pub trait BufRead: Read {
// Required methods
fn fill_buf(&mut self) -> Result<&[u8]>;
fn consume(&mut self, amt: usize);
// Provided methods
fn has_data_left(&mut self) -> Result<bool> { ... }
fn read_until(&mut self, byte: u8, buf: &mut Vec<u8>) -> Result<usize> { ... }
fn skip_until(&mut self, byte: u8) -> Result<usize> { ... }
fn read_line(&mut self, buf: &mut String) -> Result<usize> { ... }
fn split(self, byte: u8) -> Split<Self> ⓘ
where Self: Sized { ... }
fn lines(self) -> Lines<Self> ⓘ
where Self: Sized { ... }
}
Expand description
A BufRead
is a type of Read
er which has an internal buffer, allowing it
to perform extra ways of reading.
For example, reading line-by-line is inefficient without using a buffer, so
if you want to read by line, you’ll need BufRead
, which includes a
read_line
method as well as a lines
iterator.
§Examples
A locked standard input implements BufRead
:
use std::io;
use std::io::prelude::*;
let stdin = io::stdin();
for line in stdin.lock().lines() {
println!("{}", line.unwrap());
}
RunIf you have something that implements Read
, you can use the BufReader
type to turn it into a BufRead
.
For example, File
implements Read
, but not BufRead
.
BufReader
to the rescue!
use std::io::{self, BufReader};
use std::io::prelude::*;
use std::fs::File;
fn main() -> io::Result<()> {
let f = File::open("foo.txt")?;
let f = BufReader::new(f);
for line in f.lines() {
println!("{}", line.unwrap());
}
Ok(())
}
RunRequired Methods§
sourcefn fill_buf(&mut self) -> Result<&[u8]>
fn fill_buf(&mut self) -> Result<&[u8]>
Returns the contents of the internal buffer, filling it with more data from the inner reader if it is empty.
This function is a lower-level call. It needs to be paired with the
consume
method to function properly. When calling this
method, none of the contents will be “read” in the sense that later
calling read
may return the same contents. As such, consume
must
be called with the number of bytes that are consumed from this buffer to
ensure that the bytes are never returned twice.
An empty buffer returned indicates that the stream has reached EOF.
§Errors
This function will return an I/O error if the underlying reader was read, but returned an error.
§Examples
A locked standard input implements BufRead
:
use std::io;
use std::io::prelude::*;
let stdin = io::stdin();
let mut stdin = stdin.lock();
let buffer = stdin.fill_buf().unwrap();
// work with buffer
println!("{buffer:?}");
// ensure the bytes we worked with aren't returned again later
let length = buffer.len();
stdin.consume(length);
Runsourcefn consume(&mut self, amt: usize)
fn consume(&mut self, amt: usize)
Tells this buffer that amt
bytes have been consumed from the buffer,
so they should no longer be returned in calls to read
.
This function is a lower-level call. It needs to be paired with the
fill_buf
method to function properly. This function does
not perform any I/O, it simply informs this object that some amount of
its buffer, returned from fill_buf
, has been consumed and should
no longer be returned. As such, this function may do odd things if
fill_buf
isn’t called before calling it.
The amt
must be <=
the number of bytes in the buffer returned by
fill_buf
.
§Examples
Since consume()
is meant to be used with fill_buf
,
that method’s example includes an example of consume()
.
Provided Methods§
sourcefn has_data_left(&mut self) -> Result<bool>
fn has_data_left(&mut self) -> Result<bool>
buf_read_has_data_left
#86423)Check if the underlying Read
has any data left to be read.
This function may fill the buffer to check for data,
so this functions returns Result<bool>
, not bool
.
Default implementation calls fill_buf
and checks that
returned slice is empty (which means that there is no data left,
since EOF is reached).
