VILLASnode/lib/hooks/drop.cpp

/* Drop hook.
 *
 * Author: Steffen Vogel <post@steffenvogel.de>
 * SPDX-FileCopyrightText: 2014-2023 Institute for Automation of Complex Power Systems, RWTH Aachen University
 * SPDX-License-Identifier: Apache-2.0
 */

#include <cinttypes>

#include <villas/hook.hpp>
#include <villas/sample.hpp>

namespace villas {
namespace node {

class DropHook : public Hook {

protected:
  struct Sample *prev;

public:
  using Hook::Hook;

  virtual void start() {
    assert(state == State::PREPARED || state == State::STOPPED);

    prev = nullptr;

    state = State::STARTED;
  }

  virtual void stop() {
    assert(state == State::STARTED);

    if (prev)
      sample_decref(prev);

    state = State::STOPPED;
  }

  virtual Hook::Reason process(struct Sample *smp) {
    int dist;

    assert(state == State::STARTED);

    if (prev) {
      dist = smp->sequence - (int64_t)prev->sequence;
      if (dist <= 0) {
        logger->debug("Dropping reordered sample: sequence={}, distance={}",
                      smp->sequence, dist);

        return Hook::Reason::SKIP_SAMPLE;
      }
    }

    sample_incref(smp);
    if (prev)
      sample_decref(prev);

    prev = smp;

    return Reason::OK;
  }

  virtual void restart() {
    assert(state == State::STARTED);

    if (prev) {
      sample_decref(prev);
      prev = nullptr;
    }
  }
};

// Register hook
static char n[] = "drop";
static char d[] = "Drop messages with reordered sequence numbers";
static HookPlugin<DropHook, n, d,
                  (int)Hook::Flags::BUILTIN | (int)Hook::Flags::NODE_READ, 3>
    p;

} // namespace node
} // namespace villas