1 // Copyright 2018 Developers of the Rand project.
2 // Copyright 2013 The Rust Project Developers.
3 //
4 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
5 // https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
6 // <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
7 // option. This file may not be copied, modified, or distributed
8 // except according to those terms.
9 
10 //! A wrapper around any Read to treat it as an RNG.
11 
12 use std::fmt;
13 use std::io::Read;
14 
15 use rand_core::{impls, Error, RngCore};
16 
17 
18 /// An RNG that reads random bytes straight from any type supporting
19 /// [`std::io::Read`], for example files.
20 ///
21 /// This will work best with an infinite reader, but that is not required.
22 ///
23 /// This can be used with `/dev/urandom` on Unix but it is recommended to use
24 /// [`OsRng`] instead.
25 ///
26 /// # Panics
27 ///
28 /// `ReadRng` uses [`std::io::Read::read_exact`], which retries on interrupts.
29 /// All other errors from the underlying reader, including when it does not
30 /// have enough data, will only be reported through [`try_fill_bytes`].
31 /// The other [`RngCore`] methods will panic in case of an error.
32 ///
33 /// # Example
34 ///
35 /// ```
36 /// use rand::Rng;
37 /// use rand::rngs::adapter::ReadRng;
38 ///
39 /// let data = vec![1, 2, 3, 4, 5, 6, 7, 8];
40 /// let mut rng = ReadRng::new(&data[..]);
41 /// println!("{:x}", rng.gen::<u32>());
42 /// ```
43 ///
44 /// [`OsRng`]: crate::rngs::OsRng
45 /// [`try_fill_bytes`]: RngCore::try_fill_bytes
46 #[derive(Debug)]
47 pub struct ReadRng<R> {
48     reader: R,
49 }
50 
51 impl<R: Read> ReadRng<R> {
52     /// Create a new `ReadRng` from a `Read`.
new(r: R) -> ReadRng<R>53     pub fn new(r: R) -> ReadRng<R> {
54         ReadRng { reader: r }
55     }
56 }
57 
58 impl<R: Read> RngCore for ReadRng<R> {
next_u32(&mut self) -> u3259     fn next_u32(&mut self) -> u32 {
60         impls::next_u32_via_fill(self)
61     }
62 
next_u64(&mut self) -> u6463     fn next_u64(&mut self) -> u64 {
64         impls::next_u64_via_fill(self)
65     }
66 
fill_bytes(&mut self, dest: &mut [u8])67     fn fill_bytes(&mut self, dest: &mut [u8]) {
68         self.try_fill_bytes(dest).unwrap_or_else(|err| {
69             panic!(
70                 "reading random bytes from Read implementation failed; error: {}",
71                 err
72             )
73         });
74     }
75 
try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error>76     fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error> {
77         if dest.is_empty() {
78             return Ok(());
79         }
80         // Use `std::io::read_exact`, which retries on `ErrorKind::Interrupted`.
81         self.reader
82             .read_exact(dest)
83             .map_err(|e| Error::new(ReadError(e)))
84     }
85 }
86 
87 /// `ReadRng` error type
88 #[derive(Debug)]
89 pub struct ReadError(std::io::Error);
90 
91 impl fmt::Display for ReadError {
fmt(&self, f: &mut fmt::Formatter) -> fmt::Result92     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
93         write!(f, "ReadError: {}", self.0)
94     }
95 }
96 
97 impl std::error::Error for ReadError {
source(&self) -> Option<&(dyn std::error::Error + 'static)>98     fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
99         Some(&self.0)
100     }
101 }
102 
103 
104 #[cfg(test)]
105 mod test {
106     use std::println;
107 
108     use super::ReadRng;
109     use crate::RngCore;
110 
111     #[test]
test_reader_rng_u64()112     fn test_reader_rng_u64() {
113         // transmute from the target to avoid endianness concerns.
114         #[rustfmt::skip]
115         let v = [0u8, 0, 0, 0, 0, 0, 0, 1,
116                  0,   4, 0, 0, 3, 0, 0, 2,
117                  5,   0, 0, 0, 0, 0, 0, 0];
118         let mut rng = ReadRng::new(&v[..]);
119 
120         assert_eq!(rng.next_u64(), 1 << 56);
121         assert_eq!(rng.next_u64(), (2 << 56) + (3 << 32) + (4 << 8));
122         assert_eq!(rng.next_u64(), 5);
123     }
124 
125     #[test]
test_reader_rng_u32()126     fn test_reader_rng_u32() {
127         let v = [0u8, 0, 0, 1, 0, 0, 2, 0, 3, 0, 0, 0];
128         let mut rng = ReadRng::new(&v[..]);
129 
130         assert_eq!(rng.next_u32(), 1 << 24);
131         assert_eq!(rng.next_u32(), 2 << 16);
132         assert_eq!(rng.next_u32(), 3);
133     }
134 
135     #[test]
test_reader_rng_fill_bytes()136     fn test_reader_rng_fill_bytes() {
137         let v = [1u8, 2, 3, 4, 5, 6, 7, 8];
138         let mut w = [0u8; 8];
139 
140         let mut rng = ReadRng::new(&v[..]);
141         rng.fill_bytes(&mut w);
142 
143         assert!(v == w);
144     }
145 
146     #[test]
test_reader_rng_insufficient_bytes()147     fn test_reader_rng_insufficient_bytes() {
148         let v = [1u8, 2, 3, 4, 5, 6, 7, 8];
149         let mut w = [0u8; 9];
150 
151         let mut rng = ReadRng::new(&v[..]);
152 
153         let result = rng.try_fill_bytes(&mut w);
154         assert!(result.is_err());
155         println!("Error: {}", result.unwrap_err());
156     }
157 }
158