lossy_fd_adapter.hh

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#ifndef SPONGE_LIBSPONGE_LOSSY_FD_ADAPTER_HH
#define SPONGE_LIBSPONGE_LOSSY_FD_ADAPTER_HH
 
#include "file_descriptor.hh"
#include "tcp_config.hh"
#include "tcp_segment.hh"
#include "util.hh"
 
#include <optional>
#include <random>
#include <utility>
 
template <typename AdapterT>
class LossyFdAdapter {
  private:
    std::mt19937 _rand{get_random_generator()};
 
    AdapterT _adapter;
 
    bool _should_drop(bool uplink) {
        const auto &cfg = _adapter.config();
        const uint16_t loss = uplink ? cfg.loss_rate_up : cfg.loss_rate_dn;
        return loss != 0 && uint16_t(_rand()) < loss;
    }
 
  public:
    operator const FileDescriptor &() const { return _adapter; }
 
    explicit LossyFdAdapter(AdapterT &&adapter) : _adapter(std::move(adapter)) {}
 
    std::optional<TCPSegment> read() {
        auto ret = _adapter.read();
        if (_should_drop(false)) {
            return {};
        }
        return ret;
    }
 
    void write(TCPSegment &seg) {
        if (_should_drop(true)) {
            return;
        }
        return _adapter.write(seg);
    }
 
 
    void set_listening(const bool l) { _adapter.set_listening(l); }      
    const FdAdapterConfig &config() const { return _adapter.config(); }  
    FdAdapterConfig &config_mut() { return _adapter.config_mut(); }      
    void tick(const size_t ms_since_last_tick) {
        _adapter.tick(ms_since_last_tick);
    }  
};
 
#endif  // SPONGE_LIBSPONGE_LOSSY_FD_ADAPTER_HH