BufReader in async_std::io - Rust (original) (raw)
pub struct BufReader<R> { /* private fields */ }Expand description
Adds buffering to any reader.
It can be excessively inefficient to work directly with a Read instance. A BufReaderperforms large, infrequent reads on the underlying Read and maintains an in-memory buffer of the incoming byte stream.
BufReader can improve the speed of programs that make small and repeated read calls to the same file or network socket. It does not help when reading very large amounts at once, or reading just one or a few times. It also provides no advantage when reading from a source that is already in memory, like a Vec<u8>.
When the BufReader is dropped, the contents of its buffer will be discarded. Creating multiple instances of a BufReader on the same stream can cause data loss.
This type is an async version of std::io::BufReader.
§Examples
use async_std::fs::File;
use async_std::io::BufReader;
use async_std::prelude::*;
let mut file = BufReader::new(File::open("a.txt").await?);
let mut line = String::new();
file.read_line(&mut line).await?;Creates a buffered reader with default buffer capacity.
The default capacity is currently 8 KB, but may change in the future.
§Examples
use async_std::fs::File;
use async_std::io::BufReader;
let f = BufReader::new(File::open("a.txt").await?);Creates a new buffered reader with the specified capacity.
§Examples
use async_std::fs::File;
use async_std::io::BufReader;
let f = BufReader::with_capacity(1024, File::open("a.txt").await?);Gets a reference to the underlying reader.
It is inadvisable to directly read from the underlying reader.
§Examples
use async_std::fs::File;
use async_std::io::BufReader;
let f = BufReader::new(File::open("a.txt").await?);
let inner = f.get_ref();Gets a mutable reference to the underlying reader.
It is inadvisable to directly read from the underlying reader.
§Examples
use async_std::fs::File;
use async_std::io::BufReader;
let mut file = BufReader::new(File::open("a.txt").await?);
let inner = file.get_mut();Returns a reference to the internal buffer.
This function will not attempt to fill the buffer if it is empty.
§Examples
use async_std::fs::File;
use async_std::io::BufReader;
let f = BufReader::new(File::open("a.txt").await?);
let buffer = f.buffer();Unwraps the buffered reader, returning the underlying reader.
Note that any leftover data in the internal buffer is lost.
§Examples
use async_std::fs::File;
use async_std::io::BufReader;
let f = BufReader::new(File::open("a.txt").await?);
let inner = f.into_inner();Attempt to return the contents of the internal buffer, filling it with more data from the inner reader if it is empty. Read more
Tells this buffer that amt bytes have been consumed from the buffer, so they should no longer be returned in calls to poll_read. Read more
Seeks to an offset, in bytes, in the underlying reader.
The position used for seeking with SeekFrom::Current(_) is the position the underlying reader would be at if the BufReader had no internal buffer.
Seeking always discards the internal buffer, even if the seek position would otherwise fall within it. This guarantees that calling .into_inner() immediately after a seek yields the underlying reader at the same position.
See Seek for more details.
Note: In the edge case where you’re seeking with SeekFrom::Current(n) where n minus the internal buffer length overflows an i64, two seeks will be performed instead of one. If the second seek returns Err, the underlying reader will be left at the same position it would have if you called seek with SeekFrom::Current(0).