1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137

// 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);
    }
}