Struct Page 

pub struct Page { /* private fields */ }

A single fixed-size page: a header and a payload in one aligned buffer.

A Page owns a buffer aligned for Direct I/O, so it can be read into and written from a PageFile without an intermediate copy. Build one with Page::new (an empty page) or get one back from PageFile::read_page / PageFile::allocate_page.

The checksum is not maintained on every mutation — it would be wasted work to rechecksum after each set_lsn or payload write. Instead the page is checksummed once, when it is written (PageFile::write_page stamps it), or on demand via Page::from_bytes, which verifies as it loads.

Examples

use page_db::{Page, PageSize, Lsn};

let mut page = Page::new(PageSize::new(4096)?);
page.set_lsn(Lsn::new(42));
page.payload_mut()[..3].copy_from_slice(b"abc");

// Serialize to a checksummed byte block and load it back, verified.
let bytes = page.to_checksummed_bytes();
let loaded = Page::from_bytes(PageSize::new(4096)?, &bytes)?;
assert_eq!(loaded.lsn(), Lsn::new(42));
assert_eq!(&loaded.payload()[..3], b"abc");

Implementations

impl Page

pub fn new(page_size: PageSize) -> Self

Create an empty, zeroed page of the given size with a valid header.

pub fn from_bytes(page_size: PageSize, bytes: &[u8]) -> PageResult<Self>

Load a page from a byte block, verifying its header and checksum.

The block must be exactly page_size bytes. This is the inverse of Page::to_checksummed_bytes and the same validation PageFile::read_page performs after a read.

Errors

• PageError::ShortRead if bytes.len() is not page_size.
• PageError::BadMagic / PageError::UnsupportedVersion if the header is not a page-db page this build understands.
• PageError::ChecksumMismatch if the checksum does not match.

pub fn page_size(&self) -> usize

The page size in bytes.

pub fn id(&self) -> PageId

The id stamped in the header. For a page from Page::new this is 0 until the page is written to a slot.

pub fn lsn(&self) -> Lsn

The log sequence number stamped in the header.

pub fn set_lsn(&mut self, lsn: Lsn)

Set the log sequence number. Takes effect in the checksum the next time the page is stamped (on PageFile::write_page).

pub fn payload(&self) -> &[u8]

The payload — the page bytes after the header.

pub fn payload_mut(&mut self) -> &mut [u8]

The payload, mutably.

pub fn to_checksummed_bytes(&self) -> Vec<u8>

The whole page as a checksummed byte block, ready to persist elsewhere.

The returned vector is page_size bytes with a freshly computed checksum in the header; feed it back through Page::from_bytes to recover and verify the page. The stamped id is left untouched (0 unless the page came from a file).

Trait Implementations

impl Clone for Page

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Page

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.