Trait tokio::io::AsyncBufReadExt [−][src]
pub trait AsyncBufReadExt: AsyncBufRead {
fn read_until<'a>(
&'a mut self,
byte: u8,
buf: &'a mut Vec<u8>
) -> ReadUntil<'a, Self>
where
Self: Unpin,
{ ... }
fn read_line<'a>(&'a mut self, buf: &'a mut String) -> ReadLine<'a, Self>
where
Self: Unpin,
{ ... }
fn split(self, byte: u8) -> Split<Self>
where
Self: Sized + Unpin,
{ ... }
fn fill_buf(&mut self) -> FillBuf<'_, Self>
where
Self: Unpin,
{ ... }
fn consume(&mut self, amt: usize)
where
Self: Unpin,
{ ... }
fn lines(self) -> Lines<Self>
where
Self: Sized,
{ ... }
}Expand description
An extension trait which adds utility methods to AsyncBufRead types.
Provided methods
Reads all bytes into buf until the delimiter byte or EOF is reached.
Equivalent to:
async fn read_until(&mut self, byte: u8, buf: &mut Vec<u8>) -> io::Result<usize>;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.
If this function returns Ok(0), the stream has reached 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.
Cancel safety
If the method is used as the event in a
tokio::select! statement and some other branch
completes first, then some data may have been partially read. Any
partially read bytes are appended to buf, and the method can be
called again to continue reading until byte.
This method returns the total number of bytes read. If you cancel
the call to read_until and then call it again to continue reading,
the counter is reset.
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 tokio::io::AsyncBufReadExt;
use std::io::Cursor;
#[tokio::main]
async fn main() {
let mut cursor = Cursor::new(b"lorem-ipsum");
let mut buf = vec![];
// cursor is at 'l'
let num_bytes = cursor.read_until(b'-', &mut buf)
.await
.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)
.await
.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)
.await
.expect("reading from cursor won't fail");
assert_eq!(num_bytes, 0);
assert_eq!(buf, b"");
}Reads all bytes until a newline (the 0xA byte) is reached, and append them to the provided buffer.
Equivalent to:
async fn read_line(&mut self, buf: &mut String) -> io::Result<usize>;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.
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.
Cancel safety
This method is not cancellation safe. If the method is used as the
event in a tokio::select! statement and some
other branch completes first, then some data may have been partially
read, and this data is lost. There are no guarantees regarding the
contents of buf when the call is cancelled. The current
implementation replaces buf with the empty string, but this may
change in the future.
This function does not behave like read_until because of the
requirement that a string contains only valid utf-8. If you need a
cancellation safe read_line, there are three options:
- Call
read_untilwith a newline character and manually perform the utf-8 check. - The stream returned by
lineshas a cancellation safenext_linemethod. - Use
tokio_util::codec::LinesCodec.
Examples
std::io::Cursor is a type that implements
AsyncBufRead. In this example, we use Cursor to read all the
lines in a byte slice:
use tokio::io::AsyncBufReadExt;
use std::io::Cursor;
#[tokio::main]
async fn main() {
let mut cursor = Cursor::new(b"foo\nbar");
let mut buf = String::new();
// cursor is at 'f'
let num_bytes = cursor.read_line(&mut buf)
.await
.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)
.await
.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)
.await
.expect("reading from cursor won't fail");
assert_eq!(num_bytes, 0);
assert_eq!(buf, "");
}Returns a stream of the contents of this reader split on the byte
byte.
This method is the asynchronous equivalent to
BufRead::split.
The stream returned from this function will yield instances of
io::Result<Option<Vec<u8>>>. Each vector returned will not have
the delimiter byte at the end.
Errors
Each item of the stream has the same error semantics as
AsyncBufReadExt::read_until.
Examples
use tokio::io::AsyncBufReadExt;
let mut segments = my_buf_read.split(b'f');
while let Some(segment) = segments.next_segment().await? {
println!("length = {}", segment.len())
}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.
Equivalent to:
async fn fill_buf(&mut self) -> io::Result<&[u8]>;Errors
This function will return an I/O error if the underlying reader was read, but returned an error.
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 less than the number of bytes in the buffer
returned by fill_buf.
Returns a stream over the lines of this reader.
This method is the async equivalent to BufRead::lines.
The stream returned from this function will yield instances of
io::Result<Option<String>>. Each string returned will not have a newline
byte (the 0xA byte) or CRLF (0xD, 0xA bytes) at the end.
Errors
Each line of the stream has the same error semantics as AsyncBufReadExt::read_line.
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 tokio::io::AsyncBufReadExt;
use std::io::Cursor;
#[tokio::main]
async fn main() {
let cursor = Cursor::new(b"lorem\nipsum\r\ndolor");
let mut lines = cursor.lines();
assert_eq!(lines.next_line().await.unwrap(), Some(String::from("lorem")));
assert_eq!(lines.next_line().await.unwrap(), Some(String::from("ipsum")));
assert_eq!(lines.next_line().await.unwrap(), Some(String::from("dolor")));
assert_eq!(lines.next_line().await.unwrap(), None);
}