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//! Helper module to compute a CRC32 checksum
use std::io;
use std::io::prelude::*;
use crc32fast::Hasher;
/// Reader that validates the CRC32 when it reaches the EOF.
pub struct Crc32Reader<R> {
inner: R,
hasher: Hasher,
check: u32,
/// Signals if `inner` stores aes encrypted data.
/// AE-2 encrypted data doesn't use crc and sets the value to 0.
ae2_encrypted: bool,
}
impl<R> Crc32Reader<R> {
/// Get a new Crc32Reader which checks the inner reader against checksum.
/// The check is disabled if `ae2_encrypted == true`.
pub(crate) fn new(inner: R, checksum: u32, ae2_encrypted: bool) -> Crc32Reader<R> {
Crc32Reader {
inner,
hasher: Hasher::new(),
check: checksum,
ae2_encrypted,
}
}
fn check_matches(&self) -> bool {
self.check == self.hasher.clone().finalize()
}
pub fn into_inner(self) -> R {
self.inner
}
}
impl<R: Read> Read for Crc32Reader<R> {
fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
let invalid_check = !buf.is_empty() && !self.check_matches() && !self.ae2_encrypted;
let count = match self.inner.read(buf) {
Ok(0) if invalid_check => {
return Err(io::Error::new(io::ErrorKind::Other, "Invalid checksum"))
}
Ok(n) => n,
Err(e) => return Err(e),
};
self.hasher.update(&buf[0..count]);
Ok(count)
}
}
#[cfg(test)]
mod test {
use super::*;
#[test]
fn test_empty_reader() {
let data: &[u8] = b"";
let mut buf = [0; 1];
let mut reader = Crc32Reader::new(data, 0, false);
assert_eq!(reader.read(&mut buf).unwrap(), 0);
let mut reader = Crc32Reader::new(data, 1, false);
assert!(reader
.read(&mut buf)
.unwrap_err()
.to_string()
.contains("Invalid checksum"));
}
#[test]
fn test_byte_by_byte() {
let data: &[u8] = b"1234";
let mut buf = [0; 1];
let mut reader = Crc32Reader::new(data, 0x9be3e0a3, false);
assert_eq!(reader.read(&mut buf).unwrap(), 1);
assert_eq!(reader.read(&mut buf).unwrap(), 1);
assert_eq!(reader.read(&mut buf).unwrap(), 1);
assert_eq!(reader.read(&mut buf).unwrap(), 1);
assert_eq!(reader.read(&mut buf).unwrap(), 0);
// Can keep reading 0 bytes after the end
assert_eq!(reader.read(&mut buf).unwrap(), 0);
}
#[test]
fn test_zero_read() {
let data: &[u8] = b"1234";
let mut buf = [0; 5];
let mut reader = Crc32Reader::new(data, 0x9be3e0a3, false);
assert_eq!(reader.read(&mut buf[..0]).unwrap(), 0);
assert_eq!(reader.read(&mut buf).unwrap(), 4);
}
}