audit_trail/readers/
file.rs

1//! Streaming reader for audit log files. Requires the `std` feature.
2
3use std::fs::File;
4use std::io::{self, BufReader, Read};
5use std::path::Path;
6
7use crate::codec;
8use crate::error::{Error, Result};
9use crate::owned::OwnedRecord;
10
11/// Iterator that yields [`OwnedRecord`] values decoded from an audit log
12/// produced by [`crate::FileSink`].
13///
14/// The format header is validated lazily on the first `next()` call. On
15/// header failure the iterator yields `Some(Err(...))` once and then
16/// `None` on every subsequent call.
17pub struct FileReader<R: Read> {
18    reader: R,
19    state: State,
20    /// Reusable frame buffer. Resized as needed; never shrunk.
21    scratch: Vec<u8>,
22}
23
24enum State {
25    /// Header not yet validated.
26    Fresh,
27    /// Header validated successfully — reading records.
28    Reading,
29    /// Iteration is terminated (either by EOF or a previous error).
30    Done,
31}
32
33impl FileReader<BufReader<File>> {
34    /// Open `path` for reading. The header is not validated until the
35    /// first record is requested via `next()`.
36    ///
37    /// # Errors
38    ///
39    /// Surfaces I/O errors from opening the file.
40    pub fn open(path: impl AsRef<Path>) -> io::Result<Self> {
41        let file = File::open(path)?;
42        Ok(Self::new(BufReader::new(file)))
43    }
44}
45
46impl<R: Read> FileReader<R> {
47    /// Wrap an existing reader positioned at the start of an audit log
48    /// (i.e. at the format header).
49    #[inline]
50    pub fn new(reader: R) -> Self {
51        Self {
52            reader,
53            state: State::Fresh,
54            scratch: Vec::with_capacity(256),
55        }
56    }
57
58    /// Consume the iterator and return the underlying reader.
59    #[inline]
60    pub fn into_reader(self) -> R {
61        self.reader
62    }
63
64    fn read_header(&mut self) -> Result<()> {
65        let mut header = [0u8; codec::FILE_HEADER_LEN];
66        match self.reader.read_exact(&mut header) {
67            Ok(()) => codec::verify_file_header(&header),
68            Err(e) if e.kind() == io::ErrorKind::UnexpectedEof => Err(Error::Truncated),
69            Err(_) => Err(Error::Io),
70        }
71    }
72
73    fn read_record(&mut self) -> Option<Result<OwnedRecord>> {
74        let mut len_buf = [0u8; 4];
75        match self.reader.read_exact(&mut len_buf) {
76            Ok(()) => {}
77            Err(e) if e.kind() == io::ErrorKind::UnexpectedEof => return None,
78            Err(_) => return Some(Err(Error::Io)),
79        }
80        let body_len = u32::from_be_bytes(len_buf) as usize;
81        let frame_len = 4 + body_len;
82        self.scratch.clear();
83        self.scratch.resize(frame_len, 0);
84        self.scratch[0..4].copy_from_slice(&len_buf);
85        if let Err(e) = self.reader.read_exact(&mut self.scratch[4..]) {
86            return Some(Err(match e.kind() {
87                io::ErrorKind::UnexpectedEof => Error::Truncated,
88                _ => Error::Io,
89            }));
90        }
91        match codec::decode_record(&self.scratch) {
92            Ok((record, consumed)) if consumed == frame_len => Some(Ok(record)),
93            Ok(_) => Some(Err(Error::InvalidFormat)),
94            Err(e) => Some(Err(e)),
95        }
96    }
97}
98
99impl<R: Read> Iterator for FileReader<R> {
100    type Item = Result<OwnedRecord>;
101
102    fn next(&mut self) -> Option<Self::Item> {
103        loop {
104            match self.state {
105                State::Fresh => match self.read_header() {
106                    Ok(()) => self.state = State::Reading,
107                    Err(e) => {
108                        self.state = State::Done;
109                        return Some(Err(e));
110                    }
111                },
112                State::Reading => match self.read_record() {
113                    None => {
114                        self.state = State::Done;
115                        return None;
116                    }
117                    Some(Err(e)) => {
118                        self.state = State::Done;
119                        return Some(Err(e));
120                    }
121                    Some(Ok(record)) => return Some(Ok(record)),
122                },
123                State::Done => return None,
124            }
125        }
126    }
127}
audit_trail/readers/file.rs

audit_trail/readers/
file.rs
