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// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
use prelude::v1::*;
use io;
use io::ErrorKind;
use io::Read;
use slice::from_raw_parts_mut;
// Provides read_to_end functionality over an uninitialized buffer.
// This function is unsafe because it calls the underlying
// read function with a slice into uninitialized memory. The default
// implementation of read_to_end for readers will zero out new memory in
// the buf before passing it to read, but avoiding this zero can often
// lead to a fairly significant performance win.
//
// Implementations using this method have to adhere to two guarantees:
// * The implementation of read never reads the buffer provided.
// * The implementation of read correctly reports how many bytes were written.
pub unsafe fn read_to_end_uninitialized(r: &mut Read, buf: &mut Vec<u8>) -> io::Result<usize> {
let start_len = buf.len();
buf.reserve(16);
// Always try to read into the empty space of the vector (from the length to the capacity).
// If the vector ever fills up then we reserve an extra byte which should trigger the normal
// reallocation routines for the vector, which will likely double the size.
//
// This function is similar to the read_to_end function in std::io, but the logic about
// reservations and slicing is different enough that this is duplicated here.
loop {
if buf.len() == buf.capacity() {
buf.reserve(1);
}
let buf_slice = from_raw_parts_mut(buf.as_mut_ptr().offset(buf.len() as isize),
buf.capacity() - buf.len());
match r.read(buf_slice) {
Ok(0) => { return Ok(buf.len() - start_len); }
Ok(n) => { let len = buf.len() + n; buf.set_len(len); },
Err(ref e) if e.kind() == ErrorKind::Interrupted => { }
Err(e) => { return Err(e); }
}
}
}
#[cfg(test)]
mod tests {
use prelude::v1::*;
use io::prelude::*;
use super::*;
use io;
use io::{ErrorKind, Take, Repeat, repeat};
use test;
use slice::from_raw_parts;
struct ErrorRepeat {
lr: Take<Repeat>
}
fn error_repeat(byte: u8, limit: u64) -> ErrorRepeat {
ErrorRepeat { lr: repeat(byte).take(limit) }
}
impl Read for ErrorRepeat {
fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
let ret = self.lr.read(buf);
if let Ok(0) = ret {
return Err(io::Error::new(ErrorKind::Other, ""))
}
ret
}
}
fn init_vec_data() -> Vec<u8> {
let mut vec = vec![10u8; 200];
unsafe { vec.set_len(0); }
vec
}
fn assert_all_eq(buf: &[u8], value: u8) {
for n in buf {
assert_eq!(*n, value);
}
}
fn validate(buf: &Vec<u8>, good_read_len: usize) {
assert_all_eq(buf, 1u8);
let cap = buf.capacity();
let end_slice = unsafe { from_raw_parts(buf.as_ptr().offset(good_read_len as isize),
cap - good_read_len) };
assert_all_eq(end_slice, 10u8);
}
#[test]
fn read_to_end_uninit_error() {
let mut er = error_repeat(1,100);
let mut vec = init_vec_data();
if let Err(_) = unsafe { read_to_end_uninitialized(&mut er, &mut vec) } {
validate(&vec, 100);
} else {
assert!(false);
}
}
#[test]
fn read_to_end_uninit_zero_len_vec() {
let mut er = repeat(1).take(100);
let mut vec = Vec::new();
let n = unsafe{ read_to_end_uninitialized(&mut er, &mut vec).unwrap() };
assert_all_eq(&vec, 1u8);
assert_eq!(vec.len(), n);
}
#[test]
fn read_to_end_uninit_good() {
let mut er = repeat(1).take(100);
let mut vec = init_vec_data();
let n = unsafe{ read_to_end_uninitialized(&mut er, &mut vec).unwrap() };
validate(&vec, 100);
assert_eq!(vec.len(), n);
}
#[bench]
fn bench_uninitialized(b: &mut test::Bencher) {
b.iter(|| {
let mut lr = repeat(1).take(10000000);
let mut vec = Vec::with_capacity(1024);
unsafe { read_to_end_uninitialized(&mut lr, &mut vec) }
});
}
}
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