shadow_rs/utility/
give.rs

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1use std::io::Write;
2
3// this code has been adapted from the `Take` implementation
4
5/// Writer adapter which limits the bytes written to an underlying writer.
6///
7/// Intended to be a [`std::io::Write`] counterpart to [`std::io::Take`] for [`std::io::Read`]. This
8/// does not force the write limit, for example `give.get_mut()` can be used to write directly to
9/// the underlying writer without updating the internal state of the `Give` object.
10pub struct Give<T> {
11    inner: T,
12    limit: u64,
13}
14
15impl<T> Give<T> {
16    pub fn new(writer: T, limit: u64) -> Self {
17        Self {
18            inner: writer,
19            limit,
20        }
21    }
22
23    /// Returns the number of bytes that can be written before this instance will return a write of
24    /// 0 bytes.
25    pub fn limit(&self) -> u64 {
26        self.limit
27    }
28
29    /// Sets the number of bytes that can be read before this instance will return a write of 0
30    /// bytes. This is the same as constructing a new `Give` instance, so the amount of bytes read
31    /// and the previous limit value don't matter when calling this method.
32    pub fn set_limit(&mut self, limit: u64) {
33        self.limit = limit;
34    }
35
36    /// Consumes the `Give`, returning the wrapped writer.
37    pub fn into_inner(self) -> T {
38        self.inner
39    }
40
41    /// Gets a reference to the underlying writer.
42    pub fn get_ref(&self) -> &T {
43        &self.inner
44    }
45
46    /// Gets a mutable reference to the underlying writer.
47    pub fn get_mut(&mut self) -> &mut T {
48        &mut self.inner
49    }
50}
51
52impl<T: Write> Write for Give<T> {
53    fn write(&mut self, buf: &[u8]) -> std::io::Result<usize> {
54        // don't call into the inner writer at all at EOF because it may still block
55        if self.limit == 0 {
56            return Ok(0);
57        }
58
59        let max = std::cmp::min(buf.len() as u64, self.limit) as usize;
60        let n = self.inner.write(&buf[..max])?;
61        self.limit -= n as u64;
62        Ok(n)
63    }
64
65    fn flush(&mut self) -> std::io::Result<()> {
66        self.inner.flush()
67    }
68}
69
70#[cfg(test)]
71mod tests {
72    use super::*;
73
74    #[test]
75    fn test_give_write_1() {
76        let mut buf = vec![];
77        let mut give = Give::new(&mut buf, 5);
78        assert_eq!(give.write(&[0u8; 20]).unwrap(), 5);
79        assert_eq!(give.write(&[0u8; 20]).unwrap(), 0);
80        assert_eq!(buf.len(), 5);
81    }
82
83    #[test]
84    fn test_give_write_2() {
85        let mut buf = vec![];
86        let mut give = Give::new(&mut buf, 5);
87        assert_eq!(give.write(&[0u8; 3]).unwrap(), 3);
88        assert_eq!(give.write(&[0u8; 3]).unwrap(), 2);
89        assert_eq!(give.write(&[0u8; 3]).unwrap(), 0);
90        assert_eq!(buf.len(), 5);
91    }
92
93    #[test]
94    fn test_give_write_all_1() {
95        let mut buf = vec![];
96        let mut give = Give::new(&mut buf, 5);
97        assert!(give.write_all(&[0u8; 3]).is_ok());
98        assert!(give.write_all(&[0u8; 2]).is_ok());
99        assert!(give.write_all(&[0u8; 1]).is_err());
100        assert_eq!(buf.len(), 5);
101    }
102
103    #[test]
104    fn test_give_write_all_2() {
105        let mut buf = vec![];
106        let mut give = Give::new(&mut buf, 5);
107        assert!(give.write_all(&[0u8; 7]).is_err());
108        assert!(give.write_all(&[0u8; 1]).is_err());
109        assert!(give.write_all(&[0u8; 7]).is_err());
110        assert!(give.write_all(&[0u8; 1]).is_err());
111        assert!(give.write_all(&[0u8; 3]).is_err());
112        assert_eq!(buf.len(), 5);
113    }
114}
shadow_rs/utility/give.rs

shadow_rs/utility/
give.rs
