1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46

use super::ParseBytes;
use crate::result::SQLiteResult;
use core::ops::Deref;

/// # File change counter (4 Bytes)
///  The file change counter is a 4-byte big-endian integer at offset 24 that is
/// incremented whenever the database file is unlocked after having been
/// modified. When two or more processes are reading the same database file,
/// each process can detect database changes from other processes by monitoring
/// the change counter. A process will normally want to flush its database page
/// cache when another process modified the database, since the cache has become
/// stale. The file change counter facilitates this.
///
/// In WAL mode, changes to the database are detected using the wal-index and so
/// the change counter is not needed. Hence, the change counter might not be
/// incremented on each transaction in WAL mode.
#[derive(Debug)]
pub struct FileChangeCounter(u32);
impl FileChangeCounter {
  pub fn get(&self) -> u32 {
    self.0
  }
}
impl Deref for FileChangeCounter {
  type Target = u32;

  fn deref(&self) -> &Self::Target {
    &self.0
  }
}

impl ParseBytes<&[u8]> for FileChangeCounter {
  fn bytes_length() -> usize {
    4
  }

  fn struct_name() -> &'static str {
    "FileChangeCounter"
  }

  fn parsing_handler(bytes: &[u8]) -> SQLiteResult<Self> {
    let buf: [u8; 4] = bytes.try_into()?;

    Ok(Self(u32::from_be_bytes(buf)))
  }
}