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/*
* Copyright (C) 2018 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef NETDUTILS_BACKOFFSEQUENCE_H
#define NETDUTILS_BACKOFFSEQUENCE_H
#include <stdint.h>
#include <algorithm>
#include <chrono>
#include <limits>
namespace android {
namespace netdutils {
// Encapsulate some RFC 3315 section 14 -style backoff mechanics.
//
// https://tools.ietf.org/html/rfc3315#section-14
template<typename time_type = std::chrono::seconds, typename counter_type = uint32_t>
class BackoffSequence {
public:
struct Parameters {
time_type initialRetransTime{TIME_UNITY};
counter_type maxRetransCount{0U};
time_type maxRetransTime{TIME_ZERO};
time_type maxRetransDuration{TIME_ZERO};
time_type endOfSequenceIndicator{TIME_ZERO};
};
BackoffSequence() : BackoffSequence(Parameters{}) {}
BackoffSequence(const BackoffSequence &) = default;
BackoffSequence(BackoffSequence &&) = default;
BackoffSequence& operator=(const BackoffSequence &) = default;
BackoffSequence& operator=(BackoffSequence &&) = default;
bool hasNextTimeout() const noexcept {
return !maxRetransCountExceed() && !maxRetransDurationExceeded();
}
// Returns 0 when the sequence is exhausted.
time_type getNextTimeout() {
if (!hasNextTimeout()) return getEndOfSequenceIndicator();
mRetransTime = getNextTimeoutAfter(mRetransTime);
mRetransCount++;
mTotalRetransDuration += mRetransTime;
return mRetransTime;
}
time_type getEndOfSequenceIndicator() const noexcept {
return mParams.endOfSequenceIndicator;
}
class Builder {
public:
Builder() {}
constexpr Builder& withInitialRetransmissionTime(time_type irt) {
mParams.initialRetransTime = irt;
return *this;
}
constexpr Builder& withMaximumRetransmissionCount(counter_type mrc) {
mParams.maxRetransCount = mrc;
return *this;
}
constexpr Builder& withMaximumRetransmissionTime(time_type mrt) {
mParams.maxRetransTime = mrt;
return *this;
}
constexpr Builder& withMaximumRetransmissionDuration(time_type mrd) {
mParams.maxRetransDuration = mrd;
return *this;
}
constexpr Builder& withEndOfSequenceIndicator(time_type eos) {
mParams.endOfSequenceIndicator = eos;
return *this;
}
constexpr BackoffSequence build() const {
return BackoffSequence(mParams);
}
private:
Parameters mParams;
};
private:
static constexpr int PER_ITERATION_SCALING_FACTOR = 2;
static constexpr time_type TIME_ZERO = time_type();
static constexpr time_type TIME_UNITY = time_type(1);
constexpr BackoffSequence(const struct Parameters ¶ms)
: mParams(params),
mRetransCount(0),
mRetransTime(TIME_ZERO),
mTotalRetransDuration(TIME_ZERO) {}
constexpr bool maxRetransCountExceed() const {
return (mParams.maxRetransCount > 0) && (mRetransCount >= mParams.maxRetransCount);
}
constexpr bool maxRetransDurationExceeded() const {
return (mParams.maxRetransDuration > TIME_ZERO) &&
(mTotalRetransDuration >= mParams.maxRetransDuration);
}
time_type getNextTimeoutAfter(time_type lastTimeout) const {
// TODO: Support proper random jitter. Also, consider supporting some
// per-iteration scaling factor other than doubling.
time_type nextTimeout = (lastTimeout > TIME_ZERO)
? PER_ITERATION_SCALING_FACTOR * lastTimeout
: mParams.initialRetransTime;
// Check if overflow occurred.
if (nextTimeout < lastTimeout) {
nextTimeout = std::numeric_limits<time_type>::max();
}
// Cap to maximum allowed, if necessary.
if (mParams.maxRetransTime > TIME_ZERO) {
nextTimeout = std::min(nextTimeout, mParams.maxRetransTime);
}
// Don't overflow the maximum total duration.
if (mParams.maxRetransDuration > TIME_ZERO) {
nextTimeout = std::min(nextTimeout, mParams.maxRetransDuration - lastTimeout);
}
return nextTimeout;
}
const Parameters mParams;
counter_type mRetransCount;
time_type mRetransTime;
time_type mTotalRetransDuration;
};
} // namespace netdutils
} // namespace android
#endif /* NETDUTILS_BACKOFFSEQUENCE_H */
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