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//! Module exposing APIs based around `BufRead` from stdlib.
use std::io::{BufRead, Error};
/// Provides iteration over bytes of input, split by line.
///
/// Unlike the implementation in the standard library, this requires
/// no allocations and simply references the input lines from the
/// internal buffer. In order to do this safely, we must sacrifice
/// the `Iterator` API, and operate using `while` syntax:
///
/// ```rust
/// use bytelines::*;
/// use std::fs::File;
/// use std::io::BufReader;
///
/// // construct our iterator from our file input
/// let file = File::open("./res/numbers.txt").unwrap();
/// let reader = BufReader::new(file);
/// let mut lines = ByteLines::new(reader);
///
/// // walk our lines using `while` syntax
/// while let Some(line) = lines.next() {
/// // do something with the line, which is Result<&[u8], _>
/// }
/// ```
///
/// For those who prefer the `Iterator` API, this structure implements
/// the `IntoIterator` trait to provide it. This comes at the cost of
/// an allocation of a `Vec` for each line in the `Iterator`. This is
/// negligible in many cases, so often it comes down to which syntax
/// is preferred:
///
/// ```rust
/// use bytelines::*;
/// use std::fs::File;
/// use std::io::BufReader;
///
/// // construct our iterator from our file input
/// let file = File::open("./res/numbers.txt").unwrap();
/// let reader = BufReader::new(file);
/// let mut lines = ByteLines::new(reader);
///
/// // walk our lines using `for` syntax
/// for line in lines.into_iter() {
/// // do something with the line, which is Result<Vec<u8>, _>
/// }
/// ```
pub struct ByteLines<B>
where
B: BufRead,
{
buffer: Vec<u8>,
reader: B,
}
impl<B> ByteLines<B>
where
B: BufRead,
{
/// Constructs a new `ByteLines` from an input `BufRead`.
pub fn new(buf: B) -> Self {
Self {
buffer: Vec::new(),
reader: buf,
}
}
/// Retrieves a reference to the next line of bytes in the reader (if any).
pub fn next(&mut self) -> Option<Result<&[u8], Error>> {
self.buffer.clear();
crate::util::handle_line(
self.reader.read_until(b'\n', &mut self.buffer),
&mut self.buffer,
)
}
}
/// `IntoIterator` conversion for `ByteLines` to provide `Iterator` APIs.
impl<B> IntoIterator for ByteLines<B>
where
B: BufRead,
{
type Item = Result<Vec<u8>, Error>;
type IntoIter = ByteLinesIter<B>;
/// Constructs a `ByteLinesIter` to provide an `Iterator` API.
#[inline]
fn into_iter(self) -> ByteLinesIter<B> {
ByteLinesIter { inner: self }
}
}
/// `Iterator` implementation of `ByteLines` to provide `Iterator` APIs.
///
/// This structure enables developers the use of the `Iterator` API in
/// their code, at the cost of an allocation per input line:
///
/// ```rust
/// use bytelines::*;
/// use std::fs::File;
/// use std::io::BufReader;
///
/// // construct our iterator from our file input
/// let file = File::open("./res/numbers.txt").unwrap();
/// let lines = BufReader::new(file);
/// let lines = bytelines::from_std(lines);
///
/// // walk our lines using `for` syntax
/// for line in lines.into_iter() {
/// // do something with the line, which is Result<Vec<u8>, _>
/// }
/// ```
pub struct ByteLinesIter<B>
where
B: BufRead,
{
inner: ByteLines<B>,
}
impl<B> Iterator for ByteLinesIter<B>
where
B: BufRead,
{
type Item = Result<Vec<u8>, Error>;
/// Retrieves the next line in the iterator (if any).
#[inline]
fn next(&mut self) -> Option<Result<Vec<u8>, Error>> {
self.inner.next().map(|r| r.map(|s| s.to_vec()))
}
}
/// Represents anything which can provide iterators of byte lines.
pub trait ByteLinesReader<B>
where
B: BufRead,
{
/// Returns a structure used to iterate the lines of this reader as `Result<&[u8], _>`.
fn byte_lines(self) -> ByteLines<B>;
}
/// Blanket implementation for all `BufRead`.
impl<B> ByteLinesReader<B> for B
where
B: BufRead,
{
/// Returns a structure used to iterate the lines of this reader as Result<&[u8], _>.
#[inline]
fn byte_lines(self) -> ByteLines<Self> {
super::from_std(self)
}
}
#[cfg(test)]
#[allow(clippy::needless_range_loop)]
mod tests {
use super::*;
use std::fs::File;
use std::io::BufReader;
#[test]
fn test_basic_loop() {
let file = File::open("./res/numbers.txt").unwrap();
let mut brdr = BufReader::new(file).byte_lines();
let mut lines = Vec::new();
while let Some(line) = brdr.next() {
let line = line.unwrap().to_vec();
let line = String::from_utf8(line).unwrap();
lines.push(line);
}
for i in 0..9 {
assert_eq!(lines[i], format!("{}", i));
}
}
#[test]
fn test_basic_iterator() {
let file = File::open("./res/numbers.txt").unwrap();
let mut lines = Vec::new();
for line in BufReader::new(file).byte_lines().into_iter() {
let line = line.unwrap();
let line = String::from_utf8(line).unwrap();
lines.push(line);
}
for i in 0..9 {
assert_eq!(lines[i], format!("{}", i));
}
}
#[test]
fn test_empty_line() {
let file = File::open("./res/empty.txt").unwrap();
let mut lines = Vec::new();
for line in BufReader::new(file).byte_lines().into_iter() {
let line = line.unwrap();
let line = String::from_utf8(line).unwrap();
lines.push(line);
}
assert_eq!(lines.len(), 1);
assert_eq!(lines[0], "");
}
}