Examples
#![feature(buf_read_has_data_left)]
use std::io;
use std::io::prelude::*;
let stdin = io::stdin();
let mut stdin = stdin.lock();
while stdin.has_data_left().unwrap() {
let mut line = String::new();
stdin.read_line(&mut line).unwrap();
// work with line
println!("{line:?}");
}
Runsourcefn read_until(&mut self, byte: u8, buf: &mut Vec<u8>) -> Result<usize>
fn read_until(&mut self, byte: u8, buf: &mut Vec<u8>) -> Result<usize>
Read all bytes into buf
until the delimiter byte
or EOF is reached.
This function will read bytes from the underlying stream until the
delimiter or EOF is found. Once found, all bytes up to, and including,
the delimiter (if found) will be appended to buf
.
If successful, this function will return the total number of bytes read.
This function is blocking and should be used carefully: it is possible for an attacker to continuously send bytes without ever sending the delimiter or EOF.
§Errors
This function will ignore all instances of ErrorKind::Interrupted
and
will otherwise return any errors returned by fill_buf
.
If an I/O error is encountered then all bytes read so far will be
present in buf
and its length will have been adjusted appropriately.
§Examples
std::io::Cursor
is a type that implements BufRead
. In
this example, we use Cursor
to read all the bytes in a byte slice
in hyphen delimited segments:
use std::io::{self, BufRead};
let mut cursor = io::Cursor::new(b"lorem-ipsum");
let mut buf = vec![];
// cursor is at 'l'
let num_bytes = cursor.read_until(b'-', &mut buf)
.expect("reading from cursor won't fail");
assert_eq!(num_bytes, 6);
assert_eq!(buf, b"lorem-");
buf.clear();
// cursor is at 'i'
let num_bytes = cursor.read_until(b'-', &mut buf)
.expect("reading from cursor won't fail");
assert_eq!(num_bytes, 5);
assert_eq!(buf, b"ipsum");
buf.clear();
// cursor is at EOF
let num_bytes = cursor.read_until(b'-', &mut buf)
.expect("reading from cursor won't fail");
assert_eq!(num_bytes, 0);
assert_eq!(buf, b"");
Runsourcefn skip_until(&mut self, byte: u8) -> Result<usize>
fn skip_until(&mut self, byte: u8) -> Result<usize>
bufread_skip_until
#111735)Skip all bytes until the delimiter byte
or EOF is reached.
This function will read (and discard) bytes from the underlying stream until the delimiter or EOF is found.
If successful, this function will return the total number of bytes read, including the delimiter byte.
This is useful for efficiently skipping data such as NUL-terminated strings in binary file formats without buffering.
This function is blocking and should be used carefully: it is possible for an attacker to continuously send bytes without ever sending the delimiter or EOF.
§Errors
This function will ignore all instances of ErrorKind::Interrupted
and
will otherwise return any errors returned by fill_buf
.
If an I/O error is encountered then all bytes read so far will be
present in buf
and its length will have been adjusted appropriately.
§Examples
std::io::Cursor
is a type that implements BufRead
. In
this example, we use Cursor
to read some NUL-terminated information
about Ferris from a binary string, skipping the fun fact:
#![feature(bufread_skip_until)]
use std::io::{self, BufRead};
let mut cursor = io::Cursor::new(b"Ferris\0Likes long walks on the beach\0Crustacean\0");
// read name
let mut name = Vec::new();
let num_bytes = cursor.read_until(b'\0', &mut name)
.expect("reading from cursor won't fail");
assert_eq!(num_bytes, 7);
assert_eq!(name, b"Ferris\0");
// skip fun fact
let num_bytes = cursor.skip_until(b'\0')
.expect("reading from cursor won't fail");
assert_eq!(num_bytes, 30);
// read animal type
let mut animal = Vec::new();
let num_bytes = cursor.read_until(b'\0', &mut animal)
.expect("reading from cursor won't fail");
assert_eq!(num_bytes, 11);
assert_eq!(animal, b"Crustacean\0");
Runsourcefn read_line(&mut self, buf: &mut String) -> Result<usize>
fn read_line(&mut self, buf: &mut String) -> Result<usize>
Read all bytes until a newline (the 0xA
byte) is reached, and append
them to the provided String
buffer.
Previous content of the buffer will be preserved. To avoid appending to
the buffer, you need to clear
it first.
