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.
25/// - Version 4 (Phase 7): cell encoding gains the `KIND_VECTOR` value
26///   tag (length-prefixed dense f32 array) for the new `VECTOR(N)`
27///   column type, plus the `KIND_HNSW` cell tag for vector ANN
28///   indexes. All Phase 7 storage additions (VECTOR cells, JSON cells,
29///   HNSW index nodes) live inside the v4 envelope.
30/// - Version 5 (Phase 8c): adds the `KIND_FTS_POSTING` cell tag for
31///   persisted FTS posting lists. Bumped **on demand** — a database
32///   without any FTS index keeps writing v4. The first save with at
33///   least one FTS index attached writes v5 instead. Decoders accept
34///   both v4 and v5; v5 reading a v4-shaped DB just sees zero FTS
35///   indexes in `sqlrite_master`. See [Phase 8 plan Q10].
36pub const FORMAT_VERSION_V4: u16 = 4;
37pub const FORMAT_VERSION_V5: u16 = 5;
38/// The version a brand-new write defaults to when no FTS index forces
39/// a bump. Existing databases keep their on-disk version unchanged
40/// across reads + non-FTS writes; FTS-bearing saves switch to V5.
41pub const FORMAT_VERSION_BASELINE: u16 = FORMAT_VERSION_V4;
42
43/// Parsed header. `page_count` includes page 0 itself.
44#[derive(Debug, Clone, Copy, PartialEq, Eq)]
45pub struct DbHeader {
46    pub page_count: u32,
47    pub schema_root_page: u32,
48    /// On-disk format version this header carries. Tracked explicitly
49    /// so save can preserve a v4 file as v4 (no FTS) or bump it to v5
50    /// (FTS present), per Phase 8c's on-demand bump strategy.
51    pub format_version: u16,
52}
53
54/// Encodes the header into a `PAGE_SIZE`-sized buffer.
55pub fn encode_header(h: &DbHeader) -> [u8; PAGE_SIZE] {
56    let mut buf = [0u8; PAGE_SIZE];
57    buf[0..16].copy_from_slice(MAGIC);
58    buf[16..18].copy_from_slice(&h.format_version.to_le_bytes());
59    buf[18..20].copy_from_slice(&(PAGE_SIZE as u16).to_le_bytes());
60    buf[20..24].copy_from_slice(&h.page_count.to_le_bytes());
61    buf[24..28].copy_from_slice(&h.schema_root_page.to_le_bytes());
62    buf
63}
64
65/// Decodes the header from a `PAGE_SIZE`-sized buffer. Returns an error if
66/// magic bytes, format version, or page size don't match what we wrote.
67/// Both V4 and V5 are accepted; the result's `format_version` echoes
68/// what was on disk so a no-op resave preserves it.
69pub fn decode_header(buf: &[u8]) -> Result<DbHeader> {
70    if buf.len() != PAGE_SIZE {
71        return Err(SQLRiteError::Internal(format!(
72            "header buffer length {} != PAGE_SIZE {PAGE_SIZE}",
73            buf.len()
74        )));
75    }
76    if &buf[0..16] != MAGIC {
77        return Err(SQLRiteError::General(
78            "file is not a SQLRite database (bad magic bytes)".to_string(),
79        ));
80    }
81    let version = u16::from_le_bytes(buf[16..18].try_into().unwrap());
82    if version != FORMAT_VERSION_V4 && version != FORMAT_VERSION_V5 {
83        return Err(SQLRiteError::General(format!(
84            "unsupported SQLRite format version {version}; this build understands \
85             {FORMAT_VERSION_V4} and {FORMAT_VERSION_V5}"
86        )));
87    }
88    let page_size = u16::from_le_bytes(buf[18..20].try_into().unwrap()) as usize;
89    if page_size != PAGE_SIZE {
90        return Err(SQLRiteError::General(format!(
91            "unsupported page size {page_size}; this build expects {PAGE_SIZE}"
92        )));
93    }
94    let page_count = u32::from_le_bytes(buf[20..24].try_into().unwrap());
95    let schema_root_page = u32::from_le_bytes(buf[24..28].try_into().unwrap());
96    Ok(DbHeader {
97        page_count,
98        schema_root_page,
99        format_version: version,
100    })
101}
sqlrite/sql/pager/header.rs

sqlrite/sql/pager/
header.rs
