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// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// https://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
//! A wrapper around any Read to treat it as an RNG.
use std::io::Read;
use rand_core::{RngCore, Error, ErrorKind, impls};
/// An RNG that reads random bytes straight from any type supporting
/// `std::io::Read`, for example files.
///
/// This will work best with an infinite reader, but that is not required.
///
/// This can be used with `/dev/urandom` on Unix but it is recommended to use
/// [`OsRng`] instead.
///
/// # Panics
///
/// `ReadRng` uses `std::io::read_exact`, which retries on interrupts. All other
/// errors from the underlying reader, including when it does not have enough
/// data, will only be reported through [`try_fill_bytes`]. The other
/// [`RngCore`] methods will panic in case of an error.
///
/// # Example
///
/// ```
/// use rand::{read, Rng};
///
/// let data = vec![1, 2, 3, 4, 5, 6, 7, 8];
/// let mut rng = read::ReadRng::new(&data[..]);
/// println!("{:x}", rng.gen::<u32>());
/// ```
///
/// [`OsRng`]: ../struct.OsRng.html
/// [`RngCore`]: ../../trait.RngCore.html
/// [`try_fill_bytes`]: ../../trait.RngCore.html#method.tymethod.try_fill_bytes
#[derive(Debug)]
pub struct ReadRng<R> {
reader: R
}
impl<R: Read> ReadRng<R> {
/// Create a new `ReadRng` from a `Read`.
pub fn new(r: R) -> ReadRng<R> {
ReadRng {
reader: r
}
}
}
impl<R: Read> RngCore for ReadRng<R> {
fn next_u32(&mut self) -> u32 {
impls::next_u32_via_fill(self)
}
fn next_u64(&mut self) -> u64 {
impls::next_u64_via_fill(self)
}
fn fill_bytes(&mut self, dest: &mut [u8]) {
self.try_fill_bytes(dest).unwrap_or_else(|err|
panic!("reading random bytes from Read implementation failed; error: {}", err));
}
fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error> {
if dest.len() == 0 { return Ok(()); }
// Use `std::io::read_exact`, which retries on `ErrorKind::Interrupted`.
self.reader.read_exact(dest).map_err(|err| {
match err.kind() {
::std::io::ErrorKind::UnexpectedEof => Error::with_cause(
ErrorKind::Unavailable,
"not enough bytes available, reached end of source", err),
_ => Error::with_cause(ErrorKind::Unavailable,
"error reading from Read source", err)
}
})
}
}
#[cfg(test)]
mod test {
use super::ReadRng;
use {RngCore, ErrorKind};
#[test]
fn test_reader_rng_u64() {
// transmute from the target to avoid endianness concerns.
let v = vec![0u8, 0, 0, 0, 0, 0, 0, 1,
0 , 0, 0, 0, 0, 0, 0, 2,
0, 0, 0, 0, 0, 0, 0, 3];
let mut rng = ReadRng::new(&v[..]);
assert_eq!(rng.next_u64(), 1_u64.to_be());
assert_eq!(rng.next_u64(), 2_u64.to_be());
assert_eq!(rng.next_u64(), 3_u64.to_be());
}
#[test]
fn test_reader_rng_u32() {
let v = vec![0u8, 0, 0, 1, 0, 0, 0, 2, 0, 0, 0, 3];
let mut rng = ReadRng::new(&v[..]);
assert_eq!(rng.next_u32(), 1_u32.to_be());
assert_eq!(rng.next_u32(), 2_u32.to_be());
assert_eq!(rng.next_u32(), 3_u32.to_be());
}
#[test]
fn test_reader_rng_fill_bytes() {
let v = [1u8, 2, 3, 4, 5, 6, 7, 8];
let mut w = [0u8; 8];
let mut rng = ReadRng::new(&v[..]);
rng.fill_bytes(&mut w);
assert!(v == w);
}
#[test]
fn test_reader_rng_insufficient_bytes() {
let v = [1u8, 2, 3, 4, 5, 6, 7, 8];
let mut w = [0u8; 9];
let mut rng = ReadRng::new(&v[..]);
assert!(rng.try_fill_bytes(&mut w).err().unwrap().kind == ErrorKind::Unavailable);
}
}