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//! This module contains the `ByteIterator` struct, which is used to iterate
//! over the bytes of a file. This allows us to read a file byte by byte,
//! instead of reading the entire file into memory at once.
use std::{
fs::File,
io::{self, BufReader, Read},
};
/// Verifies that the first character of the file is a '['.
///
/// # Arguments
///
/// * `first_char` - The first character of the file.
///
/// # Panics
///
/// * If the first character of the file is not a '['.
///
/// # Examples
///
/// ```
/// use jsonl_converter::reader::verify_first_char;
///
/// let first_char = '[';
/// verify_first_char(&first_char);
/// ```
pub fn verify_first_char(first_char: &char) {
if first_char != &'[' {
panic!(
"The first character of the file must be a '[', not a '{}'.",
first_char
);
}
}
/// This struct is used to iterate over the bytes of a file.
///
///
/// # Fields
///
/// * `reader` - A `BufReader` that reads the file.
pub struct ByteIterator {
reader: BufReader<File>,
}
impl ByteIterator {
/// Creates a new `ByteIterator` from a file.
///
/// # Arguments
///
/// * `filename` - The name of the file.
///
/// # Errors
///
/// * If the file cannot be opened.
pub fn new(filename: &str) -> io::Result<Self> {
let file = File::open(filename)?;
let reader = BufReader::new(file);
Ok(Self { reader })
}
/// Returns the next character of the file.
pub fn next_char(&mut self) -> Option<char> {
self.next().unwrap().unwrap().chars().next()
}
}
impl Iterator for ByteIterator {
type Item = io::Result<String>;
/// Returns the next byte of the file.
fn next(&mut self) -> Option<Self::Item> {
let mut buffer = [0; 1];
match self.reader.read_exact(&mut buffer) {
Ok(_) => Some(Ok(String::from_utf8_lossy(&buffer).into_owned())),
Err(error) if error.kind() == io::ErrorKind::UnexpectedEof => None,
Err(error) => Some(Err(error)),
}
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_bytes_iterator_new_instance_accepts_valid_filename() {
let bytes_iter = ByteIterator::new("src/reader.rs");
assert!(bytes_iter.is_ok());
}
#[test]
#[should_panic]
fn test_bytes_iterator_new_instance_panics_on_invalid_filename() {
let bytes_iter = ByteIterator::new("bad_filename");
assert!(bytes_iter.is_ok());
}
#[test]
fn test_can_iterate_over_bytes() {
let bytes_iter = ByteIterator::new("src/reader.rs").unwrap();
let mut bytes = String::new();
for byte in bytes_iter {
bytes.push_str(&byte.unwrap());
}
assert_eq!(bytes, include_str!("reader.rs"));
}
#[test]
fn test_verify_first_char_passes() {
verify_first_char(&'[');
}
#[test]
#[should_panic]
fn test_verify_first_char_panics_on_invalid_first_char() {
verify_first_char(&'a');
}
}