third_party/raft-rs/src/util.rs

//! This module contains a collection of various tools to use to manipulate
//! and control messages and data associated with raft.

// Copyright 2017 PingCAP, Inc.
//
// 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,
// See the License for the specific language governing permissions and
// limitations under the License.

use std::prelude::v1::*;
use std::u64;

use protobuf::Message;

/// A number to represent that there is no limit.
pub const NO_LIMIT: u64 = u64::MAX;

/// Truncates the list of entries down to a specific byte-length of
/// all entries together.
///
/// # Examples
///
/// ```
/// use raft::{util::limit_size, prelude::*};
///
/// let template = {
///     let mut entry = Entry::new();
///     entry.set_data("*".repeat(100).into_bytes());
///     entry
/// };
///
/// // Make a bunch of entries that are ~100 bytes long
/// let mut entries = vec![
///     template.clone(),
///     template.clone(),
///     template.clone(),
///     template.clone(),
///     template.clone(),
/// ];
///
/// assert_eq!(entries.len(), 5);
/// limit_size(&mut entries, 220);
/// assert_eq!(entries.len(), 2);
/// ```
pub fn limit_size<T: Message + Clone>(entries: &mut Vec<T>, max: u64) {
    if max == NO_LIMIT || entries.len() <= 1 {
        return;
    }

    let mut size = 0;
    let limit = entries
        .iter()
        .take_while(|&e| {
            if size == 0 {
                size += u64::from(Message::compute_size(e));
                true
            } else {
                size += u64::from(Message::compute_size(e));
                size <= max
            }
        }).count();

    entries.truncate(limit);
}