1 // Copyright 2013 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
4 //
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
10
11 //! A wrapper around any Read to treat it as an RNG.
12
13 use std::io::{self, Read};
14 use std::mem;
15 use Rng;
16
17 /// An RNG that reads random bytes straight from a `Read`. This will
18 /// work best with an infinite reader, but this is not required.
19 ///
20 /// # Panics
21 ///
22 /// It will panic if it there is insufficient data to fulfill a request.
23 ///
24 /// # Example
25 ///
26 /// ```rust
27 /// use rand::{read, Rng};
28 ///
29 /// let data = vec![1, 2, 3, 4, 5, 6, 7, 8];
30 /// let mut rng = read::ReadRng::new(&data[..]);
31 /// println!("{:x}", rng.gen::<u32>());
32 /// ```
33 #[derive(Debug)]
34 pub struct ReadRng<R> {
35 reader: R
36 }
37
38 impl<R: Read> ReadRng<R> {
39 /// Create a new `ReadRng` from a `Read`.
new(r: R) -> ReadRng<R>40 pub fn new(r: R) -> ReadRng<R> {
41 ReadRng {
42 reader: r
43 }
44 }
45 }
46
47 impl<R: Read> Rng for ReadRng<R> {
next_u32(&mut self) -> u3248 fn next_u32(&mut self) -> u32 {
49 // This is designed for speed: reading a LE integer on a LE
50 // platform just involves blitting the bytes into the memory
51 // of the u32, similarly for BE on BE; avoiding byteswapping.
52 let mut buf = [0; 4];
53 fill(&mut self.reader, &mut buf).unwrap();
54 unsafe { *(buf.as_ptr() as *const u32) }
55 }
next_u64(&mut self) -> u6456 fn next_u64(&mut self) -> u64 {
57 // see above for explanation.
58 let mut buf = [0; 8];
59 fill(&mut self.reader, &mut buf).unwrap();
60 unsafe { *(buf.as_ptr() as *const u64) }
61 }
fill_bytes(&mut self, v: &mut [u8])62 fn fill_bytes(&mut self, v: &mut [u8]) {
63 if v.len() == 0 { return }
64 fill(&mut self.reader, v).unwrap();
65 }
66 }
67
fill(r: &mut Read, mut buf: &mut [u8]) -> io::Result<()>68 fn fill(r: &mut Read, mut buf: &mut [u8]) -> io::Result<()> {
69 while buf.len() > 0 {
70 match try!(r.read(buf)) {
71 0 => return Err(io::Error::new(io::ErrorKind::Other,
72 "end of file reached")),
73 n => buf = &mut mem::replace(&mut buf, &mut [])[n..],
74 }
75 }
76 Ok(())
77 }
78
79 #[cfg(test)]
80 mod test {
81 use super::ReadRng;
82 use Rng;
83
84 #[test]
test_reader_rng_u64()85 fn test_reader_rng_u64() {
86 // transmute from the target to avoid endianness concerns.
87 let v = vec![0u8, 0, 0, 0, 0, 0, 0, 1,
88 0 , 0, 0, 0, 0, 0, 0, 2,
89 0, 0, 0, 0, 0, 0, 0, 3];
90 let mut rng = ReadRng::new(&v[..]);
91
92 assert_eq!(rng.next_u64(), 1_u64.to_be());
93 assert_eq!(rng.next_u64(), 2_u64.to_be());
94 assert_eq!(rng.next_u64(), 3_u64.to_be());
95 }
96 #[test]
test_reader_rng_u32()97 fn test_reader_rng_u32() {
98 let v = vec![0u8, 0, 0, 1, 0, 0, 0, 2, 0, 0, 0, 3];
99 let mut rng = ReadRng::new(&v[..]);
100
101 assert_eq!(rng.next_u32(), 1_u32.to_be());
102 assert_eq!(rng.next_u32(), 2_u32.to_be());
103 assert_eq!(rng.next_u32(), 3_u32.to_be());
104 }
105 #[test]
test_reader_rng_fill_bytes()106 fn test_reader_rng_fill_bytes() {
107 let v = [1u8, 2, 3, 4, 5, 6, 7, 8];
108 let mut w = [0u8; 8];
109
110 let mut rng = ReadRng::new(&v[..]);
111 rng.fill_bytes(&mut w);
112
113 assert!(v == w);
114 }
115
116 #[test]
117 #[should_panic]
test_reader_rng_insufficient_bytes()118 fn test_reader_rng_insufficient_bytes() {
119 let mut rng = ReadRng::new(&[][..]);
120 let mut v = [0u8; 3];
121 rng.fill_bytes(&mut v);
122 }
123 }
124