sqlrite/sql/pager/
header.rs

1//! Database file header (page 0).
2//!
3//! The first 28 bytes of every `.sqlrite` file identify the format and point
4//! at the schema catalog. The rest of page 0 is reserved for future use.
5
6use crate::error::{Result, SQLRiteError};
7use crate::sql::pager::page::PAGE_SIZE;
8
9/// File magic. Distinct from SQLite's `"SQLite format 3\0"` so the formats
10/// can't be confused on inspection.
11pub const MAGIC: &[u8; 16] = b"SQLRiteFormat\0\0\0";
12
13/// On-disk format revision. Bump when the page layout changes incompatibly.
14///
15/// History:
16/// - Version 1 (Phases 2 / 3a / 3b): schema catalog and table data were
17///   opaque bincode blobs chained across typed payload pages.
18/// - Version 2 (Phases 3c / 3d): tables are stored as cell-based B-Trees;
19///   the schema catalog is itself a table called `sqlrite_master` with
20///   four columns `(name, sql, rootpage, last_rowid)`.
21/// - Version 3 (Phase 3e): `sqlrite_master` gains a `type` column
22///   (first), distinguishing `'table'` and `'index'` rows; secondary
23///   indexes persist as their own cell-based B-Trees whose cells use
24///   the new `KIND_INDEX` format.
25pub const FORMAT_VERSION: u16 = 3;
26
27/// Parsed header. `page_count` includes page 0 itself.
28#[derive(Debug, Clone, Copy, PartialEq, Eq)]
29pub struct DbHeader {
30    pub page_count: u32,
31    pub schema_root_page: u32,
32}
33
34/// Encodes the header into a `PAGE_SIZE`-sized buffer.
35pub fn encode_header(h: &DbHeader) -> [u8; PAGE_SIZE] {
36    let mut buf = [0u8; PAGE_SIZE];
37    buf[0..16].copy_from_slice(MAGIC);
38    buf[16..18].copy_from_slice(&FORMAT_VERSION.to_le_bytes());
39    buf[18..20].copy_from_slice(&(PAGE_SIZE as u16).to_le_bytes());
40    buf[20..24].copy_from_slice(&h.page_count.to_le_bytes());
41    buf[24..28].copy_from_slice(&h.schema_root_page.to_le_bytes());
42    buf
43}
44
45/// Decodes the header from a `PAGE_SIZE`-sized buffer. Returns an error if
46/// magic bytes, format version, or page size don't match what we wrote.
47pub fn decode_header(buf: &[u8]) -> Result<DbHeader> {
48    if buf.len() != PAGE_SIZE {
49        return Err(SQLRiteError::Internal(format!(
50            "header buffer length {} != PAGE_SIZE {PAGE_SIZE}",
51            buf.len()
52        )));
53    }
54    if &buf[0..16] != MAGIC {
55        return Err(SQLRiteError::General(
56            "file is not a SQLRite database (bad magic bytes)".to_string(),
57        ));
58    }
59    let version = u16::from_le_bytes(buf[16..18].try_into().unwrap());
60    if version != FORMAT_VERSION {
61        return Err(SQLRiteError::General(format!(
62            "unsupported SQLRite format version {version}; this build understands {FORMAT_VERSION}"
63        )));
64    }
65    let page_size = u16::from_le_bytes(buf[18..20].try_into().unwrap()) as usize;
66    if page_size != PAGE_SIZE {
67        return Err(SQLRiteError::General(format!(
68            "unsupported page size {page_size}; this build expects {PAGE_SIZE}"
69        )));
70    }
71    let page_count = u32::from_le_bytes(buf[20..24].try_into().unwrap());
72    let schema_root_page = u32::from_le_bytes(buf[24..28].try_into().unwrap());
73    Ok(DbHeader {
74        page_count,
75        schema_root_page,
76    })
77}
sqlrite/sql/pager/header.rs

sqlrite/sql/pager/
header.rs
