/
read_limiter.rs
120 lines (109 loc) · 4.48 KB
/
read_limiter.rs
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// Copyright (c) 2013-2015 Sandstorm Development Group, Inc. and contributors
// Licensed under the MIT License:
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
#[cfg(feature = "sync_reader")]
pub use sync::ReadLimiter;
#[cfg(feature = "sync_reader")]
mod sync {
use crate::{Error, Result};
use core::sync::atomic::{AtomicUsize, Ordering};
pub struct ReadLimiter {
limit: AtomicUsize,
error_on_limit_exceeded: bool,
}
impl ReadLimiter {
pub fn new(limit: Option<usize>) -> ReadLimiter {
match limit {
Some(value) => {
ReadLimiter {
limit: AtomicUsize::new(value),
error_on_limit_exceeded: true,
}
}
None => {
ReadLimiter {
limit: AtomicUsize::new(usize::MAX),
error_on_limit_exceeded: false,
}
}
}
}
#[inline]
pub fn can_read(&self, amount: usize) -> Result<()> {
// We use separate AtomicUsize::load() and AtomicUsize::store() steps, which may
// result in undercounting reads if multiple threads are reading at the same.
// That's okay -- a denial of service attack will eventually hit the limit anyway.
//
// We could instead do a single fetch_sub() step, but that seems to be slower.
let current = self.limit.load(Ordering::Relaxed);
if amount > current && self.error_on_limit_exceeded {
return Err(Error::failed(format!("read limit exceeded")));
} else {
// The common case is current >= amount. Note that we only branch once in that case.
// If we combined the fields into an Option<AtomicUsize>, we would
// need to branch twice in the common case.
self.limit.store(current.wrapping_sub(amount), Ordering::Relaxed);
}
Ok(())
}
}
}
#[cfg(not(feature = "sync_reader"))]
pub use unsync::ReadLimiter;
#[cfg(not(feature = "sync_reader"))]
mod unsync {
use crate::{Error, Result};
use core::cell::Cell;
pub struct ReadLimiter {
limit: Cell<usize>,
error_on_limit_exceeded: bool,
}
impl ReadLimiter {
pub fn new(limit: Option<usize>) -> ReadLimiter {
match limit {
Some(value) => {
ReadLimiter {
limit: Cell::new(value),
error_on_limit_exceeded: true,
}
}
None => {
ReadLimiter {
limit: Cell::new(usize::MAX),
error_on_limit_exceeded: false,
}
}
}
}
#[inline]
pub fn can_read(&self, amount: usize) -> Result<()> {
let current = self.limit.get();
if amount > current && self.error_on_limit_exceeded {
Err(Error::failed(format!("read limit exceeded")))
} else {
// The common case is current >= amount. Note that we only branch once in that case.
// If we combined the fields into an Option<Cell<usize>>, we would
// need to branch twice in the common case.
self.limit.set(current.wrapping_sub(amount));
Ok(())
}
}
}
}