareFailed, // append rejected: insufficient tailroom
  kTxFailed       // backend refused the packet; buffer freed
};
 
template<typename Backend>
class BufGuard
{
public:
  BufGuard(Backend& backend, void* buf)
    : m_backend(backend)
    , m_buf(buf)
  {
  }
  ~BufGuard()
  {
    if (m_buf != nullptr) {
      m_backend.free(m_buf);
    }
  }
  BufGuard(const BufGuard&) = delete;
  BufGuard& operator=(const BufGuard&) = delete;
  BufGuard(BufGuard&&) = delete;
  BufGuard& operator=(BufGuard&&) = delete;
 
  void release() { m_buf = nullptr; }
 
private:
  Backend& m_backend;
  void* m_buf;
};
 
// Allocate, build, and transmit one packet.
//
//  - build(dst) writes exactly packet_bytes into dst.
//  - If pre_tx_copy is non-null, the constructed bytes are copied there before
//    the transmit attempt.  The buffer is not readable after a successful
//    transmit, so this copy is the only record of the transmitted bytes.
//  - on_sent() runs only after a successful transmit.
template<typename Backend, typename BuildFn, typename OnSentFn>
TxOutcome
send_packet(Backend& backend, std::size_t packet_bytes, std::uint8_t* pre_tx_copy, BuildFn&& build, OnSentFn&& on_sent)
{
  void* buf = backend.alloc();
  if (buf == nullptr) {
    return TxOutcome::kAllocFailed;
  }
  BufGuard<Backend> guard(backend, buf);
 
  std::uint8_t* dst = backend.prepare(buf, packet_bytes);
  if (dst == nullptr) {
    return TxOutcome::kPrepareFailed;
  }
 
  build(dst);
  if (pre_tx_copy != nullptr) {
    std::memcpy(pre_tx_copy, dst, packet_bytes);
  }
 
  if (!backend.transmit(buf)) {
    return TxOutcome::kTxFailed;
  }
 
  guard.release();
  on_sent();
  return TxOutcome::kSent;
}
 
} // namespace dunedaq::dpdklibs::sender
 
#endif // DPDKLIBS_INCLUDE_DPDKLIBS_SENDER_TXENGINE_HPP_