vapcore-light 1.12.0

Tetsy Vapory (VapCore) Light Client Implementation (Block Import IO Service, Blockchain Data Fetching, Light Client Header Chain Storage, Tetsy Light Protocol (PLP) Provider, Light Transaction Queue, CHT Definitions, Light Client Data Cache), Tetsy Light Protocol (PLP) Implementation, P2P Network I/O and Event Context Generalization, Peer Error Handling & Punishment, Request Load Timer & Distribution Manager, Pending Request Set Storage, Request Credit Management, Light Client Request Types, Request Chain Builder Utility, On-demand Chain Request Service over LES (for RPCs), ResponseGuard Implementation)
Documentation 
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// Copyright 2015-2020 Parity Technologies (UK) Ltd.
// This file is part of Tetsy Vapory.

// Tetsy Vapory is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// Tetsy Vapory is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with Tetsy Vapory.  If not, see <http://www.gnu.org/licenses/>.

use failsafe;
use std::time::Duration;

type RequestPolicy = failsafe::failure_policy::ConsecutiveFailures<failsafe::backoff::Exponential>;

/// Error wrapped on-top of `FailsafeError`
#[derive(Debug, PartialEq)]
pub enum Error {
	/// The call is let through
	LetThrough,
	/// The call rejected by the guard
	Rejected,
	/// The request reached the maximum of backoff iterations
	ReachedLimit,
}

/// Handle and register requests that can fail
#[derive(Debug)]
pub struct RequestGuard {
	backoff_round: usize,
	max_backoff_rounds: usize,
	state: failsafe::StateMachine<RequestPolicy, ()>,
}

impl RequestGuard {
	/// Constructor
	pub fn new(
		consecutive_failures: u32,
		max_backoff_rounds: usize,
		start_backoff: Duration,
		max_backoff: Duration,
	) -> Self {
		let backoff = failsafe::backoff::exponential(start_backoff, max_backoff);
		// success_rate not used because only errors are registered
		let policy = failsafe::failure_policy::consecutive_failures(consecutive_failures as u32, backoff);

		Self {
			backoff_round: 0,
			max_backoff_rounds,
			state: failsafe::StateMachine::new(policy, ()),
		}
	}

	/// Update the state after a `faulty` call
	pub fn register_error(&mut self) -> Error {
		trace!(target: "circuit_breaker", "RequestGuard; backoff_round: {}/{}, state {:?}",
			   self.backoff_round, self.max_backoff_rounds, self.state);

		if self.backoff_round >= self.max_backoff_rounds {
			Error::ReachedLimit
		} else if self.state.is_call_permitted() {
			self.state.on_error();
			if self.state.is_call_permitted() {
				Error::LetThrough
			} else {
				self.backoff_round += 1;
				Error::Rejected
			}
		} else {
			Error::Rejected
		}
	}

	/// Poll the circuit breaker, to check if the call is permitted
	pub fn is_call_permitted(&self) -> bool {
		self.state.is_call_permitted()
	}
}

#[cfg(test)]
mod tests {
	use std::iter;
	use std::time::Instant;
	use super::*;

	#[test]
	fn one_consecutive_failure_with_10_backoffs() {
		// 1, 2, 4, 5, 5 .... 5
		let binary_exp_backoff = vec![1_u64, 2, 4].into_iter().chain(iter::repeat(5_u64).take(7));
		let mut guard = RequestGuard::new(1, 10, Duration::from_secs(1), Duration::from_secs(5));
		for backoff in binary_exp_backoff {
			assert_eq!(guard.register_error(), Error::Rejected);
			let now = Instant::now();
			while now.elapsed() <= Duration::from_secs(backoff) {}
		}
		assert_eq!(guard.register_error(), Error::ReachedLimit, "10 backoffs should be error");
	}

	#[test]
	fn five_consecutive_failures_with_3_backoffs() {
		let mut guard = RequestGuard::new(5, 3, Duration::from_secs(1), Duration::from_secs(30));

		// register five errors
		for _ in 0..4 {
			assert_eq!(guard.register_error(), Error::LetThrough);
		}

		let binary_exp_backoff = [1, 2, 4];
		for backoff in &binary_exp_backoff {
			assert_eq!(guard.register_error(), Error::Rejected);
			let now = Instant::now();
			while now.elapsed() <= Duration::from_secs(*backoff) {}
		}

		assert_eq!(guard.register_error(), Error::ReachedLimit, "3 backoffs should be an error");
	}
}