Rollup merge of #128406 - lolbinarycat:bufreader_peek, r=Mark-Simulacrum · patricklam/verify-rust-std@1bd5338 (original) (raw)
`@@ -94,6 +94,40 @@ impl<R: Read> BufReader {
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`pub fn with_capacity(capacity: usize, inner: R) -> BufReader {
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`BufReader { inner, buf: Buffer::with_capacity(capacity) }
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`}
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/// Attempt to look ahead n bytes.
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///
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/// n must be less than capacity.
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///
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/// ## Examples
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///
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/// ```rust
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/// #![feature(bufreader_peek)]
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/// use std::io::{Read, BufReader};
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///
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/// let mut bytes = &b"oh, hello"[..];
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/// let mut rdr = BufReader::with_capacity(6, &mut bytes);
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/// assert_eq!(rdr.peek(2).unwrap(), b"oh");
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/// let mut buf = [0; 4];
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/// rdr.read(&mut buf[..]).unwrap();
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/// assert_eq!(&buf, b"oh, ");
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/// assert_eq!(rdr.peek(2).unwrap(), b"he");
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/// let mut s = String::new();
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/// rdr.read_to_string(&mut s).unwrap();
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/// assert_eq!(&s, "hello");
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/// ```
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#[unstable(feature = "bufreader_peek", issue = "128405")]
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pub fn peek(&mut self, n: usize) -> io::Result<&[u8]> {
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assert!(n <= self.capacity());
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while n > self.buf.buffer().len() {
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if self.buf.pos() > 0 {
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self.buf.backshift();
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}
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self.buf.read_more(&mut self.inner)?;
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debug_assert_eq!(self.buf.pos(), 0);
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}
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Ok(&self.buf.buffer()[..n])
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}
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`}
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`impl<R: ?Sized> BufReader {
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