sstable 0.11.1

Sorted String Tables, an on-disk format for storing immutable maps consisting of string,string pairs, and retrieving values by key efficiently. This crate also features bloom filters, checksums and skipping bad blocks. It is based on the code implemented for the rusty_leveldb crate.
Documentation 
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use std::cmp::Ordering;

use crate::block::BlockContents;
use crate::options::Options;

use integer_encoding::{FixedIntWriter, VarIntWriter};

/// BlockBuilder contains functionality for building a block consisting of consecutive key-value
/// entries.
pub struct BlockBuilder {
    opt: Options,
    buffer: Vec<u8>,
    restarts: Vec<u32>,

    last_key: Vec<u8>,
    restart_counter: usize,
    counter: usize,
}

impl BlockBuilder {
    pub fn new(o: Options) -> BlockBuilder {
        let mut restarts = vec![0];
        restarts.reserve(1023);

        BlockBuilder {
            buffer: Vec::with_capacity(o.block_size),
            opt: o,
            restarts: restarts,
            last_key: Vec::new(),
            restart_counter: 0,
            counter: 0,
        }
    }

    pub fn entries(&self) -> usize {
        self.counter
    }

    pub fn last_key<'a>(&'a self) -> &'a [u8] {
        &self.last_key
    }

    pub fn size_estimate(&self) -> usize {
        self.buffer.len() + 4 * self.restarts.len() + 4
    }

    pub fn add(&mut self, key: &[u8], val: &[u8]) {
        assert!(self.restart_counter <= self.opt.block_restart_interval);
        assert!(
            self.buffer.is_empty()
                || self.opt.cmp.cmp(self.last_key.as_slice(), key) == Ordering::Less
        );

        let mut shared = 0;

        if self.restart_counter < self.opt.block_restart_interval {
            let smallest = if self.last_key.len() < key.len() {
                self.last_key.len()
            } else {
                key.len()
            };

            while shared < smallest && self.last_key[shared] == key[shared] {
                shared += 1;
            }
        } else {
            self.restarts.push(self.buffer.len() as u32);
            self.last_key.resize(0, 0);
            self.restart_counter = 0;
        }

        let non_shared = key.len() - shared;

        self.buffer
            .write_varint(shared)
            .expect("write to buffer failed");
        self.buffer
            .write_varint(non_shared)
            .expect("write to buffer failed");
        self.buffer
            .write_varint(val.len())
            .expect("write to buffer failed");
        self.buffer.extend_from_slice(&key[shared..]);
        self.buffer.extend_from_slice(val);

        // Update key
        self.last_key.resize(shared, 0);
        self.last_key.extend_from_slice(&key[shared..]);

        self.restart_counter += 1;
        self.counter += 1;
    }

    pub fn finish(mut self) -> BlockContents {
        self.buffer.reserve(self.restarts.len() * 4 + 4);

        // 1. Append RESTARTS
        for r in self.restarts.iter() {
            self.buffer
                .write_fixedint(*r as u32)
                .expect("write to buffer failed");
        }

        // 2. Append N_RESTARTS
        self.buffer
            .write_fixedint(self.restarts.len() as u32)
            .expect("write to buffer failed");

        // done
        self.buffer
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    fn get_data() -> Vec<(&'static [u8], &'static [u8])> {
        vec![
            ("key1".as_bytes(), "value1".as_bytes()),
            (
                "loooooooooooooooooooooooooooooooooongerkey1".as_bytes(),
                "shrtvl1".as_bytes(),
            ),
            ("medium length key 1".as_bytes(), "some value 2".as_bytes()),
            ("prefix_key1".as_bytes(), "value".as_bytes()),
            ("prefix_key2".as_bytes(), "value".as_bytes()),
            ("prefix_key3".as_bytes(), "value".as_bytes()),
        ]
    }

    #[test]
    fn test_block_builder_sanity() {
        let mut o = Options::default();
        o.block_restart_interval = 3;
        let mut builder = BlockBuilder::new(o);
        let d = get_data();

        for &(k, v) in d.iter() {
            builder.add(k, v);
            assert!(builder.restart_counter <= 3);
            assert_eq!(builder.last_key(), k);
        }

        assert_eq!(149, builder.size_estimate());
        assert_eq!(d.len(), builder.entries());

        let block = builder.finish();
        assert_eq!(block.len(), 149);
    }

    #[test]
    #[should_panic]
    fn test_block_builder_panics() {
        let mut d = get_data();
        // Identical key as d[3].
        d[4].0 = b"prefix_key1";

        let mut builder = BlockBuilder::new(Options::default());
        for &(k, v) in d.iter() {
            builder.add(k, v);
            assert_eq!(k, builder.last_key());
        }
    }
    // Additional test coverage is provided by tests in block.rs.
}