This function will read bytes from the underlying stream until the
newline delimiter (the 0xA
byte) or EOF is found. Once found, all bytes
up to, and including, the delimiter (if found) will be appended to
buf
.
If successful, this function will return the total number of bytes read.
If this function returns Ok(0)
, the stream has reached EOF.
This function is blocking and should be used carefully: it is possible for
an attacker to continuously send bytes without ever sending a newline
or EOF. You can use take
to limit the maximum number of bytes read.
§Errors
This function has the same error semantics as read_until
and will
also return an error if the read bytes are not valid UTF-8. If an I/O
error is encountered then buf
may contain some bytes already read in
the event that all data read so far was valid UTF-8.
§Examples
std::io::Cursor
is a type that implements BufRead
. In
this example, we use Cursor
to read all the lines in a byte slice:
use std::io::{self, BufRead};
let mut cursor = io::Cursor::new(b"foo\nbar");
let mut buf = String::new();
// cursor is at 'f'
let num_bytes = cursor.read_line(&mut buf)
.expect("reading from cursor won't fail");
assert_eq!(num_bytes, 4);
assert_eq!(buf, "foo\n");
buf.clear();
// cursor is at 'b'
let num_bytes = cursor.read_line(&mut buf)
.expect("reading from cursor won't fail");
assert_eq!(num_bytes, 3);
assert_eq!(buf, "bar");
buf.clear();
// cursor is at EOF
let num_bytes = cursor.read_line(&mut buf)
.expect("reading from cursor won't fail");
assert_eq!(num_bytes, 0);
assert_eq!(buf, "");
Runsourcefn split(self, byte: u8) -> Split<Self> ⓘwhere
Self: Sized,
fn split(self, byte: u8) -> Split<Self> ⓘwhere
Self: Sized,
Returns an iterator over the contents of this reader split on the byte
byte
.
The iterator returned from this function will return instances of
io::Result<Vec<u8>>
. Each vector returned will not have
the delimiter byte at the end.
This function will yield errors whenever read_until
would have
also yielded an error.
§Examples
std::io::Cursor
is a type that implements BufRead
. In
this example, we use Cursor
to iterate over all hyphen delimited
segments in a byte slice
use std::io::{self, BufRead};
let cursor = io::Cursor::new(b"lorem-ipsum-dolor");
let mut split_iter = cursor.split(b'-').map(|l| l.unwrap());
assert_eq!(split_iter.next(), Some(b"lorem".to_vec()));
assert_eq!(split_iter.next(), Some(b"ipsum".to_vec()));
assert_eq!(split_iter.next(), Some(b"dolor".to_vec()));
assert_eq!(split_iter.next(), None);
Runsourcefn lines(self) -> Lines<Self> ⓘwhere
Self: Sized,
fn lines(self) -> Lines<Self> ⓘwhere
Self: Sized,
Returns an iterator over the lines of this reader.
The iterator returned from this function will yield instances of
io::Result<String>
. Each string returned will not have a newline
byte (the 0xA
byte) or CRLF
(0xD
, 0xA
bytes) at the end.
§Examples
std::io::Cursor
is a type that implements BufRead
. In
this example, we use Cursor
to iterate over all the lines in a byte
slice.
use std::io::{self, BufRead};
let cursor = io::Cursor::new(b"lorem\nipsum\r\ndolor");
let mut lines_iter = cursor.lines().map(|l| l.unwrap());
assert_eq!(lines_iter.next(), Some(String::from("lorem")));
assert_eq!(lines_iter.next(), Some(String::from("ipsum")));
assert_eq!(lines_iter.next(), Some(String::from("dolor")));
assert_eq!(lines_iter.next(), None);
Run§Errors
Each line of the iterator has the same error semantics as BufRead::read_line
.
Implementors§
impl BufRead for &[u8]
impl BufRead for Empty
impl BufRead for StdinLock<'_>
impl<A: Allocator> BufRead for VecDeque<u8, A>
BufRead is implemented for VecDeque<u8>
by reading bytes from the front of the VecDeque
.