jammdb 0.11.0

An embedded single-file database for Rust
Documentation 
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use std::hash::Hasher;

use fnv::FnvHasher;

use crate::{bucket::BucketMeta, page::PageID};

#[repr(C)]
#[derive(Debug, Clone)]
pub(crate) struct Meta {
    pub(crate) meta_page: u32,
    pub(crate) magic: u32,
    pub(crate) version: u32,
    pub(crate) pagesize: u64,
    pub(crate) root: BucketMeta,
    pub(crate) num_pages: PageID,
    pub(crate) freelist_page: PageID,
    pub(crate) tx_id: u64,
    pub(crate) hash: u64,
}

impl Meta {
    pub(crate) fn valid(&self) -> bool {
        self.hash == self.hash_self()
    }

    pub(crate) fn hash_self(&self) -> u64 {
        let mut hasher = FnvHasher::default();

        hasher.write(&self.meta_page.to_be_bytes());
        hasher.write(&self.magic.to_be_bytes());
        hasher.write(&self.version.to_be_bytes());
        hasher.write(&self.pagesize.to_be_bytes());
        hasher.write(&self.root.root_page.to_be_bytes());
        hasher.write(&self.root.next_int.to_be_bytes());
        hasher.write(&self.num_pages.to_be_bytes());
        hasher.write(&self.freelist_page.to_be_bytes());
        hasher.write(&self.tx_id.to_be_bytes());

        hasher.finish()
    }
}

// OldMeta is the metadata format for versions <= 0.10
// For now we check all databases for either metadata version,
// but always write the new format.
use std::io::Write;

use bytes::BufMut;
use sha3::{Digest, Sha3_256};

#[repr(C)]
#[derive(Debug, Clone)]
pub(crate) struct OldMeta {
    pub(crate) meta_page: u32,
    pub(crate) magic: u32,
    pub(crate) version: u32,
    pub(crate) pagesize: u64,
    pub(crate) root: BucketMeta,
    pub(crate) num_pages: PageID,
    pub(crate) freelist_page: PageID,
    pub(crate) tx_id: u64,
    pub(crate) hash: [u8; 32],
}

impl OldMeta {
    pub(crate) fn valid(&self) -> bool {
        self.hash == self.hash_self()
    }

    pub(crate) fn hash_self(&self) -> [u8; 32] {
        let mut hash_result: [u8; 32] = [0; 32];
        let mut hasher = Sha3_256::new();
        hasher.update(self.bytes());
        let hash = hasher.finalize();
        assert_eq!(hash.len(), 32);
        hash_result.copy_from_slice(&hash[..]);
        hash_result
    }

    fn bytes(&self) -> bytes::Bytes {
        let buf = bytes::BytesMut::new();
        let mut w = buf.writer();
        let _ = w.write(&self.meta_page.to_be_bytes());
        let _ = w.write(&self.magic.to_be_bytes());
        let _ = w.write(&self.version.to_be_bytes());
        let _ = w.write(&self.pagesize.to_be_bytes());
        let _ = w.write(&self.root.root_page.to_be_bytes());
        let _ = w.write(&self.root.next_int.to_be_bytes());
        let _ = w.write(&self.num_pages.to_be_bytes());
        let _ = w.write(&self.freelist_page.to_be_bytes());
        let _ = w.write(&self.tx_id.to_be_bytes());

        w.into_inner().freeze()
    }
}

impl From<&OldMeta> for Meta {
    fn from(val: &OldMeta) -> Self {
        let mut m = Meta {
            meta_page: val.meta_page,
            magic: val.magic,
            version: val.version,
            pagesize: val.pagesize,
            root: val.root,
            num_pages: val.num_pages,
            freelist_page: val.freelist_page,
            tx_id: val.tx_id,
            hash: 0,
        };

        m.hash = m.hash_self();
        m
    }
}

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

    #[test]
    fn test_meta() {
        let mut meta = Meta {
            meta_page: 1,
            magic: 1_234_567_890,
            version: 987_654_321,
            pagesize: 4096,
            root: BucketMeta {
                root_page: 2,
                next_int: 2020,
            },
            num_pages: 13,
            freelist_page: 3,
            tx_id: 8,
            hash: 64,
        };

        assert!(!meta.valid());
        meta.hash = meta.hash_self();
        assert_eq!(meta.hash, meta.hash_self());

        meta.tx_id = 88;
        assert_ne!(meta.hash, meta.hash_self());

        meta.hash = meta.hash_self();
        assert_eq!(meta.hash, meta.hash_self());
    }

    #[test]
    fn test_old_meta() {
        let mut meta = OldMeta {
            meta_page: 1,
            magic: 1_234_567_890,
            version: 987_654_321,
            pagesize: 4096,
            root: BucketMeta {
                root_page: 2,
                next_int: 2020,
            },
            num_pages: 13,
            freelist_page: 3,
            tx_id: 8,
            hash: [255; 32],
        };

        assert!(!meta.valid());
        meta.hash = meta.hash_self();
        assert_eq!(meta.hash, meta.hash_self());

        meta.tx_id = 88;
        assert_ne!(meta.hash, meta.hash_self());

        meta.hash = meta.hash_self();
        assert_eq!(meta.hash, meta.hash_self());
    }
}