66 lines
2.1 KiB
Rust
66 lines
2.1 KiB
Rust
use anyhow::{bail, Result};
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use std::convert::TryInto;
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#[derive(Debug, Eq, PartialEq)]
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pub enum BTreePage {
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InteriorIndex = 2,
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InteriorTable = 5,
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LeafIndex = 10,
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LeafTable = 13,
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}
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#[derive(Debug)]
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pub struct PageHeader {
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pub page_type: BTreePage,
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pub first_free_block_start: u16,
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pub number_of_cells: u16,
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pub start_of_content_area: u16,
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pub fragmented_free_bytes: u8,
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pub right_most_pointer: Option<u32>,
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}
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impl PageHeader {
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/// Parses a page header stream into a page header
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pub fn parse(stream: &[u8]) -> Result<(usize, Self)> {
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let page_type = match stream[0] {
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2 => BTreePage::InteriorIndex,
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5 => BTreePage::InteriorTable,
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10 => BTreePage::LeafIndex,
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13 => BTreePage::LeafTable,
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x => bail!("Invalid page value encountered: {}", x),
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};
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let first_free_block_start = u16::from_be_bytes(stream[1..3].try_into()?);
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let number_of_cells = u16::from_be_bytes(stream[3..5].try_into()?);
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let start_of_content_area = u16::from_be_bytes(stream[5..7].try_into()?);
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let fragmented_free_bytes = stream[7];
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match page_type {
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BTreePage::InteriorIndex | BTreePage::InteriorTable => Ok((
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12,
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PageHeader {
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page_type,
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first_free_block_start,
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number_of_cells,
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start_of_content_area,
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fragmented_free_bytes,
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right_most_pointer: Some(u32::from_be_bytes([
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stream[8], stream[9], stream[10], stream[11],
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])),
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},
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)),
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BTreePage::LeafIndex | BTreePage::LeafTable => Ok((
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8,
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PageHeader {
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page_type,
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first_free_block_start,
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number_of_cells,
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start_of_content_area,
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fragmented_free_bytes,
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right_most_pointer: None,
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},
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)),
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}
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}
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}
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